pLEMENTS OF (hemistry Sin: PARI) THE CALDWELL COLLECTION THE GIFT OF THE FAMILY OF GEORGE CHAPMAN CALDWELL TO THE DEPARTMENT OF CHEMISTRY whose senior Professor he was from J 868 to 1903 45'3 Comell University Library QD 33.S55 Elements of Inorganic ''•'*"''**'T'[™?,|''' 3 1924 002 975 864 The original of tliis book is in tlie Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924002975864 ELEMENTS INORGANIC CHEMISTRY, DESCRIPTIVE AND QUALITATIVE. BY JAMES H. SHEPARD, Professor of Chemistry, Sodth Dakota Agricttltukal College, AND Chemist for the Experiment Station. oXKo BOSTON, U.S.A., D. C. HEATH & CO., PUBLISHERS. 1892. 5 Entered according to Act of Congress, in the year 1885, by JAMES H. SHEPARD, m the Office of the Librarian of Congress, at Washington., PH E aa or BOSTON PEEFAOE. This elementary treatise is based upon plans and methods which have been employed in the author's laboratory throughout a series of years, and no work has been incorporated in the text or in the exercises that has not there been proven practicable. A love for the science of chemistry would have for- bidden any attempt to add another text-book to the already too extended list of Elementary Chemistries had not the hearty commendations of teachers of national reputation and undoubted ability encouraged both the author and the publisher to put this work in permanent form. During the correspondence which grew out of the issue of this work, it has become evident that many of the best teachers in all sections of the country are pursuing independently a plan essentially the same ; and the deepest regret which the author feels in seeing the work go to press arises from the fact that it signals for the close of his correspondence and labors with such an enthusiastic corps of fellow-workers. If it shall be IV PEEPACE. found that this work, towards which they have contrib- uted so freely, meets with their hearty commendations, he will rest satisfied with his labor of love. It now only remains to return thanks tO' those who, so patiently and ofttimes so laboriously, have assisted the author in completing this work. Dr. Ira Remsen, Professor of Chemistry in Johns Hopkins University, has critically read the work in man- uscript and in proof, and has contributed much toward the accuracy and the arrangement of the topics treated, particularly those which pertain to chemical theories. The following well-known and enthusiastic teachers of chemistry have read the work in proof, and have given the author constant advice as, from time to time, the sheets appeared : — Otis Coe Johnson, Assistant Professor of Applied Chem- istry, University of Mich. ; Robt. B. Warder, Professor of Chemistry, Purdue University, and State Chemist of Ind. ; W. W. Daniells, Professor of Chemistry, University of Wis. ; Jas. A. Dodge, Professor of Chemistry, University of Minn.; E. J. Bartlett, Professor of Chemistry, Dart- mouth College ; Delos Fall, Professor of Natural Science, Albion College; Albert C. Hale, Instructor in Chemis- try, Central Grammar School, Brooklyn, N.Y. ; George Weitbrecht, Chemist and Instructor Natural Science, High School, St. Paul, Minn. ; Leroy Griffin, Professor of Natural Sciences, Lake Forest University, 111. ; Herbert C. Foote, Chemist and Instructor Natural Science, High PREFACE. V School, Cleveland, O. ; Louis McLouth, Professor of Natural Science, Michigan State Normal School, Ypsi- lanti (now of Michigan Agricultural College, Lansing) ; H. N. Chute, Instructor Natural Science, High School, Ann Arbor, Mich. ; W. G. Rappleye, Teacher of Physics and Chemistry, Normal School, Oswego, N.Y. ; Adolf T. Bechdolt, Supt. Schools, Mankato, Minn.; J. C. Crawford, Supt. Schools, Green Bay, Wis. ; and many other teach- ers of Chemistry in preparatory, normal, and collegiate departments. Article 234 on the Natural Classification of the Elements is due to the kindness of Professor Warder. The author is aware that many data, not usually given in works for beginners, appear in the text; but, in the laboratory, these will be found to be useful and valuable additions. It has been the constant aim, in preparing this book, to make the labors of the teacher as light as possible, and to place the laboratory work where it would do the most good, in the hands of the students. J. H. S. Oct. 15, 1885. TO THE TEAOHEE. I. Methods. It is with no little diffidence that the author approaches the subject of Methods. He is fully aware that every teacher has his own method, and that all successful methods are entitled to respectful consideration. There are, however, some principles upon which all are agreed, and a classiflcation and a brief dis- cussion of the different methods which have been employed may at least prove suggestive. The problems before us are these : — 1. If we teach chemistry at all, what advantages has this science to offer as factors in developing the youthful mind, and what good results will follow its study ? 2. If the study of chemistry be positively desirable, what method of presentation will best accomplish the desired results ? 1. Neglecting for the present the claims of those who would become chemists by profession, let us consider chemistry as a means of education. In this capacity, when properly taught, chemistry awakens and cultivates a spirit of investigation ; it encourages the student to ask Nature questions, and it is unex- celled by any other branch of learning in the clearness and con- clusiveness of the answers received ; it insists upon the strictest habits of observation ; it leads to the concentration of thought and of energy ; it educates the senses ; it trains the hand to delicate manipulation ; it exercises the faculty of reason and the power of judging ; it affords useful information peculiarly Viii TO THE TEACHER. its own, and thus forms an important part of a good, general education. Backed by such advantages as these, it really seems that chemistry should be deemed worthy of a place in all liberal as well as in purelj' scientific education. 2. "When it comes to methods of instruction, the teacher has many from which to choose. These methods may be arranged approximately under four general divisions : — (1) The Classical or Didactic method. (2) The Laboratory method, in which the teacher does all the experimentation in the presence of the class, and accompanies the experimentation by didactic instruction. (3) The Working-Laboratory method, in which the student does his own experimentation, and receives little or no didactic instruction. This method varies somewhat, in its application : — (a) The student may be required to work with no aid from text-books, etc., relying upon his work alone for the benefits to be obtained, the instructor in this case acting really as a demonstrator. (6) The student may have a text-book as a guide, the in- structor acting as before. (4) A method which the author begs leave to christen the SCIENTIFIC METHOD ; tMs embodics all the good features of the preceding methods. The experience of many careful insti-uetors would warrant the following estimate of the relative value of these methods : — The first method affords some special information ; otherwise, chemistry, when thus taught, is equalled as an educational factor, by history, and by kindred subjects ; and is excelled by mathe- matics and the classics. The second method accomplishes as much as the first, and to a very limited extent cultivates observation ; farther than this, no advantages are to be gained by its use. The third method incites to investigation ; trains the senses to TO THE TEACHER. ix observe ; trains the hand to careful manipulation ; and encour- ages the student to originate. But (a) is too slow ; it requires more time than can be devoted to this study ; and although the student may " know well what little he does know," his rea- soning powers are not developed, and his fund of information is not suflflciently increased. (6) accomplishes its ends somewhat more rapidly than (a), and consequently yields more informa- tion in a given length of time ; otherwise, it is not better than (a). As a rule, students taught by the third method are very weak in chemical theory. An insight into the fourth method may best be obtained by a description of the manner of its application. This method contemplates : didactic instruction by the teacher ; a good text- book, and as many books of reference as possible ; much work by the student, who should keep a careful record of all work done, and who should recite frequently ; and work by the teacher, either in the presence of the class where the class is large, or personal directions to the student when the class is small. The use of this method is extremely simple. The teacher assigns a lesson from the text, indicating such parallel reading as the time at the student's disposal may permit ; he then goes over the lesson, and gives such working directions and cautions as the subject and the student's capabilities may demand, thus, in most cases at least, saving the student from wasting his time in repeating the useless blunders of those who worked centuries ago ; if the experiments be dangerous, or if the line of work be new, the teacher either makes the experiment for the class with little or no explanation, or he explains the general principles, leaving the student, when safety permits, to work out the details ; after this, the student i^ sent to his desk, where he works, reads, and makes his notes for the next recitation. The following day the student is questioned concerning his work, and is encouraged to tell truthfully and exactly how he succeeded, if he has succeeded, or why he failed, if he has failed. X TO THE TEACHER. In case the student has failed, and does not know the reason, or gives the wrong reason, the teacher, meanwhile explaining nothing himself, calls upon other members of the class until the point in question is elucidated. If all have failed, which rarely happens, the teacher gives directions anew, and the students try again. In general, the teacher aims to do as little work for the class as possible, and to tell the student nothing that he can find out for himself in a reasonable length of time. Reviews and those topics which are necessary to the science as a whole, and which are not covered by the student's work, are faithfully taught by didactic methods. Variety is introduced and practical results are obtained in several ways, and thus the student's interest is never permitted to flag. Students are assigned essays upon various topics ; are given unknown substances to analyze ; are required to make analyses of substances witfi which they are familiar, such as coins, worn-out articles of jewelry, alloys, common salt, baking- powder, samples of drinking-water, crude drugs from the drug store, etc., etc. In keeping his notes, the student constantly recognizes the fact that the knowledge he is seeking is to be drawn from phenomena observed while working with known factors. A good form for the headings of a note-book is as foUows : — 1. Required Conditions. 2. Known Conditions. 3. Operations. 4. Conclusions. Under 1 the student enumerates what he wishes to know; under 2 he enumerates his working materials ; under 3 he tells what he does ; and under 4 what conclusions he has reached. In making his notes, the student is warned that he may err : (1) by taking a trivial required condition; (2) by assuming a required condition that will not follow from the premises; (3) by an indefinite or obscure description of his operations ; (4) by reaching a conclusion more general than the premises TO THE TEACHER. xi warrant ; and (5) by employing bad English in any of the pre- ceding divisions. In this book, written with special reference to the fourth method, the student's work, so far as practicable, is not fore- stalled by telling him what phenomena are to occur, and many queries are left to be answered by an experiment which the student may devise. In the closing portions of the book, all experiments (as such) are purposely omitted with the sugges- tion that, as the student is no longer, in the strict sense of the word, a beginner, he should be thrown still farther upon his own resources. He is asked to prepare various salts and com- pounds of the metals, and to describe their- preparation as experiments ; this is work well adapted to afford an exercise more exacting than anything previously attempted. Another good exercise for the student is to prepare working solutions for himself and his classmates, starting with the crude materials. By this method, the student wUl not only secure a lasting benefit from chemistry, as an educator of hand and mind, but in case he so desires, he will find himself amply prepared for further pursuing this delightful study. n. What should the Student memorize? As in aU other studies, this question is frequently asked con- cerning chemistry. In the curriculum of all schools in which chemistry is taught to beginners other studies are found, or should be found, which are peculiarly adapted to cultivate the faculty of memory ; the amount of memorizing required in chemistry should be quite limited, depending more or less upon the curriculum itself. In general, it is safe to say that much valuable time has been frittered away by requiring the student to memorize unimportant details which not even an expert retains. Because certain facts Xll TO THE TEACHER, or numerical data are giveu in a text, it does not follow that the student's memory must be burdened with them ; there are other uses for such data, and especially so in a working text. Thus, for example, the weight of one litre of a gas, atomic heats, specific gravities, densities, etc., etc., may be utilized in solving problems. It is not even necessary to memorize the atomic weights or such units as the weight of one litre of hydrogen, since the stu- dent will learn these data by frequently using them, just as we aU have learned the multiplication table. It is, however, a positive advantage to have these data given in the body of the text, since a frequent reference to them serves in a certain way as a review. Again, the author has never required his classes to memorize tests and separations, and still his students, by way of final work, have been able correctly to analyze complex unknown solu- tions without the aid of reference books or of text-books ; this was accomplished by simply giving the student much work to do, and then hy asking him to explain his work. And again, it would be manifestly absurd to require the student to memorize the language of the text in experiments. And finally it should suffice to bear in mind that to be able to do, to reason, to origi- nate, is far better than to be able to repeat from memory things not half understood. ni. A Briefer Course. Foe various reasons some teachers may wish to use certain portions of the text and to omit the rest. There is no reason why this may not be done. Experience has shown that, in a working text, even of the most elementary character, it is desirable to have the book quite complete, thus lightening the labor of the teacher, and providing for emergencies which often TO THE TEACHER. xiii and unexpectedly arise. For example, one piece of apparatus may be broken, or it may be wanting, while another, which may be made to answer the same purpose, is available ; or, a student in his work may come upon something which not even the teacher could foresee ; one chemical may have been entirely ' consumed, while another, which will answer, may still be plenti- ful, etc., etc. In view of all these considerations, it is evident that a somewhat full text will be more satisfactory to both student and teacher, even though certain portions of it are omitted, or dwelt upon quite lightly. There is no truth in the tradition that " to omit certain parts of a book causes the student to be less thorough " ; on the contrary, such a process should teach him to select what he reaUy wants from what he does not want, — a lesson he must learn sooner or later. There is one thing, at least, that a full text certainly does do, and that is, it forever banishes from the student's mind the idea that he has learned all there is to know of chemistry. The following hints may serve to show how the work may be lessened or how the course may be shortened : — 1 . Omit the experiments marked op. 2. When two or more experiments tend toward the same general result, omit as many as desirable, selecting those most readily performed bj- the apparatus and working material available. 3. Omit the rarer elements and their compounds. 4. In the compounds of the common elements, dwell at length upon the most useful ones, e.g., in the compounds of nitrogen, place the stronger work upon ammonia, nitrogen monoxide, and nitric acid, omitting or dwelling but briefly upon the remaining compounds. 5. The qualitative work may be curtailed by omitting some of the separations, etc. 6. Sometimes, also, the teacher may prefer to modify the order of presenting the various topics ; for example, he may wish to discuss molecules more thoroughly at the outset, or he XIV TO THE TEACHEK. may wish the class to experiment with the oxides of nitrogen before discussing them in their bearing upon the law of multiple proportions, etc., etc. In this way he may conform to his own! ideas of presentation. OOI^fTENTS. HISTORICAL SKETCH. The Ancients — The Arabs. — Alchemy of the Middle Ages. — j^Medical Chemistry. — Pneumatic Chemistry. — Modern Chemistry 1 INTEODUCTIOIT. Experimentation. — Elements. — Compounds. — Chemistry Defined. — Three Forms of Matter. — Chemism. — Laws of Definite and Multiple Proportions. — Combining Number. — Atomic Theory. — Atomic Weight. — Determination of Atomic Weight. — Names of the Elements. — Symbols. — A Table of the Elements 8- CHAPTEE I. Oxygen: its occurrence, preparation, properties, and tests. — The Bunsen Burner and the Blow-pipe. — Ozone: prepara- tion, properties, and tests 23- CHAPTER 11. Hydrogen: its occurrence, etc. — Water: its occurrence, etc. — Composition of Water. — The Oxy-hydrogen Blow-pipe. — Impurities in Drinking-\rater, and Tests for. — Hydrogen Dioxide : its preparation, etc ... 34-' CHAPTER III. Nitrogen : its occurrence, etc. — Ammonia : its occurreiKie, etc. — Nitrogen Monoxide : its occurrence, etc. — Nitrogen Xvi CONTENTS. Dioxide. — Nitrogen Trioxide. — Nitrogen Tetroxide. — Nitrogen Pentoxide. — The Nitrogen Acids: Hyponitrous, Nitrous, and Nitric Acids. — Hydroxylamine. — Estimation of Ammonia in Drinking-water 50-72 CHAPTER IV. Binary Compounds. — Acids. — Bases. — Salts. — Acid and , Normal Salts. — Writing Equations 73-81 CHAPTEE V. The Atmosphere. — Atmospheric Pressure. — Measurement of the Temperature of the Atmosphere. — Impurities in the Atmosphere. — Determination of the Volumes of Oxygen and. Nitrogen in the Atmosphere. — Effects of Heat and Pressure on the Volume of a Gas. — Weight and Density of Gases. — Useful Problems . 82-91 CHAPTER VI. Chlorine : its occurrence, etc. — Hydrochloric Acid : its preparation, etc. — Oxides of Chlorine: Monoxide, Trioxide, Tetroxide ; their preparation, etc. — The Chlorine Oxacids : Hypochlorous, Chlorous, Chloric, and Perchloric Acids, and their preparation, etc. — Estimation of Chlorine in Drinking- water 92-107 CHAPTEE Vn. Bromine : its occurrence, etc. — Hydrobromic Acid : its prepara- tion, etc. — Hypobromous, Bromous, and Perbromic Acids, . and their preparation, etc 108-114 CHAPTER Vin. Iodine and Fluorine. — Occurrence, etc., of Iodine. — Hydrl- odic Acid: its preparation, etc. — Iodic and Periodic Acids, and their preparation, etc. — Fluorine. — Hydrofluoric Acid 115-124 CONTENTS. XVll CHAPTER IX. PASS. Cakbon : its occun-ence, etc. — Methane. — Ethylene. — Acety- lene. — Uluminating Gas. — Carbon Monoxide. — Carbon Dioxide. — The Carbonates. — Cyanogen. — Prussic Acid. — Estimation of Carbon Dioxide in Living-rooms . . . 125-148 CHAPTER X. Molecules. — Avogadro's Hypothesis and the Computation of Molecular Weights. — Determination of Atomic Weights by Means of Avogadro's Hypothesis. — Valence. — Substituting Power and Valence 149-156 CHAPTER XL Sulphur : its occurrence, etc. — Hydrogen Sidphide. — Hydro- gen Per-sulphide. — Sulphur Dioxide. — Sulphur Trioxide. — Sulphurous Acid. — Sulphuric Acid. — Nordhausen, or Fuming Sulphuric Acid. — Thiosulphuiic Acid and the Thiosulphates. — Carbon Bisulphide. — Selenium : its occur- rence, etc. — Tellurium : its occurrence, etc 157-183 CHAPTER XIL Silicon and Boron. — Occurrence, etc., of Silicon. — SUica. — The Silicon Oxacids and the Silicates. — Other Compounds of Silicon Occurrence, etc., of Boron. — Boron Com- pounds, etc 184-192 CHAPTER XIII. Phosphorus: its occurrence, etc. — Phosphorus and Hydrogen. — Phosphorus Oxides. — Phosphorus Oxacids : Hypophos- phorus Acid, Phosphorous Acid, Phosphoric Acid, Metar phosphoric Acid, Pyrophosphoric Acid. — Examination of Unknown Substances for the Acids previously given . . 193-207 CHAPl'ER XIV. Intboddction to the Metals. — Properties. — Alloys. — Analytical Classification of the Metals. — Salts of the Metals. _ A Natural Classification of the Elements 20a-223 XVIU CONTENTS. CHAPTEE XV. PAGE. The First Geottp Metals. — Lead, and its occurrence, prep- aration, properties, uses, compounds, and tests. — Silver : its occurrence, preparation, etc. — Mercury : its occurrence, etc. — Separation and Identification of Lead, Silver, and Mercury 224-240 CHAPTEE XVI. The Second Group Metals. — Arsenic, and its occurrence, preparation, properties, uses, compounds, and tests. — Anti- mony : its occurrence, etc. — Tin : its occurrence, etc. — Separ ration and Identification of Arsenic, Antimony, and Tin. — Bismuth: its occurrence, etc. — Copper: its occurrence, etc. — Cadmium : its occurrence, etc. — Separation and Identification of Bismuth, Copper, and Cadmium. ■ — Separation, etc., of the Metals of the Second Group. — Separation of the Metals of Groups I. and 11. — The Rare Metals of the Second Group: Gold, Platinum, Palladium, Ruthenium, Iridium, Rhodium, Osmium, Tungsten, Molybdenum . . , . . 241-272 CHAPTEE XVn. The Third Group Metals. — Iron .' its occurrence. — Iron Ore. — Preparation of Iron. — The Iron Furnace Wrought Iron. — Steel. — Properties, Uses, and Compounds of Iron. — Tests for Iron. — Chromium: its occurrence, etc. — Tests for Chromium. — Aluminum : its occurrence, etc. — Tests for Alu- minum. — Separation and Identification of Iron, Chromium, and Aluminum — Nickel : its occurrence, etc. — Tests for Mckel. — Cobalt : its occurrence, etc. — Tests for Cobalt. — Separation and Identification of Nickel and Cobalt. — Man- ganese : its occurrence, etc. — Tests for Manganese. — Zinc : its occurrence, etc — Separation and Identification of Nickel, Cobalt, Manganese, and Zinc — The Rare Metals of the Third Group : Beryllium, Indium, Gallium, Yttrium, Lan- thanum, Cerium, Didymium, Terbium, Erbium, Thorium, Titanium, Zirconium, Uranium, Tantalum, Niobium, and Vanadium 273-30S CONTENTS. XIX CHAPTER XVni. The Fourth Group Metals. — Barium : its occurrence, etc. — Tests for Barium. — Strontium : its occurrence, etc. — Tests for Strontium. — Calcium : its occurrence, etc. — Tests for Calcium. — Separation and Identification of Barium, Stron- tium, and Magnesium. — Magnesium : its occurrence, etc. — Tests for Magnesium 309-319 CHAPTER XIX. The Fifth Group Metals. — Potassium: its occurrence, etc. — Tests for Potassium. — Sodium : its occurrence, etc. — Soda Preparation by the Black Ash and Ammonia Processes. — Tests for Sodium. — Ammonium. — The Ammonium Salts. — The Analysis of Unknown Substances 320-340 APPENDIX. Devoted to The Laboratory, Apparatus, Working Material, Reagents, etc., etc 311-366 HISTOEIOAL SKETCH. 1. The word Chemistry is probably derived from Chi mia, which is an old name for Egypt. The word signifie simply the Egyptian art ; and it was so called since chem istry was first practised by the Egyptians. Like aU sciences which have to deal with Nature chemistry has been developed by a long and tediou series of experiments. Since the art of experimentin; is a comparatively modern one, the Ancients, as om would naturally infer, were not deeply versed in thi science. The principal obstacle in the way of their prog ress is apparent when we know that they made great usi of the speculative method ; that is, when they wanted ai explanation of any fact .in Nature, they simply though about it, without seeking to verify their conclusions b^ the test of rigid experiment. The Egyptian priests were the learned class of thei time ; and their researches were carried on with such ai air of mystery, and at such uncanny times, and in sucl secret places, that Chemistry was spoken of as the Black or Secret Art. We find, however, that the Egyptiani possessed a considerable knowledge of the arts of dye ing, painting, and glass-making ; and that they were quit( skilled in metallurgy and the manufacture of pottery. About the time of Aristotle (fourth century B.C.) it was 2 HISTOKICAL SKETCH. believed byso"ie that all bodies are only modifications of one fundamental substance ; by others, that all substances are but the dwelling-places of four properties, — viz., heat, cold, moisture, and dryness, — and that these four prop- erties of matter are best represented in the four sub- stances, fire, air, water, and earth. It was further believed that these properties could be transferred from one body to another, and, as a consequence, that the ordinary metals, such as iron, could be transformed into the noble metal, gold. It will be readily understood that this thought fur- nished a powerful incentive to work,, which incidentally contributed something towards the advancement of chem- istry. Considering the object he had in view, it is not surprising that the chemist practised his art in caverns and at night, where no prying eyes could see his opera- tions, nor that he recorded his transactions in ambiguous terms and in mysterious characters. We thus find the ancients making but little progress in true chemical science. Moreover, we now know that their pernicious methods and theories were detrimental for many centuries afterwards, notwithstanding the fact that chem- istry originated in these self-same theories and methods. 2. The Arabs, in the year 640 A.D., invaded Egypt and became acquainted with the Egyptian sciences. Geber, an Arabian alchemist of the eighth century (the Arabs gave chemistry the name Al-Ohemia'),-WTote the first book on chemistry. He understood many chemical manip- ulations, discovered a solvent for gold, a mixture of nitric and hydrochloric acids or aqua regia, and proposed the first theory of the chemical composition of the metals, viz., that sulphur and mercury were the simple or primary sub- stances from which all the different metals are derived. HISTORICAL SKETCH. 3 In this period, then, we find an encouraging advance ; chemical processes are becoming more generally known, and a suggestive though erroneous theory is announced, which is destined to develop, through many modifications, from error into truth. As an instance of the manner in which this theory was afterwards modified and extended, we may here mention the fact that Basil Valentine of the fourteenth century, accepting sulphur and mercury as the. primal elements, extended the conception to aU sub- stances ; and that Boyle, three centuries later, doubtlessly influenced by this same theory to investigate this problem, announced the true solution. 3. During the Middle Ages the Arabians fostered the sciences. Their academies in Spain were sought by stu- dents from aU parts of the civilized world ; these philoso- phers, returning to their native countries, taught chemistry there. Thus we find, in the thirteenth century, Raymond Lully in Spaia, Albertus Magnus in Germany, Arnold Villanovanus in Prance, and Roger Bacon in England. All these believed in the transmutation of the metals, and the philosophy of their time teemed with mysticism and nonsense. We must here note that the all-absorbing theme was the Philosopher's Stone, a substance which should transform the baser metals into precious gold. The writings of this period are extravagant, confused, and purposely so written that they are nearly unintelligible. Bacon, however, to clear himself of the charge of sorcery (chemistry was still the Black Art), wrote a treatise in which he showed that many things supposed to be caused by supernatural agencies are produced by natural causes. The search for the Philosopher's Stone during this period brought to light many facts in inorganic chem- 4 HISTORICAL SKETCH. istry; and thus do we find alchemy slowly but surely paving the way for genuine chemistry. 4. In the era of Medical Chemistry, chemists directed their investigations into a different channel.' They then sought the Elixir Vitae, or Elixir of Life, — a cordial which should cure all the ills of mankind, and give per- petual youth. By a strange misinterpretation of Aristotle, some chemists also conceived the idea that the Philoso- pher's Stone, when found, would achieve the same results. Paracelsus (1493-1541) was the most noted of these investigators. By his great achievements he earned the title, The Father of Medicine. Agricola (1490-1555) wrote the first treatise on Metal- lurgy and Mining. Libavius wrote the first Hand-Book of Chemistry, his Alchemia, which was published in 1595. Van Helmont (1577-1644) deserves special mention, since he was the first to emancipate himself from the theories of the Aristotelian school. He also discovered various gases, and showed that metals are not destroyed when dissolved in acids. But he, too, had his delusion: it was his Alkahest, a universal solvent as well as a universal medicine. Robert Boyle (1627-1691) advanced still further: he claimed that the exact number of the elements was not known, and he clearly stated the difference between the elements and the compound substances. He also raised chemistry to the dignity of a true science, which was not to be studied as a part of any other, but as one of the great Natural Sciences. During this period many useful and potent medicines were discovered, and, although error was by no means HISTOEICAIi SKETCH. completely banished, the fundamental principles of chem- istry were well grounded in truth. Hereafter, the history of chemistry is a history of improvements, discoveries, and researches extending to all the different branches into which this science has developed. 5. Pneumatic Chemistry was the next phase in the development of our science. This period was remarkable for the investigation of the properties of gases, and the phenomena of combustion. Stahl sought to explain combustion by assuming the existence of a combustible principle, or element, which he termed Phlogiston. According to his views, this element must be taken away from combustible bodies to render them incombustible. Among the believers in Phlogiston were three remarka- ble men : — 1. Joseph Priestley, who discovered oxygen gas in 1774, and afterwards other and important gases. 2. Henry Cavendish (1731-1810), who experimented with inflammable air (hydrogen gas), determined the density of the gases, and discovered the unvarying com- position of the atmosphere. 3. Charles William Scheele (1742-1786), a Swedish chemist, who discovered chlorine gas, prussic acid, gly- cerine, and the pigment, Scheele's green. He also made such other researches that he is entitled to be placed among the founders of Quantitative Analysis. ■ None of these three ever discovered the true explana- tion of combustion. The Phlogiston theory, however, could not stand the test of rigid experiment ; and Lavoi- sier, by exposing its fallacies, ushered in the new era of chemistry, or 6 HISTORICAL SKETCH. 6. The Modern Era. — From his own experiments and those of his predecessors, Lavoisier determined that a burn- ing body unites with, or tahes up a combustible element, oxygen. By the use of the balance he discovered the great fundamental truth, that, however great the changes matter may undergo, no loss in weight occurs, or, in other words, that matter is indestructible. He also introduced a system of chemical nomenclature, which has been of inestimable value, as chemists not only disagreed as to the names of the substances with which they were acquainted, but often and purposely called one substance by so many names that their meaning was not at all certain. Dalton, next to Lavoisier, gave a great impetus to the study of chemical phenomena by the discovery of the laws of combination, known as the laws of " definite and mul- tiple proportions," and by the propounding of the atomic theory. Gay Lussac discovered the law of combination of gases by volume. In 1808 Sir Humphry Davy discovered, by means of electrolysis, the compound nature of the alkalies. In 1828 Wohler prepared urea from inorganic sub- stances, thus crossing out the division line between or- ganic and mineral chemistry. Spectrum analysis, dating back scarcely farther than 1860, has not only revealed the existence of many new terrestrial elements, — such as caesium, thallium, rubi- dium, indium, etc., — but has enabled us to determine the composition of the sun and stars themselves. Chemistry is no longer the Black Art, nor the handmaid of astrology, but a legitimate science, exact in its methods, and beneficent in its results. While, as a pure science, its HISTORICAL SKETCH. 7 aim is the investigation of truth, it has in its practical application formed an important factor in the industries of all civilized countries. SuGGESTios-. Bead Rodwell's Birth of Chemistry; Boscoe's Spectrum Analysis; Whewell's History of the Inductive Sciences, pp. 261-310 ; Boscoe and Schorlemmer's Treatise, pp. 1-40. Write short biographical sketches of the chemists mentioned (consult an Encyclopedia). IIsTTEODUOTIOI*!". DEFINITIONS. — LAWS OF COMBINATION IN DEFINITE AND MULTIPLE PEOPOBTIONS. — ATOMIC THEOBT. — ATOMIC WEIGHTS. — NAMES OF ELEMENTS. — SYMBOLS. — TABLE OF THE ELEMENTS. 7. To Sxperiment with a substance is to place it under certain .conditions or with certain substances to iscertain its properties and behavior. An experiment is a question intelligently put to Nature. Experiment 1 p. (To the student.) Since this is your irst experiment in chemistry, you may feel uncertain as to prhat you are expected to do, or how you are to derive the Host benefit from your work. In general, it is a safe policy ilways to work carefully, and to note all phenomena that aecur ; from these phenomena you are then expected to derive jertain desired conclusions. It is true, that, for various rea- sons, you may sometimes need assistance in reaching these 3onelusions ; in such cases you must necessarily rely upon the 3xperience of others. Although this latter method is a legiti- mate and often an indispensable way of obtaining knowledge, we may safely say that he has the most truly scientific spirit md methods, who, so far as possible, works and observes for tiimself. In the experiments you are about to make, you may watch for any changes that take place in the substances experimented upon. Some of these changes may be perceptible to the sense INTRODUCTION. 9 of sight, and some to the sense of smell ; others may be per- ceptible to the sense of touch ; and still others to general sensi- bility ; but, as a usual thing, the chemist depends mainly upon sight and smell to detect any changes in the substances upon which he is working. Now let us ask of Nature a few ques- tions. Steadily and persistently hold a platinum wire in a Bunsen flame (Art. 28). What occurs? Now cut off a very short piece (say 2°"°) of the wire, place it upon a piece of charcoal, and heat it by means of the blow-pipe flame (Art. 28) . What takes place? Then cover the bit of wire with a mixture of sodium carbonate (NajCOa) and potassium nitrate (KNOg), and slightly moisten the whole. Again heat in the blow-pipe flame as before. Wliat results? Now wash the piece of wire clean, and place it in a test-tube ; then add nitric acid (HNO3) , and warm gently in the Bunsen flame. What occurs? Again wash the wire, add hydrochloric acid (HCl), and warm as before. What have you obsei-ved? You may possibly be inclined to answer, " Nothing of importance." But let us see. Did you succeed in separating the platinum into two or more different substances ? Assuredly not ; nor could you have so separated it by any process known to man. Now that is important, since there are, besides platinum, about sixty- eight other substances that have not been separated into simpler ones : and these should have a class name. Hence the fol- lowing name and definition : — 8. An Element is a substance that has not been divided into two or more simpler substances. Examples. Gold, Iron, Silver, Tin, Oxygen, Potassium. Note (to the student). You are not to infer that all these sixty-eight elements would behave precisely like platinum : such, indeed, is not the case. Very few of them could have withstood the above treatment with- out undergoing marked changes. None of them, however, would have yielded two different substances, in which respect alone do they all agree with platinum. 10 INTRODUCTION. QuEKT. What is a definition ? Suggestion. Try, as above, bits of lead, copper, iron, zinc, etc. Com- pare the results with those obtained from platinum. Exp. 2 p. Place in a test-tube a short piece of thoroughly dried pine wood as thick as a lead-pencil. Heat it over a Bunsen flame, or a spirit-lamp. What collects on the sides of the tube, what escapes, and what remains behind? Burn this remainder on platinum foil, and what will then remain? Queries. What did you obtain from the wood % What became of the charcoal when burned ? Did any tar escape with the smoke f How do you know? Any water ? Prove it. (SuG. Hold a piece of cold glass in the escaping vapors.) Will a piece of brick give the same results? Try it. Exp. 3 p. Place in a hard glass tube, open at both ends, a small piece of galena (PbS) . Hold the tube somewhat slant- ing in the Bunsen flame, so that the greatest heat shall strike underneath the galena. Notice the odor of the fumes which soon issue from the tube. These are the fumes of burning sul- phur. Now place the residue in a shallow, cup-shaped cavity, which you are to make in a piece of charcoal. Cover the resi- due with sodium carbonate (NajCOg) , and slightly moisten the whole. Heat it before the blow-pipe flame and you will obtain a metallic bead. What metal is it ? It is evident that vrood and galena are not elements ; and, as the student's experience increases, he will learn that there is a very large class of substances which can thus be separated into simpler ones, and that these simpler substances are united in definite proportions by weight. Hence the following name and definition : — 9. A Compound (chemical) consists of two or more ele- ments chemically combined in definite proportions. (Art. 17.) Ex. Salt (NaCl) ; Water (H^O) ; Sugar (Cj^Hj^Oji). INTBODUCTION. 11 Exp. 4 p. Mix thoroughly. 0.56^ of very fine iron-filings and 0.32^ powdered sulphur. Although the mixture resembles neither iron nor sulphur, this is only a mechanical mixture, and the microscope reveals the particles of iron and sulphur lying side by side : moreover, they may be separated by mechanical means. Now heat one-half the mixture to red- ness in an iron spoon ; a glow diffuses itself throughout the mass, and the iron combines with the sulphur in definite pro- portions. No microscope can now distinguish the iron and sulphur particles, nor can thej' be separated except by chemi- cal means. The iron and sulphur have exactly entered into chemical uniSn. Qtteries. Can you, with a magnet, separate the iron from the sulphur before heating? Try it. Will bisulphide of carbon (CS^) dissolve out the sulphur from the iron particles before heating ? Try it. Should the sul- phur dissolve, evaporate the solution to dryness on a watch crystal, and see a the sulphur will remain as a residue. After heating, pulverize the mass and try as above. What difference do you find '' From the above we derive the two following defini- tions : — 10. A Mechanical Mixture is formed when substances are put together in no definite proportions, and the result- ing substance retains the properties of its constituents. 11. A Chemical Combmatlon or Keactlon takes place when two or more substances unite in definite proportions to form one or more substances entirely different from the original ones. 12. Chemistry is that science which treats of the ele- ments found in nature, their properties, compounds, and actions and reactions upon one another. Matter exists in three forms ; viz., Solids, Liquids, and Gases. 12 INTEODUCTIOK. 13. Solids do not readily . cTiange their forms, since in them the attractive (inter-molecular) forces exceed the repellent forces. 14. Liquids do readily change their forms, since their attractive and repellent (inter-molecular) forces are equal, or nearly so. 15. In G-ases, the repellent forces are greater than the attractive forces, consequently gases always tend to occupy a larger space. m SuG. Name several solids. Liquids. Gases. Show, by heating a piece of ice till it vaporizes, that water exists in all three conditions. 16. Chemism is an attractive force which is exerted between the elements, causing them to enter into com- bination with one another. Note. Cohesion and chemism tend to draw particles together. In all solid and liquid compound todies, both chemism and cohesion operate : the former holds the elements together, and determines the composition of the body ; the latter holds the particles of the compound togetlier, and gives us the mass. Seat is a repellent force, and tends to separate the small particles of all bodies, as is shown by the expansion of bodies when heated. 17. Law of Definite Proportions. — If we examine any chemical compound, — such, for example, as water, which consists of the elements hydrogen and oxygen; common salt, which consists of the elements sodium and chlorine, — we find that the compound always contains exactly the same proportions of its constituents. Water always contains 88.89 per cent of oxygen and 11.11 per cent of hydrogen; common salt always contains 39.32 per' cent of sodium and 60.68 per cent of chlorine. As a re- sult of the careful analysis of a very large number of INTBODUCTION. 13 chemical compounds, the law of definite proportions was propounded. The law may be stat'ed in this form : — Any given chemical compound always contains the same elements in the same proportions by weight. Bem. It is, of course, impossible for the beginner to prove the cor- rectness of this law, for the reason that the proof cannot be furnished without the employment of some of the most delicate and diflScult chemi- cal processes. 18. Law of Multiple Proportions. — Some elements form more than one compound with each other. Thus hydrogen and oxygen form not only water but hydrogen dioxide ; iron and sulphur form three compounds : nitro- gen and oxygen form five compounds. If we examine the proportions by weight in which the elements unite, we find very curious and interesting relations. Thus, in water we find : hydrogen 1 part, oxygen 8 parts ; in hydrogen diox- ide, hydrogen 1 part, oxygen 16 parts. (See Art. 38.) In the compounds of iron and sulphur (Art. 293), there are: Compound 1 , 32 parts of sulphur and 56 parts of iron. Compound 2, 64 " " " 56 " Compound 3, 96 " " " 112 " " In the compounds of nitrogen and oxygen (Art. 56), there are: Compound 1, 28 parts of nitrogen and 16 parts of oxygen. Compound 2, 28 " " " 32 " " Compound 3, 28 " " " 48 " Compound 4, 28 " " " 64 " Compound 6, 28 " " " 80 " The amount of oxygen in the second compound of hydrogen and oxygen is just twice as great, — not one 14 INTKODUCTION. and one-half, nor any fractional number of times, as great, as in the first. The amounts of sulphur in the three compounds of iron and sulphur bear to each other the relation of 1 : 2 : 3 j and the amounts of iron are to each other as 1:1:2. Finally, in the compounds of oxygen and nitrogen, the amounts of oxygen are to each other as 1:2:3:4:5; the amount of nitrogen remaining constant. These cases illustrate what is known as the law of multi- ple proportions, which may be stated thus : If two elements, A and B, form several compounds with each other, and we consider any fixed amount of A, then the different amounts of B which combine with this fixed amount of A hear a simple ratio to each other. 19. ComMnlng Number. — For each element we can select a certain number which will enable us always to express the proportion by weight in which this element enters into combination. Thus, we may select the number 16 for oxygen, and we find that no matter what the compound may be in M^hich we find the oxygen, its proportion may be expressed by 16 or some simple multiple of 16. In the same way we find that 32 may be selected for sulphur ; 14 for nitrogen ; 56 for iron, etc., etc. The figures thus selected are known as the combining numbers. Elements always combine with each other in the proportions expressed by their combin- ing numbers, or by simple multiples of these numbers. Thus, according to this, if sulphur and oxygen unite, we would expect to find them in their compounds in the proportions of 32 parts of sulphur to 16 parts of oxy- gen ; 32 parts of sulphur to 32 parts of oxygen ; 32 parts of sulphur to 48 parts of oxygen, etc. Compounds cor- INTROfcUCTION. 15 responding to the last two proportions are known. (See Art. 164.) 20. Atomic Theory. — To account for the fact that ele- ments unite in fixed proportions, it is assumed that all matter is made up of indivisible particles called atoms, and that each different kind of atom has its own particular weight. When chemical combination takes place, it is supposed that this consists of a union of the atoms of the elements which take part in the action. Thus, when iron and sulphur are brought together, at first no action takes place ; but when they are very intimately mixed, and the mixture heated, it is believed that each atom of iron seizes upon an atom of sulphur, uniting with it. Now, as these atoms have definite weights, it follows that, no matter how many unite, the compound formed must always contain the elements in the proportion of the weights of the atoms. The simplest kind of combination is that in which the elements unite in the proportion of one atom of one ele- ment to one of the other. But the elements may unite in the proportion of one atom of one to two, or three, or even four of the other, etc. Or, two atoms of one may unite with three of another, etc. Hence, it follows that the amounts of any element found in different compounds must bear simple relations to each other. 21. Atomic Weights. — The numbers called combining numbers are believed to express the relative weights of the atoms of the elements, and are now called atomic weights. The numbers now in use are intended to express the weights of the atoms of the elements as compared with the weight of the atom of hydrogen taken as unity. Thus, when we say that the atomic weight of oxygen is 16, and that of nitrogen 14, we mean that the weight of the atom 16 ESTTEODtJCTtOK. of oxygen is 16 times as great as that of the atom of hj^drogen ; and that the weight of the atom of nitrogen is 14 times as great as that of hydrogen. 22. Determination of Atomic Weights. — To deter- mine the atomic weight of an element is by no means a simple matter; indeed, it is extremely difBcult. If all the elements united with each other in only one propor- tion it would not be difficult to agree upon atomic weights. Thus chlorine and hydrogen unite with each other in the proportion of 35.5 parts of chlorine to 1 of hydrogen; bromine and hydrogen in the proportion of 80 parts of bromine to 1 of hydrogen; iodine and hydrogen in the proportion of 127 parts of iodine to 1 of hydrogen ; and these elements do not unite with hydrogen in any other proportions. Hence, we may assume that in the com- pounds formed we have, in the first place, one atom of chlorine united with one atom of hydrogen ; in the second, one atom of bromine with one of hydrogen ; and in the third, one of iodine with one of hydrogen. We are thus led to the conclusion that the atom of chlorine weighs 35.5 times as much as the atom of hydrogen, or that the atomic weight of chlorine is 35.5 ; and, in the same way, that the atomic weight of bromine is 80, and that of iodine 127. When, however, two elements unite in more than one proportion, — and this is the rule rather than the excep- tion, — it is clear that we must be left in doubt as to the number to select as the atomic weight. Thus, hydrogen and oxygen, as was remarked above, unite in two different pro- portions. In the first there are 8 parts of oxygen to 1 of hydrogen ; in the second, 16 parts of oxygen to 1 of hydro- gen. From this we might conclude that 8 is the atomic INTRODtrCTION. 17 weight of oxygen. But we may just as well express the proportions by saying that in the first there are 16 parts of oxygen to 2 of hydrogen ; and in the second, 16 parts of oxygen to 1 of hydrogen. And we might, with equal justice, conclude that 16 is the atomic weight of oxygen. We shall find that two methods are in general use for the determination of atomic weights. The first is based upon a consideration of the specific gravity of elements and compounds in the form of gas or vapor ; the second, upon the specific heat of elements and compounds. These methods will be described after some of the elements and their compounds have been considered. (Art. 157.) 23. Names of the Elements. — The ancients were acquainted with only seven elements ; viz., gold, silver, copper, iron, mercury, lead, and tin. They dedicated these to the heavenly bodies ; e.g., silver was dedicated to the moon or luna. ' In this fanciful way some of the names of chemical compounds originated ; e.g., nitrate of silver is yet called lunar caustic. The elements have i-eceived their names in different ways : — 1. Some retain their ancient names. 2. Some are named from some marked characteristic ; e.g., phosphorus, light-bearer ; bromine, a stench. 3. The names of some end in " ine " or " on," to indi- cate a similarity of properties in those so terminating. 4. Some are named from the place of their discovery. 5. The names of recently discovered substances pos- sessing metallic properties end in " um " or " ium." SuG. Student find illustrations to above from Art. 25. 24. Symbols. — In expressing the composition of chemi- cal compounds, it is desirable to have a system of symbols. 18 INTRODUCTION. Those now in use consist of letters which stand for the names of the different elements. Thus, O stands for Oxy- gen, H for Hydrogen, N for Nitrogen, etc. When only one element is known, whose name begins with a certain letter of the alphabet, that letter is used as the symbol. When two or more are known, the names of which begin with the same letter, that one best known or first discov- ered is generally designated by the letter, while the others are designated by this letter and some other letter occur- ring in the name, e.g.. Carbon, C ; Chlorine, CI ; Calcium, Ca ; Caesium, Cs ; Cadmium, Cd ; Cobalt, Co ; etc. Some elements have symbols derived from their Latin names. This is perplexing to the student, but this list will explain: — Antimony, Sb, from Stibium. Copper, Cu, " Cuprum. Gold, Au, " Aurum. Iron, Fe, " Ferrum. Lead, Pb, " Plumbum. Mercury, Hg, " Hydrargyrum. Potassium, K, from Kalium. Silver, Ag, " Argentum. Sodium, Na, " Natrium. Tin, Sn, " Stannum. Tungsten, W, " Wolframium. The symbol stands not only for the name of the element, but for its atom. Thus, O means not only oxygen, but an atom of oxygen ; 2 or O2 means two atoms of oxygen, etc. In expressing the composition of bodies by means of these symbols, we simply place the latter side by side. Thus, HCl stands for a body which consists of hj'drogen and chlorine in the proportions, 1 part by weight of hydro- gen to 35.5 of chlorine ; or, in terms of the Atomic Theory, it stands for a body which is formed by the union of hydro- gen and chlorine in the proportion of 1 atom of hydrogen to 1 of chlorine. An expression like HCl is called a for- mula. INTRODUCTION. 19 In expressing the composition of a body in which more than one atom of the same kind is present, a small figure is added below the line to the right of its symbol. Thus, potassium nitrate, which consists of potassium, nitrogen, and oxygen, in the proportion of 1 atom potassium, 1 nitrogen, and 3 oxygen, is written KNO3. A large figure placed before a formula affects every symbol in the for- mula. Thus, if we want to express two parts of potassium nitrate, we usually write 2 KNO3, and not (KN03)2. We repeat a group of atoms (NO3, NH4, etc.) which we wish to keep together as a whole (Art. 159), thus : Pb(N03)2, (NHO^S. Following is a list of the elements which have thus far been discovered. The table includes not only the names of the elements, but their atomic symbols, atomic weights, — as determined by every available method, — and their specific gravities. The small Roman numerals or indices added to the sym- bols are intended to indicate the valence (see Art. 158) of the elements. Usually the symbol is written without these. 20 rNTftODtrCTION. 25. A Table of the Elements • Names. Symbols. Atomic Weights. Physical condition at ordinary temperature. Speciflo Gravity. Aluminum Al"" 27. Solid 2.60 Antimony Arsenic Sb'"'^ As'"'' 120. 75. U 6.71 5.73 Barium Ba" 137. ii 3.75 Ber^-llium Be" 9. u 2.07 Bismuth Bi"'.v 208. (; 9.80 Boron Bo'" 11. ii 2.5? Bromine Cadmium Br'.v Cd" 80. 112. Liquid Solid 3.187 8.60 Caesium Cs' 133. a 1.88 Calcium Ca" 40. u 1.57 Carbon C"" 12. u 3.5-6 Cerium Ce'"'"" 141. ii 6.68 Chlorine Cl''^ 35.5 Gas 2.450 Chromium Cr""." 52. . Solid 6.50 Cobalt Co"'"" 59. it 8.5-.7 Copper Didymium Erbium Cu" D'" E'" 63.3 142.3 166. n u 8.95 6.54 Fluorine F' 19. — 1.313 Gallium G"" 69. Solid 6.95 Gold Au'''" 196.5 ii 19.32 Hydrogen Indium H' In"" 1. 113.6 Gas Solid 0.069 7.42 Iodine I',v 127. it 4.948 Iridium Jj.», »(',vi 193. a 22.42 Iron JigJd »/(,vi 56. ti 7.86 Lanthanum La'" 138.2 it 6.10 Lead Pb". "" 207. Li 11.37 Lithium Li' 7. (4 0.59 Magnesium Manganese Mn" 24. 55. ii ti 1.74 8.03 Mercury Molybdenum Nickel Hg" Mo"'""'" jif [11,1111 200. 96. 58. Liquid Solid 13.55 8.60 8.90 rNTRODUCTIOK. 21 Physical Names. Symbols. Atomic Weights. condition at ordinary Specific Gravity. temperature. Niobium Nb' 94. Solid 7.06 Nitrogen N'".v 14. Gas 0.971 Osmium Os"'""'''i 199. Solid 22.48 Oxygen 0" 16. Gas 1.105 Palladium Pd"."" 106. Solid 11.40 Phosphorus P'. "',v 31. :: ! Colorless 1.83 Red 2.20 Platinum Pt"'"" 195. 21.50 Potassium K' 39. 0.87 Rhodium Ro"'""'^ 104. 12.10 Rubidium Rb' 85. 1.52 Ruthenium Ru"'"">^ 103.5 12.26 Samarium Sm 150. Scandium Sc 44. Selenium Se".""." 79. 4.50 Silicon Si"" 28. 2.39 Silver Ag' 108. 10.53 Sodium Na' 23. 0.978 Strontium Sr" 87.5 2.54 Sulphur S", '"/,vi 32. 2.05 Tantalum Ta^ 182. 10.40 Tellurium Te"'""'" 125.? 6.40 Terbium Tb 148.5? Thallium Tl''"' 204. 11.85 Thorium Th"" 232. 11.00 Tin Sn"'"" 118. 7.29 Titanium Tj", nil 48. Tungsten Tj^nii, vi 184. 19.12 Uranium TJ"">" 239.8 18.70 Vanadium y///,y 51.5 5.50 Ytterbium Yb 173. — Yttrium Y'" 89. — Zinc Zn" 65. 7.15 Zirconium Zr"" 90. 4.15 22 INTRODUCTION. Rem. 1. Many elements occurring in the earth have also been dis- covered in the sun and stars. Ebm. 2. Some elements occur in such very small quantities that their properties are not accurately known ; while others have heen discovered so recently that they have not been fully investigated. { See Chem. News, Nov. 7, 1883, for List of Elements.) Rem. 3. More elements will be discovered, undoubtedly; and some sub- stances now known as elements may prove to be chemical compounds, as our chemical researches advance. SuG. Student, learn to spell the names of the elements. Learn to give the symbol when the element is named, and vice versa. Rem. 4. In estimating the specific gravity of the elements, water is taken as the standard for solids and liquids, while air is taken for gases. Rem. 5. The chemist also uses hydrogen as a standard for estimating the density of gases, as will be explained later. SUMMARY OF STUDENT'S WORK IN INTRODUCTION. 1. Make those experiments whose numbers are followed by the letter " p." General Note. When "p" follows the number of an experiment, the student should be able to do the work : if, however, the student cannot do the work, owing to various causes for which no text can provide, or if the teacher wishes the work done differently, a few simple oral directions from the teacher to the class will assist greatly. Experiments marked "t" are to be made by the teacher before the class. Let the pupils assist as much as possible. In experiments marked " tp," it is advisable for the teacher to make the experiment for the class before requiring the student to do it. Experiments marked " op " are optional. Encourage the student to exert his ingenuity in overcoming obstacles and he will soon become quite independent in manipulation. CHAPTER I. OXYGEN : ITS OCCTJEEENCE, PEBPARATION, PEOPEETIES, AND TESTS. — OZONE. THE ELEMENT OXYGEN. Symbol O". — Atomic Weight, 16; Specific Gravity, 1.1056. 26. Occurrence. — Oxygen occurs well-nigh everywhere in nature. It constitutes 44 to 48 per cent of the weight of the earth's crust, 88.89 per cent of water, and about 23 per cent of the atmosphere. Oxygen occurs in combination with every known ele- ment except fluorine. 27. Preparation. — Exp. 5 p. Heat one gram mercuric oxide, HgO, in a hard glass test-tube. The oxygen is driven off, whUe the mercury is condensed on the sides of the tube. Test the presence of the gas with a glowing match. (HgO = Hg + 0.) Query. Aug. 1, 1774, Joseph Priestley made this experiment for the first time. What gas did he discover ? Exp. 6 p. Minium, or red oxide of lead, PbjO^, is to be heated as above. A part of the oxygen is driven from the red oxide of lead with great difficulty. (PbsOi = 3 PbO -f O.) Test as before. Sua. Try KCIO3 with and without MnOj, as above. Also heat, as above, KCIO3 with a pine splinter. What occurs 1 Explain. 24 THE ELEMENT OXYGEN. Queries. Why does not the red oxide of lead, Fhfii, part with its oxygen as readily as mercuric oxide, HgO ? Arts. The lead has a stronger chemism for oxygen than mercury has. It is upon the principle of variable degrees of chemism existing between different substances, that double chemical reactions are always based. Do you obtain metallic lead in this experiment ? Heat some red oxide of lead on charcoal, witli sodium car- bonate (Na^COj), before the blow-pipe. Do you now obtain metallic lead ? What effect do the sodium carbonate and charcoal have on substances treated thus ? Ans. The charcoal abstracts oxygen from the oxide, or acts as a strong reducing agent. The sodium carbonate serves as a " flux,'' preventing the lead from again taking up atmospheric oxygen. Oxygen can be prepared most easily from the com- pounds which it forms with other elements ; as, mercuric oxide, HgO ; manganese dioxide, MnOa ; potassium chlo- rate, KClOs, etc. Potassium chlorate, KCIO3, is the most available sub- stance for preparing moderately large quantities in small laboratories ; but if very large quantities are required, it may be prepared more cheaply from manganese dioxide, although special apparatus is necessary. Potassium chlorate gives up its oxygen more readily and at a lower temperature when mixed with manganese dioxide (KCIO3 = KCl -f 3 O ). The manganese dioxide is unchanged. This method is best for laboratory use. Exp. 7t. Pulverize 100^ potassium chlorate, KCIO3, and mix thoroughly with 25^ manganese dioxide, Mn02. Place the mix- ture in an iron or copper retort,^ and arrange to wash the gas through two Woulff bottles : the first containing water, the sec- ond sodium hydroxide, NaOH. Now heat strongly but care- fully, and, when the air is expelled from the apparatus (test with a match) , connect with the gas receiver. Notice that at a certain point the gas is given ofE with great rapidity. The heat must be moderated immediately to avoid accident. You will thus obtain about 30' of pure oxygen gas. THE ELEMENT OXYGEN. 26 Caution. Organic matter or carbon, when present, may produce a serious explosion. It is best, therefore, to try a little of this mixture in a test-tube before heating the retort. Use C. P. materials. Note. It is always best to liave the class present when preparing such experiments as this last. Arrange the pneumatic trough, bell jare, wires, etc., and make the following experiments in a dark room. 28. Properties of Oxygen. — Exp. 8 t. Plunge into a jar of oxygen a glowing pencil of thoroughly charred bark charcoal. It will burn with brilliant scintillations. (C + 2 0= 002-) Note. This illustrates the combustion of fuel. Exp. 9 t. Place a bundle of very fine iron wires, tipped with sulphur and ignited, in a jar of oxygen. The wires will burn with a reddish light, and at times with beautiful scintilla- tions. (3 Fe + 4 O = Fe304. ) Note. This illustrates the great chemical activity of pure oxygen. Exp. 10 T. File the end of a -watch-spring till very thin. Draw the temper in a spirit-lamp, and uncoil it. Make a hook on the thin end, tip with sulphur, and ignite. Place in a jar of oxygen. The spring will burn with great energy. (3Fe+40 = Fe304.) Exp. 11 t. Place a piece of phosphorus in a jar of oxygen. Ignite. It burns with a brilliant white light. (2P-|-50 = P20s.) See Phosphorus. Exp. 12 t. Treat a piece of sulphur as in last experiment. It burns with a violet light. (S + 2 O = SOj.) Note. Do not allow the fumes from the burning of phosphorus and sulphur to escape in the room, as they are very disagreeable. Exp. 13 t. Cut zinc foil into fine strips ; make into a bundle ; tip with sulphur ; ignite. White light iu oxygen. (Zn-|-0 = ZnO.) Note. The product formed is called " Philosopher's Wool." 26 THE ELEMENT OXYGEN. Now that you have prepared and experimented with oxygen, you will be ready to appreciate several of its physical and chemical peculiarities which we term prop- erties. Oxygen is an invisible, odorless, tasteless gas. Its specific gravity is 1.10563; and 1' at 0° and 760"""" pressure weighs 1.430^. It has been liquefied by a pressure of 25.85 atmospheres at a temperature of — 131.6°. (Read R. jnd S., p. 516, Vol. II., Pt. II.) Exp. 14 op. Place a live mouse upon a cork raft, under a bell jar filled with air, over the pneumatic trough. Secure the jar so that no communication with the outside air is possible. Does the water rise in the jar ? What does this indicate ? Queries. How does the oxygen come in contact with the blood? What harm ensues from persons living in a room without ventilation 1 Is the blood purified by a physical or chemical process ? Oxygen is that constituent of air which is essential to breathing, and all animals consume it. "When inhaled, it enters into combination with some of the tissues of the body, actually burning them out, and thus liberating heat and energy. Air that has been breathed over too many times loses its vitality, the oxygen having been consumed. As oxygen occurs in the atmosphere, it is largely diluted with nitrogen. Exp. ]5 op. Place a live fish in a sealed jar of water. What follows? Why? Water absorbs free oxygen, and fishes consume this oxygen by means of their gills, which serve as lungs. QuERT. How does a jet fountain render water fit for preserving the life of fishes? THE ELEMENT OXYGEN. 27 Exp. 16 of. Place a burning taper in a closed jar of air. When the oxygen of the air is consumed, what occurs ? Queries. Why does blowing the fire cause it to burn more briskly ? Why does blowing a candle extinguish it ' (See next Exp.) Fire or Combustion is produced by the union of the fuel with atmospheric oxygen. Before a substance can unite with oxygen, it must be heated to what is called its burning temperature or kindling point ; and to produce flame, it must be converted into a gas. A flame is a burn- ing gas. Exp. 17 p. Carefully place a bent glass tube very near the wick of a lighted candle, within the flame zone. The gas Bscaping from the wick will be forced up through the tube, and may be lighted at the other end of the tube. Since the gas which escapes from the wick burns only when mixed with air, the flame of a candle has but a thin outer zone, in which the gas is entirely consumed. (Fig- 1-) Explanation of Fig. 1. T, bent glass tube. c, centre of unconsumed gas. p, zone of incomplete combus- tion. p, light zone, or zone of com- plete combustion. p', unconsumed gas burning at end of glass tube. Queries. What does this ex- periment prove? Why can you not ignite a lump of anthracite coal with a match? Why does a blow-pipe give such a hot flame? Fig. 1. 28 THE ELEMENT OXYGEN. BuNSEN BuENEB. — This burner is almost exclusively- used in laboratories provided with gas for heating purposes. It gives a very hot, clean flame, owing to the fact that it is so arranged that the gas, before ignition, is thoroughly mixed with air, which insures its complete combustion. The tube e, shown in Fig. 2, is pierced with holes at its base, and the gas is discharged at about the height of these holes. Now, as the gas ascends the tube e, it draws a current of air along with it ; the air and gas mix in their ascent through e, and burn with a hot, non-luminous flame when ignited at the top of e. A ring a pierced with holes surrounds e ; by turning this ring, the holes dd maybe closed, when the gas burns with an ordinary luminous flame, which is the flame used for the blow-pipe. And here the student may learn the meaning of the terms Oxidizing Flame and Reducing Flame, for which he will hereafter find frequent application. The way in which these flames are produced is as follows : — 1. The Oxidizing Flame. — First close the openings ii, and make a moderately small luminous flame. Now place the tip of the blow-pipe in the centre of the luminous flame, and blow gently, using the cheeks like a bellows. The oxidizing flame should be non-luminous. In case you do not succeed in making it so, do not try to remedy the evil by blowing harder, which will end only in ex- hausting you, but moderate the flow of gas, and try again. After a little practice you should be able to keep the flame steady for half an hour, without becoming much fatigued. This flame tends to oxidize substances when they are placed in it, since it contains an excess of oxygen at a very high temperature. THE ELEMENT OXYGEN. 29 Queries. Whence comes this excess ? Should air from the lungs be used in blow-piping 1 "Why '! ScG. Examine a blow-pipe, and give a short description. 2. The Reducing Flame is made by placing the jet of tlie blow-pipe just outside of the luminous flame from the burner, with the openings closed. This flame is slightly luminous, and reduces or takes oxygen away from bodies placed in it, since it contains an excess of hydrogen and carbon (illuminating gas is a hydrogen-carbon compound) at a high temperature ; both hydrogen and carbon have a strong aifinity for oxygen. '' Moreover, the bead, or assay, is to be kept within the zone of complete combustion (Fig. 1) when you are using the oxidizing flame ; when using the reducing flame, the proper position of the assay is Avithin the zone of incom- plete combustion. QuEET. If you use your lungs for bellows, can you keep the blow-pipe flames steady ? Exp. 18 p. Make a borax bead by fusing borax on a loop of platinum wire. Slightly moisten this bead in ferrous sulphate, FeS04, and heat a short time in the oxidizing flame. The bead thus treated should be of a reddish color when hot, fading to a light yellow when cold. Now heat the same bead persistently in the reducing flame. It should become colorless unless too strongly saturated with the ferrous sulphate, when it becomes pale green. Unless the proper flames are used, these results cannot be obtained. Spontaneous Combustion. — The combination of oxygen and other substances always produces a definite amount of heat depending upon the nature of the substance. When iron rusts slowly, the heat is imperceptible ; but when greasy rags or waste are thrown in a heap, the heat pro- 30 THE ELEMENT OXYGEN. duced by the oxidation of the oils may, in time, be suffi- cient to raise the mass to the temperature of ignition. This kind of action, known as spontaneous combustion, is not unfrequently the cause of disastrous fires. Exp. 19 p. Sift very flue iron-filings over the flame of an ordinary lamp. What results? QtjEST, Why is this ' What does it illustrate 1 SuG. Try fine dust from a malt house, flour mill, wood-working shop, etc., as above. The best place to collect the dust is from rafters or high beams. Why ■? Fine dust collecting in the attics of large mills and malt houses has sometimes exploded when ignited, causing great destruction of life and property. Again, the sun's rays, when brought to a focus on inflammable substances, or steam pipes coming in too close proximity to inflammable substances, have produced unlooked-for conflagrations. Exp. 20 p. Place green plant-leaves in the sunlight, under a bell jar filled with water. Bubbles of oxygen will collect at the top of the jar. Oxygen is given off by plants growing in the sunlight. Enough oxygen is returned to the air in this way to keep its composition nearly uniform. 29. Tests for Free Oxygen 1. Char a small pine stick, as a match, and, with one end glowing, place it in a jar or current of free oxygen, when it will burst into flame. 2. Fill a flask with oxygen gas. Pour in a small quan- tity of potassium hydroxide, KOH. Shake, and no change in the liquid takes place. Then add a small quantity of pyrogallic acid, C6H3(OH)s. Shake again, and the liquid turns brown, oxygen being absorbed. OZONE. 31 N.B. In testing an unknown gas in this way, it is absolutely necessary to exclude all air, as the free oxygen of the air gives this reaction. It is best, therefore, to fill the flask over mercury. (See App.) OZONE. 30. Ozone is a peculiar or allotropic form of oxygen found in the atmosphere, and produced by electrical dis- charges, or by evaporation, or by both. "When an element occurs in more thau one form, the unusuaL one is called an allotropic form. It is easily prepared by several methods. 31. Preparation. — Exp. 21 p. Place a small quantity of a solution of potassium permanganate, KsMujOg, in a flask or test-tube. Add a few drops strong sulphuric acid, H2SO4. Notice the odor of the gas given off. It is ozone. Applj' Test 1 for ozone. Ozone may be prepared by suspending a clean stick of phosphorus in a closed jar containing a little water and atmospheric air at a temperature of 15° to 20°. Ozone is formed very rapidly. When an electrical machine, in good working order, is in action, a peculiar odor is observed which is due to ozone. (Use Test 1, Art. 33, for ozone.) Ozone may also be obtained by passing a silent electri- cal discharge, carefully avoiding sparks, through a closed jar of oxygen. S0G. Produce ozone by one or all of the above methods. 32. Properties. — Ozone is three volumes of oxygen condensed to two volumes, the condensation being proba- bly accompanied by some deep-seated change in the relation of the atoms. 32 OZONE. There are good reasons for believing that the molecule (Art. 155) of ordinary oxygen consists of two atoms, as indicated by the formula O2, and that the molecule of ozone should be represented by the formula O3. Ozone is readily changed into ordinary oxygen. It is an active oxidizing agent. When brought in contact v?ith mercury and some other substances in the dry state and at ordi- nary temperatures, it converts them into oxides, and itself becomes ordinary oxygen. Ozone readily acts upon organic substances, and is sup- posed to destroy the germs of contagious diseases. When present in large quantities, ozone has an irritating effect on the lining membranes of the throat and nostrils, where- fore it should be dilute if inhaled. Atmospheric ozone is more plentiful in the open country than in cities, and more is found out of doors than in dwellings. (Why ?) Note. It is extremely difficult to determine whether the suhstance in the atmosphere which is commonly called ozone, is really ozone or not. There are certainly other substances present which in some of their properties closely resemble it; such, for example, as hydrogen dioxide (Art. 44). 33. Tests for Ozone. — 1. A paper strip saturated with a solution of starch paste and potassium iodide, KI, turns blue when exposed to the action of ozone. Eem. This test is the one employed to determine the presence and amount of ozone in the atmosphere ; but it is not reliable, since some of the oxides of nitrogen, which also exist in the atmosphere, affect the paper similarly. 2. Its odor, resembling dilute chlorine, beti?ays ozone when present in considerable quantities. 3. Metallic mercury, Hg, when dropped into a flask containing ozone, immediately tarnishes. OZONE. 33 SUMMARY OF STUDENT'S WORK IN O. AND OZONE. 1. Make the experiments as indicated. 2. Make Tests 1 and 2, Art. 29 ; also test a flask of common air by 2. 3. Make Tests 1, 2, and 3, Art. 33; also fit a delivery tube to the florence flask used in Exp. 21 p, and direct the jet of ozone against a globule of Hg in the bottom of a test-tube. What result ? 4. Allow the jet of ozone to pass into a test-tube containing a solution of starch paste and KI. What occurs ' 5. Read R. and S., Vol. 1., p. 194, et seq., for a more complete discus- sion of ozone. 6 Read Huxley's Elementary Lessons in Physiology on the arterialization of the blood. 7. The manganese bead (Art 316) will furnish the student excellent practice in the use of the oxidizing and reducing flames. 8. Will ozone give the oxygen test with the glowing match 1 How can you distinguish between ozone and oxygen 1 OHAPTER II. HYDROGEN. — ITS OCCUREENCE, ETC. ■ HYDROGBK DIOXIDE. WATER. - HYDROGEN. Symbol H'. — Atomic Weight, 1; Specific Gbavity, 0.0692. 34. Occurrence. — Hydrogen is found, nearly always, combined with other substances. It occurs free, however, in very small quantities in certain volcanic gases, and absorbed in meteorites. It occurs combined with oxygen in the form of water, of which . it constitutes 11.11 per cent by weight. It is a constituent of ammonia, coal gas, marsh gas, and of nearly aU organic sub- stances. 35. Preparation. — Exp. 22 t. Use the apparatus shown in Fig. 3. Add 1 part by weight of pure sulphuric acid, H2SO4, to 20 parts distilled water ; then open the stop-cocks S and S'. Pour the acidulated water into the tube B until it issues from the tubes O and H. Then close the stop-cocks, and fill B up to the bulb. Connect the platinum wire Z, which is melted through the tube H, and terminates in a platinum strip, with the zinc pole of a Grove's Fig. 3. battery consisting of five or six cells. Also connect the platinum wire P (which is like Z in every respect) to the platinum pole of the battery. Hydrogen collects in tube H, and oxygen in tube O. The hydrogen in tube H may be tested by slightly opening the stop-cock S', and igniting. Hydrogen burns with a very hot flame, although it emits but little light. Queries. oxygen ' In which tube is the Tolurae of gas greater 1 How test the Exp. 23 t. Make an amalgam by rubbing, in a porcelain mortar, one-half gram metallic sodium, or potassium, together with 5^ mercury. Fill a jar with water, and arrange as in Fig. 4. Place the amalgam in a wire gauze cage, and insert under the mouth of the jar. Hydrogen is liberated, which rises, and fills the jar. Test by carefully raising the jar, mouth downwards. Fig. 4. and plunging a lighted taper upward into the jar. The taper is extinguished, but the hydro- gen burns at the mouth of the jar. The taper may be relighted in this flame. Note. This experiment usually ends with a slight but not dangerous explosion. QuEBiBS. What becomes of the mercury of the amalgam after being dipped into the water ? Drop a piece, not larger than a, pea, of metallic sodium or potassium into a dish of warm water. What results ? Do you now see the reason for amalgamating the K or Na ? What is the reason ? Is the water alkaline 1 Note. Alkalies turn a strip of red litmus paper, blue. Acids turn blue litmus paper, red. 36 HYDROGEN. Hydrogen is best prepared in a pure state by the de- composition of water. It may be prepared in many other ways ; but it then contains impurities from which it is difficult to free it. The action of potassium on water is expressed by the equation K + H2O = KOH + H. Now let us inquire particularly as to the meaning of an equation. Primarily, it means that potassium and water give a substance called potassium hydroxide (KOH) and hydrogen. It will be seen that the sign -)- is read and, and the sign = is read give. But the equation means more than this. It tells us the exact proportions in which the substances act. For each one of the symbols stands for a. certain proportion of the element corresponding to its atomic weight. In the above, 39 parts of potassium act upon 18 parts of water (made up of 2 x 1 parts of hydro- gen and 16 parts of oxygen), and give the compound potassium hydroxide (made up of 39 parts of potassium, 16 parts of oxygen, and 1 part of hydrogen), and 1 part of hydrogen. These relations are maintained whenever potassium acts upon water. From the use of a given amount of potassium, provided there be enough water, we get a definite amount of hydrogen. Problem. How much hydrogen will be formed if 1008 of potassium were allowed to act upon water in such a way as to prevent the burning of the hydrogen ? How much potassium hydroxide will be formed t How much water will be decomposed ? SuG. Teacher will give a number of other similar problems, calling attention to the fact that instead of saying parts we may say grams, ounces, pounds, tons, or whatever unit of weight we may choose to take. Student review the equations inclosed in parentheses, and explain. HYDROGEN. 37 Exp. 24 t. Place a quantity of granulated zinc in tho gener- ating flask A, Fig. 5. Through the funnel tube B introduce a liberal quantitj- of dUute sulphuric acid, H2SO4, consisting of one part acid by weight to four of water. Allow the gas to escape through the delivery tube D for some time, to free the apparatus from air. Then collect in gas bags, or in the gas receiver, or in jars over the pneumatic trough. The reaction is represented by the equation Zn + HoSO, = ZnSOi + 2 H. We take no account of the water added, as it serves merely as a solvent for the zinc sulphate, ZiiSQj, as fast as formed. Fig. 5. Hydrogen is prepared in large quantities, when absolute purity is not especially requisite, by allowing dilute acids (HCl, H2SO4) to act on certain metals, such as iron and zinc. Note. Hydrogen made in this way may contain sulphuretted hydro- gen and other impurities, which, for the most part, are destroyed by pass- ing the gas through a solution of potassium permanganate. The gas may be dried by passing it through sulphuric acid or calcium chloride, or both. (Student should arrange an apparatus for making and purifying hydro- gen.) Having a quantity of hydrogen stored, teacher and students make the following experiments : — 88 HYDROGEN. 36. Properties. — Exp. 25 p. Fill collodion balloons to illustrate the lightness of hydrogen. Allow one or two of them to rise to the ceiling, and remain as long as they will. Even though they do not leak, they will, nevertheless, sink to the floor after a time. Why? Exp. 26 tp. Make hydrogen soap-bubbles, which will burn when touched with the flame of a taper. QuEKiES. Are these bubbles heavier or lighter than air 1 How can you tell the same of other gases t Exp. 27 tp. Discharge the hj-drogen pistol, illustrating the explosiveness of hj-drogen and oxygen. QuEET. Should you fill the pistol full of H, could you discharge it ■? Why? Exp. 28 tp. Produce singing flame. To succeed well with this, fit a long, straight jet into a generating flask containing metallic zinc and dilute sulphuric acid. When the gas is coming off freely, light the jet. Hold glass tubes of various lengths arid bores, down over the burning jet. In this way diflferent tones may be produced. Query. What produces the tones ? Exp. 29 tp. Fill a bell jar with hydrogen, by holding the mouth of the jar downward, and allowing the hydrogen to flow up into the jar. Now reach up into the jar with an inverted dipper (ordinary) . Keeping the dipper bottom side up, draw it slowly downward out of the jar, and remove it some distance awaj' ; then bring a lighted taper under the dipper. What ensues ? Explain. Pure hydrogen is an odorless, tasteless, invisible gas, which was discovered and described by Cavendish in 1766. Its specific gravity (air = 1) is 0.0692. Hydrogen is the lightest substance known: 1' at 0° C. and 760""" pressure, weighs 0.0896*. HYDROGEN. 39 Prob. How many grams H, at 0° and 760™"", will a bell jar of 20' capacity hold ? M. Pictet claims to have liquefied hydrogen at —140° C, and 650 atmospheres ; but the so-claimed liquid gave no meniscus in the tube in which he was endeavoring to condense the gas. SuG. Student, half fill a. test-tube with water, and note the meniscus at the upper level of the liquid. Hydrogen is highly combustible, burning with a very hot but slightly luminous flame, and, when mixed with considerable quantities of air or free oxygen, explodes with violence. The metal palladium absorbs hydrogen in large quan- tities at moderate temperatures. Platinum and iron also absorb it, but in much smaller proportion than palladium. It seems as if the hydrogen forms an alloy with them, acting very much like a metal itself. When a jet of hydrogen is directed against a piece of spongy platinum, at ordinary temperatures, so much heat is evolved as to cause the jet to ignite. Hydrogen is slightly soluble in water. It is not directly poisonous, but produces a weak- ening and sharpening effect on the voice, when inhaled. It is very diffusible, and is apt to contain atmospheric air. The extreme lightness of hydrogen caused it to be used for filling balloons ; but, owing to its great diffu- sibility and the expense of its manufacture, it has been superseded by coal-gas. One gram of hydrogen, when burned, produces enough heat to raise the temperature of 34,462^ of water through one degree. Hence its ca- lorific power is said to be equal to 34,462 thermal units, — the thermal unit or Calorie being the amount of heat necessary to raise the temperature of one gram of water one degree Centigrade. 40 HYDKOGBN AND OXYGEN COMPOUNDS. 37. Test. — Hydrogen may be recognized by its flame and behavior, as in the preceding experiments. HYDROGEN AND OXYGEN COMPOUNDS. 38. Hydrogen and Oxygen form two chemical com- pounds ; viz. : — 1. Water, H2O ; and 2. Hydrogen dioxide, H2O2. Water, H2O. 39. Occurrence. — With water we are all well acquainted. It occurs everywhere, — in streams, lakes, and the bound- less ocean. It exists in the atmosphere as vapors, fogs, and clouds, and is precipi- tated upon the earth as dew, rain, hail, and snow. It is absorbed by the soil and rocks, while in crystalline structures it enters into closer combination as water ^ of crystallization. 40. Preparation. — It is not necessary to prepare water chemically, owing to its great abundance every- where, but for the sake of illustration use the apparatus shown in Fig. 6. G is a hydrogen generator. B is a drying bulb, containing granulated calcium chloride. R is a bell jar. The hydrogen jet burning in this jar unites with the oxygen of the air, producing water, which soon collects, and falls down in drops. Fig. 6. HYDROGEN AND OXYGEN COMPOUNDS. 41 SuG. student, write the equation. Also write a description of the vrhole apparatus and manipulations. 41. Question. — What is the chejoical composition of water, and what its formula ? We may determine the composition of water, first by analysis, and then, if possible, by synthesis. The experi- ment described on page 34 showed that when water is decomposed by the electric current, it yields only hydro- gen and oxygen, and these in the proportion of 2 vol- umes of hydrogen to 1 of oxygen. Knowing the relative weights of the gases, we see that they are obtained from water in the proportion of 1 part by weight of hydrogen to 8 of oxygen, or 2 of hydrogen to 16 of oxygen. SuG. Student, show that this statement is correct. To prove that hydrogen and oxygen alone are necessary to form water, and that they are present in the proportions found by analysis, we may cause the two gases to unite as follows : — Exp. 30 tp. The apparatus shown in Fig. 7 is called Ure's Eudiometer. The graduated limb and part of the plain limb are flUed with mercury ; then, by means of a curved tube, 10 divisions of the graduated limb are filled with pure oxygen ; then fill say 25 more with pure hydrogen. An elec- tric spark is now passed through the wires attached to the graduated limb, while the thumb is held firmly over the plain limb. 20 divisions of hydrogen will unite with 10 divisions of oxygen; i.e., 2 of hydrogen to 1 of oxj'gen. QuEET. After passing the spark, where is the water to be seen t N.B. Before passing the spark, see that the plain limb is not entirely full of mercury, and hold the thumb as firmly as possible. 42 HYDEOGBN AND OXYGEN COMPOUNDS. Stjs. Student, examine this apparatus, and write a full description of it and the experiment. We see, thus, that the analysis and synthesis of water both lead us to the conclusion that in it hydrogen and oxygen are united in the proportions above stated, and these proportions are expressed in the formula H2O, the full significance of which cannot be. explained at this stage. For the present, suffice it to say that formulae express primarily the composition of bodies by weight. Hereafter, we shall see that they also have to deal with the volumes of bodies when in the form of a gas. Prob. How many grams of O in 100s of H^O ? How many of H ? 42. The Oxy-Hydrog-en Blow-Pipe. — Small laborato- ries will not be likely to contain this apparatus; but, owing to its great value and the frequent references made to it, the student should become acquainted with it. The oxygen and hydrogen holders are not shown in this cut (see App.). They may be provided with safety- valves, to prevent the flow of the gas from one to the other. J is a jet containing a jet within, a space heing left between the inner jet and the outer one for hydrogen to pass through. H is a stop-cock to admit hydro- gen into this space. is a stop-cock to admit oxygen into the inner jet, which is not quite so long as the outer jet. By this arrangement the two gases are thoroughly mixed upon issuing into the air. C is an adjustable cup for holding a piece of chalk in the flame, when the design is tc produce the brilliant calcium light. Fig. 8. HYDROGEN AND OXYGEN COMPOUNDS. 43 The heat of the flame of this blow-pipe is intense enough to melt most of the refractory metala. The calcium light is equaled only b}' the electric light. 43. Properties of Water. — Water is an almost univer- sal solvent; consequently, pure , water does not occur in nature. Snow and ice waters are nearly pure, but they still contain dust, and various gases found in the air. Lake Superior water is also very nearly pure, since the bed of the lake is composed of the old Azoic rocks whicli are but slightly soluble, and the lake is fed with ice,, snow, and rain. Sea water contains nearly eveiy known sub- stance in solution. Water is at its maximum density at +4° Centigrade. When the temperature passes either above or below tliis point, water expands. This is a most fortunate provision, as otherwise, ice would be heavier than water and would sink to the bottom; thus, man}' of our lakes and rivers might be frozen solid to their beds, and the summer sun would not suffice to thaw them. Aquatic plants and animals could not exist, and our temperate zones would become uninhabitable. QuEKT. Why does the pail burst when the water freezes in it 7 Exp. 31 op. Place a thermometer through an opening in the ice of a frozen lake. At any depth it will read nearly -f 4° C. QuKET. What deductions may be derived from this experiment t The Latent Heat of Water is 7U Calokies oit Thermal Units. Illustrate this statement, thus : — Exp. 32 op. Mix 1" of -ice at 0° C. with 1" of water at 79° C. The ice will melt, and the temperature of the 2'' of water 44 HYDROGEN AND OXYGEN COMPOUNDS. will be 0° C. Hence we see that the 79 thermal units contained in the kilogram of water have disappeared while melting the ice, or, in other words, have become latent. When water freezes, it gives off its latent heat. QuEKT. What effect, upon the temperature of a room, would be pro- duced by a tank of freezing water. The Latent Heat op Steam is 536 Thermal Units. To illustrate this, proceed thus : — Exp. 33 op. Into 5.86'' of water at 0° C. pass steam at 100° C. until the water boils. You will then have 6.36* of water at 100° C. Now, since 1'' of steam has parted with sufficient latent heat, while condensing to water (of the same temperature, i.e., 100°), to raise S.Se'' of water 100°, or 536" 1°, we have measured its latent heat, which is 536 thermal units. Note. Experiments 32 p and 33 p involre quite large experimental errors. When steam condenses to water it gives off all its latent heat ; hence its great usefulness for heating dwellings, etc. Drinking -Water. Drinking-water is apt to contain manj^ impurities, organic and inorganic, some of which are believed to be very deleterious to health, frequently leading to various forms of disease, such as typhoid fever, etc. QuEKY. How does drinking-water become contaminated with impuri- ties ? Let the student make the following tests upon drink- ing-water obtained from his own well, or from the usual source of water for drinking purposes. HYDROGEN AND OXYGEN COMPOUNDS. 46 Tests foe Impurities in Deinking-Water. Exp. 34 p. For Organic Impurities. — Fill a tall glass jar with the water to be tested. Add a few drops of sulphuric acid, HoSOj ; then add a solution of potassium permanganate, K2Mn208, until the whole assumes a deep purplish tint. Stand in a warm place for one hour. If organic impurities are present, the solution will be decolorized. Anotlier Test. — When much organic matter is present. — Fill a tightly-stoppered bottle nearlj- full of the water to be tested. Set in a warm place for several daj-s. An offensive odor indicates organic impurities. Such impure water, it is dan- gerous to drink. A good charcoal and gravel filter will remove organic impurities if only a small amount be present. SuG. Teacher explain the construction of a filter, and how to take care of it. Test for Ammonia. Exp. 35 p. Distil the water \n perfectly clean glass apparatus (after dissolving a small quantity of sodium carbonate, NajCOs, in the water to be tested) . Collect the distillate in tall glass jars in volumes of 50" each, numbering them successively 1, 2, 3, 4, etc. Add about 2°° of Nessler's Test Solution (see App.) to each of these jars. If ammonia be present in any or all of tiem, such as contain it will bo tinged brownish-yellow. N.B. Drinking -water containing much ammonia is unfit to drink, since the presence of ammonia indicates that the water of the well has percolated through decaying vegetable or animal substances. Test foe Chloeine or Chi-oeidbs. Exp. 36 p. Concentrate 50"^° of water to be tested to 25. Acidulate with nitric acid ; then add a few drops of a solution of silver nitrate, AgNOj. If a white precipitate is made wUi 11. In practice one determines the amount of ammonia present in drinking-water, thus : Proceed as in Exp. 35, using 1' of tlie water to be tested. The first jar contains three-fourths of all the ammonia in the sample (Wanklyn). In a similar tall jar is placed 50™ pure water and about 4== Nessler's solution. To this, from a burette graduated to tenths of a cubic centimetre, is added a standard solution of ammonium chloride, NH^Cl, drop by drop, with constant stirring until the same color is reached as in the first jar (Exp. 35). The number of cubic centimetres standard solution added equals the number of milligrams of ammonia per litre. The standard solution of ammonium chloride is prepared by dissolving 3.15g of the dry salt in 1' distilled water. See App., Art. 78. Good drinking-water should not contain over 0.08 parts per 1,000,000, of free ammonia. Query. Should the qualitative tests fail to detect organic matter, ammonia, nitrites, etc., can there be a question as to the potableness of the water under examination ? 12. Nitric acid containing oxides of nitrogen may be freed from the latter by passing through it for some time a current of pure air. General Note. Recent investigations throw doubt upon the existence of free nitrogen trioxide in a gaseous condition. Some authors also give ammonium hydroxide, NH^OH ; but there are grave doubts as to its exist- ence. It is, at least, decomposed by boiling. CHAPTER IV. BINARY COMPOUNDS. — ACIDS. — BASES. — SALTS. — CHEMICAL NOMENCLATURE. 77. Binary Compounds are those which consist of but two elements. Oxygen unites with all other elements except fluorine, and the compounds thus formed are known as oxides. Similarly, the binary compounds of sulphur are known as sulphides ; those of chlorine, bromine, and iodine, as chlorides, bromides, and iodides. The principal elements whose binary compounds are named in this way are bromine, chlorine, fluorine, iodine, oxygen, selenium, sulphur, and tellurium. To distinguish between the different oxides, chlorides, etc., the name of the element in combination with oxygen, chlorine, etc., is prefixed. Thus sodium chloride is the compound of sodium and chlorine ; magnesium, chloride is the compound of magnesium and chlorine ; barium oxide, is the compound of barium and oxygen ; potassium iodide, the compound of potassium and iodine, etc. SuG. Student, name the compounds, the formulae of which are here given:— ^^q^ j^^f.y^^ -^f, Nal, MgO. It sometimes occurs that oxygen, chlorine, bromine, etc., unite with other elements in more than one proportion, as illustrated by the formulae, HgO and HgaO, CuO and CU2O, FeCl2 and FcjCle, etc. In these cases the simple prefixing of the name of the element which is in combina- tion with oxygen, chlorine, etc., will not suffice. Hence 74 BINARY COMPOUNDS. the name is modified by the suiBxes -ic and -ous. We have not simply mercury compounds, but mercuric and mercurous compounds, etc. That compound which con- tains the smaller proportio'n of oxygen, chlorine, etc., is designated by the suffix -ous, and that which contains the larger proportion is designated by the suffix -ic. Thus, of the two compounds of mercury and oxygen, that which has the formula Hg20 is called mercurous oxide, because it contains less oxygen in proportion to the mer- cury than the other compound, HgO. The latter is called mercuric oxide. In naming compounds of copper, iron, tin, lead, and some other elements, when the syllables 4c and -ous are necessary, the Latin names of the elements are used. Instead of speaking of copperous and copperic, or of ironous and ironic compounds, we use the words cuprous and cupric, ferrous and ferric, compounds, etc. The compounds CuO and CU2O are known respectively as cupric and cuprous oxides : FeCl2 and Fe2Cl6 are called ferrous and ferric chlorides. There are cases in which a given element unites with oxygen, chlorine, etc., in more than two proportions. It is then necessary to use other methods in naming the com- pounds. Manganese forms four compounds with oxygen. These have respectively the compositions expressed by the formulas MnO, Mn203, MngO,, and MnOj. To these are sometimes given the names manganous oxide, MnO ; man- ganic oxide, MujOa; manganoso-manganic oxide, MnjOi, the name signifying that the compound is made up of manganous and manganic oxides ; and manganese dioxide, MnO^. It is not uncommon to indicate by the name the number of oxygen atoms represented in the formula, as in the ease of oxides. ACIDS. 75 Those containing one atom of oxygen are called monoxides; " two atoms " " diooddes; " three " " " trioxides; " four " " " tetr oxides; " Jiiie " " " pentoxides, etc. The relation 2 to 3 is sometimes expressed by the word " sesqui," e.ff., Fe203, sesquioxide of iron, which is the old name for what is now called /emc oxide. 78. Acids. — Among the compounds thus far considered are nitric and nitrous acids; and frequent reference has been made to sulphuric acid and hydrochloric acid. Indeed, it would be diiBcult to write a page on any chemical sub- ject without the use of the word "acid." What is an acid ? An exact definition cannot well be given. By the term " acid " we mean a body with certain physical and chemical properties, the chief of which are the following : a sour taste ; the power to turn certain vegetable colors, as to turn blue litmus red ; the power of giving up hydro- gen, and taking up metals (bases) in its place. Exp. 67 p. Student, test with blue litmus every acid to be found in the laboratory. Do all the acids have the same effect on the color? In testing, take a few drops of the acid in a test-tube half fuU of water. Try substances which are not acids, as common salt. What effect is produced? According to the above statement regarding the proper- ties of acids, all acids must contain hydrogen. It does not follow that all bodies which contain hydrogen are acids. Ammonia, NH3, for example, has properties quite the opposite of those possessed by acids; and many other examples might be cited. In order to have acid proper- ties, we must have the hydrogen in combination with cer- tain elements, or groups of elements. 76 ACIDS. The elements whose hydrogen compounds are markedly acid are chlorine, bromine, iodine, and fluorine, which give hydrochloric acid, HCl ; hydrobromic acid, HBr ; hydriodic acid, HI; and hydrofluoric acid, HF. The hydrogen com- pounds of sulphur, selenium, and tellurium, are weak acids. Most acids consist of hydrogen in combination with oxygen and some other element, as nitric acid, HNO3 ; nitrous acid, HNO2; sulphuric acid, H2SO4, etc. They are commonly called oxygen acids to distinguish them from those which contain no oxygen. There are a great many acids belonging to this class, but only a few of them are in common use. In naming the oxygen acids, the same sufSxes -ous and -io are used, as in the case of binary compounds, and with the same significance. If an element forms only one acid with oxygen and hydrogen, the suffix -ic is used. If it forms two acids, that which contains the smaller proportion of oxygen is designated by the suffix -ous, and that which contains the larger proportion of oxygen, by the suffix -io. Thus we have Nitrous acid, HNO2, and Nitric acid, HNO3 ; Sulphm'ous acid, H2SO3, and Sulphuric acid, H2SO4, etc. In those cases in which more than two acids are formed by the same elements, prefixes are used in addition to the suffixes. A good illustration of the use of these prefixes is furnished by the acids of chlorine. This element forms four acids with oxygen and hydrogen. They .are repre- sented by the formulae HCIO, HCIO2, HCIO3, and HCIO^. Of these the second and third are known as chlorous and BASES AND SALTS. 77 chloric acids. The first is called hypochlorous acid, which signifies that it is below chlorous acid as regards the amount of oxygen it contains. The fourth is called per- chloric acid, which signifies that it is beyond chloric acid in the series. These prefixes hypo- and per- are frequently used in this sense. 79. Bases. — There are certain compounds which have properties almost exactly the opposite of those of acids. They are called hases. The name "base" has been applied to various bodies, and with different meanings. In general, we mean by a base a substance which has the power of neutral- izing acids, that is, destroying their acid properties. The bases, like the acids, consist of certain elements in combi- nation with oxygen and hydrogen. Some elements unite with oxygen and hydrogen to form acids; and others unite with oxygen and hydrogen to form bases. Nearly all the compounds which the metals form with hydrogen and oxygen are bases. Examples are : potassium hydrox- ide, KOH ; calcium hydroxide, Ca(0H)2, etc. The stronger bases are known as alkalies, among which are the hydrox- ides of potassium and sodium, formerly called caustic potash and caustic soda. 80. Salts. — When an acid and a base react, they tend to neutralize each other. The acid properties and the basic properties are usually both destroyed, and a new body is formed which is neither acid nor base. This new body is called a salt. The relation between an acid and the salts derived from it will readily be seen by examining the following formulae : — r NaCl, Hydrochloric acid, HCl, yields the salts j KCl, ICaClz, etc. 78 SALTS. r KNOs, Nitric acid, HNO3, yields the salts . j NaNOj, (Ba(N03)2, etc. r K2SO4, Sulphuric acid, H2SO4, yields the salts j BaSOi, (.Na2S04, etc. On comparing the salts with the acid from which they are derived, we see that the difference between them is simply this, that the acid contains hydrogen while the salts contain something in the place of the hydrogen. We shall see later that this something which takes the place of hydrogen is called a metal. Thus, in the exam- ples given above, the metals sodium, Na, potassium, K, calcium, Ca, and barium, Ba, take the place of hydrogen in the acids. Each acid can yield at least one salt with every metal, and in some cases more than one. The salts of each acid receive a general name, and we distinguish between the different salts of the same acid by prefixing the name of the metal. The salts of the simplest acids, such as hydrochloric, hydrobromic, and hydriodic acids, are named, as described above, under the liead " Binary Compounds " (see p. 73). Salts of the oxygen acids are named thus: when the name of the acid ends in ic, the name of its salts ends in ate ; and, when the name of the acid ends in ous, the name of its salts ends in ite. Thus, a salt of nitric acid is called a nitrate ; of nitrous acid, a nitrite ; of sulphuric acid, a sulphate ; of sulphurous acid, a sulphite, etc. From nitric acid we thus have a series of nitrates corresponding to the different metals. We distinguish between them by using the names of the metals as adjectives, as in the case of binary compounds. The potassium, sodium, and cal- SALTS. 79 cium salts of nitric acid, for example, are called potassium nitrate, KNO3, sodium nitrate, NaNOs, and calcium nitrate, CaCNOs)^. The metals mercury, iron, copper, and some others yield two different classes of salts, corresponding to the lower and higher oxides alreadj^ mentioned. Just as we have mercurous and mercuric oxides and chlorides, ferrous and ferric chlorides, etc., so also we have mercurous and mer- curic nitrates, sulphates, etc., and ferrous and ferric ni- trates, sulphates, etc. The two nitrates of mercury will serve as examples. We have Mercurous nitrate, Hg2(NOa)2, and Mercuric nitrate, Hg(N03)2. The principle of nomenclature adopted for these salts is the same as that described in connection with the oxides, chlorides, etc. The name of that salt which contains the smaller proportion of the acid constituent ends in ous, while the name of that one which contains the larger pro- portion of the acid constituent ends in to. The action of metals upon acids may be illustrated by the following equations : — Zn + H2SO4 = ZnSOi -|- 2 H ; Zn + 2HC1 =ZnCl2 +2 H. In these cases the metal simply replaces the hydrogen which is set free. This action takes place only in the case of the stronger acids. When an acid acts upon a base, the action is as repre- sented below : — KOH+HN03=KN03 + H^O ; NaOH + HN03= NaNOs + H2O ; 2 KOH + USOi = K2SO4 + 2 H2O ; Ca(OH)2 + H,SO. = CaSO, -f-2H20. 80 ACID AND NORMAL SALTS. This kind of action takes place between all acids and all bases. 81. Acid and Jformal Salts. — The simplest acids, such as hydrochloric and nitric acids, yield only one salt each with most of the metals. Thus hydrochloric acid and potassium yield only one potassium chloride, KCl, which is a neutral body ; nitric acid and sodium yield only one sodium nitrate, NaNOs, which is also neutral. There are some acids, like sulphuric acid, H2SO4, which have the power of yielding two or more salts with the same metal. Thus sulphuric acid yields with potassium not only the salt, K2SO4, potassium sulphate, but another salt, of the formula KHSO4, which contains only half as much potassium as the first. In the first case all the hydrogen of the acid has been replaced, and the resulting compound has no acid properties. It is a normal salt. In the second case a part of the hydrogen is left, and the. compound still has acid properties. It is both acid and salt, and is called an acid salt. A normal salt is one which is formed by replacing all the hydrogen of an acid with a metal. An acid salt is one which is formed by replacing only a part of the hydrogen of an acid with a metal. In naming the acid salts it is customary to indicate the number of atoms of the metal which are represented in the formula. Thus the salt KHSO4 is called mono-potas- sium sulphate ; the salt Na2HP04 is called disodium phos- phate. Sometimes they are referred to as acid salts, mono-potassium sulphate being called acid potassium sul- phate. Applications of these principles of nomenclature will be met with when the salts are considered. Meanwhile the ACID AND NOliMAL SALTS. 81 student should familiarize himself with the main points by means of examples furnished by the teacher. A few examples are here given. Student, name the compounds, the formulae of which are given below : — Cufik, KNOs, Ca(N03)2, Fe(N03)2, HgO, NaHSO,, CuCl^, NaNOg, Ba(N08)2, FesCNOa)^, Hg^O, K^SO^. WRITING EQUATIONS. It is important to know how to write chemical equations, and thus avoid the necessity of committing them to memory . In the first place we know what substances we put together or experiment upon, and these are placed in the first member, and connected by the sign +. The substances formed are determined by experiment, or, when our knowledge is sufficient, by analogy or by induction. They are then placed in the second member, and connected by the + sign. It now remains to balance the equation. The fundamental principle to be remembered here is, that " matter is in- destructible " ; that is, Just as many atoms of a given element as appear in one member, just so many must also appear in the other. Let us, for example, write the equations for the reaction of NaCl and H^SO^ : we first write NaCl + H2SO4 = ■ • • ; by experiment, we know that under certain conditions (Art. 94) HCI and HNaSO^ are formed, and we proceed to the next step, thus : NaCl + HjSO^ = HNaSOj + HCI. By inspection, we see that the equation balances and is complete. But let us suppose that the conditions are different, and that NajSOj and HCI are produced; the second step gives us NaCl + H2SO4 = Na2S04 + HCI. By inspection we here see that the equation is not true, since two atoms of Na appear in the second mem- ber, and but one in the first ; also one atom of H in the second, and two in the first. We may obtain the required amount of Na by doubling the NaCl ; and, when this is done, the necessity for doubling the HCI becomes apparent, and the equation balances, thus : — 2 NaCl -f H2SO4 = Na^SOi + 2 HCI. Water, which is almost always present, must sometimes be taken into consideration. The equations previously given will afford good prac- tice, also those to follow, especially those relating to the metals. Before we reach that point, however, molecular equations will be explained. CHAPTER V. THE ATMOSPHERE. — LAWS OF PRESSURE, TEMPERATURE, DENSITY, AND VOLUMES OF GASES. — PROBLEMS. THE ATMOSFHZiRi:. 82. The earth is everywhere surrounded by an ocean of gaseous vapor, called the atmosphere, which varies from fiifty to one hundred miles in height. This variation at any one point is never ceasing, for just as in the oceans of water, so in this ocean of air, do huge waves continually surge to and fro, — waves so vast that their altitudes are measured in miles. Everj"^ object upon the surface of the earth is subjected to the pressure exerted by the weight of air above. This pressure varies constantly, and, owing to the great mobility of the particles of air, it is exerted in all directions, — downwards, upwards, and side- wise. This pressure is measured by an instru- ment called a barometer (Fig. 15). A is a glass tube about 800""" long, sealed at the upper end, open at the lower, and provided with a scale. This tube is filled with mer- cury, and inverted in a cup of mercury, C. Now, since the tube itself . sustains the pressure which the atmosphere would Fis. 15. exert on this column of mercury within the THE ATMOSPHERE. 83 tube, in every direction except upwards, it follows that the column will remain at a higher altitude than the level of the mercury in the cup. The height of this column of mercury will depend upon how hard the atmosphere presses it upward. At the level of the sea, in the latitude of Paris, and at 0° C, the average height of this column is 760""" ; hence 760"™ is taken as the standard pressure of the air. As you ascend from the sea-level the- column falls (why?), and as you descend it rises (why?). As the density (Art. 88) of the "mercury and the at- mosphere varies, owing to changes of temperature, the height of the barometer varies ; hence the necessity of taking a standard temperature, which is 0° C. 83. Measurement of the Temperature of the Atmos- phere. — This is accomplished by means of instruments called thermometers. There are three scales in use, — Centigrade, Fahrenheit, and Reau- f. c. b. mur (Fig. 16). Thermometers are made by blowing bulbs on capillary tubes. The bulbs and tubes are filled with mercury, and then heated till the mercury issues in vapor, when the ends are suddenly sealed by the blow-pipe flame. They are graduated by first plunging them into melting ice, the height of the column of mer- cury being marked 0° C, 0° R., or 32° F. The instruments are next placed in the steam of boiling water, and the height of the column of mercury marked 100° C, 80° R., or 212° F. The distances between these points are ^ % Fig. 16. 84 THE ATMOSPHERE. then divided into spaces (or degrees), there being 100 divisions C, 80 R., or 180 F. ; divisions of the same length are also made above and below these points. From the manner of laying off these scales, it follows that 5° C. = 4° E. = 9° F. The following formulae will assist in changing from the reading of one scale to another : — (a)C. = (F.-32)f. (&) F. =f C.+32. (c) R.=fC. Peob. Change 98° C. to F. ; 87° R. to F. ; 91° F. to R. ; -18°C. toF. ; -40°F. to C. SuG. It would be advisable for the student to learn the points of a good thermometer from his text-book in physics, and to review the metric system in his arithmetic. Note. The centigrade thermometer and the metric system of weights and measurements are used throughout this work, as they best answer its purposes, and are the ones used by scientists in general. 84. Impurities in the Atmosphere. — As we already learned, air is a mechanical mixture of nitrogen and oxygen. By this we mean pure air. But atmos- pheric air is never pure. It contains, — (a) Moisture, as invisible vapors, clouds, and fogs. These, being lighter than the atmosphere, cause a lower barometer, especially when they are present in large quantities. (6) Carbon dioxide, CO2, produced by combustion, by the respiration of all air-breathing animals, and by the decomposition of animal and vegetable tissues. (c) Ammonia (Art. 51). (^) Ozone (Art. 30), or other substances having marked oxidizing power. THE ATMOSPHERE. 86 (e) Dust and smoke. (/) Other gases in small quantities, which are liberated in various ways. 85. Determination of tlie Volumes of Nitrogen and Oxygen In the Atmosphere. — This determination is made by means of Ure's eudiometer. A measured quan- tity of pure air is introduced into the graduated limb, and then a volume of hj-^drogen, more than sufficient to combine with the oxygen of the air, is added. The whole volume is now carefully noted, the spark passed, and the diminution of volume carefully ascertained. One-third of this diminution equals the volume of the oxygen contained in the air. The volume of oxygen is subtracted from the volume of air introduced at the beginning, and this gives the volume of the nitrogen. In this way we learn that the air consists of oxygen 21 volumes, and nitrogen 79 volumes, in 100 parts. These proportions vary but slightly in any locality or season. Queries. What chemical action takes place when the spark is passed ? How do you know one-third of the volume of diminution to be the volume of ? Through what substances would you pass air to remove its im- purities ? 86. Effect of Pressure on the Volume of a Gas. — If a mass of gas be confined in an air-tight cylinder, and a perfectly-fitted piston be pressed down- into the cylinder, the gas will be compressed into a smaller volume. The law for the volume of a gas under such conditions is : — Law I. Tlie volume of any gas, its temperature remaining constant, varies inversely as the pressure. 86 THE ATMOSPHERE. We mean by this that volume 1 under pressure 1 becomes volume J under pressure 2, volume J under pressure 3, or volume J under pressure 4, etc. ; and the reverse of this is also true when the temperature remains the same in both cases. (How could this law be discov- ered if it were unknown ?) Note. On li"™, at the standard pressure of 760""", the atmosphere exerts a pressure of '1033.3s (nearly 15 lbs. per sq. in.), which is called a pressure of 1 atmosphere. A pressure of 2 atmospheres is 2 X 103.3.3s, etc. Now, since gases are subject to the pressure of the atmosphere, their volume varies with every change of the barometer. Sne. The student should consult some work on physics for the experi- mental demonstration of the above law, as well as for that of the succeed- ing law, since we use them as an application of physics to chemistry. Problems. 1. What volume will 10' of gas at 762""" occupy when the barometer stands at 758"™? Solution. Since the volume varies inversely as the pressure, we have the proportion, 758 : 762 : : 10 : x = 10.0527 + litres. Ans. 2. 190™ of gas at 760""™ pressure becomes how many cubic centimetres at 765™™? 3. A mass of gas, 100' under 755™™, is subjected to a pressure of 4.5 atmospheres; what volume will it occupy? Ans. 22.076+ litres. Note. In these problems the temperature is considered constant. 87. Effect of Heat on the Volume of Gases. — It has been found by experiment that 273 volumes of any gas at 0° become 274 volumes when its temperature is raised 1°, 275 when raised 2°, etc., increasing one volume for each degree of increase in its temperature ; also that 273 volumes at 0° become 272 volumes when its temperature is lowered 1°, 271 volumes when lowered 2°, 270 when lowered 3°, THE ATMOSPHERE. 87 etc., decreasing one volume for each degree of decrease in its temperature. According to tliis, the volume of a gas at — 273° C. would be ; and this point is designated as the absolute of temperature. Hence the absolute tempera- ture of any body is the temperature above the ordinary + 273, or t ■+- 273. Taking these ideas into account, we have : — Law II. The volume of any gas, its pressure remaining cmi- stant, varies as its absolute temperature, i.e, in the ratio of 273 + t to 273 + t'. Rem. 1. t is the observed temperature of the gas, and t' the required temperature. Rem. 2. Since any gas surrounded by the atmosphere will usually be of the same temperature as the atmosphere itself, it follows that the volume of that gas will vary as the thermometer varies. Problems. 1. At +15° the vokime of a gas is 84'; what will be its volume at + 85° ? Solution. 273 + 15 : 273 + 85 : : 84 : a; = 104.4166 + litres. Ans. 2. A gas at — 15° has a volume of 18'; what will be its volume at 100°? SoLnTiON. 273 - 15 : 273 + 100 : : 18 : a; = 2Q^ litres. Ans. 3. 98' of gas at — 4° become how many at — 24°? 4. 176' of gas at + 100° become how many at — 140°? 5. 80' of gas at 0° become how manj' at — 18°? 6. 144' of gas at — 15° become how many at 0°? Note. In these problems the pressure is considered constant. Problems in which both pressure and temperature vary : — 1. A mass of gas at + 15° and 762""" pressure occupies 94' ; what will be its volume at + 25° and 758™™ pressure? Solution. We here have a combination of the principles of Arts. 86 and 87, pressure and temperature both afiectirig the volume of the 94' in 88 THE ATMOSPHBliE. question. We will consider them separately ; hence the compound pro- portion : — f (1) Temperature, 273 + 15 : 273 + 25 "I . . g^ . ^ ^ g^ ^^^^i ^^^ I (2) Pressure ... 758 : 762 ) " ' 2. 90"" of gas at 0° and 760'""' occupy what volume at - 140° and 40 atmospheres? A.ns. 1.09+ cubic centimetre. Note. From this the student may judge of the efiect of pressure and reduction of temperature. 3. 72' at — 12° and 4 atmospheres pressure become how many litres at 100° and 760"""? 4. In the evening a quantity of oxygen gas was generated in a laboratory. The oxygen receiver, holding 112', was filled while the barometer read 760"" and the thermometer + 15° C. The next morning the barometer fell to 758"", and the janitor allowed the temperature of the room to reach + 40°. At 4 p.m. that day the barometer read 760"" and the thermometer + 18°, when the master ascertained that he had but 94' of the gas remaining ; upon which he charged a student, who alone had access to the laboratory-, with having used some of the oxygen. Allowing half a litre to have been absorbed by the water during the night, the temperature and pressure remaining constant mean- while, how much gas, measured at + 15° and 760""", was lost owing to the fall of the barometer and negligence of the janitor? Was the master justifiable in making the charge against the student? How much (if any) of the oxygen did the student use? 88. Relation of Weight to Density. — By the density of a substance vs^e mean the amount of that substance contained iu a given volume. We have seen hov7 the volume of a gas varies under differences of pressure and of temperature. Now, it is evident that its density varies also ; i.e., v\rhatever tends to make the volume less makes the density greater, and whatever tends to make the vol- THE ATMOSPHERE. 89 ume greater makes the density less. Again : it is evident that the denser a given amount of gas, the greater will be its weight, and the less dense the gas, the less its weight ; or, — The weight of a -given volume of gas varies directly as its density. Problems. 1. How much will 10' of oxygen weigh at +15° and 766"""? Solution. We know that 1' of oxygen at 0° and TeO"" weighs 1.4308 ; therefore we will find how many litres this gas will he at 0° and 760'"™, as in Art. 87, and then multiply that result hy 1.430, thus : — f 288 ; 273 ■) . . jQ . ^ ^ 9.54151 ; and 9.5415 X 1.430 = 13.644s. Ans. I 760 : 765 J ■2. How much will 20' of hydrogen weigh at 755""" and +20° ? 3. How much will 15' of nitrogen weigh at —112° and 29 atmospheres pressure? 89. Useful Problems. — I. To find the percentage com- position of a compound. We will explain this by solving a problem : What per cent of N and H in NH3 ? Solution. jfow, it is evident that ^j of NH3 is hydrogen, and {j N = 14 is nitrogen, -^j expressed in the form of per cent equals 3H = 3 300 -H 17 = 17.65 % of H. One can also readily understand NH3 = 17 tliat 100 % - 17.65 % = 82.35 % of N. These percentages are valuable in that they enable us to make computations more rapidly. For example, if we wish to know how much hydrogen there is in 10^ of am- monia, we have simply to multiply 10« by the per cent of hydrogen, and divide the result by 100, when we have the weight of the hydrogen in grams, thus : — (17.65 X 10)--100=1.7658:. 1 . What per cent of oxygen in HgO ? KCIO3 ? 2. What per cent of chlorine in NaCl? Of sodium? 90 THE ATMOSPHERE. II. To find what volume will he occupied hy a gas obtained from a certain weight of chemicals. We can also best understand this by a problem : How many litres of oxygen can be obtained from 10^ of potassium chlorate, KCIO3, when the barometer reads 750™ and the thermom- eter 25°? Solution. We will first ascertain what weight of oxygen 10« of KCIO3 will yield. We ca"n best do this by multiplying 10 by the per cent of in KCIO3. Thus we find the weight of oxygen to be 3.918b. We will now ascertain how many litres 3.918s of oxygen will occupy at 760""" and 0' One litre of oxygen under these conditions weighs 1.430s; hence, 3.918 H- 1.430 = 2.7398', or the number of litres at 0' and 760™"'. We can now finish the problem by Arts. 86 and 87, thus : — I '^^ • '^^*' I : : 2,7398 : x = 3.0305'. 1 273 : 298 / 1. How many litres of oxygen gas may be had from 100^ HgO when the barometer stands at 755""", the thermometer reading 20° ? SuG. HgO (heated) = Hg + 0. 2. How many litres of oxygen gas may be had from 500*^ MnOa, at 20° and 4 atmospheres pressure? SuG. 3 MnOj (heated) = Mn304 +2 0. 3. How many litres of nitrous oxide may be obtained from P of NH4NO3 when the barometer reads 750"" and the ther- mometer + 22° ? Sue. See Nitrogen Monoxide. III. To find the weight of chemicals required to yield a certain volume of gas. Let us again have recourse to a problem : How many grams of KCIO3 will be required to fill with oxygen a receiver of 32' capacity at 20° and 760"°' ? THE ATMOSPHEKE. 91 Solution. We will first find what volume 32' of oxygen at 20^ and 750""" would become when reduced to ' and 760""", in order to find the required weight of the oxygen, thus : — 'l!!^'!!^! == 32 :x = 29.4231. I 760 : 750 J Now, 29.423 X 1-430 = 42.0748, or the required weight of oxygen. We may now obtain the desired weight of the potassium chlorate by dividing the weight of the oxygen by the percentage of in KCIO3, or by the proportion: 48 : 42.074 :: 122.5 : r. 1. How many grams KCIO3 will be required to yield 20' of oxygen at - 20° and 760"""? 2. How many grams of zinc and sulphuric acid are needed to yield 40' of ^hydrogen at + 24° and .t)5"'""? SuG. Zn + HjSOj = ZnSOj + 2 H. 3. What weights of CaO and NH4CI are required to make 25' of NH3 at 15° and 749"'"'? SuG. CaO + 2 NH4CI = CaCl^ + H^O + 2 NH3. EXERCISES. 1. The following equations may be of service in making calculations upon gases : — ,j. VH _ VH' 273 + t 273 + t' V, H, and I represent respectively the volume, height of barometer, and temperature of a gas under observed conditions, while V, H', and I' rep- resent the same under required conditions, one of which will be unknown. When t = t' vie have, (2) VH= VH' (Art. 86). When H= H' we have, (3) ^ = ^' (Art. 87). ^ ' 273 + t 273 + «' ' 2. Make a table showing tlie relations between the acids and their salts CHAPTER VI. CHLORINE. — ITS OCCURRENCE, ETC. — HYDROCHLORIC ACID. — AQUA RBGIA. — CHLORINE OXIDES. — CHLO- RINE OXACIDS. CHLORINE. Symbol Cl'. — Atomic Weight, 35.5; Specific Geavity, 2.450. 90. Occurrence. — Chlorine does not occur free in nature, owing to its great chemical activity ; in combi- nation with certain metals, however, it occurs in large quantities, as in sodium chloride, NaCl, or common salt. Silver chloride, AgCl, potassium chloride, KCl, calcium chloride, CaCU, and magnesium chloride, MgCl2, occur in smaller quantities. 91. Preparation. — Exp. 68 p. In a test-tube place a small quantity of manganese dioxide, MnOj, and add hydro- chlorio acid, HCl. Upon gently warming, chlorine is evolved as a heavy, yellowish, suffocating gas, thus : — MnOs + 4 HCl = MaClg + 2 HjO + 2 Cl. Hold in the escaping gas strips of moistened litmus paper and calico printed in organic colors ; they will be bleached. Also note the fumes. This method is sometimes employed in making chlorine gas for the manufacture of bleaching-powder. (Art. 349.) Exp. 69 p. Drop three or four small crystals of potassium chlorate into a test-tube, and add hydrochloric acid. Warm CHLORINE. 93 gently, and, when the chlorine fames begin freely to appear, immediately add 3™ or 4""" of cold water. What occurs may be indicated thus : — 4 HCl + 2 KCIO3 = 2 KCl + 2 H^O + CIA + 2 CI. Try the effect of this solution upon vegetable colors as before Also add a few drops of the solution to tinctures of litmus, carmine, and indigo ; they will be bleached. The above method is one often employed by the chemist in preparing chlorine water for such purposes as testing iodine and bromine. Hereafter the student will find frequent use for chlorine water thus prepared. It might be well to say that the CI2O4 and KCl are in no wise detrimental to the solution. Another method of preparing chlorine in the manufac- ture of bleaching-powder is of interest, since it is con- tinuous and quite inexpensive. Hydrochloric acid gas, mixed with air, is passed over heated cupric sulphate, CUSO4 ; the cupric sulphate undergoes no change, while the oxygen of the air and the hydrochloric acid react, thus : — 2 HCl -f- O = H2O H- 2 CI. Another and common method of preparing chlorine is as follows : — Exp. 70 t. In the generating-flask A (Fig. 17) place equal weight of common salt, NaCl, and manganese dioxide, MnOa, which have been thoroughly pulverized and mixed. Then add to this mixture twice its weight of dilute sulphuric acid (con- sisting of equal weights of water and acid). Apply a gentle heat, and chlorine gas is plentifully given off. The Woulfl bottle B (Fig. 17) contains a little warm water to absorb any hydrochloric acid gas that may be produced, while C contains strong sulphuric acid to dry the gas. The thistle-top tube con- 94 CHLORINE. tains a little sulphuric acid. Collect the chlorine in tall jars. This may be accomplished by delivering the gas by means of a long glass tube extending to the bottom of the upright jar. The air will be pushed up and out of the jar. Note. This method of collecting a gas is called displacement, and is employed with those gases heavier than air. If a pure, aqueous solution of chlorine be desired, it may be obtained by attaching two or three Woulff bottles, nearly tilled with cold water, and surrounded with a cooling or freezing mixture. Sliould the tem- perature of any bottle con- tained in the series nearly reach 0°, a crystalline hy- drate of chlorine is formed, whose composition is CI + 5 H2O. In thus pre- paring chlorine we may rep- resent the reaction by, — Pie. 17. 2NaCl + Mn02+3H2S04 : 2NaHS04+MnS04 + 2H2O + 2C1. In reality, however, two distinct processes are involved. In the first place the sulphuric acid, H5SO4, acts upon the sodium chloride, NaCl, giving hydrochloric acid, HCl, and mono-sodium sulphate, NaHS04. Then the manganese dioxide, Mn02, acts upon the hydrochloric acid, HCl, giving manganous chloride, MnCU, free chlorine, and water, H2O. If an excess of sulphuric acid is present, it decomposes the manganous chloride, MnClj, giving man- ganous sulphate, MnS04, and hydrochloric acid ; and the latter again acts upon manganese dioxide, yielding chlorine. CHLORINE. 95 The equations which give the best insight into the reactions are the following : — 2 NaCl + H2SO4 = IHaSOt + 2 HCl, and 4 HCl +Mn02=MnCl2 +2H2O+2CI. Manganese dioxide readily gives up one part of its oxygen, and it is this which, uniting with the hydrogen of hydro- chloric acid, sets the chlorine free. Queries. Why can you not collect chlorine over water or mercury ? How can you collect hydrogen by displacement ? 92. Properties. — Chlorine is a heavy, greenish-yellow gas having a strong and suffocating odor, and producing great irritation to the lining membranes of the throat and nostrils ; and, when inhaled in sufficient quantities, it is capable even of producing suffocation and death. Exp. 71 p. Write with an organic (carmine) ink upon a slip of printed paper ; moisten, and hold it in a large test-tube full of chlorine gas. The writing disappears and the printing remains. Printer's ink is made of lampblack (carbon), and is not bleached. Queries. How can you distinguish between organic and mineral colors ? Try wall paper. Would chlorine water answer as well ? Chlorine in the presence of moisture is an invaluable bleaching reagent, acting upon vegetable coloring-matters thus : — 2 CI + H2O = 2 HCl + O. Now this oxygen (liberated, as it is, within the fibres of the substance to be bleached), while in a nascent condi- tion, seizes upon the coloring-matters, and destroys them, or changes them into colorless compounds. Exp. 72 t. Saturate with hot turpentine, CjoHje, a strip of blotting-paper, and plunge .it into a jar of dry chlorine gas. 96 CHLOEINB. The turpentine takes fire, the chlorine and hjdrogen uniting, while carbon is deposited as soot. SnG. Student, write the equation. Exp. 73 p. Plunge a lighted taper into a large test-tube of chlorine. It continues to burn with a dull, red, smoky flame, the chlorine again uniting with the hydrogen contained in the substance of which the taper is composed, while the carbon is set free. Rem. Oils, resins, gums, waxes, tallows, etc., are compounds containing C, H, and 0, in varying proportions. We thus see that chlorine possesses a powerful chemism for hydrogen, even decomposing compounds to obtain it. We shall hereafter see that the great chemism of chlorine enables it to displace from their binary compounds the nearly-allied elements, bromine and iodine. The sulphides are also dissociated thus : — H2S + 2C1=2HC1 + S. Chlorine is extensively used as a deodorizer and disin- fectant, owing its efficiency to its power of liberating from water oxygen, which, as already explained, while in a nas- cent state^ oxidizes putrefactive vapors and disease germs to their destruction. Chlorine is soluble in water, 1'° of water absorbing nearly 3°° of this gas. It may be condensed to a liquid at 0° by a pressure of 6 atmospheres, or by 1 atmosphere at - 34°. 1' at 0° and 760-™° weighs 3.1738, and its specific gravity is 2.450. 93. Tests for Chlorine. — Free chlorine gas or its aqueous solution may be recognized by its color, odor, or behavior, as in the preceding ^experiments. CHLORINE AND HYDROGEN. 97 CHLORINE AND HYDROGEN. Hydrochloric Acid, HCl. 94. Occurrence and Preparation. — We now come to an important and useful acid, the only compound formed by hydrogen and chlorine, — hydrochloric acid, HCl. This acid rarely occurs in nature, although it is a staple ar- ticle of commerce. The following is the general method of its preparation : — Exp. 74 t. Heat to redness, in a crucible, 5^ of common salt, NaCl; pulverize, and place in a generating-flask. Now add 10^ strong sulphuric acid, H2SO4, and heat gently. Hydro- chloric acid, in the form of a gas, is freely given off, and can be collected by displacement, or over mercury. By passing through two or three wash bottles, it may be obtained in aqueous solution, the form in which it is used and found for sale. The reaction is : — NaCl + H2SO4 = HNaSOi + HCl. If a larger proportion of salt be used, the reaction may be represented by this equation : — 2 NaCl + H2SO4 = NajSO^ -f- 2 HCl. As we shall hereafter see, commercial hydrochloric acid is almost exclusively obtained as a by-product of the alkali works where common " soda " is prepared. 95. Properties. — Hydrochloric acid gas is extremely soluble, 1°° water at 0° dissolving no less than 505°° of this gas. Its specific gravity is 1.247, it condenses at — 4° under 25 atmospheres pressure, and 1' weighs 1.632^. The aqueous solution of hydrochloric acid is one of the r'Dst useful chemicals. It acts upon bases to form chlo- 98 CHLOEINE AND SYDROGEN. rides; the principal one of these, common salt or sodium chloride, NaCl, occurs in nature in large quantities. The gas has a pungent odor. In contact with the air it forms dense white fumes, in consequence of its attraction for water. The strong water solutions give off the gas read- ily ; weak ones may be concentrated by boiling. Exp. 75 p. Take three test-tubes. In the first, place a solu- tion of silver nitrate, AgNOs ; in the second, a solution of mer- curous nitrate, Hg2(N03)2; and in the third, a solution of plumbic acetate, Pb(C2H302)2. To all three now add hydro- chloric acid. What takes place ? As the silver, lead, and mercurous chlorides are insolu- ble in water, it precipitates these metals from solutions in which thej^ are contained. Other chlorides, as a rule, are soluble. This fact is taken advantage of in analyzing unknown substances. Suppose, for example, we have a solution which may contain any or all known metals. If we add liydrochloric acid to it, and get a precipitate, we know that one or more of the metals whose chlorides are insolu- ble in water must be present. We know, in other words, that one or more of the three metals, silver, lead, and mercury, must be present ; and further, as their chlorides are insoluble, we know that the addition of hydrochloric acid to the solution removes these metals. By the use of other chemical substances, other groups may be precipitated in a similar way; and thus the problem of determining what is in the substance under examination is more and more narrowed down, until we know exactly what is present. Substances which are used for the pur- pose of precipitating groups of metals in analysis are called Geoup-Reagekts. CELLOEINE AiJD OXyGBN. 99 When hydrochloric acid is mixed with one-third its volume of nitric acid, Aqua Regia or nitro-hydrochlorie acid is produced, which is the strongest solvent known ; even gold and platinum are dissolved in it. The great power of aqua regia lies in the fact that it readily gives up chlorine, which, in a nascent condition, is very active. The salts formed by aqua regia are chlorides. In using this solvent it should be but slightly warmed ; a stronger heat drives off chlorine to waste. 96. Test for Hydrochloric Acid, or Chlorides. — Their solutions, even when acidulated with nitric acid, give a white precipitate of silver chloride, AgCl, with silver nitrate, AgNOs. This precipitate is insoluble in nitric acid, and soluble in ammonia. SuG. Student, try a solution of NaCl. Write the equation. CHLORINE AND OXYGEN. 97. Chlorine and oxygen unite to form three compounds, which have been isolated, viz., — Chlorine monoxide CI2O, Chlorine trioxide (?) • . . . CljOs, and Chlorine tetroxide CI2O4. These oxides never occur free in nature, nor can they be produced by the direct union of chlorine and oxj'gen ; they may, however, be obtained by indirect processes. Since they are unimportant, and dangerous to prepare, owing to the ease with which they decompose, we shall treat each but briefly. 98. Chlorine Monoxide, CI2O. — This substance is a 100 CHLOBINE AND OXYGEN. yellow-colored gas, prepared by passing chlorine gas over dry mercuric oxide in the cold, thus : — HgO + 4 CI = HgClg + CI2O. This gas may be pressed into a U-tube, surrounded with a freezing mixture, and condensed to a yellow liquid ; but if the tube be suddenly jarred or scratched, as with a file, it explodes with great violence. If exposed to direct" sun- light, it is also decomposed, but without explosion. It unites with water, thus : — CI2O + H2O = 2 HCIO. (See Hypochlorous Acid.) 99. Chlorine Trioxide, CI2O3. — This is a greenish-yel- low gas, of great instability and explosive power. It can be prepared in different ways, one of which is as follows : Make a thin paste of 4 parts potassium chlorate, KClOj, and 3 parts of arsenious oxide, AS2O3, with water ; place in a generating-flask, and add a solution of 12 parts nitric acid and 4 parts water ; warm gently. This gas may also be condensed to a liquid, but, owing to its extremely uncertain and explosive propensities, the student should not attempt its preparation. It unites with water, forming chlorous acid, thus : — CI2O3 + H2O = 2 HCIO2. (See Chlorous Acid.) 100. Chlorine Tetroxide, CI2O4 or CIO2. — This is a dark-yellow gas of small importance, as it forms no acids, and consequently no distinct series of salts (it is also dan- gerously explosive) ; but some idea of its deportment, as well as that of the other chlorine oxides, may be gained by the following experiment, which may be safely made if care be used : — THE CHLORINE OXACIDS. 101 Exp. 76 p. Drop into a test-tube three or four small crys- tals of potassium chlorate, KCIO3 ; then, holding the tube with a pair of tongs, its mouth turned away from all persons pres- ent, add a few drops of strong sulphuric acid. Warm gently, when chlorine tetroxide gas will appear; but a sharp and vicious explosion soon terminates the experiment. The con- tents of the tube are thrown violently out, but the tube itself is seldom broken. Note the odor of the gas. THE CHIiORINE OXACIDS. 101. This series contains four acids, none of which are of commercial importance, nor are they of special value as reagents ; and they all decompose upon standing. Their salts, however, are stable, well known, and of great util- ity. These acids are : — Hypochlorous acid .... HCIO, Chlorous acid HCIO2, Chloric acid HCIO3, and Perchloric acid HCIO4. SuG. Student, name the salts these acids form witli potassium. Hypochlorous Acid, HCIO. 102. Preparation. — Tins acid has been prepared only in dilute aqueous solution. Owing to its instability, the student must prepare it freshly for the purpose of studying its properties. It is obtained by treating freshly-precipi- tated mercuric oxide, HgO, with chlorine water, thus : — 3 HgO 4- 4 CI -h H2O = 2 HgO, HgCl + 2 HCIO. Exp. 77 t. Dissolve as much mercuric chloride, HgCl2, as possible in 250"= hot water ; then add KOH as long as a pre- cipitate (yellowish-red) is formed. You thus obtain the fresh mercuric oxide : — 102 THE CHLOEINE OXACIDS. 2 KOH + HgCla = HgO + 2 KCl + H^O. Filter out tbis precipitate, and wash it by adding much water to it as it lies upon the filter-paper. Finally make a hole in the point of the filter-paper, and wash the precipitate through into a half-litre flask by means of 250°° cold water. Then gradually add chlorine water, thoroughly shaking meanwhile, until the remaining brownish-red precipitate ceases to dissolve (i.e., be careful to keep an excess of HgO. If the chlorine water be fairly -well saturated, you will require less than 200°°) . The remaining precipitate is the compound represented by the formula HgO, HgCl. Allow the flask to stand in a cool place until this precipitate settles, when you will be able to pour off the slightly-colored aqueous solution of hypochlorous acid, which may be used for experimental purposes. Note the odor of the acid difl'ering from chlorine. Exp. 78 p. In a florence flask fitted with a bent delivery tube, generate chlorine gas from sodium chloride, manganese dioxide, and sulphuric acid. Pass this gas into a cold, dilute solution of potassium hydroxide, stopping short of saturation. You will thus obtain for experimental purposes a solution of potassium hypochlorite, KCIO, thus : — 2 KOH -I- 2 CI = KCIO -|- KCl + H^O. 103. Properties. — Hypochlorous acid, when in dilute aqueous solution, is a yellowish liquid, possessing a char- acteristic odor and strong bleaching properties. A con- centrated solution cannot be distilled without undergoing decomposition ; indeed, it soon decomposes at ordinary temperatures, of its own accord, giving off chlorine and oxygen gases. Exp. 79 p. Moisten in dilute hydrochloric acid pieces of unbleached cotton cloth and suspend them for a moment in the solutions of hypochlorous acid and potassium hypochlorite, as prepared above. Finally wash them in pure water, allow them THE CHLOEINE OXACIDS. 103 to dry, and note that they are bleached. Also make this experiment with a solution of bleaching-powder. The hypochlorites are of great importance, especially the calcium compound, which is used in bleaching-factor- ies under the name of bleaching-powder. Enormous quan- tities of this powder are prepared by passing chlorine gas into chambers containing slaked lime, Ca(0H)2, thus : — 2 Ca (OH) 2 + 4 CI = 2 H2O + (CaCls + Ca(ClO)g). It thus appears that bleaching-powder is a mixture of cal- cium hypochlorite with calcium chloride. The cloth to be bleached, after a thorough cleansing, is drawn through a solution of bleaching-powder, and then .through very dilute sulphuric acid, which decomposes the powder, liberating free chlorine in the fibres of the cloth. By this means, as previously explained, the color- ing-matters are destroyed. The effect, upon hypochlorous acid or the hypochlorites, of stronger acids may be seen, thus : — • HCIO-I-HCI =H20-f-2Cl, and KCIO -F 2 HCl = KCl + H^O -F 2 CI. 104. Tests for Hypoclilorous Acid, or the Hypochlo- rites. — 1. An aqueous solution of the free acid bleaches litmus paper or solution. 2. The odor of the free acid identifies it. 3. Hypochlorites in solution require acidulating with an acid, as acetic or hydrochloric acid, before they produce their bleaching effects. Query. Will a hypochlorite bleach when acidified with HNO3? HjSO^? Try it. SuG. Carefully distinguish between bleaching a substance and chanc/ing its color, as from blue to red. When it has been bleached, an alkali will not restore the original color; when simply changed, the color may thus be restored. 104 THE CHLORINE OXACIDS. Chloeous Acid, HClOj. 105. This acid and the salts it forms are unimportant. As alreadj' explained, it may be obtained by dissolving chlorine trioxide in cold water, but it does not bear con- centration. It is readily decomposed by heat, as likewise are its salts, the chlorites. It also possesses bleaching properties. Its action upon the alkaline bases is very slow and feeble. 106. Tests for Chlorous Acid and the Chlorites. — Test as for a hypochlorite, when the same results are obtained. Then to a fresh portion add a small quantity of arsenious oxide, AS2O3, and a drop or two of nitric acid. If the solution be that of a hypochlorite, its bleaching pow- er is destroyed. If that of a chlorite, it will still bleach. Note. This acid and its salts may well be dismissed with simply a reading of the two preceding paragraphs. Chloeic Acid, HCIO3. 107. This acid is also unimportant, and, moreover, somewhat dangerous to experiment upon ; its prepara- tion, therefore, should be omitted. Potassium chlorate, KCIO3, the most important salt of chloric acid, is made by passing chlorine into a concen- trated, warm solution of potassium hydroxide, KOH : — 6 CI + 6 KOH = 5 KCl + 3 H2O + KCIO3. Query. What takes place when the solution of potassium hydroxide is cold and dilute ? In order to get the free acid from this potassium salt, the latter is treated with a solution of hydrofluo-silicic acid, H2SiF6 : — 2 KCIO3 -J- HjSiFe = K^SiFe + 2 HCIO3. THE CHLOKINB OXACIDS. 106 The potassium salt thus formed is insoluble ; conse- quently, after it has subsided, the dilute solution of chloric acid may be poured off, and afterwards concen- trated iu a vacuuna over sulphuric acid. Concentrated chloric acid is, indeed, a powerful oxidiz- ing agent, uniting so eagerly with vegetable tissue, as paper and wood, that it ignites them. ScG. Student, name the uses of KCIO3 as suggested by the experi- ments up to this point. 108. Tests for Chloric Acid and the Chlorates. — 1. Free concentrated chloric acid may be recognized by its odor and by its charring a slip of paper. 2. The dry chlorates, when treated with strong sul- phuric acid, yield a yellowish, explosive gas, CI2O4 (see Exp. 76); with hj^drochloric acid, they yield free chlorine gas. (Exp. 69.) Peechlokic Acid, HCIO4. 109. This acid and its salts are also of but small impor- tance, and the free acid should not be prepared. It is to be had by distilling dry potassium perchlorate, KCIO4, with strong, boiled sulphuric acid. Perchloric acid is one of the most powerful oxidizing agents known. When dropped upon charcoal, it explodes with violence, while dry wood and paper are instantly ignited. Upon the skin it produces deep and dangerous wounds. One of its salts, potassium perchlorate, may be prepared as follows : — Exp. 80 p. Heat in a generating-flask 5^ potassium chlorate, carefully noting when the flSygen ceases readily to be evolved, and the mass becomes pasty or semi-solid, — - 2 KCIO3 = KCl -I- KCIO4 -1-2 0. 106 EXERCISES IN CHLOKINB. Remove the heat, allow the flask to cool, and dissolve its con- tents in much hot water. Upon cooling, the potassium per- chlorate separates out in crystals, while the potassium chloride remains in solution. These crystals may be removed, dried, and used for experimental purposes. 110. Tests for Perchlorates. — 1. Dry perchiorates yield no yellow explosive gas with sulphuric acid, and with hydrochloric acid yield no free chlorine. 2. They require for their decompositiou a higher tem- perature than the chlorates. CHLORINE AND NITRO&EN. 111. Chlorine and nitrogen unite to form a dangerous explosive, which rivals nitro-glycerine, and whose composi- tion is not definitely known. It is prepared by passing a current of chlorine through a moderately warm solution of ammonium chloride. Under no circumstances should the student thus bring these chemicals together. The eminent chemists, Dulong, Davy, and Faraday, were seriously maimed while experimenting with this capricious com- pound. EXERCISES IN CHLORINE. 1. Given: NaCl, H^SO^, MnOj, HgO, As^Og, and KOH. From these chemicals show how you could prepare chlorine and all the compounds treated in this chapter. 2. Pkob. How many tons of salt, NaCl, would it require to prepare 10 tons of hydrochloric acid ■? 3. Peob. How many litres of chlorine gas can be obtained from 75'' of NaCl when the barometer reads TSS'n'^nd the thermometer 18° C. f 4. How are acids formed from their anhydrides '! 5. Given: The formula of an acid to determine the formula of its anhydride. Proceed thus : 2 HNO3 — HjO = 'Sfi^. In a like manner EXERCISES IN CHLOKINE. 107 determine the anhydrides of HClOj, HNOj, HjSO^, HCIO, HCIO3, and HIO3. 6. "What per cent of HCI is hydrogen 1 Chlorine 1 7. Determine the percentages of H, N, and in the nitrogen oxacids. 8. Prob. 20' of CI, measured at standard temperature and pressure, increased to 20.5' owing to a fall in the barometer. How many millimetres did the barometer fall ? 9. Chlorine gas was discovered in 1774. Who was its discoverer ? He used the chemicals HCI and MnOj. Describe the process, and write the equation. 10. An aqueous solution of chlorine changes, upon standing, to an aqueous solution of HCI. What gas is liberated ? Write the equation. 11. How can you prepare chlorine gas from bleaching-powder ? 12. The water analyst, in determining by titration the amount of chlorine in drinking-water, proceeds thus: He first prepares a standard solution of silver nitrate, by dissolving 4.79s AgNOj in 1' of distilled water ; he then measures out "lO^ of the drinking-water, and adds suflScient potas- sium chromate, K2Cr04, to tinge the water liglit-yellow. Now, from a burette graduated to tenths of a cubic centimetre, he adds to the water thus prepared the standard silver solution, drop by drop, with constant stirring, until the red color at first formed in the liquid becomes perma- nent. The number of cubic centimetres silver solution added is equal to the number of grains of chlorine per imperial gallon. How much silver nitrate does 1™ of the standard solution contain 1 How much silver? Show how this amount of silver will precipitate 1"S of chlorine. (SuG. lOSras' of Ag precipitate 3-5.5'"e' of CI ; therefore, to precipitate l™e of CI requires 108 -^ 35.5 = S.OS^S' Ag.) The permanent red color is due to the formation of silver chromate, Ag2Cr04; this formation does not occur until the chlorine is all precipitated. The potassium chromate thus serves as an indicator, showing when the right amount of AgNOj has been added. Why does the silver unite with the chlorine first ? General Note. Recent investigators doubt the existence in a free state of chlorine trioxide. CHAPTER VII. BROMINE, ITS OCCURRENCE, ETC. — THE BKOMINE ACIDS, BROMINE. Symbol Br'. — Atomic Weight, 80 ; Specific Gravity, 3.1872. 112. Occurrence. — Bromine does not occur in a free condition, but is found combined witli magnesium, sodium, potassium, and perhaps with some organic compounds, as bromides in sea water, certain mineral waters, and in most saline deposits. It also occurs combined with silver in the silver mines of Mexico and South America. Balard, in 1826, discovered bromine in sea water. He obtained it from the concentrated solution or "mother liquor" from which the crystals of common salt, NaCl, had been removed. Bromine, although by no means a plentiful element, is, nevertheless, an article of commerce, considerable quanti; ties of it being produced from the concentrated "mother liquors " of salt wells in various parts of the world. The United States produces the greater part of the commercial article. 113. Preparation. — Exp. 81 p. Dissolve in a test-tube a crj-stal of potassium bromide, KBr ; add a small quantity of chlorine water. Notice that the liquid turns somewhat darker than the chlorine water added ; this is due to free bromine. Now add three or four drops of carbon bisulphide, CSj, and BKOMINE. 109 shake thoroughly. What color does the carbou bisulphide assume ? Exp. 82 t. Thoroughly mix 30^ granulated manganese di- oxide, MnOj, with 40^ potassium bromide, KBr, and place in a retort. Use the same apparatus as for nitric acid, excepting that the condenser must contain 0.4' cold water, and the neck of the retort must dip 'below the water in the condenser; or a rubber cork with a bent tube dipping below the water may be fitted into the neck of the retort. Now pour into the retort 105^ sulphuric acid, H2SO4, previously diluted with 70™ water, and warm gently. Bromine will distil over in reddish-brown fumes and condense under the water in the condenser. A part of the bromine will also be dissolved in the water, thus giving bromine and bromine water at one operation. Save them both, each in separate bottles accurately fitted with ground glass stoppers, and keep in a cool place. Query. The specific gravity of the H^SOj is 1.84. How many cuhic centimetres equals 10.5b 1 Bromine is best prepared for class purposes by treating potassium bromide, KBr, with manganese dioxide and sulphuric acid, thus: — 3 H2SO4 -i- 2 KBr + MnOs = MnSOi -f 2 HKSO^ -f- 2 H2O -F 2 Br . SuG. Student compare this equation with that given in Preparation of Chlorine, Art. 90. Bromine is liberated when occurring in saline waters, by adding a small quantity of manganese dioxide, and then just enough sulphuric acid to liberate sufficient chlorine to free the bromine. This process depends upon the fact that free chlorine gas liberates bromine from its compounds. Query. Which possesses the greater chemism, chlorine or bromine? no BROMINE AND HYDROGEN. 114. Properties of Bromine. — Bromine is a dark-red colored liquid, at ordinary temperatures always giving off pungent, irritating fumes. It bleaches organic coloring- matter, but not so powerfully as chlorine. Its principal use is as a disinfectant. Bromine has a specific gravity of 3.1872 at 0°, freezes at - 7.5°, and boils at + 59.3°. Note. When removing the stopper of a bottle containing bromine or its aqueous solution, always turn your face away. Why 1 115. Tests for Free Bromine. — 1 . Free Bromine, even in dilute solutions, when shaken (in a test-tube) with carbon disulphide, CSa, colors the latter brownish-red. 2. Colors ether yellowish-red, which color is destroyed by shaking with potassium hydroxide, KOH. 8. Colors starch-paste solution orange-yellow. SuG. Student make these tests upon a dilute solution of the bromine water prepared as above. Also try the bleaching effect as with chlorine. BROMINE AND HYDROGEN. 116. Hydrobromic Acid, HBr, is the only acid formed by bromine and hydrogen. It is unimportant to the be- ginner, and he should not attempt its preparation. It is usually obtained by allowing liquid bromine to act upon amorphous phosphorus and water. This is accomplished by placing 10 parts of liquid bromine in a stoppered funpel provided with a stop-cock to allow the bromine to fall drop by drop into a generating-flask containing one part phosphorus and two parts water : — P -I- 5 Br -f- 4 H2O = HaPO, -f- 5 HBr. What takes place in this reaction can best be understood BROMINE AND HYDROGEN. Ill by considering it in two phases. When bromine acts upon phosphorus the two unite directly, forming either phosphorus tribromide, PBrs, or the pentabromide, PBr^, according to the relative quantity of bromine present. Now each of these compounds is decomposed by water, a» represented in the following equations : — PBrg + 3 H2O = H3PO3 + 3 HBr ; PBrs + 4 H2O = H3PO4 + 5 HBr. Thus, in each case, all the bromine appears finally in combination with hydrogen in the form of hydrobromic acid. We should naturally expect that the simplest method for making hydrobromic acid would be like that used for making hydrochloric acid, but strong sulphuric acid decom- poses hydrobromic acid, and hence, although the reaction, 2 KBr + H2SO4 = K2SO4 + 2 HBr, actually does take place, a further reaction also takes place, as follows : — 2 HBr + H2SO4 = 2 U,0 -f- SO2 + 2 Br, giving the gas, sulphur dioxide, SO2, and free bromine in the form of vapor, and from these it is very difficult to separate the hydrobromic acid. This acid is a colorless, irritating gas whose chief inter- est to us lies in the fact that it yields the salts called bromides, some of which are applied to useful purposes, thus : silver bromide, AgBr, is used in photography ; potassium bromide is used in medicine ; while others, as magnesium bromide, MgBra, are much esteemed ingredi- ents of certain mineral springs. Hydrobromic acid is used in organic laboratories, and it is now an article of commerce. 112 BROMINE AND HYDKOGBN. 117. Tests for the Bromides. — 1. Place the solution in a test-tube, and liberate the bromine by means of chlorine water; then add a few drops of carbon bisul- phide, CSa, and shake thoroughly. The carbon bisulphide is colored brownish-yellow. Note. An excess of CI must be avoided, otherwise a chloride of bromine is formed which does not color the bisulphide. 2. With silver nitrate, AgNOs, this solution gives a yellowish-white precipitate, AgBr, insoluble in /litric acid, difficultly soluble in ammonia, and easily soluble in potas- sium cyanide, KCy. Query. How do HCl and the chlorides deport themselves with AgNOj, etc.? Note. When bromides and nitrates occur in the same solution, the tests interfere. The bromine may be readily detected, but not so the nitrates, since the HjSOj and FeSOj liberate free bromine which obscures the ring. SuG. Student try a bromide as if testing a nitrate. 118. Bromine, Oxygen, and Hydrogen. — No com- pounds of bromine and oxygen have been isolated, but two, and possibly three, acids have been prepared, viz : — HBrO, Hypobromous acid, HBrOg, Bromie acid, and HBrO^, Perbromic acid. In regard to the existence of the last there is much doubt. These acids never occur in nature, and are of small importance to the beginner, so we shall here notice them but briefly. 119. Hypobromous Acid, HBrO, may be prepared in the same way as bypochlorous acid, HCIO, thus: — HgO -t- 4 Br -f- H2O = HgBr^ + 2 HBrO. (See HCIO.) BROMINE AND HYDROGEN. 113 It possesses bleaching powers, is of a straw-yellow color, and easUy breaks up into water, bromine, and oxygen. QtiEKT. What salts does this acid form ? 120. Bromic Acid, HBrOs, is formed by treating silver bromate, AgBrOa, with bromine water, thus : — 5 AgBrOa + 6 Br + 3 H,0 = 5 AgBr + 6 HBrOa. The salts (bromates) formed hj this acid somewhat re- semble the chlorates in their properties, but are of little importance commercially. Exp. 83 p. The easiest way to get a bromate is to dissolve bromine in a strong solution of potassium hydroxide, when a mixture of potassium bromate and bromide is formed : — 6 Br + 6 KOH = 5 KBr + KBrOa + 3 HjO. The bromate will soon separate out in crystals, which the student may try as he did the chlorates. 121. Tests for the Bromates. — 1. They are decom- posed by hydrochloric acid, giving free bromine (which may be detected as in Art. 115). QuEKT. What effect does HCl have upon KClOg ? 2. The bromates yield no explosive gas with sulphuric acid, but they are decomposed, affording free bromine and oxygen. Query. How does H2SO4 affect the chlorates "i EXERCISES IN BROMINE. 1. What chemicals are needed to prepare hromine and its compounds? 2. What per cent of KBr is potassium ? Bromine ? 3. How many grams of NaBr would be required to prepare lOs Br t 4. Compare the bromine and chlorine acids from a commercial stand- point. 114 BROMINE AND HYDKOGEN. 5. What does the word Bromine signify ? 6. In analyzing a sample of mineral water, a chemist found 0.1678e bromine per litre. In combining his bases and acids he united this bro- mine with magnesium. How many grams per litre of magnesium bromide, MgBr^, did he report ? Ans. 0.1929g. 7. How many grams of chlorine gas would be required to free the bromine of one gram KBr ? (KBr + CI = KCl + Br.) 8. To precipitate all the bromide in 50"° of a solution, required 0.215b silver nitrate. How much bromine per litre did the solution contain? SuQ. 108 parts Ag precipitate 80 parts Br. 9. Try to prepare HBr by passing H^S through bromine water. Explain the equation, — HjS + 2Br = 2HBr + S. Filter the solution and test for HBr. Can you prepare HCl by passing HjS through chlorine water ? Write the equation. 10. Boil in an evaporating dish a mixture of solid KgCrjOj and HjSOj until the mixture turns bright red. When cool, place a portion of the substance thus formed in a test-tube fitted with a bent delivery tube, and add a solid chloride, as NaCl. Note the bright brownish-red gas evolved : — 4 NaCl -f KjCr^O, -f 3 H^SO^ = 2CrO.,Cl, -|- 2 NajSO^ + KjSOj -|- 3 H^O. Now lead this gas, which becomes plentiful by applying a gentle heat, into a test-tube containing a dilute solution of ammonia. Note the yellow liquid formed : — ■ 2 NHj -I- 2 H^O + CrOjClj = (NH^),CrO^ -f 2 HCl. Acidify this solution with acetic acid, and add lead acetate : — PbCCjHgO^)^ -l-,(NHJjCr04= PbCrOj -f 2 NHjC^HgOj. Note the yellow precipitate thus obtained. Thus try with KBr instead of NaCl. What results ? Try the same with a mixture of KBr and NaCl. Do you obtain the same reaction as with NaCl alone 1 How can you distinguish a, chloride in presence of a bromide ■? See Douglas and Prescott, Qual. Anal., p. 159. CHAPTER VIIL IODINE. THE IODINE ACIDS. — SEPARATION OF CHLO- KIDES, BROMIDES, AND IODIDES. FLUORINE. — HYDRO- FLUORIC ACID. IODINE. Symbol I'. — Atomic Weight, 127; Specific Gravity, 4.948. 122. Occurrence. — Iodine, like bromine and chlorine, does not occur free. It is chiefly obtained from sea water, from which it is taken up by seaweeds. These weeds, especially on the coasts of Ireland and Scotland, are washed ashore during storms ; then they are collected, placed in shallow trenches, dried and burned in. thin layers so that the temperature may not rise high enough to "vaporize the iodides of sodium, potassium, etc., con- tained in the ashes or kelp, as it is popularly termed. These iodides are soluble in water, and are removed, by washing, from the ashes. Small quantities of bromides are also obtained in this process. Plantations of this sea- weed are cultivated in some parts of the ocean, and at the proper times vessels are sent to collect the weed. Iodine also occurs together with Chili saltpetre in the form of sodium iodide, Nal, and of late a considerable quantity of that which comes into the market has been obtained from this source. It also occurs as silver iodide, Agl, in certain American silver mines. 116 IODINE. 123. Preparation. — Exp. 84 p. Treat a crystal of potas- sium iodide, KI, as in Exp. 81. Wtiat results do you obtain? Exp. 85 t. It is not necessary to prepare iodine for class purposes, since it is an article of commerce, procurable at any drug store. It may be readily obtained, however, by treating potassium iodide, KI, with manganese dioxide and sulphuric acid, as in preparing bromine and chlorine. The iodine vapors may be condensed in a suitable flask surrounded by a cooling mixture. Commercial iodine is prepared from the iodides by treating them, as above, in iron retorts, when it is liberated in violet vapors and condensed in black, shining crystals upon the sides of suitable condensers : — 2 KI + Mn02 + 3 H2SO4 = MnSOi + 2 HKSO4 + 2 HjO + 21. SuG. Compare this equation with that for bromine and chlorine. 124. Properties. — Exp. 86 p. Heat a small crystal of iodine -in a test-tube. What is the color of the vapor? Note the odor. Iodine at ordinary temperatures is a black, shining solid, possessing a decidedly metallic appearance, .and always giving off fumes of a peculiar odor. When heated, iodine is easily converted into vapor of a splendid violet color and characteristic odor. The specific gravity of this vapor is 8.72. Query. Courtois discovered iodine in the year 1811. He named it from ioiiSrjs, violet-colored. Why did he thus name it ? Iodine is much used in medicine for various purposes, especially in reducing swellings, such as goitre and weep- ing sinews. It is also, used in checking the spread of eruptive diseases, like erysipelas. When thus applied it is used in the form of a solution prepared by taking, by IODINE AND HYDEOGEN. 117 weight: iodine, 20 parts; potassiiim iodide, 30 parts; water, 900 parts. Free iodine when brought in contact with the skin turns it brown. Iodine is only slightly soluble in water, but easily soluble in alcohol, carbon bisulphide,' chloroform, and in. an aqueous solution of potassium iodide. 125. Tests for Free Iodine. — 1. Free iodine colors carbon bisulphide, CSs, violet. 2. Colors starch paste blue. Note. Those substances heretofore mentioned as coloring a solution of starch paste and potassium iodide blue, produce this effect by liberat- ing iodine which unites with the starch to form a blue substance. Query. What substances act in tliis way ? IODINE AND HYDROGEN. 126. Hydriodic Acid, HI, is the only compound of hydrogen and iodine. This is a colorless gas resembling hj'drochloric acid. It is of no commercial importance, owing to its instability. Its principal use is for organic work and as a blow-pipe reagent. Exp. 87 p. Suspend in a test-tube half full of cold water a few crystals of iodine. Pass through this solution sufHcient sulphuretted hydrogen, HjS (Art. 167), to decolorize it. Hy- driodic acid will be formed and sulphur deposited : — H2S + 2I = S + 2HI. The sulphur will soon subside, and the clear solution of the acid may be poured off. Reserve this solution for the next experiment. Hydriodic acid may also be made by the method which was described under hydrobromic acid ; that is, by gradually adding iodine to amorphous phosphorus under 118 IODINE AND HYDEOGEN. water. The reactions are the same as in the case of bromine, the iodides of phosphorus being first formed, but afterwards decomposed by the water. Exp. 88 p. In oije test-tube place a solution of mercuric chloride, HgClg ; in another, a solution of silver nitrate, AgNOa ; in a third, a solution of lead acetate, Pb(C2H302)2. To each of these now add a portion of the hydriodic acid solution prepared as above. Note the brilliantly colored precipitates which are respectively the iodides of mercury, silver, and lead. Eepeat the experiment, using a solution of potassium iodide, KI, in place of the acid. Do you obtain the same results ? Hydriodic acid unites with bases to form the iodides, many of which are valuable. Some of these iodides possess very bright and distinctive colors which are of service in identifying some of the metals whose salts are in the solution to be analyzed. Since the acid itself is unstable and somewhat troublesome to prepare, the chem- ist preferably uses a solution of potassium iodide for this purpose. SuG. Explain these equations : — HgCl3 + 2HI=Hgl2 + 2HCl; Pb(C,H30J,+ 2HI = PbI, +2HC,H30,; AgNOa + HI = Agl + HNO3. Also write the same equations with KI in place of HI. 127. Tests for Hydriodic Acid or the Iodides. — 1. To the solution add chlorine water. Then add a few drops of carbon bisulphide and shake. Iodine is freed and colors the bisulphide violet. Note. If the iodide is not readily soluble, the iodine may be freed by wanning the insoluble iodide in a test-tube with a crystal of potassium chlorate and hydrochloric acid ; the bisulphide may then be directly added. IODINE AND HYDROGEN. 119 2. With silver nitrate, AgNOs, a yellow precipitate is given, insoluble in nitric acid; sparingly soluble in am- monia; soluble in potassium cyanide, KCy. SnG. Compare this test with the similar ones for chlorine and bromine. QuEKY. Which test in the case of chlorine is distinctive ? Of bro- mine 1 Of iodine ? Note. Solutions of iodides and nitrates do not readily yield a test for nitric acid for the same reasons as those given under bromine. The test for the iodide is readily obtained. Try a solution of KI as for a nitrate. Try a solution of KI and KBr with CSj, etc. Which test do you obtain ? 128. Detection of Chlorides, Bromides, and Iodides in the same Solution. — The stbdeut is probably aware that the precipitates obtained with silver nitrate do not afford sufficiently marked characteristics to distinguish these compounds, and that the carbon bisulphide tests also fail, especially in the case of bromides in presence of iodides. To separate and distinguish these substances is not an easy task, and of the many ways proposed, none are entirely satisfactory and at the same time simple and convenient. The following method requires careful ma- nipulation. Exp. 89 p. Let us suppose the solution to contain NaCl, KBr, and KI. Divide it in three portions and add to numbers 1 and 2 an excess of silver nitrate, when the precipitates ob- tained in each will consist of AgCl, AgBr, and Agl. Filter out these precipitates and wash them thoroughly with hot water, then wash them through a hole in the point of the filter-paper into separate beakers. To the first beaker now cautiously add but two or three drops of potassium bromide, and to the second carefully add three or four drops of potassium iodide, and boil for a short time. Again filter the contents of the first beaker, and test the clear liquid which runs through for chlorides, 120 IODINE, OXYGEN, AND HYDEOGEN. Art. 96. Filter the contents of the second beaker, and test the solution for bromides (Art. 117, 1). Try a part of the third portion directly for iodides by Art. 127, 1. In case you do not succeed, proceed thus : To the re- mainder of the third add a few drops of ferrous sulphate, FeSO^, and copper sulphate, CUSO4, when a light-green pre- cipitate of cuprous iodide, CujL, will be thrown down. Test this insoluble iodide by Art. 127, 1, Note. Explanation. What occurs in the three cases may thus be ex- plained : — 1. In number 1, AgCl + AgBr + Agl + KBr = Agl + 2 AgBr + KCl. The KBr and AgCI react, yielding KCl, which is soluble and in the solution tested for chlorides. 2. AgCl -f- AgBr + Agl + 2 KI = 3 Agl + KBr -1- KCl. The KCl and KBr are soluble and readily yield the test for bromides. 3. This last is readily understood when we remember that the iodine is partially precipitated in the Cu^I^. Note. The foregoing method is not sufficiently accurate for quanti- tative determinations where an excess of potassium bromide or iodide would necessarily be employed. Care must be used to avoid an excess of either reagent when employed for /jualitative work. IODINE AND OXYGEN. 129. There is but cue known oxide of iodine. Iodine Pentoxide, I2O6. This oxide may be obtained by heat- ing iodic acid, HIO3 as described in the next article. IODINE, OXYGEN, AND HYDROGEN. 130. There are but two oxygen acids of iodine, viz: — Iodic Acid, HIO3, Periodic Acid, HIO4. IODINE, OXYGEN, AND HYDROGEN. 121 These acids and their salts are unimportant; we shall therefore notice only the first, and that but briefly. Exp. 90 op. Heat one part, by weight, of free iodine with ten parts strong nitric acid (sp. grav. 1.5) until red fumes cease to come off and the iodine is dissolved. Evaporate the solution to dryness and heat in the air-bath to 200°. The resulting white powder is iodine pentoxide. The first product formed in this process is iodic acid, HIOs. When this acid is heated to 200° it breaks up into water and iodine pentoxide : — 2 HIO3 = lA + H^O. By again dissolving the pentoxide in water, pure iodic acid may be obtained. StiG. Write the equation for the action of iodine on nitric acid, remembering that NO, HIO3, and HjO are formed. Also show the action of H2O on I2O5. Iodic acid rapidly oxidizes organic substances. When this acid or the pentoxide is heated with powdered char- coal, phosphorus, sulphur, etc., it oxidizes them so rapidly that the action is accompanied by flame. It forms normal salts, the iodates, as KIO3. Acid salts, as KIO3HIO3 or HK(I03)2, are also known. 131. Tests for Iodic Acid or the Iodates. — To a solution containing either the free acid or its salts add starch paste and chlorine water; no change in color occurs. Now add a solution of sodium sulphite, NajSOs, when iodine is liberated and the solution turns blue. 122 FLUOKINE. FLUORINE. Symbol, F'. — Atomic Weight, 19 ; Specific GEAVITr, UNKNOWN. 132. Occurrence. — Free fluorine is unknown. It occurs combined with calcium as calcium fluoride, CaFs, or fluor spar, in cubical crystals which are usually somewhat trans- lucent and often quite transparent. It also occurs in the mineral cryolite, which is a fluoride of sodium and aluminium. Other sources of fluorine are unimportant. Fluorine has resisted all attempts to isolate it, and they have been many. This fact appears to be due to its great chemism when nascent, at which time, it invariably attacks and combines with the vessel in which it is gener- ated. Nothing is known of its physical properties, and but little of its chemical deportment other than its great chemism. Fluorine forms no oxides, no oxygen acids, and but one hydrogen acid, viz. : — Hydeopluobic Acid, HF. 133. Preparation. — This acid is also a gas correspond- ing to hydrochloric, hydrobromic, or hydriodic acid. It is best prepared by treating calcium fluoride in a leaden evaporating-dish, with sulphuric acid : — CaFs + H2SO4 = CaSOi + 2 HF. This gas is a dangerous poison, and great cai'e must be exercised in its preparation. 134. Properties. — Exp. 91 t. Pulverize 4^ calcium fluor- ide, and place in a leaden dish, which can be made by cutting FLUOKINB. 123 ofif a piece of lead pipe, splitting it open lengthwise, and then placing it in an iron mortar where it can, by the aid of an iron pestle, be hammered out into the shape of an evaporating-dish. Next prepare a sheet of glass by coating both sides with beeswax or paraffin. Upon one side of this glass engrave, by means of a pin or sharp, soft wire, some design. Now put the evaporating-dish, supported by a ring-stand, in a gas- chamber or where there is a current of air to carry off all fumes, and support the plate a short distance above the dish. Add strong sulphuric acid to the calcium fluoride, when hydro- fluoric acid will be quickly liberated, especially if a gentle heat be cautiously applied. In a few minutes the design will be neatlj' etched into the glass. Be very careful not to inhale any hydrofluoric acid fumes, as they are exceedingly poisonous. Hydrofluoric acid is often employed as above in etching thermometer scales. This acid seems to have great chemism for such sub- stances as calcium, silicon, and potassium, in consequence of which glass is immediately attacked and can not be used to store the gas or its aqueous solution. Leaden or vulcanite bottles are employed for this purpose. The action of hydrofluoric acid upon sand and glass, which is a compound of sand with bases, is largely due to the action represented by the equation , — Si02 -F 4 HF = 2 H2O + SiF,. The silicon tetrafluoride, SiFi, thus formed, escapes as a gas. 135. Tests for Hydrofluoric Acid in Fluorides. — The best is the etching test, but care must be taken not to scratch the glass with the graver used in cutting through the wax. 124 EXERCISES IN IODINE AND FLUOillNE. EXERCISES IN IODINE AND FLUORINE. 1. How many grams of silver nitrate would be required exactly to combine with 10s of potassium iodide t 2. How many pounds of iodine can be obtained from one-half ton of sodium iodide ? 3. What chemicals are necessary to prepare from potassium iodide iodine and its compounds ? 4. Make a comparison between the commercial values of the acids of chlorine, bromine, and iodine. 5. Compare the same three elements according to their physical con- ditions at ordinary temperatures ; also according to their atomic weights, specific gravities, and chemism. Make a table comprising the acids they form. 6. "Will nitro-hydrochloric acid liberate bromine and iodiiie from their compounds 1 Try it. 7. Class prepare a sheet of glass as directed in Exp. 91, writing the names of the class through the wax. Under the teacher's direction etch with HE. This will be a good memento to leave in the Laboratory. 8. Test a solution of NaCl and KNO3 for the different acids combined with bases in these salts. 9. Under potassium and sodium learn the tests for these metals, and try for them in the above solution. 10. It would now be well for the student to practise daily upon unknown solutions, as in 8 and 9. These solutions should not contain acids that interfere, and the bases with which the acids are combined should preferably be potassium, sodium, and ammonium. 11. In working upon an unknown solution a student obtained tests for K, Na, NH3 and H^SO^, HCl, and HNO3. What salts may have been dissolved in the solution ? In case the laboratory contains only NH^NOj, NHjCl, KNO3, KCl, NaCl, and KjSO^, what salts may the teacher have employed in preparing this solution ? 12. See Trans. Roi/. Soc. Canada, 1883, sec. 3, pp. 65 et seq., for " Hy- driodic Acid as a Blow-pipe Reagent." Dr. Haanel's paper on this topic is accompanied by very fine plates. 13. To a solution containing an iodide and a bromide add OS,; now by the addition of suflicient chlorine water try to obtain first the color foi iodine, and second the color for bromine. Explain. CHAPTER IX. Caebon. — Caebon and Hydeogen. — Oxides op Caebon. — Caebonic Acid. — Cyanogen. — Petjssic Acid. CARBON. Symbol C". — Atomic Weight, 12. — Specific Gravity: Dia- mond, 3.5-.6 ; Graphite, 2.25 ; Charcoal, 1.67. 136. Occurrence. — Carbon is a very widely distributed element, occuring chiefly in an impure state or in chemical compounds. It is an important constituent of all organic substances, mineral carbonates, carbonic acid gas, and the cyanides. In a free condition, it exists in three widely differing forms. 1. In pure, transparent, glittering, octahedral crystals, as Diamonds, which are found in earthy detritus or clayey shales in Africa, South America, Australia, and other localities. Sua. Write an essay on diamond-raining, diamond-cutting, and famous diamonds. 2. In dark, shining, six-sided slabs as Graphite, Plum- bago, or Black Lead, which occurs in England, Cej'lon, the United States, and other countries. 3. In impure forms as Coal, Soot, and Lamp-black. Of coal we find a number of varieties, as Charcoal, Anthracite coal. Bituminous coal, etc. SuG. Write a short paper on coal-mining. 126 CARBON. 137. Preparation. — It is not necessary to prepare car- bon for class illustration, since any of the above-named modifications are easily to be obtained. Small diamonds are said to have been made artificially by a somewhat complicated process, which cannot be profitably described at this stage. The method of their formation in nature is not understood. Q-rapMte has been frequently observed in iron-smelting furnaces, having been artificially produced at high tem- peratures. In Exp. 2, Charcoal was obtained by heating wood in a test-tube. The principles therein involved are made use of in preparing charcoal for commerce. In practice the wood is heated in closed iron cylinders, or burned in large pits or kilns with a limited supply of air. In the latter case a part of the wood thus treated is completely consumed in order to furnish the heat requisite for charring the remainder. Lamp-black or soot is prepai'ed by burning a carbonaceous substance, such as oil, resin, etc., in a limited supply of air. The lamp-black appears as a black smoke which is easily collected upon a cold surface. Qderies. What makes a lamp smoke? Why is the lamp-chimney blackened 1 Explain the deposition of soot in stovepipes and chimneys. Can soot be obtained from the Bunsen flame 1 Luminous flame ■? Alcohol flame ■? Ordinary candle flame ? Why does pitch-pine give such a smoky flame ? If one wishes to know a fact which comes within the province of Experiment, how should he proceed ? 138. Properties. — Carbon is absolutely indispensable to all organic structures. With other elements, such as hydrogen, oxygen, and nitrogen, it is capable of forming an almost endless number of chemical compounds. As a matter of convenience these are generally considered CAEBON. 127 under the head of the Chemistry of the Compounds oj Carbon, or Organic Chemistry. CarboD has many industrial uses. It is chiefly used in reducing metals from their ores and for heating and illuminating j)urposes. The colorless diamond is highly prized as a jewel. A colored variety is used in glass-cutting, while its dust is employed for polishing hard and refractory substances. Drills armed with diamond points are used by miners and others ; these drills will quickly cut through the hardest rocks. Smoky or black diamonds and carbonado, an impure massive form, are principally used for this latter purpose. The diamond is the hardest substance known, its value in the " scale of hardness," by which mineralogists estimate the hardness of minerals, being 10°. This scale, in which each substance is able to scratch all that are below it in the scale, is as follows : — Diamond 10" Sapphire 9° Topaz 8° Quartz 7° Feldspar 6° Apatite 5° Fluorspar 4° Calcspar 3° Gypsum 2° Talc 1° The primary form of a diamond crystal is octahedral : but it occurs in many different forms derived from this primary crystal. When first removed from its matrix, the diamond is often rough and lustreless, and afterwards requires cutting and polishing ; this latter is accomplished by means of its own dust. Like all hard substances it is brittle and quite easily broken. In acids and alkalies the diamond is completely insoluble. When heated to a high temperature in a current of oxygen it burns, the product being carbon-dioxide gas, COj, with a small amount of 128 CAEBON. residual ash. Upon light the diamond exerts a very high refractive influence, to which property it owes its great brilliancy. Query. What properties cause the diamond to be so highly esteemed as a jewel ? Q-rapMte is greasy to the touch. It is largely used for polishing purposes, such as for coating shot and powder, and, owing to its great permanence in the air, is largely employed in the manufacture of stove-polish. Its particles, however, are very hard, and the saws used in cutting it are quickly worn out, and a knife, when employed for the same purpose, soon loses its edge. Graphite, owing to its great infusibility, is now mixed with clay and extensively used in making crucibles which are employed by metallurgists, while its employment in the manufacture of leads for the common lead-pencil is a well-known application. SuG. Prepare a paper on the manufacture of lead-pencils. Coal is probably the remains of a magnificent vegeta- tion which flourished during the carboniferous age. It has been brought into its present condition by heat and pressure. The heat is thought to have been supplied by the heated interior of the earth, while the pressure was due to the influence of water and the rocks which subse- quently formed above the coal. This explanation con- templates the idea that during some post-carboniferous convulsion which swept over the globe, the land sank down, and the vegetation was overwhelmed by the inrush of water, while the rocks were afterward deposited. The ashes and " clinkers " of burned coal are the mineral sediments which were entangled by the vegetation, as well as the mineral constituents of the plants themselves. CARBON. 129 Anthracite coal is i^sed for heating purposes, and for reducing metals from their ores. Its reducing power depends upon the chemism of carhon for oxygen. Query. What is meant by reduction ? Bituminous coal differs from anthracite in that the former contains more hydrogen-carbon compounds, and evidently has not been subjected to so high a temperature or to so great a pressure by natural agencies. This variety of coal burns with a very hot and sooty flame, and needs a large supply of air for its combustion. Coke is a form of carbon obtained by driving off, at a high temperature, the volatile constituents of coking- coal. It is left behind in the retorts when coal is distilled for the purpose of making illuminating gas. Gas Carbon is also produced in distilling coal. This form of carbon is much used in making negative plates for batteries and for the terminals of electric lamps. Peat is a form of fuel nearly akin to bituminous coal, and is formed from the roots and stems of certain plants growing in bogs or marshes. Lignite is a peculiar form of coal formed from such sources as our present deciduous trees, and often exhibits a distinctly woody structure. Jet is a black variety of lignite, much used in jewelry. Jet readily takes a high polish. Lampblack is much used as a paint, and in making printers' ink. C7tarcoflZ is employed as a- reducing agent in preparing iron from its ores. Queries. For what purposes do yoa use charcoal in the laboratory t What class of artisans employ charcoal ? What other common uses does it have 1 130 CARBON. Charcoal possesses some remarka.ble properties: — Exp. 92 p. Place a filter-paper in a funnel ; then fill the paper nearly full of bone-black or freshly-burned charcoal powder. With a filter thus arranged see if you can produce any changes in the following solutions by filtering them several times: 1. Vinegar; 2. Syrup of brown sugar; 3. Dilute black molasses; 4. Indigo solution; 5. Carmine solution; 6. Beer; 7. Potassium dichromate solution. QuBKiES. What changes occurred 1 Does 7 behave like the others 1 Why ? Explain the changes. We thus see that charcoal is capable of decolorizing and purifying such organic liquids as were mentioned. The reason why it is employed in filtering drinking-water is now apparent. It is supposed that this action of charcoal is partially due to the fact that it absorbs oxygen, and possesses the power of causing certain organic substances to combine with this oxygen. However this may be, the charcoal soon loses its efficacy unless it be frequently washed and exposed to the air. For the same reason charcoal will destroy the gases from putrefying sub- stances. Queries. Why should a filter be frequently cleaned 1 Is it best con- tinuously to keep a filter full of water 1 What is the use of gravel in filters ■? Why should a rapid river flowing over stones and with numerous falls be purer than one with a sluggish current and a sandy or muddy bottom t Exp. 93 p. Place in an evaporating-dish a few grains of common sugar ; add a few drops of strong sulphuric acid. Do you obtain carbon ? Also thus try starch. What results ? From the above experiment and from previous work the student may learn that many substances, such as sugar, oils, resins, fats, waxes, tallow, and alcohol are CARBON. 131 compounds of carbon. We may add to this list nearly every substance used as food by man and by animals, and all the vegetable drugs known to chemistry and com- merce. We should not forget also that it is to the compounds of carbon that we are indebted for our rai- ment, and even for a portion of our dwellings. Query. How could we obtain light without the aid of carton 2 Kerosene, gasoline, naphtha, benzine, and paraffin are all derived from Petroleum, or rock oil, which is a mixture of many compounds of carbon and hydrogen found in company with coal deposits. The limits of our work forbid a further notice of these interesting sub- stances. 139. Tests for Carbon. — 1. Free carbon, as soot, coal, lampblack, etc., may be recognized by its physical proper- ties and by its insolubility in all acids and alkalies ; also by the manner in which it burns when heated on platinum foil. 2. Graphite may be recognized by its properties, and by the black, insoluble streak which it leaves when drawn across paper. SuG. Write with a lead-pencil on white paper. Try to bleach it. What results ? 3. The diamond is recognized by its brilliancy and hardness, being able to produce a scratch upon the hard- est substance. ' Query. The hardness of glass is less than 6°. Is the fact that a given substance makes a scratch upon glass sufficient evidence that it is si diamond ? 132 CAEBON AND SYDROGEK. CARBON AND HYDROGEN. 140. Carbon and Hydrogen form many compounds, but three of which we shall notice here : — 1. Methane, or Marsh Gas, CH4; 2. Ethylene, or Oleflant Gas, CjHi; 3. Acetylene, C2H2. Methane, CH^. 141. Methane, or Marsh Gas, may thus be prepared for illustration : — Exp. 94 p. 2^ sodium acetate, NaC2H302, are heated in a hard glass test-tube fitted with a jet, with 8^ sodium hydroxide, NaOH, and 2^ flnely-powdered quick-lime, CaO. As soon as the gas issues freely from the jet it may be ignited, when it burns with a bluish-yellow, non-luminous flame. Tlie reaction '^ "" NaCsHsOs 4- NaOH = NaaCOg + CH,. QuEBT. What purpose does the CaO serve 1 (Compare the use of Mn02 in producing oxygen from KCIO3.) This gas occurs free in nature, and is formed in stagnant pools by the decay of leaves and other vegetable material, whence it derives its name. Marsh Gas. It also occurs in coal seams and in , coal mines, where it is known as Fire Damp. Methane condenses at —10° under 50 atmospheres, and boils at — 160° under 1 atmosphere. Exp. 95 p. Discharge the hydrogen pistol by means of a mixture of marsh gas and air. When mixed with air or oxygen, methane is often the cause of most violent explosions. To prevent these ex- plosions. Sir Humphrey Davy invented his Safety Lamp, which consists of an ordinary lamp, the flame of which is «IS:fi. CAKBON AKD HYDEOGElJ^. 133 surrounded with a wire-gauze cage. This cage prevents the temperature of the surrounding mixture of methane and air from rising to the point of ignition. The specific gravity of methane is 0.558. QnERT. Why does the wire gauze placed between the Bunsen flame and chemical vessels prevent them from breaking ? Sue. Student ascertain the particulars of several noted colliery ex- plosions. Exp. 96 p. Hold moistened strips of red and blue litmus paper iu a jet of methane. The gas does not affect them. We are thus led to the conclusion that methane does not resemble either the acid or the alkaline gases already studied. These compounds of carbon and hydrogen differ in many respects from the compounds of other elements with hydrogen. A very large number of the hydrogen- carbon compounds is known and new ones are being con- stantly discovered. We may regard as derived from these the compounds treated in organic chemistry. Since methane is not readily acted upon by reagents, the color of its flame, and its explosiveness when mixed with air, will answer our purposes as tests. Ethylene, or Olepiant Gas, C2H4. 142. Ethylene is formed in distilling coal, and is, there- fore, a constituent of coal gas. It is prepared most readily by the following method, which may be shown for class illustration : — Exp. 97t. Heat in a generating-flask fitted with a jet delivery-tube 10^ of ethyl alcohol, CjHeO, with 50^ strong sulphuric acid. Note the odor and taste of the gas issuing from the jet, and tlien ignite it. It burns with the ordinary 134 cAebok and hydeogek. gas-flame. The sulphuric acid simply abstracts one molecule of water from the alcohol, thus : — Query. How many cubic centimeters of alcohol and acid are required above, the specific gravity of H^SOj being 1.843 and that of ordinary alcohol being 0.815 1 Ethylene is explosive when mixed with three times its volume of oxygen. Query. What substances are formed ■? Student write the equation. When equal volumes of ethylene and chlorine gases are brought together, an oily liquid, called " Dutch Liquid," C2H4CI2, the odor of which resembles chloroform, is formed. The specific gravity of ethylene is 0.9784; it can be condensed to a liquid at 10° by a pressure of 51 atmos- pheres, and boiling under 1 atmosphere at — 100°. 143. Test for Ethylene. — Fill a jar with the gas sup- posed to contain ethj'lene ; then pass a current of chlorine gas into the jar. If the oily Dutch Liquid mentioned above be formed, ethylene is present. Note. This liquid is insoluble in water. Acetylene, C2H2. 144. Acetylene is also a gas, and possesses a powerful and disagreeable odor, which is particularly noticeable when an ordinary Bunsen burner strikes back and con- tinues to burn at the base. It has been prepared by passing sparks from a powerful battery through an atmosphere of hydrogen, the termi- nals of the electrodes being carbon. No other hydro- carbon compound has been thus directly produced. It CAEBOK AND HYDROGEN. 136 burns with a bright, luminous flame, and has a specific gravity of 0.92. The odor of acetylene betrays its presence. 145. Illuminating Oas is obtained, together with many bye-products, by distilling coal in retorts. It contains hydrogen, methane, and ethylene, and many other hydro- carbon compounds. It also contains in small quantities the impurities: ammonia; hydrogen-sulphide, HjS; carbon dioxide, CO2; carbon monoxide, CO; atmospheric oxygen; and nitrogen. These impurities are mostly removed by passing the gas through a series of washing and absorbing reagents. SuG. Student visit the gas works. Write a description of the process of gas manufacture. Consult R. and S. The student may test for these impurities thus : — 1. Ammonia is detected by holding a strip of moistened faintly-red litmus paper iu a stream of the illuminating gas. The paper turns blue if ammonia be present. 2. Hydrogen sulphide will blacken a strip of bibulous paper moistened with lead acetate, Pb(C2H302)2, when the paper is held in a current of the gas. 3. Carbon dioxide may be detected by shaking lime-water, Ca(0H)2, in a flask of the gas (see test foi- CO2). 4. Oxygen may be detected as directed under tests for oxygen. Art. 29, 2. 5. The nitrogen and carbon monoxide cannot be detected with certainty bj' anj- means likely to be at the beginner's disposal. Coal Tar. — It has been mentioned that there are many bye-products formed in distilling coal in the manufacture of illuminating gas: of these coal tar is, from a chemical standpoint, the most remarkable. It is used directly for 136 CARBON AND OXYGEN. various industrial purposes which are so well known as to need no description. The attention of many chemists has been given to this substance, and from it they have produced a large number of articles which are in daily use in the arts and manufactures. The beautiful aniline anthracine and naphthaline dyes are obtained from this source, and their production has revolutionized not only the art of dyeing, but also the industries of whole coun- tries, and made it possible for even the laborer to em- bellish his home with colors which before were only accessible to the opulent. From coal tar, then, we may see the artificial production of substances which formerly were only obtained from natural sources ; and thus is the distinction between the so-called organic and inorganic substances rapidly passing away. SuG. The student who reads German may obtain valuable information upon this topic by consulting Schultz's Chemie des Steinkohlentheers. QuEKY. What are the natural sources of indigo ? Cochineal ? CARBON AND OXYGEN. 146. There are two oxides of carbon, viz : — 1 . Carbon Monoxide, CO ; 2. Carbon Dioxide, COg. Of these two oxides the latter is to us of the greater im- portance. Both are gases under ordinary conditions. Cakbon Monoxide, CO. 147. Preparation, etc. — This gas is a product of com- bustion, and is formed when carbon is burned in a limited supply of oxygen : — C -I- O = CO. CARBON AND OXYGEN. 137 It 19 also formed at high temperatures by the action of carbon on carbon dioxide : — CO2 + C = 2 CO. Query. Of what kind of action is this an example ? Exp. 98 p. Carefully heat in a generating-flask with a de- livery-tube, 2s potassium ferrocyanide, KjFeCye, with 20* strong sulphuric acid. Ignite the stream of escaping gas, CO ; care- fully note its odor, if any, and the color of the flame. Carbon monoxide burns with a lambent blue flame, as seen in coal stoves when the supply of air is limited, and at the upper surface of the coal in grate fires. The com- bustion at the bottom of the coal first produces carbon dioxide ; this substance coming in contact with the heated coal near the upper surface is reduced to carbon monoxide; and when this latter meets the air above the coal, it again burns, forming carbon dioxide, the combustion now being complete : — CO H- O = CO2. Carbon monoxide is colorless and tasteless, and has a faint and peculiar odor. It acts upon the animal economy as a deadly poison, producing headache, giddiness, and insensibility. It seems to produce its effects upon the system by combining with the haemoglobin of the blood, leaving traces which betray its action even after death. Great care should be taken not to allow this poisonous gas to accumulate in rooms warmed by coal fires. One per cent is a sufficient quantity to prove fatal. The joints of the stove should be tight, the draft strong, and, above all, the ventilation should be perfect. Death has been produced from warming poorly-ventilated rooms by means of charcoal fires in open vessels from which carbon mon- 138 CAKBON AND OXYGEN. oxide is given off ; and people have perished by going to sleep beside a lime or brick kiln or a charcoal pit, being suffocated and poisoned by the gaseous oxides of carbon. Tobacco smoke contains more or less carbon monoxide. Hence, the inhalation of the air of a room in which many persons are smoking may produce pernicious effects upon the system. Carbon monoxide has a specific gravity of 0.968, and condenses at —139.5°, under a pressure of 35.5 atmos- pheres ; under 1 atmosphere it boils at — 190°. 148. Test for Carbon Monoxide. — This gas may be recognized, when present in sufficient quantity, by its bluish flame. Caebon Dioxide, CO^. 149. Occurrence. — This gas, commonly known as car- bonic acid gas, occurs widely distributed in nature. It occurs free in the atmosphere in small but persistent quantities, and combined in all the carbonates, from which it is readily liberated by the stronger acids. Calcium carbonate, or limestone, CaCOs, is a very plentiful sub- stance. Whole geological formations consist of this material. It also is the chief constituent of shells and most corals. Whole islands are being constantly built up by the corals in the tropical regions. SuG. Write a paper on coral formations. 150. Preparation. — Exp. 99 p. In a wide test-tube or a small beaker place about 5°° calcium hydroxide solution, Ca (OH) 2. By means of a small glass tube force air from the lungs through the solution, when a white precipitate will be formed. Continue to breathe some minutes through the liquid ; the pre- cipitate dissolves. CARBON AND OXYGEN. 139 This white precipitate is calcium carbonate, CaCOj, and was produced by the action of the carbon dioxide which , is thrown out of the lungs as a waste product at every respiration : — Ca(0H)2 + CO2 = CaCOa + H^O. Large quantities of carbon dioxide must thus neces- sarily be liberated in the air, since it is produced in the same way by all air-breathing animals. Query. Why does the air in poorly-ventilated living-rooms contain more carbon dioxide than those that have good ventilation ? Exp. 100 p. Carefully lower into a wide-mouth bottle a burning taper. When the taper is extinguished, add a small quantity of calcium hydroxide ; cork the bottle, and shake. Do you again obtain the white precipitate ? All carbon compounds when burning in the air produce carbon dioxide. This gas is also emitted during volcanic action. Query. In what ways may CO2 be liberated in living-rooms ? Exp. 101 p. To a dilute solution of sugar or molasses in water add a little bakers' yeast. Place in an evaporating-dish a small quantity of this solution ; also fill a test-tube with the solution, invert the tube, and place its mouth below the solution in the evaporating-dish. The whole is now to be left standing in a warm place. Fermentation soon begins, bubbles of gas rise in the tube, and the liquid is forced down. When the tube is full of gas, pour the latter out into another tube (as if it were water), add calcium hydroxide, and shake as before. Is the gas carbon dioxide ? Carbon dioxide is also produced in fermentation, and in the spontaneons decomposition of animal and vegetable substances. Quest. In what ways is carbon dioxide liberated in the atmosphere t 140 CARBON AND OXYGEN. Exp. 102 p. Break into pieces about 10^ calcium carbonate, or marble, CaCOg. Place in a generating-flask, and cover with water. Fit the flask with a V-shaped delivery-tube, and collect the materials mentioned in the following experiments. Upon adding hydrochloric acid to the contents of the flask, carbon dioxide will be plentifully given off, although a gentle heat may sometimes be required. The equation is : — CaCOg -f 2 HCl = CaCls -|- H2O + CO2. Note. The CaClj solution should be evaporated to dryness, fused in a sand crucible, and kept in a tightly-corked bottle. It is useful for drying gases and for other purposes. Carbon dioxide may be readily obtained in larger quan- tities by treating the carbonates with strong acids. With the gas which the student is now ready to prepare he may proceed to study the 151. Properties. — Exp. 103 p. Fill a wide test-tube with carbon dioxide. Note the odor and color, if any, and try the effect upon a glowing match ; a burning match ; a lighted taper. What results? Trj- to ignite a jet of this gas. Carbon dioxide is a colorless, odorless gas which does not support combustion. Advantage has been taken of this fact in making an engine to extinguish fires. The gas is generated from sodium carbonate, NaaCOj, and sul- phuric acid, and allowed to escape through a hose. ScG. Explain the construction of a Babcock fire extinguisher. Write the equation for the reaction of Na^COj and H^SO^. For HNaCGj and H2SO4. Exp. 104 P. In the centre of a pine ruler 2"" wide and 100™ long drive two needles. This ruler will serve as the beam of a balance, while the needle-points will serve instead of a knife-edge bearing. These points are to be placed upon a flat metallic surface. Now from one end of the beam suspend, by means of a thread, a small paper sack, and from the other CAKBON ASD OXYGEN. 141 end a larger paper sack. Into the smaller sack carefully drop small pieces of iron, chalk, sand, or any heavy substance, until the beam is in equilibrium. Into the larger sack now deliver a jet of carbon dioxide. The larger sack will soon become heavier and sink. Queries. With what gas was the larger sack filled before introducing the CO2 ? Is CO2 lighter or heavier than air ? Suppose the sack be sus- pended mouth downwards, what would occur if a jet of hydrogen were allowed to flow up into it ? In what other way have you compared the weight of air with that of gases ■? How should ajar be placed when filling it with COj, mouth down or up ? Exp. 105 p. Place a lighted taper in an open jar of air. Now fill a second jar with carbon dioxide, and then pour the contents of this jar into the first. As soon as the taper is immersed in carbon dioxide it is extinguished. Try to transfer by means of a siphon the contents of a jar of carbon dioxide into another arranged with a taper like the first, treating the gas as if it were a liquid. Carbon dioxide is heavier than air, its specific gravity being 1.529. 1' at 0° and 760""" weighs 1.965«. It can be condensed to a liquid by pressure or by reduction of its temperature. Under one atmosphere it liquefies at — 78° ; a still further reduction, which may be accomplished by allowing the liquid to escape into a box with a sieve-like bottom, freezes the liquid to a snow-like solid. Exp. 106 op. Place any small animal in a jar of carbonic acid gas ; note the symptoms and time of death. Also thus proceed with a jar of carbon monoxide. How do the symptoms compare ? The time of death ? Pure carbon dioxide seems to produce its deadly effects by asphyxiation, the lungs being unable to effect the decomposition of the gas, and thus to appropriate the needed oxygen, which it certainly contains, but holds with 142 CARBON AND OXYGEN. an exceedingly tenacious grasp. As one would infer, this gas is very stable ; but its decomposition can, nevertheless, be accomplished. Exp. 107 p. Into a jar of carbon dioxide place a brightly burning magnesium ribbon. It continues to burn. Is carbon set free? Also trj- a piece of burning sodium. Is the gas again decomposed? Are other products than carbon formed? If these products are MgO and Na20, write the equations. Since carbon dioxide is liberated in so many different ways, it is present in the atmosphere in considerable quantities. It varies from 2.7 to 3.5 volumes in 10,000 volumes of air. This gas is more plentiful in living-rooms than out of doors, but the amount present should never be allowed to exceed 7 or 8 parts per 10,000. It is not so much that carbon dioxide is itself very poisonous, as that other and more dangerous animal impurities are thrown off by the lungs together with the carbon dioxide. We may therefore practically employ the amount of car- bon dioxide present in a living-room as an index to meas- ure the purity of the air, as will hereafter be explained. Prob. Calculate the number of cubic metres of COj in the atmosphere, assuming the extent of the air to be as stated under Atmosphere. Compute its weight. Carbon dioxide gas is often found in mines, caves, old wells, and vats. When so occurring it is termed Choke ■ Damp, and many persons yearly lose their lives through a lack of caution in entering such places. Before ventur- ing into a place where choke damp is likely to occur, it is best to lower a lighted candle ; should the candle be ex- tinguished, it is unsafe to go in. A well may sometimes be freed from choke damp by dashing in much water, the CARBON AND OXYGEN. 143 gas being thus absorbed ; and, again, a vat may be made safe by making an opening in the bottom. Why ? Carbon dioxide is indispensable to plant life. It can be shown that in sunlight the leaves, roots, and green parts of plants absorb carbon dioxide and give off oxygen ; also on moonlight nights and under the influence of the electric light the same processes go on more slowly ; but, in the dark, carbon dioxide is given ofP, and oxygen is quite freely absorbed. SuG. Devise an experiment to show the effect of a growing plant, in sunlight, upon carbon dioxide. Queries. Are plants in a living-room conducive to health 'i In a sleeping-room ■? How are plants and animals interdependent through carbon dioxide and oxygen 'i What prevents the excessive accumulation of carbon dioxide in the atmosphere? What would result if all the oxygen of the air were consumed ? All the carbon dioxide ? If there were an excess of the latter gas ? Exp. 108 p. Fill a bottle of about 1' capacity with water, and invert it over the pneumatic trough, or better, over a basin of pure water. Now fill the bottle thi'ee-fourths fuU of carbon dioxide. Cork the bottle with its mouth under water ; remove, and shake it thoroughly. Again place the mouth of the bottle under water, and uncork. Does the water rise in the bottle? Is carbon dioxide soluble in water? Reduce the temperature of the bottle by means of a freezing mixture, and shake as before. Again remove the cork under water. Does a greater diminution of the volume of the gas take place? Boil a portion of the water in the bottle, and test by adding calcium hydroxide (Art. 161). Does the boiled water give a reaction? Testa portion of the water in the bottle, with blue litmus paper. Is it acid? Taste of the water in the bottle, or drink of it if you wish. How does it taste ? Note. The gas for this experiment should be washed through a solution of sodium carbonate. Why ? 144 CARBON AND OXYGEN. Although carbon dioxide is injurious when inhaled, it is, nevertheless, when taken into the stomach, sometimes an aid to digestion. Certain springs and artesian wells owe their excellent properties to the carbon dioxide absorbed in their waters, while soda water is simplj"- pure water highly charged (under pressure) by this gas. SuG. Examine and describe a soda-water fountain. Queries. Wliat causes the effervescence of cliampagne? Beer? Cider ? Wliat effect does vinegar produce upon common baking-soda ? Can you thus generate carbon dioxide 1 Wliat causes dough or " empty- ings " to rise 1 By what process is the gas furnished in this latter case ? What is meant by heavy bread ? Carbon dioxide is soluble in cold water, 1°° of water at 0° dissolving about 1.8°° of the gas ; if the pressure be increased, the solubility is also increased. An increase of the temperature of the water drives off the gas, the process being complete at 100°. Qdbeies. What Exp. shows that limestone is soluble in water contain- ing free carbon dioxide, but insoluble in water containing none of this gas ? How is the deposition of limestone formations to be explained 1 How the crust formed in the tea-kettle ? The formation of caves f When carbon dioxide is passed into water, the solution is slightly acid, and it is believed that an acid of the formula H2CO3 is thus formed : — CO2 + H2O = H2CO3. We also consider that the carbonates, such as calcium carbonate, are derived from this acid. The acid itself, if it exist at all, is very unstable, thug breaking up when liberated : — H2CO3 = H2O + CO2. The carbonates, however, are very stable and of great CARBON AND NITROGEN. 145 importance, and they occur, as previously noted, in im- mense quantities. 152. Tests for Carbon Dioxide and the Carbonates. — 1. The free gas is detected by conducting it through a solution of calcium hydroxide, Ca(0H)2, with which it forms the white precipitate, calcium carbonate, CaCOa. 2. The free gas in water solution may be detected by adding the same solution as before. 3. The carbonates will effervesce with any strong acid, preferably nitric or hydrochloric acids, yielding free carbon dioxide, which may be tested as in 1. carbon and nitrogen. Cyanogen. 153. Cyanogen, CN or Cy, is the only known compound of carbon and nitrogen. It has been ' isolated ; but its constituents do not directly unite to produce it. The cyanogen compounds, as potassium cyanide, KCy, prussic acid, HCy, and other substances containing the group of atoms, CN, are of importance. Cyanogen gas is prepared by heating mercuric cyanide, HgCya, in a hard glass test-tube provided with a delivery- tube so arranged that the gas may be collected over mercury. It is soluble in water, and can be condensed at moderate temperature under a pressure of four atmos- pheres. It possesses an agreeable odor resembling peach blossoms, and burns with a purple flame. This gas is so poisonous that the student should hesitate to experiment with it. The specific gravity of cyanogen gas is 1.806. 146 CAEBON AND NITROGEN. Hydrocyanic oe Peussic Acid, HON oe HCy. 154. Prussic Acid is one of the most deadly poisons known. It acts so quickly that antidotes are of little use, though in some cases ammonia and chlorine have been of service in counteracting its effects. It is formed by the de- composition of amygdalin, a complicated substance which occurs in the leaves of some plants, and in the kernels of peach pits, bitter almonds, and other fruits. It can be prepared in a pure, liquid state by passing hydrogen sul- phide gas, H2S, over mercuric cyanide, HgCy2: — HgCy2-|-H2S = 2HCy + HgS. It should be remembered, however, that this acid is a volatile liquid, and that its vapors are a deadly poison and instantaneously fatal if inhaled in any considerable quanti- ties. The deadly effects of even dilute hydrocyanic acid may be illustrated by the following experiment which would better by far be omitted : — Exp. 109 op. Dissolve 9^ tartaric acid, CiHeOe, in 60'" of Water ; place in a 70°" flask, and add 4« potassium cyanide, KCy. Shake, and allow to settle, when a dilute solution, containing about 3.6 per cent prussic acid, will be obtained (R. and S.). Administer to a cat about a teaspoonful, and note effects. The specific gravity of hydrocyanic acid at 18° is 0.6969. Note. See larger manuals for the remaining numerous compounds of cyanogen. The more important cyanides of the metals will be noted under the metals in question ; hut the student is not to forget that many of them are extremely poisonous. 155. Tests for Hydrocyanic Acid and the Cyanides. — 1. Prussic acid, HCy, when in dilute solution, may be thus detected : To the solution add ammonium sulphide, EXERCISES IN CARBON. 147 NH4HS, and evaporate nearly to dryness on the water- bath. Ammonium sulphocyanate, NHiSCy, is formed ; this substance, when dissolved in water and treated with ferric chloride, FegCle, turns to a deep-red color. 2. To detect a cyanide in solution, add a few drops of potassium hydroxide, KOH, and then add ferrous sul- phate ; shake well, and acidify with hydrochloric acid, when Prussian blue will be formed if a cyanide be present. Sua. Use a solution of KCy for these tests. EXERCISES IN CARBON. 1. Prepare carbon from 10 different articles of food. 2. Write a short description of the carboniferous age in respect to the condition of the atmosphere and vegetation. (Consult some text-book on Geology.) 3. Collect snail shells, clam shells, oyster shells, and a few specimens of limestone, and test for carbonates. 4. Pkob. The temperature of the laboratory is 72° F., and the barom- eter reads 752™™. How many litres of 00^ gas may be generated from 25s CaCOj ? How many grams of HCl are necessary 1 How many grams of CaClj will be produced ' 5. Fill a common clay pipe with walnut, hickory-nut, or butternut meats. Seal the bowl by means of a thick paste of plaster of paris and water. Allow the paste to dry, then heat the bowl in the Bunsen flame. Ignite the gas which soon issues from the stem, and prove that it contains hydrogen and carbon. SuG. Hold a cold glass tube over the flame. Also hold a piece of cold porcelain against the flame. 6. Produce carbon from marble, snail shells, etc. 7. The value of a sample of coal for reducing iron from its ores is ascertained by making the following quantitative determinations ; 1. Moist- ure; 2. Volatile matter; 3. Fixed carbon; 4. Ash; 5. Phosphorus; 6. Sul- phur. The first four determinations may be made thus : Place in a weighed porcelain crucible about 5e of the coarsely-powdered sample, and heat at 100° for several hours. Weigh, and note the loss of weight as " Moisture." Lute on the cover of the crucible by means of a paste of wood ashes, leaving a very small opening in one side. Allow the luting 148 EXERCISES IN CARBON. to dry, and weigh the whole. Now heat to redness for one hour; weigh, and the loss in weight equals the "Volatile matter." The last weight minus the weight of crucible and luting equals the weight of "Coke." Now remove the cover, carefully clean off the luting, aijd weigh again ; then burn the residue in the crucible, and weigh, noting the loss of weight as " Fixed carbon." The last weight minus the weight of crucible equals the "Ash." The value of a coal partly depends upon the amount of fixed carbon it contains. (See Sulphur and Phosphorus.) 8. For valuable information concoi'ning the varieties of coal, coal analysis, etc., see Dana's System of Mineralogy, pp. 751-760. 9. As previously stated, it is customary to measure the amount of carbon dioxide as an index to the purity of the atmosphere of a room. This is accomplished by titration ; and a litre-flask and two reagent solu- tions are required. The first solution consists of 5s barium hydroxide, Ba(0H)2, dissolved in 1^ of distilled water ; the second, 2.863b pure freshly-crystallized oxalic acid, "B^Cfi i[S.2'^)-i^ ™ ^1'^ same amount of water. From the manner of using this latter solution, 1"=" corresponds to l"g carbon di9xide. The litre-flask is filled, by several puffs of a hand-bellows, with the air to be tested, and the temperature of the room carefully noted. A quantity of the first solution, equal to the space above the litre-mark on the neck of the flask, is now added, and the flask vigorously shaken. A portion of the solution in the flask is neutralized, — Ba(0H)2 -1- CO2 = BaCOs -f H^O, and a portion is unchanged. The remainder is now carefully neutralized oy means of the second solution, — Ba(0H)2 4- H2C204,(H20)j = BaC^ + * H^O, and the number of cubic centimetres is carefully noted ; a phenol phthalein solution is employed as an indicator. An amount of the first solution equal to that placed in the flask is now directly titrated with the second solution, and the number of cubic centimetres of the latter noted. It is evident that the difference between the two numbers thus obtained equals the number of milligrams of COj per litre. Queries. Why do we take 2.863s oxalic acid ? Having the number of milligrams COj per litre, multiply the result by 10, and then calculate the number of cubic centimetres per 10,000. What principles apply 1 What is titration ? An indicator ? 10. The student who wishes to obtain a clearer insight into the processes employed in the Chemistry of the Carbon Compounds, will do well to consult Dr. Remsen's work on that subject. CHAPTER X. MOLECULES. — MOLECULAR FORMULAE. — VALENCE. 156. Molecules. — What is meant by the word, atom has already been explained. The chemical atom is the smallest particle of an element that can take part in chemical reactions. Now, if we consider any chemical compound as, for example, hydrochloric acid, it is clear that the smallest particle of this compound which can he imagined must contain both hydrogen and chlorine, and must contain at least one atom of each of these elements. Such a smallest particle of a compound is called a molecule. The molecules ,of compound bodies are made up of atoms of different kinds. The molecules of the elements are made of atoms of the same kind. The theory com- monly held is that when the elements exist in the free state their atoms unite to form molecules. The formulae which we use to represent compounds are intended to represent molecules, just as the symbols of the elements are intended to represent atoms. Thus the formulae HjO, NH3, HCl, HNO3, etc., represent the mole- cules of water, ammonia, hydrochloric and nitric acids; and we see from them that the molecule of water is made up of 2 atoms of hydrogen and 1 of oxygen; that the molecule of ammonia consists of 1 atom of nitrogen and 3 atoms of hydrogen, etc. Knowing the weights of tlie 150 MOLECULES. atoms which make up a molecule, we know the weight of the molecule. It is the sum of the weights of tlje atoms contained in it. The molecular weight of water is 18, which is the sum of the weight of 2 atoms of hydrogen (2 X 1) and of 1 atom of oxygen, 16. The molecular weight of ammonia is 14 (the atomic weight of nitrogen) + 3 (the weight of three atoms of hydrogen) = 17. Query. What is the molecular weight of hydrochloric acid ? of nitric acid? 157. Avogadro's Hypothesis. — If the atomic weights of all the elements were known to us there would be little difficulty in determining the molecular formulae of com- pounds. Thus, if we knew that the atomic weight of oxygen is 16, and on analysis found that water consists of hydrogen and oxygen in the proportion of 1 part of hydro- gen to 8 of oxygen, the simplest formula which we could give to the compound would be H2O, and we might assume that this represents the molecule. A molecular formula, according to this, would be nothing more than the simplest formula which could be used to express the composition of a body, assuming the correctness of the commonly accepted atomic weights. In reality, the molec- ular formulae mean more than this ; they are dependent upon a very ingenious and valuable hypothesis, known as the hypothesis of Avogadro. On comparing the specific gravities of a number of gaseous compounds with the molecular weights of the same compounds, it is found that the two sets of figures bear the same relation to each other. In other words, the specific gravity of any compound gas is to the molecular weight of the compound, as the specific gravity of any other gas is to its molecular weight. This leads to the MOLECULES. 151 conclusion that equal volumes of bodies in the form of gas or vapor contain the same number of molecules, and this is Avogadro's hypothesis. According to the hypothesis, if a cubic inch of hydrochloric acid gas contains (say) 1000 molecules, a cubic inch of any other gas or vapor, measured under the same conditions of pressure and temperature, also contains 1000 molecules. We can not determine the absolute number of molecules present in any given volume, and hence, of course, can not determine the absolute weight of the molecules; but accepting the hypothesis we can easily determine the relative weights of molecules of all substances which are gaseous or can be converted into vapor. These relative weights compared to some standard are what we know as the molecular weights. We may take any simple molecule, as hydrochloric acid, as a standard. The simplest formula which can be assigned to this substance to express its composition is HCl, in which the atomic weight of chlorine is assumed to be 35.5. The molecular weight of a compound of this formula is 36.5. Let this be the standard molecule. The problem now is to determine the weights of the molecules of other bodies in terms of this standard, and in accordance with the principle laid down in Avogadro's hypothesis. We simply determine the relative weights of equal vol- umes of hydrochloric acid and the other gases or vapors, and, knowing that the molecular weights bear to one another the same relation as these relative weights, the molecular weights can easily be deduced. The figures which express the relative weights of equal volumes of bodies are called the specific gravities. We have then only to compare the specific gravities of gases 152 MOLECULES. with that of hydrochloric acid to know the molecular weights of these bodies. If S' is the specific gravity of hydrochloric acid, and 36.5 its molecular weight ; S the specific gravity of some other gas, and M its molecular weight, we have : — S':36.5::S:M, but S' is known. It is 1.247. Hence we have: — 1.247 : 36.0 : : S (the sp. gr. of any gas) : M (its molecular wt.) . In other words, the relation between the specific gravity of any gas and its molecular weight is represented by a constant quantity which is about 28.8, i.e., — ^ = 28.8, or M = 28.8 X S. The molecular weights of all bodies which can be con- verted into the form of vapor have been determined by means of this rule, and the molecular formulae are based upon these determinations. 158. Determination of Atomic Weights by means of Avogadro's Hypothesis. — In order to determine atomic weights by means of the hypothesis of Avogadro, we first determine the molecular weights of all compounds which are gaseous or can be converted into vapor. We then analyze these same compounds. On now examining the results of the analysis, we select the smallest quantity of an element which occurs in any of its compounds, as its atomic weight. The method may be illustrated by taking some of the compounds of carbon as examples. MOLECULES. Molecular Wt. Found. Constituents. Carbon monoxide . 27.96 12 parts C ; 16 parts 0. Carbon dioxide . . 44'.16 12 " C; 32 " 0. Marsh gas . . . 16.1 12 " C; 4 '• H. Ethylene . . 28.0 24 " C; 4 " H. Acetylene . . . 26.0 24 " C- 2 " H. 153 The smallest quantity of carbon contained in any of these compounds is represented by the figure 12, and consequently this is accepted as the atomic weight, unless there is some other compound the molecular weight and analysis of which lead us to a smaller figure. 159. Valence. — Having determined the molecular for- mulae of chemical compounds, we see that they differ markedly from .one another. Take, for example, the hydrogen compounds of some of the elements thus far considered. We have hydrochloric acid represented by HCl, water by H2O, ammonia by H3N, and marsh gas by H4C. A fundamental difference between these compounds is noticed in the number of hydrogen atoms contained in each one. In HCl we have 1 H ; in H2O, 2 H ; in H3N, 3 H; and in H4C, 4 H. The atoms of chlorine, oxygen, nitrogen, and carbon are thus seen to differ from one another in regard to the number of hydrogen atoms which they can hold in cottibination. The power of any atom to hold a certain number of the simplest atoms in combina- tion is called its valence. This term is also applied to the elements. We speak of a univalent element meaning an element the atom of which has the power of holding one of the simplest atoms in combination. Thus chlorine and hydrogen are univalent elements. We may measure the valence of any element by any 154 MOLECULES. univalent element with which it will unite. Thus we measure the valence of oxygen by hydrogen. It is bivalent because its atom unites with two atoms of hydro- gen. In the same way we regard nitrogen as trivalent because its atom unites with three atoms of hydrogen ; and carbon as quadrivalent because its atom unites with four atoms of hydrogen. Some elements do not unite with hydrogen. In these cases we may measure the valence by means of any other univalent element, as chlorine. Thus potassium does not unite with hydrogen, but it does unite with chlorine, forming the compound KCl, which shows that potassium is univalent; calcium forms the compound CaCl2, which shows that calcium is bivalent. The valences of all the elements have thus been determined by a study of the formulae of their compounds. In many cases one and the same element has more than one valence, as shown in the two chlorides of phosphorus, PCI3 and PCI5, in the first of which phosphorus appears as a trivalent and in the second as a quinquivalent element. 160. Substituting Power and Valence, — We have seen that in the formation of salts the hydrogen of the acids is replaced by metals. The number of atoms of hydrogen which the atom of any metal can replace is determined by the valence of the metal. The atom of a univalent metal replaces 1 atom of hydrogen, as is shown in the formation of potassium nitrate, KNOs, from HNO3; the atom of a bivalent metal replaces 2 atoms of hydrogen, as in the formation of calcium nitrate, Ca(N03)2, from HNO3, in which case the calcium atom is represented as taking the place of two atoms of hydrogen in two mole- cules of nitric acid. In barium sulphate, BaSO^, one EXERCISES IN EQUATIONS. 155 atom of the bivalent metal barium takes the place of the two hydrogen atoms in sulphuric acid H2SO4. In making hydrogen by treating sulphuric acid with zinc, we had another illustration of the replacement of the two hydro- gen atoms of sulphuric acid by one atom of the bivalent metal zinc. Numerous illustrations of the different sub- stituting powers of the metals will present themselves when the salts come up for consideration. Note. It is customary to consider the part of an acid which remains in combination with a metal after the hydrogen has been displaced as a group of atoms, and when we wish to take this group more than once, as above, we write Ca(N03)2 and not CaN205. By so doing the formula shows at a glance what acid took part in forming the compound. EXERCISES IN EQUATIONS. -USEFUL PROBLEMS. 1. The equations previously given might with propriety be termed "Atomic Equations," since they show what we believe takes place at the instant dissociation of a compound occurs. We may also write "Molecular Equations," showing the state of affairs after all reactions are complete. In order to do this we only need, in addition to what we have already practised, to represent the molecules of the free elements in some appropriate manner, so that the formula for the molecule shall show the number of atoms it contains. It is now becoming customary to do this by the use of subscript figures ; thus, 0^, H2, Nj, P^ S2, etc., represent the molecule of oxygen, nitrogen, phosphorus, etc. Let us now again take up some of the atomic equations already given, and rewrite them to represent molecular conditions : — K + HjO = KOH + H, when rewritten gives 2 K + 2 II fi = 2 KOH + H^ , Zn + H2SO4 = ZnSOj + 2 H becomes Zn + HjSOj = ZuSO^ + H^ ; 2 P + 5 O = PjOs becomes 2 P4 + 10 O2 = 4 PjOj ; S + 2 = SOj becomes S^ + 2 O^ = 2 SO^. By inspecting the equations thus rewritten it becomes apparent that molecular equations are somewhat the more complex of the two, and that to write them properly requires a knowledge of the molecular formulae of the elements. In the compounds, as previously stated, the formula also represents the molecule ; not so however with the symbols of the elements ; and since it is first necessary to determine the vapor density of an element 156 EXERCISES IN EQUATIONS. before we can determine its molecular formula, it is evident that when we come to solids not readily volatilized it is manifestly absurd to write such a formula as Auj, Ptj, etc., especially if we agree to represent the mole- cules of elements by subscript figures. "Write in molecular formulae : — KCIO3 =KCl + 30; Na + H20 = NaOH + H; C + 20 =00^; 3re + 40 =Fefii; Zn + O = ZnO. 2. To calculate the weight of a given volume of any gas from its molecular weight : — Proe. 1. How much does 1' of HCl gas weigh at 0° "^ Solution. The molecular weight equals 35.5 + 1 = 36.5, and the dcnsitij (with reference to H) equals 36.5^2 = 18.25. Now li of H at 0° and 760™™ weighs 0.0896s, and it is evident that the required weight equals 18.25 X 0.0896. In case the temperature and pressure vary from standard conditions the problem may be finished by Art. 87. Note. Note that The density of a gas (H = 1) equals one-half its molec- ular weight. This follows from the fact that we take the hydrogen molecule, Hj, as 2 ; or the half molecule, H, as unity. Peob. 2. How much do 6' of chlorine weigh at 15° and 750"™ % Sno. The molecular formula of chlorine is CI2, and its density equals 2x35.5 -=-2 = 35.5 or the atomic weight of CI. We may here note that the density and atomic weights of the gaseous elements are numerically equal. Prob. 3. Compute the weights of 1' of the following gases : O, N, N2O, N2O3, NHg, H^S, SO2, CO2, CO. 3. To compute the specific gravity (air= 1) of a gas from its molecular weight. Divide the weight of 1' of that gas by the weight of 1' of air, or 1.293. Proe. 4. What is the specific gravity of COj 1 H^S ? CO ? NH3 ? 4. Show that one needs simply to remember the atomic weights of the elements to compute : 1. The molecular weight of any gas ; 2. Its density ; 3. The weight of 1'. CHAPTER XI. SULPHUR. SELENIUM AND TELLURIUM. — THEIE OCCUE- EENCE, PEEPAKATION, TESTS, ETC. SULPHUR. Symbol, S". — Atomic Weight, 32. — Specific Gravity (Ckystals), 2.05. 161. Occurrence. — Sulphur occurs native in volcanic 'regions, and in its compounds with other elements it is widely distributed. The most plentiful of these com- pounds are the sulphides, iron pyrites, FeS2, or Fool's Gold ; galena, PbS ; cinnabar, HgS ; and the sulphates, gypsum, CaS04 + 2 H2O ; heavy spar, BaS04; green vitriol or ferrous sulphate, FeS04 + 7 H2O, etc. Native sulphur occurs in regular, yellowish, transparent, octahedral crystals, and in other forms derived from this primary crystal. It is also found in a massive state being then known as volcanic sulphur. 162. Preparation. — Since sulphur in its various forms is a common article of commerce it may readily be pro- cured for class purposes. The common roll sulphur or brimstone is prepared by distilling the crude ore in large earthen-ware retorts, and condensing the vapors in stone- ware condensers. More frequently, however, it is ob- tained by building up the crude ore in the form of a kiln 158 SULPHUE. or charcoal pit, where the ore is roasted by burning a portion of the sulphur as a fuel. The sulphur is melted from its accompanying impurities, and runs down into a receptacle prepared to receive it at the bottom of the pit. It is afterwards purified by distillation, and cast into the ordinary rolls or sticks. Flowers of Sulphur, also an article of commerce, are obtained by vaporizing a quantity of sulphur and bringing the vapor into a cold condenser, where this variety is pro- duced in a manner analogous to snow. Exp. 110 p. Dissolve 2^ flowers of sulphur in 13™ of water, to which has been added 1^ slacked lime (prepared by treating 1 part quicklime with 3 parts water). The product calcium pentasulphide, CaSj, is formed. Write the equation. Now add to the solution hydrochloric acid, when the liquid turns white, very finely divided sulphur being obtained. The substance thus prepared is an article of commerce known as lac sulphuris or milk of sulpKur. 163. Properties. — Exp. Ill p. Dissolve 1« sulphur in 3^ carbon bisulphide, CSa- Place the solution in a beaker glass, and allow it to evaporate, without heat, in the atmosphere. Octahedral sulphur crystals will be obtained. Allow these crystals to stand for several days, noting from time to time any changes that may occur. Sulphur crystals occur in no less than thirty different forms all derived from the primary octahedron. The specific gravity of these primary crystals at 0° is 2.05. Exp. 112 t. Melt in an evaporating dish 100^ sulphur and heat to 230°, when the molten mass will turn black. Now pour into a basin of cold water, and when cold remove and examine the product obtained. Leave for several days in the water, and occasionally observe what changes occur. SULPHUR. 159 The modification of sulphur thus obtained is known as plastic sulphur, and at first strongly resembles caoutchouc, in that it is elastic; it soon becomes brittle, however, upon standing. The specific gravity of this form is 1.96. Exp. 113 t. Melt in a sand crucible a quantity of sulphur and allow it to cool slowly. "When a crust forms over the surface of the moltea sulphur make an opening through the crust and pour off the liquid portion. Note the peculiar needle- shaped crystals attached to the solid crust. QuEKiES. How many different forms or modifications of sulphur have you observed'' What changes take place in the crystals last obtained when they are allowed to stand ' Sulphur is extensively used in making sulphuric acid and in the manufacture of riibber goods. When heated at moderate temperatures with crude rubber gum, 2 to 3 per cent of sulphur is absorbed, and the product obtained is firmer and better adapted to some industrial require- ments than the pure gum itself. When the temperature is raised to a higher degree the substance called vulcanite or ebonite is obtained. Query. What developments in the rubber industry are due to Charles Goodyear? Exp. 114 p. Dip into powdered sulphur a pine splinter and ignite ; note the flame and the odor emitted. What does the odor resemble? The fumes have the formula SO2. Write the equation. Sulphur is used in the manufacture of matches and is burned for bleaching straw goods. Some forms are also employed in medicine. It is capable of uniting directly with most metals to form sulphides. 160 STTLPHTJE AND HyDROGEN. 164. Tests for Free Sulphur. — 1. Free sulphur is dis- tinguished, if in considerable quantities, by its physical properties, and by its flame and the odor of its fumes. 2. If the quantity be too small to test as in 1, fuse it on platinum foil with sodium carbonate, NajCOs; then place the fused mass, which is sodium sulphide, NajS, on a bright piece of silver, and moisten with a drop of water. If free sulphur be present, a black spot of silver sulphide will be obtained. C AtiTiON. The 1^32003 and charcoal must be free from sulphur ; like- wise the illuminatiug gas used for the blow-pipe flame. The alcohol lamp is best to use for this test. Note. Since sulphur blackens silver, egg spoons, mustard spoons, etc. are gilt to prevent their tarnishing. Silver ware blackened by sulphur is easily brightened by washing in a solution of potassium cyanide, KCy ; this is better than scouring, since the cyanide does not attack the pure silver. How may the black spot obtained in 2 be removed 1 SULPHUR AND HYDROGEN. 165. Sulphur and hydrogen form two compounds, viz. : — Hydrogen Sulphide, HjS, Hydrogen Persulphide, H2S2( ?) . • Of these the first alone is of importance to the beginner. Hydeogen Sulphide. 166. Occurrence. — Hydrogen sulphide, commonly known as sulphuretted hydrogen, is of wide occurrence, both free and combined. The waters of many famous " sulphur springs " contain this gas in large quantities. It is a product of volcanic action and of the decomposition of albuminous substances; thus the peculiar odor of SULPHUR AND HYDROGEN. 161 rotten eggs is partly due to the hydrogen sulphide evolved. The sulphides, which may be regarded as derived from this acid, are found in great abundance, as already mentioned. 167. Preparation. — Exp. Hop. Place in a test-tube a small quantity of water, say 10'=", and add a small piece of ferrous sulphide, FeS ; now add 1'"= of sulphuric acid, and close the tube quickly with a perforated cork containing a glass U-shaped jet delivery-tube. The gas will soon issue through the jet, when it may be ignited. Note the odor, but do not allow more gas than is necessary to escape, since it is some- what poisonous. The contents of the tube should be poured into the sink as soon as a sufficient amount of gas has been obtained, but in case a considerable piece of the sulphide re- mains this may be saved for further use. This is the general method and the one almost exclus- ively employed in laboratory practice for the production of hydrogen sulphide. The chemist thus produces it for analytical purposes, as will subsequently be explained. It is well to have a gas chamber wherein this gas may be produced and wherein the whole contents of the test-tube may be retained, since another reagent, ferrous sulphate, is thus pfoduced : — FeS + H2SO4 = H2S + FeS04. This latter compound may be separated by crystallization. In case large quantities of sulphuretted hydrogen are required, a generating flask maj'^ be employed instead of a test-tube, and the gas may be washed through warm water. An aqueous solution in cold water is to be had, but the gas itself, freshly generated, is preferable for qualitative work. 162 STTLPHUE AND HYDEOGEK. Hydrogen sulphide is also formed by the action of some of the other acids on the sulphides ; by burning sulphur in an atmosphere of hydrogen; by passing hydrogen through boiling sulphur, and by heating parafSne with sulphur. All these methods are, for various reasons, not well adapted for obtaining the gas in practice. 168. Properties. — Hydrogen sulphide is a colorless, inflammable gas, possessing a disagreeable odor somewhat resembling rotten eggs. It is condensed, at ordinary tem- peratures under a pressure of 17 atmospheres, to a color- less liquid which boils at — 61.8° and freezes at — 85°. Its specific gravity at 0° is 1.191, and 1' weighs 1.522^. 1°° of water at 0° absorbs about 4.4°° hydrogen sulphide, forming a slightly acid solution. Exp. 116 p. Place in several different test-tubes solutions of metallic salts, such as copper sulphate, CuSOi ; mercuric chloride, HgCls; lead acetate, Pb(C2H302)2, and silver nitrate, AgNOg. Generate hydrogen sulphide as in Exp. 115, and successively place the jet into these solutions, allowing the gas to bubble up through them. Precipitates which are respectively the sulphides of the different metals will be formed. It is thus that the chemist employs hydrogen sulphide in analytical operations, and the great utility of this gas becomes apparent when it is known that by its aid the metals may be separated into groups. In short, it is another group reagent (p. 98). The same is true of one of its compounds, ammonium sulphide, (NH4)2S. SnG. Try the effect of H^S upon solutions of arsenic, antimony, cadmium, copper, and tin. Note the colors of the precipitates. Exp. 117 p. Pass sulphuretted hydrogen through nitric acid ; aqua regia ; strong hydrochloric acid ; sulphuric acid. Do you StTLPHUR AND HYDROGEN. 163 obtain precipitates? If so, collect and burn on a pine splinter. Note the odor of tlie fumes. What is the sediment obtained ? What effect do stronger acids have upon hydrogen sulphide? Make a solution of lead nitrate, Pb(N03)2, and strongly acidify with nitro-hydrochloric acid. Now pass hydrogen sulphide. Do you obtain lead sulphide ? Whj- ? 169. Tests for the Sulphides. — 1. Free hydrogen sul- phide in quantity is distinguished by its odor and by its blackening effect upon paper moistened with lead acetate, Pb(C2Hs02)2. Also see Exp. 38. 2. A sulphide, when fused on platinum foil or a bit of porcelain, — as a piece of broken evaporating dish, — with sodium carbonate, and moistened, produces a black spot when placed on a clean piece of silver. Qtjeries. How do the sulphides, as FeS, behave with sulphuric acid 1 What is meant by a test ? Note. The salts of easily reducible metals, such as those of lead and mercury, must not be fused on platinum, since these metals form with the platinum alloys which are fusible at high temperatures. The platinum may thus be ruined. In such cases it is necessary to fuse on charcoal or porcelain. What disadvantage does this latter process involve ? Hydrogen Peesulphidb, H2S2(?). 170. Hydrogen persulphide may be prepared by boiling (say) 1^ slacked lime with 16°° water and 2^ flowers of sulphur. The cold clear solution is then poured into dilute hydrochloric acid, when the persulphide falls to the bottom of the vessel as an oily liquid. It has a very disagreeable odor, more pungent than that of hydrogen sulphide. It is not important for the be- ginner. 164 sclphue and oxygen. SULPHUR AND OXYGEN. 171. There are two oxides of sulphur deserving special mention, viz. : — Sulphur Dioxide, SOj, and Sulphur Trioxide, SO3. These oxides are respectively the anhydrides of sulphurous and sulphuric acids. The manner in w^hich they combine with a molecule of water is worthy of notice : — 1. H2O + SO2 = H2SO3 ; 2. H2O + SO3 = H2SO4. It will be seen that in either case one molecule of water and one molecule of oxide form but owe molecule of acid. In the case of the oxacids of' nitrogen, bromine, chlorine, and iodine two molecules of acid were thus formed. Two other oxides corresponding to the formulae, S2O3 and SaOj, are known. Sflphue Dioxide, SO2. 172. Occurrence. — This oxide is the gas formed when sulphur is burned in the atmosphere. It occurs free in volcanic gases, and combined with other elements, as in the sulphites or salts of sulphurous acid. 173. Preparation. — Exp. 118 p. Place in a generating flask fitted with a deUvery-tube 1^ very fine copper filings and 6°° strong sulphuric acid. Heat until a gas begins to escape. Note the odor, and collect by displacement in a large test-tube, or small, tall jar. SuG. Some other metals when thus treated also yield sulphur dioxide, Try several, such as iron, mercury, and lead- StTLPHUR AND OXYGEK. 165 When sulphur dioxide is thus prepared the reaction may be indicated by the equation : — Cu + 2 H2SO4 = CuSOi + 2 H2O + SO2. Notice the difference between this reaction and that which takes place when sulphuric acid and zinc are brought together. In the latter case the reaction is represented thus : — Zn + H2SO4 = ZnSOi + H2; Whenever a metal reacts with an acid the first action con- sists in the replacement of the hydrogen of the acid by the metal. Tlie hydrogen is liberated and a salt is formed. In the case of copper and sulphunc acid, however, the reaction does not take place at ordinary temperatures, a,nd at higher temperatures the hydrogen which is first liberated acts upon the sulphuric acid reducing it to sulphur dioxide : — H2SO4 + H2 = 2 H2O + SO2. A common method of preparing this gas is to burn sulphur in the air. Many other methods are also known, such as heating sulphur and carbon with sulphuric acid, roasting pyrites, etc. 174. Properties. — Sulphur dioxide gas is easily con- densed by passing it through a spiral glass tube surrounded by a freezing mixture. It is very soluble in water, 1"= of which dissolves, at 0°, about 79.8" of this gas. Its specific gravity is 2.211, and 1' weighs 2.862«. It condenses at -I- 59° under 79 atmospheres and boils at — 8° under 1 atmosphere. Sulphur dioxide is used in great quantities for preparing sulphuric acid, in which case it is prepared by burning sulphur or iron pyrites in a current of air. 166 StTLPHtTK AND OXYGEN. Exp. 119 p. Suspend in a jar of sulphur dioxide a strip of moistened unbleached silk ; a moist wheat straw ; a piece of white woollen yarn. Sulphur dioxide is used for bleaching such goods as chlorine would injure. It produces its effects by reduc- tion instead of oxidation, as in the case of those bleaching reagents previously noticed. It unites with the oxygen of water, liberating hydrogen, and this latter gas enters into combination with the coloring matter to form color- less compounds. Queries. How do milliners prepare the sulphur dioxide which they use in bleaching straw goods ? What other substances have been men- tioned as reducing agents 1 What is meant by reduction ? A solution of sulphur dioxide in water becomes oxidized if it comes in contact with air, sulphuric acid being formed. It is probable that in the solution sulphurous acid, H2SO3, is present, and that this takes up oxygen, thus passing into sulphuric acid. Write the equations. Sulphur dioxide is also a good disinfectant, and will prevent the decay of meats and vegetables when applied for that purpose. It also prevents fermentation. 175. Tests for Sulphur Dioxide. — 1. Its odor is marked and well known, resembling that of burning matches. 2. Suspend in this gas a strip of paper which has been dipped into a solution of starch paste and potassium iodate, KIOs. Iodine is liberated, and the paper becomes blue : — 2 KIO3 + 5 SO2 + 4 H2O = 2 HKSO4 + 3 H2SO4 + Ij. Note. The sulphur dioxide must not be present in excess, or the paper will be bleached, hydriodic acid being produced. Write the equation. THE SULPHITE OXACIDS. 16T Sulphur Teioxide, SO3. 176. Sulphur trioxide is somewhat difficult of prepara- tion and very unstable owing to the eagerness with which it unites with water. It is prepared for commerce by passing sulphur dioxide together with oxygen over finely divided platinum in a highly-heated porcelain tube. It may also be prepared by heating strong sulphuric acid with phosphorus pentoxide : H2SO4 + PA = 2 HPO3 + SO3. Sulphur trioxide was formerly supposed to be the true sulphuric acid, but as soon as it was separated it proved to be a white crystalline solid without action upon the metals in absence of moisture. The discovery of this substance brought about a marked change in the views held in regard to salts and acids, and was one of the many causes which have led up to our present conceptions concerning chemical reactions and chemical formulae. THE SUIiFHTTR OXACIDS. 177. In this series eight different acids are known, the names and formulae of which are shown by the subjoined list: — Hyposnlphurous acid Sulphurous acid . Sulphuric acid . Thiosulphuric acid Dithionic acid . Trithionic acid . Tetrathionic acid Pentathionic acid H2SO2 ; H2SO3; H2SO4; H2S2OJ ; £[28208 ; HaSjOg ; HaSA ; HAOe? Note. The root "thion" is of Greek derivation, signifying sulphur. 168 THE SULPHtJK OXACIDS. By inspection, it will be seen that all these acids are dibasic, possessing two atoms of replaceable hydrogen; hence, they yield both acid and normal salts, e.g., mono- sodium sulphite, HNaSOs ; sodium sulphite, NajSOs, etc. Acids which contain but one replaceable hydrogen atom are called monobasic acids; those which contain two re- placeable hydrogens are called libasic acids; those with three are called tribasic acids, and those which contain four are called tetrabasic acids. Most common acids belong to the first two classes. All the acids previously considered, excepting carbonic acid, are monobasic ; the latter and the sulphur acids are bibasic. The principal tribasic acid is phosphoric acid, H8PO4. There is no common tetrabasic acid. SuG. Name the salts formed by the sulphur acids and potassium. Write their formulae. Note. The student who has thus far followed these pages will have noted that the rarer acids are chiefly of interest to the scientist, and that they are all unstable and somewhat difficult of preparation. His experi- ence, moreover, with these unimportant compounds will have served to give him a sufficient conception as to the characteristics of the class of substances to which they belong. We shall therefore note but three acids of this series ; viz., sulphurous, sulphuric, and thiosulphurio acids. SuLPHtTEous Acid, HaSOs. 178. This acid, as previously noted, is formed when sulphur dioxide is passed into water. It is an unstable acid constantly giving ofP sulphur dioxide fumes ; but the sulphites are a well known class of salts. Exp. 120 p. Pass sulphur dioxide gas into a test-tube of cold water ; also into a cold solution of sodium or potassium hydroxide. What does each tube contain after passing the THE SULPHUR OXACIDS. 169 gas? Gently evaporate to dryness the contents of the second tube, and a salt is obtained. Complete this equation, — H20 + S02 + KOH= . . . Use the contents of these tubes for the following : — 179. Tests for Sulphurous Acid and the Sulphites. — 1. Free sulphurous acid in quantity is recognizable by its odor. 2. In traces it may be detected by a solution of starch paste and potassium iodate, owing to the blue tinge pro- duced. It will also blacken a strip of paper moistened with silver nitrate. 3. The sulphites in solution upon addition of a stronger acid (HCl, H2SO4) remain clear, yielding sulphur dioxide fumes. (See Thiosulphuric Acid.) 4. When barium chloride is added to a solution of a sulphite, the white precipitate barium sulphite, BaSOg, is thrown down. Divide this precipitate in two parts: to the first add hydrochloric acid ; it is soluble. To the second add nitric acid ; the sulphite is oxidized to barium sulphate, Ba§04, a white precipitate insoluble in acids. Sue. Complete and balance the following equations, and explain the principles they illustrate : — SHjSO, +2KI03 = I+HKS04+HjSOi+ . . .; NajSOj + HCl = SO2 + . . . + NaCl ; NajSOa + BaCIj =NaCH- . . .; BaSOj +HlfOg =BaS04+H20+ . . . Sulphuric Acid, H2SO4 180. Occurrence. — Although sulphuric acid does not occur in nature except in volcanic waters, it is the most important acid known to the chemist and to commerce. 170 THE STJLPHUK OXACIDS. It has even been stated that the prosperity of a country may be estimated by the amount of sulphuric acid which that country consumes. Its salts are very stable and of great value, as, for ex- ample, blue vitriol, CUSO4 + 5 H2O, a salt of copper used for galvanic batteries and many other purposes ; gypsum or land plaster, CaSO^ + 2 H2O, used by farmers as a manure ; green vitriol or ferrous sulphate, FeSOi + T H2O, a well- known salt used in the laboratory as a reagent, and also used for purifying water-closets, sewers, etc. ; Glauber salts, NasSOi + 10 H2O ; Epsom salts, MgSOi -|- 7 H2O, and the sulphates of the alkaloids used in medicine. 181. Preparation. — Exp. 121 t. Although the student will have this acid upon his table, where he may study its properties at bis leisure, it might be well to illustrate the inter- FiG. IS. esting process of its manufacture. The formation of sulphuric acid may be beautifully shown by employing the apparatus illustrated in Fig. 18. Gr is a glass globe used as a condensing chamber. B is a generator containing copper filings and THE SULPHUR OXACIDS. 171 sulphuric acid for the purpose of producing sulphur dioxide. C is a flask containing water for generating steam. A contains copper filings and nitric acid for generating nitrogen dioxide and nitrogen trioxide. D is used to convey air into the con- densing chamber, and is attached to a hand-bellows. E is an escape-pipe to allow the waste gases, nitrogen and nitrogen dioxide, etc., to be forced out of the chamber. In practice most of these gases are utilized, but in this experiment E must be placed in a good ventilating draft. When the products of A, B, and C begin to iill the condenser, a steady, but gentle, current of air from the bellows must be forced through G until the close of the experiment. Sulphuric acid is thus produced, and falls to the bottom of the condenser. In preparing commercial sulphuric acid the materials and principles used vary but slightly from those illustrated in the foregoing experiment. The sulphur dioxide is prepared by burning sulphur or roasting iron pyrites, FeSa, in a current of air. The fumes are conducted into immense lead-lined chambers where they are mixed with air and steam and the higher oxides of nitrogen, as N2O3 and NO2 ; or at first a little nitric acid formed from sodium nitrate and sulphuric acid is used. The steam is obtained from a boiler and is blown into the chamber through jets stationed at different points. The chemical processes involved in the manufacture of sulphuric acid are quite complicated. The essential features will appear from the following brief description : When the sulphur dioxide and nitric acid first come to- gether in the presence of steam this reaction takes place : — 2 HNO3 H- 3 SO2 -I- 2 H2O = 3 H2SO, -I- 2 NO. As will be seen, the nitric acid is reduced to nitric oxide, NO, and this is incapable of oxidizing any more sulphur 172 THE SITLPHUE OXACIDS. dioxide ; but the oxygen of the air which is present im mediately transforms the nitric oxide into nitrogen tetrox- ide, NO2 (NO + O = NO2), and this, in the presence of steam, converts a further quantity of sulphur dioxide into sulphuric acid, as indicated in this equation: — SO2 + H2O + NO2 = H2SO4 + NO, an J is itself again reduced to nitric oxide. This NO again takes up oxygen to form nitrogen tetroxide, which in turn oxidizes sulphur dioxide, anfl" so on, indefinitely. Thus, theoretically, starting with a small quantity of nitric acid, an infinite quantity of sulphur dioxide could be converted into sulphuric acid, as, after the nitric oxide, NO, is once formed, it simply serves the purpose of trans- ferring oxygen from the air to the sulphur dioxide. Prac- tically, of course, there is always some loss of the oxides of nitrogen, and this loss must be made good by a fresh supply in order to make the operation continuous. The acid formed in the leaden chambers is a weak acid having a specific gravity of 1.55. It is withdrawn into large leaden pans, and concentrated until its specific gravity reaches 1.71, when it is quickly removed, since any further concentration would result in the destruction of the pan. It is further concentrated and purified in glass or plati- num stills until its specific gravity becomes 1.84, when it is ready for the market. 182. Properties. — -Commercial sulphuric acid has an oily appearance, and was formerly prepared by distilling green vitriol or ferrous sulphate : owing to these facts it received the name oil of vitriol. When exposed to the atmosphere it soon absorbs mois- THE SULPHUR OXACIDS. 173 ture," thereby becoming dilute. In consequence of its great hygroscopic power, it is employed under the receiver of the air-pump to aid in concentrating aqueous solutions of such substances as would not bear heating without undergoing decomposition. Pumice stone moistened with sulphuric acid is used to dry those gases upon which the acid has no action. The pure acid may also be used in a wash-bottle. Queries. For which gases already considered may it be used ■? For which ones should it not be used ? When sulphuric acid is brought together with water in quantities proportional to their molecular weights, the hydrate of sulphuric acid, H2SO4 + H2O, is formed. When this acid mixes with water much heat is evolved. In diluting it with water it is best slowly to add the acid to the water, and not the water to the acid, otherwise the vessel containing the acid may be broken and a serious accident ensue. Exp. 122. Try the eflfect of strong sulphuric acid upon a splinter of wood ; a bit of cloth ; a lump of sugar. What occurs ? Sulphuric acid chars vegetable substances by abstracting water, or the elements of water, hydrogen and oxygen. In its industrial uses, sulphuric acid is employed very extensively in the manufacture of soda (sodium carbonate, NajCOj), artificial fertilizers, nitroglycerine, etc., and in the refining of petroleum. Query. For what purposes has sulphuric acid thus far been employed in the laboratory? 183. Tests for Sulphuric Acid and the Sulphate^. — 1. Sulphuric acid or a soluble sulphate may be detected by 174 THE SULPHUR OXACIDS. adding to the solution barium chloride, BaClz, when' the white precipitate, barium sulphate, BaSOi, is obtained. This precipitate is insoluble in acids. 2. An insoluble sulphate may be fused on platinum foil or a bit of porcelain with sodium carbonate ; the moist- ened residue produces no spot on silver. If fused in the same way on charcoal a spot will be produced. Queries. If a sulphate, when treated on charcoal with sodium carbon- ate, yields sodium sulphide, NajS, what action upon the acid has occurred ? If the black spot on silver be Ag^S, what other compound is probably formed in the reaction : — 2 Ag + 5ra,S = Ag,S + . . . ? (SuG. H and are present in HjO to unite with Na.) Write this equation in full, and balance. How can you distinguish a sulphate from a sulphide, by fusing, etc. ? NOEDHAUSBKT, OH FUMING- SULPHUEIC ACID, H2S20r. 184. This acid is made by heating dried ferrous sulphate which still contains a little moisture. The reaction is represented thus : — 4 FeSO^ + H26 = 2 Fe^Os + 2 SO^ + USiOj. It may also be made by passing sulphur trioxide, SO3, into strong sulphuric acid : — H2S04 + S03=H2SA- It breaks up readily, forming sulphur trioxide and sul- phuric acid. When a vessel containing it is opened, fumes of the trioxide escape ; hence it is called fuming sulphuric acid. Water acts violently upon it, converting it into ordinary sulphuric acid : — H2S A + H2O = 2 H2SO,. THE SULPHUK OXACIDS. 175 The principal uses of this acid are for dissolving indigo in the process of dyeing Saxony blue and for manufactur- ing the coal-tar colors. Query. Since H^SjO, = 11280^ + SO3, should this acid be regarded as a distinct acid or as a solution of SO3 in H2SO4 ? Thiostjlphuric Acid, H2S2O3. 185. This acid, in a free state, is so unstable that its existence is somewhat problematical; but its salts, the thiosulphates, are well-known articles of commerce. The principal one, sodium thiosulphate, NasSzOg, is used by photographers as a solvent for the unchanged silver salts in their prints, which are thus " fixed," as the process is termed. This salt is formed by fusing sodium sulphite with flowers of sulphur, thus : — Na^SOs -I- S = Na^SA- When a thiosulphate in a hot solution is treated with hydrochloric acid or sulphuric acid, free sulphur is de- posited, and sulphur dioxide fumes evolved, thus : — NaaSA -I- 2 HCl = 2 NaCl + S + SO2 4- H^O. ' QuBKT. How does a sulphite behare with hydrochloric acid ■? Note. This sulphur acid was formerly known as hyposulphurous acid, and its salts as hyposulphites ; while the acid of the formula H^SO, was called hydrosulphurous acid, and its salts hydrosulphites. Sodium thiosulphate is still commonly known to druggists as hyposulphite of sodium. 186. Tests for the Thiosulphates. — 1. With hydro- chloric acid their solutions yield a precipitate of sulphur, and give off sulphur dioxide fumes. 2. Barium chloride, when added to a solution of a thio- sulphate, yields a white precipitate soluble in hydrochloric acid, but leaving a residue of sulphur. 176 THE StTLPHITR OXACIDS. 187. To distinguish bet-ween the Soluble Salts of the Sulphur Acids. — The solution may contain a sul- phide, a sulphite, a sulphate, or a thiosulphate. There are many ways of making this distinction, one of which is as follows : — 1. Evaporate a portion of the solution to dryness, and fuse on charcoal with sodium carbonate, etc. A black spot on silver indicates any of these acids. Then fuse on porcelain, etc. ; no spot indicates a sulphate. 2. To a portion of the solution add silver nitrate, AgNOa: — (a) A black precipitate formed at once indicates a sul- phide. (6) No precipitate indicates a sulphate. (c) A white precipitate, obtained by adding a single drop of the silver nitrate, and which does not dissolve upon shaking, indicates a sulphite. This precipitate, upon stand- ing, or upon being heated, turns black, metallic silver being the final product obtained. (cZ) A white precipitate from a single drop of the nitrate, which dissolves upon shaking, indicates a thiosulphate. Add an excess of nitrate, and boil. A black precipitate, AggS, is finally obtained. (e) If the student is still in doubt as to whether the solution contains a sulphite or a thiosulphate, add hydro- chloric acid to a fresh portion of the solution; sulphur dioxide fumes from a clear solution indicate a sulphite; the same fumes from a clouded solution indicate a thio- sulphate. SuG. Try to distinguish these acids by means of barium chloride, Bad,, etc. STJLPHUR AND CARBON. 177 SULPHUR AND CARBON. 188. Carbon Bisulphide, CSa, is the only known com- pound of sulphur and carbon. This is a colorless, inflam- mable, highly refracting liquid, boiling at +46°, and possessing a specific gravity of 1.292. It has a powerful odor, in its impure commercial forms, and its fumes are poisonous ; when pure it has a pleasant, ethereal odor. It is prepared by passing the vapor of sulphur through a cylinder heated to redness and containing charcoal. Carbon bisulphide is employed for a variety of purposes. In the laboratory it is used as a solvent for bromine and iodine, as we have previously seen ; in the manufac- tures it is employed as a solvent for various gums, such as rubber gum ; shoemakers mend shoes with a cement made by dissolving crude rubber in carbon bisulphide ; in woollen manufacture it is used to regain the oils with which the wool is treated during some of the necessary processes; in optics the hollow prisms used for decomposing light, and for spectrum analysis, are filled with carbon bisul- phide ; in agriculture it is employed as an insecticide, and (in the form of salts) in combating the phylloxera. It is also said to be of value in exterminating woodchucks and other burrowing animals, for which purpose it is placed in their burrows, which are then tightly closed with earth. The odor of carbon bisulphide betrays its presence, and serves as a test. SELENIUM. Symbol, Se". — Atomic Weight, 79. — Specific Gravity (Crystalijne) , 4.3. 189. Occurrence. — Selenium is a rare element closely resembling sulphur. It was discovered in 1817 by Berzelius 1T8 &BLE!NmM. while examining the deposits of the sulphuric acid chambers at Gripsholm. It does not occur native, but is found in the selenides, such as lead selenide, PbSe, and the double selenides of mercury, lead, silver, and copper. 190. Preparation. — Owing to the rarity of this element, the student will probably do no work with it, therefore general processes alone will be briefly given. The residue of the sulphuric acid chambers is mixed with potassium nitrate and then thrown into a red-hot crucible, where it deflagrates, forming ' potassium selenate, K2Se04, which is now (Contaminated with many impurities contained in the chamber residue. This impure mass is now digested with hydrochloric acid, and the solution filtered and evaporated nearly to dryness, selenious acid, HsSeOs, being formed. This acid is then treated with sulphurous acid, thus r — H^SeOg + 2 H2SO3 = 2 H2SO4 + H2O + Se. The finely divided selenium thus produced is separated by filtration. 191. Properties. — Finely divided selenium when viewed by transmitted light has a reddish color. In its properties and compounds it resembles sulphur. It is known in three mojdifi- cations ; viz., amorphous, vitreous, and crystalline. Flowers of selenium, a scarlet powder, is obtained in a manner similar to flowers of sulphur. The specific gravity of selenium varies from 4.5 to 4.8. 192. Selenium Compounds. — 1 . Selenium and hydrogen form hydrogen selenide, HgSe, a poisonous g.as obtained by the direct union of the vapor of selenium with hydrogen, or by treating potassium selenide with hydrochloric acid. 2. Selenium and oxygen form selenium dioxide, SeOj, when the former is burned in a current of the latter, or by treating the former with strong nitric acid. TELLUKIUM. 179 Selenium dioxide and water form selenious add, HjSeOj, from which the selenites may be derived. Selenium dioxide has the odor of rotten cabbage or horseradish. 3. Selenic acid, HjSeO^, is obtained by passing a stream of chlorine gas through water in which finely divided selenium is suspended, thus : — Se + 3 CI2 + 4 H2O = 6 HCl + HjSeOi. This' acid forms salts called selenates. 193. Tests for Selenium and its Compounds. — 1. Free selenium burned in the air gives the odor of the dioxide. 2. Hydrogen selenide is distinguished by its very offensive odor. It causes inflammation of the eyes and seriously affects the lining membranes of the nose. 3. The selenides when heated on charcoal give the dioxide fumes ; when fused with potassium nitrate, and when the solu- tion of the residue in hydrochloric acid is treated with sulphur dioxide, they yield free selenium. 4. The selenites when heated on charcoal also give the fumes of burning selenium ; their solutions with sulphur dioxide yield free selenium. 5. The selenates, with sulphur dioxide, yield free selenium when acidulated with hydrochloric acid. The fumes of a selenate heated on charcoal are also those of the dioxide. TELLURIUM. Symbol, Te". — Atomic Weight, 128.? — Specific Gkavitt, 6.24. 194. Occurrence. — Tellurium is a rare element which occurs native in small quantities and in combination with certain metals, as tellurides, particularly with gold, silver, lead, and bismuth. 180 TBLLUKItrM. 195. Preparation. — Tellurium is prepared by mixing bis- muth telluride (which also contains some sulphur as an im- purity) with sodium carbonate and oil ; this mixture is rubbed to a paste, placed in a closed crucible, and strongly heated. The mass is then lixiviated with water, when a solution of sodium telluride and sulphide is obtained- Upon exposure to light and air tellurium, in the form of gray powder, is deposited in this solution ; this powder is purified by distilling it in an atmosphere of hydrogen. 196. Properties. — Tellurium is a very brittle, bluish- white solid, possessing a metallic lustre, and a specific gravity of 6.24. It burns in the air with a bluish flame, giving white fumes of tellurium dioxide. 197. Compounds. — 1. Hydrogen telluride., HjTe, is a very poisonous gas resembling hydrogen sulphide. It is prepared thus : — ZnTe + 2 HCl = ZnClj + HaTe. It burns with a blue flame, is soluble in water, and forms the' tellurides. 2. Tellurium dioxide, Te02, is obtained by burning the metal in the air or in oxygen. It also occurs native in tellurite. When melted it forms a light-yellow liquid. 3. Tellurous acid, HgTeOs, is formed by dissolving the metal in dilute nitric acid and pouring the liquid into water. 4. Tellurium trioxide, TeOs, is prepared by strongly heating telluric acid, thus : — H2Te04 = H2O -f TeOg. This oxide is an orange-yellow crystalline solid. 5. Telluric acid, H2Te04, is produced by oxidizing tellurium with potassium nitrate. 198. Tests for Tellurium and its Compounds. — 1. Free tellurium, when dissolved in strong sulphuric acid, EXERCISES. 181 forms a purplish-red solution, from which tellurium may be pre- cipitated by adding water. 2. Tellurium in any compound may be detected bj' mixing with sodium carbonate and a little charcoal dust, after which it is placed in a sealed tube and heated to redness. When cool the tube is broken and the contents dissolved in hot water. Sodium telluride, NajTe, is dissolved out, coloring the water purple. Upon standing, free tellurium is deposited. 3. Tellurates are first heated to redness, whereby they are reduced to tellurites. The tellurites when dissolved in hydro- chloric acid and afterwards treated with sulphurous acid yield tellurium. EXERCISES. 1. In what experiment did sulphur unite directly with a metal to form a sulphide ? In how many ways may a salt be formed ? 2. "What varieties of sulphur may be purchased at the drug store ? (Spg. Ask your druggist what varieties he has for sale, and by what names they are known.) 3. Try to obtain sulphur from a piece of vulcanized rubber. 4. Try to prepare H^S from various sulphides that you may find in the laboratory. Use H^SO^, HCl, and HNO3. Try "Fool's Gold" or iron pyrites. If the acids do not give the desired results, fuse the pyrites on charcoal with sodium carbonate and again apply the acids. Do you thus obtain HjSI Why? 5. The amount of hydrogen sulphide in a solution, as in mineral water, may easily be determined by titration. For this purpose a standard solu- tion of iodine and a fresh solution of starch paste (an indicator) are required. The standard solution is prepared thus : — Weigh out in a small corked vial (weighing flask) about 18 of pure iodine ; then dissolve about 5s potassium iodide in 20"= distilled water ; uncork the vial and immerse it in the iodide solution. When the iodine is dissolved, dilute with water so that 1"= of the standard solution shall contain V°^ of free iodine ; preserve this in a perfectly corked bottle in a dark place. The titration is made thus : To 100™ of the water to be tested add about 2™ starch paste, and then, in the usual manner, add the standard solution of iodine, until a permanent light-blue color is reached. The 182 EXERCISES. number of cubic centimetres standard solution required (N) equals the number of milligrams of iodine required to decompose the hydrogen sulphide : — 2I + HjS = 2HI + S. It is usually safe to deduct from N 1 or 2"'S' to allow for the iodine required to color the starch paste, although this is best determined by trial. (As soon as the HjS is decomposed, upon what does the I act ? What causes the blue color ■?) The computation is made thus : — 254 : N : : 34 : a; = wt. of H^S in 100=°. In case the amount of HjS per litre is required, it = 10 x. Why ? How obtain the number of cubic centimetres of HjS gas per litre ? Whence come the numbers, 254 and 34 ? How compute the number of cubic inches of HjS per U.S. gallon ' 6. Coal containing much sulphides is not adapted to reducing iron from its ores. Why ' Sometimes the sulphides are oxidized to sulphates, which are not so objectionable, by piling coal in heaps exposed to the air : — FeS2+xO= . . .? 7. Try to obtain a sulphate by treating sulphur or a sulphide with a mixture of KCIO3 and HNO3. Test for the sulphate with BaClj. 8. Sulphuric acid or a sulphate is determined quantitatively, thus : To (say) 50=° of the solution containing a sulphate (e.g., K^SO^) add hydrochloric acid and boil ; while hot add an excess of barium chloride and thoroughly agitate : — BaClj + K2SO4 = BaSO^ + 2 KCl. Now filter out the BaSO^ and thoroughly wash with much hot water ; the ash of the iilter-paper used should be known; the precipitate and filter- paper are now carefully dried and the precipitate carefully transferred (as completely as possible) to a weighed porcelain crucible ; the filter-paper is now burned and its ash placed within the crucible, which is then heated to redness; when the crucible is cool its weight (W) is determined: — W — wt. of cruc. — wt. of filter-ash = wt. of BaSOj. Sometimes the chemist estimates the anhydride of an oxacid. How much SO3 in 17.241E BaSO,? With how much potassa, KjO, will this amount of SO3 unite, and how much KjSOj will it yield ? 9. The salts of many acids are decomposed and their acids set free by sulphuric acid. Why ^ EXERCISES. 183 Complete and balance these equations: — KNOj +HjSOi= . . . NaCl +HjS04= . . . NajC03 + HjS04= . . . 10. Make a table showing the similarity of the formulae of the oxides and acids of S, Se, and Te. 11. An Exercise in Valence. If to the number representing the valence of an element we assign a positive or negative sign, we shall find that the algebraic sum of these numbers in any stable chemical compound ' always equals zero, — provided we take ; — 1. The number f or H = + 1. 2. The number for O = -2. 3. The number for any metal in combination as + (except As, Sb, etc., with H). We may utilize these data to determine the valence of an element in combination ; e.g., what is the valence of I in HIOj '' Solution. 03 = 3x— 2 = — 6. H = + l. Now the question simply is, what number must be added to the + 1 to make +6 (or a number which added to —6 will give 0). The number required is evidently + 5. Accord- ingly we may conclude that I in HIO3 is a pentad. Queries. What is the valence of S in the following compounds: H^S; HjSO^s HjSOa; H^SO,, H^SA'? Of CI in: HCl; HCIO; HCIO,; HCIO3 ; KCIO4 ■? Of Br in : HBr ; HBrO ; HBrOs ; HBrO^ ' Of P, Si, B, and N in their compounds ? SuG. Eead Johnson on Oxidation in Douglas and Prescott's Qualitative Analysis, pp. 261-253. CHAPTER XII. SILICON AND BOKON. SILICON. Stmbol, Si''. — Atomic Weight, 28. — Specific Gravity, 2.49. 199. Occurrence. — Silicon, is a very abundant element, occurring in combination with, oxygen, or with oxygen and other elements. Silica, SiOj, known under the names quartz, sand, agate, etc., is a very widely distributed sub- stance, found in every geological formation. The silicates, such as feldspar, mica, and certain clays, are well-known compounds. Silicon constitutes from 22.8 to 36.2 per cent of the earth's crust. In a free state, it may be prepared in three modifications, — amorphous, graphitoidal, and crystalline. 200. Preparation. — Exp. 123 t. Silicon may be obtained by heating iu an iron tube potassium hydrofluosilicate, KjSiFe, with metallic sodium or potassium : — • KSiFe -I- 4 K = 6 KF + Si. A violent reaction occurs. When cool the fused mass is treated with water to dissolve the potassium fluoride, while the silicon remains as a brown amorphous powder. (See Art. 208 for KjSiFe.) Exp. 124 t. Place in a porcelain crucible a small quantity of amorphous silicon. Carefully lute on the cover with a paste SILICON AND OXYGEN. 185 of wood ashes, and after thoroughly drj-ing heat the crucible, gently at first, and finally to redness. The amorphous mass contracts, becoming denser, and assuming the form of plates oj graphite. Exp. 125 t. Crystalline silicon is best obtained by the fol- lowing method : A mixture of 3 parts dry sodium hydrofluo- silicate, Na^SiF^, and 1 part sodium cut in pieces, is rapidly introduced into a hessian crucible heated to bright redness. Then 9 parts well dried granulated zinc are rapidly added ; and finally, the whole covered with a layer of dried sodium chloride. The crucible is then closed, the fire allowed to go down, and the crucible allowed to cool in the furnace. The silicon undei these circumstances crystallizes from its solution in molten zinc, and the zinc afterward solidifies, enclosing the crystals of silicon. By treating the mass with hydrochloric acid the zinc is dissolved and the crystals left behind. 201. Properties. —Amorphous silicon, as obtained above, is inflammable in the air, when strongly heated, producing silicon dioxide. The graphitoidal form is not so readily- inflammable. At a high temperature, and in absence of oxygen, silicon can be fused. Hydrochloric acid does not dissolve it, but in strong alkalies it is soluble, thus • — Si + 2 KOH 4- H2O = KnSiOs + 2 Hj. Note. The student will not meet with free silicon in his work unless he prepares it or buys it as such, when he can examine it, ignite it, and test for silicon dioxide. Art. 205. SIIiICON AND OX7GEN. Silicon Dioxide, oe Silica, SiOj. 202. Occurrence. — Silicon and oxygen form one well- known compound, which occurs in many modifications, as : 186 SILICON AND OXYGEN. 1. Quartz crystals, glassy hexagonal prisms terminating in hexagonal pyramids. 2. Amethyst, smoky quartz, rose quartz, and chrysoprase, colored varieties of quartz. 3. Quartzite, a sedimentary rock. 4. Sand and sandstone, fine fragments of quartz more or less cemented together. 5. Honestone or novaculite, a fine-grained quartz rock. 6. Chalcedony, a mixture of crystalline and non-crystalline quartz. 7. Agate, consisting of layers of crystallized and amorphous quartz of various colors. 8. Flint and chert, a coarse variety of chalcedony. 9. Opal, a hydrated form of silica. 10. Various modifications of the above in which one form is passing into another. 203, Preparation. — Silica may be artificially obtained in two forms : as the so-called " soluble silica," and as an insoluble pow^der. Exp. 126 p. Melt in a crucible, 6^ each, potassium carbonate and sodium carbonate ; then add 3^ pulverized quartz or white sand, and heat till the whole is melted. The molten mass is now to be poured out and dissolved in dilute hydrochloric acid. The solution thus obtained is now placed in a tray (dialyzing) , which may be prepared by stretching parchment paper over a wooden hoop, say lO""" in diameter. This tray is now floated on a tub of pure water, when the hydrochloric acid and saline substances of the solution pass through the parchment into the water of the tub, while the soluble silica remains in the tray. It will take about four days to effect this separation, and there must be much water in the vessel on which the tray is floated, or it must be often changed. SILICON Alto OXYGEN. 187 Note. This method of separation is called Dialysis, and depends upon the fact that crystallizable substances will pass through the parchment, while colloid or non-crystallizable substances will not pass through. In this manner a colorless, tasteless, limpid solution is obtained, which may be concentrated in a generating-flask; but if the concentration be carried too far, the solution becomes of a jelly-like consistency. Though we here speak of having silica in solution, the substance dissolved is really a form of silicic acid, probably ortho-silicic acid, H4Si04. This loses water very readily, and is converted into meta-silicic acid, HgSiOa, and this, when dried, loses more water, and passes into silicon di- oxide, Si02. Note. The relations between silicon dioxide and silicic acid, H^SiOj, are similar to those existing between carbon dioxide and carbonic acid- Student will indicate the points of resemblance. Exp. 127 p. Evaporate strictly to dryness (in an evaporat- ing-dish) a portion of the solution obtained in the last experi- ment. The powder thus obtained is pure silica. Is it now soluble In acids ? In alkalies ? 204. Properties. — ■ Natural crystals of silicon dioxide or quartz are of a glassy lustre, and rank 7° in the scale of hardness. They present no cleavage, and a conchoidal fracture. The specific gravity of quartz is 2.6 ; of tridyT mite, another form, it is 2.3. All forms of silica are somewhat soluble in alkalies, especially when digested under pressure; consequently many waters, such as those of the Hot Springs in Arkan- sas, and the geysers of Iceland, contain, in solution, silica, which is deposited upon standing. This explains the existence of siliceous sedimentary rocks, like quartzite, etc., and of the siliceous petrifactions which so frequently occur, especially in the rocks of the Cretaceous Period. 188 THE SFLICOTSr OXACIDS. Tripoli is the siliceous remains of the shells or valves of microscopic plants, — the Diatoms. Sandstone is composed of fragments of quartz cemented together by deposited silica ; while Conglomerates are larger pebbles similarly joined. Arti- ficial conglomerate is now used as a building stone. The many different colors which quartz assumes are due to the fact that soluble silicon compounds readily absorb coloring matters. These colors are either destroyed or changed upon application of heat. Some forms of quartz, owing to their hardness, and sus- ceptibility to a high polish, are prized as ornaments. Agates are somewhat porous ; when soaked in honey, then treated with sulphuric acid, and afterwards polished, they exhibit curious and beautiful markings. 20S. Tests for Silicon Dioxide. — The student will soon learn to recognize any of the natural forms of silica by their appearance when crystallized, and by their hardness and fracture. (Also see tests for Silicates.) THE SILICON OXACIDS. 206. The silicon acids are hardly known in the free state, being very unstable like carbonic acid. Notwith- standing the instability of the acids of this series, there are three well-marked classes of salts which we may fairly suppose to be derived from these acids : — 1. The mono-silicates. 2. The bi-silicates. 3. The tri-siUcates. WoUastonite, CaSiOj, and steatite, Mg5H2(Si03)4, are THE SILICON OXACIDS. 189 examples of the first; serpentine, MgsSiaOj, and ortlio- clase, Al2K2(Si308)2, are examples cf the second and third. Besides these there are known many polymeric forms of each of these classes. Sno. Bead R. and S., Vol. I., p. 573. The various forms of silicic acid may be regarded as derived from the acid HiSiO^ by abstraction of water in different proportions. The simplest case is represented thus : — H4Si04 - H2O = HsSiO.,, the salts of the acid thus formed being the monosilicates. Then we have : — ■ 2 H4Si04 - HjO = nskOu from which the bisilicates are derived ; and, finally, 3 USiOi - 4 H2O = H^SiaOs, from which the trisilicates are derived. 207. Tests for the Silicates. — Fuse the solid substance with sodium carbonate on charcoal; dissolve the fused mass in hydrochloric acid, and evaporate the solution to dryness. If a white powder (SiOj), insoluble in hydro- chloric acid, and soluble in potassium hydroxide, be obtained, silicic acid, or some of its derived forms, is present. Other Compounds of Silicon. 208. Silicon may be made to unite with nearly all the elements previously considered, but their compounds are unimportant. "We may mention here that ; — 1. Silicon hydride, SiH4, is a gas prepared by acting upon an alloy of magnesium and silicon with very dilute hydrochloric acid, in the absence of air. 190 BORON. If this gas be allowed to escape through water in bubbles, each bubble, upon coming in contact with the oxygen of the air, ignites spontaneously, forming ring- shaped clouds of silicon dioxide. 2. Silicon fluoride, as we have previously seen, is ob- tained by acting upon glass or silicon with hydrofluoric acid (Art. 134). 3. Sydrofluo silicic acid, H2SiF6, is prepared when silicon fluoride is dissolved in water : — 3 SiF^ + 4 H2O = H4Si04 + 2 HsSiFj. The sodium or potassium salts of this acid may thus be prepared : — Exp. 128 t. Silicon fluoride is first prepared by treating in a generating-flask sand and fluorspar, CaFj, with sulphuric acid. This gas Is led into water, thus forming a solution of hydrofluosilicic acid. When potassium or sodium carbonate is added to this solution, a precipitate of the sodium or potassium salt is obtained. Care must be taken to avoid an excess of the alkaline carbonate, as the salts of hydrofluosilicic acid are de- composed by alkalies. BORON. Symbol, B'". — Atomic Weight, 11. — Specific Gravitt (Crystals), 2.5. 209. Occurrence.^ — Boron occurs only in combination with other elements. The chief compounds are boric acid, H3BO3; borax, Na2B407 -|- 10 H2O ; and boracite, 2 MgsBsO:,, MgCls. 210. Preparation. — Boron may be prepared in two modifications, viz., amorphous and crystalline. r.OEON. 191 Exp. 129 t. Amorphous boron, a dark-brown, odorless, tasteless powder, may be obtained by heating boron trioxide, B2O3, witli metallic potassium in an iron tube. Exp. 130 t. Crystalline or adamantine boron is obtained by fusing amorphous boron, in the absence of air, with metallic aluminium. This modification of boron ranks 9° in tlie scale of hard ness, and its crystals are prisms or monoclinic octahedra. 211. Boron Compounds. — 1. Boron trioxide, BaOs, is the only known oxide of boron, and may be obtained by heating to redness boric acid, H3BO3. It is a brittle, glassy solid, readily uniting with water to form boric acid. SuG. Write the equation. 2. Boric acid, H3BO3, occurs dissolved in the waters of certain lagoons in Tuscany, and the market is mostly sup- plied from that source. In. the vicinity of these lagoons are volcanic jets of steam, whose heat is used to evaporate the water containing the acid, which is thus obtained in crystals; its purification is effected by re crystallization from a water solution. There are in California several dried up lake beds containing massive borax, said to be sufficient to supply our wants. Here the acid is obtained by treating the borax with hydrochloric acid, and dissolving in hot water. From this solution boric acid is also obtained by crystal- lization. Boric acid is soluble in water and in alcohol. It forms the borates. 212. Tests for Boric Acid and the Borates. — 1 . When in solution, the free acid turns a strip of turmeric paper 192 EXERCISES. brown, and this color is not changed by dilute hydrochloric acid, as is the case with the alkalies. Note. It is best for the beginner to compare the action of an alkali on this paper with the action of boric acid, noting how the hydrochloric acid affects the colors. Also dip a piece of turmeric paper in boric acid ; then moisten with Na2C03 and note the greenish-black color produced. 2. When a solid borate is heated on a platinum loop in the reducing flame, the flame is tinged green. Note. This test is most striking when the solid has first been calcined, then dipped in sulphuric acid and heated to expel the acid, and finally moistened with glycerine and treated as in 2. EXERCISES. 1. Silicates in solution are estimated quantitatively as follows : The solution is acidulated with hydrochloric acid and evaporated strictly to dryness, without allowing the temperature to rise sufficiently high to cause the silica, SiO^, obtained again to unite with any bases present. The residue is again treated with hydrochloric acid ; the white insoluble powder SiOj is next removed by filtration, .and in a manner similar to that employed in estimating the sulphates directly determined as silica. 2. Soak bits of agate in honey ; treat with sulphuric acid, and polish on a grindstone or emery wheel. The peculiar markings of the agates are thus brought out. 3. Unite the edges of broken bits of glass with the so-called " soluble silica"; allow the mended articles to dry for two days; then test the strength of the silica as a cement. 4. What is glass f Write an essay on the manufacture of glass. 5. Ask a blacksmith for what purposes he uses borax. Ask him if a mixture of salt and sand will answer as well. What is a flux ? 6. Eor what use does the barber employ borax ? 7. Does borax soften " hard " water ? Try it. 8. What is the anhydride of boric acid, H3BO3 ? 9. Dissolve a little borax in HCl ; then to the solution add alcohoi. Warm and ignite the alcoholic solution of boric acid thus obtained and note the characteristic green flame. 10. The waters of all our streams abound in diatoms. Examine some under the microscope. CHAPTER XIII. PHOSPHORUS. — ITS OCCUERBNCE, COMPOUNDS, ETC. — GENBBAIi EXAMINATION OF UNKNOWN SUBSTANCES VOE ACIDS. PHOSPHORUS. Symbol, P. — Atomic Weight, 31. — Specific Gkavity, 1.83. 213. Occurrence. — Owing to its great affinity for oxygen, phosphorus, although widely distributed, never occurs in the free state. Its principal compounds are with calcium ; as, phosphorite, Ca3(P04)2, and apatite, 3 Ca3(P04)^ -f CaClF. It also unites with iron to form vivianite, Fe3(P04)2 + 8 H2O. It is also found in the igneous rocks, from whose disintegration our alluvial soils have been produced ; hence every fertile soil must contain phosphates. These phosphates are taken up from the soil by growing plants, of whose ripened seeds they form an essential constituent. Again, animals consume the plant and its seeds, and appropriate the phosphates for building up the solid or inorganic portion of their bones ; and it is from bones that the greater part of our commercial phos- phorus is now obtained. Sombrerite, an impure form of calcium phosphate, found in the island of Sombrero, is another source of commercial phosphorus. 214. Preparation. — Phosphorus is obtained from the ashes of burned bones. As a matter of economy, the bones 194 PHOSPHORUS. are not directly burned, but are subjected to a preliminary treatment, in order to save some of their other constitu- ents. Thus they are either first digested with water, under pressure, in closed vessels, in order to extract the gelatine ; or they are distilled in closed retorts, the vola- tile products (bone oil) being utilized to some extent; while the remaining solid substance, or "bone black" is used for clarifying sugar until worthless for that purpose. In either case the remaining solid residue of the bones is reduced to ashes by burning in the open air. Bone ash, which consists largely of calcium phosphate, Ca3(P04)2, is first treated with sulphuric acid, when an acid calcium phosphate, soluble in water, is obtained : — Ca3(P04)2 + 2 H2SO4 = CaH4(PO,)2 + 2 CaS04. This solution of " super-phosphate of lime," as it is usually called, is then evaporated to dryness, and afterward heated nearly to redness, when calcium m eta-phosphate is ob- tained : — CaH4(P04)2 = CaCFOa)^ -|- 2 H^O. The meta-phosphate is then intimately mixed with fine charcoal dust, and heated to redness in earthen crucibles placed in tiers inside of a furnace, their necks extending outside of the furnace, and dipping under water in a con- denser. Only one-half of the phosphorus is thus liber- ated and condensed under the water. The phosphorus is now removed, melted under water, and purified by strain- ing through chlamois leather under water, when it is cast into the ordinary sticks of commerce. Before it is cast into sticks, the phosphorus may be purified by treating it with sulphuric acid and potassium dichromate, KjCrjO,. All the phosphorus contained by the bone ash may be PHosPHORtrs. 195 liberated by mixing the m eta-phosphate with sand and charcoal dust, after which it is treated as before. The reactions are : — 1. 2 Ca(P0s)2 + 5 C = Ca^PA + 5 CO + 2 P. 2. 2 Ca(P03)2 + 2 Si02 + 10 C = 2 CaSiOs + 10 CO + 4 P. 215. Properties. — Phosphorus is a highly inflammable substance, taking fire at low temperatures. When exposed to the air it slowly oxidizes, emitting a phosphorescent glow, or luminous and evanescent flashes of light. A slight blow or scratch is often sufficient to ignite it. It burns with great heat, and when in contact with the flesh it produces deep and painful wounds; hence great care should be exercised in handling it. It should not be taken in the hands nor cut in the air, but should be held by a pair of forceps, and cut under water. Phosphorus should always be stored, for safe keeping, in a bottle of water fitted with a good cork to prevent the water from evaporating ; the bottle should then be kept in a tightly-covered can, and the whole placed in a cool place. Owing to the low temperature of its ignition, phosphorus is employed in tipping the common lucifer match. The composition of match-tips varies ; but nearly all the com- pounds employed for making tips contain phosphorus, sulphur, and potassium nitrate. Phosphorus is also used as an ingredient of many ver- min "exterminators," but about five-sixths of all the phosphorus produced is consumed for making matches. The fumes of phosphorus are characteristic, possessing poisonous properties, and an odor with a faint resemblance to garlic. When taken internally, phosphorus is a virulent 196 PHOSPHORUS. poison; one decigram may produce fatal results. Severe pains in the stomach, vomiting of substances with an odor of garlic, and even the characteristic fumes emitted with the breath, are the symptoms of phosphorus poisoning. Turpentine is a proposed antidote. Phosphorus is known in three different modifications, viz. : — 1. Ordinary, or waxy phosphorus, the form usually seen in sticks. 2. Crystalline phosphorus, obtained by dissolving the common form in carbon bisulphide, and allowing the solu- tion to evaporate. 3. Red, or amorphous phosphorus, obtained when either of the other two modifications is heated to 240° in the absence of the air. This variety is not so inflammable as the ordinary phosphorus, nor does it give off poisonous fumes ; hence it is sometimes used by the matchmakers, who thus avoid the dreaded effects of phosphorus poisoning. The specific gravity of this variety is 2.106. All three varieties of phosphorus burn in the air with a bright, luminous flame, forming dense white fumes of phos- phorus pentoxide. QuEKT. Should an excess of phosphorus he employed In experiment 41, of what variety would the remainder he 1 216. Tests for Free Phosphorus. — 1. Phosphorus, in considerable quantity, may be detected by its physical properties and odor. 2. In minute quantity, as in cases of phosphorus pois- oning, phosphorus is detected by dissolving in water the substance to be tested, after which it is boiled in a gen- erating-flask, and the steam is led through a glass con- densing-tube into another flask containing cold water. PHOSPHORUS AND HYDKOGEK. 197 Now, if the room be dark, and if phosphorus be present, a phosphorescent glow is noticeable at the point where the steam condenses. PHOSPHORUS AND HYDROGEN. 217. Phosphorus and hydrogen form three compounds : — 1. Gaseous phosphoretted-hydrogen or hydrogen-phosphide, PHj. 2. Liquid phosphoretted-liydrogen or hydrogen-phosphide, PH,. 3. Solid phosphoretted-hydrogen or hydrogen-phosphide, (PjH?). Of these we shall consider only the first. 218. Graseous Hydrogen Phosphide, or Phosphine, PHa, is a gas which ignites spontaneously upon coming in contact with the oxygen of the air, owing to the presence of traces of the liquid compound PH2, this latter substance being obtained by the same process that yields the former. If the tube from which the phosphine escapes be bent upward under water, each bubble upon reaching the air ' ignites, forming beautiful ring-shaped clouds of phosphorus pentoxide, P2O5. In a still atmosphere these clouds have a peculiar rotary motion, illustrating what is known as vortex motion. This striking experiment may be exhibited thus : — Exp. 131 t. In a generating-flask place a strong solution of potassium hydroxide, KOH, and add several small pieces of stick phosphorus. Now gently warm, and as soon as flames begin to appear at the mouth of the flask, insert a cork carry- ing a bent delivery -tube. The lower end of this tube is to dip under water placed in an open vessel. As each bubble of the gas comes into the air, it ignites with a slight report : — 4 P -f- 3 KOH -f 3 H2O = 3 KH2PO2 + PH3. 198 PHOSPHOEtrS AND OXYGEN. It Is somewhat safer to put the apparatus together, and then to pass hydrogen through it long enough completely to displace the air ; or the air may be expelled by pouring a little ether over the solution before warming. During the experiment cur- rents of air in the room are to be avoided. Save the contents of the generating-flask for work under hypophosphorous acid. QoEEiES. "What is the object of these last precautions 1 What other gas behaves like PHj ? Show how PH^Br and PH4I are obtained from PH3, HI, and HBr. Does PH3 form salts similar to NH3 1 In this experiment liquid Lydrogen-phosphide may be obtained by passing the gas througli a suitable condensing- tube, but both this and the solid form are of no impor- tance to the beginner. None of the hydrogen phosphides possess acid jjroperties. SuG. Make a list of the binary acids. Also make a list of the non- acid hydrogen compounds of the elements previously considered. Which one is alkaline f PHOSPHORUS AND OXYGEN. 219. There are two known oxides of phosphorus, viz. : — 1. Phosphorus Trioxide, PaOj. 2. Phosphorus Pentoxide, P2O5. 1. Phosphorus trioxide is formed when phosphorus is burned in a limited supply of air. It is a white powder, which possesses a garlio odor, and unites with water to form phosphorous acid : — 3H20-|-PA=2H3P03. 2. Phosphorus pentoxide is obtained by burning phos- phorus in the open air or in oxygen. It is also a white powder, which eagerly unites with hot water to form phos- phoric acid : — 3 H2O -I- PA = 2 H3PO4. THE PHOSPHOKUS OXACIDS. 199 THE PHOSPHORUS OXACIDS. 220. There are three acids in this series : — 1. H^-pophosphorous acid . H3PO2, 2. Phosphorous acid . . . H3PO3, 3. Phosphoric acid . . . H3PO4, from which are derived : — a. Metaphosphoric acid . . HPO3, h. Pyrophosphoric acid . . H^PaOj. Since the last two acids may be derived from phosphoric acid, all three will be treated under one article, after the consideration of the first two acids in the series. Hypophosphojbous Acid, H3PO2. 221. Exp. 132 p. In a generating-flask place 10'=° of a solution of barium hydroxide, Ba(0H)2, and add two or three small pieces of phosphorus. Add a little ether and boil until the following reaction is completed : — • 3 Ba(0H)2 + 2 P4 + 6 HjO = 3 BaCH^POs)^ + 2 PH3. The remaining solution is now to be filtered, when the barium hypophosphite is obtained in clear solution. To this solution carefully add dilute sulphuric acid to precipitate the barium, when hypophosphorous acid is obtained, thus : — Ba(H2P02)2 + H2SO4 = BaS04 + 2 HsPOj. This acid is a colorless liquid, oxidizing to phosphorous and phosphoric acids, when standing exposed to the air. It is mono-basia, only one atom of its hydrogen being displaceable. If we represent by M' any univalent metal, the general formula for a hypophosphite may be repre- sented thus: M'CHaPOj). The hypophosphites may be prepared as in Exp. 131 T, by boiling phosphorus with an alkali. The principal use 200 THE PHOSPHORUS OXACIDS. of these salts is for medicinal purposes. The acid and its salts are strong reducing agents. 222. Tests for Hypophosphorous Acid and the Hypo- phosphites. — 1. The acid or its salts when heated in a test-tube yield phosphine, PHs. 2H3P02 = PH3 + H,P04. 2. With silver nitrate a solution of the acid or its salts gives a white precipitate, which soon changes to brownish- black : — 4 AgNOg + H3PO2 -1- 2 H,0 = 4 HNO3 -f- HsPO^ -|- .4 Ag. 3. To the solution of this acid'or of its salts add an ex- cess of cupric sulphate, CuS04i an insoluble hydride of copper, CuH, is formed. Boil a short time ; hydrogen is liberated and metallic copper is obtained. Note. No. 3 distinguishes HjPOj from H3PO3. Thus test the latter. SuG. Try hypophosphorous acid, or a hypophosphite, with mercuric chloride, HgClj. Do you obtain metallic mercury ' In which tests do you find examples of reduction ? Write the equations for HgCl^ and CuSOi with KHjPOj. Phosphorous Acid, H3PO3. 223. This acid may be obtained by passing chlorine gas through a layer of melted phosphorus under water. Phosphorus trichloride, PCls, is at first formed, and im- mediately reacts upon the water, thus : — PCI3 -I- 3 H2O = HsP03 + 3 HCl. The hydrochloric acid is expelled by heat. If the addition of the chlorine gas does not stop short of saturation, i.e., before ths phosphorus has all disappeared, phosphoric acid is produced. Indeed, it is difficult thus to obtain phos- phorous acid free from traces of phosphoric acid. THE PHOSPHORUS OXACIDS. 201 Phosphorous acid is generally dibasic, and M'2(HP03) may be taken as a general formula for the phosphites, although there are some phosphites known in which the acid is tribasic, all the hydrogen being displaced. 224. Tests for Phosphorous Acid or a Phosphite. — 1. To the solution add a few drops of sulphuric acid, and then add potassium permanganate until a purplish tint is reached. This color fades slowly in a cold solution, but rapidly when heat is applied. Sno. Thus try H3PO2. How does it behave ? Also try H3PO3 with CuSOj, as you tried HgPOj. What results ^ 2. To the solution add calcium hydroxide, Ca(0H)2; a white precipitate is thrown down. Sdg. Thus try a hypophosphite. Do you obtain a precipitate ? Quest. How can you distinguish between a phosphite and a hypo- phosphite '? Phosphokic Acid, HsPOj. 225. This acid is also known as orthopJiosphorio acid, and its salts as the orihophosphates. It may be obtained thus : — Exp. 133 p. In an evaporating-dish place a small quantity of red phosphorus, and add reagent nitric acid (sp. grav. 1.2) ; now heat gentlj', adding more nitric acid, until the phosphorus disappears and red fumes cease to come off. The evaporation is to be continued until the excess of nitric acid is expelled. The acid thus obtained is a thick, syrupy mass, free from odor and readily soluble in water ; when allowed to stand, rhombic, six-sided crystals are obtained. Phosphoric acid is a tribasic acid, forming acid and normal 202 THE PHOSPHOBTJS OXACIDS. salts, the phosphates. M'sPO^ is ii general formula for the phosphates. Phosphoric acid is used in medicine, and its salts are of common occurrence and much used as fertilizers. The phosphates are found in the blood and fluids of animals; they are excreted from the kidneys as acid phosphate of sodium and phosphates of calcium and magnesium. When urea in urine decomposes a double salt of ammonium and sodium, NaNHiHPO^, or microcosmie salt is formed. It was from this source that, in 1669, Brandt first prepared phos- . phorus. Metaphosphokic Acid, HPO3. This acid is formed when orthophosphoric acid is heated to 400°. It is the form in which phosphoric acid is com- monly met with in the market (glacial phosphoric acid). Its formation is illustrated thus : — H3PO4 - H2O = HPO3. At ordinary temperatures, in solution in water, it is slowly changed to orthophosphoric acid ; the change takes place rapidly in boiling water. Salts of metaphosphoric acid are formed by igniting phosphates belonging to the class represented by the formula M'HjPOi as, for example : — KH2PO4 - H2O = KPO3. QuEKT. In what process already considered does a transformation from an orthophospliate to a metaphosphate take place ? Pyeophosphoeic Acid, H4P2O7, Is formed when orthophosphoric acid is heated at 200- 300°, until a small specimen neutralized with ammonia gives a pure white precipitate with silver nitrate. The change is : — 2 HsPO^ - H2O ±= HiPA- THE PHOSPHOKUS OXACIDS. 203 Its salts are formed by igniting phosphates of the order M'jHPOi, thus: — 2 K2HPO4 - H2O = K^PA- Query. In what connection have ijyrophosphates been mentioned in this book ? 226. Tests for the Phosphates or their Correspond- ing Acids. — 1. To the solution add a few drops of silver nitrate, AgNOs. (a) A light-yellow precipitate, soluble in ammonia, nitric acid, and acetic acid, H(C2H302), indicates phosphoric acid or its salts. (i) A white precipitate, soluble in nitric acid (witjiout effervescence) and in ammonia, indicates pyrophosphoric acid or its salts. (c) A gelatinous white precipitate, soluble in nitric acid, indicates metaphosphoric acid or its salts. 2. We may also distinguish metaphosphoric acid or its salts by acidulating its solution with acetic acid and add- ing the white of an egg, which immediately coagulates. Stig. Try H3PO4 and H^PjOj with the white of an egg. W^hat results ? 3. The most delicate test for orthophosphoric acid or its salts is made by adding to the acid or to one of its salts dissolved in nitric acid an excess of ammonium molybdate, (NH4)2MoOi; upon heating, a yellow precipitate of am- monium phospho-molybdate is obtained. See App. for reagent ammonium molybdate. Note. This test is sufficiently delicate to detect even very minute traces of phosphoric acid or of the phosphates. 4. An orthophosphate with ammonium chloride, am- monia and magnesium sulphate, gives a crystalline precipi- tate of magnesium-ammonium phosphate, MgNHiPO^. SuG. Try the phosphorus oxacids with salts of lead, calcium, barium, and mercury. What results "i 204 EXAMINATION OP UNKNOWN SUBSTANCES. EXAMINATION OF UNKNOWN SUBSTANCES FOE ACIDS. 227. We have now learned something about the principal inorganic acids. As we have already seen, Art. 79, some elements are acid formers, others form bases ; and we may now mention that there are still other elements — as, for example, chromium and manganese — that are indifferent, acting in certain compounds as acids, in other compounds as bases. The consideration of the acids of the indifferent elements will be deferred for a time. It frequently occurs that the chemist, while working, comes upon substances entirely unknown to him ; and among other things that he is called upon to determine are the acids, which form essential constituents of all salts. It is true that the substance may not be acid, but, as we have previously seen, the salt of any acid yields the test for that acid. Thus, KNO3 gives the test for nitric acid, and NaCl the test for hydrochloric acid, etc. Now since there are many acids, it is neither best nor profitable to test at random for first one acid and then another; some methodi- cal plan should be followed. One method of procedure is as follows : — If the substance be in liquid form and neutral, evaporate it to dryness or nearly so, carefully avoiding a high heat, which might decompose certain unstable compounds and drive off their acids in vapors. If the substance under examination be a solid, no preliminary treatment is neces- sary. If the substance in solution be acid, it is either a free acid or an acid salt ; in this case the solution must be directly tested. Thus two cases naturally arise. I. Let us suppose that the substance is neutral and a EXAMINATION OF UNKNOWN SUBSTANCES. 205 ♦ solid, or, if a neutral solution, that we have evaporated it to dryness. Proceed thus : — Place a small portion of the substance in a test-tube ; add sulphuric acid ; heat it gently, and note the results as follows : — 1. If a rapid effervescence of an odorless, colorless gas occur, the substance is probably a carbonate or an oxalate. Now turn to the test for Carbonates or Carbonic Acid, Art. 152, and try a fresh portion of the substance by all the tests there given. In case it prove not to be a carbonate, it is, very likely, an Oxalate, a salt of the organic oxalic acid, H2C2O4. This acid (in this connection) may be recognized by its giving with calcium chloride, CaCl2, a white precipitate of calcium oxalate, CaC204, soluble in hydrochloric acid, • but insoluble in acetic acid. 2. Slower effervescence of a colorless gas possessing odor, (a) The odor of rotten eggs indicates a sulphide. Test by Art. 169. (6) The odor of burning matches; try for H2SOJ, Art. 179, or H2S2O3, Art. 186. (c) Odor of peach blossoms ; try for HCy, Art. 155. ((i) Odor of vinegar; try for acetates, which are the salts of acetic acid, HC2H30^, thus : Dissolve the original substance in water, add ferric chloride, Fe2Cl6, and boil. A red solution of ferric acetate, Fe2(C2H302)6, is formed ; the color is destroyed by adding hydrochloric acid. (e) An irritating odor indicates HCl, Art. 96 ; HNO3, Art. T5 ; or HF, Art. 135. 3. If a gas having a color and an irritating odor be liberated, try for HI, Art. 127; HNO2, Art. 72; HCIO, Art. 104; or HBr, Art. 117. 206 EXAMINATION OF UNKNOWN SUBSTANCES. 4. If a sudden explosion occur, try for HClOg, Art. 108. 5. If none of the preceding phenomena occur, try for H2SO4, Art. 183; H3PO4, Art. 226; HsPOg, Art. 224 j H^SiO^, Art. 207; H3BO3, Art. 212; HIO3, Art. 131 ; or HBrOs, Art. 121. The student should remember that the foregoing data are valuable as indications only, and that these indications point toward certain acids to which he should refer, and which he should try until he is satisfied that he has found the right one. II. If the solution be an acid one, proceed thus : — 1. To a portion of the solution add HCl; then add BaCls- If a white precipitate be obtained, the acid present is H2SO4, since barium sulphate, BaSd, is the only barium salt (except the salt formed with the rare acid HaSiFg) which is insoluble in hydrochloric acid. 2. To a fresh portion of the solution add HNOs, and then AgNOa. The following acids give a precipitate insoluble in nitric acid: HCl; HI; HBr; H^S ; HCy; HCIO; and the rarer acids, hydro-ferro-cyanic acid, HiFeCye, and hydro-ferri- cyanic acid, HjFeCye. For these last two acids, see Iron. 3. Test in order for the following acids, using each time afresh portion of the solution: HNO3; H2CO3; HgPOi; H^SiO^; H3BO3; H2S2O3; H2SO3; HNO2; H2CA; HCC^HjOO; HCIO3. If the acid is not discovered by working carefiilly up to this point, it is a rare acid, and the student will be obliged to try for all those previously mentioned in the text and not mentioned above. It is true that the acid may be quite a common one, belonging to the acids of the indiffer- ent acid-forming elements, such as chromium, arsenic, or manganese. EXERCISES. 207 In such a case the student needs farther experience to determine the acid. He will find directions under the elements just named. EXERCISES. 1. Phosphorus in iron ores, or in coal used in reducing iron ores, malses the iron brittle. The presence of phosphorus in coal may be determined by testing tSie ash for phosphates. 2. Make a list of the commonly occurring acids; also a list of the rarer acids previously mentioned. In testing for acids a substance that occurs native, would you expect to find rare acids ? 3. Dissolve the salt of an acid, and test with litmus paper ; some salts are acid, some are neutral, and some are alkaline. By trying many salts and tabulating the results, the student may learn that normal salts may belong to any of the three classes. Do any of the acid salts that you have tried belong to the last two classes ? 4 If in an unknown solution NHg and HNOg be found, what salt is present f If Na and HCl, what salt '! 5, The student should be assigned many unknown (to him) salts and, by reference to the text, he should determine the acids present. In this way he will soon Jcnow the tests for the common acids. More than one acid may be assigned in one solution, provided the acids do not decompose one another, or their tests do not interfere. The metals of many metallic salts obscure the test for the acids of the salts ; in this case the metals must first be removed, as will hereafter be explained. Na, K, NH^, Ca, Mg, Sr, and Ba do not thus interfere. 6. For an improved method of obtaining phosphorus, see Chemical News, Apr. 4, 1879, p. 147. CHAPTER XIV. THE METALS. INTRODUCTION. 228. The elements have been divided arbitrarily into Metals and !N"on-metals, but the dividing line is nowhere distinctly drawn. Certain elements, such as arsenic, anti- mony, and bismuth, stand midway, in regard to their phys- ical and chemical properties, between the two proposed classes, and may be fairly placed in either ; consequently we may justly consider the elements as forming but one class with a regular gradation of properties. In view of these facts it is impossible to give a strict and valid definition of a metal ; but, in general, we may say : — Definition. • — • A metal is an element which possesses a peculiar lustre, known as a metallic lustre, especially when in a solid or coherent condition, and the higher oxides of which only, and then in very few instances, are acid-forming compounds. SuG. All, or nearly all, of the oxides of the non-metals form acids. State a few exceptions. Note. Opacity, high specific gravity, and great atomic weight are not exclusively characteristic of the metals. 229. Properties of the Metals. — Some of the metals are barely known to exist, while others have been known since the highest antiquity, and their properties have been thoroughly investigated. THE METALS. 209 Of the properties of metals we may note the following : — (a) Specific G-ravity. — As a rule the specific gravity of a metal is greater than unity; only three — sodium, potassium, and lithium — are less than 1.000. Osmium (sp. grav. 22.48) is the heaviest metal, while lithium (Sp. grav. 0.59) is tlie lightest. (See Art. 25.) Queries. With what are solids and liquids compared to determine their specific gravities % Gases 1 How is specific gravity determined ? (V) Specific Heat. — The specific heat of an element is equal to the number of thermal units required to raise one kilogram of that element through 1° C. The specific hsat of any metal is less than unity, and varies somewhat according to the temperature at which the observation is mad^. The following observations, which were made at 55°, will serve as an illustration : — Cd 0.0567 Zn ' 0.0955 Ag 0.0570 Mn 0.1220 Co 0.1070 Ni 0.1080 Au 0.0324 Pt 0.0324 (c) Atomic Heat. — When the specific heat of any ele- ment is multiplied by its atomic weight, a nearly constant quantity (about 6.4) is obtained. This product, in the case of any element, is termed the atomic heat of that ele- ment. Take, for example, gold and zinc : — 0.0324 (sp.ht. of Au) X 196.5 (at.wt.of Au) = 6.4— (at.ht.of Au). 0.0955 (sp.ht. of Zn) x 65.0 (at.wt.of Zn)= 6.4 — (at.ht.of Zn). From an inspection of the results thus obtained was deduced Dulong and Petit's law, viz. : — The specific heat of an element varies inversely as the atomic ^rUM. CEEIUM. — DIDYMIUM. YTTRIUM. Stmbol, Yt. — Atomic Weight, 89. 325. Yttrium occurs along with erbium. It is detected by the spark spectrum of its chloride, which gives many bright lines, of which the most marked are two groups near the sodium line. LANTHANUM. Symbol, La. — Atomic Weight, 138.2. 326. Lanthanum occurs in the mineral Lanthanite as La2(C03)j + 8 HjO. It is best prepared by the electrolysis of its chloride, and is a soft grayish metal which readily tarnishes in the air, assuming a steel-blue tint. It is detected by its spark spectrum containing many characteristic lines. CERIUM. Symbol, Ce. — Atomic Weight, 141. 327. Cerium occurs along with Lanthanum, and is similarly prepared. It is a soft, gray metal which tarnishes in damp air, assuming, successively, the colors yellow, blue, and green. It burns with great brilliancy when heated in the air, and is detected by its spark spectrum which contains three bright lines in the green. DIDYMIUM. Symbol, Di.— Atomic Weight, 142.3. 328. This metal occurs along with the rare metals previously mentioned, and is prepared similarly to Lanthanum. It has a yellowish lustre, and burns brightly when heated in the air. It is detected by its absorption spectrum. Its salts have a rosy tint, and it colors the microcosmic bead rose-red. TERBIUM. — EKBIUM. — THOKItTM. — TITANIUM. 305 TERBIUM. Symbol, Tb. — Atomic Weight, 148.5. 329. This metal has not been prepared, but its oxide, TbgOj, is an orange-yellowish powder. It is difficult to separate ter- bium from the preceding kindred metals, and no sure means of detection is known, since it gives no absorption spectrum. ERBIUM. Symbol, Er.— ^Atomic Weight, 166. 330. This metal occurs with the foregoing, and has not been obtained pure. It is detected by its continuous luminous spec- trum, which is crossed by bright lines which are darkened in the same position in the absorption spectrum. THORIUM. Symbol, Th. — Atomic Weight, 232. 331. Thorium occurs in Thorite and other complex minerals, and is prepared by heating its chloride with potassium. This metal as thus prepared is a gray powder which burns brightly in the air. Thorium is detected by the precipitation of its carbonate or hydroxide ; these are soluble in an excess of the precipitant. TITANIUM. Symbol, Ti. — Atomic Weight, 48. 332. This metal occurs in Rutile and in Titanite, TiCaSiOj, and other minerals. It forms a considerable per cent of some of the Lake Superior iron ores. Titanium is prepared by heating a double fluoride of potassium and titanium in a closed crucible with metallic potassium; the fused mass is then lixiviated with water, when the titanium remains as a dark-gray powder. 306 ZIECONITTM. — tJEANlUM. At a high temperature this metal unites directly with nitro- gen, — a marked peculiarity ; it also burns when heated in the air. In blast furnaces, when reducing iron ore containing titanium, a peculiar compound. Titanium Cyano-nitride, TiCjj + 3 TigNj, is obtained. Titanium is detected by imparting to the microcosmic bead in the reducing-flame a yellow color when hot, violet when cold ; when iron is present the bead is red. The oxidizing-flame gives no color. ZIRCONIUM. Symbol, Zr. — Atomic Weight, 90. 333. Zirconium occurs in the mineral Zircon, ZrSi04, and is prepared in the same way as titanium, which metal it strongly resembles. The amorphous form burns easily, but a crystalline variety takes iire in the air only at the highest temperatures. Zirconium is detected by precipitating its sulphate by K2SO4, which gives a basic salt insoluble in water and hydrochloric acid. Its spectrum is characteristic. URANIUM. Stmbol, U. — ^ Atomic Weight, 239.8. 334. Uranium occurs in pitch blende, UgOg, and is prepared in the wet way, or by fusing its chloride with potassium. This is a hard, grayish-white metal, which also burns in the air. The black oxide, U2O5, is used for painting on porcelain. The uranium salts are fluorescent, and impart this property to " canary" glass. Uranium is detected by its giving to the microcosmic bead in the oxidizing-flame a yeyow color when hot, green when cold ; when farther heated the color is darkened. The spectrum of uranium is distinctive. TANTALUM. — KIOBIUM. — VANADIUM. 307 TANTALUM. Symbol, Ta. — Atomic Weight, 182. 335. Tantalum occurs together with many of the rare metals previously noticed, but more especially with niobium, from which metal it has not been separated. Tantalite, Columbite, Pyrochlor, Yttrotantalite, Pitch Blende, and many other minerals contain small quantities of this metal. Tantalum has not been obtained pure. It is detected by converting the compound into tantalic acid, and adding potassium ferrocyanide to its solution ; this yields a yellow precipitate. The conversion is effected by heating the compound with carbon in a current of chlorine to obtain the chloride TaClj ; this chloride, when mixed with water, yields the acid HTaOs. A solution of nut-galls gives a yellow precipi- tate with solutions of this acid. NIOBIUM. Symbol, Nb. — Atomic Weight, 94. 336. Niobium occurs with Tantalum, and is prepared by passing the vapor of its chloride and hydrogen through a red- hot porcelain tube. It is a steel-gray metal, burning easily in the air. Niobium is detected similarly to tantalum, the precipitate with KiFeCye being brown ;' with nut-galls solution, orange-red. VANADIUM. Symbol, V. — Atomic Weight, 51.5. 337. This metal occurs in Vanadanite, 3 Pb3(V04)2 + PbCla, and is prepared as a grayish powder by heating its chloride in hydrogen. 308 VAKADIUM. Vanadium bronze, or metavanadic acid, is now used in place of gold bronze for gilding. Vanadium is detected by placing a strip of zinc in a solution of vanadium chloride ; the solution turns blue. When hj-drogen dioxide and ether are added to the solution of a vanadate, the solution turns red. General Note. Observe those formulae like Co(Ni, FejASj; these do not signify that both Ni and Fe are present, but that one or the other is found in such a compound. CHAPTER XVIII. THE POTJKTH GROUP METALS. 338. The fourth group metals are commonly known as the Metals of the Alkaline Earths. Their chlorides, hj'droxides, and sulphides are soluble in water, acids, and alkalies. In the course of analysis they are precipitated as carbonates by ammonium carbonate, (NH4)2C03, in the presence of ammonia and ammonium chloride. We must except magnesium, however, from the above statement, since its carbonate is soluble in ammonium compounds. It is best to filter out the precipi- tates obtained by ammonium carbonate, and to precipitate the magnesium from the filtrate by means of di-sodium phosphate, NajHPOi. THE EOXJETH GROUP METALS ARE: — / Barium, Ba. Division A < Strontium, Sr. Division B | Magnesium, Mg. ' Calcium, Ca. These metals oxidize easily in the air, and consequently never occur free ; they are strongly basic, hence they are not easily reduced to a metallic state ; they form no acids ; they decompose water to form alkaline hydroxides. 310 BARIUM. BARIXTM. Symbol, Ba". — Atomic Weight, 137. — Specific Heat, . Melting-Point, higher than Cast Ikon. 339. Occurrence. — The most abundant ore of this metal is Heavy Spar, BaS04. Barium also occurs in small quantities in Witherite, or BaCOg, in certain silicates in feldspathie rocks, in seaweeds, and in mineral waters. 340. Preparation. — Barium amalgam is prepared by electrolyzing a thick paste of BaCla and dilute HCl in the presence of mercury. This amalgam is then heated to vaporize the mercury, thus leaving a porous mass of metallic barium. Barium oxidizes rapidly in the air, and burns with great brilliancy. 341. Compounds and Uses of Barium. — Metallic barium is not used in the arts. ITS PKINCIPAi COMPOUNDS AKE : (a) Barium Monoxide, or Baryta, BaO, which is prepared by heating the nitrate until nitrous fumes cease escaping. Barium Hydroxide, or Caustic Baryta, Ba(0H)2, is obtained by moistening BaO with water ; a solution of this hydroxide is used as a reagent known as Baryta Water. Caustic baryta is now largely used in refining cane sugar, which it precipitates from its impure solutions as CisHjjOuBaO. The barium is after- wards removed by treatment with carbon dioxide gas, which precipitates the insoluble compound, BaCOg, while the sugar dissolves. Barium hydroxide is now prepared in large quantities by passing moist carbon dioxide gas through heated barium sul- BARIUM. 311 phide, which gives BaCOj ; this carbonate is then treated with superheated steam, when this reaction occurs : — BaCOa + H2O = Ba(0H)2 + CO2. (6) Barium Chloride, BaCla. This salt is used as a reagent to detect and estimate sulphuric acid ; it is prepared by dissolv- ing barium carbonate, BaCOs, "i hydrochloric acid. "Write the equation. (c) Barium lodate, Ba(I03)2, which is used to prepare iodic acid, HIO3 ; this iodate is prepared thus : — BaCl2 + 2 KIO3 = Ba (103)2 + 2 KCl. (d) Barium Sulphate, or Heavy Spar, BaSOi. This mineral is an important barium ore, used for weighting paper and as a paint. It is prepared for commerce thus : — BaClj + H2SO4 = BaS04 + 2 HCl. (e) Barium Nitrate, Ba(N03)2. This. is prepared thus: — BaC03 + 2 KNO3 = Ba(N03)2 + H2O + COj. It is used in making green fires for tableaux and pyrotechnics. (/) Barium Carbonate, BaCOs, which occurs in nature as Witherite; it is also the group-reagent precipitate, prepared by precipitating a barium salt by means of an alkaline carbonate. It is largely used to prepare soluble barium salts. 342. Tests for Barium. — 1. Solids are fused vrith sodium carbonate, if necessary, and then dissolved in hydrochloric or nitric acid ; this solution gives these pre- cipitates : — (a) With K2Cr20r and ammonia, a yellow precipitate, BaCrOi, insoluble in acetic acid. (6) With H2SO4, a virhite precipitate, BaSO^, insoluble in acids. (e) CaSOi gives an immediate precipitate of BaS04 even in dilute solutions. 312 STRONTIUM. 2. Barium salts tinge the non-luminous flame green. 3. The barium spectrum, although complicated, is readily distinguished by the green lines Baa and Ba^S. STRONTIUM. Symbol, Sb". — Atomic Weight, 87.2. — Melting-Point, a red heat. I 343. Occurrence. — Strontium occurs most plentifully in the two ores, Celestine, SrSOi, and Strontianite, SrCOs. It also occurs in a few mineral waters and in sea-water. 344. Preparation. — This metal is prepared by electro- lyzing its chloride, or by heating this compound with a sodium amalgam ; the strontium amalgam thus formed is then washed, dried, and, finally, ignited in a current of hydrogen. 345. Properties, Compounds, and Uses of Strontium. — Strontium is a yellow, malleable metal, oxidizing in the air, and burning brightly when heated. THE PRINCIPAL STRONTIUM COMPOUNDS ARE: — (a) Strontium Carbonate, SrCOg. This precipitate is ob- tained hj precipitating a strontium salt solution with an alkaline carbonate. (6) Strontium Nitrate, Sr(N03)2. This is prepared thus : — SrCOa + 2 HNO3 = 8r(N03)2 -f-H^O -|- CO^. It is used in producing red fire for tableaux, etc. Material for red fire is best produced by mixing about equal parts of finely pulverized and thoroughly dried Sr(N03)2 and KCIO3 with an CALCIUM. 313 equal bulk of powdered shellac, or with one-fourth part flowers of sulphur ; the shellac is preferable, as it gives off no suffo- cating fumes of sulphur dioxide. Green flre is obtained simi- larly, by using barium nitrate, Ba(N03)2, in place of strontium nitrate. Caution. These ingredients must be powdered separately, and after- wards mixed with a bone knife on paper, since any concussion may pro- duce an explosion. 346. Tests for Strontium. — 1. Most strontium com- pounds, when moistened with hydrochloric acid, impart a beautiful crimson tint to the non-luminous flame. Sul- phates should be reduced to sulphides in the reducing- flame and then moistened with HCl before ignition. Note. When both barium and strontium are present, the strontium color appears when the substance is first brought into the flame. A cau- tion, also, is needed here lest the student mistake the pale yellowish-red flame of calcium for that of strontium. Compare the colors yielded by the pure salts of these two metals. 2. The spectrum of strontium contains the prominent lines : Sra, orange ; Sr/3, red ; and SrS, blue. 3. In the wet way, strontium when precipitated with carbonates, phosphates, and oxalates, resembles barium. It may be separated from barium by precipitating the latter with ammonia and KjCraOr. It may be separated from calcium by precipitating strontium with CaS04. CALCIUM. Symbol, Ca". — Atomic Weight, 40. — Specific Heat, 0.1804. — Melting-Point, a red heat. 347. Occurrence. — The most abundant compound of calcium is the carbonate, CaCOs. This mineral occurs in enormous quantities and widely distributed; uncrystal- 314 CALCIUM. lized CaCOs occurs as limestone and chalk ; the crystal- lized forms are many, such as marble, Iceland Spar, Calc Spar, and Dog-tooth Spar. Shells and corals are chiefly carbonates o£ calcium, while bones and teeth are princi- pally phosphates of this metal. Calcium Sulphate, CaS04, occurs in Gypsum, Anhydrite, and Selenite. Some moun- tain ranges and geological formations are chiefly composed of these calcium compounds. 348. Preparation. — This metal is prepared by electro- lyzing its chloride, or by fusing calcium iodide with metallic sodium in closed iron retorts. 349. Properties, Compounds, and Uses of Calcium. — Calcium is a malleable metal, which oxidizes most rapidly in moist air, and burns with an orange-yellow light. THE MOST TTSEPUL COMPOUNDS OF CALCIUM AEE: — (a) Quick-lime, CaO, prepared by heating the carbonate, CaCOg. Give the equation. Calcium Hydroxide, Ca(0H)2, which is prepared by treating CaO with water. When this substance is in a dry powder or of the consistency of paste, it is called "slaked lime." Why? A saturated water solution of calcium hydroxide, called lime- water, is used as a reagent for detecting free carbon dioxide gas. Slaked lime is used for many purposes, such as for making mortar, purifying illuminating gas, wliitewashing, etc. Mortar consists of sand, three to four parts, and lime, one part, thoroughly mixed with water. Sus. Describe the method of making mortar. (Ask a mason or plasterer, if you do not know.) What is "putty coat" or "hard finish"? Lime containing about ten per cent of silica is known as hydraulic cement or water-lime, and possesses the pecuUar CALCIUM. 315 property of hardening under water. This cement is artificially prepared by mixing finely pulverized burnt clay and limestone. Calcium hydroxide absorbs carbonic acid gas from the air, which fact explains the hardening of the mortar. It may also combine with the silica. Query. Does age improve the hardness of cement or mortar ? Does the cement of the ancient Roman masonry owe its stone-like character to its age or to the process of manufacture '' (b) Gypsum, CaS04 + 2 HjO. This occurs native, and when ground is used as land plaster ; when calcined, it is known as "Plaster of Paris," which is used yi making casts and for filling writing-paper. QuEET. What is the object of the calcining ? Explain the setting of the plaster. (c) Calcium Chloride, CaCls. This substance is prepared by dissolving Iceland spar or pure marble in hydrochloric acid. When fused, it is used as a dryer for gases, owing to its great absorptive power for moisture. (d) Fluor Spar, CaFa, a well-known mineral used in prepar- ing fluorine compounds. (e) Bleaching Powder. This is an article of commerce, and one of the most useful substances known to the arts. It is made by passing chlorine gas into large chambers, on the floors of which slaked lime is spread. It is used in bleaching paper, rags, cotton goods, etc. This powder affords a convenient source of chlorine, which is liberated by the addition of an acid, as sulphuric or hydrochloric acid. QtjEKT. Upon what does the bleaching power of chlorine depend t (/) Superphosphate of Lime is a substance obtained by treat- ing bones with sulphuric acid ; it is used in preparing phos- phorus, and also as a fertilizer. The superphosphate is a mix- ture of calcium sulphate and acid phosphate. (o) Calcium Carbonate, CaCOs, previously mentioned under 316 MAGNESIUM. the carbonates. This substance forms one of the constituents called " hardness'' in drinking-water (see p. 49). When a soap is brought into a hard water, insoluble calcium salts are formed with the organic acids contained in the soap ; hence the peculiar, unpleasant feeling experienced on attempt- ing to wash the hands with soap in hard water. All the cal- cium carbonate in solution must be precipitated before the soap will act in the desired way and form a lather. Iceland Spar, a beautiful crystalline variety, possesses the property of " double refraction." 350. Tests for Calcium. — 1. The volatile calcium salts tinge the flame orange-red. 2. The spectrum shows the green line Cay3 and the orange line Cao, which are distinctive. 3. In solutions, calcium may be separated from barium and strontium by precipitating the latter metals with KjSOi; to the filtrate ammonia and ammonium oxalate, (NH4)2C204, are added; the oxalate gives a white precipi- tate, CaC204, which under the circumstances is distinctive. QnEKT. Is calcium sulphate easily soluble in water ? Try it. MAGNESIUM. Symbol, Mg." — Atomic Weight, 24. — Specific Heat, 0.245. Melting-Point, 750°. 351. Occurrence. — Magnesium ores are found plenti- fully in many localities, among which we notice : Magne- site, MgCOs; Dolomite, CaMg(C03)2; Kieserite, MgS04+ H2O; Carnallite,(Mg,K)Cl2 + 6H20; Spinelle, MgOAlA; Asbestos, (Mg,Ca)Si03; Talc, Mg3H2(Si03)4 ; and Meer- schaum, Mg2H2(Si03)3. Magnesium sulphate also occurs in certain medicinal springs, while the chloride is a constituent of sea-water. MAGNESIXJM. 317 Magnesium limestone is a double carbonate of calcium and magnesium. 352. Preparation. — Magnesium, like calcium, may be prepared by the electrolysis of its chloride, but the com- mercial article is obtained by fusing a mixture of the dry chloride, fluor spar, and metallic sodium in a closed cruci- ble. The metal is afterward purified by distillation, and, when in a semi-molten condition, it is pressed into wires, which are flattened finally into ribbons. 353. Properties, Uses, and Compounds of Magnesium. — Magnesium is a silver-white metal, quite permanent in dry air ; in damp air, however, its surface becomes coated with oxide. It takes fire readily in any ordinary luminous flame, and burns with a painfully bright and dazzling light, which is very rich in chemical rays.- Owing to this important property, magnesium ribbon is now employed in photographing caverns and other objects inaccessible to the sun's rays. This metal is also employed in pyrotechny and signaling. It is further employed in chemical analy- sis, especially in cases of arsenic poisoning, in place of zinc, since magnesium contains no traces of arsenic. THE MOST IMPORTANT COMPOUNDS OF MAGNESIUM ARE THE FOLLOWING: — (a) Magnesia, MgO, which is prepared by igniting the car- bonate, MgCOg. It is used in medicine. (6) Magnesium Chloride, MgCla, is obtained from sea-water and salt springs. It is used in dressing cotton gj)ods. (c) Epsom Salts, MgSOi + 7 H2O, are prepared from Kie- serite, or by treating MgCOg with sulphuric acid. It is used in medicine as a cathartic, and is also used in dressing cotton aroods. 318 KEACTIONS IN GKOUP IV. (d) Magnesium Carbonate, or Magnesite, MgCOj, an ore of magnesium. This is artificially prepared by roasting dolomite, and treating the moistened residue with carbon dioxide gas under pressure ; a bicarbonate is thus formed, which is decomposed by means of superheated steam. This compound as thus formed is a white powder, which is an important article of commerce. It is used in medicine ; also used as a face-powder. 354. Tests for Magnesium. — 1. After removing the metals of the fourth group by ammonium carbonate, etc., di-sodium phosphate, Na2HP04, when added to the filtrate, throws down a white precipitate, Mg]SrH4P04 ; this forms in a dilute solution after stirring the solution with a glass rod for a few minutes. This precipitate, under the circum- stances, is distinctive. Note. The spectrum of magnesium is not a practical test, as it is not very marked at the temperature of the Bunsen flame. 355. Separation and Identification of the Fourth Group Metals. — 1. Make the solution to be tested neu- tral or slightly alkaline, and then remove the metals of Groups I., II., and III. by the usual methods. Save the filtrate, and boil for some time to expel free RS; filter. 2. Add ammonia, NH4CI, and (NH4)2C03 to precipitate barium, strontium, and calcium. Filter out this precipi- tate, and save it to test by 3 ; also save the filtrate, and test it by 4 for magnesium. 3. Dissolve this precipitate in acetic acid. (a) Test a small portion of the solution for barium by adding K'CrjOr and ammonia; a yellow precipitate, BaCr04, indicates barium. If barium be present, thus re- move it from the whole solution. This precipitate may be filtered out and dissolved in hydrochloric acid ; then, EEAOTIONS IN GBOUP IV. 319 upon addition of H2SO4, the insoluble sulphate, BaSO^, will confirm the test. (J) Test a portion of the filtrate from (a) for calcium by Art. 350, 3. (c) Precipitate the calcium and strontium from the fil- trate not used in (6) by means of ammonia and ammonium carbonate. Filter out the precipitate, and dissolve it in HCl, and expel excess of acid ; then add CaSO,. A white precipitate, SrSO^, formed after a few minutes, indicates strontium. Further test this precipitate by 346, 1. 4. To the filtrate from 2 add NasHPO*, and stir for some time with a clean glass rod, if necessary; a white precipitate, MgNHiPOi, indicates magnesium. KBACTIONS IN GROUP IV. (1) CaClj + (NHJ2CO3 = CaCOa + NH^Cl. (2) Sr(N03), + (NHJ.COj = SrCO, + NH^NOj. (3) BaCla + (NHJ^COj = BaCOa + NH^Cl. (4) MgSOj + NajHPO^ = MgHFO^ + NajSOj. (5) CaCOj + H(C,H30,) = CalC^HgO,), + H^O + CO, (6) SrC03 + H(C2H30,) = Sr(C,H30J,+ (7) BaC03+H(C,H302) = (8) Ca(C,H30J, + (NHJ.CA = CaC,0, + (NHJlC^HjOJ. (9) BalC^HjO^jj + KjCr^O, + H^O + NH3 = BaCrO^ + KCjHjOj + (NH,),Cr0,. (10) Ba{C2H302)2 + HjSOi = BaSO, + H(CjH302). (11) BaCl, + K,C0a = BaCO,, + KCl. (12) MgSOj + NajC03 = MgCOs + (13) CaC03 + HCl= + SuG. The student should do much work with the preceding groups ; the quickest way to become acquainted with a substance is to work with it. Unknown solutions give an added zest to the student's desire for mastering processes. CHAPTER XIX. THE FIFTH GKOUP METALS. 356. The metals of the fifth group are known as the " Metals of the Alkalies." They do not yield precipitates with the usual reagents, since the compounds thus formed are soluble; but they are detected by the color which their compounds impart to the non-luminous flames, or by their spectra. These metals are Potassium and Sodium, also the com- pound Ammonium, NH4; the rare metals are Lithium, RuBiBiUM, aifd CESIUM. Of course ammonium is not to be considered a true metal, but its compounds are alkaline, and it behaves much like metals of this group. In distinction from the other or " Fixed Alkalies," ammonium is termed the "Vol- atile Alkali," since most of its salts are volatile. The metals of this group form a natural series ; they are all acted upon by the moisture of the air, and hence they must be kept under naphtha ; all decompose water at ordinary temperatures to form strongly alkaline hydrox- ides; each one forms but one series of salts, many of which are exceedingly stable and useful. Queries. To what group do these metals belong In MendelejefE's Table t "Which belong to the < series '! Does Na or K show the I even more intense action when thrown upon the water ? POTASSIUM. 321 POTASSIUM. Symbol, K'. — Atomic Weight, 39. — Specific Heat, 0.1655(?). — Melting-Point, 62.5°. 157. Occurrence. — The potassium-bearing compounds widely distributed; they occur in mineral waters, sea- ters, and all fruitful soils, and are utilized by plants and mals. Sheep Excrete, through the skin, potassium and ler compounds, termed " Fat " and Suint. These com- inds are of considerable commercial value ; they are ained by the wool, of which, before washing, they con- ;ute nearly one-third part by weight, some potassium compounds are the following minerals : [vite, KCl; Saltpetre, KNO3; Orthoclase, K2Al2(Si308)2; raallite, (KMg)Cl3; and Alum, K2Al2(S04)4 + «4 H2O. (58. Preparation. — Acid potassium tartrate is first ited in closed iron retorts ; in this way, a very intimate iture of potassium carbonate and carbon is obtained, is mixture is then placed in iron tubes covered with y, which are afterwards placed in a furnace, and heated a white heat. Metallic potassium is given off in the m of vapors, which are passed into shallow, TDox-like idensers placed outside the furnace ; in these con- isers they are quickly cooled to a liquid state ; the lid potassium then flows out into vessels containing k oil. (See Fig. 20.) ?'ormerly frequent explosions occurred, owing to the mation of a black substance, KCO; but this trouble low obviated by the shallow condensers, sir Humphry Davy first prepared potassium by electro- ing the moistened hydroxide. This marked a new era 322 POTASSIUM. in chemistry, as the alkalies were previously supposed to be elements ; and, moreover, with the discovery of potas- sium, the discovery of other rare metals became possible. QuEKT. What rare metals are now prepared by the aid of metallic potassium or sodium ■? 359. Properties, Uses, and Compounds of Potassium. — Potassium is a silver-white metal when first cut, but soon afterward exposes a bluish surface. It is brittle at 0° C, and waxy at ordinary temperatures. It ignites at a low heat, — -often while being cut, — and requires the utmost care while being handled; it must be kept under rock oil or naphtha. It quickly decomposes water, liberating hydrogen with such violence that it frequently takes fire and explodes. It dissolves in ammonia, forming a blue solution, from which it may be again obtained unchanged. The princi- pal use of metallic potassium, other than for class demon- stration, is in preparing the rare metals, as previously noticed. THE PEINCIPAL POTASSIUM COMPOUNDS NOT HEEBTO- rOEB NOTICED AKB : — (a) Potassium Hydroxide, or Caustic Potash, KOH. This is prepared by treating potassium carbonate with slaked lime, thus : — K2CO3 +Ca(0H)2 = 2 KOH -f- CaCOs. The aqueous solution thus prepared is evaporated to dryness, fused, and marketed. In this condition, it is extensively used as a lye. It is purified for reagent purposes by dissolving the crude salt in alcohol, and, after evaporation, again fusing and casting it into sticks. It is kept in air-tight bottles, since it has a powerful attraction for carbon dioxide and moisture, and soon POTASSItlM. 323 deliquesces ; neither must it be handled with the hands, since it destroys the skin. SuG. Leech some common wood ashes by passing water through them. Examine the filtrate obtained. (6) Potassium Chloride, KCl, occurs naturally as Sylvite, and in many brines. It is used as a fertilizer and in preparing other potassium salts. (c) Potassium Bromide, KBr. This salt is obtained together with bromate of potassium by dissolving bromine in potassium hydroxide ; the bromate is afterwards decomposed by a gentle heat. It is used in medicine as a sedative, and in the labora- tory as a source of bromine for demonstration. QoEBT. How is Br prepared ? (d) Potassium Iodide, KI, may be prepared in the same way as the bromide. It is used extensively in medicine and for other purposes ; in the laboratory it is a source of iodine for purposes of demonstration and is a reagent. SuG. The potassium salts will be found in the laboratory; let the student examine them, note the forms of the crystals, etc., and write a, description. (e) Potassium Chlorate, KCIO3, is obtained by passing a cur- rent of chlorine gas through a solution of caustic lime until calcium chlorate, Ca (€103)2, is formed ; potassium chloride is then added with the following results : — Ca(C103)2 -f 2 KCl = 2 KCIO3 -f CaCl^. The chlorate of potassium is obtained from this solution by crystallization. This salt is used in medicine for inflammation of the throat, and in the laboratory as a source of oxygen. QuEKT. How is oxygen obtained from KCIO3 ? How may potassium chlorate be prepared from chlorine and potassium hydroxide ? How is KCIO4 prepared ? (See Perchloric Acid.) (/) Potassium Sulphate, KSOt, occurs native, and is pre- pared as a by-product in the manufacture of other potassium 324 POTASSIUM. compounds, as the bichromate, etc. It is used in medicine as a purgative ; it is further used in the manufacture of alum, and in the laboratory as a reagent. An acid sulphate, KHSO4, is obtained in manufacturing nitric acid. SuG. Write the equation. (g) Saltpetre, or Nitre, KNO3, occurs as an incrustation on the soil of some hot, dry climates, as in India and in Egypt, where it is produced by the oxidation of nitrogenous organic substances in contact with the potassium compounds contained in the soil. It has recently been shown that the formation of nitrates which takes place in the soil is caused by minute organisms or fer- ments. The process is similar to the familiar fermentation of sugar, which causes the formation of alcohol and carbon dioxide. It is artificially prepared by treating sodium nitrate, which occurs native in immense deposits, with potassium chloride, thus : — NaNOs + KCl = KNO3 + NaCl ; and also in the so-called "saltpetre plantations." These are constructed by piling up refuse animal matter, mixed with wood ashes and lime, and moistening with urine or stable drainings., At intervals the outer layer is removed, and extracted with water. The term " saltpetre" is derived from the fact that this salt was and is still obtained from certain oily or feldspathic rocks by boiling the weathered rock with slaked lime and potash. Saltpetre is used in the laboratory as a source of nitric acid for demonstration, as an oxidizing agent (substances are fused with KNOg for this purpose), and in preparing cooling mix- tures. Query. How are freezing mixtures prepared 1 Explain the philoso- phy of the process. POTASSIUM. 325 111 domestic economy, it is used as a preservative of meat ; but the most important purpose for which nitre is used is in manufacturing gunpowder. Gunpowder consists of an intimate mixture of nitre, sulphur, and charcoal, in somewhat varying proportions. Sporting pow- der consists of niti'e, 78.99, sulphur, 9.84, and charcoal, 11.17 parts. The explosive force of gunpowder depends upon the fact that it contains within itself the necessary amount of oxy- gen for its own combustion, whereby large volumes of heated gases (principally carbon dioxide and nitrogen) are liberated. Query. What effect has the invention of gunpowder had on civiliza- tion ■! Give the philosophy of explosions in general. (h) Potassium Carbonate, or Potash, KjCOs, is usually ob- tained from wood ashes. The ashes are lixiviated or "leached," and the lye thus obtained is evaporated till the solution is satu- rated, when impure crystals of the carbonate are deposited. These crystals are purified by roasting in a reverberatory furnace. Other sources of potash are potassium sulphate, beet-root ashes, and suint. Potassium carbonate is used in preparing other salts, as potassium cyanide, chromate, acetate, etc., and as a reagent. An acid salt, KHCO3, is prepared by passing a current of carbon dioxide gas through a solution of the normal carbonate. (i) Potassium Cyanide, KCN or KCy, is an important com- pound, used in the laboratory as a reducing agent ; also used in photography, and as a solvent for silver sulphide or oxide. It is prepared by heating the ferro-cyanide with the carbo- nate to a red heat in iron crucibles, thus : — K4Fe(CN)g + K2CO3 = 5 KCN -|- KCNO + CO^ -f- Fe. The chemically pure cyanide is prepared by passing hydrocyanic acid gas into an alcoholic solution of potassium hydroxide. (_;■) There are other potassium salts in which the metal is 326 SODIUM. combined with organic acids, and some of which are used in the laboratory. The student will notice the tartrate, oxalate, and acetate. 360. Tests for Potassium. — 1. Potassium compounds, on the platinum loop, color the Bunsen flame violet ; but the presence of sodium obscures this test, hence it is neces- sary to observe the flame through thick cobalt-blue glass, which shuts off the sodium rays but transmits the potas- sium color. Note. Always thoroughly clean the wire before testing. 2. The spectrum furnishes two easily distinguished lines, — Ka in the extreme red, and K/3 in the violet. 3. Potassium salts, iu concentrated solutions, and in the absence of all non-alkaline bases, yield, with tartaric acid, a white, distinctive precipitate, KHC4H4O6, this is granular- crystalline, and may be tested further by 1. SODIUM. Symbol, Na'. — Atomic Weight, 23. — Specific Heat, 0.2394. — Melting-Point, 95.6°. 361. Occurrence. — The cliief and most plentiful sodium compound is common salt, sodium chloride, NaCl. Salt occurs in sea-water, most mineral waters, and drinking water, while traces of it are to be found in nearly all river waters. In some localities in the United States — as at Syracuse, N.Y., and the Saginaw Valley, Mich. — salt water or brine is found in vast reservoirs at a considerable depth below the surface of the earth. Wells are sunk iu such localities, and the brine is raised to the surface by pumps, and utilized as a source of the salt used in com- merce. Again, large beds of native salt or rock salt occur in various localities. SODIUM. 327 Another source of sodium is the native nitrate, NaNOg, or Chili saltpetre, which occurs in beds in Chili and Peru. A large tract of territory in the western United States is known as the Alkali Plains, owing to the occurrence of sodium compounds: the water and the very earth itself are saturated with alkali to such an extent that but scant vegetation grows, and, with the exception of one or two species of worms, the waters of the lakes, although clear as crystal, are uninhabited. Fig. 20. A is the iron tube retort coated with clay. C is the condenser. D is the cup containing rock oil. In its distribution, sodium is the most persistent and universal of all the metals ; indeed, it is nearly impossible to find a compound that will not yield the sodium test. 362. Preparation. — Sodium is prepared precisely like potassium, excepting that the carbonate and charcoal, instead of the tartrate, are employed. It is somewhat 328 SODIUM. more easily obtained, however, and no explosive compound is formed. Fig. 20 will give a good idea of the furnace employed in obtaining metallic sodium and potassium. After the condenser is filled with the metal, it is taken off and put under rock oil, after which the metal is scratched off. 363. Properties, Uses, and Compounds of Sodium. — Sodium is a light, silver-white metal which oxidizes readily in damp air. It does not act upon water with as much violence as potassium, but it will take fire when thrown upon hot water, starch paste, or wet paper. Queries. What purpose does the starch paste serve 1 Explain the phenomenon of sodium burning on hot water. What metals are obtained by the aid of metallic sodium ? SODIUM POEMS MANY USBFUIi SALTS, OF WHICH WB NOTICE THE FOLLOWING: — (a) Sodium Hydroxide, or Caustic Soda, NaOH, is prepared on the large scale by decomposing sodium carbonate with slaked lime, thus : — Ca(0H)2 + Na^COa = 2 NaOH + CaCOa. The aqueous solution is then treated precisely in the same man- ner as caustic potash. Caustic soda is also prepared in large quantities from the red liquors from which the black crystals obtained in the soda-ash process are deposited. QuEKiES. When metallic sodium acts on water, is NaOH obtained ? Try it. How can you decide what this substance is ? The principal use of caustic soda is in soap making. In the laboratory it is a useful reagent. (&) Sodium Chloride, or Common Salt, NaCl, is obtained from various sources, as previously indicated. The strong brine of the salt wells is evaporated in shallow tanks by the aid SODIUM. 32 ) of steam until the salt crystals are deposited. Salt is obtained from sea-water by allowing it to flow into large, shallow pans or vats called "salterns," where it is evaporated through the agency of the wind and sun. Sua. Student mention the many uses of common salt. (c) Sodium Nitrate or Chili Saltpetre, NaNO,, occurs in vast deposits in Peru and Bolivia, and is now used as a source of nitric acid and as a fertilizer. QuEKiES. What other use of NaNOj was me^ptioned above under potassium 1 What element is obtained from Chili saltpetre ? (d) Acid Sodium Hyposulphite, NaHS02, is obtained by treating a solution of sodium hydrogen sulphite, NaHSOa, with granulated zinc. It is used by dyers and calico printers to reduce indigo, and in the laboratory for estimating free oxygen quantitatively. (e) Sodium Sulphate, NajSOi, with some admixture of the acid sulphate, NaHSO^, is prepared in the first stage in the manufacture of soda or sodium carbonate. It is known as "salt-cake." (/) Sodium Thiosulphate, Na2S203 + 5 HjO, is used as an antichlor by paper manufacturers, and in the photographic proc- ess for dissolving out the unaltered silver salts. It is prepared by boiling caustic soda with sulphur, and then passing sulphur dioxide gas until the yellow solution obtained is decolorized. Its solvent action on silver salts is due to the formation of a double salt of sodium and silver, NaAgSjOj : — Na^SA + AgCl = NaAgSA + NaCl. (g) Sodium Hypophosphite, NaHjPOz, is prepared by adding calcium hypophosphite to a solution of sodium carbonate. The filtered solution is then evaporated in vacuo. It is used in medicine. (h) Disodium Phosphate, NajHPO^, is used in medicine as a mild cathartic, and in the laboratory as a reagent. It is pre- pared by treating phosphoric acid with sodium carbonate. 330 SODIUM. {i) Sodium Carbonate, Na2C03, is the chief product of soda- ash manufacture. Soda-ash is a mixture of the carbonate and hydroxide. The normal carbonate is used as an indispensable reagent in dry reactions in the laboratory. The manufacture of soda-ash is a great industry by itself. The English process is thus described by Eoscoe : — "This substance, known in commerce as soda-ash, is manu- factured in England on an enormous scale, and used for glass making, soap making, bleaching, and various other purposes in the arts. Formerly it was prepared from barilla or the ashes of sea-plants, but now it is wholly obtained from sea-salt by a series of chemical decompositions and processes, which may be divided into two stages : — "1. Manufacture of sodium sulphate, or salt-cake, from sodium chloride (common salt) ; called salt-cake process. " 2. Manufacture of sodium carbonate, or soda-ash, from salt-cake ; called soda-ash process . "1. Salt-Oake Process. — This process consists in the decomposition of salt by means of sulphuric acid. This is effected in a furnace called the Salt-Cake Furnace. Fig. 21 shows the section of such a furnace. This is drawn to a scale from one actually in use. It consists of (1) a large covered iron pan, a, placed in the centre of the furnace, and heated by Are placed underneath ; and (2) two roasters or reverberatory furnaces, dd, placed one at each end, and on the hearths of which the salt is completely decomposed. The charge of half a ton of salt is first placed in the iron pan, and then the requisite SODIUM. 331 quantity of sulphuric acid allowed to run in upon it. Hydro- chloric acid gas is evolved, and escapes through a flue, e, with the products of combustion into towers or scrubbers filled with coke or bricks moistened with a stream of water. The whole of the acid vapors are thus condensed, and the smoke and heated air pass up the chimnej'. By recent act of Parliament, the alkali makers are compelled to condense at least 95 per cent of the hj'drochloric acid gas they produce ; and so perfectly is this condensation as a rule carried out, that the escaping gases do not cause a tui-bidity in a solution of silver nitrate, proving the absence of even a trace of the acid gas. After the mixture of salt and acid has been heated for some time in the iron pan, and has become solid, it is raked on to the hearths of the furnaces at each side of the decomposing pan, where the flame and heated air of the fire complete the decomposition into sodium sulphate and hydrochloric acid. Fig. 22. "2. Soda- Ash Process. — This process consists (1) in the preparation of sodium carbonate, and (2) in the separation and purification of the same. The first chemical change which the salt-cake undergoes in its passage to soda-ash is its reduction to sulphide, by heating it with powdered coal or slack : — Na3S04 -I- C4 = NaaS + 4 CO. The second decomposition is the conversion of the sodium sulphide into sodium carbonate, by heating it with chalk or limestone (calcium carbonate) : — Na^S -t- CaCOa = NasCOa -j- CaS. These two reactions are in practice carried on at once, a mixture 332 SODIUM. of ten parts of salt-cake, ten parts of limestone, and seven and a half parts of coal being heated in a reverberatory furnace called the Balling Furnace (shown in section in Fig. 22) until it fuses and the above decomposition is complete, when it is raked out into iron wheelbarrows to cool. This process is gen- erally termed the black-ash process, from the color of the fused mass. " The next operation consists in the separation of the sodium carbonate from the insoluble calcium sulphide and other impuri- ties. This is easily accomplished bj- lixiviation, or dissolviug the former salt out in water. On evaporating down the solu- tion, for which the waste heat of the black-ash furnace is used, the heated air passes over an iron pan (see 6, Fig. 22) contain- ing the liquid. On calcining the residue, the soda-ash of com- merce is obtained." Ammonia Process. — Another process for converting sodium chloride into sodium carbonate is now used extensively. It consists in treating a solution of sodium chloride with ammonia and carbon dioxide : — NaCl + NH3 -I- HoO + CO2 = NaCl -f NH^HCO™. The acid ammonium carbonate acts upon the sodium chloride, forming acid sodium carbonate, NaHCOj, which is difficultly soluble and is deposited : — NaCl + NH.HCOg = NH4CI + NaHCOj. The acid carbonate is heated and thus converted into the neu- tral salt : — 2 NaHCO, = CO2 -f H,0 + Na^COs ; and the carbon dioxide given off is used for the purpose of satu- rating the ammonia contained in the original solution. The ammonium chloride obtained in the second stage of the process is decomposed either by lime, CaO, or magnesia, MgO, and the ammonia thus recovered. This process is also known as SODIUM. 333 the Solvay process, as its introduction is due to the exertions of M. Solvay. Soda Crystals, or Sal Sodae, much used in softening hard water, are obtained by dissolving soda-ash in water, and allow- ing the crystals to deposit from a saturated solution. These crystals possess the formula NajCOs +10 H2O. Acid Sodium Carbonate, NaHCOs, can be obtained from soda crystals by allowing them to be acted upon by CO2 gas. This substance is known as Bicarbonate of Soda, and is employed in medicine and for preparing effervescing drinks. In domestic economy it is used as Saleratus and as an ingredient of Baking Powder. (/) Silicates. Glass is a silicate of calcium and either sodium or potassium. Ordinary glass contains sodium. The diflflcultly fusible Bohemian glass contains potassium. For some purposes, lead is introduced instead of calcium. Glass made in this way, having a high refractive power, is very use- ful for optical purposes. Ordinary glass is made by melting together quartz and quicklime or calcium carbonate and sodium carbonate. (Jc) Many other salts of sodium may be obtained in the shops, and are very useful in preparing test solutions, especially when the student is working for acids in the non-metals. 364. Tests for Sodium. — 1. Sodium compounds color the non-luminous flame intensely yellow, and this color is obscured by the blue glass. Note. Any substance, as dirt on the platinum wire, will give this test for sodium. Therefore, clean the wire carefully, and convince yourself that the color is not caused by the ordinary impurities. Try some known sodium compound till you recognize the flame. 2. The sodium spectrum gives two intense lines in the yellow which lie so close that they often seem but ono. They coincide with Fraunhofer's D lines in the ?olai spectrum. 334 AMMONIUM. AMMONIUM. Symbol, NH4. — • Molecular "Weight, 18. 365. When sodium amalgam containing one to three per cent of sodium is thrown into a strong solution of ammouium chloride, a curious spongy substance is formed, which gradually rises in the vessel, filling a large amount of space. It is very unstable, giving off ammonia and hydrogen, and leaving metallic mercury. This substance, according to the most careful examinations, contains nitro- gen and hydrogen in the proportions indicated in the for- mula NH4, and this is simply in, combination with mercury. As this group plays the part of a metal in the salts obtained from ammonia and the acids, — as in (NH4)C1, (NH4)N03, (NH4)2S04, etc., — it is called ammonium, and the compound with mercury, ammonium amalgam ; hence, further, the salts obtained with ammonia are called ammo- nium salts. The metal ammonium, NH4, is, however, hypothetical. OF THE AMMONIUM SALTS "WE NOTICE: (a) Ammoniuvi Chloride, or Sal Ammoniac, NH4CI, which occurs as a natural deposit, but is now prepared from the ammoniacal liquors of gas works. The ammonia gas is liber- ated from the gas liquors by adding slaked lime, and is led into a dilute solution of hydrochloric acid, from which this salt is obtained by evaporation ; the chloride is afterwards purified by sublimation. This salt is used as a reagent and as a source of ammonia in the laboratory, and as an important aid in solder- ing, welding, etc. (6) Ammonium Nitrate, NH4NO3, is used as a source of Laughing Gas or Nitrous Oxide, and can be prepared by neu- tralizing nitric acid with ammonia. THE EAREE METALS OF THE FIFTH GEOtJP. 335 (c) Sodium -Ammonium Phosphate, or Microcosmic Salt, HNaNHiPO^ + 4 HjO, is much used in blow-pipe work, since it forms a colorless bead on the platinum wire, and receives a color by adding certain substances. It is formed by the decom- position of urine, and is artificially prepared by dissolving five parts of sodium phosphate with two parts of ammonium phos- phate in hot water, and allowing the solution to cool. (d) Ammonium Carbonate, (NH4)2C03, is used as a group reagent, and is now prepared by subliming CaCOs with ammo- nium sulphate, and digesting the product formed with strong aqua ammoniae. (e) Ammonium Sulphide, (NH4)2S, is used as a group reagent, and is very unstable, passing into (NH4)2Sx upon exposure. This reagent is readily prepared in the laboratory when needed by passing a current of hydrogen sulphide gas into aqua ammoniae until the solution will not precipitate mag- nesium sulphate. 366. Tests for Ammoniuiu. — The tests for ammonium have already been given (Art. 55), and it only remains to add that, in the course of analysis, although the ammo- nium salts remain in the fifth group, it is necessary to apply these tests directly to the original solution. THE KARBR METALS OF THE FIFTH GEODP. UTHIUM. Stbibol, Li'. — Atomic "Weight, 7. 367. Lithium is a rare metal which is found in Lepido- lite, Triphylline, (Li,Na)8P04-f(Fe,Mn)8P04, and some other minerals. This metal occurs in most surface waters and in many mineral waters, and easily finds its way into the animal and vegetable kingdoms. 336 RTTBIDIUM. — CESIUM. It is prepared by electrolyzing its chloride, and is a silver-white metal, readily oxidizing in the air. The principal salt is the carbonate, which is used in medicine. The chloride, nitrate, sulphate, etc., can be prepared by treating the carbonate with the proper acid. QuEET. Why are the carbonates of the metals chiefly employed In preparing the rarer salts f 368. Tests for Lithium. — 1. Lithium compounds color the flame intensely crimson ; this color is obscured only by very thick blue glass. 2. The spectrum of lithium affords a certain test, yielding the bright-red line, Lia, and the weak yellow line, hij3. RUBIDIUM. Symbol, Rb'. — Atomic "Weight, 85. 369. Rubidium is prepared like potassium, which metal it closely resembles. It is widely distributed, but occurs only in very minute quantities. It is found in Lepidolite, Triphylline, Mica, Orthoclase, and other minerals, as well as in various waters and soils. Rubidium is detected by its coloring the flame some- what more red than potassium, but more certainly by its spectrum, which yields two violet lines, Rba and Rb/3. CSiSIUM. Symbol, Cs'. — Atomic Weight, 133. 370. Caesium is the first metal discovered by the spectro- scope, and occurs with the other alkali metals. It has not been prepared, but its salts are known. Ccesium is detected by its spectrum, which yields the bright-blue lines, Csa and Cs;8. DETECTION OP THE FIFTH GROTTP METALS. 337 371. Detection of the Fifth Group Metals. — 1. Test the original solution for ammonium. 2. Free the solution from the first four groups (magne- sium excepted) by adding NH3, NH4CI, and (NH4)2COs; Ae filtrate is to be tested for Na, K, and Li ; accordingly,' evaporate the solution nearly to dryness, and proceed thus : — (a) The sodium flame is to be observed by the naked eye, and is intensely yellow. Note. Remember that traces of sodium are usually present. (J) Sodium obscures the violet potassium flame, but the potassium flame becomes visible when observed through the blue glass which shuts ofl^ the sodium color. («?) The lithium flame is readily determined by its crim- son color. It is obscured only by very thick blue glass. The lithium flame is visible even when Na and K are present. Geuhral Note. The student is not to infer that the analytical grouping of the metals or the numbering of the groups is otherwise than purely arbitrary. Many different groupings can be made, depending upon the reagents employed in the course of analysis. The following table will enable the student to compare the grouping and numbering used in this book with those used by Eresenius : — I K,Na, NH4,Li V. II Ba, Sr, Ca, Mg IV. m Al, Cr. ) jjj^ rV....Zn, Mn, Ni, Co, Fe... 5 V ( Ag,Hg,Pb I. Bi, Cu, Cd ) jj VI As, Sb.Sn... The Roman numerals in the first column indicate the groups given in Fresenius. 372. To Analyze an Unknown Solution. — In making a complete qualitative analysis of an unknown solution, it 338 TO ANALYZE AN UNKNOWN SOLUTION. is desirable to proceed by a methodical plan. From what has preceded, it is evident that the first step should be to determine the bases ; this may be accomplished as indi- cated in the following table. When we know what bases are present, we are then prepared to determine the acids. In case we obtain arsenic, chromium, manganese, etc., we know that these elements are apt to be present as acids. Accordingly we first try for tbe acids formed by those elements. In case these elements are not present, we remove the bases by E (as explained farther on), and then test for acids as in Art. 227. The solution may contain a salt of : - 1. Pb, Ag, or Hg' 2_ llg, Cd, Pb, Cu, Bi, As, Sb, Sn 3. Fe, Cr, Al, Zn, Mn, Ni, Co.... 4. Ba, Sr, Ca, Mg 5. K, Na, NH^, Li The precipitates : — ^ K- - + HCl = ?^, ^g^^ , Hg,Cl,, _|_ J Solutions of 2, 3, 4, white white white and J Filter out the precipitate, and proceed by Art. 247. Treat the filtrate by B. Filtrate from A : 2. Hg, Cd, Pb, Cu, Bi, As, Sb, Sn 3. Fe, Cr, Al, Zn, Mn, Ni, Co.... 4. Ba, Sr, Ca, Mg S. Na, K, NH,, Li The precipitates : — +H,S = As,Sa _ Sb,Sa, Sb.,S, SnS SnS, FbS yellow orange i J^iA, iili§_, CdS ^ HgS ( Solut [ black black' yellow' black I 3, 4, brown yellow black HgS ( Solutions of and 5. Filter out the precipitate, and proceed by Art. 278. Boil the filtrate to expel H^S, and add a little HNO3, and boil a short time to oxidize ferrous to ferric salts, and then proceed by C. TO ANALYZE AN UNKNOWN SOLUTION. 339 c. Filtrate from B : — The precipitates : — - Fe, Cr, Al, Zn, Mn, Ni, Co.... Ba, Sr, Ca, Mg Xa, K, NH^, Li + NH3 + NH,C1 = ZM^lIo , Cr,(OH)e Al,(OH)e ^ reddish brown bluieli green white gelatinous Solutions of Zn, Mn, Ni, Co, 4, and 5. Filter out these, precipitates.^ and proceed by Art. 303. (To the filtrate ) + (NHJjS = i^, ^, ^^^^ ZnS flesh col. black black white Solutions containing 4 and 5. Filter out this precipitate, and proceed by Art. 321. Boil the filtrate to expel H2S, and proceed by D. D- Filtrate from C : — The precipitates : — 4. Ba, Sr, Ca, Mg ' ' ^^^^^^| + NH3+NH,CH(NH,).CO.,=M3,^,^ + Mg and 5. Filter out these precipitates, and proceed by Art. 856. Divide the filtrate in two parts; to one of these parts add Na^HPOj: . MgNH^PO, precipitate, ^^ite ' Test the second part by Art. 371 for 5. Test for acids by E. E. 1. If the solution contains arsenic, chromium, or manganese, etc., test the solution for the acids formed by these elements. 2. When the solution contains only the metals of the fifth group, test the original solution directly for acids, following the directions under Art. 227, and as given under each acid in the non-metals. 3. When other metals, not acid forming, are found, it is best to make the solution neutral with KOH, and then to add KjCOj to precipitate them. Filter out the precipitate, and test the filtrate. In case calcium super- phosphate be present, the phosphate will be found in the precipitate. Now, since we have added a carbonate, the filtrate contains the added carbonate. In consequence of this, we must test the original solution for carbonates. Before proceeding as in Art. 227, it is best to remove the added carbonate by means of HCl ; in this way we get a solution which 840 TO ANALYZE AN UNKNOWN SOLUTION. may be tested for all the non-metallic acids excepting HCl. We may pre- pare another portion of the filtrate containing the added carbonate by adding HNOj ; this solution is to be tested for HCl. Test for some Organic Acids given under F. 1. Tartaric Acid, 112(0^11405), is detected by adding AgNOj to the nor- mal solution ; a white precipitate is thrown down, which turns black on boiling. And further, when tartaric acid is ignited, it gives oH the odor of burnt sugar. CaClj gives a white precipitate, Ca,(Cfifi^), soluble in cold solution of KOH. 2. Acetic Acid, H(C2H302), forms a red solution with re2Clj, which is not decolored by adding HgClj, while red KCyS solutions with FejClg are thus decolored. Also, when warmed with sulphuric acid and a little alcohol, acetifc acid gives off the odor of acetic ether. 3. Citric Acid, H3(CsH50,), gives a white precipitate with AgNOg, which does not blacken on boiling; also it gives a white precipitate with lead acefete. Further, concentrated nitric acid produces from it acetic and oxalic acids. 4. Oxalic Add, 'RJ^jdi^ is decomposed into CO2 and CO by H2SO4. When treated with CaClj, the oxalates give a white precipitate, soluble in HCl, insoluble in acetic acid. (See Art. 227.) APPE]^DIX. APPEI^DIX. THE LABORATORY. 1. The Room selected for the chemical lahoratory should be dry, well lighted, and well ventilated. Generally an upper room is preferable to a basement ; basements are apt to be damp, and poorly lighted, and the laboratory fumes are not so easily restrained from diffusing them- selves through the building ; with proper precautions, however, little or no inconvenience will arise from the use of a dry, well ventilated basement room. It is desirable that the rooms devoted to chemistry and physics should be adjacent to each other, as many pieces of apparatus will illustrate portions of both studies. If communication between the two rooms can be secured by sliding doors, so much the better ; this arrangement offers many advantages in those schools where chemistry and physics are taught by the same teacher. In case the rooms cannot be adjacent, they should be as near together as possible. GENERAL FIXTURES. In case the building is heated by steam, and lighted by gas, many of the general fixtures are easily provided. 2. The Condenser for procuring distilled water may be connected directly to the steam-pipes used in heating the building. A plain sheet copper cylinder 30'='" in diameter, and 135""° high, will afford all the distilled water thirty students will require : this cylinder simply needs a faucet at the bottom, through which the water may be drawn when needed, and a small pet-cock at the top, through which the air is to be blown out when the steam is first turned on. The steam is admitted at the top of the cylinder which stands upright, and which needs no internal coil nor external jacket. The cylinder should be able to carry all the pressure that the boilers are likely to put upon it, and it may stand in any convenient part of the room, as no hissing or other disagreeable noise is heard. 344 APPENDIX. In case the building does not contain steam, permission may be obtained from some factory or mill to connect such a condenser to the boilers used there. The connecting pipe should be as small as possible, and the steam should be allowed merely to leak through the valve, by means of which the condenser is shut oH from the boiler. Many other devices are to be had, some of which are applicable under one condition, while under other conditions another device may succeed more satisfactorily, e.g. Small quantities of distilled water are to be had by means of a Liebig condenser, in connection with a still heated by a' gasoline stove, or by kn ordinary stove ; a coil may be passed through a cask containing cold water, etc., etc. One fact should be noted here ; ordinary rain-water, and water as usually prepared by distillation, usually contain tree ammonia. Water free from ammonia may be obtained as explained in App. 77. 3. The Tank for Wash-Water may be placed in a corner of the room, and its bottom should be four or five feet higher than the faucets from which the water is drawn. Pipes leading from the tank may carry the water to a sink and to each student's desk. Pure cistern water is best for ordinary washing purposes in a labor- atory ; the water may be raised to the tank by a force-pump, or a cistern may be constructed under the roof of the building. 4. A Gas Chamber is useful for many purposes. It may be built of sash with glass, and it may stand in any convenient place, so that it may be connected to a good ventilating shaft. By means of such an arrange- ment, the operator can observe what is taking place, and the unwhole- some gases generated are carried out of the building. It is convenient to have two or three separate apartments not in communication with one another, and each one with a separate door. The size of such a chamber will depend upon the requirements of the school, but one 3 ft. square X 6 ft. high will answer for most small laboratories. 5. Cases for chemicals, apparatus, etc., are convenient and inexpen- sive. It is desirable to have a portion of the case provided with sash doors, and the remainder is to be cased with panel doors, thus providing dark closets in which stock chemicals and reagents may be kept to better 6. Working Tables may be placed against the walls of the room, or through its centre. A table 15 ft. long, 3 ft. 1 in. high, and 3 ft. 4 in. wide, and standing from the walls, will afford ample room for eight APPARATUS FOR STUDENT'S DESK. 345 students to work at a time. If the class be divided into two working divisions, such a table will accommodate sixteen students, while the apparatus per student will thereby be materially lessened. In the centre of the table are placed four desks, while sink-bowls are placed between. One side of such a desk is shown in the Frontispiece ; this cut is taken from the photograph of a desk in Ypsilanti High School Laboratory. In the table just under the desk is a drawer, used by the student to keep his apron and other personal property which he requires in his work. The tables may be supported by legs or by square posts ; in the latter case, cupboards may be constructed under the tables ; but in case cup- boards are made, a bottom or an extra floor should be put in, so that the base-board under the doors may not form an obstruction in sweeping out any dust, etc., that may collect in the cupboard. The dimensions of the desk shown are as follows : Height, 2 ft. 4 in. ; length, 2 ft. 6 in. ; breadth at bottom, 14 in. ; at top, 12 in. ; space under- neath first shelf, 11 in. ; second space, 8 in., and third space 6 in. The top of the desk may be utilized as a shelf. A partition through the desk divides it into halves, thus forming two working cupboards, one on each side of the desk. The gas chamber, tables, desks, and cases, can be made by any car- penter. APPARATUS AND REAGENTS. In considering the materials under this heading, it will be convenient to follow the order : — (a) Apparatus for the student's desk ; (b) Reagents for the student's desk ; (c) Reagents for the side table ; (d) Working material; (e) General apparatus for the laboratory. APPARATUS FOR THE STUDENT'S DESK. Perishable apparatus, such as glass and porcelain ware, should be kept in stock in order to supply quickly any loss by breakage, etc. 7. Test-Tubes. — At the start the student should have twelve 4-in. test- tubes, and two 8-in. test-tubes of a larger diameter. The latter are to be fitted with rubber stoppers pierced with one hole, through which is inserted a bent delivery-tube ; they are used as generators. Test-tubes are perishable, but they are not expensive. A liquid may 346 APPENDIX. be heated in a test-tube by placing the tube directly in the Bunsen or alcohol flame, provided the flame does not strike the tube at the upper level of the liquid. When heating a substance in a test-tube, the student should never hold the mouth of the tube towards himself nor towards others, since any explosion, as of steam or other gases, might result seriously ; it is best to move the test- tube gently through the flame when heating any substance. With a little practice the student may mend a test-tube, the bottom of which has been broken. To accomplish this, the tube is first to be cleaned and dried ; the broken end is then strongly heated in the Bunsen flame until the glass becomes soft; the broken edges of the tube are now forced ' together by means of a bit of glass tubing ; when the bottom is closed, the end of the tube is freed from unnecessary material by carefully draw- ing out the highly heated end of the tube with the glass rod ; the end of the tube is now strongly heated until it becomes somewhat thicker than the walls of the tube ; now the mending is to be finished by blowing gently into the tube, in order to give the end a rounded form. When heating the tube, it should be rolled over constantly in the flame, so that all sides may be heated alike. An alcohol or gas blast-lamp may be used to good advan- tage for this work, and for such other glass-work as usually must be done in the laboratory. 8. Hard Glass Tubing. — Each student should have a tube 8 in. long, and with a bore of about \ in. ; this is used for heating solids as in Exp. 3 p. ■A hard glass test-tube has been mentioned in the text. These are more expensive than ordinary test-tubes ; f of most purposes mentioned a com- mon tube may be used, but it is almost invariably ruined ; this is of no great moment, however, if a tube that has been mended is employed. 9. A Test-Tube Rack for holding test-tubes is shown in the Frontis- piece. The student can make this for himself by taking a suitable block of wood and setting in one edge of it a row of wooden pins 3 in. high ; in the other edge holes are bored, which will serve to hold tubes containing liquids. 10. A Test-Tube Swab for washing out test-tubes is also to be made by the student. It is simply a wooden stick as large as a lead-pencil, upon the end of which a bit of sponge is fastened. Test-tube brushes of various designs are also to be had in the market, but the swab will answer for nearly every purpose. 11. A Glass Stirring-Rod may be made from suitable solid glass rods AJPAKATUS FOR STUDENT'S DESK. 347 which are to be kept in the laboratory. This rod should be about as large and long as a common slate-pencil. The ends of the rod must be melted smooth and round in the Bunsen flame. 12. Platinum Wire and Platinum Foil are much used. The wire should be about 3 in. long, and one end of the wire should be fused into a short glass tube ; the other end of the tube should be closed. The plat- inum foil may be about 1 in. X i in. The uses of these articles are described in the text in the appropriate places. 13. A Blo-VF-Pipe of the form shown in the Frontispiece (Bp), known as Black's, is the best of the cheaper forms. A blow-pipe should last many years. 14. Steel Tongs (T in Frontispiece) are useful to handle hot evap- orating dishes, hot crucibles, etc. The student may readily hold a test- tube while boiling solutions, etc., by putting a narrow strip of cloth around the upper end of the tube and clasping the ends of the strip in these tongs. These tongs should last five or six years. 15. Funnels are shown in Fn ; these are of glass. The student should have two, — one 2 in. and one 3 in. or 4 in. in diameter. The fun- nels should have their stems ground off at an acute angle to facilitate the process of filtration. Funnels are seldom broken. 16. FUter-Papers should be cut round, and should be furnished the student in packages. The proper size papers for the funnels are 4 in. and 6 in. in diameter. These papers should be kept in a tin box of prope- form and size. The filter-papers are placed in the funnel as follows : First, they are folded through the centre ; then another fold, at right angles to the first, is made, which leaves the paper in the form of a sector of a circle ; now, by inserting the apex of the sector into the funnel, the paper may be opened out in form of a cone that will fit the funnel. It will be seen that • two pockets are formed in the paper, either of which will serve as a recep- tacle for the fiuid to be filtered. It is best to wet the paper with distilled water before filtering a solution containing a precipitate, as this tends to prevent the precipitate from adhering so closely to the paper. Beginners are often at a loss as to how they may divide small precipi- tates into several parts ; this may be accomplished in different ways, of which these two are as convenient as any : First, the point of the filter- paper containing the well-washed precipitate may be pierced, and the damp precipitate may be washed through into a beaker glass by means of dis- tilled water; the precipitate may now be agitated with a stirring-rod 348 APPENDIX. until it is suspended in the water, when portions of it may be poured out , Second, the precipitate may be left on the filter-paper, and whether damp or dry may be separated into portions by tearing the filter-paper into the requisite number of parts. If the precipitate be damp, it may be washed off each part as needed, by means of water. If the precipitate be dry, and the student wishes to dissolve the dried precipitate, he may put the paper and all in a test-tube, and after dissolving may remove the particles of the filter-paper by passing the solution through a new filter. For filtering acids a little spun glass is best ; this may be crowded down into the stem of the funnel, and after passing the acid through it may be washed and preserved for further use. 17. Generating Flasks, one each of 2-oz. and 4-oz. capacity, will answer for the student's needs. These flasks are used for generating gases, etc., and are fitted with delivery-tubes as shown in the Erontispiece, F. These flasks are sometimes broken. 18. Two Beaker Glasses (see Bk in Frontispiece), one of 2-oz. and the other of 4-oz. capacity, are needed. In them solutions are boiled, crystals are allowed to form, and solutions for working purposes are kept temporarily, etc., etc. Neither these beakers nor the Florence flasks men- tioned in 17 should be heated in the naked Bunsen flame. They should always be placed on wire gauze or on a sand-bath. 19. Evaporating Dishes (see E in Frontispiece), one each of about 3-oz. and 4-oz. capacity, are needed. These should be heated on the sand- bath or on wire gauze. They are seldom broken. Prof. Weitbrecht's stu- dents frequently use saucers as evaporating dishes. 20. A Bunsen Burner is shown at B. The use of this has been ex- plained. In laboratories not containing gas for heating purposes, alcohol lamps are the best substitute. In nearly every place in the text where "Bunsen flame " has been used, " alcohol flame " may be substituted. 21. A Wash-Bottle, or " Blow-Bottle " as it is familiarly termed by students, is shown at W in Frontispiece, as made by a student from whose desk this cut was taken. Each student can make his own bottle ; the de- livery-tube should be drawn out into quite a fine jet, so that the stream of water issuing from it, upon blowing into the mouth-piece, shall be quite small. 22. Each Student should provide himself with a toy magnet, a clay tobacco pipe for blowing soap-bubbles, a sp'onge, a towel, a bundle of soft white rags, a box of matches, a watch-crystal, an oil-cloth apron, and a pair of rubber sleeves. The uses of these are too evident to need men- tioning. APPARATUS FOll student's DESK. 349 23. A Ring Stand is shown at A. This is used to support funnels while filtering, and sand-baths, retorts, generating flasks, etc., while heat- ing. The rings may be removed or clamped in any position upon the upright standard. 24. A Blue-Glass is shown at G. This is a frame containing two thick- nesses of glass. One blue-glass will answer for two desks. 25. A Sand-Bath is shown at S, resting on a ring. This is a saucer- shaped sheet-iron dish, which may be hammered out by any tinsmith. It must be large enough to rest on the largest ring. The dish is filled with clean white sand, and in this sand beakers, evaporating dishes, etc., are set ; the heat is applied to the sand-bath. There is one objection to a sand-bath, — the sand is apt to get scattered on the student's desk and find its way into the waste pipes leading from the sink-bowls. It is safer, how- ever, to heat glass ware, etc., in a sand-bath than it is on a Wire Gauze. This gauze is of fine brass wire, and is placed between the flame and the evaporating dish. It will be found to be neater and less objectionable in several respects than the sand-bath, but it is not quite so safe to heat fragile ware upon it. Professor Foote recommends asbestos paper in place of the sand-bath and wire gauze. 26. A Match-Safe should be furnished to each desk, and the student should not be allowed to put matches in his drawer. Employ sulphur matches ; parlor matches are too dangerous. 27. If the student is to do a little quantitative work, he will need, in addition to the foregoing, a porcelain crucible with cover, a. feather, a sheet of glazed paper, and a triangle made by joining three common clay tobacco-pipe stems by means of iron wire. 28. Iiltmus Papers. These papers may be purchased ready for use, or they may be prepared in the laboratory by dipping sheets of bibulous paper in litmus solution ; the papers thus prepared are blue. Red and blue papers are needed ; the red papers may be prepared by moistening the bl ue papers in dilute acetic acid. The papers should be cut into strips 4="' long and 4""" wide ; they may be kept in a bottle or cardboard box. 29. Charcoal. A fine variety of charcoal is to be purchased of chem- ical dealers, but selected pieces may be obtained from ordinary charcoal that will answer all purposes. Charcoal should not be kept in the drawers or on the desk. Separate pans with legs should be provided to avoid dan- ger from fireg. 360 APPENDIX. The reagents for the student's desk should be kept in stock in the lab- oratory, i.e., a sufficient quantity of the dry salts and of the liquid reagents should be purchased at the beginning of the year to last throughout that year. Some of these reagents are more convenient in a dry form ; but most of these are used in the form of solutions. The solutions should be kept in good glass-stoppered bottles, holding ^' or 4 oz., similar to those shown in the Prontispiece. It is desirable that these bottles have permanent acid-proof names and symbols. The dry salts should be kept in small 2-oz. salt-mouth bottles, and these are best when provided with glass stoppers. A few words of caution concerning the care of reagent bottles are in place here. A good reagent bottle must have its stopper ground to fit it, and this stopper will not fit any other bottle in the set. Consequently the stoppers should never be interchanged. Again, the stoppers of all re- agent bottles, excepting sulphuric acid, should be paraffined with gum- stock paraffin, otherwise they are quite apt to stick ; often the bottles are ruined or cracked by trying to remove the stoppers. There is no excuse for breaking a reagent bottle. The solutions should not be allowed to freeze, as the bottles may thus be broken. The student should not lay down the cork of a reagent bottle while pouring out a solution, since he may thus change stoppers with his bottles or contaminate his reagents. Again, no solution but the one correspond- ing to the name on the bottle should ever be placed in a reagent bottle. Another important item is that each bottle have a place on its shelf, and always be put in its place ; thus the student comes to know where to find a reagent, just as a printer knows where to find the letters in his case. Since some order must be followed, that in which the reagents are described below may be insisted on. Commencing with the first name in the list on the upper shelf, left-hand side, arrange the bottles toward the right ; and, when the shelf is full, begin again on the left-hand of the next. Since systems of nomenclature vary somewhat, and since labels and names are apt to vary decidedly, all the names are given in connection with each reagent, the most preferable coming first, the symbol next, and thereafter the various other names, in order of their preference, excepting the name given in italics, which is that of the United States Pharmaco- poeia ; its position has no reference to its preferment. In naming the acids, the common names are given first, for the reason that these names are good ones, and in spite of all attempts to do away with them, they still persist in remaining ; and it is perhaps but wise to submit to the inevitable. Thus, that acid whose formula is H^SOj, is called sulphuric acid ; hydrogen sulphate, for some reasons, would be better, LIQUID KEAGENTS. 361 but the change Is not universally accepted. Again, hydric sulphate has i)een proposed, but this is still less favorably received ; while the oldest name of all, oil of vitriol, is scarcely used or known by the last generation of chemists, though still retained by manufacturers. The reagents enumerated below (with a few exceptions, which are noted) should be chemically pure. Of all persons, a beginner should have the best materials to work with ; moreover, good material is now so cheap that there is neither profit nor sense in using goods of a poor quality. LIQUID REAGENTS. 30. Sulphuric Acid, H^SO^; Hydrogen Sulphate; Hydric Sulphate ; Dihydric Sulphate ; Oil of Vitriol ; Acidum Sulphuricum. This acid should be bought in a concentrated form, sp. grav. 1.843, and should be dealt out to students in this form ; it should evaporate on plati- num foil without leaving any residue, and it should be colorless. The commercial acid may be contaminated with arsenic, antimony, iron, aluminum, calcium, potassium, sodium, lead, magnesium, hydrochloric acid, nitrous acid, nitric acid. 31. Nitric Acid, HNOj ; Hydrogen Nitrate ; Hydric Nitrate ;, Aqua Fortis ; Acidum Nitricum. This acid may be bought in a concentrated form, and afterward re- duced with water to reagent strength, which is 32 per cent acid, sp. grav- 1.32. (See 34 for computation.) Pure nitric acid is colorless, but, on standing exposed to the light, it may become colored by the lower oxides of nitrogen, which, as a usual , thing, are not harmful. They may be removed by passing a current of air through the acid by means of a glass tube attached to a hand-bellows. The commercial acid may contain calcium, sodium, iron, oxides of nitro- gen, hydrochloric acid, sulphuric acid. 32. Hydrochloric Acid, HCl ; Hydrogen Chloride ; Hydric Chloride ; Muriatic Acid ; Chlorhydric Acid ; Chlorhydrate ; Spirit of Salt ; Acidum Hydrochloricum. This acid may likewise be purchased in a concentrated form, and after- wards reduced to the reagent strength, 24 per cent acid, sp. grav. 1.12. The pure acid is colorless, and leaves no residue upon evaporation ; upon standing, it may become colored by free chlorine. The commercial acid may contain iron, sodium, aluminum, arsenic, sul- phuric acid, sulphurous acid. 33. Acetic Acid, H(C5H,02) ; Hydrogen Acetate ; Hydric Acetate ; Acidum Aceticum. 352 APPENDIX. Since acetic acid is not so extensively used as the preceding acids, it may be purchased of a reagent strength, 30 per cent acid, sp. grav. 1.04. The pure acid is colorless, and leaves no residue upon evaporation. The commercial acid may contain sodium chloride, lead, copper, iron, empyreumatic substances, sulphuric acid, sulphurous acid, nitric acid- 34. Ammonia, NHg. The reagent solution contains 10 per cent of the gas NHg, and has a sp. grav. 0.96. It is prepared from the "Stronger Water of Ammonia," or Aqua Ammonia (28 per cent gas; sp. grav. 0.90; U. S. P.), by the addition of distilled water. The concentrated form is more convenient to keep in stock, as it requires less space for storage. In the case of ammonia, and of the concentrated acids previously mentioned, the label of the original package should state the per cent and sp. grav. Commercial aqua ammonia may contain ammonium chloride, ammonium carbonate, calcium sulphate, empyreumatic matei-ial. The amount of water to be added to a given volume of a stronger solu- tion may be determined by calculation. Thus, in the case of ammonia : We know that 1^ of the strong solution weighs 900s, and that 28 per cent of that weight, or 252s, is NHj. It is evident that this 252s is to form 10 per cent of the weight of the reagent solution ; hence, the whole weight of the reagent solution will be 252 ^ .1 = 2520s. Now, we already have taken 900s of the strong solution ; consequently 2520 — 900 = 1620s, or the weight of distilled water to be added to 1' or 1000"^° of the strong solution. It is further evident that one part, by volume, of the strong solution requires 1.62 parts, by volume, of distilled water. 35. Ammonium Carbonate, (NH^jjCOj; Carbonate of Ammonia; Am- monic Carbonate ; Volatile Salt ; Ammonii Carbonas. This solution is prepared by dissolving 1 part by weight of the dry salt in 4 parts by weight of water, after which one part of reagent ammonia solution is added. Tlie commercial salt may contain calcium, iron, lead, chlorides, iodides, sulphates. It is not necessary to weigh the water, since 1™ of water weighs Is. The graduated ware used in measuring solutions is graduated at a certain temperature, usually 15° C. When accuracy is required, the temperature of the water or of the solution to be measured should be that at which the apparatus is graduated. 36. Ammonium Sulphide, (NHiJ^S ; Sulphide of Ammonium ; Ara- monic Sulphide. This solution may be purchased ready for use, or it may be prepared in LIQUrD EEAGENTS. 358 the laboratory by passing hydrogen sulphide gas through a reagent solu- tion of ammonia until the solution no longer precipitates magnesium sulphate. This reagent changes, upon standing, to the yellow variety. Although the formula of the yellow ammonium sulphide has been given as (NHjjjSj, its composition varies greatly. 37. Ammonium Chloride, NH^Cl ; Chloride of Ammonium ; Am- monic Chloride ; Muriate of Ammonia; Sal Ammoniac; Ammonii Chloridum. To prepare this reagent solution, dissolve 1 part of the crystallized salt in 8 parts of water. TJie commercial salt may contain iron, sulphates, organic matter. 38. Ammonium Oxalate, (NH4)2C204; Oxalate of Ammonium; Am- monic Oxalate. This is prepared by dissolving the crystallized salt, (NH^jjCjO^+HjO, in 24 parts of water. The commercial salt may contain sodium, potassium, calcium, aluminum, lead, sulphates, nitrates. 39. Potassium Hydroxide, KOH ; Potassium Hydrate ; Potassic Hydrate ; Caustic Potash. This solution is prepared by dissolving 1 part of the dry sticks in 20 parts water. It is not absolutely essential that this salt be strictly C. P. ; there is a good white article {"rein weiss") containing a little silica, and perhaps a trace of chlorine, that will answer most purposes, and it is much cheaper than the C. P. article. The commercial article may contain iron, aluminum, sodium, calcium, or- ganic matter, silica, chlorides, sulphates, carbonates. 44'. Sodium Hydroxide, NaOH, is preferred by many chemists to potassium hydroxide, since the former is much cheaper. This solution is made by adding 1 part of the fused substance to 9 parts water. The im- purities are much the same as in the potassium compound. 40. Potassium Carbonate, K^COj ; Carbonate of Potassium ; Potas- sic Carbonate ; Carbonate of Potash (potassa) ; Potassii Oarbonas. Make this solution by dissolving 1 part of the dry salt, KjCOj + SHjO, in 10 parts water. The commercial article may contain iron, aluminum, silica, sodium, chlo- rides, sulphates, sulphides. 41. Potassium Iodide, KI; Iodide of Potassium; Potassic Iodide; Potassii lodidum. Dissolve 1 part of the salt in 20 parts of water. 354 APPENDIX. The commercial article may contain sodium, iodates, sulphates, chlorides, carbonates. 42. Potassium Bichromate, K2Cr20, ; Bichromate of Potassium; Po- tassium Bichromate ; Potassic Bichromate ; Bichromate of Potash ; Red Chromate of Potash ; Potassic Acid Chromate ; Potassii Bichromas. 1 part of the salt is dissolved in 10 parts of water. The commercial salt may contain iron, calcium, aluminum, sulphates, chlorides. 43. Potassium Sulpho-Cyanide, KCyS; Sulpho-Cyanide of Potas- sium; Potassic Sulpho-Cyanide; Potassium Sulpho-Cyanate. This solution is made by dissolving 1 part of the salt in 25 parts of water. The commercial article may contain iron, sulphates, chlorides. 44. Potassium Ferro-Cyanide, K^PeCyg; Perro-Cyanide of Potas- sium ; Potassic Perro-Cyanide ; Yellow Prussiate of Potash ; Potassii Ferro- cyanidum. This solution is made by dissolving 1 part of the crystallized salt, KjPeCyj, 3 HjO, in 12 parts of water. 46. Disodium Pliosphate, NajHPO^; Sodium Phosphate ; Phosphate of Sodium ; Disodium-Hydrogen Phosphate ; Disodic-Hydric Phosphate ; Sodii Thosphas. This solution is prepared by dissolving 1 part of the crystallized salt, Na^HPOi-l- B..fi, in 10 parts of water. The commercial salt may contain arsenic, iron, lead, sulphates, chlorides. 46. Barium Cliloride, BaClj ; Chloride of Barium ; Baric Chloride ; Barii Chloridum. Dissolve 1 part of the crystallized salt, BaClj -1- 2H2O, in 10 parts of water. The commercial article may contain calcium, strontium, iron, aluminum, silica. 47. Calcium Hydroxide, Ca(0H)2; Calcic Hydrate ; Lime Water; Liquor Oalcis. This solution is best prepared in jthe laboratory. " Slake the lime by the gradual addition of 6 parts of water, then add 30 parts of water, and stir occasionally during half an hour. Allow the mixture to settle, decant the liquid and throw this away. Now add to the residue 300 parts of distilled water, stir well, and wait a short time for the coarser particles to subside, and then pour the liquid, holding the undissolved lime In suspen- sion, into a glass-stoppered bottle. When wanted for use, pour ofE the clear liciuid." — U. S. P. LIQUID eeagekts. 355 48. Magnesium Sulphate, MgSO^ ; Sulphate of Magnesium ; Mag- nesic Sulphate; Sulphate of Magnesia ; Epsom Salt; Magnesii Sulphas. Dissolve 1 part of the crystallized salt, MgSO,+ 7HjO, in 10 parts of water. TTie commercial salt may contain calcium, iron, silica, zinc, manganese, chlorides. 49. Mercuric Chloride, HgClj; Bichloride of Mercury; Perchloride of Mercury; Corrosive Sublimate; Corrosive Chloride of Mercury; Hi/drargyri Chloridum Corrosivum. Dissolve 1 part of the crystallized salt in 70 parts of water. The commercial salt may contain iron, lead, calcium, antimony, tin. 50. Silver Nitrate, AgNOj; Nitrate of Silver; Argentic Nitrate; Lunar Caustic ; Argenti Nitras. Dissolve 1 part of salt in 70 parts of water. The commercial salt may contain iron, lead, copper. 51. lisad Acetate, PblCjHjOJj; Acetate of Lead; Plumbic Acetate ; Sugar of Lead ; Plumbi Acetas. Dissolve 1 part of the crystallized salt, Pb(CjH302)2 + 3 H^O, in 10 parts of water. If the solution is not clear, filter it. The commercial salt may contain sodium, calcium, iron, lead, copper, chlorides, nitrates. 52. Ferric Chloride, Fe^Clg ; Perchloride of Iron ; Sesquichloride of Iron ; Ferri Chloridum. Dissolve 1 part of the solid salt, re^Clj + e H^O, in 15 parts of water. 77ie commercial article may contain ferrous chloride, aluminum, nitrates, sulphates. 53. Alcohol, CjHgO ; Ethyl Alcohol ; Spirits of Wine. The alcohol used should be the " Spirits of Wine," having a specific gravity of .815, and containing about 95 per cent of the spirit. This should be purchased ready for use. 54. Cobaltous Nitrate, Co(N03)2. This solution is prepared by dissolving 1 part of the crystalline salt, Co(N03)2 + SHjO, in 20 parts of water. This solution is used merely for moistening the bead on the platinum wire, and should be kept in a small half-ounce bottle, as this amount will last a long time. 366 APPENDIX. DRY REAGENTS. 55. Ferrous Sulphate, !FeS04+7H20; Sulphate of Iron; Green Vitriol; Ferri Sulphas. This reagent is used in solution, 1 part of the salt to 10 parts of water; but the solution oxidizes rapidly to a ferric condition, in consequence of which, it is best to make the solution in a test-tube, as required from time to time ; the proportions need not be exact. The dry salt also oxidizes by standing ; hence, in practice, a crystal of the salt is dropped into the test-tube, and a little water added ; the crystal is now shaken until the white coating of the ferric salt disappears, and the crystal is of a clear green color ; this water is now thrown out, and a fresh portion added ; heat is then applied to hasten the solution. 56. Sodium Carbonate, Na2C03 ; Carbonate of Sbdium ; Sodie Car- bonate ; Soda Carbonas. This reagent is used in the form of the dry, powdered salt ; the bottle containing it should be kept well corked to prevent the reagent from absorbing the gases of the laboratory. The commercial salt may contain iron, aluminum, silica, calcium, lead, chlorides, sulphates, sulphides. 57. Sodium Borate, Na20(B203)2; Borate of Sodium; BSrax; Sodii Boras. This reagent is used in a dry, powdered form. The commercial article may contain iron, sodium, aluminum, silica, cal- cium, chlorides, sulphates. 58. Sodium-Ammonium Pliosptaate, NaNH^HPO^ . iHjO ; Microcos- mic Salt; Sodii et Ammonii Phosphas. This is used in a dry state. 59. Ferrous Sulphide, FeS. The method of using this sulphide is explained in the text. Art. 167. 60. Potassium Chlorate, KCIO3; Chlorate of Potassium; Potassic Chlorate; Chlorate of Potash; Potassii Chloras. The crystallized salt is used. 61. Metallic Zinc, Zn. The granulated metal is employed. This form is obtained by pouring molten zinc into water. It must be absolutely free from arsenic. (See Art. 319.) EEAGBafTS FOE THE SIDE-TABLE. g57 REAGENTS FOE, THE SIDE-TABLE. ■ These reagents are those required occasionally by the student. One set should be prepared and placed on a side-table, or in a cupboard conven- iently located, so that it is accessible to all the students in the laboratory. The solutions may be kept in 4-oz. bottles similar to those on the student's desk. The corks of all these bottles, excepting those for ether and carbon bisulphide, should be paraflSned. The dry salts are to be kept in convenient broad-mouth bottles. 62. Carbon Bisulphide, CS2 ; Carbon Bisulphide ; Bisulphide of Car- bon; Carhonei Bisulphidum. This reagent is purchased ready for use. It is very volatile, and the bottle should be closed with a good chemical cork stopper. 63. Ether, (CjHsJ^O; Aether; Sulphuric Ether. This reagent is purchased ready for use, and the bottle should be closed with a chemical cork stopper. 64. Potassium Sulphate, K2SO4 ; Sulphate of Potassium; Potassic Sulphate ; Sulphate of Potash ; Potassii Sulphas. Dissolve 1 part of the crystallized salt in 12 parts of water. 65. Potassium Ferri-Cyanlde, KjEeCye; Ferricyanide of Potas- sium ; Red Prussiate of Potash. Dissolve 1 part of the salt in 12 parts of water. This solution will not keep long without undergoing decomposition. 66. Potassium Chromate, KjCrO^; Chromate of Potassium; Potas- sic Chromate. Dissolve 1 part of the salt in 10 parts of water. 67. Potassium Cyanide, KCy; Cyanide of Potassium; Potassic Cyanide ; Potassii Cyanidum. 1 part of the solid is dissolved in 4 parts of water. The poisonous nature of this reagent should not be forgotten. 68. Potassium Permanganate, K^MUjOs; Permanganate of Potas- sium ; Permanganate of Potash ; Potassii Permanganas. Dissolve 1 part of the crystallized salt in about 500 parts of water. 69. Sodium Sulphite, Na^SOg; Sulphite of Sodium ; Sodic Sulphite ; Sodii Sulphis. Dissolve 1 part of the crystallized salt, NajSOj -1- 7 HjO, in 6 parts of water. 858 APPENDIX. 70. Calcium Sulphate, CaSO^; Sulphate of Calcium; Calcic Sul- phate ; Calcii Sulphas. This solution is made by dissolving all the salt, CaS04+ ZHjO, that the water will take up ; or, in other words, it is a saturated solution. 71. Calcium Chloride, CaClj; Chloride of Calcium; Calcic Chloride ; Calcii Ohloridum. Dissolve 1 part of the salt, CaCIj + 6 HjO, in 8 parts of water. 72. Stannous Chloride, SnClj ; Protochloride of Tin. To 6 parts of water add 1 part of the crystallized salt, SnCl^ + 2 HjO ; then add hydrochloric acid, drop by drop, until the solution turns clear. 73. Copper Sulphate, CuSO^; Sulphate of Copper; Cupric Sulphate; Blue Vitriol ; Blue Stone ; Oupri Sulphas. Dissolve 1 part of the crystallized salt, CuSO^ + 5 H2O, In 8 parts of water. 74. Starch Paste. This solution is made by dissolving 1 part of starch in 500 parts of water. In case the student desires a solution of starch paste and potassium iodide, he may place a little of the starch paste solution in a test-tube, and add a drop or two of the reagent potassium io- dide solution. 75. Ammonium Molybdate, (NH^jjMo^. Dissolve 60s of the dry salt in 400"" of reagent ammonia solution ; add 400=" of distilled water ; then cautiously add 500"" nitric acid (sp. grav. 1.4). GRADUATED SOLUTIONS, Etc. 76. Clark's Soap Solution is prepared by dissolving lOe of good castile soap in 1' of dilute alcohol containing about 35 per cent of the spirit. The dilute alcohol may be prepared from the reagent alcohol by mixing 368.5"" alcohol with 631.5"" distilled water. To test the soap solution a reagent solution of calcium chloride is required. This solution is prepared by dissolving 18 of Iceland spar in hydrochloric acid ; the solution is then evaporated to dryness to expel any excess of acid, after which the residue is dissolved in !■ of distilled water. Now if 12"" of the solution just formed be diluted to 70"" and brought into a flask, it will require just 13"" of the soap solution to make a permanent lather, provided the soap solution be of the right strength. In case the soap so- lution is not of the right strength, it must be made so, or allowances must be made when calculating the degrees of hardness of a sample of water. The soap solution deteriorates by standing. INDICATORS. 359 77. Nessler's Solution is prepared by dissolving 13s mercuric chlo- ride, HgClj, ia about 400='= of distilled water; now 35k of potassium iodide, KI, are dissolved in (say) 200='= of water, and these two solutions are then mixed. To this solution add 1008 of soUd potassium hydroxide, KOH, and when it is dissolved and the solution cool, dilute the whole with water to 1'. Keep this solution in a dark, cool place, and take a portion of it in a small bottle for immediate use. Before using the solution it is necessary to "sensitize" it; this is accomplished by adding slowly a saturated solution of mercuric chloride, with constant stirring, untU the red precipitate first formed ceases to dis- solve. Either filter the solution or allow it to stand till the solids have all subsided. It is now ready for use, and should be of a light, straw-yellow color. This solution loses its sensitiveness by standing. 78. A Few Graduated Solutions have been mentioned in the text ; as, for example. Barium Hydroxide Solution and Oxalic Acid Solution, p. 148; Silver Nitrate Solution, p. 107; Iodine Solution, p. 181; Ammo- nium Chloride Solution, p. 72. These have been sufficiently described, so that there is nothing to add, unless it be to note that in case these solu- tions prove too strong that they may be diluted to some other standard of strength ; for example, it is evident that if 1™ of the ammonium chloride solution be added to 99™ of distilled water, l'" of the solution thus formed will correspond to .01"S of ammonia. It is usually necessary to work, when estimating the ammonia of drinking-water, with this dilute solution. Now, if the burette used be graduated to .1™, it is evident that by this means the ammonia in drinking-water, etc., may be determined to .OOl'iiK. It might be well, in this connection, to call attention to the extreme accu- racy obtainable in titration. N.B. A few words of caution concerning the estimation of chlorine may be in place here. It is evident the chromate used for an indicator must be free from chlorine ; also, in order to have the end reaction sharp, the solution must be exactly neutral. In estimating ammonia, the water used in connection with the standard solution of NH^Cl must be free from ammonia. This may be obtained by taking (say) 2' of distilled water, and distilling until the distillate gives no reaction for ammonia. The water remaining in the retort is evidently free from ammonia. DTOICATOKS. Solutions of various substances are employed to indicate what is called "End Reactions." The method of using these indicators has been ex- 360 APPENDIX. plained in the text. It now remains to show how a few of these solutions are made. 79. Litmus Solution is prepared by digesting for several hours 10b of solid litmus with 500=" of distilled water ; allow the liquid to become clear, or filter it when it is ready for use, when the end reaction is to be acid ; one portion of it may be prepared for solutions, when the end reaction is to be alkaline, by adding to it a few drops of acetic acid. 80. Cochineal Solution is obtained by diges,ting 3s of the powder in 250™ of 20 per cent alcohol. This is very sensitive ; acids bleach it, alka- lies redden the bleached solution. 81. Phenol-Phtlialeln Solution is made by dissolving 1 part of the solid in 100 parts of 60 per cent alcohol ; this gives a colorless solution which is reddened by alkalies. This red solution is bleached by acids. It may be used as a qualitative test for carbon dioxide. See "American Chemi- cal Journal," 3, 55, 232. For a paper on Lakmoid, Phenol-Phthalein, and other indicators, see " The Chemical News " of July 10, 1885, p. 18, and July 17, 1885, p. 29. 82. A Soap-Bubble Solution is prepared thus : To about IOOe of finely-cut best castile soap in a litre flask add nearly a, litre of distilled water ; shake until the solution is saturated with soap ; then allow it to settle clear ; to two volumes of soap solution add one volume of glycerine. Gbneeal Note. In order to lessen the first cost of equipping the laboratory, many of the reagents, enumerated as belonging to the student's desk, may be placed on the side-table. Many good laboratories are thus arranged. WORKING MATERIAL. The substances enumerated under this heading are arranged in the same order as the Elements and their compounds in the text, and none are repeated. It is not necessary in every case that the chemicals which fol- low should be chemically pure. The reagents, etc., already named are not given. 83. Introduction. Galena; iron filings; flowers of sulphur. 84. Oxygen. Mercuric oxide; red lead; manganese dioxide {C. P.); bark charcoal ; iron wire ; broken watch-springs ; phosphorus ; zinc foil ; pyrogallic acid. 85. Hydrogen. Metallic sodium and potassium ; mercury ; well-water barium dioxide. WORKING MATERIAL. 361 Note. For generating large quantities of hydrogen when purity is not especially requisite, sheet zinc may be employed ; this is cut into bits, and to help the action along a few nails may be thrown into the generator. 86. Nitrogen. Quicklime ; ammonium chloride ; ammonium nitrate (C. P.); copper filings ; potassium nitrate ; spirits of turpentine. 87. Chlorine. Indigo solution ; sodium chloride. 88. Bromine. Potassium bromide ; bromine. 89. Iodine. Iodine. 90. Fluorine. Calcium fluoride ; beeswax, or paraflBn. 91. Carbon. Lampblack; graphite; various kinds of coal; bone- black; sugar; sodium acetate; yeast; calcium carbonate; magnesium ribbon ; clam shells, snail shells, corals, and other carbonates. 92. Sulphur. Roll sulphur; iron pyrites. 93- Silicon. As many varieties of silicon dioxide as possible. 94r. Boron. Boric acid. 95- Phosphorus. Stick phosphorus ; red phosphorus. When working with the metals, it is desirable to have as many ores of each metal as possible ; not that these ores are absolutely indispensable to the work in the text, but because of the advantage the student may derive from tlieir examination or from working with them. 96. The First Group Metals. Metallic silver and ores of silver; metallic mercury and ores of mercury; metallic lead in its commercial forms, and ores of lead. 97. Second Group Metals. Arsenic and arsenic trioxide ; antimony, antimony sulphide, and ores of antimony ; metallic tin in its commercial forms, and ores of tin ; metallic bismuth and ores of bismuth ; sheet copper, native copper, and ores of copper ; metallic cadmium, ores of cadmium. 98. The Third Group Metals. Iron in its commercial form and ores of iron ; chrome alum or other chromium salts ; metallic aluminum and as many commonly occurring aluminum compounds as possible ; metallic nickel and ores of nickel ; cobalt ores ; manganese ores ; commercial forms of metallic zinc. 99. The Fourth Group Metals. Barium dioxide, hydroxide, and as many barium-bearing minerals as possible ; strontium nitrate ; many cal- cium bearing minerals ; metallic magnesium ribbon, and many magnesium- bearing minerals. The Fifth Group Metals are already provided for. 362 APPENDIX. GENERAL APPARATUS. Under this heading is included that apparatus which is of genera, utility. The teacher may need some of it for special purposes, while some of it is so placed that the students may have access to it at any time. Much of this apparatus may be used in physics also. 100. A Becker or Troemner Balance, Fig. 23, is to be recommended on account of its cheapness, neatness, accuracy (sensitive to 2"'S), and durability. By placing a small shelf or table over one pan, so that the Fig. 23. balance may play freely, it will answer well for specific gravity. The author's students have used this balance for three years, and it is still as good as new. Accompanying it is a set of weights in a polished, velvet- lined box, with forceps, and a tray divided into compartments for the small weights, and covered with a glass slide. These weights were im- ported at a cost of $3.50 ; they run from 50e to IB in brass and 500">8» to 1"'B in platinum. 101. A Pair of Counter-Poised Watch-Crystals are useful in weighing those substances which would attack the pans of the balance. GENERAL APPAEATUS. 363 102. A WeigMng Flask for iodine and other volatile substances is desirable. 103. A Specific Gravity Bottle of 50"° capacity is useful in deter- mining the specific gravity of fluids. 104r. A Pair of Hydrometers. One for fluids lighter than water, and one for fluids heavier than water. 105. A Pair of Good Centigrade Chemical Thermometers. One graduated from —20= to + 240', and one from — 10° to + 360°. 106. Graduated Flasks. One 1', one J' , and one J'. These are fitted with glass stoppers, and bear only one mark around the neck. These are useful when 1', etc., is wanted quickly. 107. Liitre Cylinder for mixing reagent solutions. These are gradu ated into cc's to read up and down. 108. Two Burettes, capacity 50™ each; graduated to O.l"". These are used in titration. 109. A Pipette, capacity 5"=, graduated to 0.1"°. Used for taking out small quantities of liquids from bottles, etc. 110. A tipped Graduated Jar, capacity 100"=, graduated to l"". Used in measuring out liquids. 111. Ure'B Eudiometer. This is shown and explained in Fig. 7. 112. Hofmann's Apparatus, as shown and explained in Fig. 3. 113. Spectroscope. Spectroscopes are now to be had quite reasoi; dbly. The needs of the school should determine the expense of the instru- ment purchased. 114. Bell Jars are used in experimenting with gases. Those used in connection with the air-pump may be employed, or large bottles may be cut off at the bottom. This may be accomplished by cutting a crease around the bottle with a three-cornered file ; this crease is then followed up with a minute blow-pipe flame until the bottom cracks off. The edges may then be ground smooth on a sheet of emery-paper stretched on a flat board. 115. Large Beakers, Funnels, Evaporating Dishes, and Ring Stands similar to those shown in the Frontispiece, only larger, are found useful in preparing solutions, reagents, etc. 116. Retorts and Receivers, similar to those shown in Fig. 14, are Q used in distillation, etc. 364 APPENDIX, 117. A liiebig's Condenser is often used in connection with the retorts. 118. Tall Jars are useful in experimenting with gases. 119. An Iron Mortar and a Porcelain or a Wedgeivood-Ware Mortar, with pestles. 120. Assorted Glass Tubing of various sizes suitable for " hydrogen tones," connections, etc. 121. Funnel Tubes for Generators, as shown in Fig. 5. 122. Blast-Iiamp, for alcohol or gas, is useful in working glass. 123. A Copper Oxygen Retort, for generating oxygen. An iron retort may be used, or a common glass generating flask will serve the same purpose. 124. Mercury Trough of Porcelain. 125. A Hydrogen Pistol may be made from a gas-pipe IJ in. in diameter, And 6 in. long. One end is closed with a cap ; a small opening is drilled in for a vent, and the mouth is closed with a common cork. 126. A Pneumatic Trough. There are many designs in use. As a general rule, the simpler the trough, the better. 127. Gas Holders. Any tinsmith can make very satisfactory gas holders. Or they can be made from a, barrel, and a cask that will go inside the barrel. The heads are removed ;-the barrel is filled with water, and the cask is inserted in the barrel and suitably weighted ; a stop-cock, for attaching rubber-hose, is inserted in the head of the cask. 128. Chemical Corks and Eubber Stoppers of assorted sizes. 129. Rubber Tubing of assorted sizes, for connections, etc. 130. Rubber Gas-Bags. One of 2 gals., and one cf 1 gal. capacity. 131. Oxyhydrogen Blovf-Pipe. One form of this apparatus is shown in Fig. 8. Prof. Weitbrecht has constructed a cheap instrument from ^in. gas fixtures. The instrument is T shaped ; into the stem of the T is screwed a, Springfield musket cap-nipple which serves as a jet; in each arm of the T is a stop-cock. The hydrogen is admitted into one arm and the oxygen into the other. Illuminating gas may be used in place of hydrogen. 132. A Furnace, known as the Fletcher Purnace, and proYided with bellows and a blast-jet for illuminating gas, is not expensive, and will fuse such metals as gold, silver, etc. THE LIBEAEY. 365 133. Crucibles. Hessian crucibles and plumbago crucibles are used. The sand, or Hessian crucible, is inexpensive, and may be bought in nests. THE LIBBARY. A reference library should be kept in the laboratory. It should be easy of access, and the students should be permitted to make use of any book at any time. Books should not be taken out of the laboratory. In the following list no attempt at completeness is made ; a, few good books that are within the reach of all schools are named. Eoscoe and Schor- lemmer's " General Treatise " will be found useful for general descriptive work. Douglas and Prescott's " Qualitative Analysis,'' or a standard edition of lYesenius's " Qualitative Analysis,'' will be useful in qualitative work. Sutton's " Volumetric Analysis " is recommended for methods of titration. Fresenius's " Quantitative Analysis " is useful, if quantitative work is attempted. Elderhorst's " Blow-Pipe Analysis " is to be used in expanding any work with the blow-pipe. * Wanklyn's " Analysis of Water, Milk, and Air," may be used in case it is desired to do work in that direction. These books are published in separate volumes. Dana's " Mineralogy " is valuable as afEording information concerning ores, coal, etc. Gore's " Electro-Metallurgy " will afford information in that direction. Some good work on Spectrum Analysis is desirable. Schellen, though popularly written, is good. Eoscoe's work is more technical. The " U. S. Dispensatory," and the " Pharmacopoeia" are often useful. Bailey's " Chemist's Pocket-Book " contains many valuable data for com- putations, conversions, etc., etc. One or two chemical journals, as " The Chemical News " and the "American Journal of Chemistry," will serve to create an interest, by calling the student's attention to the present tendencies of the science. In response to numerous inquiries from teachers, concerning apparatus, etc., the author would take this occasion to say that he will gladly give any information in his power concerning the same; and, in case any school wishes aid in purchasing, that he has made arrangements with Messrs. Eberbach and Son, Ann Arbor, Mich., whereby any apparatus or chemicals necessary for this text can be supplied promptly, and at th? 366 APPENDIX. lowest market price for the high grade of goods recommended. All cor- respondence on this subject should be addressed to the author. A priced list will be sent on application. Data fok Contebting Metkic and English Weights and Measures. !■»■" = 0.0394 in. 1« = 15.43235 grains. 1™ = 0.3937 in. 1 grain = 0.06486. 1 in = 2.539954™. 1 lb. avoirdupois = 453.59b. 1 cu. in. = le.SSeire^c. l oz. avoirdupois = 28.34954s. l"" = 0.06103 cu. in. 1 gal. U. S. = 231. cu. in. 1' .-= 61.02709 cu. in. 1 gal. Imp. = 277^ cu. in. II^DEX. [The numbers refer to pages.] Acetic acid 340 Acetylene 134 Acid, Antimonic 249 Boric 191 Bromic 113 Chloric '. 104 Chlorous 104 Citric 340 Puming sulphuric 174 Hydriodic 117 Hydrobromic 110 Hydrochloric 97 Hydrocyanic 146 Hydrofluoric 122 Hydrofluosilicic 190 Hypobromous 112 Hypochlorous 101 Hyponitrous 65 Hypophosphorous 199 Iodic 120 Manganic 296 Meta-phosphoric 202 Meta-stannic 253 Nitric 67 Nitrous 66 Nordhausen 174 Orthophosphoric 201 Oxalic 340 Perchloric 105 Permanganic 296 Phosphoric 201 Acid, Phosphorous 200 Prussic ; 146 Pyrophosphoric 202 Acids, Basicity of 168 defined 76 General examination for, 204, 339 Acid salt 217 Acid, Selenio 179 Selenious 179 Sodium carbonate 333 Stannic 253 Sulphuric 169 Sulphurous 168 Tartaric 340 Telluric 180 Tellurous 180 Thiosulphuric 175 Agate 186 Agricola 4 Albite 286 Alchemy 2 Alkali plains 327 Alloys 211 Alum 321 Alumina 286 Aluminum hydroxide 287 Aluminum, Occurrence 286 Preparation 286 Properties 287 Compounds 287 368 QTDEX. Aluminum, Tests 288 sulphate 287 Alums 287 Amalgams 211 Amethyst 186 Amorphous iron ore 276 Ammonia, Albuminoid, Estima- tion of 49 Ammonia, Estimation of 72 in drinking-water 45 Occurrence 52 Preparation 52 Process 332 Properties 55 Tests 58 Ammonium 334 carbonate 335 chloride 334 molybdate 272 nitrate 334 phospho-molybdate 272 sulphide 335 Analysis defined 216 of unknoM'n substances, 337-340 Ancients, Chemistry of 1 Ancient copper-miners 259 Anhydrite 314 Anthracite 129 Antimonic acid 249 Antimony black 247, 272 Antimony, Butter of 249 Occurrence 247 Preparation 247 Properties 248 Compounds 249 Tests 250 oxides 249 trichloride 249 trisulphide 249 Apatite 193 Arabs, Chemistry of 2 Argentite 229 Argillaceous iron ore 276 Aristotle, Doctrines of 2 Arsenic, Occurrence .^. 242 Preparation 242 Properties 243 Compounds 244 Tests 24G pentoxide 245 trioxide 242, 244 Arsenious sulphide 245 Arseniuretted hydrogen 244 Asbestos 316 Atomic heat 209 theory 15 weights. Determination of, 15, 16, 152 Atmosphere 82 Estimation of oxygen and nitrogen of 85 Impurities of 84 Temperature of 83. Avogadro's hypothesis 150 Azurite 258 Bbracite 190 Barium carbonate 311 chloride 311 hydroxide 310 iodate 311 monoxide 310 nitrate 311 Barium, Occurrence 310 Preparation 310 Compounds 310 Tests 311 sulphate 311 Barometer 82 Baryta, Caustic 310 water 310 Bases defined 77 nSTDEX. 369 B«sic salt 218 Bauxite ' 280 Bell metal 211 Beryl 288 Beryllium 302 Bessamer process 279 Bismuthite 255, ' 257 Bismuth nitrate 257 ochre 255 Bismuth, Occurrence 255 Preparation 255 Properties 256 Compounds 257 Tests J 257 oxides 257 subnitrate 257 Binary compounds 73 Bituminous coal 129 Bog iron ore 276 Borax 190 Boron, Occurrence 190 Preparation 190 Tests 191 Botryoidal iron ore 276 Boyle 4 Black lead 125 Blanc de fard ; 257 Blanc d'Espagne 257 Blast furnace 277 Bleaching powder 315 Brass 211 Braunite 295 Breithauptite 290 Brimstone 157 Britannia 211 Bromic acid 113 Bromine oxacids 112 Bromine, Occurrence 108 Preparation 108 Properties 110 Tests 110 Bronze 211 Brown haematite 276 Bunsen burner 28 Cadmium iodide 263 Cadmium, Occurrence 262 Preparation 262 Properties 262 Compounds 263 Tests 263 Sulphate 263 Sulphide 263 Caesium 336 Calcium chloride 315 carbonate 315 hydroxide 314 Occurrence 313 Preparation 314 Properties 314 Compounds 314 Tests 315 sulphate 313, 314 Calc spar 313 Carbonado 127 Carbon bisulphide 178 dioxide, Estimation of 148 dioxide. Occurrence 138 Preparation 138 dioxide, Properties 140 Tests 145 hydrides 132 monoxide. Preparation 136 Tests 138 Occurrence 125 Preparation 126 Properties 126 Tests 131 oxides 136 Carnallite 316, 321 Carrfe, ice machine 57 Cassiterite 251 370 INDEX. Cast iron 278 Caustic potash 322 soda 328 Cavendish 5 Celestine 312 Cerium 304 Chalcedony 186 Chalk 314 Chameleon mineral 297 Charcoal 126 Chemical reaction 11 Chemism 12 Chemistry defined 11 Chemistry, Derivation of 1 Chert 186 Chili saltpetre 327 China clay 286 Chloric acid 104, 105 Chlorine, Estimation of 107 in drinking-water 45 Occurrence 92 Preparation 92 Properties 95 Tests 96 oxacids 101 oxides 99 monoxide 99 trioxide 100 tetroxide 100 Chlorous acid 104 Choke damp 142 Chrome alum 283 Iron stone 282 yellow 228, 284 Chromium hydroxide 283 Occurrence 282 Preparation 282 Properties 283 Compounds 283 Tests 285 oxides 283 Chrysophrase 166 Cinnabar 234, 235 Citric acid 340 Claus 270 Coal 125, 128 Coal analysis 147 Cobalt, Occurrence 292 Preparation 29S Properties 292 Compounds 293 Tests 294 glance 292 Cobaltous chloride 294 nitrate 294 sulphate 294 Cobalt ultramarine 294 Coin, gold, silver, bronze 211 Coke 129 Columbite 307 Combining number 14 Combustion . . . .■ 27 Spontaneous 29 Compounds 10 Conductivity 210 Condy's disinfecting liquid 297 Conglomerates 188 Copperas '. 280 Copper glance 258 nitrate 260 Copper, Occurrence 258 Preparation 259 Properties 259 Compounds 260 Tests 261 oxides 261 pyrites 258 sulphate 260 sulphides 260 Corundum 286 Crocoisite 282 INDEX. 371 Cuprite 258 Cyanogen 145 Dalton 6 Davy 6 Dialysis 187 Diamonds 125, 126, 127 Dldymium 304 Disodium phosphate 329 Dog-tooth spar 314 Dolomite 316 Dulong and Petit's law 209 Dutch liquid 134 Ekaluminum 303 Egyptians, Chemistry of 1 Elements defined 9 Elements, Names of 17 Classification of . .' 219-222 Table of 20 Elixir Vitae 4 Epsom salts 317 Equations, Atomic and molecular, 155 Meaning of 36 Writing of 81 Emery 286 Erbium 305 Etching on glass 122 Ethylene 133 Test for 134 Experiment defined 8 Fat 321 Feldspar 286 Fermentation 139 Ferric chloride 280 hydroxide 280 Ferrous chloride 280 sulphate 280 sulphide 281 Fire 27 Fire damp 131 Fixed alkalis 320 Flint 186 Flowers of sulphur 158 Fluorine 122 Fluorspar 315 Fly-powder 243 Fool's gold 281 Formula 18 Franklinite 298 Fresenius's analytical classifica- tion of the metals 337 Fusible metal '. . 211 Galena 224, 227 Gallium 303 Gas carbon 129 Geber 2 German silver 211 Glass 333 Glucinum 302 Gold 266 Granular iron ore 276 Grape iron ore 276 Graphite 125, 126, 128 Greeuockite 263 Green vitriol 280 Guignet's green 283 Gunpowder .' 325 Gypsum 314, 315 Hardness of water 47, 316 Estimation of 49 Haematite 276 Hausmannite 295 Heavy spar 310, 311 Hone stone 186 Horn silver 229 Hydriodic acid 117, 118 Hydrobromic acid 110-112 Hydrochloric acid, Occurrence . . 97 372 INDEX. Hydrochloric acid, Preparation. . 97 Properties 97 Tests 99 Hydrofluoric acid, Preparation. . 122 Properties 122 Tests 123 Hydrofluosilicic acid 190 Hydrogen arsenide 244 Hydrogen dioxide 47, 48 Hydrogen, Occurrence 34 Preparation 34 Properties 38 Test 40 persulphide 163 phosphides 197 selenide 178 stibide 250 sulphide. Estimation of 181 sulphide, Occurrence 160 Preparation 161 Properties 162 Tests 163 telluride 180 Hydroxyl 71 Hydroxylamine 70 Hypobromous acid 112 Hypochlorous acid 101-103 Hyponitrites 65 Hyponitrous acid 65 Hypophoshorous acid 199, 200 Iceland spar 314, 316 Illuminating gas 135 Indium 303 Iodic acid 121 Iodine, Occurrence 115 Preparation 116 Properties 116 Tests 117 oxacids 120 oxides 120 Iridium 270 Iron arsenide 242 Iron, Occurrence 275 Preparation 276 Properties 279 Compounds 280 Tests 281 oxides 280 pjTites 281 Jet 129 Kaolin 286 Kelp 115 Kieserite 316 Kupfer-nickel 290 Lac sulphuris 158 Lampblack . . 126 Lanthanite 304 Lanthanum 304 Lapis lazuli 288 Laughing gas 60 Law of definite proportions 12 of multiple proportions 13/ Lavoisier 6 Lead chloride 228 chromate 228, 284 Lead, Occurrence 224 Preparation 224 Properties 226 Compounds 227 Tests 228 Lepidolite 335 Libavius 4 Lignite 129 Limestone 314 Lithium 335, 336 Liquation 251 Lodestone 276 Lunar caustic , 232 INDEX. 373 Magnesia 317 Magneslte 316, 317 Magnesium carbonate 317 chloride 92, 317 limestone 316 Magnesium, Occurrence 316 Preparation 316 Properties 316 Compounds 317 Tests 317 Magnetite 276 Manganese acids. . . : 296 Manganite 295 Manganese, Occurrence 295 Preparation 295 Properties 295 Compounds 296, 297 Tests 298 oxides 296 sulphides 297 Marble 314 Massicot 227 Matter 12 Mechanical mixture 11 Meerschaum 316 Melting-points 210 MendelejefE's classification . .220, 221 Mercuric chloride 235 Mercurous chloride 235 nitrate 236 Mercury, Occurrence 233 Preparation 234 Properties 235 Compounds 235 Tests 237 Ked oxide of 235 Metal, Analytical classification of 212, 216 Metal defined 208 Metals of the alkalies 320 Metals, Salts of 216 Metaphosphoric acid 202 Metastannic acid 253 Methane 132 Meteorites 275 Micaceous iron ore 276 Microcosmic salt 335 Mispickel : 242 Molecules- 149 Molecular heat 211 Molecular weight, Determination of 151, 152 Molybdenite 272 Molybdenum 272 Nickel ammonium sulphate 291 arsenide 242 blende 290 glance 290 Nickel, Occurence 290 Preparation 290 Properties 291 Compounds 291 Tests 291 Nickel oxides 291, 293 sulphate 291 sulphide 291 Niobium 307 Nitre 324 Nitric acid 67-69 Nitrites 66 in drinking-water 46 Nitrogen chloride 106 dioxide 61, 62 monoxide 59-61 Nitrogen, Occurrence, etc 50, 51 Nitrogen oxacids 65 oxides 58 pentoxide 64 tetroxide 64 trioxide 63 Nitrous acid 66, 67 374 INDEX. Mtrous oxide 59 Novalculite , 186 Odontolite 288 Oil of vitriol 172 Opal 186 Oriental amethyst 286 emerald r 286 topaz 286 Orpiment 242 Orthoclase 189, 321 Orthophosphoric acid 201 Osmium 271 Oxalic acid 340 Oxidizing-flame 28 Oxygen, Occurrence 23 Preparation 23, 24 Properties 25 Tests 30 Oxy-hydrogen blow-pipe 42 Ozone 31, 32 Palladium 269 Paracelsus 4 Peat 129 Perchloric acid 105, 106 Pewter 211 Philosopher's stone 3 Phlogiston 5 Phosphate of aluminum 287 Phosphates, Tests for 203 Phosphoric acid 201 Phosphorite 193 Phosphorous acid 200, 201 Phosphorus, Occurrence 193 Preparation 193 Properties 195 Tests 196 Phosphorus oxacids 199 oxides 198 pentoxide 198 Phosphorous trioxide 198 Pitch blende 306, 307 Plastic sulphur 159 Platinum 268 Plumbago 125 Pneumatic chemistry 5 Potash 325 Potassium bichromate 284 bromide 323 carbonate 325 chlorate 323 chloride 323 chromate 283 chromium sulphate 283 cyanide 325 f errocyanide 281 hydroxide 322 iodide 323 Potassium, Occurrence 321 Preparation 321 Properties 322 Compounds 322 Tests 326 Potassium permanganate 297 sulphate 323 Priestley 5 Prussic acid 146 Pyrochlor ; 307 Pyrolusite 295 Pyrophosphoric acid 202 Quartz 186 Quartzite 186 Queen's metal 211 Quicklime 314 Eealgar 242 Eed precipitate 235 Reducing-flame 29 Rhodium 271 Rhodocrosite 295 INDBX. 375 llinmann's green 294 Eose's metal 211 Rubidium 336 Ruby 286 silver 229 Ruthenium 270 Entile 305 Safety-lamp 132 Salt-cake process 330 Saltpetre 321, 324 Sal sodae 383 Salts, Acid and normal 80 defined 77 Sand 186 Sandstone 188 Sapphire 286 Scale of hardness 127 Scheele 5 Schweinf nrth's green 245 Scheele's green 5, 245 Selenite 314 Selenic acid 179 Selenious acid 179 Selenium dioxide 178 Selenium, Occurrence 177 Preparation 178 Properties 178 Tests 179 Separation of arsenic, antimpny, and tin 254 of bismuth, copper, and cad- mium 263 of chlorides and bromides . . 114 of chlorides, bromides, and iodides 119 of copper and bismuth 261 of cobalt, manganese, nickel, and zinc 300 of first group metals 238 Separation of first and second group metals 265 of fourth group metals 318 of iron, chromium, and alu- minum 289 of nickel and cobalt . . . 295, 302 of second group metals .... 264 Serpentine 189 Siderite 276 Silica 184, 188 Silicates '. 188, 189 of cobalt 294 Siliceous springs 187 Silicon fluoride 190 hydride 189 Silicon, Occurrence, etc. . . . 184, 185 Silver bromide 233 chloride 92, 232 copper glance 229 iodide 115 nitrate 232 Silver, Occurrence 228 Preparation 229 Properties 231 Compounds 232 Tests 233 plating solution 232 Skutterrudite 292 Slaked lime 314 Smalt 294 Soda-ash 330 process 331 Soda crystals 333 Sodium aluminate 287 Sodium ammonium phosphate . . 335 arsenate 245 carbonate 830 chloride 92, 328 hydroxide 328 hyposulphite 329 hypophosphite 329 376 INDEX. Sodium nitrate. 329 Sodium, Occurrence 326 Preparation 327 Properties 328 Compounds 328 Tests ,. 333 .silicates 333 thiosulphate 329 Solder 211 Sombrerite 193 Soot 126 Spathic iron ore 276 Specific heat 209 Spectra '.. 303 Specular ore 276 Speculum metal 211 Speiss cobalt 292, 293 Spinelle 316 Spirits of hartshorn 55 Stannic acid 253 sulphide 253 Stannous sulphide 253 chloride 253 Steam, latent heat of 44 Steatite 188 Steel 279 Stibnite 247, 249 Stream tin 251 Strontianite 312 Strontium carbonate 312 nitrate 312 Strontium, Occurrence, etc. 312, 313 Substituting power and valence . 154 Suint 321, 325 Sulphur acids, Tests for 176 Sulphur dioxide. Occurrence, etc 164, 166 Sulphuretted hydrogen 160 Sulphuric acid. Estimation of . . . 182 fuming 174 Hydrate of '. 173 Sulphuric acid, Occurrence 169 Preparation 170 Properties 172 Tests 173 Sulphur, Occurrence 157 Preparation 157 Properties 158 Tests 160 Sulphur oxacids 167 oxides 164 Sulphurous acid 168, 169 Sulphur trioxide 167 Superphosphate of lime 315 Sylvite 321 Symbols, Chemical 17 Talc 316 Tantalite 307 Tantalum 307 Tartar emetic 249 Tartaric acid 340 Tellurium acids 180 dioxide 180 Tellurium, Occurrence 179 .Preparation, etc 180 Tellurium trioxide 180 Terbium 305 Thenard's blue 294 Thermometers 83 Thiosulphuric 175 Thorite 305 Thorium 305 Tin foil 252 Tin, Occurrence, etc 251-253 Tin stone 251 Titanite 305 Titanium 305 Titanium cyano-nitride 306 Topaz 288 Triphylline ". 335, 336 Tripoli 188 rSDBX. 377 Tungsten 271 Tvirquois 287 Type metal 211 Ultra marine 288 Uranium 306 Useful problems 89 Valence IS'S Vanadium 307 bronze 308 Van Helmont 4 Vivianite 193 Volatile alkali 320 Volume of a gas affected by heat, 86 by pressure 85 Formulae for computing the, 91 Water 40-43 drinking, Impurities of . . . 45-47 "Water-lime 314 Weight and density 88 White lead 227 Willemite 298 Witherite 310, 311 Wohler 6 Wood's alloy 211 Wolfram 271 WoUaston 271 Wollastonite 188 Wrought iron 279 Yttrium 304 Yttrotantalite 307 Zinc blende 298 Zinc, Occurrence, etc 298-300 Zircon 306 Zirconium 306