CORNELL 
 
 UNIVERSITY 
 
 LIBRARY 
 
1 ^ Cornell University 
 
 Vif Library 
 
 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/cu31924012369710 
 
ELEMENTS 
 
 QUALITATIVE AND QUANTITATIVE 
 
 CHEMICAL ANALYSIS 
 
 BY. 
 
 G. C. CALDWELL, B.S., Ph.D., 
 
 PROFESSOR OF AGRICULTURAL AND ANALYTICAL CHEMISTRY IN CORNELL UNIVERSITY ; 
 
 AUTHOR OF AGRICULTURAL CHEMICAL ANALYSIS ; MANUAL OF INTRODUCTORY 
 
 CHEMICAL practice; MANUAL OF QUALITATIVE ANALYSIS. 
 
 SECOND EDITION, REVISED AND ENLARGED. 
 
 PHILADELPHIA: 
 P. BLAKISTON, SON & CO., 
 
 I0I2 WALNUT STREET. 
 
 1892. 
 
/^ nsin 
 
 Entered according to Act of Congress, in the year 1892, by 
 
 P. Blakiston, Son & Co., 
 in the office of the Librarian of Congress, at Washington. 
 
 Press of Wm. F. Fell & Co., 
 
 I270-24 SANSON! ST., 
 
 PHILADELPHIA. 
 
PREFACE. 
 
 In this work the author has brought together what has already 
 been published, separately, in the " Manual of Qualitative 
 Chemical Analysis," by himself and Dr. S. M. Babcock, and 
 the "Notes on Chemical Analysis," by himself alone; he has 
 added thereto much matter on qualitative analysis, all of Parts 
 III and IV on quantitative analysis, and nearly all of Part V. 
 
 Of course no such work as this can be satisfactorily prepared 
 without frequent reference to the standard treatises of Prescott 
 and Johnson, and of Fresenius, in one of which the whole 
 subject of qualitative analysis is very thoroughly treated, and 
 in the other both qualitative and quantitative analysis. The 
 author would acknowledge his indebtedness to these works, 
 while claiming for himself at least some novelty in the arrange- 
 ment of the matter, as well as in some of the matter itself, in 
 this attempt to prepare a book that is much needed in his own 
 laboratory. 
 
 Also, for valuable suggestions in the revision of the work for 
 the second edition, he is indebted to Professor Dennis, and 
 Instructors Chamot and Preswick, of the University. 
 
 Certain modifications in the spelling of chemical terms, 
 adopted. after careful consideration by the chemical section of 
 the American Association for the Advancement of Science, are 
 used in this second edition. 
 
 HI 
 
TABLE OF CONTENTS. 
 
 INTRODUCTION. 
 
 PART I. 
 
 THE PROCESSES OF ANALYTICAL CHEMISTRY AND SOME OF 
 THE PRODUCTS OF ITS OPERATIONS. 
 
 4 
 
 Chapter I. — Solution and Solids from Solution. 
 
 The solvent agents used ; physical solution ; chemical solution ; table of 
 solubilities; solution of metals; solubility and temperature ; solubility 
 of salts in acids; comparative range of solvent power of different 
 solvents ; saturated solutions ; solution of gases or vapors ; solids from 
 solution, by cooling of saturated solutions ; by removal of the solvent 
 agent. 
 
 Chapter II. — Acids, Bases, Salts. 
 
 The terms defined; anhydrids; normal salts; acid salts ; basic salts. 
 
 Chapt'er III. — Oxidation, Chlorination, Reduction. 
 
 The terms defined ; conditions under which oxidation or chlorination may 
 take place ; reduction defined ; conditions under which reduction may 
 take place ; the reactions of oxidation and reduction, with free oxygen ; 
 nitric acid ; aqua regia ; potassium chlorate and hydrochloric acid ; 
 bromin ; chromic acid ; sulfuric acid ; changes in valence aceompany- 
 ing oxidation or chlorination or their reverse. 
 
 Chapter IV. — Metathesis. 
 
 Term defined; conditions under which it takes place; important law of; 
 several kinds of metathesis made use of; on some of the products of 
 metathesis; metathesis requires time. 
 
 Chapter V. — Writing Equations. 
 
 Requirements for the correct writing of an equation ; structural or graphic 
 formuliK of compounds ; valence of elements and compounds ; table of 
 elements and hypothetical compounds entering into the equations for 
 the reactions of chemical analysis ; special Sighs attached to the equa- 
 tion ; additional directions ; common errors in writing equations ; 
 writing the history of a substance in equations. 
 V 
 
VI TABLE OF CONTENTS. 
 
 Chapter VI. — The Manipulations of- Analytical Chemistry in 
 General. 
 
 Making solutions; fluxing; evaporation, ignition, acidification, all<aliza- 
 tion, neutralization ; adding a reagent in excess ; precipitation ; how 
 precipitates are described ; digesting ; boiling ; filtration ; washing 
 precipitates ; dissolving precipitates ; cleanliness in the laboratory ; 
 rapidity of work. 
 
 PART II. 
 
 SYSTEMATIC COURSE- OF QUALITATIVE ANALYSIS. 
 Chapter VII. — The Mode of Procedure in General. 
 
 Introduction ; the grouping of the substances ; the sulfids, how produced, 
 and important "characteristic properties, solubility, oxidation, chlorina- 
 tion) reduction; the hydroxids, how produced, when the action of the 
 reagents normal, and when not, solubility ; the final tests, place of in 
 the course of analysis, two classes of; order of arrangement of the 
 work; tabular view of the course of analysis. 
 
 Chapter VlII. — The Solution of Substances. 
 
 Solution of non-metallic substances ; of metallic substances ; treatment of 
 insoluble substances. 
 
 Chapter. IX. — The Acidigens (or Acids). 
 
 Solubility of compounds, reactions, and systematic course for their detec- 
 tion. 
 
 Chapter X. — The Systematic Course for the Separation and De- 
 tection OF the Basigens (or Metals). 
 
 The silver group; occurrence, reactions and detection of the members of 
 the group, and explanations of the chemistry of the work ; the tin 
 group, ditto; the copper group; the iron group; the aluminum group; 
 the calcium group ; the potassium group. 
 
 PART III. 
 
 THE OPERATIONS OF QUANTITATIVE ANALYSIS. 
 
 Chapter XI. — Methods of Measuring, in Gravimetric Analysis. 
 
 Introduction ; the balance described ; its proper care and use ; the weighing 
 of the substance for analysis; the manipulations of weighing; the 
 weighing of the products of the analysis. 
 
 Chapter XII. — Measuriijg in Volumetric Analysis. 
 
 Standard and normal solutions defined ; determination of strength of 
 measuring solutions ; the instruments for measuring, measuring flask. 
 
TABLE OF CONTENTS. VU 
 
 pipette, burette; cleaning tliese instruments; chromic acid cleaning 
 mixture ; calibration of graduated instruments ; special precautions for 
 use of these instruments. 
 
 Chapter XIII. — Seven Important Operations of Quantitative Work. 
 Weighing the substance ; preparation of the solution ; the precipitation ot 
 the substance, for gravimetric estimation ; filtration, and use of suction ; 
 washing the precipitate ; the asbestos filter, in Gooch crucible ; prepara- 
 tion of precipitate for weighing, by ignition. 
 
 Chapter XIV. — Miscellaneous Matters. 
 
 Determination of specific gravity of liquids, by specific gravity _ pipette ; 
 calculations of results of analysis ; the quantitative note book ; special 
 maxims for the young analyst. 
 
 PART IV. 
 EXAMPLES FOR PRACTICE IN QUANTITATIVE ANALYSIS. 
 Chapter XV. — Iron and Sulfur Trioxid. 
 
 Iron, gravimetric method ; products of the analysis described ; the process 
 for the determination ; volumetric method, process described ; prepara- ■ 
 tion of standard solution of dichromate ; assay of limonite ; sulfur 
 trioxid; product of the analysis described; process for the determination. 
 
 Chapter XVI. — Acidimetrv and Alkalimetry. 
 
 The principles of these methods of determining free acid or base ; the 
 indicators used ; preparation of the standard solutions, and determina- 
 tion of their relative strength ; determination of absolute strength of the 
 acid by silver nitrate ; actual determination of free acids and bases. 
 
 Chapter XVII. — Lead, Phosphorus Pentoxid, and Calcium. Iod- 
 ometry. 
 Lead, products of the analysis described ; the process for the determination ; 
 phosphorus pentoxid, product of the analysis described ; the process for 
 the determination ; calcium, by a gravimetric and a volumetric method, 
 principles of the methods ; product of the analysis described ; prepara- 
 tion of the standard solution ; the processes foi: the determination, 
 lodometry; principles of this method of volumetric analysis; prepa- 
 ration of the solutions ; determination of antimony. 
 
 Chapter XVIII. — Analysis by Electrolysis. 
 
 Separation of copper and silver; determination of the silver and copper 
 by electrolysis ; determination of silver as chloride. 
 
 PART V. 
 
 MISCELLANEOUS MATTER. 
 List of apparatus for qualitative work. 
 
 Lists of apparatus for quantitative work, for shorter course, and for full 
 course. 
 
TABLE OF CONTENTS. 
 
 Special directions concerning the use of apparatus. 
 
 List of reagants used, arranged in the alphabetical order of their full names, 
 
 and also in the alphabetical order of their formulas. 
 Directions in regard to the preparation of reagents. 
 Table of atomic weights. 
 Tables showing per cent, of NH3, SOg HCl, N2O5 and HNO3, in solutions, 
 
 different specific gravities. 
 Table of comparison of weights and measures. 
 Course of laboratory work in chemistry. 
 Index and glossary. 
 
INTRODUCTION. 
 
 At Cornell University a large number of students in some of 
 the technical courses are required to take an elementary course 
 of practice in chemical analysis, including both qualitative and 
 quantitative work, after having had the elements of general 
 chemistry in this University or elsewhere. 
 
 There are many comprehensive and excellent works on 
 chemical analysis in general, and on particular branches of 
 chemical analysis, with which every special student of chemistry 
 is acquainted ; but these works are too large and expensive for 
 any but the professional chemist. There are also numerous 
 smaller works on the general subject. But in such of these as 
 the author has met with no special chapters are devoted to the 
 enlightenment of the student beginning this study, on the 
 chemistry of the operations of qualitative and quantitative 
 analysis in general ; he must, therefore, be referred to the larger 
 works for this important information. 
 
 Consequently either every beginner, whether his proposed 
 course be thorough or elementary, must possess the works of 
 Fresenius, or some other treatise of equal scope on the subject, 
 or else copies of these works must be placed in the laboratory, 
 for reading or reference, — many copies, if the number of students 
 is large. Each plan has its manifest disadvantages. 
 
 In these considerations the author finds the reason for the pub- 
 lication of this little volume, for the • convenience of his own 
 students, — that they may have always at hand such full details as 
 to the chemistry and manipulation of these operations that they 
 are called upon to' perform, many of which are entirely new to 
 them, that they need never be at a loss as to what to do, or how 
 to do it, or why they do it, if they will read with care what is 
 here given. When the work laid out in this book is mastered^ 
 the student who wishes to go further in general or special direc- 
 tions will find himself prepared to use the general or special 
 treatises on chemical analysis, for no one of which this introduc- 
 tion can be taken as a substitute. 
 
2 INTRODUCTION. 
 
 Chemical analysis is studied usually because the student expects 
 to make some application of it in his business or profession ; in 
 so far it is a practically useful study. But beyond this it has, as 
 does the study of every branch of science, its special disciplinary 
 value. It enforces the importance of attention to even small 
 details in manipulation; the student learns, if he is capable of 
 learning anything by experience, that the only sure way to suc- 
 cess in any part of the work is by the closest following of the 
 directions given him, at least till he has proved, by conclusive 
 results of his own experiments or observations, that there is a 
 better way ; but this better way must in its turn be followed no 
 less precisely. 
 
 No one of the analytical processes in use is absolutely perfect ; 
 it is this that makes accuracy and precision in the manipulation 
 of so much the greater account. Such discipline as this practice 
 affords of the hand, eye, and judgment is useful in many of the 
 professions for which the first special training is given in the 
 University. 
 
 Chemical analysis comprises two kinds : — 
 
 Qualitative analysis, by which we ascertain what chemical ele- 
 ments or compounds a substance contains. 
 
 Quantitative analysis, by which we ascertain how much of one 
 or more of its constituents the substance contains. 
 
 The chemistry and manipulation common to both kinds of 
 analysis is treated in Part I of this work. The systematic course 
 of qualitative analysis follows in Part II. In Part III a descrip- 
 tion is given of some of the special operations of quantitative 
 analysis, and in Part IV the special examples for practice com- 
 prised in this short course are described and explained. Finally, 
 in Part V, lists of apparatus and reagents are given, with some 
 instructions concerning their proper use, and several Tables for 
 reference. 
 
PART I. 
 
 THE PROCESSES OF ANALYTICAL CHEMISTRY, 
 
 AND THE 
 
 PRODUCTS OF ITS OPERATIONS. 
 
 CHAPTER I. 
 
 SOLUTION AND SOLIDS FROM SOLUTION. 
 
 1. The getting of substances into solution, and getting them 
 out of solution into the solid form, are fundamental operations 
 of analytical chemistry with which the student has to deal more 
 than with any others, especially in the earlier stages of his work. 
 Some general acquaintance with the principles and methods of 
 the solution of substances is essential at the very outset. 
 
 2. Solution: — The solvent agents used. The more important 
 solvent agents used in chemical analysis are, besides water, 
 aqueous solutions of hydrochloric acid, nitric acid, and acetic 
 acid, of the alkaline hydroxids, KOH, NaOH, or NH^OH, of 
 alkaline sulfids, especially ammonium sulfid, and alcohol, 
 ether, and carbon disulfid. 
 
 3. Since all thes^ acids and alkaline solvents consist largely of 
 water, a substance that is insoluble in water cannot, so long as it 
 is the same chemical substance, be dissolved by any one of them. 
 Therefore when a substance that is insoluble in water is dissolved 
 with the aid of a solution of an acid, such as the hydrochloric 
 acid of the laboratory, or of an alkaline hydroxid, or an alkaline 
 salt, such as a sulfid or a chlorid, some chemical change must 
 precede such solution. On these grounds two kinds of solution 
 may be distinguished, physical solution and chemical solution. 
 
 4. Physical solution is the resultant solely of the mutual action 
 of physical forces among the particles of the solid and of the 
 liquid, the final result of which is the disappearance of the solid 
 
 3 
 
4 ELEMENTS OF CHEMICAL ANALYSIS. [§§ 5-6. 
 
 as a separate substance, visibly distinct from the liquid ; it 
 becomes completely merged in the liquid, but suffers no chemical 
 change; on removing the solvent, in any way that does not 
 chemically affect the substance dissolved in it, as by evaporation, 
 this substance reappears possessing the same chemical properties 
 as before. This is the kind of solution that is commonly effected 
 by water. 
 
 5. Chemical solution involves a chemical alteration of the sub- 
 stance dissolved, and the production of a new substance that is 
 soluble. It may take place with water alone, when the substance 
 is an oxid that can form a soluble hydroxid. CaO is probably 
 insoluble in water, but Ca(0H)2, formed as soon as this oxid is 
 brought in contact with water, is slightly soluble. We cannot 
 say that we know whether K^O is soluble or insoluble in water ; 
 for in the instant of contact between the two KOH is formed, 
 which is very soluble. 
 
 Most commonly, it is a more active agent than water, which 
 serves to bring about the solution by chemical change, such as 
 an acid or an alkaline solution ; and if the<»excess of acid or 
 alkali, remaining after the solution is completed, be wholly 
 removed, leaving nothing but water, the solution still continues 
 undisturbed, which is evidence that a new substance has been 
 formed, soluble in water ; and it has, been formed by chemical 
 changes affecting the solvent agent as well as the substance dis- 
 solved, as illustrated by the following equations : — 
 
 CaCOj + 2HCI = CaCla + H^O + CO^. 
 Ca3(P0,), -f 4HCI = CaH,(PO,), +2CaCl,. 
 3Pb + 8HN0, =^Pb(N03|3 + 4H2O + 2NO. 
 As.S, + 3(NH,),S = 2(NH,)3AsS3 . 
 
 The substances whose formulas are underlined are new sub- 
 stances, which are soluble in water. 
 
 6. Table of solubilities. Some acquaintance with the solu- 
 bility of the chemical compounds met with in the ordinary work 
 of chemical analysis is very helpful to the student. In the fol- 
 lowing Table, W in the square corresponding to any salt indi- 
 cates easy solubility in water, w sparing solubility, wa solubility 
 in water only when at least slightly acidified, A insolubility in 
 water but solution by moderately dilute mineral acids, and / 
 insolubility in water or dilute acids. Slight trace of solubility 
 in water or dilute acids, or solubility or insolubility in acetic 
 
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 SOLUTION AND SOLIDS FROM SOLUTION. 
 
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6 ELEMENTS OF CHEMICAL ANALYSIS. [§§ ^-8^ 
 
 acid is not taken account of, nor solubility or insolubility of 
 other than normal salts (§ 15), except when, as in the case of 
 many carbonates, for example, basic salts are those ordinarily 
 met with. 
 
 An examination of this Table shows at once that all normal 
 nitrates and acetat.es, and all the salts of the alkaline metals 
 (potassium, sodium) are soluble. Other similar general conclu- 
 sions can be deduced by the student himself, which, once 
 familiarly learned, will be very useful in working out equations. 
 
 Of solubility in strong acids, but not in dilute, the following 
 instances are specially important : nearly all insoluble sulfids are 
 soluble in concentrated nitric acid ; many insoluble silicates are 
 decomposable by concentrated hydrochloric acid, with solution 
 of the bases. 
 
 7. Solution of metals. As to the solubility of the commonly 
 occurring metals, it is to be noticed that all are absolutely in- 
 soluble in pure water; that those of the aluminum and iron 
 groups are soluble in hydrochloric or sulfuric acid, with evolu- 
 tion of hydrogen, and with the formation of chlorids or sulfates ; 
 they are soluble in nitric acid, with the formation of the usual 
 products (§ 24 b); that the rest, except gold and platinum, are 
 dissolved by nitric acid, forming, solutions except in cases of 
 antimony and tin, that gold and platinum are attacked by aqua 
 regia or any mixture evolving free chlorin. 
 
 8. Miscellaneous considerations, a. Solubility and tempera- 
 ture : The solubility of salts is in most cases much greater in 
 hot than in cold solvents. 
 
 b. Solubility of salts in acids. A salt that is perfectly soluble 
 in water may be insoluble in strong acid : the salt, if separated 
 out or precipitated in the acid, usually takes a somewhat crystal- 
 line form, often to the confusion of the young analyst ; on the 
 addition of sufficient water, solution takes place readily. For 
 instance, barium chlorid, which is easily soluble in water, is not 
 soluble in strong hydrochloric acid ; hence, if barium carbonate 
 is dissolved in too strong a solution of the acid, the chlorid is 
 apt to appear as a crystalline deposit. 
 
 c. Comparative range of solvent power of different solvents. 
 In the operations of chemical analysis, the solubility or insol- 
 ubility of substances is utilized in, more particularly, water, 
 alcohol, mineral acids, organic acids, and solutions of alkaline 
 hydroxids or hydrates, or alkaline solutions as they are com- 
 monly called. Of these, water has by far the widest range of 
 
§ 9-J SOLUTION AND SOLIDS FROM SOLUTION. 7 
 
 solvent power ; it may, in fact, be called i/ie solvent upon which 
 we depend in nearly all cases for solution of substances : a 
 chemically active agent does not dissolve, but, as has been 
 already shown, only makes new compounds that are soluble 
 in water. For this preparatory work, hydrochloric and nitric 
 acids have the widest range of action ; comparing these two 
 acids, it may be observed that while nitric acid will dissolve nearly 
 all substances that are dissolved by hydrochloric acid, it will, in 
 virtue of being an oxidizing agent (§ 20), dissolve many sub- 
 stances that hydrochloric acid will not dissolve, such as some 
 metals and their sulfids. 
 
 d. A saturated solution. For each substance and each neutral 
 solvent in which it is soluble, there is a definite limit to the 
 amount of the substance that can be dissolved at a given tem- 
 perature ; when this limit is reached the solution is said to be 
 saturated. When the temperature of such a solution falls, or, in 
 a very few cases, is raised, or when any of the solvent is removed, 
 a portion of the substance separates out in the solid form. When 
 thus separated it is more or less crystalline. Therefore, when a 
 crystalline deposit appears in a solution, for no other apparent 
 reason than a possible change in one or both of these conditions 
 mentioned above, it can be re-dissolved either by adding more 
 of the solvent, usually only water being required, or by raising 
 the temperature. 
 
 e. In the case of chemical solution, the quantity of the sub- 
 stance dissolved is dependent on the quantity of water present to 
 dissolve the new substance formed, and also, in accordance with 
 the laws of stochiometry, on the quantity of the chemically 
 active, solvent agent present. So far as this active agent is con- 
 cerned, it is independent of the temperature, except that, as 
 chemical action is stronger at high than at low temperatures, the 
 solution will proceed more rapidly if the mixture of substance 
 and solvent is heated. 
 
 9. Solution of gases or of vapors. -Some of the reagents used 
 in chemical analysis are solutions of gases or vapors in water, 
 such as hydrochloric acid and ammonia ; and some reactions 
 that are made use of in the analytical work depend to some 
 extent on such solution. 
 
 As in the solution of solids in water, there is a definite limit 
 to the amount of the gas dissolved for any given temperature ; 
 but the amount dissolved increases, instead of diminishing, as 
 the temperature falls, and increases also as the pressure of the 
 
8 ELEMENTS OF CHEMICAL ANALYSIS. [§§ lO-II. 
 
 particular gas dissolved increases on the surface of the liquid, or, 
 in other words, as the proportion of that gas increases in the 
 air to which the dissolving liquid is exposed. 
 
 From what has been stated above, except when a solution of a 
 gas is very dilute, that is, has but a very little of the gaseous 
 substance in it, if the solution is warmed a portion of the sub- 
 stance will escape; or, if a strong solution is poured from a 
 closed vessel into an open dish, or even if the stopper of the 
 bottle containing it is left out, the gas will escape. 
 
 Other reagents in common use are solutions of substances that 
 are volatile only at moderately elevated temperatures, or of 
 vapors, such as bromin water. On heating such a solution the 
 substance dissolved will escape in part, and the more rapidly the 
 lower the temperature at which it assumes the vaporous form. 
 In a solution containing a mixture of such substances, the more 
 volatile one may be almost entirely expelled by heat, while a 
 large portion of the other still remains ; thus nitric acid or hy- 
 drochloric acid may be removed from a solution by heating it 
 for a sufficient length of time with a large excess of sulfuric 
 acid. 
 
 10. Solids from Solution : — There are many ways by which 
 the reverse of solution of solids can be accomplished ; some of 
 these have been referred to in the preceding sections. 
 
 The cooling of saturated solutions. This is of little account in 
 analytical work. In a few cases, when the cooling is slow, the 
 crystalline form assumed by the solid may be a convenient 
 means of identifying it or confirming results of other tests. 
 
 11. The removal of the solvent agent. This may be accom- 
 plished in three ways. 
 
 a. By its slow escape, as it passes into vapor by simple ex- 
 posure to the air. This takes place readily with the chemically 
 inactive solvents, water, alcohol, common ether, petroleum ether, 
 and carbon disulfid. The process is of little use in analytical 
 work, except when, as also in the case of slow cooling of satu- 
 rated solutions referred to in the preceding section, the solid 
 obtained may exhibit some characteristic crystalline form that 
 will aid in its identification. Such an operation is best applied 
 to a small quantity of the liquid in a watch glass, and it is usually 
 necessary to examine the deposit with the microscope. 
 
 b. By the rapid removal of the solvent by the aid of heat. 
 This is a very important analytical process, for it often becomes 
 necessary to obtain the product of some operation, or series 
 
§ 1 2. J ACIDS, BASES, SALTS. 9 
 
 of Operations, in the solid form, expeditiously : see Evaporation, 
 Chap. VI. 
 
 c. By the removal of an active solvent through neutralization. 
 Many precipitates are soluble in acids, and some are soluble in 
 solutions of alkaline hydroxids or salts, forming new, soluble 
 compounds ; on neutralizing the acid or the base, or decompos- 
 ing the solvent salt by an acid, the original substance is precip- 
 itated again, in some cases ; in other cases, another substance ip 
 formed, of the same qualitative composition, but different quan- 
 titative composition. The solution of ammonium magnesium 
 phosphate in acid and the effect of the neutralization of the acid 
 by ammonia, also the solution of aluminum hydroxid in sodium 
 hydroxid and the result of the neutralization of the alkali by 
 acid, are good illustrations of the first mentioned kind of action. 
 See aluniinum and magnesium in the aluminum and calcium 
 groups. Chap. X. The precipitation by acids of the sulfids 
 of arsenic, tin, and antimony from their solutions in ammonium 
 sulfid, illustrates the second kind of action ; see the tin group. 
 Chap. X. 
 
 b. By the formation, through chemical action, of 3. new insolu- 
 ble compound containing at least one of the constitutents of the 
 substance dissolved. This method of obtaining solids from solu- 
 tion, which is of fundamental importance in analytical chemistry, 
 will be more fully considered in Chapter IV, on Metathesis. 
 
 CHAPTER II. 
 
 ACIDS, BASES, SALTS. 
 
 12. A solution made in any of the ways described in Chap. I 
 may contain acids, bases, or salts. 
 
 For our present purposes, an acid may be defined to be a body 
 always containing (i) hydrogen, (2) a so-called electro-negative 
 or acidigenic (acid-generating) element, such as chlorin, sulfur, 
 phosphorus, and (3) sometimes oxygen; its hydrogen being 
 replaceable by an electro-positive or basigenic (base-generating) 
 element or compound, such as potassium, calcium, magnesium. 
 An acid may, however, contain, in the place of one of the reg- 
 ular acidigenic elements, an element usually basigenic, as iron. 
 
lO ELEMENTS OF CHEMICAL ANALYSIS. [§§ 13-16, 
 
 or manganese in manganic or permanganic acid. The presence 
 of an acid in solution is indicated by the reddening of blue 
 litmus paper. 
 
 13. A base is a body containing (i) a basigenic or base- form- 
 ing element or compound, such as potassium, ammonium, cal- 
 cium, or iron, and (2) the hypothetical hydroxyl, HO, this 
 hydroxyl being replaceable by an acid minus its basic hydrogen. 
 The presence of a base in solution is indicated by the blue color 
 given to red litmus, or the brown color given to turmeric. 
 
 By the abstraction of the elements of water from one or two 
 molecules of an acid or a base, the so-called anhydrids are pro- 
 duced : these anhydrids are also called oxids, with the prefixes 
 di, tri, tetra, pent, used to indicate the number of atoms of oxygen, 
 when more than one atom is present. 
 
 Thus:— 
 
 2HNO3 = N2O5 (nitrogen pentoxid) -|- HjO. 
 HjS04= SO3 (sulfur trioxid) + HjO. 
 2KOH = K2O -t- HjO. 
 Ca(OH)j = CaO-|- HjO. 
 
 14. A salt is the body formed when the hydrogen of an acid 
 replaceable by a basigenic element or compound, or the hydroxyl 
 of a base replaceable by an acid minus its basic hydrogen, is so 
 replaced. 
 
 Thus : — 
 
 KOH -f- HCl = KCl + H^O. 
 2NaOH + HjSOi = NajSO^ -|- 2H2O. 
 
 It will be seen that in all cases where a salt is formed by the 
 mutual action of a base and an acid, water is produced from the 
 hydrogen of the hydroxyl and a part or all of the oxygen. 
 Salts may also be formed by the direct union of acidigenic and 
 basigenic oxids. 
 
 A most characertistic property of an acid and a base, respect- 
 ively, is this tendency to react with each other, and, neutralizing 
 each other's marked properties, to form a salt. 
 
 15. Of salts there are several kinds. A normal salt is one in 
 which the basigenic element or compound is substituted for all 
 the replaceable hydrogen of the acid ; for example, K^SOj, 
 NaNO,, Al, 1:504)3. 
 
 16. An acid salt is one of an acid haying more than one re- 
 placeable atom of hydrogen, in which less than the whole num- 
 ber is replaced by a basigenic element ; for example, KHSO4 ; 
 NaHjPOi, compared with Nas PO,. 
 
§§ I7-20.J OXIDATION, CHLORINATION, REDUCTION. II 
 
 17. A basic salt is one, following the same line of definition, 
 in which only a part of the hydroxyl of a base having more 
 than one molecule thereof is replaced by an acid minus its 
 hydrogen, or in which there is a smaller number of molecules of 
 the acidigenic part of the salt, as compared with the basigenic 
 part, than in the normal salt ; for example, PbOHNOg, 
 PbjOjOHNOj, compared with the normal salt Pb (N03)2 ; 
 Bi(OH)2NO„ BiOCl, compared with the normal salt Bi(.N03)3. 
 
 Basic salts are often difficultly soluble, when normal salts of 
 the same acid are soluble, and sometimes cause the an.alyst 
 much trouble : thus, while solubility in water is an eminent 
 characteristic of all normal nitrates, many basic nitrates are in- 
 soluble in water. 
 
 18. A double salt is defined as one containing with one 
 acidigen two basigens, as KNaSO,, KPtCle. 
 
 CHAPTER III. 
 .OXIDATION, CHLORINATION, RKDUCTION. 
 
 19, These processes play an important part in the operations 
 of chemical analysis, and a clear understanding of their nature, 
 and of the conditions under which they take place, is essential 
 to intelligent work. 
 
 Oxidation is the addition of oxygen to a substance, in chem- 
 ical combination : chlorination is the addition of chlorin to a 
 substance in chemical combination ; the reverse of either of these 
 operations is reduction. 
 
 20. Conditions under which oxidation or chlorination may take 
 place. 
 
 a. The substance must be one capable of taking oxygen or 
 chlorin into chemical combination. Such substances are all 
 the basigenic elements, in the list in the Table, § 37, whether 
 these elements are in the free state, or combined with sulfur as 
 sulfids. In the latter case the sulfur is displaced by the oxygen 
 or chlorin. Moreover, several of these elements are met with 
 in ordinary analytical work in combination with more than 
 
ELEMENTS OF CHEMICAL ANALYSIS. [§ 20. 
 
 one proportion of oxygen or 
 
 chlorin, as shown in the following 
 
 table :— 
 
 
 
 FeO, FeClj; 
 
 Fefi,, 
 
 Feci, 
 
 NiO, NiCl,; 
 
 NiPs, 
 
 NiCl, 
 
 CoO, C0CI2 ; 
 
 CoA. 
 
 CoClj 
 
 
 Cr,0„ 
 
 CrCl,; CrOs 
 
 MnO, MnClj; 
 
 MnPa, 
 
 MnCls; MnOj; MnOj; MtijO, 
 
 Cup, CuCl; 
 
 CuO, 
 
 CuClj 
 
 Hgp, HgCl; 
 
 HgO, 
 
 HgCI, 
 
 Au^O, AuClj; 
 
 AUjOg, 
 
 AuClj 
 
 ASjOj, AsCIj; 
 
 AsA 
 
 
 SbjOj, SbClj; 
 
 SbA, 
 
 SbCls 
 
 SnO, SnClj; 
 
 SnOj, 
 
 SnCl^ 
 
 Therefore any one of these elements, although already in com- 
 bination with oxygen or chlorin, may possibly combine with an 
 additional quantity. 
 
 Further, in our analytical work, we may meet with compounds 
 of certain acidigenic elements with oxygen in different propor- 
 tions. Such elements are nitrogen, sulfur, and carbon. 
 
 b. There must be an oxidizing or chlorinating agent. Such 
 agents, as used in analytical work, are especially nitric acid and 
 free chlorin. The free oxygen of the air, or the oxygen dis- 
 solved in water, may oxidize. Hydrochloric acid alone may 
 act as a chlorinating agent on the metallic elements, but without 
 ever carrying the chlorination higher than the first stage, if there 
 be more than one with the metal in question ; when this acid 
 chlorinates, in this sense, its hydrogen is set free. 
 
 Fe + 2HCI = FeClj + 2H. 
 
 Also, when an oxid is dissolved in hydrochloric acid a chlorid 
 is formed, but hydrogen is not set free. 
 
 In compounds of bromin and chlorin with oxygen, the union 
 is a feeble one, and these compounds may serve as active oxidiz- 
 ing agents. Such are chlorates (KCIO3), and hypobromites 
 (NaBrO). See § 24, d and e, for examples. 
 
 Any element capable of combining with oxygen or chlorin in 
 more than one proportion may yield compounds in these higher 
 proportions, which themselves become oxidizing or chlorinating 
 agents, when brought into contact, under the requisite condi- 
 tions, with a substance capable of being oxidized or chlorinated. 
 
 4FeS04 -I- H^MnOj + sU^SO^ — 2Fej(SO,)8 + MnSO^ -|- 4H2O. 
 
§ 2 1. J OXIDATION, CHLORINATION, REDUCTION. 1 3 
 
 Iron is changed from a ferrous t,o a ferric salt, and manganese 
 is reduced from manganic acid to a raanganous salt. 
 
 c. In case the oxidizing agent is the acid constituent of a salt, 
 it must usually be set free by an excess of another and a stronger 
 acid before action will take place in solution. Hence, a nitrate 
 in solution in water, as sodium nitrate or silver nitrate, is not an 
 oxidizing agent as free nitric acid is ; further, nitric acid, as 
 formed free in an aqueous solution, is usually too much di- 
 luted to act as an oxidizing agent. Potassium chlorate in solu- 
 tion does not oxidize till an excess of concentrated hydrochloric 
 acid or other stronger acid is added. To get oxidizing action 
 from potassium dichromate strong acid must be added in excess. 
 
 These substances may, however, act as oxidizing agents with- 
 out such assistance, when fused. 
 
 d. Usually, heat favors oxidation or chlorination, as it does 
 chemical action generally. 
 
 e. When an element can take more than one degree of oxida- 
 tion or chlorination (see list in a of this section) the higher 
 oxid or chlorid will commonly be formed (or a salt correspond- 
 ing with the higher oxid), if the oxidizing or chlorinating agent 
 be in excess to a considerable extent, and especially if its action 
 be aided by heat. If the element itself is in excess, so that, as 
 in the case of a solution of a metal by nitric acid, and especially 
 if the acid be not very strong and the operation be conducted 
 without heat, and a portion of the metal remains undissolved 
 when the action of the acid has ceased, the lower oxid or chlorid 
 is more likely to be formed. These rules as to chlorination 
 apply, however, only to cases where the work is done by free 
 chlorin, and have nothing to do with the simple solution of 
 metals in hydrochloric acid. 
 
 In cases where an element, or one of its compounds, is 
 attacked by free chlorin in the presence of water, and the chlorid 
 of this element cannot exist under the conditions of the attack, 
 but the oxid or a compound of the oxid can exist, this oxygen 
 compound may be formed, the oxygen being derived from the 
 water present. 
 
 As, S3 + loCl + SHjO = 2H3ASO4 + loHCl -t- 3S. 
 
 21. Reduction. This operation, the reverse of oxidation or 
 chlorination, takes place under conditions the reverse of those 
 required for oxidation or chlorination. 
 
 a. The compound must be one that is capable of giving up 
 
14 ELEMENTS OF CHEMICAL ANALYSIS. [§ 22. 
 
 oxygen or chlorin under the given conditions. Such compounds 
 are any of those formed with oxygen or chlorin by the basigenic 
 elements, and by certain acidigenic elements And as an element 
 may combine first with one quantity of oxygen or chlorin, and 
 then with an additional quantity (§ 20 a), so in reduction under 
 certain conditions, a part of the acidigenic element may be with- 
 drawn, and' under the same conditions continued in force, or 
 under other more powerfully active conditions, another portion 
 may be >vithdrawn. 
 
 2HgCl2 + SnClj = 2HgCl + SnCl^ 
 2HgCl + SnClj = 2Hg + SnCl^ 
 PtCl^ + SnClj = PtClj + SnCl^ 
 PtCl^ + 2H = Ft + 2HCI 
 
 b. There must be a reducing agent. This may be any element 
 having under the given conditions a stronger attraction for, the 
 oxygen or chlorin in combination, than is exerted by the other 
 element in the compound ; or it may be a compound of one of 
 these elements with oxygen or chlorin in a lower proportion, that 
 is capable of combining with more than one proportion. (§ 20 a). 
 
 22. A reducing agent excelling all others, in the scope and 
 power of its action is nascent hydrogen, or hydrogen taken just 
 at the moment when it is liberated from combination, as when zinc 
 is dissolved in dilute sulfuric acid. Further, hydrogen compounds 
 in which the hydrogen is rather loosely bound, and especially if 
 associated with elements that are themselves capable of oxidation, 
 are a strong reducing agent; sometimes the other element of the 
 compound is set free. 
 
 AsH, + 6AgN03 + 3H2O = 6Ag + HjAsO, + 6HNO3. 
 
 Oxalic acid, HjCjOj, sulfurous acid, H2SO3, and hydrogen 
 sulfid, often occur as agents of reduction in analytical wo'rk; 
 carbon dioxid and water, sulfuric acid and water, and free sulfur 
 being the products from the reducing agents in the several 
 cases. 
 
 As to the hydrogen, it may be observed in general that when- 
 ever any oxidation, chlorination, or reduction is taking place, and 
 there is any hydrogen in the substances engaged, it is very likely 
 to appear in H^O or HCl in the products of the action ; the 
 bond of union between hydrogen and oxygen, or between 
 hydrogen and chlorin, is one of the strongest in chemistry; 
 consequently the tendency to form one or the other of these 
 
§§23-24-] OXIDATION, CHLORINATION, REDUCTION. 15 
 
 compounds, whenever there is any opportunity so do so, is very 
 powerful. 
 
 6H2C2O4 (oxalic acid) + 2KMn04 + 2H2SO4 = SH^O + 12CO2 
 + K3SO4 + MnSO^j. 
 
 Free hydrogen not nascent is a strong reducing agent when 
 aided by heat. Also at higher temperatures, a red heat or above, 
 carbon is a powerful reducing agent, carbon monoxid or carbon 
 dioxid being the product. 
 
 23. Except when oxidation or chlorination is effected directly 
 by free oxygen or chlorin, these processes and reduction go hand 
 in hand ; the simultaneous presence, and the co-operation, of 
 both a substance capable of oxidation or chlorination, and 
 a body capable of yielding oxygen or chlorin, are essential. 
 Commonly, the existence together in a solution is impossible of 
 a substance in the free state that is capable of acting as an oxid- 
 izing or a chlorinating agent under the existing conditions, and 
 of a substance capable of taking up oxygen or chlorin. 
 
 Since, as is usually the case in analytical operations, oxidation 
 or chlorination of one substance implies reduction of some other 
 substance, the same general conditions that are favorable for one 
 operation are favorable for the other. 
 
 24. The reactions of oxidation and reduction. 
 
 a. With free oxygen. When oxidation results from the action 
 of free oxygen of the air, or the oxygen dissolved in water, as 
 when moist and freshly precipitated ferrous sulfid is oxidized to 
 the sulfate, the reaction needs no explanation. 
 
 b. With nitric acid ; products of the oxidation. Water is 
 always formed by the union of the hydrogen of the acid with a 
 part of its oxygen. 
 
 When metals or their sulfids are treated, a nitrate of the 
 metal is nearly always formed ; in a very few cases, as with 
 antimony and tin, for example, oxids that are insoluble in the 
 excess of acid are produced. All such exceptions to the general 
 rule that nitrates are formed are mentioned where they occur. 
 
 In the treatment of a sulfid the sulfur is either set free or 
 oxidized to sulfuric acid (see sulfids. Chap. VII). 
 
 Products of the reduction. The nitrogen of the decomposed 
 nitric acid may be evolved as ammonia, NH3, free nitrogen, 
 nitrogen monoxid or nitrous oxid, NjO, nitric oxid or nitrogen 
 dioxid, NjOa, or NO, nitrogen trioxid, N2OS, or nitrogen tetroxid, 
 NaO,, or NO,. If the nitric acid is in excess and a Jjoiling heat 
 
l6 ELEMENTS OF CHEMICAL ANALYSIS. [§ 24. 
 
 is used, the product is nearly all NO : but excess of reducing 
 agent, a very dilute acid, and a low temperature favor the form- 
 ation of NH3 at the other extreme. Under certain conditions 
 hydrogen may be set free, although, as the presence of nascent 
 hydrogen and nitric acid together is incompatible, such condi- 
 tions can occur but rarely. In general, NO, a colorless gas, is 
 formed in analytical work, which in contact with the air takes 
 up oxygen, forming N2O3 and NO2, the latter appearing as 
 brown fumes. 
 
 The following diagram illustrates the manner in which HNO3 
 may be supposed to be' broken up in the oxidation of substances, 
 or in the production of nitrates of the metals, with NO as the 
 product of the reduction : — 
 
 In oxidation. formation of nitrates. 
 
 N = H - 01-0- !N = 
 
 H- OJ-0 
 H-l O -O 
 
 ]Sf = o H-^-O- N = 
 
 H-|"cr-0- N = 
 
 H- O -O- N = 
 
 It will be seen that in simple oxidation 2 molecules of 
 HNOs yield 3 atoms of oxygen : and that, in order to get the 
 product H2O, which is always formed, the number of molecules 
 of HNO3 taken must always be 2 or some multiple thereof; and 
 that the number of atorns of oxygen used for the oxidation 
 must always be 3 or some multiple thereof. Observe, also, that 
 just half of the oxygen of the HNO3 consumed goes to oxidize 
 the metal, and the other half appears in the H^O and NO. 
 
 It is also shown that in the formation of nitrates, 4 molecules 
 of HNO3 yield 3 molecules of the hypothetical NO3 ; and that, 
 in order to get the product HjO, the number of molecules of 
 HNO3 used must be 4 or some multiple thereof, and the number 
 of molecules of NO3 used directly in the production of, and 
 appearing in, the nitrate in the right hand member of the equa- 
 tion must be 3 or some multiple thereof. 
 
 . 3Sn + 4HNO3 = sSnOj + ■iB.f) + 4NO. 
 3Pb + 8HNO3 = 3Fb(N03) , + 4HjO + 2Na 
 
 c. With aqua regia (3 parts cone. HCl, i part cone. HNO3). 
 These acids react with each other as follows : — 
 
 3HCI + HNOs = NOClj + CI + 2HjO, 
 or 3HCI + HNO3 = NOCl + 2CI + 2HjO. 
 
 The products vary according to the existing conditions. 
 
§ 24-] OXIDATION, CHLORINATION, REDUCTION. 17 
 
 The reaction is aided by heat, and takes place only very 
 slowly between moderately dilute acids. These compounds of 
 nitrogen, oxygen, and chlorin, or nitrosyl chlorids, are gaseous 
 and very unstable ; they are dissolved by that part of the acid 
 still undecomposed : when the solution 'is saturated their produc- 
 tion ceases. If a metal is put into this solution, action (chlorina- 
 tion) takes place, these compounds being decomposed and sup- 
 plying chlorin, while oxids of nitrogen escape; the solution 
 being then no longer saturated with these gases a fresh quantity 
 is formed : thus the operation goes on, as long as these 
 chlorinating products are consumed by a body capable of chlori- 
 nation. It is especially the production of this abundance of free 
 and nascent chlorin that makes aqua regia such a powerful 
 chlorinating agent. 
 
 The products of the action of aqua regia are, therefore, a 
 chlorid of the metal attacked, and water, and, for the reduction, 
 lower oxids of nitrogen, probably nitric oxid for the most part. 
 
 d. Potassium chlorate and hydrochloric acid. This mixture 
 gives when heated a greenish yellow gas, a mixture of chlorin 
 and chlorin dioxid. 
 
 KCIO3 -I- 2HCI = CI -f ClOj -t- KCl + HjO. 
 
 The chlorin dioxid is very unstable, giving nascent chlorin 
 and oxygen by its decomposition. The mixture is, therefore, a 
 very efficient chlorinating agent : in the presence of water it 
 may act also as a strong oxidizing agent. 
 
 The products of the action of this mixture on substances 
 capable of oxidation or chlorination are oxids and chlorids of the 
 basigenic element. 
 
 e. Bromin. This acts as an oxidizing agent in the presence 
 of water, by reason of its strong attraction for hydrogen, and the 
 generally greater stability of the oxids than of the bromids. 
 Being much more soluble in concentrated hydrochloric acid than 
 in water, this acid solution is often used in preference to an 
 
 "aqueous solution. Hydrobromic acid and oxygen are the pro- 
 ducts of the reaction with water, in the presence of a substance 
 capable of oxidation. 
 
 Dissolved in solutions of potassium or sodium hydroxid it 
 yields a mixture of hypobromite, KBrO or NaBrO, and bromite, 
 KBrOa or Na BrOj, powerfully oxidizing substances : a bromid 
 of the alkaline metal is the product of the reduction. 
 
 CHjNjO (urea) + sKBrO = CO, -f 2HjO + 3KBr + 2N. 
 2 
 
l8 ELEMENTS OF CHEMICAL ANALYSIS. [§§ 25-26. 
 
 f. Chromic add. In a solution of a chromate containing free 
 acid, the chromic acid is liberated from its base, and acts as 
 an oxidizing agent, or chlorinating in the presence of hydro- 
 chloric acid. 
 
 Salts containing chromium as a basigenic constituent are the 
 products of the reduction. 
 
 2HjCrO, + 6HC1 + sHjS = SH^O + 2Cras + 3S. 
 
 g. Sulfuric acid. This when concentrated and hot may act as 
 an oxidizing agent, sulfurous acid being the product of the reduc- 
 tion, and a sulfate of the metal oxidized. As under e above, the 
 carbon and hydrogen of organic substances may be oxidized in 
 this way, but the nitrogen nearly always appears in the form of 
 ammonia. Kjeldahl's exceedingly useful method of determining 
 nitrogen in organic compounds is based on this reaction. 
 
 25. Changes in valence accompanying oxidation or chlorination, 
 or their reverse. Thus far, these operations have been regarded 
 only as involving the addition or removal of oxygen and chlorin : 
 other important changes, as in valence, may, however, take place 
 simultaneously, supposing that more than one valence be allowed 
 to the same element. The higher degrees of valence are found 
 in the higher grades of oxidation or chlorination. Illustrations 
 will be found in the Table, § 37, where the same element is 
 given in more than one group. The student should notice the 
 very marked changes in chemical properties that sometimes 
 accompany such changes in valence. 
 
 CHAPTER IV. 
 METATHESIS. 
 
 26. Constant use is made in chemical analysis of the ki-nd 
 of chemical change designated as metathesis, from the Greek, 
 meaning to set over. 
 
 Conditions under which metathesis takes place. 
 
 a. Metathesis takes place as a rule only between substances 
 that are liquefied either by solution or fusion. Only under such 
 conditions is there that closeness of contact, and freedom of mo- 
 tion among the particles of the substances acting on one another, 
 which permits or facilitates chemical change. 
 
§ 2 7- J METATHESIS. 1 9 
 
 In the case of exceptions to this rule, which are to be found 
 in the course of the qualitative work, it will be noticed that at 
 least one of the substances engaged is in solution, while the other 
 is often freshly precipitated and moist, when it may reasonably 
 be supposed to exist in a much more porous condition, exposing 
 a larger surface to attack by the dissolved reagent, than when 
 even in the finest powder of the previously dried substance. 
 
 PF or wa in the Table of Solubilities, § '6, may be taken as 
 indicating sufificient solubility for a precipitating reaction ; and 
 such a reaction will be given, provided that the reagent used is 
 capable of giving it in any solution of the substance. 
 
 b. That one and the same elementary or compound substance 
 exhibits unequal attraction for different elementary or compound 
 substances is an important fundamental principle of chemistry, 
 which the student learns very early in his study of the science. 
 But the formation or decomposition of chemical compounds, or, 
 in other words, the kind of metathesis that takes place, is some- 
 times powerfully modified by conditions quite independent 
 of the relative forces of attraction that make or break these 
 compounds. 
 
 27. The following law illustrates this statement, and at the 
 same time bears a very important relation to the operations of 
 analytical chemistry. 
 
 On bringing together a substance from the acidigen column. 
 Table, § 37, and one from the basigen column, if a substance 
 can be formed by their union that is insoluble in the medium 
 of contact, or one that is gaseous at the temperature of contact, 
 such union will take place ; or such changes will take place in 
 the arrangement of the constituents of compounds containing 
 these substances as may be necessary to produce the new insol- 
 uble or gaseous compound. 
 
 It is above all upon the unfailing operation of this law that the 
 success of the work of the analytical chemist depends ; if, for 
 instance, he could not rest assured beyond all doubt of the cer- 
 tainty of the reaction expressed by the following equation : — 
 NbjSOi + BaClj = BaSO< + NaClj, 
 
 or, that in a solution prepared in a certain definite manner a 
 barium salt would always react with a sulfate, yielding a precipi- 
 tate of barium sulfate, and at least almost completely removing 
 the sulfuric acid from the solution, no dependence could be 
 placed on the reliability of his qualitative or quantitative results. 
 
20 ELEMENTS OF CHEMICAL ANALYSIS. [§§ 28-Z9. 
 
 where the detection or quantitative estimation of either barium 
 or sulfuric acid is concerned. 
 
 28. In cases where insoluble compounds cannot be formed by 
 interchange of the constituent parts of the substances brought 
 together, it may be supposed that new compounds are neverthe- 
 less formed, even though there may be no visible changes. If, 
 for instance, the substances brought together in solution were, 
 instead of those in the above equation, sodium sulfate and 
 ferric chlorid, a part of the chlorin may go to the sodium and a 
 part of the sulfuric acid to the iron, so that four salts, Na2S04, 
 FeClj, NaCl, Fe2(S04)3 exist in the solution instead of the two 
 original ones, or instead of only one salt, as in the second mem- 
 ber of that equation. Evidence of such change is found in 
 certain color reactions, as, for instance, the deep red color which 
 results from the reaction between a ferric salt and a sulfocyanate, 
 (§ 92): no insoluble substance is formed, but there must be, 
 nevertheless, a partial interchange of acids and bases. Moreover, 
 when a new compound can be formed by interchange of the con- 
 stituents, or by metathesis, that is partially or slightly soluble in 
 the medium of interchange, a portion of the new compound will 
 be precipitated, while the rest may remain in solution as such, 
 and we will have also some of the original, undecomposed salts ; 
 thus, with the first letters of the alphabet, used as coefficients, 
 representing known quantities and the last letters unknown 
 quantities: — 
 
 aCaClj -I- bKjSO^ = uCaSO^ -f- zKCl -|- vCaSO^ -|- yCaClj + xKjSOi. 
 
 Calcium sulfate is slightly soluble in water, and while one 
 portion is precipitated, another will remain in solution, together 
 with a portion of the original calcium salt. 
 
 Such will be the result, as may now be readily understood, 
 if the conditions under which a complete precipitation is to be 
 made are not carefully fulfilled : errors may follow, which may 
 be especially serious in quantitative work, and often in qualita- 
 tive analysis as well, and which the student is too prone to 
 attribute to the fallibility of the reaction instead of his own 
 want of care. 
 
 29. If, as a result of the metathesis, one of the new substances 
 produced be an acid, or any other solvent agent that will dis- 
 solve the other possible product of the metathesis, of course the 
 conditions are not fulfilled, according to the law stated above. 
 
§3°- J METATHESIS. 21 
 
 for the production of that substance, and there may be no visible 
 evidence of its production. 
 
 FeClj + HjPO^ = FePO^ + 3HCI 
 
 may not be a correct representation, since FePO^, though in- 
 soluble in water, is soluble in hydrochloric acid ; but the following 
 is correct : — 
 
 s FeCl3 + {NH,)3PO^ = FeP04 + 3NH,Cl. 
 
 A precipitate may be formed in the first case, however, since 
 the small quantity of HCl set free can make only a very dilute 
 acid liquid, perhaps insufficient to keep the phosphate from 
 separating out. 
 
 30. Several kinds of metathesis are made use of in analytical 
 work. Between two salts giving : — 
 
 a. An insoluble new salt ; 
 
 NaCl + AgNOj = AgCl + NaNOj. 
 
 b. No insoluble salt, but at least a partial exchange of acids 
 and bases, and some evidence of the exchange visible to the 
 senses ; 
 
 FeCla + 3NH4CNS = Fe(CNS)8 (deep red solution) + sNH^Cl. 
 
 A more nearly correct equation would, however, be similar to 
 that in § 28, but without any precipitation at all. 
 
 Between an acid and a salt giving : — 
 
 c. An insoluble salt, insoluble in water, but possibly not in 
 the new acid produced, unless very dilute ; 
 
 Hg NO3 + HCl = HgCl + HNO3, 
 
 But 
 
 CaCl2 + H2C2O4 -|- 2HCI ^= no visible reaction, possibly. 
 
 d. A gaseous product. 
 
 KjCOs + 2HC2H3O2 = 2KC2H3O2 + CO2 + H^O. 
 
 Between an hydroxid and a salt giving : — 
 
 e. Metallic hydrates or hydroxids, insoluble : — 
 
 AICI3 + 3NaOH = Al (OH), + 3NaCl. 
 
22 ELEMENTS OF CHEMICAL ANALYSIS. [§§ 31-33- 
 
 f. Insoluble salts into which the basigenic element of the 
 hydroxid enters: — 
 
 Ba(0H)2 + KjSO^ = BaSO^ + 2KOH. 
 
 g. A gaseous product : — 
 
 NH4CI + KOH = KCl + NHj + HjO. 
 
 • . 31. Metathesis is not completed instantaneously, although it 
 may set in the moment that the substances reacting upon one 
 another are brought together. If a slightly soluble salt is the 
 product, this slight solubility may retard the completeness of 
 the separation, or prevent it altogether ; but if time is allowed, 
 the separation may be carried much further than at the beginning 
 of contact, and it may ih the end be quite complete. Instances 
 in illustration of these points will be met with in the course of 
 the analytical work that follows, where directions are given to 
 allow the mixture of reagent and solution of substance to stand 
 for several hours, in order that the desired reaction may be 
 obtained or completed. 
 
 CHAPTER V. 
 WRITING EQUATIONS. 
 
 32. All the chemical changes that take place in the operations 
 of chemical analysis, and upon which these operations are based, 
 are comprised under these three heads of (i) solution, (2) oxida- 
 tion and reduction, and allied processes in which chlorin, bromin, 
 iodin or sulfur may take a part, like that taken by oxygen, and 
 (3) metathesis. 
 
 The working out of chemical equations explaining these 
 changes may be justly regarded as a valuable test of the student's 
 insight into their chemistry ; the writing of these equations is an 
 important part of his stjidy of chemical analysis, and it may be 
 made to give some intefcctual zest to what would otherwise be 
 little more than mere machine work. 
 . 33. The correct writing of an equation requires : — 
 
 a. A knowledge of the formulas of the substances originally 
 acting upon each other. 
 
 b. A knowledge of the products of this action. 
 
§§ 34-35-] WRITING EQUATIONS. 23 
 
 c. A balancing of the equation so that its two members shall 
 be equal in respect to kind and number of atoms, without in- 
 cluding any substances, elementary or compound, whose presence 
 is impossible or unreasonable under the existing conditions, and 
 in which every simple or compound hypothetical body in- 
 cluded shall have its supposed combining power or valence 
 satisfied. 
 
 The information under a is given in the text-books, or often 
 on the labels of the bottles ; that under 6 is usually partly given 
 in the description of the reaction ; what is not thus explained 
 must be worked out under the general rules to be found in this 
 text-book or in other works. 
 
 The law stated in § 27 can be usefully applied, in combination 
 with the study of the table of solubilities, in the working out of 
 this part of the problem, where it becomes necessary to decide 
 whether any reaction will take place. 
 
 The work under c is accomplished by the application of prin- 
 ciples laid down in this or other text-books. Under this head 
 it is important to understand some of the principles upon which 
 formulas are constructed. 
 
 34. Structural or graphical formulas of compounds. The or- 
 dinary formula of a compound shows only the relative and most 
 reasonable number of atoms of each of the elements composing 
 it. In the structural formula an idea is presented to the eye of 
 the manner in which the component elements may reasonably be 
 supposed to be grouped together, as illustrated by the following 
 examples : — 
 
 Fe=0 
 
 K— 
 
 > 
 
 Fe=0 
 
 K2 = 0, = S=02or /^\l 
 K— 
 
 In these formulas each element is supposed to have a certain 
 combining power, measured in terntls of a monovalent atom, 
 which is called its valence ; this is shown in the formula by the 
 number of dashes connected with its- symbol, or by Roman 
 numerals in small type above and to the right of it ; the valence 
 of each of the elements in the second plan of the formula of 
 potassium sulfate is indicated with perfect clearness by the 
 method first stated. 
 
 35. The true valence of many of the metallic elements is not 
 yet settled : and this whole matter of valence should be strictly 
 
24 ELEMENTS OF CHEMICAL ANALYSIS. [§§ 36-37- 
 
 regarded as merely a working theory, and one which can be 
 made useful in the study of chemical equations. 
 
 In the following Table the apparent valence is assigned, in 
 such unsettled cases, that corresponds with the most generally 
 adopted formulas of the compounds of these elements. To silver 
 the valence one is assigned, which is apparent in the formulas 
 AgCl, AgNOs, Ag^SOj, etc., although there are reasons for re- 
 garding it as a dyad metal with a valence of two. Lead is prob- 
 ably a tetrad element, but the formulas of all its common salts 
 can be and are constructed on a dyad basis : the same may be. 
 said of barium, strontium, etc. Iron is regarded by many as 
 dyad in ferrous compounds and tetrad in ferric compounds, while 
 others regard it as tetrad in both. Again, more recent researches 
 tend to show that it is triad in the ferric compounds, instead 
 of tetrad ; although the question is, perhaps, not yet fully set- 
 tled, the simpler formulas on the triad basis are given in the case 
 of iron, and of some other elements also, in regard to which the 
 same view is at least permissible. 
 
 36. In the equations of the more simple forms of metathesis 
 certain groups of elements are invariably transferred from one 
 member of the equation to the other, apparently without being 
 broken up in the actual course of the changes involved in the 
 reaction ; thus, in the equation 
 
 KjSO^ -1- Ba(N03)2 = BaSO^ + 2KNO.,. 
 
 SO, and NO3 changes places ; in the structural formula for 
 KjSO, (§ 34), it is seen that the group SO, is dyad ; so in the 
 structural formula for sodium nitrate Na-O-N = Oj, the group 
 -0-N=0.i is monad ; if, in writing equations for metathesis 
 the student supposes these and similar acidic groups to be broken 
 up he is very likely to end his work in confusion. Hence, for 
 his purposes in equation writing, the most practical course is to 
 regard these groups as actually transferred from one basigen to 
 another, and as bearing the valence indicated by the composition 
 of the compounds containing them. But he must not forget 
 that they are purely hypothetical groups which have not been 
 isolated, or proved to exist as such in any chemical compound 
 apparently containing them. 
 
 37. For assistance in explaining by equations the reactions 
 that take place in the course of ordinary qualitative analysis, the 
 following classification is given of elements, and of certain hypo- 
 thetical compounds of which examples were mentioned in the 
 preceding section. 
 
§§ 38-39J WRITING EQUATIONS. 25 
 
 In any product of the ordinary metatheses of chemical analysis 
 there will be at least one basigen and one acidigen, but not 
 necessarily only one atom ch- molecule of each : very rarely will 
 there be more than one acidigen (see basic salts § 17) ; more often 
 there will be more than one basigen, provided that the acidigen 
 is more than monovalent (see acid salts § 16), as illustrated 
 in the following formula of sodium ammonium phosphate : Na 
 NH.HPO^. 
 
 Basigens (base-forming). Acidigens {acid-forming'). 
 
 H, K, Na, NHj, Ag, Hg(ous), CI, I, Br, F, OH, NO3, CIO,, Cy, 
 
 Cu. (or CN), CyS (or CNS), C^HjOj. 
 
 Ba, Sr, Ca, Mg, Zn, Mn, Fe(ous), O, S, SO,, SO,, CO3, Cp,, CrO, 
 
 Ni, Co, Pt, Hg(ic), Cd, Cu, Pb. SiOs, SnOj, C^H^Oj. 
 
 Au, Bi, Fe. P0„ AsOj, AsO„ SbO„ C.HjO,, 
 
 Fe(CNj) (in ferricyanid). 
 
 FeCyj (or Fe(CN)8) (ip ferrocyanid). 
 
 DYAD OR TETRAD. 
 
 Sn, Pt. 
 
 Sb, As. 
 
 TRIAD OR PENTAD. 
 
 38. In order that a chemical equation shall exhibit at a glance 
 as much as possible of the nature of the products formed, the 
 
 sign — , is always to be put underneath the formula of an 
 
 insoluble compound precipitated, and the sign — " — over the 
 formula of any gaseous product evolved. In the case of the 
 solution of a substance originally insoluble in water, effected by 
 any active solvent agent, by which a new compound soluble in 
 water is formed, the special, new, soluble product of the solution 
 is to be indicated by a straight line under its formula. See 
 equations, § 5. 
 
 39. In writing equations it must be remembered that water 
 is always present when the reactions are obtained in the wet way, 
 that is in solutions, and that water can always be incorporated 
 into the equation if necessary for reasonable results. 
 
26 ELEMENTS OF CHEMICAL ANALYSIS. [§ 4°- 
 
 Also, when solution is made by an acid, an excess of the acid 
 is always supposed to be present, and the possible effect of such 
 excess must be regarded, such, for instance, as its tendency to 
 form salts with oxides (§ 40 c). 
 
 Also, that any soluble salt of an acid will give the same reac- 
 tion as will the acid itself, but will not, of course, act as a solvent, 
 like the free acid. Thus NaCl and HCl give the same charac- 
 teristic product with silver salts. 
 
 40. Providing against some of the common errors in writing 
 equations, a. An equation written is to be regarded as repre- 
 senting some chemical change of which there is sensible proof, 
 such as the disappearance of a solid as it passes into solution by 
 an acid, a case of oxidation or an allied process, or of reduction, 
 a precipitate formed, or a gas evolved, or a change of color of 
 the liquid. Metatheses may take place, and doubtless do when 
 there is no plain evidence of it presented to the senses (§ 28) : 
 but they are not such as are expressed by the ordinary equations 
 explaining the operations of chemical analysis. The student 
 must be able to give one of the above reasons for every equation 
 that he writes. Failure to meet this requirement is a very com- 
 mon source of error. 
 
 b. As a result of the metatheses made use of in analytical 
 work, in the wet way, it is not common that the metals them- 
 selves appear as precipitates ; they of course never exist as such 
 in a solution, for they are not soluble; it is only their com- 
 pounds that are soluble. Therefore an equation that leaves a 
 metal in a free state, and at the same time unprecipitated, 
 cannot be a correct one. 
 
 c. The oxids of the metals do not exist as such, in a free 
 state, in a solution, since every oxid which is capable of forming 
 a base soluble in water, immediately on contact therewith forms 
 such a base. 
 
 KjO-|-HjO = 2KHO. 
 CaO-l-HjO =Ca(0H)2. 
 
 Nor do the oxids, whether in solution or insoluble, exist as 
 such in the presence of an excess of a free acid, provided that 
 they are capable of yielding soluble salts with that acid ; any 
 explanation of a metathesis which results in this condition of 
 things must therefore be incorrect. 
 
 d. It is more common to meet with the acidigenic elements 
 in the elementary form, as the products of metathesis or other 
 operations of analytical work ; they may be in solution, as in the 
 
§ 41 -J WRITING EQUATIONS. 27 
 
 case of bromin or chlorin, or precipitated, as iodin or sulfur, or 
 gaseous, as chlorin. 
 
 e. The anhydrids of the acids, such as N2O5, SO3, correspond- 
 ing to the oxids of the bases, cannot exist in a free state, in an 
 excess of water, provided that they are capable, as is the fact in 
 most cases, of forming a soluble acid : for such an acid will be 
 immediately formed on contact with the water, and will go into 
 solution. 
 
 f. Of course an acid and a base cannot exist free in the same 
 solution ; whichever is in excess, or present in quantity more 
 than sufficient to combine with all of the other, will take it all 
 up to form a salt, no iriatter whether the salt so formed be 
 soluble or insoluble. In this connection it is to be remembered 
 that a hydroxid or hydrate (Chap. VIII) answers to the definition 
 of a base (§ 13). 
 
 g. In writing equations a reagent added is always to be con- 
 sidered, as in the actual use of it, in excess, more or less above 
 what is required of it for the actual work of precipitation or 
 solution : and in completing an equation the possible effect of 
 such excess must be taken into account ; as, for example, when 
 the reagent is a strong base, like KOH or NaOH, and an acid is 
 one of the products of the reaction. Other illustrations of this 
 principle occur in some of the equations given out. 
 
 41. Students are too ready to extricate themselves from some 
 difficulty in completing an equation, by indicating some chemical 
 element which they cannot dispose of readily in any other way, 
 as left in the free state ; and usually, as the element so left free 
 is often a very active one, as oxygen, chlorin, hydrogen, etc., 
 this is done in direct violation of well established chemical laws. 
 Some common errors of this kind are noticed in the preceding 
 paragraphs with reference to some of the elements and to some 
 compounds. A few other elements need mention in this con- 
 nection. 
 
 a. Oxygen. Except by the action of the electric current this 
 element is left in the free state only when liberated from com- 
 pounds containing it loosely held in combination, such as 
 nitrates, chlorates or other compounds containing both chlorin 
 and oxygen, and many of the metallic oxids, especially higher 
 oxids where more than one is formed with the same metal — and 
 in the absence of any substance with which it can combine at 
 the temperature of liberation, such as metals especially of the 
 potassium, calcium, aluminum, and iron groups, and some lower 
 
28 ELEMENTS OF CHEMICAL ANALYSIS. [§ 41- 
 
 oxids where more than one is formed with the same metal (§ 20), 
 or any of the reducing agents mentioned in § 22, to which might 
 be added hydrogen sulfid. 
 
 This liberation of oxygen very rarely takes place except by 
 heating the dry substance or mixture of substances, the temper- 
 ature required for such liberation being in nearly all cases above 
 the boiling point of water or of any aqueous solution. Free 
 oxygen is therefore so very rarely a product of metatheses taking 
 place in solution, that such a result would always be specially 
 stated in the description of the metathesis. 
 
 This statement as to the liberation of oxygen from its com- 
 pounds does not refer to cases where it is withdrawn from oxid- 
 izing agents, that readily yield it at temperatures within the 
 boiling point of solutions, when bodies are presented that are 
 capable of combining with it under such conditions : no free 
 oxygen appears, however ; the element simply passes, so far as 
 our observation extends, from one compound into another. 
 
 b. Chlorin. This element is set free : — 
 
 1. By heating, in the dry condition, certain chlorids of metals 
 of the copper and tin groups. 
 
 2. When a substance containing chlorin and one containing 
 loosely bound oxygen are brought together; and in case the 
 chlorin is in the form of a stable salt, the cooperation of a 
 strong acid is necessary. The common method of making 
 chlorin, with MnOj and HCl illustrates the principle. For 
 other illustrations see § 24 c, d, and f. 
 
 But chlorin canot appear in the free state simultaneously with 
 any body that will readily combine with it, like a metal, or hydro- 
 gen, or a compound containing hydrogen loosely bound, as hy- 
 drogen sulfid, or in the presence of any other sulfid, of which it 
 at once takes the metal, or in the presence of water and an easily 
 oxidizable substance, such as a sulfite or any organic substance. 
 
 c. Hydrogen. When this element appears in the free state, as 
 the result of a chemical reaction, and evolved from a liquid, it 
 is the product : — 
 
 1. Of the action of certain metals of the first and second 
 groups on water, these metals having such an exceedingly strong 
 attraction for oxygen as to be able to take it from this most 
 stable compound. 
 
 2. Of the action of certain metals, as zinc, aluminum, or tin, 
 on an aqueous solution of an alkali (KOH, NaOH), the metal 
 displacing the hydrogen. 
 
§ 42.J WRITING EQUATIONS. 
 
 29 
 
 3. By the substitution, in a solution of an acid, of a metal for 
 the hydrogen. The common method of preparing hydrogen by 
 means of zinc and H^SOi is a familiar illustration of this prin- 
 ciple. 
 
 It will be seen that a common reaction characterizes all these 
 methods : regarding water as a compound of the hypothetical sub- 
 stance hydroxy!, HO, with hydrogen (HO + H = H-0-H) 
 the hydrogen which appears may be always considered as this 
 second atom of the element, as shown in the following equa- 
 tions, illustrating each mode of production above mentioned : — 
 
 H-O-H-fK equals KOH + H. 
 
 2KOH + Zn equals K^ = 0^= Zn + 2H. 
 
 H2 = Oj = S = O2 -f Zn equals Zn = Oj = S = 0, + 2H. 
 
 It must not be forgotten that hydrogen in the moment when 
 it is set free is in its nascent state and possessed of powerful 
 reducing properties; and that, therefore, it cannot appear in 
 the second member of the equation if there is present at the same 
 time any oxidizing or chlorinating agent, or any of the sub- 
 stances in the list in § 20 a, that readily give up oxygen or 
 chlorin (or bromin or iodin). 
 
 d. Nitrogen. Although this is not, like the elements already 
 considered, powerfully active, and eager to enter into chemical 
 combination, still it is set free from solutions only under certain 
 conditions, occurring so rarely in ordinary analytical work, as 
 always to receive special mention in the account of the reaction 
 yielding it. 
 
 e. Bromin and Iodin. The same may be said as to the ap- 
 pearance of these elements in the free state that was said of 
 chlorin. 
 
 f. Sulfur is very often set free in the reactions of sulfids, ap- 
 pearing as a very fine powder, or turbidity : its appearance in 
 the right-hand side of the equation is therefore allowable, and in 
 this respect it differs strikingly from the other elements noticed 
 above. 
 
 42. Good practice is obtained in writing equations, as well 
 as a better acquaintance with the chemistry of the analytical 
 work, by writing out, in equations, the history of each sub- 
 stance in its passage through the special course in which it is 
 tested for. Taking, for example, calcium in the scheme for the 
 
30 ELEMENTS OF CHEMICAL ANALYSIS. [§ 4 
 
 calcium group, the solution brought there contains all its bas 
 gens in the form of their chlorids, as a consideration of the pr 
 "ceding schemes will show. The first reagent added that affec 
 the calcium is (NH4)2COa, by which the carbonate is precif 
 tated ; this, then, would be the first step in the history, to 1 
 shown by an equation. 
 
 These carbonates are next dissolved in HC2H3O2, and tl 
 next equation would show the action of this acid on calciu 
 carbonate. KjCrO, has no action on the calcium in this sol 
 tion, and therefore the next step to be shown is the precipitatic 
 again by (NH4)2C08 ; next comes the solution of t^iis precip 
 tate in HCl, then the action of (NH4)2C204 on the salt of ca 
 cium in this solution, giving the final test. Thus it takes fii 
 equations to express the history of calcium, in its passage throug 
 the course for its detection. 
 
 CHAPTER VI. 
 
 THE MANIPULATIONS OF ANALYTICAL CHEMISTRY. 
 
 43. Making Solutions. The suitable preparation of a solutic 
 for analytical purposes is not so unimportant a matter as on fir 
 thought it might appear to be. There is a certain degree 
 strength, or concentration of the solution that is most suitab 
 for the work to be done with it, which may be different : 
 different cases. 
 
 Of substances soluble in water, there are few that will n^ 
 dissolve in ten times their weight of the solvent. A solution 
 such concentration is not unsuitable, as a general thing, eith 
 for reagents, or as a solution of a substance to be analyzed. As 
 reagents, however, it is better that some should be much mo 
 dilute, and others stronger; for such cases directions will 1 
 given where they are needed. 
 
 A substance to be analyzed in the wet way, that is by treatme: 
 with the reagents in solution, must first be brought into solutic 
 itself. For this purpose, only three reagents are in common us( 
 distilled water, hydrochloric acid, and nitric acid, the acids beii 
 either dilute or concentrated. In general the presence of stroi 
 acid in a solution to be analyzed is to be avoided, as liable 
 
§§ 44-4S-] MANIPULATIONS. 3I 
 
 interfere with the success of subsequent operations ; the young 
 analyst needs especially to bear this in mind. If strong acid is 
 required for the actual solution of the substance, the excess of it 
 must usually be removed by evaporation nearly to dryness ; 
 water is then added to the residue in such quantity as to make a 
 solution of about the right strength. For the details of the 
 operation of getting the substance into solution for analysis, see 
 the directions given in Chapter VIII. 
 
 44. Fluxing. Some substances can be brought into solution 
 only after a metathesis has been produced between them and 
 certain reagents in a state of fusion. Sodium and potassium 
 carbonates are used for such reagents. A soluble salt of the 
 acid of the insoluble substance and the alkali metal is formed, 
 while the carbon dioxid either escapes, or forms carbonates 
 of the basigenic elements in the insoluble substance, or is 
 disposed of in both ways. None of these new compounds being 
 insoluble in acids, the original substance can by this means be 
 brought entirely into solution for analysis ; with this exception, 
 however : in the silicates we have a large class of insoluble 
 substances ; when the flux obtained with these compounds 
 is treated with water and acid to dissolve it, a portion of the 
 silica immediately appears in an insoluble form ; but it is entirely 
 separated from the basigenic elements with which it was origin- 
 ally combined, and the condition of insolubility of the substance 
 is broken up. 
 
 In order that this operation of fluxing shall be entirely suc- 
 cessful, three conditions must be fulfilled : — 
 
 The insoluble substance must be very finely pulverized in an 
 agate mortar, till the powder does not feel gritty under the pes- 
 tle; this proper pulverization requires much patience. The 
 powder must be most carefully mixed with a large proportion of 
 the reagent, not less than three or four times its own volume. 
 This mixture must be kept in a state of fusion for not less than 
 fifteen to thirty minutes. The fusion is best performed in a 
 platinum vessel of some kind ; porcelain might itself be attacked 
 by the flux ; the heat of a blast lamp is necessary. 
 
 45. Evaporation. This operation comes into use very often 
 in analytical work, to make a solution more concentrated, or 
 to free it from some ingredient that would interfere with opera- 
 tions to follow, or to get a solid from the substance held in 
 solution. 
 
 Evidently, the larger the surface exposed for the escape of 
 
32 ELEMENTS OF CHEMICAL ANALYSIS. [§§ 46-47- 
 
 vapor, in proportion to the mass of the liquid, the greater the 
 rapidity of the evaporation ; and since the rate of evaporation 
 is more rapid, the less there is of the vapor of the solvent in the 
 air over the surface of the liquid, the more frequently this air, 
 more or less laden with the vapor, is replaced by fresh air, the 
 faster the evaporation will proceed. The porcelain evaporator 
 is the utensil most frequently employed for this purpose ; in 
 such a shallow dish the surface is large, and the vapor-laden air is 
 readily removed by air currents passing over. A flask or a nearly 
 covered beaker is most unsuitable for evaporation, for plain 
 reasons ; if the flask is laid over on its side evaporation will 
 proceed more rapidly than if it is upright ; or, if, while upright, a 
 continuous current of air is forced into it, the evaporation will 
 proceed quite satisfactorily. 
 
 46. In all quantitative work there must be no loss of substance. 
 From the surface of a boiling liquid, even if the boiling is very 
 quiet, minute particles of the solution are constantly projected 
 upward and obliquely, some of which will fall outside of the 
 dish, unless the surface of the liquid is much below its rim ; 
 therefore, in all work of this kind evaporation must be con- 
 ducted without boiling the liquid, unless it is in a deep beaker, 
 or in a flask laid on its side ; in this last case the projected par- 
 ticles strike the upper side of the flask, and are soon washed back 
 again by the condensed vapor flowing down. 
 
 As the evaporation nears the end, and some of the solid matter 
 is deposited, the sputtering of the thickened liquid may become 
 so violent that small masses of the substance may be projected 
 out even from a deep beaker. Even in qualitative analysis, 
 where the loss by the boiling of the liquid may be disregarded, 
 this closing part of the operation must be conducted with care ; 
 more loss may be suffered than can be afforded ; and, moreover, 
 particles of the substance thrown out may fall into solutions near 
 by, and thus do serious damage to other work. 
 
 47. Ignition. A residue left by evaporation, or a precipitate, 
 must sometimes be subjected to a stronger heat than is attainable 
 in a solution, that is it must be ignited. This operation must be 
 performed in a crucible, or, if-the quantity is small, on a plati- 
 num foil. It cannot be done in an evaporator without risk of 
 breakage. Therefore, when the residue from an evaporation is 
 to be ignited, with a spatula transfer it to the crucible while it is 
 still in a pasty condition, dry it over a direct, low flame, and then 
 proceed with the ignition, gently or strongly, as may be directed. 
 
§ 48.] MANIPULATIONS. 33 
 
 48. Acidification, alkalization, neutralization, adding a reagent 
 in excess. It is often directed that a solution shall be made 
 acid, alkaline, or neutral before proceeding further. With refer- 
 ence to acidification, this does not mean that the liquid shall be 
 made strongly acid, unless specially so stated, but rather that, 
 if alkaline or neutral, acid shall be added slowly, and with con- 
 stant stirring, or mixing in some other way, only till the reaction 
 is clearly acid to the test paper ; and the same is true as to 
 making a solution alkaline. The proper mode of procedure, 
 therefore, is to add the reagent in small portions at a time, care- 
 fully mixing each portion as added, and frequently applying a 
 drop of liquid to the test paper ; when the reaction indicates an 
 excess of the reagent, a little more may safely be added, in order 
 to be sure of enough. The mode of procedure is similar for 
 making a liquid alkaline. Since ammonia is the reagent com- 
 monly used for this purpose, the careful mixing is all the more 
 essential, as it is lighter than water or any solution of salts or 
 acids, and will tend to float on the surface of such a solution ; on 
 dipping the test paper into the liquid, or taking a drop out on a 
 glass rod and touching it to the paper, the reaction might be 
 Strongly alkaline, even with a strongly acid liquid in the lower 
 part of the tube. When this reagent is used to neutralize acidity, 
 as soon as the liquid smells strongly of it, after the thorough 
 mixture has been made, one can be sure that the liquid is alka- 
 line. When a solution made alkaline by an excess of an alkaline 
 carbonate, NaaCOg, K2CO3, or (NH^^jCOs, is to be made acid, 
 as soon as the addition of the acid does not cause decided effer- 
 vescence, due to the escape of carbon dioxide, the same precau- 
 tions being taken as to the careful mixing in of each portion of 
 acid added, the condition of acidity is probably reached ; but in 
 any case the final test with litmus paper should never be omitted. 
 One can never afford any uncertainty in regard to the matter. 
 
 When the liquid to be treated is in a test tube, the mixing can 
 be most easily done simply by pouring it back and forth from 
 one tube to another. 
 
 Addition of a reagent in excess. Directions are often given to 
 •add a reagent in excess; but unless the desired excess is specially 
 stated to be large, which is rarely the case, it is not meant that a 
 great quantity of it is to be added. If it is an acid or an alkali 
 that is added, it should be known, by the use of test papers, 
 when it is first in slightest excess, as directed above ; then the 
 further addition of a quantity of the reagent equal to about one- 
 
 3 
 
34 ELEMENTS OF CHEMICAL ANALYSIS. [§§ 49-5°- 
 
 tenth of the volume of the solution, will usually suffice. If it 
 is a precipitating reagent that is added, then it should be known 
 when the precipitation is first complete ; then a further addition 
 of one-tenth, as above described, will be sufficient. 
 
 49. Precipitaiion. This operation, the eduction of a solid 
 substance from solutions, as the result of some metathesis, is the 
 most important one in analytical chemistry. The reagent used 
 is commonly called the precipitant. 
 
 Qualitative analysis consists almost entirely in the production 
 of precipitates for one purpose or another, and generally under 
 certain prescribed conditions. In order that the result sought 
 for shall always be obtained, the conditions prescribed in each 
 case must be fulfilled — such as neutrality, or acidity, or alkalinity 
 of the solution, precipitation with heat or without, with time 
 given for the reaction to be completed or not. Especially in 
 quantitative analysis, the conditions under which the precipita- 
 tion is to be made, are usually very precisely indicated, since in 
 that kind of work the completeness in the reaction is of the 
 utmost importance. 
 
 But this matter of completeness of precipitation is in many 
 cases of no less importance in qualitative analysis, as in the 
 separation of groups of substances from one another, or of 
 removing one substance from the solution that may interfere 
 with the detection of another. Therefore, in the very beginning 
 of his work, whether such beginning is made in qualitative or 
 quantitative analysis, the student has to learn to be careful in 
 the preparation of his solutions for precipitation, and in the 
 management of the precipitation itself. 
 
 50. Description of precipitates. Precipitates are distinguished 
 as having this or that color, or, as to structure, as being crystal- 
 line, pulverulent, or flocculent. 
 
 A crystalline precipitate is usually characterized by the 
 property of sinking rapidly to the bottom and leaving a com- 
 paratively clear supernatant liquid. Sometimes a precipitate is 
 so finely crystalline as to show only a glistening shimmer 
 when present in very small quantity in a liquid that is gently 
 disturbed. Precipitates that take the crystalline form will 
 usually appear sooner if the liquid is strongly agitated ; some- 
 times such agitation is almost necessary to start their formation, 
 as in precipitation of morphia by ammonia. 
 
 A pulverulent precipitate is very fine, usually not settling 
 quickly nor leaving a clear, supernatant liquid. One that is 
 
§§5I-S3-] MANIPULATIONS. 
 
 35 
 
 pulverulent, if produced quickly and in large quantity, may be 
 plainly crystalline if formed slowly and in small quantity, 
 as may be seen sometimes in the formation of the precipitate of 
 ammonium magnesium phosphate. The more insoluble a pre- 
 cipitate is in the liquid in which it is produced, the more it 
 inclines to the pulverulent rather than crystalline character; 
 but even some of the most insoluble precipitates, as barium 
 sulfate, will, if produced only in traces, exhibit the glistening 
 appearance above mentioned, as indicating crystalline structure. 
 ' 51. A fiocculent or flaky precipitate, sometimes defined as 
 woolly-looking, never presents this glistening appearance, how- 
 ever slowly formed. It settles slowly, and occupies much more 
 space than a crystalline or pulverulent precipitate. It is often 
 separated from the liquid by filtration only with difficulty. It is 
 sometimes translucent, so that, if at the same time colorless, 
 it is almost invisible till gathered together in masses; of this 
 character the precipitate of aluminum hydroxid is an example. 
 
 Precipitates will usually collect together and settle to the 
 bottom more quickly, and be more easily filtered out, if the 
 ' liquid containing them is hot. 
 
 52. According as a precipitation is made simply for the 
 detection of a substance in a solution, by the appearance under 
 the prescribed conditions, of a precipitate of a certain form or 
 color, or is made for the separation of one or more substances 
 from others, the manner of making it differs. In the former 
 case, the first appearance of the precipitate suffices, and any fur-- 
 ther addition of the reagent is useless, except when there is 
 necessity for getting a large quantity of the product for confirma- 
 tory tests. But in the other case, the addition of the reagent 
 must be continued as long as a precipitate is formed ; and this 
 cessation of further precipitation must be determined beyond all 
 doubt by adding a few drops of the precipitant, either to the 
 supernatant liquid clarified by standing for the precipitate to 
 settle, or to a portion of the liquid filtered from the precipitate ; 
 sometimes it is necessary to give time for the completion of the 
 reaction, even after no further precipitation is shown by testing 
 as above. 
 
 53. Digestion. In order that a chemical reaction, and espe- 
 cially an operation of solution or precipitation, shall .be com- 
 plete, it is often necessary to leave the substance and reagent in 
 contact for a time. This is commonly called digestion. 
 Usually heat is applied, but not always; in this case we speak of 
 
36 ELEMENTS OF CHEMICAL ANALYSIS. [§§ 54-55- 
 
 digestion in the cold. Digestion at a boiling temperature is 
 sometimes specified ; but this is too often incorrectly con- 
 strued as vigorous boiling, while it means only that the liquid 
 shall be kept just at the boiling temperature. 
 
 54. Boiling. Rapid boiling of liquids is required only when 
 they are to be quickly evaporated, or some product is to be dis- 
 tilled off. It is very rarely necessary in qualitative work, and is 
 to be avoided unless specially called for. 
 
 A clear liquid can usually be boiled without any trouble, in a 
 beaker, flask, or evaporator; but in a test tube, especially if 
 half full or more, the vapor does not escape in a continuous 
 stream of small bubbles, but in very large ones, often, which are 
 formed suddenly, an& are very likely to propel a part of the 
 liquid before them in their escape. 
 
 When any solid matter is mixed with the liquid, and especially 
 if the liquid is strongly alkaline, boiling without spurting is still 
 more impracticable in a test-tube, and should never be at- 
 tempted ; even in a flask, beaker, or evaporator it is not easily 
 managed, and must be carefully watched, particularly when the 
 quantity of liquid is small as compared with that of the solid ; 
 by holding the lamp in the hand, and, with the flame very low, 
 moving it in and out under the dish, without the intervention 
 of a sand bath, thus keeping the mixture just at the simmering 
 point, the whole object of the operation may be accomplished 
 without danger. When there must be actual boiling for a time, 
 as in the treatment of the precipitated chlorids of the silver 
 group with water to dissolve out the lead chlorid, it is advisable 
 to hold the flask by the test-tube holder and keep its contents 
 in rapid motion by a movement of the hand in a small circle. 
 
 55. Filtration. It is usually necessary, after having made a 
 precipitate, to separate it from the liquid, in order to perform 
 some further operation with it. For this purpose, paper filters 
 already cut are now supplied in every laboratory. To fit a filter 
 in the proper manner, first fold it over so as to form a semicircle, 
 and then again, forming a quadrant ; then open this quadrant 
 in such a way that when it is pressed down into a funnel there 
 is a continuous lining of the paper on the sides of the funnel 
 of three thicknesses half way round and one thickness on the 
 other half The filter should always be about half or a third of 
 a centimeter smaller than the funnel when thus fitted into it. In 
 preparing for the filtration, push the filter, opened as above 
 described, down till its apex is in the throat of the funnel, and 
 
§§ 56-58.] MANIPULATIONS. 37 
 
 hold it there with the finger while wetting it with a jet of water 
 from the wash-bottle ; then by gentle pressure with the finger fit 
 it snugly to the walls of the funnel throughout. Tinie should 
 be taken to carefully adjust the filter in this manner for every 
 filtration. 
 
 56. Decantation before filtration. Filtration can often be 
 made more quickly if the liquid is first digested at a gentle heat 
 till the precipitate has settled, and the supernatant liquid is then 
 carefully decanted off before putting the mass of the precipitate 
 on the filter. If the work is qualitative and nothing further is 
 to be done with the liquid, the decantation can be made at once 
 into the sink ; otherwise it should be made into the filter. 
 
 57. Washing precipitates. It is usually important to com- 
 pletely free a precipitate from the substances in solution in the 
 liquid from which it has been filtered, and with which its 
 pores are filled. 
 
 This washing may sometimes be partially done with advantage, 
 by repeating the above described process of decantation, two or 
 three times, pouring boiling water over the precipitate, stirring 
 it up well and decanting again after a little time, and so on, and 
 finally washing once or twice after the precipitate has been put 
 on the filter. When, however, it is crystalline pulverulent, and 
 filters quickly, it may as well be thrown on the filter at once and 
 washed there. In all cases use hot water, unless otherwise 
 directed, for with this the washing is sooner finished ; and 
 use only distilled water. 
 
 In qualitative work the washings need not be saved ; but they 
 often must be preserved in quantitative work. 
 
 The completion of the washing may be tested for in two ways : 
 first, by evaporating a drop of the washings to dryness on a 
 watch glass, at a gentle heat ; no residue, or in qualitative work 
 only a slight one, should be left on the spot where the drop was : 
 second, by testing about a cubic centimeter of the washings for 
 some substance which one may know to be in the solution, and 
 for which there is some very delicate test. Such a substance is 
 a chlorid, which is usually present in qualitative solutions, from 
 the hydrochloric acid that has been added in some previous 
 operation ; the silver test for chlorin, after acidification of the 
 liquid with nitric acid is exceedingly delicate. 
 
 58. Dissolving precipitates. This often necessary operation, 
 especially in qualitative work, may be done simply by dropping 
 the solvent over the precipitate in the filter, when heat or 
 
38 ELEMENTS OF CHEMICAL ANALYSIS. [§§ 59-60. 
 
 digestion is not required ; when two or three cubic centimeters 
 of the solvent have run through, this may be again poured through 
 the filter, if the solution is not complete, thus avoiding the use 
 of a large excess of acid. If the precipitate must be removed 
 from the filter, take the latter from the funnel by slipping the 
 spatula under it, open it on the piece of window glass that is in 
 the set of apparatus, and scrape the precipitate off with the 
 spatula. 
 
 59. Cleanliness in the laboratory. Reasonable cleanliness of 
 apparatus and work table is much more conducive- to good re- 
 sults than the extreme slovenliness that is often seen. Every 
 piece of apparatus must be clean within before a liquid is put 
 into it that is under treatment for analysis ; if not clean, then 
 the constituents of the dirt that was on the walls of the vessel 
 are liable to be added to the solution, and to be reported as a 
 part of the substance analyzed. Unless a piece of glassware is 
 clean on the outside, it cannot be known whether it is clean on 
 the inside. The cleaning is never more easy than immediately 
 after the apparatus has been used ; and it is liable to be more 
 difficult if put off for days. 
 
 Therefore, the student should never leave the laboratory for 
 the day without having first cleansed every soiled piece of 
 apparatus that is not in actual use, finishing the operation by 
 rinsing each piece off with a little distilled water. By the use 
 of a little strong hydrochloric or nitric acid, pouring the same 
 portion from one piece to another, intractable dirt may often be 
 dissolved. While the student is at work his table should be 
 kept neat, everything spilled by accident or otherwise being at 
 once washed off with a sponge and an abundance of water. 
 
 If acid comes in contact with the clothing, the spot should as 
 soon as possible be saturated with a few drops of ammonia. 
 Strong nitric acid on woolen cloth makes a permanent yellow 
 stain unles^ immediately neutralized ; sulfuric acid if not 
 neutralized, even if dilute at first, becomes more and more con- 
 centrated by the slow evaporation of the water, and finally the 
 cloth is corroded ; hydrochloric acid leaves only a red stain, 
 easily removed by ammonia. 
 
 60. Rapidity of work. Much time will be spent in accom- 
 plishing little work, unless the student is always careful to keep 
 as many operations in progress as he can manage without making 
 mistakes. Early in his course of practice he should seek in this 
 way to make the best possible use of his time in the laboratory. 
 
§ 6o.] MANIPULATIONS. 39 
 
 The teacher's estimate of the proficiency of the student must be 
 based on the amount of good work accomplished in the amount 
 of time that is given to the practice. Therefore, there should 
 never be any idle waiting for a precipitation, tedious filtration, or 
 any other slow operation to be completed ; some other operation 
 should be started. If the work is qualitative, two substances can 
 be carried along at once ; or, the constituents being separated 
 into groups if the analysis is one covering the entire course, two 
 or more groups can be worked along together. In many ways 
 the student who is really in earnest, meaning to do the best that 
 he can with his time, can get over much more ground without 
 slighting any part of his work, than he will if he gives this mat- 
 ter of rapid work no serious thought. If every stage of the work 
 is properly labeled, trusting nothing to the memory, none of the 
 mistakes need be made that might seriously lessen the gain in 
 progress. 
 
PART II. 
 
 THE SYSTEMATIC COURSE OF QUALITATIVE 
 ANALYSIS. 
 
 CHAPTER VII. 
 THE MODE OF PROCEDURE IN GENERAL. 
 
 6i. Introduction. This course in qualitative analysis is, in 
 many respects, similar to that of Fresenius. The same grouping 
 of substances is followed, although under different names ; the 
 name of a familiar member of each group applied to it is more 
 easily remembered, and conveys somewhat more of meaning 
 than a mere number. Usually the methods of separating the 
 members of each group from each other, and of detecting them, 
 are the same as those given by Fresenius. But the work is much 
 abridged, in order that it may be completed in a reasonably 
 satisfactory manner in the short time that can be allowed for the 
 study in some of the University courses, and to make it possible 
 for the student in these courses to devote a little attention to 
 quantitative analysis, some knowledge of which may be of more 
 importance to him than a fuller acquaintance with qualitative 
 methods. To the student who intends to make a special study 
 of chemistry, the full course given in Fresenius, or in Prescott 
 and Johnson, is none too extended ; and for guidance in the 
 more difficult parts of the analysis, he must refer to these com- 
 prehensive works. 
 
 Whatever is peculiar to the course of analysis given here, has 
 been thoroughly tested by practical use for many years in the 
 chemical laboratory of Cornell University. This experience has 
 shown that with strict following of the directions laid down, the 
 careful student will from the beginning commit but few errors, 
 and will readily learn how to make a correct analysis of any mix- 
 ture containing the more commonly occurring elements. 
 
 40 
 
§ 62. J MODE OB' PROCEDURE. 41 
 
 62. The grouping of the substances tested for. The substances 
 that are tested for in all ordinary schemes of qualitative analy- 
 sis are of two classes, the acidigenic and the basigenic elements 
 or groups, or, as they are called in other works, the acids and 
 bases. Of the acidigens, or acids, a small number can be asso- 
 ciated together by their common property of being precipitated 
 in a neutral solution, as barium salts ; and another group con- 
 sists of those that give a precipitate with silver nitrate in a solu- 
 tion acidified with nitric acid. In other words, the barium salts 
 of the members of the group first mentioned are insoluble in 
 water, and the silver salts of the members of the other group 
 are insoluble in dilute nitric acid. 
 
 But this grouping has no such significance as there is in the 
 grouping of the basigens, as the student will understand much 
 more clearly after he has completed his qualitative work ; neither 
 the barium nor the silver group of acidigens is separated out by 
 itself, in any scheme of analysis, for the purpose of testing for 
 each member of the group in the precipitate thus obtained. 
 The analysis for the acids consists mostly of a succession of inde- 
 pendent tests applied to the original substance, or to a solution 
 of the substance prepared by boiling with sodium carbonate, so 
 as to have only sodium salts in the solution to be worked with. 
 The only use of this grouping is to determine by a single brief 
 test whether any acid of one or the other group is present, thus 
 making it possible in some cases to omit the whole series of the 
 tests required to prove the presence or absence of the several 
 members of one or both groups. On the other hand, a very im- 
 portant part of the analysis for the bases consists in their separa- 
 tion into six groups : the members of each one of these groups 
 being allied in so far as they possess at least one common prop- 
 erty, as to insolubility of certain of their compounds in water or 
 in acids of different degrees of dilution, by which they may be 
 thus brought out together. Each group is then, perhaps, subdi- 
 vided, sometimes by difference in respect to solubility in some 
 other active agent than an acid ; and, finally, each member of 
 the group is so far isolated as may be necessary to make a final 
 confirmatory test for its presence or absence. 
 
 The substances thus brought out of the solution in company 
 are often not at all chemically allied ; consequently the analytical 
 grouping is in some cases not so sharply defined as to avoid all 
 overlapping of groups. While this measure of unlikeness may 
 facilitate the sub-grouping of elements, on the other hand, ^ when 
 
42 ELEMENTS OF CHEMICAL ANALYSIS. [§§ 63-65. 
 
 members of the same group are closely allied, their separation 
 and identification may be very difficult; of this, nickel and 
 cobalt, in the iron group, furnish a striking example. 
 
 The whole course of the analysis is thus divided into eight 
 principal stages, of which the examination for the acidigens or 
 acids is the first. See Table at end of this chapter. 
 
 With reference to the basigens we have three classes of com- 
 pounds that are commonly made use of for grouping purposes, 
 namely, chlorids, sulfids, and carbonates. Of these the sulfids 
 are so important in analytical work as to be worthy of the 
 special consideration of their more important properties. 
 
 THE SULFIDS. 
 
 63. These may be produced by fusion of metals with sulfur, 
 or by the action of hydrogen sulfid or of solutions of soluble 
 sulfids on metallic salts in solution. 
 
 They are distinguished : — 
 
 a. For their different degrees of solubility in (i) water, (2) 
 acids, (3) other solvent liquids. 
 
 b. For their different degrees of susceptibility to oxidation. 
 
 c. For their variety of color. 
 
 64. Solubility of the sulfids. Most of the sulfids of the 
 basigens are insoluble in water, only those of the potassium 
 and calcium groups being soluble. 
 
 The sulfids of the iron group of metals differ much in solu- 
 bility in dilute acids, as the behavior of nickel, cobalt, and zinc 
 sulfids shows, in the course of the separation of the members of 
 this group from one another. 
 
 The sulfids of the metals of the aluminum group are in their 
 nascent state decomposed by water, forming hydroxids and 
 hydrogen sulfid. 
 
 All the remaining sulfids are insoluble, not only in water but 
 in at least moderately strong mineral acids ; some of them are 
 insoluble even in strong acid, and the metal contained in them 
 can be brought into solution only through attack by strong 
 oxidizing agents. 
 
 Thus, it is seen, we have every grade, from easy solubility of 
 the alkaline sulfids in water, to insolubility in the strongest acid 
 of sulfids of some metals of the copper and tin groups. Hence, 
 in part, the great importance of the sulfids in analytical chem- 
 istry. 
 
 65. Certain elements (tin group) are capable of forming with 
 
§ 66. J MODE OF PROCEDURE. 43 
 
 oxygen a lower oxid that is basigenic and a higher oxid that is 
 acidigenic. Similar compounds are formed in which sulfur takes 
 the place of oxygen ; and, as nearly all salts of the alkaline 
 metals are soluble, we may have soluble alkaline salts of these 
 metals in which all the oxygen is replaced by sulfur, as, for 
 instance, (NH^)sAs03, ammonium arsenite, and (NH4)3AsS3, 
 ammonium sulfarsenite. Remembering that the formulas of the 
 oxygen salts of the acids formed from these elements are as 
 follows, it is easy to see the relation of the sulfo-salts of the tin 
 group to them : M3ASO3 ; MaAsOi ; MaSbO, ; MjSnOa. M in 
 these formulas stands for any monad basigen. 
 
 These sulfo-salts are readily formed by simple treatment of the 
 solutions of compounds of these elements, or their freshly pre- 
 cipitated sulfids, by solutions of alkaline sulfids, especially such 
 as have an excess of sulfur, as (NH4)2Si, for example. Hence, 
 the easy and nearly complete separation by means of ammonium 
 sulfid of the tin group elements from those of the copper group. 
 
 It is worthy of notice that, in this treatment, the action of the 
 (NH4)2S, on the antimonous and stannous sulfids corresponds in 
 its character to one of oxidation ; for, from these " ous " sulfids 
 there is formed the sulfo-salt corresponding to the antimoniate 
 or the stannate, and the sulfid precipitated by acid from the 
 solution of the sulfo-salt is antimon/V or stannzV sulfid. 
 
 66. Oxidation of the sulfids. In the sulfids we have two 
 elements both of which are capable of combining with oxygen, 
 but the metal usually more eagerly than the sulfur. In nearly 
 all cases a nitrate of the metal is formed, if nitric acid is used as 
 the oxidizing agent; if the nitrate is not formed it is either 
 because of the production of a higher oxide of the metal not 
 basigenic, or because, the sulfate of the metal being insoluble, 
 that is formed, to the entire or partial exclusion of the nitrate. 
 
 If the metal is capable of forming more than one oxid and 
 series of salts, whether it be the lower or the higher oxid depends 
 upon the conditions of the oxidation ; if the sulfid is in excess 
 and no heat is employed, a nitrate of the lower oxid may be the 
 product ; ordinarily an excess of acid and heat are employed, 
 yielding a salt of the higher oxid. Nickel and cobalt sulfids 
 are exceptions, giving only the lower oxid salts. 
 
 The sulfur of the sulfids is mostly set free as a precipitate, 
 which in a hot liquid is liable to fuse together in small globules 
 that resist oxidation with much obstinacy. Even when the sul- 
 fate of the metal is soluble, some of the sulfur is oxidized to sul- 
 
44 ELEMENTS OF CHEMICAL ANALYSIS. [§§ 67-69. 
 
 furic acid, and some of this sulfate is formed together with the 
 nitrate which is the chief product. However, it is usual in writing 
 the equations for these reactions to assume, unless it is otherwise 
 stated, that all the sulfur is set free, and only nitrate of the 
 metal formed, at least in the first part of the reaction, as illus- 
 trated in the following equation : — 
 
 3PbS + 8HNO3 = 3Pb(NO.O, + 4HiO + 2NO + 3S. 
 
 Occasionally a sulfid is so susceptible to oxidation as to suffer 
 change by simple exposure to the oxygen of the air, or to the 
 free oxygen dissolved in the water used to wash the precipitate. 
 
 67. Chlorination of the sulfids. When a sulfid is attacked in 
 the presence of water by reagents setting chlorin free, oxidation 
 may be the result by oxygen from decomposed water; but, 
 especially if the chlorin be in excess and heat is applied, chlorin- 
 ation may also take place ; and if the metal forms more than 
 one chlorid the higher one is produced. Most of the sulfids are 
 converted into chlorids by simple treatment with more or less 
 concentrated hydrochloric acid, with evolution of hydrogen sul- 
 fids ; but this is metathesis rather than chlorination ; in the 
 latter case, as in oxidation, sulfur is set free. 
 
 68. Reduction of sulfids. Just as oxids may be reduced by 
 nascent hydrogen, which takes the oxygen to form water, so sul- 
 fids, subjected to the same treatment (with zinc and sulfuric 
 acid), may be reduced, HjS being formed instead of HjO, and 
 set free. Thus some sulfids may be decomposed that are with 
 difficulty broken up in other ways. 
 
 THE HYDROXIDS (OR HYDRATES). 
 
 69. By the action of solutions of hydroxids on salts of other 
 metals in solution, a class of reactions is produced of great im- 
 portance in analytical work : the normal product of the reaction 
 is a hydroxid of the metal acted upon. 
 
 , Regarding this action as normal in all cases where with all 
 three of the alkaline hydroxids, KOH, NaOH, and NH4OH, insol- 
 uble hydroxids are produced of normal composition, such as 
 Fe(OH)j, Zn(0H)2, A1(0H)3, it is strictly normal with the metals 
 of the aluminum group, and those of the iron group except cobalt, 
 which yields a basic salt ; with some metals of the copper and 
 tin groups the result is more or less irregular ; only with bis- 
 muth, cadmium, copper, and tin (ous) is it fully normal, but in 
 
§ 7°-] MODE OF PROCEDURE. 45 
 
 the case of copper only when the reagent is added just to satura- 
 tion : with lead and the _/?«!?(/ hydroxids, KOH, NaOH, it is regu- 
 lar, but NH,OH yields basic salts, PbOCl^, or PbsO^OHNOs, 
 according to the acid of the lead salt. With silver, AgjO 
 is precipitated, and with salts of mercury and the fixed alkalies 
 in excess, HgjO or HgO : with NHiOH, compounds are pro- 
 duced in which a part or all of the hydrogen of the NH, is re- 
 placed by mercury : these new compounds play the part of a 
 basigenic body, like the ammonium, and remain in combination 
 with the acid of the mercury salt. Example, 
 
 N g^^ NO3 N g| CI, NH&NO,, 
 
 according as Hg is monad (mercurous) or dyad (mercuric). 
 
 With arsenic compounds, soluble salts of the alkaline metals 
 are formed, arsenites and arsenates, and of course no precipi- 
 tates ; with antimonous compounds, SbjO., is precipitated ; with 
 antimonic compounds, soluble antimoniates are formed, or an 
 insoluble antimoniate, NaSbOj: with stannic salts (stannates), 
 stannic acid, HgSnOs, is precipitated. With gold only NHjOH 
 gives a precipitate, and that has a peculiar composition, (NH3)2 
 AU2O3. Platinum in the form of chlorid gives with KOH and 
 NH4OH -insoluble double chlorids, of great value in the quanti- 
 tative estimation of potassium and ammonium, aKCl.PtCliand 
 aNHjCLPtCli: NaOH gives a precipitate of Na^PtOs. 
 
 The reactions with the hydroxids are seen to be more and 
 more varied as we pass up to the tin group, where the elements 
 tend to yield acidigenic oxides even in their lower degrees of 
 oxidation ; and the reaction in such cases has little analytical 
 value. 
 
 70. Solubility of the hydroxids. All the normal hydroxids are 
 insoluble in water, except those of the potassium group, and of 
 barium, strontium, and calcium of the calcium group ; all are 
 soluble in dilute acids, forming salts of the acids used. 
 
 Most of them when freshly precipitated are soluble in solutions 
 of either KOH, NaOH, or NH^OH ; but only one, Zn(0H)2, is 
 soluble in both a fixed and a volatile hydroxid, meaning by the 
 latter ammonium hydroxid. New compounds are produced by 
 this solution, differing so widely in form for different metals, 
 that no general formula can be given for them ; some of these 
 formulas are given later. 
 
 Owing to this property of the hydroxids, we may have 
 
46 ELEMENTS OF CHEMICAL ANALYSIS. [§§ 71-74- 
 
 two metatheses produced by one reagent, an insoluble product 
 being formed first, which is afterward dissolved by an excess of 
 the precipitant, with the formation of a second new compound 
 that is soluble in water. 
 
 71. Behavior when heated. All the hydroxids, except those 
 of the potassium group, are decomposed by heat, with the 
 formation of an oxid of the metal, and water. In some cases 
 this decomposition takes place even in boiling water. 
 
 THE FINAL TESTS. 
 
 72. One after the other, the presence or the absence of each 
 substance to be tested for is proved by a final characteristic test, 
 after it has been, if present, more or less completely isolated. 
 Some of the reactions of these tests are so unique that they can 
 be made in the presence of all the other members of the group, 
 or even in the original solution, without regard to anything else 
 that may be present : this is the case with many of the tests 
 for the acids after they have been separated from all the bases 
 except the alkalies by the transposition with sodium carbonate. 
 The final tests for gold, platinum, copper, and iron are excellent 
 illustrations of such as are not interfered with by the presence 
 of other members of the groups to which they severally belong. 
 
 73. In these final tests we have two general classes of. reac- 
 tions : — 
 
 a. Color reactions, among which are some of the most deli- 
 cate, marked, and unmistakable in use. Often nothing can 
 interfere with their production. We may get them in : — 
 
 (i) solution products; 
 
 (2) precipitates from solution ; 
 
 (3) fusion products, on the foil or in the borax bead ; 
 
 (4) flame tests. 
 
 b. Precipitates without any marked color, usually white. 
 The main safeguard against error, in the interpretation of 
 results in such cases, is to have the conditions under which the 
 precipitates are obtained, precisely as laid down in the direc- 
 tions for obtaining them. 
 
 THE COURSE OF ANALYSIS. 
 
 74. Order of the arrangement of the work. Beginning with the 
 acidigen group, Chap. IX, the student reads over the description 
 of the reactions of the first acid taken up, and writes out the 
 equations explaining those reactions ; he then tries the reaction or 
 
§ 74-J MODE OF PROCEDURE. 47 
 
 reactions given in italics ; that is, to a small quantity, one or two 
 cubic centimeters, of a solution containing a salt of the acid 
 under consideration, in a test tube, he adds a small quantity of 
 the reagent, precisely in the manner described in the account of 
 the reaction, and compares the results obtained with the descrip- 
 tion of the result that should be obtained ; only in this way can 
 he become so acquainted with the reactions described, that he 
 will surely recognize them when he may meet with them again 
 in the actual analysis of an unknown substance. The italicized 
 reactions are those specially characteristic of each substance, 
 made use of each time that it is tested for ; a thorough, personal 
 acquaintance with them is therefore of great importance. The 
 other reactions come into use only in the separation of sub- 
 stances from one another, or as occasional confirmatory tests in 
 doubtful cases. 
 
 This work having been carefully performed with every sub- 
 stance in the group, the student then makes a mixture contain- 
 ing all the substances of which he has tried the characteristic 
 reactions, and proceeds to analyze it according to the directions 
 for the analysis for acids, § 85. 
 
 To simplify this part of the work with respect to the large 
 group of the acids, by reducing the number of tests to be made 
 in one solution, a mixture containing salts of only the barium 
 group may be analyzed by itself, then a mixture containing only 
 the silver group, with nitric acid added, and finally a mixture of 
 the organic acids. 
 
 In doing this work he should get, clearly and unmistakably, 
 the final, characteristic, reaction of every substance ; if he does 
 not, he should repeat so much of the work as may be required to 
 bring out this reaction ; evidently he is not prepared to take up 
 the analysis of a substance whose composition is unknown to 
 him, if there is any possible constituent of it which he should 
 find, but cannot even when he has put it in himself and knows 
 that it is present. 
 
 The student should then study carefully the explanation of the 
 chemistry of the work on the acidigens in § 84. He is not fully 
 prepared to do the best that is possible for him, in the analysis 
 of an unknown substance, till he has learned the reasons for all the 
 steps of the work, and is fully posted as to the special precautions 
 that may be necessary to avoid errors. 
 
 Being then ready for the actual analysis of an unknown 
 substance, this work is first done for the acidigens only ; when 
 
48 ELEMENTS OF CHEMICAL ANALYSIS. [§ ^(>■ 
 
 the required proficiency has been attained, the student passes 
 on to the first group of the basigens or metals, those precipitable 
 by silver nitrate from a solution acidified with nitric acid, going 
 through with the same series of preliminary operations and 
 study, before analyzing the unknown substances containing the 
 members of this group, and so on through all the groups in 
 succession. Here, however, the work with his own solution 
 begins with sub-section b of the section headed, " Preparation 
 and Analysis of the Silver Group Precipitate," and follows this 
 and sub-section c, headed "Analysis of the Silver Group Pre- 
 cipitate," with its table, to the end. Then comes the study of 
 sub-section a of the same section on the chemistry, of the analysis. 
 The same course is followed with each of the other groups fol- 
 lowing. Finally comes the test of the thoroughness with which 
 the several groups have been studied, in the analysis of sub- 
 stances in which the presence or absence of all the members of 
 all the groups has to be proved. The following tabular view of the 
 comjjlete course of analysis of a substance may be useful as a 
 general guide in this part of the work. 
 
 CHAPTER VIII. 
 
 THE PREPARATION OF THE SOLUTION OF THE SUBSTANCE. 
 
 76. As nearly all the work of the analysis, for both acidigens 
 and basigens is done with solutions, the matter of the suitable 
 preparation of these solutions is a very important one. 
 
 The solutions for the acidigens. 
 
 a. To I gm. of the original substance, finely powdered, add 
 15 c.c. of a concentrated solution of NajCOj and boil ten 
 minutes, replacing the water as it evaporates, dilute to 30 c.c. 
 and filter if a residue remains. 
 
 This solution or filtrate contains all the acids of the substance 
 except possibly phosphoric, hydrofluoric and silicic acids ; mark 
 it A, and test separate portions for the other acids as directed in 
 §85. 
 
 6. Acidify a small portion of A with HjSO,. The formation 
 of a yellow or orange ppt. shows the presence of metals of the 
 
a 
 
 •a 
 
 J3 
 
 o 
 
 O 1) •" . 
 
 ■ V -O tS l-H 
 
 in O 'O »^ 
 
 > "53 .3 n 
 
 (M w tn C 
 
 -35 
 
 O -i] 
 
 o o *- 
 
 o a 
 
 O V 
 
 Vi -l-i 
 
 ]X. 
 
 a. 
 
 ■I.S 
 
 - T3 
 
 
 
 li^ IN " 
 
 ffi' 
 
 1^ 
 
 Q 15! 13 .i! 
 
 "2 2 f .a 2 
 
 W _ 4> >« O 
 
 ii S - H ■" 
 
 o -K 3 rt o 
 
 o a 2 t, ■» 
 
 £ a .s 
 
 a. 
 
 so 
 
 no 
 
 ■ fc^a 
 
 rn ^ 
 
 O - " 
 Pi «iO 
 
 ^ 0) "^ ri rt v: 
 
 u 
 
 -.S -o 
 
 3 
 
 U 
 
 "o £ 
 "3 o 
 " -3 
 
 I c o . 
 I ■« -a a 
 
 a J ^ ? 
 
 01 Eliu 
 
 ■ 2 i^w 
 
 
 00 
 
 <U 
 
 >.S ^ 
 
 «; 2 
 
 ■ ^ "^l i^ O " 
 
 3 ",S 
 C/3 .t/3 
 
 ?. - ';;'^ 3 3 
 
 fl j3 in S Xj 
 
 cncn<!<! P-i 
 
 o 
 
 J3 -2 O « . 
 
 M 2^; PhUpqu _ 
 
 , l-so 
 
 Si-9 C o 
 
 
 =0 
 
50 ELEMENTS OF CHEMICAL ANALYSIS. [§ 77- 
 
 Sn group ; in such case acidify a large portion of A with H^SOi ; 
 filter, and boil the filtrate in a beaker or an Erlenmeyer flask 
 until HjS is entirely removed, which may be determined by 
 holding a piece of moistenejj lead-paper in the escaping vapor 
 at the mouth of the flask. Maj-k this solution B, and reserve 
 also for § 85. 
 
 77. The solutions for the basigens. 
 
 The substance is metallic. 
 
 To about half a gram add 2 c.c. of HNO3* and warm until 
 the substance is entirely. dissolved or until no further change is 
 observed, even when rpore HNO3 is added. 
 
 a. The substance \& entirely dissolved, either at once or upon 
 addition of water and boiling. 
 
 Gold, platinum, tin, and6antimony are absent, except when 
 present in alloys with very large proportions of soluble metals, 
 when some of these metals may 'be completely dissolved. Take 
 the solution to § 87 b. , 
 
 h. The substance is not completely dissolved, a white residue 
 remaining even wheij boiled with water. Sn, Sb and As may 
 be present, the residue consisting of SnOj or Sb204 and SbjOa, 
 and possibly AS2O5. 
 
 Dilute with water and ^filter. Heat the insoluble residue with 
 HCl*; if it is not all dissolved decant the liquid carefully 
 through a filter, after adding about its volume of water to it, so 
 that the strong acid shall; not cut through the paper, boil the 
 residue with water, decant this off into the same filter, and 
 repeat the treatment ' with HCl. Test the united solutions, 
 thus obtained, for As, Sb and Sn, after removal of the excess of 
 strong acid as directed in 32 § 89, c, then taking the solution to 
 
 37. b. 
 
 Evaporate a drop or two of the filtrate from the treatment 
 with HNO3 in a above (the first filtration mentioned in 6) on 
 a watch glass ; if a residue remains, showing that the liquid 
 holds something in solution, take it to § 87, b, testing, in the 
 following course for the Sn group, only for those members of the 
 group not found in the above residue. 
 
 C. A metallic residue remains in a, undissolved. Treat it 
 
 * When the formula of an acid is given in tliis heavy type, concentrated acid 
 is indicated, otherwise dilute acid. 
 
§ 78.] PREPARATION OF SOLUTIONS. 5 1 
 
 with aqua regia (§ 24, c,) and test the solution for Au and Pt, 
 as in 36 § 89, c. 
 
 Treat the filtrate from this residue, as directed for the filtrate 
 under b, above. 
 
 The substance is non-metallic. 
 
 78. a. Make a preliminary test, with about one-fifth gm. of 
 the substance, as follows: add 2 c.c. of water and heat to 
 boiling ; if a residue remains, add to the contents of the tube a 
 few drops of HCl and heat again; if a residue still remains 
 allow it to settle, pour off the clear liquid and add to the residue 
 I c.c. of HCl and warm. If a solution is not obtained in this 
 way, repeat the experiment with another portion of the sub- 
 stance, using HNO3 instead of HCl, If neither of these 
 methods gives a clear solution, treat a, third portion with aqua 
 regia (a mixture of one. part of HNO3 and three parts of HCl). 
 In a few cases, where the additiort" of acid causes a ppt., it is 
 necessary to remove the portion soluble in water before treat- 
 ment with acids. If a solution is obtained by any of the above 
 methods, treat about i gnj. of the substance by the same method, 
 and take the solution to § 87, b. 
 
 If in the above tests, there is an insoluble residue which is 
 white and gelatinous, and remains for some time suspended in 
 the liquid, it will probably consist of^,Si02 from silicates that 
 have been decomposed by acids; in this case evaporate the solu- 
 tion, with the residue, to complete dryness, moisten with a few 
 drops of HNO3, add 10 c.c. of water, boil and filter; this 
 residue, if white and gritty, consists of SiOj. Take the filtrate 
 to § 87, b. 
 
 6. A reaction obtained in the aluminum group for Al might 
 be misleading unless in every case of the solution ef a mineral 
 by acid, the silica possibly present is not removed by this 
 evaporation to dryness before proceeding with the analysis : an 
 error might also be made in the test fc^ P2O5. Therefore, in 
 important cases the silica should be removed here. 
 
 e. If HjS was found in the tests for acids, a residue of sulfur 
 may remain ; this will be yellow, will float on the liquid and 
 when heated on a crucible cover will first melt, then burn with a 
 blue flame emitting the odor of SOj. 
 
 d. If the substance is not affected by the above treatment, 
 it must be treated as directed in § 79 for insoluble substances ; 
 
5? ELEMENTS OF CHEMICAL ANALYSIS. [§ 79- 
 
 or if a residue remains that is not white and gelatinous (SiOj) 
 and is not sulfur, this residue must be so treated. 
 
 79. The substance is non-metallic, and wholly or 
 partially insoluble. 
 
 a. The only substances oC ordinary occurrence that are not 
 dissolved by the treatment described in § 78, are C, S, AgCl, 
 AgBr, Agl (possibly PtCl,, and Pbl^), PbSOi, BaSO,, SrSO* 
 [CaSOJ, SiOz, many silicates and a few oxids and fluorids. If 
 in the tests for acids no HI, HBr, HCl, HF, or H^SOi is found, 
 the insoluble substance is generally either a silicate or an oxid 
 [or chrome iron]. In this case pass to c. 
 
 If either of the above mentioned acids is found add to the resi- 
 due obtained in § 78, qr to the original substance if wholly insol- 
 uble, 5 c. c. of a mixture of equal parts of HCl and water, and 
 a piece of Zn and warm gently ; if the Zn or the residue is 
 blackened after a few minute's, PbSOi, or a salt of silver may be 
 present; let the action continue till no further change is observed 
 and decant the liquid, rejecting it, wash the residue by decanta- 
 tion, add HNO3, heat as long as any action appears to take 
 place, as indicated by the evolution of reddish fumes, and filter, 
 if solution is not complete. 
 
 6. Filtrate. Test for Ag and Pb as in § 87, b. 
 
 C. Residue, Mix the dry and very finely powdered residue 
 (See § 44) obtained above, or the residue referred to in § 78, <?, 
 or a portion of the original substance, if it was wholly insoluble, 
 and contains no lead or silver salts, with 4 or 5 parts of a flux 
 composed of about 4 parts of NajCOj and i part of KNO,, and 
 fuse 9n platinum foil, in several separate portions ; heat gently at 
 first over an ordinary burner, and then with full flame, so man- 
 aging the operation as to lose no substance by boiling over; 
 then heat over the blast lamp for about ten minutes, or till 
 bubbles of gas are no longer set free ; the mass should fuse to a 
 liquid ; if not, more flux should be added and the heating over 
 the blast lamp be repeated. Put the foil in an evaporator with 
 water, and digest (§ 53) till the fused mass is completely disinte- 
 grated ; fuse the second portion of the mixture of substance and 
 flux, and so on, digesting all the fused masses in the same por- 
 tion of water; finally, filter. 
 
 d. Filtrate. Acidify with HCl and evaporate in the hood 
 to complete dryness, moisten the residue with a few drops of HCl, 
 
§ 8o.J THE ACIDIGENS OR ACIDS. 53 
 
 evaporate to dryness again, and moisten again with HCl, add 
 20-25 c. c. of water, and heat. A white residue, gritty under 
 the glass rod indicates SiOj. 
 
 Filter, reject the residue, and take the filtrate to § 87, b. See 
 also filtrate from e, below. 
 
 e. Residue from filtration at end of C. Wash thoroughly 
 with hot water, add about 5 c. c. of HCl, and evaporate in 
 the hood to complete dryness; moisten the residue with HCl, 
 add 20-25 c. c. of water, heat and filter, rejecting the residue if 
 white. This filtrate may be put with ,the filtrate from <?, if no 
 ppt. appears on mixing small portions of them together. Take 
 the mixture, or the two solutions separately if they cannot be 
 mixed, to § 87, b. 
 
 /. If the residue from the above filtration is black, and 
 therefore appears to be unaffected by the fluxing, fuse it with 
 7-8 parts of KHSO4 (potassium bisulfate), to which a little borax 
 may be added ; the fused mass thus obtained is to be treated as 
 directed for th^fused product in c_abpie. 
 
 CHAPTER IX (A). 
 THE ACIDIGENS OR ACIDS. 
 
 DESCRIPTION. 
 
 80, The barium group : Solubility of compounds, and reactions. 
 
 Carbon dioxid; COj: — An. odorless gas, slightly soluble in 
 water, forming probably carbonic acid, H2CO3. 
 
 All normal carbonates except those of metals of the potassium 
 group are insoluble in water. 
 
 All carbonates are decomposed by dilute acids, CO'a being set 
 free with strong effervescence. 
 
 Reaction : — When Ca{ 0H\ in solution (lime water) is ex- 
 posed to COi gas, the solution is made turbid by the formation of 
 CaCOs! on longer exposure the turbidity may disappear, owing 
 to the solution of the carbonate in the excess of COj. 
 
 Sulfuric acid; HjSOi: — All sulfates except PbSOi, BaSO,, 
 SrS04, and CaSO^, are readily soluble in water; CaSOj, is 
 soluble in about 400 parts of water, and in HCl ; the other 
 three are nearly insoluble in all acids. 
 
54 ELEMENTS OF CHEMICAL ANALYSIS. [§ 8o. 
 
 PbSOj is decomposed by Zn and HCl, Pb being set free ; all 
 of these insoluble sulfates are transposed by fusion with NajCOs, 
 carbonates of the, metals and NajSO^ being formed. All sulfates 
 except the native barium sulfate (heavy spar) are similarly 
 transposed by boiling with a cone, solution of NajCO,. 
 
 Reaction: — BaCk ppts. immediately from solutions containing 
 H^SOi, or sulfates, barium sulfate, BaSOi pulverulent, white, 
 heavy and very insoluble. Traces or even more than traces 
 may not be precipitated from a solution containing ammonium 
 nitrate or normal citrates, as well as from solutions acid with free 
 HCl or HNO3. 
 
 SuLFUROus acid; H2SO3: — SO2, sulfur dioxide is a gas pos- 
 sessing a suffocating odor, and soluble in water. 
 
 Sulfites except of the potassium group are mostly insoluble in 
 water. 
 
 They are transposed by boiling with cone, solution of NajCOa, 
 NajSOs and carbonate of the base being formed. 
 
 Reaction : — SO-i reduces ferric to ferrous salts, and therefore 
 causes a blue ppt. in a mixture of FeCl^ and K^FeCy^, since ferric 
 salts give no ppt. with K^FeCy^, while ferrous salts do. 
 
 Oxalic acid ; HjCjOi : — Oxalates except those of metals of 
 the potassium group are mostly insoluble in water; all are 
 soluble in dilute mineral acids. 
 
 Oxalates except of the aluminum and iron groups are readily 
 transposed by boiling with cone, solution of NajCOs ; they are 
 decomposed by ignition, but without blackening. 
 
 Reactions : — YhiQ^^O.^^ ppts. from solutions of oxalates 
 PbCjOi white, pulverulent, insoluble in HC2H3O2, and in 
 NH4OH, soluble in HNO3. 
 
 CaSOi ppts. from neutral or acetic solutions of oxalates, 
 calcium oxalate, Ca C.^ Ot, pulverulent, hvhite, soluble in HCl or 
 HNOi, insoluble in HC^H^Oi. 
 
 Chromic acid; HjCrOi: — Chromates, except those of the 
 potassium group, are mostly insoluble. Solutions of normal 
 chromates are yellow, of acid chromates yellowish -red. All 
 chromates are colored. 
 
 Reactions : — When a solution of a chromate is acidified with 
 HCl and boiled after the addition of alcohol, aldehyd, CjH.O, 
 and a green solution of CrClj are obtained ; this solution with 
 NH4OH gives Cr(0H)3, greenish ppt. provided that, as just 
 directed, the alcohol was added after the HCl. 
 
§ 8oJ THE ACIDIGENS OR ACIDS. 55 
 
 If to a solution of a chroraate, acidified with HCl, and con- 
 taining no other oxidizing agent than the chromate, KI is added, 
 iodin is set free, which colors CSj violet, if this reagent is shaken 
 up with the liquid. This reaction is exceedingly delicate. 
 
 If a solution of a chromate is added to a mixture of lead acetate 
 and ammonium acetate acidified with acetic acid, a yellow ppt. 
 PbCrOi, appears, at once, or after standing a short time if the 
 chromate solution was very dilute ; the ppt. is insoluble in 
 acetic acid, slowly soluble in HNO3, soluble in NaOH : no other 
 acids present as normal salts interfere with the test. 
 
 Boric acid ; H3BO3 :— Borates except those of metals of the 
 potassium group are insoluble in water, but soluble in acids. 
 
 Borates are decomposed by H.SOi, with liberation of the acid, 
 and are transposed by boiling with Na^COs. 
 
 Reaction : — Boric acid liberated by a stronger acid, such 
 as H2SO4, imparts a green color to the flame of burning alcohol, 
 particularly when the alcohol is nearly burned away. 
 
 Hydrofluoric acid; HF: — Fluorids except of the metals 
 of the potassium group are mostly insoluble or difficultly soluble 
 in water. 
 
 Any fluorid in solution will quickly corrode the surface of 
 glass with which it comes in contact. 
 
 Reaction: — H2SO4 liberates from a fluorid HF, a gas which 
 corrodes glass. 
 
 Phosphoric acid; H3P04: — All normal phosphates, except 
 those of the potassium group, are insoluble in water, but are 
 readily soluble in dilute mineral acid. 
 
 Reaction : — {NH^-^MoO^ ppts. immediately or in a very short 
 time from solutions containing H^POi or phosphates, and 
 HNOz, ammonium phospho-molybdate, pulverulent, partly ad- 
 hering strongly to the sides of the tube, lemon-yellow, readily 
 soluble in NHiOH. 
 
 Silicic acid ; HjSiOj : — Silicates, except those of the potas- 
 sium group containing an excess of alkali, are insoluble in 
 water or acids. 
 
 Silicates are transposed by fusion with NajCOg, and some are 
 decomposed by strong acids with the liberation of the silica in a 
 gelatinous form. 
 
 Reaction : — When a solution containing silicic acid or a silicate 
 is evaporated to dryness with HCl, the silicate is decomposed, and 
 SiOi remains as an insoluble gritty powder. 
 
56 ELEMENTS OF CHEMICAL ANALYSIS. [§ 8l. 
 
 8i. The silver group : solubility of compounds, and reactions. 
 
 Hydrosulfuric acid ; HjS : — An ill-smelling gas, slightly 
 soluble in water. 
 
 All sulfids except those of metals of potassium and calcium 
 groups are insoluble in water. FeS, MnS, and ZiiS are soluble 
 in cold HCl, with evolution of H^S. NiS, CoS, CdS, Bi^, 
 CuS, PbS, and AgjS are soluble in hot HNO3, nitrates of the 
 metals being formed and the sulfur partially oxidized to HjSOi 
 and partly- set free, and giving in the case of PbS insoluble,iwhite 
 PbSOj. Sulfids of arsenic, tin and antimony are decomposed 
 by hot HNO3, oxids of the metals, H2SO4 and S being formed. 
 The sulfids of mercury are not decomposed by HNO3. 
 
 Most of the sulfids that are not attacked by dilute acid are 
 decomposed by such acid in the presence of metallic zinc. 
 
 Reaction : — H^S gas, liberated by HCl or H^SOi, with 
 the aid of Zn if necessary, blackens paper moistened with 
 FbliQff,0,\. 
 
 Hydriodic acid ; HI : — The iodids closely resemble the 
 chlorids in solubility (see below under hydrochloric acid). 
 
 Iodids are transposed by boiling with a cone, solution of 
 Na.COs. 
 
 Reactions ; — AgJVOs ppts. immediately from solutions of iodids 
 acidified with HNO^, silver iodid, Agl, flocculent, yellow, insol- 
 uble in NHiOH 3.Ti&. in (NHJjCOa, and decomposed by Zn and 
 H2SO4 ; it is not decomposed by ignition to low redness. 
 
 In a solution of an iodid containing free acid the addition of a 
 little K^CrOi causes the liberation of free iodin. Chlorin causes 
 the same liberation. 
 
 CSi in a solution containing free iodin will dissolve the iodin 
 if the tnixture is well shaken, and be colored violet. 
 
 Hydrobromic acid ; HBr : — Bromids closely resemble chlorids 
 in solubility (see below under hydrochloric acid). 
 
 Bromids are transposed by boiling with NajCOj, and are 
 decomposed by chlorin with liberation of Br. 
 
 Reactions : — AgNO^ ppts. immediately from solutions of bro- 
 mids acidified with HNO^ silver bromid, AgBr, flocculent, 
 yellowish-white, soon darkening in the light, slightly soluble in 
 NH4OH, and insoluble in (NH4)jC08 ; it is decomposed by Zn 
 and H2SO4, the metal being set free, but is not decomposed by 
 ignition to low redness. 
 
 ClSj added to a solution containing free Br will dissolve it if the 
 mixture is well shaken, and take a yellow or orange color. 
 
§ 8 1.] THE ACIDIGENS OR ACIDS. 57 
 
 Hydrocyanic acid ; HCy : — Simple cyanids of metals of 
 the copper and iron groups, except HgCyj are insoluble, of 
 the potassium, calcium and aluminum groups, are soluble in 
 water. 
 
 Soluble cyanids are readily decomposed by dilute acids, HCy, 
 a colorless and very poisonous gas being liberated. Cyanids are 
 transposed by boiling with NajCOj. 
 
 Reactions : — AgNO^ ppts. immediately from solutions of cyan- 
 ids acidified with HNOi silver cyanid, AgCy, flocculent, white, 
 soluble with decomposition in boiling HNO3, and soluble in 
 NHiOH and in {^Yi.^.flOi. It is decomposed by Zn and 
 H2SO4, and also by ignition to low redness, metallic silver 
 remaining. 
 
 {NH^^S^ exposed to HCy gas for a few minutes gives, in solu- 
 tion, ammonium sulfocyanate, NHiCyS ; if the drop of solution 
 is evaporated to dryness and the residue moistened with JFeCls, 
 Fe(^ CyS\, deep red, wiU be formed. 
 
 Hydroferrocyanic acid; HjFeCys: — Ferrocyanids, except 
 those of metals of the potassium and calcium groups, are mostly 
 insoluble in water, and in acids. 
 
 Ferrocyanids are transposed by boiling with NajCOa. 
 
 Reactions : — I^eSOt gives immediately with acid solutions of 
 potassium ferrocyanid, potassium ferrous ferrocyanid K^FeFeCy^, 
 flocculent, light blue, which, on exposure to air or treatment by 
 HNO3, becomes by oxidation ferric ferrocyanid {Prussian blue~), 
 Fet{FeCy^sj dark blue, insoluble, and decomposed by NaOH 
 with the formation of ferric hydrate, Fe(0H)3, reddish brown. 
 
 FeCli gives in solution of ferrocyanids, FCii^FeCy^^ 
 
 Hydroferricyanic acid; H6(FeCy6)2 or HsFeCys: — In solu- 
 bility the ferricyanids are similar to the ferrocyanids.' 
 
 Ferricyanids are transposed by boiling with cone, solution of 
 Na,CO,. 
 
 Reactions: — FeSOt, gives immediately, in acid solutions of 
 ferricyanids, ferrous ferricyanid, Fe^^FeCy^i flocculent, dark 
 blue, decomposed by Na OH, as above, giving ferrous hydrate. 
 
 FeCls gives no ppt. with ferricyanids, but a darkening of the 
 liquid. 
 
 Hydrochloric acid; HCl: — Chlorids, except AgCl, HgCl 
 and PbClj, are soluble in water. PbClj is slightly soluble in 
 cold water, and readily soluble in hot water ; AgCl and HgCl 
 are insoluble in dilute acids. 
 
S8 ELEMENTS OF CHEMICAL ANALYSIS. [§§ 82-83. 
 
 Chlorids are transposed by boiling with cone, solution of 
 Na,COs. 
 
 Reaction : — AgNO^ ppts. immediately from solutions of chlorids 
 acidified with HNO^ silver chlorid, AgCl, flocculent, white, soon 
 darkening in the light, soluble in NHiOH z.vi6. in (NH4)2C08 ; it 
 is decomposed by contact with Zn and H2SO4, Ag being depos- 
 ited, but is not decomposed by ignition to low redness. 
 
 82. The oxidizing acids, solubility of compounds, and reactions. 
 
 Nitric acid ; HNO3 : — All normal nitrates are soluble in 
 water. 
 
 Nitrates are decomposed, with liberation of the nitric acid, by 
 sulfuric acid, and are transposed by boiling with a cone, solu- 
 tion of NajCOj. 
 
 Reactions : — In presence of H2SO4 and a reducing agent the 
 liberated HNO^ is decomposed, with the formation of nitric oxide, 
 NO ; if the reducing agent is FeSO^ and the liquid is cold, 
 {FeSOi\NO is formed, giving a blackish-broijun solution. HBr, 
 HI, HaFeCye H^FeCye and HjCrOj interfere. 
 
 If a drop of phenyl-sulfuric acid is put on a dry nitrate and 
 after a few minutes two or three drops of strong NH^ OH are 
 added, a bright yellow color appears, ammonium nitro-phenylate. 
 The reaction is exceedingly delicate. Chromates interfere. 
 
 Chloric acid ; HCIO3 : — All chlorates are soluble in water. 
 
 Chlorates are decomposed by ignition, with liberation of their 
 oxygen, and by HjSOi and are transposed in boiling Na^COs 
 solution. 
 
 Reactions : — JVa^SOi ?« <^^ acidified solution of a chlorate, by 
 taking up apart of the oxygen of the chloric acid sets free chlorin 
 or sotne compound thereof, bleaching indigo solution. 
 
 With H2S04 a chlorate gives off an offensive greenish-yellow 
 product, ClO-i, which partly dissolves in the acid, coloring it green- 
 ish-yellow. The experiment should be performed in a watch- 
 glass with a very small quantity of the substance. 
 
 83. The organic acids {except oxalic'), solubility of compounds, 
 and reactions. 
 
 Acetic acid; HC2H3O2: — All acetates are soluble. On ig- 
 nition the dry salts are decomposed and blackened by separa- 
 tion of carbon with evolution of odorous products. 
 
 Reactions : — When heated with H2SO4 and a little C-iH^O, 
 acetic ether, CiH-,CiH^O.i, very volatile, is formed, possessing a 
 peculiar, pleasant vdor. 
 
§ 84.] ANALYSIS FOR THE ACIDIGENS. 59 
 
 When a neutral acetate and FeCl^ are mixed together the solu- 
 tion assumes a deep red color, not retnoved by HgCl-i, but it disap- 
 pears when the liquid is boiled after much dilution. 
 
 Tartaric acid ; HaCiH^Og : — Tartrates of the alkali metals 
 are soluble, but only sparingly so in the case of some acid tar- 
 trates ; other tartrates are partly soluble and partly insoluble in 
 water, those of metals of the aluminum and iron groups being 
 mostly quite soluble. 
 
 Tartrates are transposed by boiling with NajCO, and are de- 
 composed on ignition, turning black and giving off the odor of 
 burnt sugar. 
 
 Reactions: — With PbCCjHaOj)., tartrates give PbC4H406, white, 
 soluble in NH^OH free from carbonate. With KC^H^O^, acidi- 
 fied with HC^H^O^, concentrated neutral solutions of tartrates give 
 hydrogen potassium tartrate, KHdHiO^, white, crystalline, insolu- 
 ble in alcohol. Boric acid interferes with this test. 
 
 Citric Acid ; HaCeHjO, : — Citrates of the alkali metals are 
 readily soluble in water, those of the calcium group metals are 
 insoluble, the others are mostly soluble. 
 
 All citrates are decomposed on ignition, with separation of 
 black carbon, and evolution of odorous products of the decom- 
 position. 
 
 Reaction; — Pb(^C,,H.i0^i in solutions of citrates ppts. lead 
 citrate, Pbii^C^^O^^, white, amorphous, soluble in NHiOH free 
 from carbonate ; on digestion for several hours with water or 
 HC2H3O2 it becomes crystalline. 
 
 CHAPTER IX B. 
 THE ANALYSIS FOR THE ACIDIGENS. 
 
 84, Notes on the chemistry of the analysis. 
 
 With regard ,to the course for the detection of the acids so 
 much of the work consists in the mere application of final tests, 
 which are sufficiently explained under the description of the 
 reactions for the acids, or elsewhere, that little remains to be 
 made clear. 
 
 The transposition in a § 76 with Na^COa is made in order to 
 
6o ELEMENTS OF CHEMICAL ANALYSIS. [§ 84. 
 
 remove from the solution all bases except those of the alkaline 
 metals : these, giving only soluble salts with all the acids, will 
 themselves give no precipitates or reactions with any of the 
 reagents used, that might confuse or mislead the analyst, or inter- 
 fere with his work. 
 
 The tin group metals if present in the alkaline solution that 
 was prepared in (a) would be precipitated on acidification in 
 12 and cause difficulty. 
 
 It must not be overlooked in making this group test, in 
 1 following, that the liquid while containing an excess of 
 Ba(0H)2 may slowly become turbid by absorption of carbon 
 dioxid from the air. 
 
 Since the treatment with acid in 1, in the course' of analysis 
 following, expels the carbon dioxid of the original substance, as 
 well as of the NajCOj used for the transposition of the acids into 
 sodium salts, this' acid must be tested for in every case, whether 
 a ppt. is obtained for the barium group or not. 
 
 HjS is also a reducing agent : by metathesis with the lead 
 acetate it gives insoluble PbS, and is thus removed, in 4. 
 
 Chlorates and ferricyanids are, like chromates, oxidizing 
 agents in the presehce of free acid ; hence the iodin test cannot 
 be used as confirmatory of the lead test, in the presence of those 
 compounds, in the test for chromic acid in 7. 
 
 This precipitate for PjOs in 10, by molybdate, is more insolu- 
 ble in a liquid containing HNO3, if it is not too strong, than in 
 other acids. 
 
 It is soluble to some extent in solutions of phosphates ; hence 
 the method of making the test which secures always an excess of 
 the reagent, in 10 a. 
 
 Compounds of arsenic and phosphorus are much alike, and 
 both arsenic and phosphoric acids give lemon-yellow precipitates 
 with molybdate ; hence the removal of members of the tin group 
 in 10 b. 
 
 Ferrocyanid and molybdate react, giving a flocculent brown 
 precipitate, which might mask the yellow phospho-molybdate, 
 if only a little of it were precipitated. Zinc ferrocyanid is in- 
 soluble in dilute HNO3 while the phosphate is soluble, and the 
 former is thus removed in 10 C. 
 
 Sulfites also give HjS with zinc and free acid; hence they 
 must be removed before making the test for HjS with these 
 reagents, as in 13. 
 
 In the reaction in 14 the HI produced from the iodide by the 
 
§ 8S-J ANALYSIS FOR THE ACIDIGENS. 6l 
 
 Stronger HNOs becomes a reducing agent, its hydrogen reducing 
 the chromic acid of the chroraate, while its iodin is set free. 
 
 Solution A must be used in the test for HCy in 16 because 
 HCy was expelled from B by the H^SO^ added. The (NH4)jS, 
 which would give a black precipitate with the FeCls, added later, 
 is decomposed by the evaporation to dryness ; in this evapora- 
 tion, if the dry residue be heated too strongly the sulfocyanate 
 itself will also be decomposed. 
 
 The laboratory solution of ammonium carbonate contains 
 freeNHiOH, which, according to the required conditions of this 
 operation, should not be present : hence the treatment with 
 CO2, in the separation of AgCl from AgBr in 19 6. 
 
 While the fused residue of AgCl, Agl, and AgBr is acted upon 
 by Zn and HjSOi in the same manner that these salts are acted 
 upon when freshly precipitated, it is not so acted upon by 
 NH^OH and (NH4)2COsj hence the freshly precipitated salts 
 must be prepared again, after this decomposition of the salts in 
 the fused products, as directed in 19 c. 
 
 The tests for citric and tartaric acids are satisfactory only 
 when very carefully performed, and even then are not easily ob- 
 tained unless the solution contains at least a moderate quantity. 
 
 85. The course of analysis : — 
 
 The Barium group : — Preliminary test for this group. 
 
 1. To 3 c. c. of A from § 76, in a small beaker or flask, add 
 HCl very slowly and with constant stirring, till there is no 
 further effervescence, and the solution is slightly acid ; boil thor- 
 oughly, cool, and add Ba(OH)j till the liquid is slightly alka- 
 line, and with care to expose to the air as little as possible. 
 
 The liquid remains clear ; none of the Ba group of acids need 
 be tested for except COj. A slight turbidity, remaining after 
 the acidification of the liquid (§ 48), may be due to traces of 
 sulfuric acid, sulfates being very commonly present as impurities 
 in many ordinary chemicals. 
 
 2. Carbonic acid : — To a portion of the original substance 
 add HCl. If solution with effervescence takes place, test the gas 
 evolved with a drop of lime water in the open end of a small tube. 
 
 If no other acids of the barium group are present to 14. 
 
 3. Sulfuric acid: — Tt) 2 c.c. of A (§ 77) add HCl till acid 
 and then BaCU in excess. 
 
62 ELEMENTS OF CHEMICAL ANALYSIS. [§ 85. 
 
 4. SuLFUROUS ACID : — Acidify a portion of A with HCl, warm 
 and immediately expose to the gas in the tube in the open end 
 of a small tube, a drop of mixture of FeCls and KjFeCye. If 
 HjS is present a little PbCCjHsOa)^ should be added to A before 
 acidifying with HCl. 
 
 5. Preliminary test for the presence of either of the three or- 
 ganic acids, acetic, tartaric, or citric : — Carefully ignite about 
 0.5 gm. of the original substance on a crucible lid, heating only 
 for a moment at a time, at first gently, then more strongly, 
 removing the test repeatedly from the flame to observe the odor, 
 and any appearance of smoky products of combustion, or forma- 
 tion of a carbonaceous residue ; if none of these results are per- 
 ceived, these acids are absent, except at the most in very small 
 quantities. 
 
 6. Oxalic acid : — (a) No indication of organic acids was 
 observed in 5 — Acidify a portion of A with acetic acid^ttjd add 
 CaSO,. 
 
 (6) Organic acids are present. — Acidify 3 c.c. d^K with 
 dilute HC2H3O2 (1 of acid to 4 of water), add 8-10 c.c. of 
 neutral Pb(C2H30.2)2, filter, wash the ppt. with dilute alcohol 
 (equal parts of 95 per cent, alcohol and water), transfer to a 
 small beaker and add about 8 c.c. of NH4OH, mix well and 
 filter, saving the filtrate for 23. 
 
 Wash the contents of the filter with dilute NH4OH, treat it in 
 a beaker with 1-2 c.c. of HNO3, pass HjS through the liquid 
 and filter. Neutralize the filtrate with NaOH, acidify with 
 HC2H3O2 and add CaSO,. 
 
 7. Chromic Acid: — Acidify a portion of A with HC2H3O2 
 and add to it about 2 c.c. of" the lead and ammonium acetate 
 mixture. 
 
 8. Boric acid : — Evaporate 2 c.c. of A to dryness, moisten 
 the residue with HjSO^, add 2 c.c. of alcohol, set the mixture 
 on fire, and stir it, while burning, with a glass rod. If copper 
 is absent, as indicated by the absence of any greenish or blue 
 color in the original solution, the original substance may be used 
 directly for this test. 
 
 9. Hydrofluoric acid : — To the finely pulverized substance, 
 in a small platinum or leaden cup, add enough H2SO4 to make 
 a thin paste, and cover the dish with a piece of Bohemian glass 
 coated with wax except where the coating has been removed by 
 writing through it down to the glass with a pointed wooden 
 
§ 8s.] ANALYSIS FOR THE ACIDIGENS. 63 
 
 pencil ; heat the dish gently for an hour, warm the glass till 
 the wax is melted, and rub it off with filter paper. The etched 
 lines to be looked for may need to be brought out by breathing 
 on the clean glass ; they should reappear after the glass has been 
 rinsed off, dried, wiped, and breathed upon again. 
 
 10. Phosphoric acid : — Dissolve a small portion of the orig- 
 inal substance in HNO3 with the aid of heat, add its volume of 
 water to the liquid. Filter if solution is not complete, evapor- 
 ate the solution nearly to dryness, and dissolve the residue in a 
 little water. 
 
 (a) No members of the Sn group of metals were found in^TjV), 
 and no HiFeCy^ is present ; add 0.5 c.c. of this solution to 4 
 c.c. of (NH,)^ M0O4. 
 
 (J)) Members of the Sn group of metals were found, but no 
 HiFeCy^ is present ; remove these metals by heating the solution 
 and passing HjS through it till no further precipitation is pro- 
 duced by the reagent, boil to remove all HjS, and test the 
 cooled solution with (NH4)2Mo04, as above directed. Or the 
 test for this acid may be deferred till the work in § 89 c has been 
 completed, when, if no As has been found, the test for H3PO4 
 may be made as above, with the original solution ; if As is found 
 in § 89, c, a portion of the filtrate from the group precipitation 
 by HjS may be used for the test, after first heating it with a 
 few drops of HNO3. 
 
 (c) HiFeCy^ is present : add ZnSOj to the solution, freed 
 from Sn group metals if originally present, as long as any fur- 
 ther precipitation takes place, filter and test the filtrate as above 
 with (NHiXMoO*. 
 
 11. Silicic acid : — Evaporate a portion of A to complete 
 ' dryness, after acidification with HCl, and dry thoroughly at a 
 
 gentle heat; moisten the residue with HCl, and after a little 
 time add HCl and digest for a short time. For the detection of 
 SiOj, in an insoluble substance, see § 79. 
 
 12. Preliminary test for the silver group of acids: — Acidify a 
 small portion of B (or of A if there is no B) with HNO3, and 
 add AgNOs. The formation of a white or whitish precipitate 
 indicates the presence of either HCl, HBr, HI, H^FeCyg or 
 HCy. Inordinary case^a mere turbidity may be taken as indi- 
 cating trac^'bfHCl only/'a^jd the other acids precipitated by 
 silver nitrate maybemegardedai absent, unless there be special 
 reasons for searching for^sm^ of them. A colored precipitate 
 
64 ELEMENTS OF CHEMICAL ANALYSIS. [§ 85. 
 
 I 
 
 may contain also HjFeCye or HjCrOi. A black precipitate will 
 be due to the presence of HaS. If no precipitate appears all 
 these acids are absent from this solution. HjS may be present 
 in the original substance, in sulfids that were not transposed in 
 § 76. Pass on to 13. 
 
 13. Hydrosulfuric acid : — To a portion of the original sub- 
 stance in a test tube add HCl and warm gently. If solution 
 with effervescence takes place, test the gas evolved with moist- 
 ened lead paper. If a colored residue remains after this treat- 
 ment, it may contain sulfids, although no reaction for HjS was 
 obtained as above ; in such case, warm the contents of the tube 
 until all action ceases, to insure removal of SOj that may be 
 present, add a piece of zinc, and repeat the test with lead paper. 
 Should no reaction for HjS be now obtained, and a residue still 
 remain, remove the Zn and wash the residue several times with 
 water, to remove soluble sulfates, add to it HNO3 and warm till 
 red fumes are no longer set free, dilute with 5 or 6 parts of water, 
 filter if not clear, and add BaCl^ to the filtrate. A white ppt., 
 BaSOi, shows that a sulfid or free sulfur was present in the sub- 
 stance. If the other members of the Ag group are absent, pass 
 on to 20. 
 
 14. Hydriodic acid : — To 2 c.c. of B (or of A if there is 
 no B) add 2 c.c. of HNO3, 3 drops of K;,Cr04 and i c.c. of 
 CS2 ; bring the last mentioned reagent into contact with every 
 part of the solution by thorough shaking ; if ferrocyanid or 
 ferridyanid is present (see below), this shaking should be gentle, 
 in order not to flour the liquid. 
 
 15. Hydrobromic acid: — (a) HI was not found in the pre- 
 ceding test ; to the same test add 0.5 c.c. of moderately strong 
 chlorin water, and mix thoroughly by shaking. Too much 
 chlorin may itself color the CSj. 
 
 (6) HI was found in the preceding test ; filter out the colored 
 CS2 through a wet filter, add 2 c.c. of the chlorin water, mix 
 well, add 0.5 c.c. of CSj and mix again thoroughly bytshaking. 
 
 16. Hydrocyanic acid : — To a small portion of A add H2SO4 
 till acid, and in the open end of a small glass tube expose a drop 
 of (NHJ2S, to the gas evolved ; the tube may be supported by 
 means of a perforated cork that rests in the top of the test tube. 
 After exposure for 15 minutes, evaporate the drop of (NH4)2S, 
 to dryness, on a crucible cover, by a very gentle heat, and 
 moisten the residue with FeCl,. 
 
§ 85. J ANALYSIS FOR THE ACIDIGENS. 65 
 
 17. Hydroferrocyanic acid: — Acidify a portion of B (oi' 
 of A if there is no B) with H^SOi and add a drop of FeCls. In 
 case HI is present the same reaction will, however, be obtained 
 from HjFeCye. HI acting as a reducing agent would change 
 FeCls to FeClj ; but in any ordinary analysis an iodid and a 
 ferricyanid would rarely be found together. 
 
 18. Hydroferricyanic acid : — Dissolve i gm. of iron filings 
 in H2SO4, thus preparing a fresh solution of a ferrous salt, and 
 add a drop of the solution to a portion of B (or of A if there is 
 no B) that has been made acid with HaSOj. It must be ob- 
 served that even in the absence of ferricyanid a light blue ppt. 
 will be formed if H^FeCyg was found in 17, which will be 
 changed to dark blue on addition of a few drops of HNO3. 
 The ferrous solution must be used at once, as it oxidizes rapidly 
 in the air, becoming unfit for use. 
 
 For the more difiScult separation and identification of ferro- 
 and ferricyanid, when occurring together, see Prescott and John- 
 son, or Fresenius. 
 
 19. Hydrochloric acid : — If no HI, HBr, H^FeCys or HCy 
 has been found, and a white precipitate was obtained in 12, it 
 can be due to HCl only, and no further test need be made for 
 this acid ; the precipitate may be black, owing to the presence 
 of HjS, and still contain HCl : in this case treat it with am- 
 monia, filter, and acidify the filtrate with HNO3 ; a white pre- 
 cipitate indicates HCl. 
 
 If HI, HBr, H^FeCye or HCy has been found make a por- 
 tion of B (or of A if there is no B) acid with HNO3, add 
 AgNOs, shake well, decant the liquid, and wash the ppt. twice, 
 with water by decantation, and test it as follows: — 
 
 {a) HI only was found. — Digest the ppt. for a few minutes 
 with NH4OH, filter and acidify the filtrate with HNO3. A white 
 ppt. shows HCl. 
 
 (6) HBr is present and HCy is absent. — Add to the ppt. 2 
 c.c. of (NH4)2C03, pass CO2 through the mixture for a short 
 time and digest, shaking occasionally, for fifteen minutes, filter, 
 and acidify the filtrate with HNO3. A white ppt. shows HCl. 
 
 (c) HCy, HJFeCy^ or H^FeCy^ is present. — Put the ppt. into 
 a porcelain crucible, dry by gentle heat, ignite to low redness 
 and allow to cool ; put a piece of Zn in the crucible in contact 
 with the ppt. , add a little H2SO4 and allow the action to con- 
 tinue an hour ; pour off the liquid, add to it AgNOs, and test 
 5 
 
66 ELEMENTS OF CHEMICAL ANALYSIS. [§ 85. 
 
 the ppt., as directed in {a) or (&), remembering that in the ab- 
 sence of HI and HBr the formation of a white ppt. with AgNOs 
 is a sufficient test for HCl. 
 
 20. Nitric acid : — If A contains no chromate, evaporate a 
 drop of it to dryness on a crucible lid, at a very gentle heat, 
 cover the residue with a drop of phenyl-sulfuric acid, warm 
 gently, iand allow the action of the reagent to continue five min- 
 utes, special care being taken, by tipping the lid this way and 
 that, that every part of the residue is brought into complete con- 
 tact with the reagent ; then add two or three drops of NH4OH. 
 The yellow color to be looked for may be transient, but more 
 NHjOH will make it permanent. 
 
 If A does contain chromate, nearly but not quite neutralize it 
 with HCl, add Pb(C2H302)2 in slight excess, that is till precipita- 
 tion is quite complete, filter, evaporate a drop of the filtrate on 
 a crucible lid, then another drop on this residue, wet the last 
 residue with a drop of water, and test with phenyl-sulfuric acid 
 as above. If the solution to be tested is a very dilute one, as a 
 sample of water, several drops may be evaporated one after the 
 other on the same spot. 
 
 21. Chloric acid : — To the solution colored light blue with 
 indigo solution add a little H2SO4, and then, dropwise, NajSOsj 
 observe whether the color is discharged. The H2SO4 test should 
 be made, to confirm this result, if affirmative. 
 
 No reaction was obtained for organic acids in 5. Pass on to 
 the silver group, § 87. 
 
 22. Acetic acid : — To a small portion of the aqueous extract 
 of the original substance, or of A after neutralization with dilute 
 acid, add i c.c. of H2SO4 and a little alcohol, warm the mix- 
 ture for a moment, then cool it in a stream of cold water, and 
 observe the odor while shaking the tube gently ; to be sure of 
 the reaction, and of not mistaking it for the odor of nitric ether 
 if HNOs should be present, a comparison test should always be 
 made at the same time, with sodium acetate, HjSOi and CjH^O, 
 in another tube. 
 
 If HCy is present, this test might be dangerous, and only the 
 FeCla test should be used, 
 
 23. Tartaric acid : — Pass H2S through the filtrate saved in 
 6 6, heat the liquid gently to remove NH4OH, filter, add about 
 I c.c. of strong HC2H3O2, a volume of KC2H8O2 solution about 
 equal to the volume of the liquid, and a volume of alcohol 
 
§ 86.] THE SILVER GROUP. 67 
 
 about equal to twice the whole, shake well, and allow to stand 
 an hour. 
 
 24. Citric acid : — Evaporate the filtrate from the final 
 ppt. obtained in 23, till the CjHgO is removed, and add 
 Pb(C2H302)2 ; if a ppt. appears test its solubility in NH4OH. 
 
 CHAPTER X. 
 
 BASIGENS, OR METALS 
 
 86. The Silver Group : forms of occurrence and reactions. 
 
 Silver ; Ag : — May be met with as metal, alone or in alloys, 
 or as silver salts. 
 
 Reactions : — JICl ppts. immediately from neutral or acid solu- 
 tions of silver salts, silver chlorid, AgCl, fiocculent, white, soon 
 darkening in the light, insoluble in hot as well as in cold water, 
 insoluble in dilute acids, soluble in NHiOH, as {NH^^AgCl, 
 from which it is re-precipitated by acids. This ppt. is often so 
 fine that unless flocculated by strong agitation it passes easily 
 through the filter. 
 
 H2S ppts. immediately from all solutions, silver sulfid, Ag^S, 
 fiocculent, black, insoluble in (NH4)2Sx and dilute acids, solu- 
 ble in moderately dilute HNO3. 
 
 Lead ; Pb : — May be met with as metal, alone or in alloys, as 
 insoluble oxids or as lead salts. 
 
 Reactions : — HCl ppts. from not too dilute, cold solutions of lead 
 salts, lead chlorid, Pb Cl^, pulverulent or crystalline, white, soluble 
 in boiling water, and separating, crystalline, from this solution, 
 on cooling. 
 
 T^^CiOi ppts. from neutral solutions, PbCrOi, yellow, slightly 
 soluble in acetic acid, very slightly soluble in HNO3, easily 
 soluble in solution of KOH or NaOH. 
 
 HjS ppts. immediately from all solutions lead sulfid, PbS, 
 fiocculent, black, insoluble in (NH4)jS,i and in cold dilute acids, 
 soluble in hot moderately dilute HNO3; insoluble, white PhSO^ 
 is formed if HNO3 is used to dissolve it. 
 
 Jf^SOi ppts. in a short time, and immediately if its volume of 
 
68 ELEMENTS OF CHEMICAL ANALYSIS. [§ 87. 
 
 alcohol is added to the liquid, lead sulfate, PbSOi, pulverulent, 
 white, less soluble in H2SO4 than in pure water. 
 
 Mercury; Hg: — As mercurous salts. 
 
 Reactions : — HClppts. immediately from solutions of mercurous 
 salts, mercurous chlorid, HgCl, pulverulent, white, insoluble in 
 hot as in cold water, and in cold acids, not dissolved by NH^OH, 
 but blackened, NHjHgzCl being formed. 
 
 HjS ppts. immediately mercurous sulfid, HgaS, flocculent, first 
 white if HgiVCs was in the solution, then, after long continued 
 action of the H^S, black; this black sulfid is insoluble except 
 in aqua regia, forming then HgClj. 
 
 87. Preparation and analysis of the silver group precipitate. 
 
 a. The chemistry of the work on this group. 
 
 The members of this group are precipitated as chlorids from a 
 solution made somewhat acid by HNO3; the lead chlorid is 
 separated from the others by making use of its solubility in hot 
 water, and the silver chlorid is then obtained by itself, by means 
 of its solubility in NH4OH. 
 
 As the grouping work of the course begins thus with the pre- 
 cipitation of its members as chlorids by HCl, it is evident that 
 if the solution was originally made with this acid it is therefore 
 present in the clear liquid, and no members of the group can 
 also be present unless the acid was concentrated and no water 
 has been added. , 
 
 Many substances (Prescott and Johnson § 547), are held in solu- 
 tion by an alkaline liquid, the free alkali or the alkaline salt, to 
 which the alkaline reaction of the liquid is due, acting as a 
 chemical solvent (§ 5). New soluble salts are formed, by the 
 production, generally, of feeble acids, in which the metal of the 
 compound dissolved acts as an acidigen, yielding soluble salts 
 with the alkaline base : such salts are decomposed by stronger 
 acids with the reprecipitation of the substance dissolved, which 
 is sometimes redissolved by an excess of the acid, and sometimes 
 not. Hence, by the addition of HCl to a solution having an 
 alkaline reaction, compounds of elements belonging to other 
 groups may be precipitated together with the chlorids of this 
 group, which, besides perhaps being in the way here, might be 
 
§ 87-J THE SILVER GROUP. 69 
 
 missed where they should be tested for ; therefore this test for 
 alkalinity must be made as in 26. Nitric acid will also precipi- 
 tate these compounds not properly belonging in the HCl pre- 
 cipitate, but only one member of this group, the other two 
 remaining undisturbed, to be thrown down by HCl in the proper 
 manner : the one possibly precipitated, silver, will be found in 
 its place on following out the course of treatment laid down in 
 26, a. 
 
 Since, as above stated, some of the foreign compounds pre- 
 cipitated are redissolved on the addition of acid beyond the 
 point of neutralization, leaving the solution clear and in a proper 
 condition for the HCl precipitation, there should be certainty 
 that enough acid has been added for this purpose, while at the 
 same time any great excess is avoided. 
 
 The products of this group precipitation may contain a little 
 antimony oxychloride (§ 89), if much antimony is present ; this 
 will not, however, interfere with the examination of the precipi- 
 tate for this group, nor will this element be missed in Table III, 
 since this precipitation is only partial. 
 
 The weak points in the work of this group, which the student 
 should bear in mind, are the imperfect insolubility of the PbClj 
 in cold water, its rather sparing solubility in hot water, and the 
 slight solubility of AgCl in strong HCl or solution of alkaline 
 chlorids. 
 
 6. Preparation of the silver group precipitate. 
 
 25. If HCl was used in making the solution, and it is clear 
 when cold, or HCl was used, and the solution remains clear 
 when diluted with two or three times its volume of cold water, 
 pass on to § 87 b. 
 
 If not clear when cold, as when hot, or after such dilution, 
 proceed as in case a ppt. is obtained in 26 b, below. 
 
 26. If the substance is already in solution when received, or 
 is made with water only, test it with litmus paper ; if found to 
 be alkaline pass to {a) ; if acid or neutral, to (&). 
 
 (a) The solution is alkaline. Add HNO3 till acid ; if no ppt. 
 forms pass to (6) ; if a ppt. is formed and does not dissolve on 
 adding more acid, filter, examine the ppt. by § 78, and examine 
 the filtrate as directed in (&). 
 
70 
 
 ELEMENTS OF CHEMICAL ANALYSIS. 
 
 [§87. 
 
 (6) The solution is acid or neutral. Add a few drops of 
 HCl ; if no ppt. appears pass to § 89, &. If a ppt. is formed 
 continue to add HCl till it no longer increases, shake vigor- 
 ously, allow the ppt. to settle and decant the liquid through a 
 filter. If much Sb is present in the original substance this ppt. 
 may possibly contain a little SbjOsCla (see above.) Reserve the 
 filtrate for the tin and following groups, § 89, 6. 
 
 C. Analysis of the Silver Group Precipitate. 
 
 TABLE III. 
 
 27. Wash the precipitate with cold water, by decaatation, till the wash 
 water is no longer acid, then boil it with about 10 or 20 c.c. of water, and 
 filter while still boiling hot. 
 
 28. Filtrate. 
 
 29. Residue. 
 
 To a portion add 
 KjCrO^. , A yellow 
 ppt. or turbidity in- 
 dicates Pb. 
 
 Add about 5 c.c. of NH^OH, shake thoroughly 
 and filter if solution is not complete. 
 
 30. Filtrate. 
 
 31. Residue. 
 
 Aci dify with 
 HNO3. A white 
 ppt. indicates Ag. 
 
 This, if there is any of it, is 
 blackened by the treatment 
 with NH4OH. Hg, as mer- 
 curous salt, is indicated. 
 
§ 88. J THE TIN GROUP. 7r 
 
 88. The Tin Group: forms of occurrence, properties, and re- 
 actions. 
 
 Gold ; Au : — To be met with as pure metal or in alloys, and 
 as soluble chlorid. 
 
 Reactions : — Gold is soluble in d,qua regia, forming yellow 
 AuCls. 
 
 HjS ppts. from cold acid solution AujSg, black, from hot solu- 
 tions AujS, brown ; both sulfids are slowly soluble in (NH4)2Sx 
 as (NH4)3 AuSs and repptd. from this solution by acids as AU2S3. 
 
 If^CiOi especially in presence of {NH^^C^Oi ppts. from not 
 too acid solutions of gold, metallic gold, brown to violet, very fine 
 powder, which rubbed with a knife on a hard surface shows the 
 color and lustre of gold. 
 
 Sn CI2, to which a little chlorin water has been added to convert 
 a small portion of the stannous to stannic salt, gives in solutions of 
 gold a purple red ppt. or coloration, or sometimes violet or brown- 
 ish-red (purple of Cassius), insoluble in HCl. 
 
 Platinum ; Pt. : — To be met with as metal, alone or in alloys, 
 and as soluble chlorid.. 
 
 Reactions : — Platinum is soluble in aqua regia, forming soluble 
 PtClj. HjS ppts. from acid solutions of platinum salts, slowly 
 unless the solution is hot, PtSj, blackish-brown, soluble slowly 
 and with difficulty in (NHj)2Sx, and repptd. from this solution 
 by acids. 
 
 SnCl-i reduces platinic salts to platinous salts, which dissolve 
 in HCl, giving a deep red color. 
 
 Arsenic; As: — To be met with as, (i) arsenous oxid, 
 ASiOs, slightly soluble ; (2) as sulfids, AsjSj realgar, AS2S3, orpi- 
 ment, or AsjSj, all insoluble ; or (3) in arsenites, M^sAsOs or 
 arsenates MgAsO^, both mostly insoluble ; or (4) as a gaseous 
 compound with hydrogen, AsHj very poisonous. 
 
 Reactions : — H2S ppts. from acid solutions immediately arsen- 
 ous sulfid, AS2S3, flocculent, light yellow, soluble in (NH,)2S,i 
 forming (NH4)3AsS3 (variable), and repptd. from this solution 
 by acids as AsjSg, insoluble in HCl, but dissolved by digestion 
 with fully concentrated hydrochloric acid and KCIO3 (potassium 
 dhlorate) forming HjAsO^. 
 
 With Zn and H^SOi, solutions containing As yield arsenous hy- 
 dride, AsH, a colorless gas, which conducted into a solution of 
 
 * M stands for any monad basigen. 
 
72 ELEMENTS OF CHEMICAL ANALYSIS. [§ 88. 
 
 AgNOi causes the separation of Ag, black ppt., while the As re- 
 mains in solution as HgAsOg. HNO3 is also formed, but no NO 
 as when HNO3 is itself the oxidizing agent. The oxygen for 
 this oxidation appears to come from the water present. 
 
 To make this test, a hydrogen generator is required, consisting 
 of a small flask provided with a two-hole rubber stopper; 
 through one of these holes a funnel-tube passes, and extends 
 nearly to the bottom of the flask ; a short tube in the other hole, 
 bent at a right angle, is connected by a rubber tube with the 
 glass delivery tube that conducts the gas evolved in the flask into 
 the solution of AgNOg. Put two or three small pieces of granu- 
 lated zinc into the flask, while holding it in an inclined posi- 
 tion, so that the zinc will glide down the side, and not fall 
 directly on the thin bottom, perhaps breaking it ; put in also a 
 piece of clean platinum foil, add about 10 c.c. of HjSOj, or so 
 much that the mouth of the funnel tube will be immersed, carry 
 the delivery tube into about 10 c.c. of AgNOg, in a test tube, 
 and then add the solution containing the arsenic, or to be tested 
 for arsenic, very slowly. The gas from the generator should 
 never be allowed to escape except through the silver solution, if 
 there is any possibility that arsenic is present. 
 
 Compounds of arsenic, and especially the sulfid, when heated in 
 a bulbed tube of hard glass with a perfectly dry mixture of sodium 
 carbonate and potassium cyanid, are reduced, and the arsenic is 
 volatilized and deposited as a black, lustrous ring on the cooler 
 part of the tube. To make this test, proceed as follows : put a 
 small quantity of the perfectly dry substance in the bulb of the 
 tube, and cover it with a mixture of equal parts of dry NajCOs 
 and KCy ; the bulb should be so large, or the quantity of sub- 
 stance taken so small, that the bulb will not be more than half 
 filled. Heat the bulb gently, and with a twisted piece of filter 
 paper wipe out any moisture that may collect on the inner walls 
 of the tube ; this drying must be very thoroughly done ; now 
 heat the bulb strongly, and for some time if no black deposit 
 appears at once. 
 
 Antimony; Sb : — May be met with (1) as metal, alone or in 
 alloys ; (2) as insoluble sulfids, SbjSs, and SbaSj ; (3) as oxids, 
 SbjOe and SbzO^, insoluble, acting feebly acid igenic or basigenic, 
 and SbjOs, acting only acidigenic and forming mostly insoluble 
 compounds; (4) in combination with CI as SbClj, or SbCIs; or 
 (s) in a gaseous compound with hydrogen, SbHj, 
 
 Reactions: — Metallic antimony is oxidized by HNOj to 
 
§ 88.] THE TIN GROUP. 73 
 
 SbjOi and SbjOs, white, soluble in HCl and, when freshly pre- 
 cipitated, in tartaric acid. 
 
 HjS ppts. immediately, from acid solutions containing anti- 
 mony, antimonous sulfid, SbjSj, flocculent, orange yellow, solu- 
 ble in (NH4)aS, forming (,NHi)3SbS4, and repptd. by acids from 
 solution as Sb^Sj. Both sulfids are soluble in hot HCl forming 
 SbCls. 
 
 HjO added in large quantity to a solution containing SbClj 
 ppts. basic salt or oxychlorid, variable, but mostly Sb405Cl2, pul- 
 verulent, soluble in tartaric acid, and converted into antimonous 
 sulfid by HjS passed through water in which it is suspended. 
 
 Wttli Zn and H^SO^, in the hydrogen generator, solutions con- 
 taining antimony yield metallic antimony, deposited as an adherent 
 black coating on platinum foil kept in contact with the zinc ; this 
 deposit is insoluble in HCl, soluble in HNO^ ; at the same time 
 that this deposit is formed a part of the antimony yields antimonous 
 hydrid, SbH^ a colorless gas, which in a solution of AgNO^ gives 
 SbAgi, black ppt. The more rapid the evolution of hydrogen, the 
 more Sb is liable to be carried off as SbH^. 
 
 Tin ; Sn : — May be met with (i) as metal, alone or in alloys, 
 (2) as insoluble oxids, SnO or SnOj, one acting basigenic, the 
 other basigenic or acidigenic, (3) as insoluble sulfids, SnS or 
 SnSj, and (4) as soluble chlorids, SnClj or SnClj. 
 
 Reactions: — HNO3 oxidizes tin to SnOa, white, which at 
 once forms with the water metastannic acid, HuSngOis, variable, 
 insoluble in acids. HCl dissolves tin as SnClj, soluble. 
 
 HjS ppts. immediately from not too strongly acid solutions 
 containing stannous salts, stannous sulfid, SnS, flocculent, dark 
 brown, soluble in (NH4)2Sj forming (NH4)2SnS3, and reprecipi- 
 tated by acids as SnSj. From solutions of stannic salts H^S ppts. 
 stannic sulfid SnSa, flocculent, white at first, while the stannic 
 salt is in excess, then yellow, soluble in (NH4)2S,i with formation 
 of the same compound as in the solution of SnS. SnS and SnSj 
 are soluble in hot HCl, forming SnClj and SnClj, respectively. 
 
 With Zn and Il^SOi solutions containing tin give Sn, gray ppt. 
 deposited mostly on the zinc, and not adhering either to this or to 
 the platinum foil if deposited thereon. 
 
 HgCl-i gives with solutions of stannous salts, mercurous chlorid, 
 HgCl, pulverulent, white first and becoming grayish with excess 
 of stannous salt. 
 
74 ELEMENTS OF CHEMICAL ANALYSIS. [§ 89. 
 
 89. The preparation and analysis of the tin group precipitate. 
 
 a. The chemistry of the work on this group. 
 
 For the separation of the members of this group from those 
 that folldw, use is made of the insolubility of their sulfids in 
 moderately strong hydrochloric acid. Since the sulfids of the 
 metals of the copper group are equally insoluble in acids, both 
 groups are precipitated together by this reagent. The two 
 groups are then separated by means of the solubility of the 
 sulfids of the tin group in (NHJjSx (ammonium sulfid with 
 excess of sulfur). When this solution is treated with excess of 
 dilute acid, the metals of the tin group are again precipitated as 
 sulfids. Separate and special tests being made in the original 
 solution for gold and platinum, only arsenic, antimony and tin 
 remain to be tested for in this second precipitate. For the sepa- 
 ration of these elements use is made of their different behavior 
 with nascent hydrogen, especially in the presence of metallic 
 platinum ; the first passes off' as a gaseous compound, AsHs, and 
 is taken up by a silver solution ; the second is mostly precipi- 
 tated as an adherent coating on the platinum ; the third is precipi- 
 tated as a loose metallic deposit, or loosely adhering to the zinc ; 
 both the second and the third therefore remain in the generator. 
 
 In this Table the grouping by sulfids first comes into effect, 
 and so far as it takes place here depends upon the solubility in 
 dilute acid of sulfids of metals to be tested for in the iron and 
 aluminum groups, and the insolubility of those to be precipitated 
 here. But a study of the properties of these sulfids will show 
 that they are more or less soluble in strong mineral acids when 
 hot, and in aqua regia ; hence, especially as the precipitation 
 must be made in a hot liquid, the directions for the careful prep- 
 aration of the solution as to its acidity. 
 
 Furthermore, since these sulfids are soluble in solutions of the 
 fixed alkaline hydroxids by the formation of oxygen salts of 
 these bases, such as KjAsOa, and in solutions of alkaline sulfids 
 forming soluble sulfo-salts (§ 65), and since, if the solution con- 
 tained free alkali at the start, the first portions of H^S added 
 would be taken up to form these sulfids of the alkaline metals, 
 acidity in the beginning is also an essential condition. Also, 
 some of these sulfids are not readily precipitated in a neutral 
 solution, as will appear on writing the equation for the precipita- 
 tion of arsenic or antimony from neutral solutions of salts of the 
 alkaline metals in which they take the part of acidigens. 
 
 The fact that SbiOjCla and BiOCl, if precipitated in the course 
 
§89.] THE TIN GROUP. 75 
 
 of the preparation of the solution, may be left undissolved is an 
 interesting illustration of the principle (§ 26 a) that metathesis 
 may sometimes take place between substances when one of 
 them is in the solid condition ; that these oxychlorids cannot be 
 allowed to remain as such in the later work of the course will 
 become evident on careful study of the steps that follow, which 
 result in confining antimony to this course and sending bismuth 
 to the next, and comparison of the solubility of these oxychlor- 
 ids and of the four corresponding sulfids. 
 
 The tests for gold and platinum in 36, Table IV, exhibit a 
 nice distinction between the power of different reducing agents ; 
 oxalic acid reduces only the former, while SnCU reduces both. 
 
 In order that the color of the reduced gold may not interfere 
 with the sharpness of the other reaction, it must first be removed. 
 Concentrated HCl serves to dissolve any platinum that might be 
 precipitated in the test for gold, in the presence of the ammo- 
 nium salt added, as 2NH4Cl.PtCl4. 
 
 The group precipitation must be made in a hot solution as in 33 
 below, chiefly on account of the possible presence of arsenz^ salts. 
 Under the reactions of arsenic it will be seen that only AsjSs is 
 precipitated by H^S from any solutions containing this element ; 
 therefore, if the arsenic is not already in the form of SLTsenous 
 salts, reduction must take place before precipitation ; such reduc- 
 tion by H2S requires the aid of heat, about 70°, and consider- 
 able time, even perhaps twelve to twenty-four hours ; previous 
 treatment with a more active reducing agent, as H2SO3, greatly 
 shortens the time required for complete precipitation. 
 
 Under the reactions for mercuric salts, considered in connec- 
 tion with the first step in sub-grouping taken in § 91 c, will be 
 found another reason for keeping the solution under the influ- 
 ence of H2S for a considerable time. 
 
 The use of yellow ammonium sulfid, (NH4)2S,t, in 34, which 
 is necessary for the separation of members of this group on 
 account of the difficult solubility of tin and antimony sulfids in 
 the normal, colorless (NH4)2S, has this disadvantage, that the 
 CuS which should pass over to § gi C, is soluble in it ; but this 
 sulfid is almost completely precipitated again on boiling the 
 solution. 
 
 The constitution of the compounds formed in this solution of 
 the sulfids is explained in § 65. 
 
 In the re-solution by concentrated acid of the sulfids pre- 
 cipitated from the (NH4)aSx solution, as in 37a, the use of the 
 
76 ELEMENTS OF CHEMICAL ANALYSIS. [§89- 
 
 Strong oxidizing agent, KCIO3 in presence of HCl, is likely to 
 carry at least a portion of the elements combined with the sulfur 
 up to their highest degree of chlorination ; this makes more 
 striking the illustration furnished here of the reducing power of 
 nascent hydrogen, all the antimony, tin and arsenic being 
 reduced to the elementary form ; then, by further action in the 
 same direction, all of the arsenic and a part of the antimony 
 are carried off as gaseous products in combination with hydro- 
 gen. 
 
 The sharp separation of arsenic and antimony is a difficult 
 matter ; any one of several methods will give satisfactory results, 
 as will this one, as given in 376, if carefully executed, but 
 otherwise failure is likely to be encountered. In this method 
 arsenic may possibly remain in its reduced form in the generating 
 flask, or by misfortune in the opposite direction all the antimony 
 may be carried as SbHg out of the generator. By the slower 
 production of hydrogen in the first part of the operation, the 
 deposition of a certain portion of the antimony on the platinum 
 foil is secured, when it will be safely fixed, having passed the 
 nascent state ; a subsequent more rapid evolution of gas secures 
 the transfer of at least the largest part of the arsenic to the 
 test-tube. 
 
 Tin cannot leave the generator under any conditions. 
 
 6. Preparation of the group precipitate. 
 
 32. Before proceeding further with the analysis the solution 
 must be so prepared that it will be moderately acid with HCl, 
 and it is better that it should not contain free HNOs or strong 
 acid of any kind; if the solution was made with water and then 
 acidified with HCl, or made with dilute HCl, it is already in this 
 c ondition ; pass to 33. If HCl was used for the solution, 6 or 
 7 parts of water may be added, then pass to 33. If HNO3 was 
 used in preparing the solution, evaporate the liquid nearly to 
 dryness, in the hood, add to the residue i c. c. of HCl and 10 
 c. c. of water ; if a white ppt. forms on addition of water it 
 probably consists of Sb^OjCLj or BiOCl (see § 89 a). 1 
 
 33. Reserve about 5 c. c. of the solution for th^ests for gold 
 and platinum, and through the rest of it pass a slow current of 
 
§ 89. J THE TIN GROUP. 77 
 
 H2S for at least i^ minutes, or till no further precipitation is 
 produced by the reagent, or no further change appears in the 
 color of the ppt. For this important group precipitation the 
 liquid must be hot in the beginning ; and if the operation requires 
 much time for its completion the liquid should be heated as often 
 as may be necessary to keep it hot ; finally, on filtering, the first 
 portions of the filtrate should be heated nearly to boiling, and 
 tested with H^S for complete precipitation. 
 
 If no ppt. is formed, or only one that is white, very fine and 
 plainly only sulfur, pass on to the iron group, § 93, 6 (see 
 Table II). 
 
 If a colored ppt. is formed, filter and wash thoroughly with 
 hot water till a drop of the washings received in a little AgNOj 
 in a test tube gives at the most only a slight turbidity. Reserve 
 t\ie_filirate for following groups, beginning with the iron group, 
 § 93 b. SeDalso Table II. 
 
 34. Pres^tate. Digest a small portion in an evaporator 
 with (NHMjS,; : if it dissolves completely, only metals of the Sn 
 
 figrouD arS present in this ppt., and the remainder of it may be 
 used nawhe analysis for these metals, as directed below (37 Cb) ; if 
 a resijMe remains undissolved, metals of the Cu group are also 
 j^esent : in this case pour off the (NH4)2Ss and test it with HCl 
 J5 ; if no metals of the Sn group are shown to be present, 
 Jhe remainder of the ppt. to § 91, h, for the analysis of the Cu' 
 /gfliup. If metals of both groups are present, the whole of the 
 8t. must be treated as above, with (NH4)2Sj and the mixture 
 joiled and filtered. Reserve the insoluble residue for the Cu 
 jroup. 
 
 35. Filtrate. Dilute with 3 or 4 parts of water and acidify 
 with HCl ; if only a fine, white, or faintly yellowish ppt. appears 
 that remains suspended in the liquid it consists of sulfur from the 
 (NH4)2S;„ and As, Sn, and Sb are absent ; pass on to the Cu 
 group. A colored ppt. that is flocculent, or becomes so on warming, 
 may contain the sulfids of these metals : filter, rejecting the 
 filtrate, and take the precipitate to Table IV, following. 
 
78 
 
 ELEMENTS OF CHEMICAL ANALYSIS. 
 
 C§89- 
 
 C. Analysis of the Tin Group Precipitate. 
 
 TABLE IV. 
 
 36. Filter a small portion of the solution, reserved in 33 for this purpose, 
 not clear, and add to the filtrate i c.c of (^Yi.^Sl,.fii, and of H2C2O4, boil a: 
 let stand ten minutes ; a brown or violet ppt. indicates Au. The result m 
 be confirmed by the other reactions given for this metal. 
 
 If Au was found, filter, wash the ppt. with 0.5 c.c. of HCl and add Sn( 
 to this filtrate ; a red color shows Pt. If no Au was found add SnClj direci 
 to a small portion of solution 33. 
 
 37 (a) Transfer the ppt. brought from 34 or 35 to an evaporator, add 5 c.c. 
 fully concentrated hydrochloric acid and warm j if the ppt.. does not dissol 
 remove the lamp, add a small -crystal of KCIO3 and digest till the sulfids a 
 dissolved, or the residue is at least decolorized. Filter if a residue (sulfi 
 remains, add to the filtrate 5 c.c. of FeSO^ and 5 c.c. of H2SO4, and proce 
 as follows. 
 
 (6) Into the hydrogen generator, described under the reactions of arsenic ai 
 prepared for use as there directed, pour this solution very Slowly, only a f( 
 drops at a time, till all has been added ; if before this the zinc is wholly d 
 solved, lift the cork of the flask for a moment and drop in another piece ; 
 sure that the platinum is in contact with the zinc during the whole operatic 
 which need be continued only for a few minutes after the last portion of t 
 solution has been added. 
 
 CONTBNTS OF THE GENERATOR. 
 
 Contents of the Test-tube, 
 
 The loose ppt. 
 
 The fixed ppt. 
 
 4:0. If no black ppt. is for 
 ed As and Sb are both abse 
 
 38. Pour the contents of the 
 generator into a filter, pick out 
 ihe pieces of zinc, and rinse 
 whatever adheres loosely to 
 them and to the platinum foil 
 into the filter with the jet of the 
 wash bottle, and then with the 
 same jet collect the contents of 
 the filter down into the apex of 
 the cone ; when the water has 
 fully drained out, carefully re- 
 move the filter from the funnel, 
 tear off that part containing the 
 solid matter, and warm this 
 very gently with about two c.c. 
 of HCl, till all action ceases, 
 add about its volume of water 
 to the liquid, filter into a small 
 test tube, and to the filtrate add 
 SgCljj. A white or grayish 
 ppt. shows Sn. 
 
 39. If the platinum foil is 
 blackened, and remains black 
 after treatment with HCl, 
 antimony is probably present ; 
 to confirm the indication wash 
 the residue insoluble in HCl 
 in 38, together with the foil, 
 with water, add a few drops 
 of HNO3 and 2 c.c. of tar- 
 taric acid, heat nearly to 
 boiling, dilute with an equal 
 volume of water and add to 
 thesolutioH H2S. An orange 
 ppt. shows Sb. If this ppt. 
 is black, owing to the possible 
 presence of Cu, heat it with 
 two c.c. of tartaric acid for a 
 few minutes, filter, and apply 
 the HjS test to the filtrate. 
 
 If a black ppt. appears, filt 
 rejecting the ppt., to the 
 trate add HCl as long as 
 ppt. is formed, heat just 
 boiling and filter, pouring t 
 filtrate through the filter 
 second time to insure compli 
 removal of AgCI, and to t 
 filtrate add HjS. A yelh 
 ppt. shows As. In the p 
 sence of a large proportion 
 Sb, and little As, this ppt. m 
 be so colored by SbjSj tl 
 the indication for As is unc 
 tain. In such case collect t 
 ppt. on a filter, wash it doi 
 into the apex of the cone, c 
 it thoroughly in the drying clos 
 remove it from the filter, a 
 test it for As by heating in t 
 bulbed tube with Na2COs a 
 KCy. 
 
§ 90-J THE COPPER GROUP. 79 
 
 THE COPPER GROUP. 
 
 go. Forms of occurrence and reactions. 
 
 Copper ; Cu : — To be met with as metal, alone or in alloys, as 
 oxids, insoluble, and as copper salts. 
 
 Reactions : — HjSppts. immediately from all solutions contain- 
 ing copper, cupric sulfid, CuS, flocculent, black, insoluble in 
 cold dilute acids, slightly soluble in (NH4)2Sx, soluble in hot 
 HNO3 and in KCy (potassium cyanid) solution. 
 
 NH^OH ppts. immediately cupric hydroxid, Cu(^OH\ floccu- 
 lent, greenish-blue, soluble in excess of the precipitant forming a 
 dark blue liquid ; the formulas of the double compound of NH3 
 and copper salts, causing this blue color, vary with the nature of 
 the acid of the copper salt used, and other conditions. 
 
 Cadmium ; Cd : — To be met with as metal, alone or in alloys, 
 and as cadmium salts. 
 
 Reactions : — I/^S ppts. immediately from solutions containing 
 cadmium, cadmium sulfid, CdS, flocculent, yellow, insoluble in 
 cold dilute acids and in (NH4)2S„ soluble in hot HNO3, insolu- 
 ble in KCy. 
 
 NH4OH ppts. cadmium hydroxid, flocculent, white, soluble in 
 excess of precipitant. 
 
 Bismuth ; Bi : — To be met with as metal, alone or in alloys, 
 or as bismuth salts. 
 
 Reactions: — HjS ppts. immediately from all solutions con- 
 taining bismuth, bismuth sulfid, BiuSa, flocculent, black, insoluble 
 in cold dilute acids and in (NHJ^S,, soluble in hot HNO3. 
 
 NH4OH ppts. bismuth hydroxid, Bi(0H)3, flocculent, white, 
 insoluble in excess of precipitant, soluble in dilute acids. 
 
 H^ O added in large quantity to concentrated solutions containing 
 bismuth and a moderate quantity of HCl causes the formation of 
 bismuth oxychlorid, BiOCl, lustrous white, soluble in strong 
 acid. 
 
 Mercury; Hg: — To be met with as metal, alone or in alloys 
 (amalgams), and as mercurous or mercuric Salts. 
 
 Reactions : — H2S ppts. immediately from all solutions con- 
 taining mercuric salts, mercuric sulfid, HgS, flocculent, black 
 finally when precipitation is complete ; color at first may be 
 white, and pass through yellow, orange, and brown to black ; if 
 the mercury was originally present as nitrate, long continued 
 action of the HjS may be necessary to convert it completely into 
 the black sulfid. The black ppt. is insoluble in (NH4)2S,i, and 
 
8o ELEMENTS OF CHEMICA'L ANALYSIS. [§ 91- 
 
 is soluble only in aqua regia, forming HgClj. The lighter 
 colored ppt. consists of compounds of HgS with the original 
 salt, the HgS predominating more and more as the action of the 
 HjS is continued. ' 
 
 SnCl^ in presence of HCl gives mercurous chlorid, HgCl, pul- 
 verulent, white or gray. The darker color is due to reduction of 
 some HgCl to metal, by the excess of SnClj. 
 
 91. The preparation and analysis of the copper group precipitate. 
 
 a. The chemistry of the work on this group. 
 
 In the ordinary course of a complete analysis of a substance 
 possibly containing merhbers of all the groups, the members of 
 this group are already separated from those of the other groups, 
 in the residue insoluble in (NH4)2Sx, brought from the preparation 
 of the precipitate for the tin group. If, as when working on 
 this group by itself, as in the usual preliminary practice, the 
 original substance is at once examined for this group, or if the 
 substance is known to contain only members of this and following 
 groups, the solution of it is prepared and treated with HjS, as 
 directed in § 89 h, and the members of this group are then 
 obtained in the same form as in the insoluble residue from 34 in 
 that section. 
 
 From this precipitate the mercury is separated by the insolu- 
 bility of its sulfid even in concentrated HNO3. In the solu- 
 tion containing the other members of the group, copper and 
 cadmium are separated from bismuth by the solubility of their 
 hydroxids in NH4OH, and the copper is finally separated from the 
 cadmium by the insolubility of its sulfid in KCy. 
 
 In the ordinary course of a complete analysis of a substance, 
 we have at the opening of this group analysis, sulfids precipi- 
 tated in 33 and insoluble in (NHi^jS^; also, possibly, lead from 
 26 }}, for reasons explained at the close of § 28. By the re- 
 agent applied here in the very beginning, the first step in the 
 sub-grouping of the members of this group is effected. The 
 continuance of the red fumes indicates continuance of oxidation 
 of sulfids, and their cessation is evidently, in the simultaneous 
 presence of HgS and other black sulfids of this group, the 
 only easily observed indication of the complete solution of 
 
§ 91-!] THE COPPER GROUP. 8 1 
 
 all that can be dissolved by the acid from this mixture of 
 sulfids ; incomplete solution might result in missing one or more 
 of the substances to be tested for under 42 to 45, Table V. 
 
 For the removal of lead, if still present, in 42, Table V, ad- 
 vantage is taken of a more insoluble precipitate than the chlorid ; 
 and if any still escapes precipitation it may be arrested by the 
 NHjOH added later, so that its troublesome presence in filtrate 
 43 should never occur with proper care in the previous manipu- 
 lation. 
 
 Because lead may thus be present in the precipitate by NH4OH, 
 the formation of that precipitate is not of itself sufficient proof 
 of the presence of bismuth. 
 
 For copper we have one of those characteristic color tests 
 which might as well be applied in all ordinary cases to the origi- 
 nal solution, if, indeed, the presence of this substance is not 
 sufficiently betrayed by the blue or greenish-blue color of that 
 solution, or of the nitric acid solution made in 41. 
 
 By the addition of KCy the cuprammonium compound in the 
 deep blue solution, yielded by NH4OH with the copper, is broken 
 up by the formation of new compounds into which cyanogen 
 enters, the color is destroyed, and we have a solution in which 
 the excess of KCy prevents the formation of CuS, and, its color 
 being much lightened, the cadmium precipitate can be more 
 easily distinguished in it. 
 
 For bismuth we have a reaction in 45 that is peculiar; in that 
 the precipitate is apparently made by so general a solvent as 
 water ; it is due to the tendency of normal salts of bismuth to 
 decompose when added to a large quantity of water, forming 
 basic salts (§ 1 7). Some of these salts, and especially the oxychlo- 
 rid, are quite insoluble in water ; but as they are readily soluble in 
 acids, the reason for the use of but little acid may be understood, 
 and also, although for another purpose, for the precaution noted 
 in 42 of adding sufficient HjSOi in the precipitation of lead ; 
 the reason for evaporation to a very small bulk is also indicated, 
 since in the evaporation of an acid solution the free acid is more 
 or less completely expelled. 
 
 Since the conditions requisite for the production of this oxy- 
 chlorid are the presence together of a bismuth salt and HCl in 
 certain proportions, and a sufficient degree of concentration of 
 the solution, the precipitate may appear, as well as the similar 
 one, SbiOjClz, in the group precipitation of the Ag group ; but 
 only in case of much more caution in adding HCl than the 
 6 
 
82 ELEMENTS OF CHEMICAL ANALYSIS. [§ PI- 
 
 Student usually shows ; and, as it is altogether likely that only a 
 part of these metals would be thus precipitated in any case, the 
 occurrence of such a precipitate would do no other harm than 
 to lead to the inference that, having a group precipitate, then 
 certainly one or more of the members of the group ought to 
 be found in it. 
 
 6, The preparation of the copper group precipitate. 
 
 In the course of a complete analysis of a substance, this pre- 
 cipitate is already prepared. In the case of practice on this 
 group precipitate alone, the precipitate is prepared as described 
 in 32 and 33 under the tin group. 
 
§ pi-J THE COPPER GROUP. 83 
 
 C. The Analysis of the Copper Group Precipitate. 
 TABLE V. 
 
 41. Heat the precipitate in an evaporator with about 3 c.c. of 
 HNO3, with constant stirring and boiling, till red fumes are no 
 longer evolved, add its volume of water to the mixture, and filter. 
 
 42. Filtrate. 
 
 46. Insoluble 
 residue. 
 
 Test a small portion for Pb with alcohol and HjSO^ (see 
 reactions of Pb, \ 86) ; if Pb is found treat the whole of the 
 solution with alcohol and H^SO^, with care to add the acid in 
 excess, that is, more than enough to ppt, the Pb, so as to prevent 
 possible precipitation of Bi, and filter, to remove the Pb. To 
 this filtrate or to the remainder of filtrate 41, if Pb is absent, 
 add NH^OH till strongly alkaline. A white ppt. indicates 
 bismuth, but its presence should be confirmed as below. If 
 this ppt. is formed filter. 
 
 43. Filtrate. 
 
 If this filtrate is blue, the presence of Cu 
 is indicated. 
 
 44 (a). Copper is 
 absent. 
 
 To a portion of the 
 solution add (NH4)2S. 
 
 A yellow ppt. indi- 
 cates Cd. 
 
 44 (ft). Copper is 
 present. 
 
 To a portion of the 
 solution add KCy 
 till the blue color 
 disappears. Then 
 add (NH JjS. 
 
 A yellow ppt. in- 
 dicates Cd. 
 
 A black ppt. obtained here for Cd may be 
 due to the presence of Pb or Hg ; in the 
 latter case because the element was not 
 completely converted into black sulfid in 
 33 ; filter, wash the ppt., put it with the 
 filter into an evaporator and boil with 
 H2SO4, filter again and add to the filtrate 
 HjS. A yellow ppt. shows Cd; but if the 
 ppt. is still black, owing to presence of HgS, 
 it must be boiled with HCl, which will dis- 
 solve the CdS if present; the solution is 
 then to be diluted, and tested with H^S. 
 
 45. Precipitate. 
 
 Dissolve in a 
 little HCl; eva- 
 porate the solu- 
 tion till only a 
 few drops re- 
 main; add a little 
 of this solution to 
 a test-tubeful of 
 water. 
 
 A white ppt. or 
 turbidity i n d i - 
 cates Bi. 
 
 If no insoluble 
 residue in 41, 
 pass on to the 
 iron group, y 92 
 and 93. 
 
 Dissolve in 
 aqua regia, with 
 aid of heat, and 
 add to the solu- 
 tion SnClj. 
 
 A white or gray 
 ppt. shows Hg 
 present as mer- 
 curic salt. 
 
 Pass on to the 
 iron group, 2192 
 and 93. 
 
84 ELEMENTS OF CHEMICAL ANALYSIS. [§92. 
 
 THE IRON GROUP. 
 
 92. Forms of occurrence and reactions. 
 
 Nickel ; Ni : — To be met with as metal, alone and in alloys, 
 and as nickel salts. 
 
 Reactions : — {NH^^S ppts. from neutral or alkaline solutions 
 nickel sulfid, NiS, fiocculent, black, insoluble in cold HCl, sol- 
 uble in hot HNO3 ; somewhat soluble in excess of the precipitant, 
 giving a brown solution. 
 
 NH4OH and NaOH ppt. nickelous hydroxid, Ni(OH>, fioc- 
 culent, green, soluble in NH4OH ; i ^s ox idizedJayJ^L-in pres- 
 ence'~of NaOH to Ni(0H)3J when this compound, nickelic 
 hydroxid, is boiled with NH4OH it is reduced, with evolution of 
 nitrogen, to Ni(0H)2, and dissolved. 
 
 To the borax bead nickel compounds give a brown color. 
 To make this test, heat the clean loop of the platinum wire in 
 the lamp flame, and then quickly dip it into powdered borax ; 
 fuse this mass in the flame, heating gently at first till the effef- 
 vescence becomes moderate, and finally to redness ; if the bead 
 is thin, dip it into the borax again while hot, and fuse again, 
 and repeat till a full oval bead is obtained ; then heat it again 
 with a small quantity of the substance to be tested adhering to 
 it, till the bead is clear. If too much substance is taken the 
 bead may be opaque ; in such a case break it, and fuse a part of 
 it in a new bead. 
 
 Cobalt; Co: — May be met with as metal, and as cobalt 
 salts. 
 
 Reactions : — (NH4)2S ppts. from alkaline or neutral solutions 
 cobalt sulfid, CoS, fiocculent, black, insoluble in cold HCl, 
 soluble in hot HNO3 ; it is not soluble in excess of (NH4)2S. 
 
 NHjOH and NaOH ppt. cobaltous hydroxid, CoCOH)^, with 
 properties similar to those of nickelous hydroxid ; but the corres- 
 ponding cobaltic hydroxid, Co(OH)a, is not reduced by boiling 
 withNH^OH. 
 
 To the borax bead cobalt compounds give a deep blue color ; the 
 test is very delicate. 
 
 Iron; Fe : — To be met with as metal, ferrous and ferric 
 oxids, insoluble, and as ferrous and ferric salts. 
 
 Reactions : — Ferrous salts. HNO3 oxidizes ferrous to ferric 
 salts. 
 
 (NH4)2S ppts. immediately from alkaline or neutral solutions 
 ferrous sulfid, FeS, fiocculent, black, turning grayish on expos- 
 
§ 92. J THE IRON GROUP. 85 
 
 ure to the air, by oxidation and separation of sulfur, soluble in 
 dilute mineral acids. This oxidation of the sulfid leads to the 
 formation of FeSOi, and finally a basicferric salt, Fe20(S04)2. 
 
 NH4OH and NaOH ppt. ferrous hydroxid, Fe(OH)j, dirty 
 green, changing to reddish-brown, Fe(0H)3, on exposure to the 
 air. iBaCOs does not ppt. this hydroxid/except from" solutions 
 b£-±li&-9ttlphat©v. J ^ 
 
 K^FeCy^ and K^FeCy^give blue ppts. (see reactions of hydro- 
 ferrocyanic and hydroferricyanic acids). 
 
 KCyS gives no reaction. 
 
 Ferric salts. — HjS reduces ferric to ferrous salts, with sepa- 
 ration of sulfur, but in alkaline solutions ppts. FeS. 
 
 (NH4)2S ppts. from neutral or alkaline solutions ferrous sulfid, 
 FeS (see ferrous reactions), with separation of sulfur. 
 
 NH4OH or BaCOs ppts. ferric hydroxid, Fe(0H)3, flocculent, 
 reddish-brown, soluble in acids. 
 
 K^FeCye ppts. from neutral or acid solutions Fe4(FeCye)3 (see 
 hydroferrocyanic acid reactions). KjFeCye gives no ppt. 
 
 KCyS gives ferric sulfocyanate, Fei^CyS)^, soluble, deep red; 
 this test is very delicate. 
 
 Manganese; Mn : — To be met with in' alloys, as oxids and 
 as salts of manganese. 
 
 Reactions : — (NH4)2S ppts. from neutral or alkaline solutions 
 manganous sulfid, MnS, flocculent, flesh colored, changing to 
 brown on exposure to the air by oxidation, soluble in dilute 
 acids, including HCjHgOj. 
 
 NHjOH ppts. a part of the manganese in a solution as 
 manganous hydroxid, white, turning brown on exposure to the 
 air by oxidation to MnOOH. The rest of the manganese, 
 remaining at first in solution as an ammonium salt, is gradually 
 pptd. on standing exposed to the air, as this second hydroxid. 
 
 BaCOs does not ppt. this hydroxid in the cold/except from 
 solutions of MnSOi- j^ 
 
 Fused with Na^ COi and KNO^ compounds of manganese give 
 a dark green color to the fused mass, by formation of sodium 
 manganate, NajMnOi. 
 
 Zinc; Zn : — To be met with as metal, as oxid, and as zinc 
 salts. 
 
 Reactions : — (N'If^)2S ppts. from neutral or alkaline solutions, 
 zinc sulfid, ZnS, white, soluble in cold HCl, slightly soluble in 
 
 HCjHjOa. 
 
86 ELEMENTS OF CHEMICAL ANALYSIS. [§ 93. 
 
 NH4OH ppts. zinc hydroxid, Zn(0H)2, flocculent, white, 
 soluble in excess of precipitant, as (NH4)2Zn02, repptd. on 
 boiling as Zn(0H)2. a 
 
 BaCOs does not ppt. this hydroxidj except from solutions of 
 the sulfate. 
 
 93. Preparation and analysis of the group precipitate. 
 
 a. Chemistry of the work on this group. 
 
 This group precipitate contains also the members of the 
 aluminum group that may be present, precipitated as hydroxids. 
 
 The nickel and cobalt are separated from all the other mem- 
 bers of both groups by the insolubility of their sulfids, in HCl 
 of such dilution as will readily dissolve the other sulfids and the 
 hydroxids. These two sulfids being then dissolved by stronger 
 acid, the metals are separated, if separation is necessary, by the 
 different behavior of their tri-hydroxids with ammonia, after 
 they have been corjverted into nickelic and cobaltic salts by 
 treatment with bromin. 
 
 After the conversion of the iron into a sesquioxid salt by 
 treatment of the group precipitate with HNO3, it is then sepa- 
 rated, together with the aluminum and chromium, from the 
 manganese and zinc by precipitation of the three as hydroxids 
 by barium carbonate. This precipitate is used later for the tests 
 for aluminum and chromium. 
 
 We bring to this course a rather strongly acid solution charged 
 with H2S. It contains all the bases of the potassium, calcium, 
 aluminum, and iron groups, and the acids that were combined 
 with these bases originally, except such as would be expelled on 
 the treatment with strong acids, or converted by the reducing 
 H2S into other forms. 
 
 The first operation of the group precipitation, in 47, in the 
 course of analysis following, consists in adding NH^OH in 
 slight excess for the purpose of saving the (NH4)2S, to be 
 added later, from decomposition by the acid present ; but even 
 if this were not done, and the (NH4)2S were added at once, 
 the final condition of the solution would be the same, namely, 
 decidedly alkaline. The oxalates, phosphates, borates, silicates, 
 and fluorids of the calcium group metals are insoluble in an 
 
§ 93-] THE IRON GROUP. 87 
 
 alkaline liquid. The possibility is therefore evident of entirely 
 missing metals of that group in their proper place, in the filtrate 
 from the group precipitation for this table, if the solution is made 
 alkaline while these acids are present. 
 
 Considering in this course only two of these acids, that are 
 perhaps most likely to be in the way in an ordinary qualitative 
 analysis, one of them is removed at once by gaseous products of 
 its oxidation. The other, not being so easily removed, has to be 
 provided for as in 53 a. For the course of operations to be 
 followed in case H3BO3, HF, or HjSiOg is also present, the 
 student is referred to larger works, such as Fresenius, or Prescott 
 and Johnson. 
 
 Having evaporated the solution and ignited the residue, for 
 the removal of the oxalic acid, ammonium salts are no longer 
 present ; but NH4CI is necessary to prevent the precipitation of 
 magnesium as hydroxid, and the consequent danger of missing 
 it in its proper place. 
 
 The addition of ammonia here will precipitate a small portion 
 of the members of this group as hydroxids ; but a study of the 
 work that follows, and comparison of the solubility of hydrox- 
 ids and sulfids of the members of this group, will make it clear 
 that these hydroxids cannot be left as such after the treatment . 
 with (NH4)2S without leaving the way open to serious errors ; 
 that, nevertheless, the precipitate formed by NHjOH can be left 
 undissolved indicates another case of metathesis where only one 
 of the reacting substances is in solution. 
 
 All of the sulfids precipitated are quite insoluble in (NH4)2S 
 except the NiS, which is slightly soluble ; on this account any 
 unnecessary excess of the reagent should be avoided. 
 
 Two of the sulfids, FeS and Co^ are liable to be oxidized to 
 sulfate on exposure to the air, or'even perhaps by the oxygen 
 dissolved in water (§ 66) : wasRing, as directed in 48 following, 
 serves to avoid the error that one might fall into, if such oxida- 
 tion were permitted, these sulfates being soluble in water. 
 
 In the solution of such portion of the precipitate as is dissolved 
 by HCl, the iron, in whatever form it was originally, is present 
 now as a ferrous salt : but both for its final test and its precipita- 
 tion by BaCOa in 53 b, it must be in the ferric form : only those 
 hydroxids corresponding to the so-called sesquioxids, having the 
 general form M2O3 in which M^ represents two atoms of a triad 
 metal, are precipitated by BaCOs under the conditions of the 
 
88 ELEMENTS OF CHEMICAL ANALYSIS. [§ 93- 
 
 treatment by that reagent : hence the treatment with HNO3 in 
 52, Table VI. 
 
 The separation of the PzOj from the metals of the calcium 
 group is effected (53 a) on the following principle. In the 
 presence of enough of the ferric salt to combine with all the 
 P2O5 present, forming FePOj, on making the solution exactly 
 neutral, all of this acid will be precipitated, while metals of the 
 second group remain in solution. The exact neutrality is most 
 easily secured by the presence of BaCOj, a portion of which is 
 decomposed by any free acid present, with the formation of a 
 neutral barium salt. 
 
 Provision of sufficient ferric salt is secured by its addition till 
 the red precipitate is obtained by ammonia : ferric phosphate is 
 white: as long as there is not enough iron present to satisfy all 
 the P2O5. only white FePOiWill be precipitated by the NH4OH ; 
 as soon as there is more than enough^ the excess not going down 
 as white phosphate is precipitated as reddish-brown hydroxid. 
 
 This condition of the solution having been secured, the 
 neutralization is nearly effected with (NH4)2C03, to save BaCOj ; 
 but it must be left slightly acid, for any precipitate by excess of 
 (NH4)2COs might contain metals to be tested, for under 54 and 
 following sections ; then the BaCOj completes the neutralization 
 for the precipitation of the phosphates, besides doing its other 
 work of throwing down the aluminum, iron, and chromium as tri- 
 hydroxids. 
 
 Here again is an illustration of a metathesis in which one of 
 the substances taking part in the reaction is a solid : and it is 
 not, as in other cases previously noted, necessarily freshly pre- 
 cipitated. 
 
 When a liquid is added tp*a. liquid, the two may be at once 
 intimately mixed by agitation* *Ad the conditions are right for 
 the reaction to proceed .without further external assistance, the 
 two substances being in intimate contact throughout ; but in this 
 treatment with BaCOg the heavy solid soon settles to the bottom 
 after agitation, and the desired reaction can go on directly only 
 at the surface of contact between the particles of the reagent and 
 that part of the solution at the bottom of the flask, ^nd indirectly 
 in the rest of the liquid by the slow process of diffusion. Hence 
 the importance of frequent agitation and considerable time for 
 the full completion of the reaction. 
 
 Since, if P2O5 is present, the metals -of the calcium group are 
 
§ 93-] THE IRON GROUP. 89 
 
 to be tested for in the filtrate from the precipitate by BaCOs, 
 and since for all the work of precipitation of iron, aluminum, and 
 chromium actually done by this reagent a corresponding quantity 
 of BaClj passes into solution, as will appear on writing out the 
 equation for the reaction, barium cannot of course be tested for in 
 this filtrate. Therefore a small portioR of the solution is so pre- , 
 pared in 53 a, by taking advantage of the solubility of Ba8(P04)2 
 in acetic acid and the insolubility of the chromate, to get a 
 solution in which barium can be tested for at once. Any part 
 of the precipitate formed in the first part of this operation, and 
 insoluble in acetic acid, would consist of phosphates of iron, 
 aluminum, and chromium, i 
 
 &. Preparation of the iron {and aluminum) group precipitate. 
 
 46. (ffl) Oxalic acid is absent : pass to 47. (6) Oxalic acid 
 is present; add to the solution a little HNO3 and evaporate to 
 complete dryness, in the hood, moisten the residue with HNO3, 
 dry by gentle heat, and ignite gently ; dissolve this residue with 
 a little hot HCl, filter if not clear, and add 2 c.c. of NH4CI 
 and 25 to 30 c.c. of water. 
 
 ^-^ 47. Add NH4OH till slightly alkaline, then whether a ppt. is 
 formed or not add (NH4)2S and heat the mixture nearly to boil- 
 ing. If no ppt. appears pass on to the Ca group, § 97, 6, If a 
 ppt. does appear, filter and reserve the filtrate for the Ca group, 
 
 § 97. &• 
 
 48. Precipitate. Wash immediately and very thoroughly 
 
 with hot water to which a little (NH4)2S has been added. 
 
90 ELEMENTS OF CHEMICAL ANALYSIS. [§ 93. 
 
 C. The Analysis of the Iron Group Precipitate. 
 
 TABLE VI a. 
 
 Treat the ppt. either on the filter or after removal from 
 it (see § 58) with 5 to 15 c.c (according to quantity of ppt.) 
 oi dilute HCl (i cone, acid to 10 of water), with special care 
 to bring all parts of the ppt. in contact with the acid, by 
 stirring. Filter if necessary, and reserve filtrate for Table 
 VI ^. 
 
 49. Residue. 
 
 Any residue remaining here should be black ; if it is not, 
 it must be treated with more HCl as directed in 48. If black 
 it may consist of NiS and CoS. If the filtrate 47 has a deep 
 brown color Ni may safely be put down as present in the sub- 
 stance analyzed. 
 
 If the borax bead is colored blue by fusion with a portion 
 of this residue Co is also present ; if only a light brown or a 
 nearly colorless bead is obtained Co is absent. If Ni and Co 
 are found by these tests, pass on to Table VI b. 
 
 If the filtrate 47 is not brown, or if in testing for cobalt 
 with the borax bead the color was so dark a brown owing to 
 the presence of much nickel that the cobalt color might have 
 been masked, proceed as follows. 
 
 To the residue 49 in an evaporator, add HCl and a few 
 drops of HNOs, boil, in the hood, till the liquid is nearly 
 evaporated, add NaOH till strongly alkaline and then a quan- 
 tity of bromin solution equal to the volume of the liquid in 
 the dish, boil for a few minutes and filter, rejecting the 
 filtrate; wash the ppt., return it to the evaporator, add 
 NH4OH, boil again, and filter if a residue remains. 
 
 50. Filtrate. 
 
 Add HjS. A black ppt. indicates 
 Ni. 
 
 A mere slight brown coloration may 
 be due to Co, if its presence in con- 
 siderable quantity is indicated by the 
 bead test. 
 
 51. Residue. 
 
 Test ioxCo with borax 
 bead. 
 Pass on to Table VI iJ. 
 
§93-J 
 
 THE IRON GROUP. 
 
 91 
 
 C. Analysis of the Iron Group Precipitate, concluded. 
 TABLE VI b. 
 
 52. Filtrate from Residue 19. 
 
 Boil to expel HjS, add a few drops of HNO3 and boil agajn. 
 To a small portion of this solution add NH4CNS. A red color 
 shows Fe. A slight tinge of red is given by very small traces of 
 iron, the test being very delicate. 
 
 53 a. Phosphate is present. 
 
 53 h. Phosphate is not present. 
 
 To a small portion of the 
 solution add NH^OH till 
 alkaline, then acetic acid 
 till acid, filter if a ppt. ap- 
 pears, and test the filtrate 
 for Ba with K2Cr20, and 
 HjSOi.as in Table VIII. 
 To the remainder of the solu- 
 tion (62) add Fed 3 till a 
 drop gives a brownish red 
 ppt. with NH^OH and pro- 
 ceed as in 53 6, the PjOj 
 being now removed. 
 
 Concentrate the solution to a small bulk, nearly 
 neutralize it with (NH4)2C03, (if a permanent 
 ppt. forms on addition of (NH4)2C03, it mustjjs^ 
 redissolved with a drop of HCl), trajjsferro^ a 
 small flask, add about 10 ccof-EaCOg, shake the 
 mixture nrraiinnnlly] -fffFrr s«venil'~bcuu:s. filter, 
 and reserve the contents of the filter for the Al 
 group, Table VIII, after washing two or three 
 times with hot water. 
 
 54. Filtrate. To a portion add acetic acid 
 and then H^S. A white ppt., soluble in HCl 
 shows Zn. 
 
 55. Evaporate another small portion carefully 
 to dryness in the platinum cup, and fuse the 
 residue with a mixture of equal parts of Na2C03 
 and KNO3. A bluish-green color in the fused 
 mass shows Mn. 
 
 Phosphate was present, 
 
 56 a, and Mn and Zn 
 
 also present. 
 
 To the remainder of the 
 filtrate from the ppt. by 
 BaC03in53 6addNH^- 
 OH and (NH4)2S, warm 
 and filter; with filtrate 
 pass to 56 C. 
 
 56 h, and Mn and 
 
 Zn not present. 
 
 There being no Mn 
 or Zn to remove, by 
 (NHj2Sasin56a, 
 take remainder of fil- 
 trate from ppt. by 
 BaCOg in 53 6 to 
 66 c. 
 
 66 c. Filtrates 56 a (or 53 V). 
 
 Add to the filtrate from the ppt. by (NH4)2S 
 in 47 J and reserve for \ 96 6, remembering in the 
 analysis of the Ca group ppt. that Ba has already 
 been tested for. 
 
92 ELEMENTS OF CHEMICAL ANALYSIS. [§§ 94-95- 
 
 THE ALUMINUM GROUP. 
 
 94. Forms of occurrence and reactions. 
 
 Aluminum ; Al : — To be met with as metal and in salts. 
 
 Reactions: — NHtOH, {NII^^S or BaCO^ ppts. aluminum 
 hydroxid, Al{ OJT),, flocculeni or gelatinous, whiter slightly soluble 
 in NHiOH, soluble in NaOH as Al{ONa\, solution not repre- 
 cipitated on boiling, soluble in dilute acids. 
 
 Chromium; Cr: — To be met with as oxid and as salts of 
 chromic oxid, or of chromic acid. The acid is always reduced 
 to the oxid by H2S. 
 
 Reactions : — NH4OH, (NH4)2S or BaCOj in solutions of salts of 
 the oxid ppts. chromic hydroxid, Cr(0H)3 flocculent, green : 
 the ppt. is slightly soluble in excess of NH4OH, and is soluble 
 in NaOH as NaOOCr: Cr(0H)3 is reprecipitated from this 
 solution on long boiling, more easily in the presence of ammon- 
 ium salts. 
 
 95. The analysis of the aluminum group precipitate. 
 
 a. The chemistry of the work on this group. 
 
 For the separation of the two metals of this group, advantage 
 is taken of the easy oxidation of chromic oxid compounds to 
 chromic acid compounds, and also of the precipitation of chro- 
 mic hydroxid on boiling its solution in sodium hydroxid, 
 while aluminum hydroxid is not precipitated under similar con- 
 ditions. The reactions of chromic acid are very delicate, so 
 that the above oxidation makes it easier to detect the chromium. 
 
 The AI(0H)8 in the precipitate by BaCOa is dissolved out by 
 NaOH, made as it is wanted and in the tube in which it is to do 
 its work, by the action of Ba(0H)2 on NajCOg. This solution 
 takes place in accordance with the reactions of aluminum ; the 
 succeeding treatment with HCl breaks up the compound, 
 Al(ONa)3, that is in solution, and in this solution now contain- 
 ing no free NaOH the precipitation of A1(0H)3 takes place by 
 NH4OH in the usual manner. 
 
 Sodium hydroxid, so entirely free from impurities that it will 
 not of itself give a reaction similar to this for aluminum on treat- 
 ment with HCl and NHjOH, is difficult to make and to keep in 
 good condition ; hence its preparation for this test as wanted. 
 
§95-] 
 
 THE ALUMINUM GROUP. 
 
 93 
 
 from materials that are much more easily obtained free from 
 those impurities, such as aluminum compounds or silicate, which 
 would impair the reliability of the test. 
 
 C. The Analysis of the Aluminum Group Precipitate. 
 
 TABLE VII. 
 
 67 a. Iron was not found 
 in Table VI in more than 
 traces, and phosphate is not 
 present. 
 
 Make a preliminary test for 
 Al and Cr as follows : Dissolve 
 a small portion of the precipi- 
 tate obtained with BaCO, in 
 63, in a little HCl, add H^SO^ 
 as long as a ppt. is formed, heat 
 just to boiling, and filter ; a 
 slight turbidity in the filtrate 
 will do no harm. To about 
 3 c.c. of this filtrate, in a lo 
 cm. test tube, add NH^OH 
 very slowly from a dropping 
 tube, holding the point of the 
 tube close to the surface of the 
 liquid, so that the specifically 
 lighter reagent will fall gently, 
 and float on the solution tested. 
 At the zone of contact between 
 the two liquids there appears : — 
 
 67 6. No pre- 
 cipitate. 
 
 Even after a few 
 minutes. 
 
 Al and Cr are 
 absent. Pass to 
 the Ca group. 
 
 57 C. A pre- 
 cipitate. 
 
 Treat the 
 rest of the 
 group precipi- 
 tate as direct- 
 ed under 58- 
 
 58. Iron was found in Table VI in 
 more than traces, or phosphate is present. 
 
 69 a. Fuse a 
 portion of the ppt. 
 by BaCOj in 53 
 with about three 
 times its bulk of a 
 mixture of equal 
 parts of NajCOj 
 and NaNOj.in the 
 platinum cup. The 
 fused mass will 
 usually be yellow 
 if much Cr is pre- 
 sent. Extract it 
 with hot water, fil- 
 ter, acidify the fil- 
 trate with HCjHj- 
 O2, and test for 
 chromic acid with 
 the lead and am- 
 monium acetate 
 mixture, 7; \ 85, b. 
 A yellow ppt. indi- 
 cates, as present in 
 the original sub- 
 stance, either in the 
 form of a chromate 
 or of a salt of 
 chromic oxide, Cr. 
 
 59 h. To another 
 portion of the ppt. 
 in an evaporator, 
 add about half a 
 gram of NajCOj, a 
 quarter of a gram 
 of Ba(OH)2, and 
 loc.c. of water, boil 
 and filter, rejecting 
 the ppt. ; acidify the 
 filtrate with HCl. 
 To about 2 or 3 c.c. 
 of this solution, in 
 a 10 cm. test tube, 
 add NH4OH slowly 
 from the dropping 
 tube, holding the 
 point of the tube 
 close to the surface 
 of the liquid, so that 
 the specifically 
 lighter reagent will 
 fall gently, and float 
 on the solution to 
 be tested. A floc- 
 culent, white ppt. at 
 the zone where the 
 two solutions meet 
 shows Al. 
 
94 ELEMENTS OF CHEMICAL ANALYSIS. [§ 96. 
 
 THE CALCIUM GROUP. I 
 
 96. Forms of occurrence and reactions. 
 
 Barium ; Ba : — To be met with as barium salts. 
 
 Reactions : — (NH4)2C03 ppts. from neutral or alkaline solu- 
 tions barium carbonate, BaCOj, flocculent, afterward pulveru- 
 lent, or crystalline, white, easily soluble in acids. 
 
 KjCrOj ppts. from acetic acid solutions, if not too dilute and 
 only weakly acidified, barium chromate, BaCrOj yellow, soluble 
 in HCl. In order that this precipitation shall be certain, if but 
 little barium is present, it is important that the quantity of free 
 acetic acid be small in comparison with that of the potassium 
 chromate. 
 
 ff^SOi ppts. from all solutions, except possibly such as contain 
 but little of the element, and are strongly acid (see reactions of 
 sulphuric acid, § 80), barium sulfate, BaSOi, pulverulent, white, 
 very insoluble. 
 
 Soluble phosphates or oxalates ppt. from alkaline solutions 
 the corresponding barium salts. 
 
 Strontium ; Sr : — To be met with only as strontium salts. 
 
 Reactions : — (NH4)2C03 ppts. from neutral or alkaline solu- 
 tions strontium carbonate, SrCOj, resembling BaCOa. 
 
 CaSOi ppts. slowly from neutral solutions strontium sulfate, 
 SrSOi, pulverulent, white, 
 
 KjCrjO, gives no ppt. in acetic acid solutions. 
 
 Soluble phosphates or oxalates ppt. from alkaline solutions 
 the corresponding strontium salts. 
 
 Calcium ; Ca : — To be met with as oxid or in salts. 
 
 Reactions : — (NH4)2C03 ppts. in neutral or alkaline solutions 
 calcium carbonate, CaCOj, flocculent first, afterward crystal- 
 line, white, readily soluble in acids. 
 
 (JVJI^iCiOippts. from neutral or ^alkaline solutions calcium 
 oxalate, CaC^Oi, pulverulent, white, soluble in dilute mineral 
 acids, insoluble in acetic acid. 
 
 KjCrjO, gives no ppt. in acetic acid solutions. Soluble phos- 
 phates ppt. from alkaline solutions calcium phosphate Cas(P04)2, 
 white. 
 
 Magnesium ; Mg : — May be met with as metal, as oxid, or 
 as salts of magnesium. 
 
 Reactions : — (NH4)2CO., and (NH4)2C204 do not ppt. magne- 
 sium from solutions containing enough NHjCl. 
 ' Na^HPOi ppts., often slowly, from solutions made alkaline by 
 
§ 97-j THE CALCIUM GROUP. 95 
 
 NHiOH, ammonio-magnesium phosphate, MgNHiPO^ crystal- 
 line, white, soluble in acids ; it often adheres to the walls of the 
 tube, especially along the lines where the end of a glass rod has 
 been drawn with some pressure ; this may fiot become visible, if the 
 ppt. is abundant, till the contents of the tube are poured out. 
 
 97. The preparation and analysis of the calcium group precipitate. 
 
 a. The chemistry of the work. 
 
 The barium is separated from the calcium and the strontium 
 by the greater insolubility of its chromate in acetic acid, the 
 strontium from the calcium by the much greater insolubility of 
 its sulfate in water, and the magnesium from all the others by the 
 formation of a double carbonate of magnesium and ammonium, 
 soluble in solution of ammonium chlorid. 
 
 The solution brought to this point, 60 below, contains in addi- 
 tion to the members of the calcium and potassium groups that 
 may have been present in the original substance, a considerable 
 quantity of NH4CI, and perhaps other ammonium salts. The 
 presence of this salt is useful, since it lessens the danger of pre- 
 cipitation of MgCOs by the grouping reagent. On the other 
 hand, all the carbonates which it is desired to precipitate here 
 are slightly soluble in solutions containing NH4CI, so that the 
 action of the grouping reagent is thereby rendered more or less 
 imperfect ; and it is well in the work of preceding groups to 
 avoid the use of any unnecessary quantity of HCI, which must 
 afterward be neutralized with NH4OH in 47, thus charging the 
 solution excessively with this salt. 
 
 The precipitate by (NH4)2C03 being dissolved by acetic acid in 
 61, Table VIII, it is at once ready for the next step in the 
 separation. The BaCrO^ being slightly soluble in the acid, the 
 separation from strontium and calcium is not perfect if an 
 unnecessary excess of the acid is used in making the solution. 
 
 In the separation of strontium from calcium in 63 to 65, Table 
 VIII, we have to deal again with an imperfect action of the 
 reagents used ; the SrSO^ is slightly soluble in water and in 
 HCI : this is implied by the statement, under the reactions for 
 this element, that it is precipitated slowly by CaSOi. If much 
 water is present, or, in other words, the solution is very dilute, 
 and much more if it is more than weakly acid, and at the same 
 time the conditions are such that only a little SrSO^ can be 
 formed, the salt may remain entirely in solution : the condition 
 
96 ELEMENTS OF, CHEMICAL ANALYSIS. [§97- 
 
 last mentioned would be fulfilled, if but little of either strontium 
 or of H2SO4 were present: CaSO^ is but sparingly soluble in 
 water, and we can have at the most but a very dilute solution of 
 the reagent : therefore the second of these last two conditions is 
 fulfilled. Hence the double reason is plain for the evaporation 
 of the solution as prescribed in 63, and also for the addition of 
 but little water to the residue. The reason is also plain, from 
 the foregoing, for the direction that the test in 64 be allowed to 
 stand several minutes. 
 
 As 1,000 parts of water are required to dissolve one .part of 
 SrSOi, and only 400 parts of water for one of CaSO^, while the 
 oxalates are about equally insoluble,, and are undistinguishable 
 from each other in appearance, the reason for the treatment with 
 K2SO4, much more soluble than CaSOi and therefore yielding a 
 stronger solution of the reagent, is apparent : even if, owing to 
 the concentration of the solution, some CaSOj should also be 
 precipitated, enough would always remain in' solution for the 
 final test. 
 
 For reasons explained in the foregoing paragraphs, traces of 
 any one of these three metals might be missed in following this 
 scheme of separation : for a method of treatment in such a case 
 the student is referred to Fres^nius or Prescott and Johnson. 
 
 Either the trace of barium, strontium, or calcium that may re- 
 main unprecipitated by the group reagent, as explained above, 
 yielding a flocculent precipitate with Na^HPOi, in 66, or the 
 formation of Mg^OH)^ by the NH4OH, owing to an insufficient 
 quantity of NH^Cl in the solution, may, in case the precipitate 
 for magnesium is slight, make it flocculent instead of crystalline 
 as it should be. By taking advantage of the fact that BaSOi and 
 CaCiiOj are much more insoluble than the carbonates, a solution 
 can be prepared, if the above-mentioned difficulty is encountered, 
 that is practically free from those metals, although it may still 
 contain traces of strontium. (Fresenius 1880, p. 296.) 
 
 h. The preparation of the calcium group precipitate. 
 
 60. If the filtrate brought from the Fe group (47) is brown 
 with Ni in solution, boil and filter again ; to this filtrate add 
 (NH4)2C03 as long as a ppt. is formed, and then somewhat more 
 to be sure of an excess of the reagent, and warm. If no ppt. 
 appears, pass to 66. If a ppt. is formed, filter, and reserve both 
 precipitate and filtrate for Table VIII. 
 
§ 97-J THE CALCIUM GROUP. 97 
 
 C. The Analysis of the Calcium Group Precipitate and Filtrate. 
 
 TABLE VIII. 
 
 61. Precipitate. 
 
 66. Filtrate. 
 
 Dissolve the precipitate, on the filter, by pouring a 
 small quantity of acetic acid over it, two or three times, 
 using the same portion of acid; all of it should be 
 dissolved. To a small portion of the solution add 
 K^CrO^ ; if no precipitate is formed Ba is absent, and 
 the remainder of the solution is used for the Sr and Ca 
 tests. 
 
 A precipitate is formed : add the reagent to the 
 remainder of the solution, and filter. 
 
 62. Precipitate. 
 
 Dissolve this 
 yellow precipi- 
 tate in HCl, and 
 add to the solu- 
 tion a few drops 
 of H2SO4. A 
 white ppt. shows 
 Ba. The white 
 color may not 
 come out plainly 
 till, after allow- 
 ing the ppt. to 
 settle, the liquid 
 is decanted off, 
 and the ppt. 
 washed with a 
 little water. 
 
 63. Filtrate. 
 
 Make alkaline with NH^OH and 
 add (NH4)2C03. If no fpt. ap- 
 pears Sr and Ca are absent, and this 
 solution need be tested no further. 
 If a ppt. is formed add more 
 (NH^)2C03 till the precipitation is 
 complete, filter, rejecting the filtrate, 
 wash the ppt. with water, dissolve 
 it on the filter with HCl, evaporate 
 the solution almost or quite to dry- 
 ness, and dissolve the residue in a 
 little water. Divide this solution 
 into two portions. 
 
 Divide in two 
 portions, and re- 
 serve the larger one 
 for Table IX. To 
 the other portion 
 addNa^HPO^and 
 NH^OH, draw the 
 end of a glass rod*«. 
 with some pressure^ 
 over the inner walls I 
 of the tube along 
 three or four lines, 
 and set aside for 
 several hours. A 
 white ppt., crystal- 
 line if only small in 
 quantity, and in any 
 case adhering along 
 the lines traced by 
 the rod, after the 
 contents of the tube 
 are poured out, in-, 
 dicates Mg. 
 
 64. Portion i. 
 
 Add CaSO^, 
 heat to boiling, 
 and let stand ten 
 minutes. A fine 
 white ppt. shows 
 Sr. 
 
 65. Portion 2. 
 
 — Il-Si was fouiid ' 
 iin pnrtjpn T add 
 KjSOj, warm and 
 filter,rejecting the 
 ppt.; to the fil- 
 trate, -fir dirtdly 
 f a., /^ it pattiatt—if- • 
 
 NH4OH till al- 
 kaline and then 
 (NH,),C,04. A 
 white ppt. shows 
 Ca. 
 
 Ih^uTt, 
 
 ^VUAvf 
 
98 ELEMENTS OF CHEMICAL ANALYSIS. [§§ 98-99. 
 
 THE POTASSIUM GROUP. 
 
 98. Forms of occurrence and reactions. 
 
 Potassium ; K : — To be met with commonly only as hydroxid, 
 or as potassium salts. 
 
 Reactions : — Sodio-cobaltic nitrite, (NaN02)3 • Co(N02)3, ppts. 
 from neutral solutions containing potassium, potassio-cobaltic 
 nitrite, (KN02)3.Co(N02)3, pulverulent, yellow. 
 
 Sodium; Na : — To be met with commonly only as hydroxid 
 and as sodium salts. 
 
 Reactions: — Compounds of sodium give no ppt. containing 
 that element, which furnishes a satisfactory test for the metal, 
 and is practicable for use by the student. 
 
 Held in the platinum wire loop, in the flame of a Bunsen burner, 
 sodium compounds color the flame yellow. 
 
 This test is so delicate, and sodium is so widely diffused, and 
 common in occurrence, at least in traces, as an impurity in the 
 reagents and other materials of the laboratory, that there is 
 little difficulty in getting this reaction in nearly every substance 
 analyzed. Just before using the wire for the test it should be 
 dipped in HCl and heated in the flame till it gives no color 
 thereto. 
 
 Ammonium ; NHj : — To be met with only as ammonium 
 hydroxid or salts, or as ammonia gas, NH3. 
 
 Reactions: — Na OH decomposes ammonium salts, setting f7-ee 
 ammonia gas, NH^ which colors red litmus paper blue, or yellow 
 turmeric paper brown. 
 
 99,. Chemistry of the analysis of this group. 
 
 a. No separation is made of the members of this group from 
 each other, sodium and potassium being tested for in portions 
 of the same residue, and ammonium in a portion of the original 
 substance. 
 
 Bringing from the analysis for the calcium group a solution 
 containing much ammonium salts, the first operation performed, 
 preparatory to the analysis for this group, gives us a residue not 
 encumbered with the considerable quantity of ammonium salts 
 in the filtrate from 60, and we can thus get a surer test for 
 sodium. Furthermore, as might be inferred from the great 
 •similarity between potassium and ammonium, in all the reactions 
 with which the easy volatility of the salts of the latter does not 
 
§ 99-J 
 
 THE POTASSIUM GROUP. 
 
 99 
 
 interfere, it is necessary to have amnaonium salts entirely re- 
 moved before a reaction with (NaN02)3 • Co(N02)3 can be safely 
 taken to indicate potassium. 
 
 6, Preparation of the substance for the analysis. 
 
 67. Evaporate the solution brought from 66 Table VIII to 
 dryness, in the hood, and ignite the residue gently as long as 
 white fumes are given off, to remove ammonium salts. 
 
 C. The Analysis for the Potassium Group. 
 
 TABLE IX. 
 
 68 a. Portion 1. 
 
 68 6. Portion 2. 
 
 69. Original Sub- 
 stance. 
 
 Introduce on a platinum 
 wire a small portion of the 
 residue into the flame of a 
 Bunsen burner. If the 
 flame is colored a bright 
 yellow, Na is present. 
 
 In order to gain any approxi- 
 mate idea of the proportion of 
 Na present, account should be 
 taken of what has already been 
 found in the substance, the 
 quantity of the residue left after 
 the ignition just made, and of 
 the probable proportions of K 
 and Mg in this residue, and 
 finally of the intensity and per- 
 . sistenceof the Na flame reaction. 
 
 Dissolve the larger 
 portion of the resi- 
 due in a little water, 
 ' add to this solution 
 three or four drops 
 of sodiocobaltic ni- 
 trite, and let stand 
 for a few minutes. 
 A yellow ppt. shows 
 K. 
 
 To a small por- 
 tion of this add 
 NaOH and warm 
 gently. 
 
 If the vapors 
 evolved change 
 moistened turmeric 
 paper from yellow 
 to brown, NH4 is 
 shown. 
 
 If it was necessary to fuse the original substance 
 with Na^COj in Table E, in order to get it into solu- 
 tion, prepare a solution for the above tests for Na and 
 K as follows : mix I part of the finely pulverized sub- 
 stance with 6 parts of precipitated CaCOj and ^ part 
 of NH^Cl, and heat to bright redness in a small 
 platinum crucible for 30 minutes. Cover the crucible 
 with water in a beaker and heat to near boiUng for 
 30 minutes, filter, add a little NH^OH to the filtrate, 
 and proceed further as in 60, 67 and 68. 
 
PART III. 
 
 THE OPERATIONS OF QUANTITATIVE 
 ANALYSIS. 
 
 CHAPTER XI. 
 THE BALANCE AND ITS USE. 
 
 100. Introduction. Quantitative chemical analysis has fqr its 
 object the determination of one or more of the constituents of 
 a substance whose qualitative composition is wholly or partially 
 known. It is ultimate analysis when the elementary constituents 
 of the substance are determined, as the carbon and hydrogen of 
 sugar: it is proximate analysis when some or all of the com- 
 pounds supposed or known to exist in the substance are deter- 
 mined, as the sulfur trioxid of a sulfate, or the calcium oxid in 
 marble, or the sugar and fat in milk. 
 
 Its results are obtained by careful measurements, as is the case 
 with all accurate determinations of quantity. From a measured 
 portion of the substance the constituent to be determined is 
 converted into some new form, in which it is capable of measure- 
 ment;, and into which it can be completely transposed, or at least 
 very nearly so. In the quantitative analysis of a solid, or the 
 determination of the substances in a solution, there are two 
 general modes of procedure, called gravimetric and volumetric 
 analysis. 
 
 Gravimetric analysis. The substance to be determined is 
 usually converted into some compound that is (i) insoluble in 
 the liquid medium in which it is made, (2) has a perfectly defi- 
 nite and well known composition, and (3) is of such a character 
 that it can be finally obtained in a form in which it can be 
 weighed without difficulty. The quantity of the substance 
 sought is then calculated by simple stochiometric methods. 
 
 Volumetric analysis. To a solution containing the substance 
 to be determined, a solution is added containing another sub- 
 
 100 
 
§ lOI.J THE BALANCE AND ITS USE. lOI 
 
 Stance, that gives with the first a definite reaction ; and this 
 addition is made under such conditions that it can be sharply 
 decided when all of the first substance has been acted upon, and 
 just what volume of the solution of the second substance was 
 required to complete the reaction. The strength of this reacting 
 solution being known, and also the exact nature of the chemical 
 change that it produces, so that the same can be expressed by a 
 chemical equation, the quantity of the first substance can be 
 calculated from the quantity of the second substance required. 
 
 In setting out with the quantitative analysis of a substance, it 
 must first of all be accurately known how much of it is taken for 
 the analysis. In some laboratories for instruction, it is the 
 practice to give to the beginner carefully measured quantities 
 of a solution of a substance to be determined ; in others an in- 
 definite quantity of a solid is given to him, from which he weighs 
 out his own portions for analysis. But even in the first case he 
 very soon has to use the balance to weigh the products of his 
 operations; therefore, weighing on the chemical balance natur- 
 ally comes up first for explanation. 
 
 loi. The balance. When the beam of the balance is swing- 
 ing, its knife-edges rest on polished agate surfaces ; the sharp- 
 ness of the knife-edges and the polish of the agate must not be 
 impaired, if the balance is to maintain its sensitiveness and ac- 
 curacy. To be more sure of this preservation of the good con- 
 dition of the instrument, the knife-edges are always lifted off the 
 agate plates, and kept so all the time when the weighing is not 
 actually going on. The arrangement by which the beam is raised 
 or lowered is controlled by a small, milled-edge wheel on the 
 outside of the balance, in front. The working parts of the bal- 
 ance are inclosed in a glass case not only to protect them from 
 injurious fumes, but also to exclude currents of air that might 
 affect the swinging of the beam, and the indications of the needle 
 as its point moves to and fro over the scale in front of the post. 
 
 In order tomake this exclusion more complete just when it is 
 most essential, namely, when one is making the last adjustment 
 of the weights so as to exactly counterpoise the object weighed, 
 this final adjustment is effected by means of the rider, that can 
 be placed at any desired position on the right hand arm of the 
 beam, by means of a hook on a rod sliding through a socket, 
 near the top of the end of the balance case ; the balance can 
 therefore be entirely closed while this rider is used. 
 
 The weights. When the equilibrium is established between 
 
102 ELEMENTS OF CHEMICAL ANALYSIS. [§ 102. 
 
 substance and weights, this rider gives by its position on the 
 beam, the milligrams and fractions thereof, of the total weight, 
 or what appears in the written expression of the weight as the 
 third and fourth decimals. The number on the beam nearest to 
 the left of the rider gives milligrams (third decimal) and the rel- 
 ative distance between the rider and this number and the next 
 following one indicates tenths of a milligram. The beams of 
 some balances are graduated for milligrams and tenths, of others 
 only to milligrams and halves ; in this latter case the tenths must 
 be estimated by the eye. 
 
 The brass weights in the weight box give the grams, the 
 number of grams indicated by each weight being stamped on it. 
 The larger weights of foil, of which there are always four, 
 stamped 0.5, 0.2, 0.2, o.i, or 0.5, 0.2, o.i, o.i, give decigrams, 
 expressed by the first decimal, and by the same number and 
 relative denominations of smaller foil weights the centigrams are 
 given, occupying the place of the second decimal in the total 
 weight. In some cases the number of milligrams is stamped on 
 these foil weights, as 500, 200 ; or 50, 20, and so on. 
 
 102. The proper care and use of the balance. Thfe strict 
 observance of the following rules and precautions is important. 
 
 a. All movements of the beam should be slow, and so moder- 
 ate in extent that the needle does not swing much beyond the 
 fifth division on either side of the zero m^rk. No sharp impulse 
 should be given to this movement, either by quick raising of the 
 beam rests, or by making any changes in the weights or on the 
 other pan, while the beam is off its supports, or by touching the 
 beam, while swinging, with the rider hook, or by attempting to 
 move the rider over more than a small portion of one of the 
 divisions. At the moment when the beam is to be actually lifted 
 off the agate plates, the needle should be close to the zero point ; 
 this is easily brought about by causing the supports of the beam 
 to follow its movement as it swings towards this position, without 
 allowing them to touch it; then, just as the needle points to zero 
 the beam is lifted easily without any jar. 
 
 b. The greatest care should be taken that nothing comes in 
 contact with the substance-pan but clean and dry pieces of 
 apparatus. Of course the weighing may be worthless if any- 
 thing weighable is detached from the object weighed and left on 
 the pan, if another weighing of the same object is to be made 
 that bears any relation to this first weighing. If the substance 
 so left behind is acid, the pan is liable to be corroded and 
 
§ 103-] THE BALANCE AND ITS USE. lOJ 
 
 seriously damaged. Such a plain precaution as this would seem 
 to be superfluous; but every teacher who has had experience 
 with beginners in quantitative work, has now and then met with 
 an exhibition of such a degree of thoughtlessness, it might 
 almost be called stupidity, in the handling of delicate instruments, 
 as would hardly be supposed possible. 
 
 c. Paper should never be used to weigh a substance in. It is 
 more or less hygroscopic, and may therefore itself change in 
 weight during the weighing. For a similar reason, substances 
 that are themselves hygroscopic, or liquids that may lose weight 
 by evaporation, must always be weighed in well closed vessels. 
 
 d. Never weigh a piece of apparatus while warm, nor directly 
 after wiping it off; if necessary to wipe it with chamois skin, as 
 may be with a piece of glass apparatus, let it stand in the balance 
 for a few minutes before weighing. 
 
 e. Never touch the weights with the fingers, but only with the 
 forceps provided for the purpose. Always use the greatest care 
 to return each weight to its proper place in the box. 
 
 f. If the balance is properly adjusted, and the weights on its 
 pans are equal, the needle will stand at zero when the supports 
 are slowly lowered till the beam is free. Also, if the beam is 
 made to vibrate, so that the needle will move, to five divisions 
 to the left for instance, on swinging over to the right side, it 
 will fall a little short of five divisions ; on moving back again to 
 the left it will not go quite so far as it did on the right side, and 
 so on till it finally settles at zero when the vibration ceases. In 
 actual weighing, this vibration method is always followed, 
 because much quicker than to wait till the beam comes to rest. 
 
 103. It is usually desirable to take approximately a certain 
 quantity of a substance that is to be analyzed ; this quantity is 
 sometimes specified in the directions for the determination to be 
 made ; when not mentioned, from 300 to 500 mgms. may be 
 considered as a suitable quantity, if the constituent to be 
 determined forms a fairly large proportion of the substance ; if, 
 on the other ha,nd, it forms but a very small part, as only a few 
 hundredths of a per cent, for example, a larger quantity of sub- 
 srance must be taken, perhaps as much as four or five grams ; in 
 such a case, if a'small quantity is taken the error resulting from 
 unavoidable imperfections in the method of analysis, or from 
 want of experience, or both, may be so large in proportion to 
 the amount of the constituent weighed or otherwise measured, at 
 the end of the analysis, as to render the determination of little 
 
104 ELEMENTS OF CHEMICAL ANALYSIS. [§ I04. 
 
 value ; if the quantity of this constituent carried through all the 
 operations of the analysis is much larger, errors of equal mag- 
 nitude will count for much less in relation to the quantity of 
 substance determined, and will vitiate the result in a much 
 smaller degree. 
 
 On the other hand, unnecessarily large quantities of substance 
 are undesirable, for errors of other kinds may be introduced, 
 and the manipulations may require a longer time. Therefore 
 the quantity of substance to be taken should always be carefully 
 considered on beginning an analysis. 
 
 104. When the substance to be weighed is not at all hygro- 
 scopic, the following method of weighing out accurately an 
 approximate quantity is convenient. Get the weight of a watch 
 glass; make the sum of the weights on the weight-pan that of 
 the quantity of substance to be taken plus that of the watch 
 glass ; turn down the beam-supports till the needle takes a posi- 
 tion one or two divisions to the left of zero ; then, while holding 
 the beam there, slowly pour the substance from the tube into the 
 watch glass, till the needle swings over to the other side ; the 
 glass contains a little more than the quantity desired ; proceed 
 now to get the exact weight of the substance in the usual manner. 
 
 A hygroscopic substance must be weighed in a weighing tube ; 
 the quantity to be taken for the analysis is then to be poured 
 into the vessel in which the first treatment is to be made, and 
 the tube is weighed again. If the hygroscopicity is only moder- 
 ate, first weigh out the quantity desired, on ordinary scales 
 capable of weighing down to decigrams, pour this quantity into 
 the weighing tube, and mark the space it occupies ; then fill the 
 tube to the same mark with a fresh portion of the substance, 
 weigh, empty the entire contents of the tube into the vessel in 
 which the first treatment is to be made, and weigh again. 
 
 A convenient pair of weighing tubes is made from two test 
 tubes, one of which will just fit into the other; cut the rim off 
 the smaller tube and draw out the larger one about midway of 
 its length, and seal up and round out the bottom so as to make 
 a tube of about half the length of the other ; this serves as a cap 
 that will sufficiently exclude the moisture of the air from the 
 substance within. 
 
 Never, unless specially directed to do so, weigh out any par- 
 ticular quantity of a substance, such as exactly one gram or two 
 grams ; the last part of such a weighing, consisting, as it must, 
 of abstracting minute quantities of the substance from the con- 
 
§ I OS-] THE BALANCE AND ITS USE. IO5 
 
 tents of the glass on the substance-pan, or adding some of the 
 substance thereto, till the desired weight is obtained, consumes 
 much more time than the usual method, and no important 
 advantage is gained. 
 
 For assistance in measuring by the eye approximately the 
 quantity of the substance to be taken, it may be observed that 
 so much of a dry powder of average specific gravity as can be 
 piled on a five-cent piece will weigh from 0.8 to 1.2 grams. 
 
 In pouring a substance from the weighing tube into a beaker, 
 hold the latter in an inclined position and pour the substance 
 down the side, so that if the substance is specifically light, and 
 in a fine powder, none of it will be lost ; and, finally, tap the 
 lube gently on the rim of the beaker, to dislodge into the 
 beaker any particles adhering loosely to the lip. 
 
 105. The operation of weighing. On seating himself at the 
 balance, the student first ascertains whether its arms are in 
 equilibrium, by setting the beam in oscillation, and observing 
 the swing of the needle ; this movement of the beam need not 
 be made to extend beyond five divisions from zero, and can be 
 started easily by dropping the rider on the beam for an instant 
 near the fulcrum ; if it does not swing as it should with the arms 
 in equilibrium, that is at a uniformly decreasing rate on each 
 side, raise the beam-supports, and brush off the pans with the 
 camel's hair brush in the balance case \ if the equilibrium is not 
 then restored, the attention of the instructor in charge of the 
 balances should be called to the matter ; the beginning student 
 must not attempt to correct the fault himself. 
 
 When the balance is in order, put the object to be weighed on 
 the left-hand pan. If the weight is quite unknown, it is to be 
 settled, first of all, what the largest collection of gram weights is, 
 that is too small. For example, suppose the whole weight is 
 20.56 grams, and that, being quite sure that it is less than 20 
 grams, one begins with a lo-gram weight ; he will then go on, 
 adding one weight after another, till 19.99 grams is put on the 
 pan before the error' in judgmeiit is suspected ; ten weights have 
 been taken from the box, only to have to put them back and 
 begin over again. But if one had begun with a 20-gram weight, 
 and then added in succession the 10, 5, 2, and i gram weights, 
 finding each one too heavy, it is thus settled that the highest 
 number of whole grams that is too small is 20 ; having started 
 right with the brass weights, one proceeds in the same way with 
 the decigram foil weights, and then with the centigram weights; 
 
I06 ELEMENTS OF CHEMICAL ANALYSIS. [§ Io6. 
 
 the same number of weights will be handled as in the first case 
 supposed, but this time one has proceeded steadily towards the 
 desired end. 
 
 The beam supports must be raised between each change of 
 weights on the pan, but they need be lowered, each time, only 
 far enough to allow the needle to swing out one or two divisions, 
 showing plainly whether the last weight added was too small or 
 too large. 
 
 Too great care cannot be exercised in recording the weights. 
 In the first place, this record should always be made in the lab- 
 oratory record book, and never on loose slips of paper. Sec- 
 ondly, the reading should be made twice ; to this end the 
 student should learn the arrangement of the weights in the box, 
 so that one reading can be made by the vacant places there ; the 
 second reading is made on the weights as they are returned from 
 the balance to the box. These two readings, by such different 
 methods effectually check one another. In order that the first 
 method shall be reliable, it is evident that each student using 
 the balance should carefully return every weight to its proper 
 place in the box ; there is little danger of any mistake in this 
 respect, except as to the foil weights. Where many are using 
 the same balance, the only safe reading is the second one, that 
 of the figures stamped on each weight. 
 
 io6.. When a substance is to be weighed after ignition, which 
 in this case is usually the product of an analysis, this weight is 
 nearly always taken in a crucible or dish of porcelain or plati- 
 num. This crucible or dish must always be weighed before it 
 receives the substance ; and before being weighed it must be 
 ignited, so that it shall be subjected to the same treatment that 
 is given to it while the substance is ignited in it. 
 
 After every such ignition, the vessel, while still warm, is trans- 
 ferred from the platinum-wrapped triangle, which is always used 
 for supporting it on the ring of the lamp-stand, to the desicca- 
 tor. This transfer, as well as that from the desiccator to the 
 balance-pan, is always to be made with the crucible tongs, never 
 with the fingers. 
 
 The desiccator, a shallow, glass jar, with a ground glass cover, 
 contains some powerful absorbent of moisture, as calcium chlo- 
 rid, or sulfuric acid soaked up by pumice stone ; in the dry air 
 of this closed jar, the substance can absorb no moisture \yhile 
 cooling. If sulfuric acid is used as the absorbent, there should 
 be no more of it than can be taken up by the pumice stone ; if 
 
§ 107. j MEASUREMENT IN VOLUMETRIC ANALYSIS. I07 
 
 Otherwise, and it stands as a liquid in the bottom of the vessel, 
 a sudden jar, as when the desiccator is set down heavily on the 
 table, or is quickly moved in any way, may cause some of the 
 liquid to spatter up on to the bottom of the crucible ; this may 
 then come in contact with the balance-pan, and cause serious 
 damage. 
 
 The desiccator should be uncovered only while putting some- 
 thing into it or taking something out. 
 
 CHAPTER XII. 
 MEASUREMENT IN VOLUMETRIC ANALYSIS. 
 
 107. The standard of measurement. In this mode of analysis 
 (§ 100) the quantitative measurements are made partly by 
 weight, and partly by liquid volume. The weighing is confined 
 mostly to the substance taken for the analysis. 
 
 In gravimetric analysis, the unit of measurement is the gram ; 
 in volumetric work it is partly the gram and partly the cubic 
 centimeter ; in the gravimetric method we take such and such a 
 weight of substance, and get such and such a weight of precipi- 
 tate, the product of the analysis. In the volumetric method we 
 also take a certain weight of substance, for the analysis, but our 
 measurement of the result is made in cubic centimeters, although 
 this is afterwards calculated in weight. In the gravimetric work 
 the gram weight, with its sub-multiples and multiples, answers 
 for all the measurements ; but in volumetric work there are 
 many solutions by which we measure, and therefore many 
 analytical values of the cubic centimeter. 
 
 It is evident that anything used for A measure must itself have 
 a known value. Some of the solutions used for measuring do 
 their work by oxidizing the substance in solution whose quantity 
 it is desired to measure ; others act by neutralizing its acidity or 
 its alkalinity, others by precipitating it out of the solution ; the 
 more of the substance to be measured there is in the solution, 
 the larger the volume of the oxidizing, neutralizing, or precipi- 
 tating solution will be required for the work. We must, then, 
 be able to determine two things with accuracy; how much 
 oxidizing, neutralizing, or precipitating power there is in one 
 
I08 ELEMENTS OF CHEMICAL ANALYSIS. [§ Io8. 
 
 cubic centimeter of the measuring solution j and, secondly, the 
 exact point at which we have added just enough of the measur- 
 ing solution to complete the reaction ; this is usually accomplished 
 with the aid of some reagent^called the indicator, that gives 
 some sharp color reaction. For the determination of the 
 strength of the measuring solution we must generally use a gravi- 
 metric process of some kind. 
 
 io8. Standard and normal solutions. A solution whose 
 strength has been determined for the purpose of volumetric 
 analysis is called a standard solution ; when the standard of the 
 solution bears a certain definite relation to the molecular weight 
 of the active agent that it contains, it is called a normal solution, 
 which is thus defined : a normal solution is one of which one 
 liter contains a quantity of the substance, expressed in grams, 
 chemically equivalent to one gram of hydrogen. 
 
 Volumetric analysis may be divided into three kinds. 
 
 a. Analysis by neutralization, or saturation, in which the 
 quantity is measured of a solution of known strength of an acid 
 or a base, that is required to neutralize the unknown quantity of 
 a free base or acid. 
 
 b. Analysis by precipitation, in which the quantity is measured 
 of a solution of known precipitating power, that is required to 
 precipitate the unknown quantity of a substance from a solution. 
 
 c. Analysis by oxidation or reduction, in which the quantity 
 is measured of the reagent of known oxidizing or reducing 
 power, required to oxidize or reduce the unknown quantity of the 
 substance to be determined in this way. 
 
 Standard solutions for use in volumetric analysis are usually 
 solutions of acids, bases or salts ; one important solution contains 
 the elementary substance, iodin, for its active ingredient, and 
 another contains hydrogen peroxid, which do not belong to any 
 of these classes. A standard solution of an acid or a base is 
 used mostly for the determination of free bases or acids in 
 solution ; or an acid may be used for the determination of the 
 basic part of a salt, whereof the acid is one that can be com- 
 pletely and easily expelled, by the acid used, as in the case of 
 carbonates. A standard solution of a salt may be used as a 
 precipitant, either by its basic or its acidic part, or as an oxidiz- 
 ing or reducing agent. 
 
 That part of the reagent, of any one of these kinds, which 
 reacts with the substance to be determined is the active constituent 
 of the solution. If the reagent is an acid, the acidic part of the 
 
§ I08.] MEASUREMENT IN VOLUMETRIC ANALYSIS. I09 
 
 formula of the acid represents the active constituent ; if a base, the 
 basic part of the formula represents the active constituent. If the 
 reagent is a salt, and the reaction is the precipitation of some 
 constituent of the solution acted upon, the active constituent of 
 the standard solution is that part of the salt that enters into the 
 precipitate formed. In the same manner, if the action of the 
 standard solution is oxidizing, then that part of the substance in 
 the solution which actually produces the oxidation, whether 
 directly or indirectly, is the active constituent of the solution. 
 If the action is one of reduction, that constituent of the solution 
 which is carried to a higher degree of oxidation or chlorination 
 is the active constituent. 
 
 In the following equations, representing reactions of neutraliza- 
 tion and precipitation, the active constituent in the reagent, or 
 that part of the reagent containing it, is italicised. 
 
 2KOH + Hj50j = Kj^Oj 4- 2HjO. 
 2HCI + ^a(OH)j = BaC\, + 2HjO. 
 NaCl + ^^NOj = ^^NOa + NaNOj. 
 
 Equations illustrating the action of oxidizing agents will be 
 found further on. 
 
 In the formulas of these acids, bases, or normal salts, acting 
 as neutralizing or precipitating reagents, the valence of the 
 active constituent, shown by the number of atoms of hydrogen 
 in the acid, replaceable by a metal to form a salt, or of hydroxyl 
 in the base, or by the valence of the non -active part of the salt, 
 gives, directly or indirectly, the number of atoms of hydrogen 
 to which that quantity of the active part of the reagent repre- 
 sented by its molecular weight is equivalent. In H2S04, the 
 acidic and really active constituent is sulfur trioxid, SO3 : this 
 can be contained but once in the formula of the acid, hence SO3 
 is equivalent to H taken twice ; or, expressed in molecular 
 weight, 80.06 of SO3 is equivalent to 2 of H, or 80.06 grams of 
 SO3 is equivalent to 2 grams of H. Hence, according to the 
 definition of a normal solution, a liter of a normal solution of. 
 HjSOi should contain 40.03 grams of SO3; and the number 
 of grams of H2SO4 containing this weight of SO3 is given by 
 half the molecular weight of HjSO,, or 49.03. It is evident, 
 however, that we need not thus resolve the sulfuric acid into its 
 component parts to learn what its ultimate active constituent is, 
 the SO3. The acidigenic part of its formula is the SO^; it is 
 equivalent to Hj in that formilla ; therefore, we learn directly 
 
110 ELEMENTS OF CHEMICAL ANALYSIS. [§ lo8. 
 
 that the molecular weight represented by the ordinary formula 
 must be halved to get the figure for the weight of HzSOi, ex- 
 pressed in grams, for a liter of a normal solution. So a liter of 
 a normal solution of Ca(0H)2 must contain the number of grams 
 expressed by the figure for half its molecular weight : we need 
 not stop to consider that the really active constituent is the CaO ; 
 that this is equivalent to Hj ; that its molecular weight must be 
 halved, and, consequently the molecular weight of Ca(0H)2 ; 
 to consider that (0H)2 is equivalent to Hj shows us at once the 
 more direct course that can be taken. 
 
 If a normal solution of a salt is to be made for a precipitant, 
 consider first whether it is the basic or acid part of the salt that 
 comes into action in the use of the solution. For example, a 
 normal solution of potassium chromate, KjCrOi, is wanted as a 
 precipitant by its chromic acid. The formula of the salt shows 
 that the acidigenic constituent is bivalent, and is therefore 
 equivalent to H2 ; hence the figure given by half the molecular 
 weight of the salt, expressed in grams, represents thp weight of 
 the salt to be taken for a liter of a normal solution. 
 
 But the dichromate, KjCrjO,, may also be used as a precipi- 
 tating reagent; this is not a normal salt, and the rule given 
 above applies only to normal salts. The equation for the re- 
 action of this substance, with a barium salt for example, shows 
 that a molecule of it has twice the precipitating power of a 
 molecule of the normal chromate. 
 
 2Ba(CjH30j)j + KjCrjO, + H^O = 2BaCr04 + aKC^HjOj + aHC^HjOj. 
 Ba^qHsOz)^ + KjCiO^ = BaCrO^ -)- 2KC2H3O2. 
 
 The acidigenic part of this salt in one molecule is therefore 
 equivalent to H^. 
 
 Passing now to oxidizing agents the same general rule can be 
 applied to them. The following equation represents the oxidizing 
 action of KMnOi on ferrous oxid : in order to show more 
 plainly the course of the oxidation, the acid necessary to form 
 salts with the oxids, and to hold them in solution is omitted. 
 
 2KMn04 + i°FeO = SFcjOj -}- K^O -}- 2MnO. 
 
 This equation shows that two molecules of the permanganate 
 give up O5 for oxidizing work: O5 is equivalent to Hi,,: or 
 315.34 grams of KMnOj is equivalent to 10 grams of hydrogen ; 
 and, calculated in this way, on the basis of the actual working 
 effect of two molecules of the salt, a liter of a normal solution of 
 
§ Io8.] MEASUREMENT IN VOLUMETRIC ANALYSIS. Ill 
 
 it contains 31.5 grams. Likewise, one molecule of potassium 
 dichromate gives up in oxidation three atoms of oxygen, as 
 shown by the following equation, in which also, for greater 
 plainness, the hydrochloric acid, or some other acid necessary 
 to hold the products in solution, is omitted. 
 
 KjCfjO, + 6FeO = sFe^Oa + Cr^Os + KjO. 
 
 Os is equivalent to H^: hence the figure expressing grams of 
 KjCrjO, in a liter of a normal solution of this salt, when used as 
 an oxidizing agent, is given by one-sixth the weight of a mole- 
 cule of the salt. 
 
 In these cases, therefore, as in those of the neutralizing or the 
 precipitating reagents, the equivalency to hydrogen of the actually 
 working part of the reagent in a molecule of it, is taken as the 
 basis for the calculation in making up normal solutions. 
 
 Other standard solutions are used in technical practice, which 
 Mohr calls empirica/ solutions, and of which he gives this example. 
 A standard acid may be so made that it contains in 100 c.c. the 
 quantity of the active constituent required to saturate one gram 
 of pure NajCOs ; then, in assaying a sample of soda ash, exactly 
 one gram is taken, and the number of cubic centimeters required 
 to neutralize the sodium oxid gives, at once, the per cent, of 
 NajCOs in the sample. But this relation of acid required to 
 pure salt in the sample would hold good for sodium carbonate 
 only; another standard acid must be made for potassium car- 
 bonate, and another for calcium carbonate, and so on. Such a 
 solution is useful, therefore, only where one substance is to be 
 assayed with it, and by one and the same kind of a reaction. 
 
 These definitions and explanations should enable the student 
 to formulate the rule for the calculation of the required weight 
 of substance for any normal solution. 
 
 A normal solution of full strength is usually too strong for 
 , actual use ; it will not measure with sufficient closeness. In 
 order to measure length or weight as closely as we desire, in 
 accurate work with small quantities, we have to use a smaller 
 measure than the meter or the kilogram. In gravimetric work 
 we weigh in grams, and sub-multiples and multiples of the gram. 
 In like manner we reduce our normal solutions to half normal, 
 or one-tenth normal, containing in a liter one-half or one-tenth 
 of the quantity of substance required for a normal solution ; 
 such solutions are designated as — , — and so on. 
 
112 ELEMENTS OF CHEMICAL ANALYSIS. [§ I09. 
 
 In the use of these solutions it is better to take such a quantity 
 of the substance for analysis, that not less than about 40 c.c. of 
 the chief standard solution will be required for each determina- 
 tion made with it. 
 
 The temperature of any standard solution should be approxi- 
 mately the same at all the several times when its strength is 
 determined, and when.it is used for analytical purposes; the 
 temperature of a comfortable room is a convenient one to 
 maintain ; therefore, if a solution has been standing so long in 
 a cold room as to have fallen much below this point, it should 
 not be used till it has become warmed to about the right degree. 
 
 109. The specialinstruments used in volumetric analysis. 'These 
 are pipettes, burettes, measuring flasks, and graduated cylinders. 
 
 The pipette may be simply a graduated tube, showing cubic 
 centimeters and fractions thereof ; or it may consist of a short 
 piece of wide tube, connecting two longer pieces of narrow 
 tube, when it is intended to measure only one fixed quantity, as 
 5, 10, 25 or 50 cubic centimeters : this capacity is indicated by 
 a mark on the stem of the instrument. To use the pipette im- 
 merse the point in the liquid to be measured, and with the 
 mouth draw the liquid up till it rises a little above the mark ; 
 then quickly close the mouth of the tube with the ball of the 
 index finger, and with the mark on the stem at the level of the 
 eye, looking towards a window or a bright wall, raise the end of 
 the finger just enough to let the liquid flow out slowly, and 
 finally drop by drop, till the lowermost part of the meniscus and 
 the mark on the neck coincide ; take off the drop that may 
 adhere to the point by touching it on the side of the glass, and 
 then let the liquid flow out by its own gravity into the vessel 
 destined to receive it, the point of the pipette being held 
 against the side of the glass : then allow the pipette to drain in 
 this position for about a minute. 
 
 The burette, a long graduated tube, is closed below by a 
 rubber tube about three cetjtimeters long, carrying a short glass 
 jet at its lower end, and a small glass ball within ; on grasping 
 the tube around this ball between the ' ends of the thumb and 
 index finger, and pinching it in such a manner as to draw it out 
 to one side and away from the ball, a passage is opened for the 
 liquid in the burette, and the rate of flow can be easily regulated. 
 The rubber tube should be pushed up on the burette-point till 
 the ball in it is close to the opening of the burette, and the end 
 of the delivery tube in the rubber tube should also be close to 
 
-§ 11 O.J MEASUREMENT IN VOLUMETRIC ANALYSIS. II3 
 
 the ball. The size of the ball should be so adapted to the size 
 and elasticity of the rubber tube that, while making a tight 
 closure, still no such effort is required to open it that it cannot 
 be held open as long and as much as may be necessary, without 
 painfully straining the fingers.' 
 
 The burette is filled at the top through a funnel, till the liquid 
 rises above the zero, mark, then the valve below is quickly 
 opened as wide as possible, so that the air in the rubber tube 
 and jet will be completely displaced by the liquid, quite to the 
 point of the jet ; the liquid is then allowed to flow out, slowly, 
 till the lower part of the dark zone of the meniscus, or the line 
 on the burette-float if one is used, coincides with the zero line 
 on the burette ; the reading of the amount of liquid delivered for 
 any purpose is taken in a similar manner. In delivering a 
 large quantity of liquid at once and rapidly, a minute should be 
 allowed for the walls of the burette to drain before the reading 
 is taken. 
 
 The measuring flask has a mark on its neck indicating its 
 capacity. It is often used when it is desired to make a certain 
 volume of a solution of a substance, in hand for analysis ; ali- 
 quot parts of this solution are then taken out with a pipette, for 
 the further treatment. The volume of the whole solution being 
 known, as well as that of each part taken out, the results ob- 
 tained with each portion can be calculated to the whole amount 
 of substance taken in the beginning for analysis. 
 
 The graduated cylinder. This is a cylinder of uniform diam- 
 eter, on a foot, not graduated to less than one cubic centimeter ; 
 measurements made with it are not so accurate as with the meas- 
 uring flask or pipette, because the diameter of the column of 
 liquid where the reading is taken is so much greater. 
 
 When the liquid flows from a pipette or burette, it should 
 leave no streaks on the walls, showing more adhesion in one 
 place than in another ; in such case the readings cannot be accur- 
 ate. Such irregularity in the flow is caused by dirt of some kind 
 on the glass, usually oily matter; this can be removed most 
 easily by means of a strong oxidizing agent, as chromic acid. 
 Directions will be found in Part V, under the head of reagents, 
 for the preparation of this solution and for its use. 
 
 no. The calibration of graduated instruments. Successful 
 
 work in volumetric analysis requires that the instruments used be 
 
 correctly graduated. The testing of their graduation is called 
 
 calibration. Not only should the correctness of the several parts 
 
 8 
 
114 ELEMENTS OF CHEMICAL ANALYSIS. [§ IIO. 
 
 of the burette and the graduated pipette be tested, but also that 
 of the total capacity of each instrument, as the full pipette and 
 the measuring flask, and their relations to one another. To the 
 beginner in quantitative analysis, taking only the course in Part 
 IV of this work, the calibration o'f his burette, 25 c.c. pipette, 
 and 250 c.c. measuring flask is of most importance. 
 
 Calibration of the burette. After it has been properly cleaned, 
 fill it to the zero mark v/ith distilled water at a temperature of 
 about 20°, run out exactly 10 c.c. into a light weighing flask, 
 previously weighed with a small watch glass over its mouth, . 
 and weigh on a balance sensitive to centigrams ; nothing is 
 gained by weighing more accurately than this. Run in another 
 10 c.c. and weigh again, and so on till the lowest 10 c.c. 
 has been weighed. Repeat, and take the average for each 
 10 c.c. 
 
 For the correct scale of reading for this calibration, for i c.c. 
 on the burette scale put down in your note book one-tenth of 
 the weight of the first 10 c.c; for 2 on the burette scale, two- 
 tenths of that weight, for 3, three-tenths, and so on ; then when 
 10 on the burette scale is reached the corrected number will be 
 the same as the weight of the first 10 c.c, if the calculations 
 have been rightly made. Proceeding in the same manner, for 11 
 on the burette scale, add to the corrected number for 10 c.c. 
 on the burette scale, one-tenth of the weight of the second 10 
 c.c, and so on. If the deviation for any 10 c.c. is less than 
 0.05 gram, the graduation of that part of the burette is suf- 
 ficiently accurate, and no correction need be made. 
 
 To calibrate the pipette, weigh its contents, delivered exactly 
 as has been directed ( § 109) into the same weighing flask that 
 was used in thq calibration of the burette. Then calibrate the 
 measuring flask by means of this pipette, delivering it ten times 
 ■filled into the flask, and repeating the operation till results agree 
 closely. If the mark on the neck of the flask does not coincide 
 very nearly with the lowest part of the dark zone of the menis- 
 cus at the level of the liquid, when the flask is thus filled, a new 
 mark should be made for this calibration by putting on a short, 
 narrow strip of a gummed label, at the proper place. Now, 
 with the aid of this measuring flask and pipette, one can get 
 exactly one-tenth of the weight of a substance taken for analysis 
 and brought into solution, this solution being made up to 250 c.c. 
 in the flask, or one-tenth of the soluble part of it if not entirely 
 soluble. 
 
§ 1 1 I.J MEASUREMENT IN VOLUMETRIC ANALYSIS. 115 
 
 III. Special directions for the use of these graduated instru- 
 ments. When it is desired to get a certain volume of a solution 
 of a substance, as 250 c.c. for example, in the measuring flask, 
 and heat can be used with advantage, always treat the substance 
 first in another flask, or in a beaker, with not more than half 
 this volume of the solvent. When the solution is completed, or 
 when carried as far as it can be if the substance is not- wholly 
 'soluble, with a funnel in the mouth of the measuring flask pour 
 this solution into it, and carefully rinse the flask or beaker into 
 it with distilled water ; then pour in more water cautiously 
 almost to the mark on the neck, and finally, holding the flask in 
 a vertical position, with the mark on a level with the eye, let 
 water drop in from a pipette, or a dropping tube, till the mark is 
 reached ; close the flask tightly with its glass stopper, or with a 
 soft cork, and mix its contents by repeated inversion. After 
 this, while the solution is being used for the analysis, the flask 
 should be uncorked .only while some of its contents is being 
 withdrawn. 
 
 If the solution has stood for some time undisturbed, it is well 
 to mix the contents, except when there is some special reason 
 for not doing so, by inverting the flask two or three times, before 
 taking out a portion for analysis. If two or three portions are 
 to be used take all of them out at the same time ; if but one is 
 taken, and the pipette is laid on the table while the analysis of 
 that portion is carried through, some of the solution on the point 
 of the pipette will evaporate, leaving a soUd deposit there ; this 
 cannot be washed off without danger of getting a little water 
 into the pipette ; of course the pipette must not be dipped 
 into the liquid in the flask with this deposit still on it, or with 
 water in it. 
 
 Always after using a pipette rinse it out, finally with distilled 
 water, and dry it ; do the same with a burette when through with 
 the use of it for a particular solution, or when the work must be 
 left for some time. Only when clean and dry are these instru- 
 ments ready for use. 
 
 Never attempt to fill a burette at its mouth otherwise than 
 through a funnel ; without this precaution, some of the liquid 
 may flow down on the outside; if it is a solution of any salt the 
 water will evaporate, leaving a deposit on the glass that will ob- 
 scure the readings ; or if a beaker containing a solution to be 
 analyzed should happen to be under the burette, some of the 
 
(D 
 O) 
 CO 
 CL 
 
 (Ji 
 
Il6 ELEMENTS OF CHEMICAL ANALYSIS. [§§ 1 1 2-1 1 3. 
 
 overflowing solution might drop into it, and the analysis would 
 be ruined. 
 
 Always close the mouth of a burette carefully, on leaving a 
 standard solution in it that you expect to use again in a short 
 time ; if the work will not be continued within a very few days, 
 it is better to empty the solution out and clean and dry the 
 burette. 
 
 CHAPTER XIII. 
 SEVEN IMPORTANT OPERATIONS OF QUANTITATIVE WORK. 
 
 112. Every gravimetric analysis brings into use seven import- 
 ant operations namely, weighing of the substance and the 
 product of the analysis, the preparation of .the solution, precipi- 
 tation of the new compound, filtration, washing of the precipi- 
 tate, preparation of the same for weighing, usually by ignition, 
 and the calculation of the result. 
 
 The first, sixth and seventh operations are peculiar to quanti- 
 tative analysis ; the others are common to both qualitative and 
 quantitative work, and they differ in manipulation in the two 
 cases only in this one respect, but a very important one, that 
 they must be carried through in such a manner as to involve 
 neither loss of any of the substance that is under manipulation, 
 nor the addition of any foreign matter to it that will make it 
 other than the chemically pure product, of definite chemical 
 coniposition, which the process requires to be weighed, when 
 these manipulations are completed. 
 
 The first operation has been fully described (Chap. XI). To 
 what has already be^n given in Part I concerning the other 
 operations, the following considerations are added as bearing 
 specially on the two conditions emphasized above. 
 
 113. The solution of the substance. The liquid in which the 
 solution is being made must not be boiled, unless special direc- 
 tions are given to that effect j if boiled, it must be in a beaker 
 covered with a beaker cover, or if in a flask, with the flask turned 
 over on its side and securely supported in that position. If any 
 gas is given off during the solution, as in the treatment of a 
 carbonate with an acid, the beaker must also be covered, and the 
 
§ Il6.] SEVEN IMPORTANT OPERATIONS. I I9 
 
 thumb on one side, and the second and third fingers on the 
 other, lay the rod across the top, and hold it there with the 
 index finger; all the pouring from the beaker can now be done 
 with this hand ; and while the beaker is still inclined over the 
 funnel, a jet of water from the wash-bottle can be directed into 
 it, and all over the sides and bottom, which will immediately 
 flow out into the funnel, carrying with it in this continuous 
 stream all of this fine precipitate ; the jet-tube of the wash- 
 bottle being connected with the main tube by rubber, making a 
 flexible joint, by means of the index finger of the hand holding 
 the wash-bottle, pushing the jet-tube upwards, the stream can be 
 directed even against the upper sides of the beaker while still 
 flowing down the rod into the filter. 
 
 This transfer of the precipitate is completed only when the 
 inside of the beaker is perfectly clean, the outside being clean 
 also in order that one may plainly see anything adhering to the 
 inner walls. 
 
 116. Filtration by suction. The assistance of suction to 
 hasten filtration is much used in quantitative work. It is applied 
 in two ways, with paper filters, and with asbestos filters. 
 
 The paper filter is usually supported by a perforated platinum 
 cone in the throat of the funnel ; when the filter is crowded 
 down snugly against this cone, its rim should touch the sides of 
 the funnel at all points of its circumference ; if it does not, the 
 opening of the funnel is too wide, and another. one should be 
 taken, or the filter should be folded with a wider opening, which 
 is easily done. When the filter is put into the funnel and wetted 
 as described in'§ 55, special pains must be taken to fit it down 
 against the cone and against the glass above the cone, every- 
 where from the apex of the cone to the rim of the filter ; creases 
 made in the paper in doing this will do no harm ; but wherever 
 the paper is not directly backed up by the platinum or the glass, 
 it will probably be torn when the suction is turned on, and some 
 of the substance will pass through. Only slight suction should 
 be used at the beginning of the filtration, and more, later, when 
 the filter is well covered with the precipitate ; without care in 
 this regulation of the suction much time may be lost on account 
 of spoiled work. By the use of filters whose points have been 
 dipped in nitric acid of sp. gr. 1.42, and afterwards washed with 
 water till the acid is all removed, the use of the platinum cone 
 can be dispensed with. 
 
 When the suction is in use, it should never be turned off 
 
120 ' ELEMENTS OF CHEMICAL ANALYSIS. [§ 1 1 7. 
 
 entirely, till first disconnected from 'the filtering bottle ; other- 
 wise the water at the suction-pump, which is commonly attached 
 to the water supply at each student's table, may rush back into 
 the bottle, and the work may be spoiled. Strong bottles or 
 flasks specially made for the purpose must always be used to 
 receive the filtrate : never use an ordinary flask. Flasks of the 
 conical, Erlenmeyer form, with a lateral tube for connection 
 with the suction are now provided, and are very serviceable. 
 
 It is advisable to start every paper filtration in filters carefully 
 fitted into the cones, or treated with HNOs, so that suction may 
 be applied later if desirable. 
 
 117. Washing precipitates. Upon the thoroughness with which 
 the precipitates are washed depends in largest measure the fulfill- 
 ment of the second requirement for successful work stated in 
 § iiz. When the filtration is completed, the precipitate and 
 the filter are saturated with a solution containing all the products 
 of the reaction by which the precipitate was made, as well as, 
 sometimes, other substances that one needed to add to make the 
 precipitation as perfect as possible : and so far as these are not 
 volatile at the temperature of the burning of the filter, they will 
 remain and add to the weight of the product. It must not be 
 forgotten, therefore, that it is the filter as much as the precipitate 
 in it that needs washing. 
 
 Hot water, unless proscribed, should always be used for this 
 washing, to save time ; the jet should be made to play all over 
 the filter, from as near the rim as possible down, till the contents 
 are covered with water, or till the filter is about two-thirds filled ; 
 when all this has drained out, repeat the addition of water ; the 
 washing will be sooner completed with several small quantities 
 of water, than with as many larger quantities. 
 
 The first spurt of water from the wash-bottle is apt to be so 
 strong as to cause spattering of the precipitate up on the sides of 
 the funnel above the filter; this maybe avoided by first filling 
 the whole delivery tube and jet with water, while the jet is 
 pointed in another direction ; then, while the tube is full, pinch 
 the rubber tube between the jet and the main tube, direct the 
 jet into the filter, and release the pressure on the rubber tube 
 while the blowing in at the mouth tube is continued. Also, 
 while the delivery tube is thus held full of water, if the wash- 
 bottle is held in a much inclined position with the jet pointing 
 downwards, the delivery tube becomes a siphon by which the 
 water can be run into the filter fast or slow at pleasure, by inclin- 
 
§ Il8.] SEVEN IMPORTANT OPERATIONS. 121 
 
 ing the flask more or less ; by letting the flow run dropwise on 
 the rim of the filter for a few rounds, that more difficult part ot 
 the washing may be facilitated ; but this must be done with care 
 in the case of very fine precipitates, lest they begin to crawl up 
 on the glass. 
 
 If channels are formed in t,he precipitate by shrinkage, while 
 it is being washed on the filter, these are to be broken up, most 
 easily, by stirring the precipitate with a glass rod. This shrinkage 
 will happen only in the case of somewhat gelatinous or very 
 flocculent precipitates, such as ferric hydroxid, and it is best to 
 wash these largely by decantation before putting them on the 
 filter — pouring considerable water over the precipitate in the 
 beaker, after as much as possible of the liquid in which the 
 precipitation was made has been poured off" through the filter, 
 without removing much of the precipitate, stirring it vigorously, 
 pouring this liquid off after partial settling of the precipitate, 
 and repeating the operation several times. 
 
 There should be no guess-work as to the question of the com- 
 pletion of the washing of the precipitate ; in every case a test 
 should be made from time to time in a cubic centimeter of the 
 washings, for that substance in the solution for which there is the 
 most delicate as well as simple qualitative reaction. If, for 
 instance, we know that the solution contains a chlorid and a 
 nitrate, as the delicate test for the former by silver nitrate is more 
 simple than the very delicate test for the latter, given under nitric 
 acid in § 8 1, we would use the former test; and when we can no 
 longer get any reaction with silver nitrate in the washings acidi- 
 fied with nitric acid, we can usually assume that, together with 
 the chlorids thus proved to be washed out, nitrates and all other 
 salts are removed. The test may be made in another way, by 
 the evaporation of a drop of the washings to dryness on a clean 
 watch glass ; if no residue remains, the washing is complete. 
 
 ii8. The asbestos filter. For this, instead of a funnel, a large 
 platinum crucible is used (the Gooch crucible) with perforated 
 bottom, or a porcelain crucible without bottom, except a narrow 
 ledge to support a perforated platinum disk (the Caldwell-Gooch 
 crucible). The crucible is put in a funnel with short, perpen- 
 dicular sides, the upper edge of which is covered with a ring of 
 sheet rubber, in such a manner that as soon as the suction is 
 turned on, and the crucible is pressed down gently, this rubber 
 makes a tight joint between it and the rim of the funnel. 
 
 To prepare the filter, while the crucible is pressed down in this 
 
122 ELEMENTS OF CHEMICAL ANALYSIS. [§ Il8. 
 
 manner and the full force of the suction is turned on, pour on a 
 very little of the asbestos pulp, shaken up with very much water ; 
 then pour in a little more, down a glass rod, the end of which 
 is held close to the bottom of the crucible, so as to leave the 
 first coating over the perforated bottom undisturbed ; a third or 
 fourth portion may be added ; but. the layer of asbestos should 
 be no thicker than moderately heavy filter paper, and uniformly 
 distributed over the whole surface ; the finer the precipitate to 
 be collected, such as barium sulphate or calcium oxalate, the 
 greater the care that must be bestowed on the preparation of the 
 filter. After it has been properly made, wash it with water 
 poured in on a glass rod the end of which is close to the asbestos, 
 till the washings are clear; the washings must be frequently 
 poured out of the filtering bottle, in order that one may be able 
 to determine when the last washing is free from fibers of asbestos. 
 The crucible and filter is then to be dried and ignited over a 
 low, direct flame, the lamp being held in the hand so that the 
 flame can be made to play evenly and lightly over the whole 
 crucible, and not merely impinge forcibly against the bottom ; 
 the drying flame should be applied very gently at first, by 
 moving it in and out, under and around the crucible ; the 
 ignition, later, is complete as soon as the bottom of the crucible 
 has reached a dull redness, unless higher heating is specially 
 directed. 
 
 When this filter is to be used, first turn on the suction and 
 then put the crucible in its place in the funnel, moisten the 
 filter with a few drops of water, and proceed with the filtration, 
 always having the end of the glass rod well down in the crucible. 
 When the washing is completed the crucible and contents can be 
 dried and ignited in the same manner as directed for the treat- 
 ment of the filter before the filtration. 
 
 This method of filtration is so useful and so widely applicable, 
 especially with the cheaper porcelain crucible, that the student 
 should learn to use it very early in his course. If a thin plat- 
 inum jacket is made for the crucible, fitting it just a little 
 loosely, the ignition can be made as satisfactorily as in a plat- 
 inum crucible; and as the platinum can be spun much thinner 
 than would be practicable for a crucible, with this arrangement 
 one can have all the advantages of a platinum Gooch crucible at 
 much less cost. Any worker in platinum can make the jacket. 
 In using it lay two or three long, slender fibers of asbestos in 
 the jacket before putting the crucible into it, to avoid danger 
 
§ irP'] SEVEN IMPORTANT OPERATIONS. 123 
 
 of adhesion between the two if the ignition must be .made at a 
 high temperature. 
 
 iig. Preparation of. the precipitate for weighing. In case the 
 asbestos filter is used it is a very simple matter to prepare the 
 precipitate for weighing, as has already been explained. If the 
 precipitate is collected on paper the operation is less easy. 
 
 The precipitate must first be dried for a few hours in the dry- 
 ing chamber provided for this purpose ; to this end cover the 
 funnel with a common filter, on which your name and the num- 
 ber of the anaylsis have been written ; this filter must be about 
 a centimeter larger than the funnel, and be folded down tightly 
 over the edge, so that it will stay in place ; the moisture will 
 easily escape through the porous paper. To put this cover on 
 so that it will remain in place, set the funnel in the funnel- 
 holder, lay the filter on the edge of the funnel, and hold it in 
 position by pressing it down on this edge with the finger-ends 
 and thumb of one hand; then with the index finger of the other 
 hand fold the edge of the filter down over the edge of the 
 funnel at one point on the circumference, and while holding 
 this fold in place with this finger, with the thumb make the next 
 fold tightly over the first one ; move the index finger to this 
 second fold and hold it in place, and at the same time tucking 
 it under a third fold laid over it by the thumb ; while doing 
 this, this side of the funnel is gradually moved round and away 
 from the operator ; at no time is the pressure of the fingers of the 
 other hand to be released. Each fold is to be drawn down as 
 tightly as possible without tearing the paper. 
 
 Meanwhile the crucible is to be ignited and weighed, if this 
 has not already been done (§ 126). In this ignition adjust the 
 height of the crucible above the lamp so that about two-thirds 
 of a flame ten centimeters long will be below the crucible ; 
 there should of course be no deposit of carbon from the lamp 
 flame on the crucible : if there is it must be burned off before 
 putting the crucible in the desiccator. 
 
 To guard against any possible loss of the precipitate in trans- 
 ferring it to the crucible, the operation is to be performed over 
 glazed paper ; this paper should be in four pieces ; one (a) 
 about 37 by 50 centimeters, one (b) about 22 by 25 centimeters, 
 and two small pieces, (c, d,) each about 14 by 22 centimeters : 
 these pieces can be cut out of a sheet of the ordinary size. 
 All these pieces should be trimmed smooth at the edges ; this 
 
124 ELEMENTS OF CHEMICAL ANALYSIS. [§ II9- 
 
 paper should never be on the table except when in actual use for 
 the transfer of the precipitate to the crucible. 
 
 Lay the largest piece of paper a on the clean, dry table, on 
 that the piece b, and on that the piece <:, and finally on that 
 the crucible. In a place where there are no strong currents of 
 air, touching the filter only on the outside, press and rub it 
 together gently, where the precipitate is, all the time holding it 
 over the glazed paper, and empty as much as possible thereof 
 into the crucible ; then carefully open the filter completely ; it 
 will be seen that the precipitate is entirely confined to one half 
 of it ; with the other half towards you take hold of the rim of 
 it with the thumbs and second fingers of both hands, bring the 
 two quarters of the other half together by means of the index 
 fingers pressing upwards on the outside, and then by a back- 
 ward and forward motion of the right and left halves of the filter 
 rub the inside surfaces together, and thus loosen as far as possi- 
 ble those portions of the precipitate that still adhere to the 
 paper ; change the positions of the index fingers about, so as to 
 rub different parts of the filter together, and then empty it into 
 the crucible ; now that as much as possible of the precipitate 
 has been transferred to the crucible, fold in that edge of the filter 
 over which the precipitate was emptied, so that no particles 
 loosely adhering to it shall drop off and be lost in subsequent 
 operations, fold the filter up again as it was originally, roll it up 
 and wind the long piece of platinum wire (in a glass tube handle) 
 about it, as much as may be necessary to keep it together ; hold 
 the roll with the closed end downwards directly over the cru- 
 cible, touch the lower end with the lamp flame, and lower it at 
 once into the crucible ; when the burning and glowing have 
 ceased, raise it a little above the crucible and let the flame play 
 on any unconsumed parts, thus burning the filter as completely 
 as possible in this free access of air, before the remains drop out 
 of the wire ; a gentle tapping ol the wire on the edge of the 
 crucible will then detach any particles adhering to it. 
 
 If all this work has been carefully and skillfully done, very 
 little of the precipitate will fall outside of the crucible ; set the 
 crucible aside on the other small piece of paper d, and gather all 
 visible particles of the precipitate from sheet a on to sheet c on 
 which the crucible stood-; then putting c ox^ a gather whatever is 
 on b on to c; then, setting the crucible and the piece it is now on, 
 on b, transfer what has been collected on c to the crucible. By 
 
§ 120.] SEVEN IMPORTANT OPERATIONS. 125 
 
 conducting the operation in this manner the direct transfer of 
 precipitate to the crucible is always done from a small piece of 
 paper, and more easily than from a large one ; and each part of 
 the operation is conducted over a sufficiently large piece of paper 
 so that no particles are likely to get out of sight ; if any do not 
 move readily on the glazed paper, they can be pushed along to the 
 edge by means of the platinum wire; this is better than a brush 
 or a feather, for adhesion to either of these is quite as easy as to 
 the paper, if not more so. 
 
 Now set the crucible in the platinum-wrapped triangle on the 
 lamp ring, and put the glazed paper away in its drawer. Cover 
 the crucible, and ignite it at first gently and afterwards to full 
 redness, or as much as may be directed in any special case ; remove 
 the cover, lay the crucible on its side with its mouth towards one 
 of the twisted arms of the triangle, and the cover partly on this 
 arm and partly on the crucible, and so far down as to leave its 
 mouth about two-thirds uncovered ; some access of air is thus 
 provided for the combustion of the small remnant of carbon that 
 usually remains ; apply the full heat of the lamp to the bottom 
 of the crucible, this being set high enough so that about two- 
 thirds of the length of the flame is below it. When no further 
 change appears to take place in the contents of the crucible put 
 it in the desiccator to cool. 
 
 In a few cases there is no danger of any reduction of the sub- 
 stance to be weighed, by contact with the burning organic matter; 
 then the filter and contents may be put at once into the crucible, 
 and at first gently ignited with the cover on ; after the filter is 
 thoroughly charred the ignition is continued in the partly covered 
 crucible, as described above. In other cases the precipitate is so 
 easily reduced that it must receive special treatment after the 
 ignition, to restore it to its normal condition ; it is better to 
 collect such precipitates on the asbestos filter. 
 
 120. Calculation of the results of the analysis. In the calcula- 
 tion of these results, two important ideas are specially prominent : 
 first, the product of the analysis, that is weighed, rarely consists 
 of that substance alone for the determination of which the 
 analysis was made, or in the same form in which it existed in the 
 compound subjected to analysis. If, for example, we seek to 
 determine phosphorus in cast iron, we finally weigh it as mag- 
 nesium ammonium phosphate, a form of combination totally 
 different from that in which it existed in the iron. Secondly, 
 the result is nearly always to be given in percentage, or parts 
 
126 ELEMENTS OF CHEMICAL ANALYSIS. [§ 121. 
 
 per hundred parts of the substance analyzed ; only by comparing 
 results thus calculated can they be checked against one another, 
 since different quantities of substance are in nearly all cases 
 taken for the several determinations that are made. 
 
 In order to be able to make the first part of the calculation, 
 it is essential that the chemical composition of the product of 
 the analysis weighed be accurately known, so that its formula 
 can be written ; as one way of verifying this formula, the equa- 
 tion for the reaction by which the precipitation is made should 
 always be written out by the student. Knowing the formula of 
 the substance weighed, the amount of the substance sought is 
 calculated by stochiometric rules. Make the molecular weight 
 of the product of the analysis, or substance found, the first term 
 of a proportion ; the atomic or the molecular weight of the sub- 
 stance sought, according as this substance is elementary or com- 
 pound, taken as many times as it occurs in the formula of the 
 compound weighed, the second term; the weight of substance 
 found, the third term ; the fourth term will be the amount of 
 substance sought, for the determination of which the analysis 
 was made. With this result, and the weight of substance taken 
 for analysis, the percentage of the substance determined in the 
 substance analyzed is calculated. 
 
 In the larger works on analytical chemistry, Tables are given 
 for facilitating this calculation, to which the advanced student 
 will usually refer ; but the beginner should make it without such 
 aid till he is thoroughly familiar with the methods, and can 
 understand the principles upon which these Tables are con- 
 structed. 
 
 CHAPTER XIV. 
 
 MISCELLANEOUS MATTERS. 
 
 121. The determination of the specific gravity of solutions. 
 When a solution contains only one substance, the relation be- 
 tween the specific gravity of the solution and the quantity of the 
 substance in it can be determined and put in the form of a 
 Table; this Table can then be used for ascertaining the per 
 cent, of this substance in any solution of it, whose specific 
 gravity is known. A number of such Tables are given in the 
 
§ 122. J MISCELLANEOUS MATTERS. 127 
 
 larger text-books on analytical chemistry, as well as in many 
 smaller books devoted exclusively to Tables of various kinds. In 
 these Tables, the figure in the column under the formula of the 
 substance in the solution, against any specific gravity figure, 
 gives the number of grams of the chemical substance having 
 that formula, in 100 parts of the solution having that specific 
 gravity. If the substance column is headed SO3, it is the num- 
 ber of grams of sulfur trioxid in 100 parts of the solution of 
 the acid of the specific gravity found ; if the substance column 
 is headed HjSO,, it is the number of grams of this chemical 
 compound in loo parts of the acid of the specific gravity found, 
 and so on. 
 
 The approximate determination of the specific gravity of a 
 liquid, by means of the areometer. The use of this instrument 
 depends upon the principle that a body floating and partly 
 immersed in a liquid displaces exactly its own weight of the 
 liquid. If the liquid is a solution, and increase of the quantity 
 of the substance in the solution makes the liquid specifically 
 heavier, the floating body will not sink so deep, and vice versa. 
 The graduated scale on the stem of the instrument enables one to 
 measure the extent of the immersion ; this scale being so made as 
 to indicate the specific gravity corresponding to the extent of 
 immersion, we have thus a very quick method of making a deter- 
 mination of the specific gravity of a liquid with sufficiently close 
 approximation to the truth to answer for many purposes. 
 
 The reading is taken where the stem of the instrument meets 
 the surface of the liquid. It is well to learn to read the' scale 
 before putting the areometer into the liquid. Take the liquid 
 at the temperature of about 15" C, in a cylinder longer than the 
 areometer, and with an inner diameter of at least about a centi- 
 meter greater than the bulb of the instrument. 
 
 122. The accurate determination of the specific gravity of a 
 liquid. This determination is made by comparing the actual 
 weights of equal volumes of the liquid and of water, at the 
 same temperature. Many forms of apparatus are used for this 
 purpose. The special points to be looked after are, (i) exact 
 equality of volumes of the two liquids weighed, (2) exact 
 equality of their temperatures at the time the volumes were 
 measured, and (3) absolute security against any loss of these 
 measured volumes by evaporation till the weighings are made. 
 
 The specific gravity pipette is a convenient instrument for 
 making this determination. In this instrument the volume of 
 
128 
 
 ELEMENTS OF CHEMICAL ANALYSIS. 
 
 [§ 122. 
 
 liquid to be weighed is that which will fill the space from the 
 point a, to the mark c on the stem. The weight of this volume 
 of distilled water is to be determined first : although 15° C. 
 is the temperature usually adopted, 20° is nearer 
 the ordinary temperature of the room, and is 
 therefore more easily maintained during the ma- 
 nipulation. 
 
 Drying and weighing the pipette. Remove the 
 rubber tube, lay the pipette in the drying closet, 
 and when it is hot connect it with the air blast. 
 Then weigh it with rubber tube and screw-clamp 
 on, the tube being pushed quite down to the 
 bulb d and the clamp being close above the end 
 of the stem of the pipette. This tube should 
 slip easily on the glass tube ; if it does not, wet 
 the latter a very little over its whole surface. By 
 the platinum wire loop, which goes with the 
 pipette, hang it on the left arm of the balance, 
 and put a small watch glass on the pan under- 
 neath, to protect the pan if any of the liquid 
 should drop from the pipette during the weighing. 
 Filling the pipette. With water : fill a large 
 beaker with tap water, bring its temperature to 
 20°, and suspend in this, by means of a copper 
 wire triangle over the mouth, your smallest 
 beaker, filled with distilled water : as soon as this 
 water has taken the temperature of 20° immerse 
 the point of the pipette in it, and with the 
 clamp J open just enough, and no more, to admit 
 of suction through the rubber tube, by means of 
 another rubber tube from the tube m to the 
 mouth, slo\*ly draw the water up, while seated at the table so 
 that the eye is nearly at the same level with the upper part of 
 the instrument ; as the liquid approaches e fill very slowly, and 
 at the instant when this space is full close the clamp, the screw 
 of which is all the time held between the thumb and finger of 
 the right hand, while the stem of the pipette above the bulb d 
 is held by thumb and finger of the other hand. Screw up the 
 clamp as long as it yields to the pressure, but not any longer ; 
 it is easy to break it by screwing unnecessarily tight. Now 
 detach the tube m, and with the point of the pipette still in the 
 water, grasp the rubber tube by the part that is on the stem 
 
§ 123.] MISCELLANEOUS MATTERS. 1 29 
 
 between the clamp and the bulb, and carefully raise this tube by 
 a somewhat spiral movement, till the liquid is drawn up exactly 
 to the mark c ; if it is drawn higher the pipette must be 
 emptied, dried, weighed and filled again. 
 
 Remove the pipette from the liquid, by a quick movement of 
 the finger around the point take off the adhering drop, and then 
 by further raising of the rubber tube draw the liquid up a little 
 and thus away from the point ; now, any slight expansion of the 
 liquid while being weighed will not cause any to drop out, and 
 also the point can be wiped dry without danger of removing 
 any of the liquid. If the clamp was properly closed the con- 
 tents of the pipette will remain perfectly stationary. If any of the 
 liquid does drop out, before the weighing is completed, or even if 
 a drop collects about the point, the pipette must be emptied, dried 
 and refilled. Duplicate and closely agreeing results must be 
 obtained, both when the pipette is filled with water, and when 
 filled with the liquid whose specific gravity is to be determined. 
 
 When the pipette is to be laid aside, slip the rubber tube off, 
 and open the clamp. 
 
 This instrument may also be used very conveniently for accur- 
 ate weighing of small quantities of a liquid. When thus used 
 it must be filled at least up to the stem at ^ ; if only partly filled, 
 the liquid is apt to drop out on account of changes in the 
 volume of the air in the upper part of the bulb. The size of 
 the bulb must therefore correspond to the quantity of liquid to 
 be weighed. In emptying the pipette, force out the last drops 
 of the liquid by closing the upper end of the rubber tube on the 
 stem with the thumb and finger, and then quickly compressing 
 the tube just above the stem. 
 
 123. The use of platinum ware. Ignitions are so much more 
 easily, quickly, and satisfactorily made in platinum than in porce- 
 lain crucibles, that every student intending to make chemistry 
 his special work should own his own crucibles, and will be ex- 
 pected to procure either these or platinum jackets for the porce- 
 lain Gooch crucible. 
 
 Platinum is attacked by free chlorin. Therefore it should 
 never be allowed to come in contact with any mixture contain- 
 ing free HCl and HNOs, or with any salts of these metals under 
 such conditions that their acids can be set free, as, for instance, 
 in the presence of free H2SO4 ; nor should any other mixture 
 that can evolve chlorin be allowed to come in contact with the 
 crucible under conditions that make such evolution possible. 
 9 
 
130 ELEMENTS OF CHEMICAL ANALYSIS. [§ 1 24. 
 
 At ignition temperatures platinum should not come in contact 
 with any easily fusible metal, or with any mixture of a salt of 
 such a metal and a reducing agent. 
 
 After a platinum dish or crucible has been used for an igni- 
 tion, the outside should be polished down by rubbing with sea 
 sand on the moistened fingers till the surface is bright. If by 
 this treatment the surface of the platinum is scratched, the sand 
 is not suitable for this use, its grains not being sufj&ciently 
 rounded by attrition. 
 
 124. The quantitative note book. This book is to be provided 
 by the student for recording all the notes of the work done in 
 the quantitative laboratory. In it are to be made the original 
 entries of the results of the qualitative analysis of the substance, 
 if such analysis is required ; a brief statement of the method of 
 determination followed ; answers to the questions on the method, 
 if such are given out ; all the figures of the weighings, or the 
 volumetric read^gs ; and the calculations and results. In short, 
 it is required, in the author's laboratory, that a full and orderly 
 record of every analysis shall be given in this book, ready 
 for inspection at any time. The manner in which it is desired 
 that these records shall be entered is illustrated below. 
 
 Before beginning the actual work of the analysis, the written 
 questions ar.e to be answered, if any are issued. The student is 
 not prepared to make a successful quantitative determination till 
 he understands the reason for every step-in the work and every 
 precaution mentioned ; hence this requirement. When, as in 
 more advanced work, questions are not given, he should still 
 study the directions no less carefully, and work out the equation 
 for every unfamiliar reaction. 
 
 The beginner in this work will find the aeeded information 
 for the answers to the questions under the description of each 
 determination, or in Part II on qualitative analysis. The more 
 advanced students will need to consult the larger works in the 
 chemical library, such as those of Fresenius. In his quantita- 
 tive analysis, that author describes the properties of the products 
 of the determinations under the running title " Forms ; " the 
 manner of making the determinations under the title " Deter- 
 mination ;" and under the title "Separation," the special 
 methods of separating the substances from one another, when 
 present together in a mixture or compound, preparatory to their 
 determination. Answers to questions or inquiries, not indicated 
 under any of these heads, must be sought for in other works of 
 reference in the library. 
 
§ 125.] MISCELLANEOUS MATTERS. I3I 
 
 This note book is the property of the student. If neatly and 
 honestly kept, and for the time given to the practice showing a 
 large amount of work, with good results and few errors, and full, 
 intelligent and carefully written notes and references on the 
 work, it may be more useful than any letter of recommendation, 
 by the evidence it gives of the actual quantity, kind, and quality 
 of the work accomplished as a student. 
 
 125. Sample pages of records of a gravimetric determination. 
 
 Substance No. 10 (magnesium carbonate). 
 
 Received March 15th, 1890. 
 
 Qualitative Analysis (if called for). 
 
 Found : Mg. COj. 
 
 Quantitative Analysis. 
 
 Determination of Mg : 
 Method : 
 (Give here all references consulted.) 
 Answers to questions (if called for, or suggested by the -work). 
 
 Det. 2. 
 
 I. 
 
 
 2. Etc. 
 
 
 Mg; Det. i. 
 
 
 Vial + s, 
 Less s, 
 
 5-6643 
 4-8231 
 
 Subst. 
 
 .8412 
 
 Cr + ppt. 
 Cr. 
 
 16.8794 
 16.2486 
 
 "•• Ppt. 
 
 Less ash. 
 
 .6308 
 
 
 .6302 
 
 Calculation of results : 
 
 
 Det. I. 
 
 
 Mg,P,0, : 
 222.6 : 48 
 
 2Mg = .6302 : X 
 .6 = .6302 : X 
 
 X X 100 
 .8412 
 
 = Per cent. Mg. 
 
 Det. 2. 
 
 (Work the above calculations out by logarithms, putting all 
 the figures down here.) 
 
132 ELEMENTS OF CHEMICAL ANALYSIS. [§ 1 26. 
 
 A volumetric determination ; iron by dichromate. 
 
 The record should be about as follows, with such modifications 
 as may be necessary in individual cases. 
 
 Give first all the preliminary matter as indicated at the head 
 of the preceding page. 
 
 Det. I. Det. 2. 
 
 Vial + s, 6.7304 
 
 " less s, 5-8613 
 
 Subst., .8691 
 
 St. sol. required, 15.6 c.c. 
 I c.c. = 0.01713 gm. Fe. 
 15.6 X 0.01713 X 100 
 
 = per cent. Fe. 
 
 .8691 
 
 (Work this out by logarithms, giving all the figures here.) 
 
 If two or more constituents of a substance are determined, 
 making a complete analysis, sum up the work as follows : — 
 
 Summary of results on feldspar. 
 
 I. II. III. 
 
 AljOj 64.13 64.25 
 
 KjO 18.40 18.21 18.56 
 
 SiO, 16.91 16.80 
 
 99.44 99.26 
 
 126. Miscellaneous maxims. The best economy of time is 
 secured by doing the work as carefully as possible, from first to 
 last. All analytical processes are affected more or less by condi- 
 tions beyond control, none of them being absolutely perfect. 
 The strict observance of all known rules and precautions is there- 
 fore the more essential for the best success in the work. The student 
 who values his time cannot afford to disregard a single one of 
 the general directions and precautions for the management of 
 his work, given in the preceding pages, or of the special direc- 
 tions and precautions given in the description of each determina- 
 tion. Repetition of work made necessary by poor results hastily 
 obtained consumes more time than is required to do the work 
 carefully in the first instance, and, moreover, makes the record 
 poor. 
 
 Be always on the watch to exclude from the work in hand, 
 in all its stages, the accidental addition to it of any substance, 
 solid or in solution, that does not belong there, or the loss of 
 any of the substance to be weighed or measured. 
 
§ 12 6.] MISCELLANEOUS MATTERS. 1 33 
 
 Make duplicates of every determination, and further repetitions 
 if results do not agree on the first two. A single determination 
 is of little value till confirmed by another giving practically the 
 same result. In the case of every analysis undertaken, the 
 student should consider that he is to learn for himself, as 
 correctly as he can, what the actual proportion is in the 
 substance of the constituent that he is called upon to determine, 
 or the actual composition of the substance as a whole if that is 
 required, before making any report. This knowledge he has 
 not gained if the results that he has obtained are discordant. 
 
 Many students make the mistake in this matter of supposing 
 that if the fitst two determinations do not agree sufficiently well, 
 another two must be made, and then perhaps even another two. 
 An analytical method is worth little if only by carrying through 
 two analyses simultaneously, concordant results can be obtained. 
 The right course is this : the first two determinations do not 
 agree ; if the work has been done with reasonable care one of 
 them is probably correct; make one more determination to 
 ascertain which one of the first two is correct. But if the first 
 two results and this third are all widely apart and otherwise 
 incorrect, it is fair to presume that the student is working 
 carelessly, and that he must reform his ways of working in 
 general, paying more scrupulous attention to the general direc- 
 tions for quantitative work in Part III of the text-book, or to the 
 special directions given for each determination. After reading 
 this matter over again, carefully, he may as well begin anew on 
 the analysis that has made him so much trouble. 
 
 Be orderly, and scrupulously clean. There is no excuse what- 
 ever for slovenliness and disorder in respect to apparatus or 
 work-table. Better work can surely be done under a neat and 
 orderly system than otherwise. 
 
 Avoid use of unnecessarily large quantities of reagents. Avoid 
 the use of unnecessarily large beakers or flasks ; when precipi- 
 tates are to be filtered from them, the larger the vessel the 
 larger the surface to be washed in transferring the precipitates to 
 the filter. 
 
 Be sure that your solution is of about the right degree of con- 
 centration before beginning any operation with it ; it may be 
 too late after reagents are added. 
 
 Without careful planning of the work, very much time is 
 easily spent in accomplishing but little. In estimating the 
 capacity of a student in the laboratory, account must be taken 
 
134 ELEMENTS OF CHEMICAL ANALYSIS. [§ 1 26. 
 
 of the amount of work done, as well as of its quality. Celerity 
 is important, as well as accuracy, in all kinds of laboratory 
 practice. Always keep as many determinations in progress as you 
 can without confusion, so that you will be busily occupied with 
 some manipulation or study in connection with your work, 
 either that in hand or that to come, during all your laboratory 
 time. A slow filtration will not go on any more rapidly for 
 your watching it. Ignite and weigh your crucibles in any 
 moments of leisure ; then, kept in the desiccators, they will be 
 ready for use just when wanted, and you will not be obliged to wait 
 for your turn at the balance before you can go on with the work 
 at your own table. ♦ 
 
PART IV. 
 
 EXAMPLES FOR PRACTICE IN QUANTITATIVE 
 ANALYSIS. 
 
 CHAPTER XV. 
 
 THE DETERMINATION OF IRON AND OF SULFUR 
 TRIOXID. 
 
 127. The determination of iron. 
 
 The gravimetric method. In the gravimetric determination of 
 iron, it is nearly always weighed as ferric oxid, after precipita- 
 tion as ferric hydroxid. 
 
 Iron may be precipitated from its solutions as ferrous or as 
 ferric hydroxid, according to its state of oxidation in the solu- 
 tion precipitated. Ferrous compounds in solution, or in the 
 solid form and freshly precipitated, tend to pass rapidly into 
 ferric compounds on exposure to the air; solutions of the 
 chlorid oxidize more rapidly than those of the sulfate.' The 
 ferric compounds are much more stable than the ferrous com- 
 pounds, and they are therefore better adapted for quantitative 
 precipitation. 
 
 Ferric hydroxid, Fe(OH)j, is insoluble in water and in dilute 
 solutions of alkaline hydroxids or of ammonium salts, easily 
 soluble in acids. If precipitated with the alkaline hydroxid, 
 not in excess, a basic salt (§ 17) is obtained; if, on the other 
 hand, the alkali is in excess, some of it adheres to the pre- 
 cipitate with great tenacity, and is difficult to remove unless 
 volatile. 
 
 On ignition the hydroxid is converted to oxid ; if only super- 
 ficially dried before the ignition, there may be loss of particles 
 of the substance thrown out of the crucible by the sudden forma- 
 tion of steam from the inclosed moisture. 
 
 Ferric chlorid, volatile at the temperature of the ignition, can 
 
 13s 
 
136 ELEMENTS OF CHEMICA'L ANALYSIS. [§ 1 28. 
 
 be formed by reaction between ferric hydroxid and ammonium 
 chlorid. 
 
 Ignited ferric oxid is not easily soluble in acids. 
 
 The operation. To the solution, not less than about 200 c. c. 
 in volume, better in a porcelain dish than in a beaker, add NH^OH 
 in small excess, heat almost to boiling, let settle, decant into 
 the filter, add boiling water, and stir well ; let settle and decant 
 again ; wash in this way two op'^ree times, then transfer the 
 t whole of the precipitate to the filter, and wash with hot 
 water. Dry it thoroughly before ignition. 
 
 Give the results as Fe. 
 
 128. The volumetric method. The ready passage of iron from 
 one state of oxidation or chlorination to the other, and the 
 delicate qualitative tests that can be used to show when this con- 
 version is complete, combine to provide several very satisfactory 
 volumetric methods for the determination of this element. ' The 
 permanganate method and the dichromate method are more 
 commonly used ; in both of these the iron is first completely 
 transformed by reducing agents into the ferrous condition, and 
 it is then ascertained how much of a standard solution of the 
 oxidizing agent is required to convert it to the ferric condition. 
 If permanganate is used, the highly colored oxidizing agent 
 itself is its own indicator, a single drop of it perceptibly color- 
 ing a large quantity of solution, while the products of its decom- 
 position when reduced and held in solution are nearly colorless. 
 The only objection to this method is its unreliability in solu- 
 tions containing HClj a reaction takes place between the H CI 
 and the KMnO^, by which chlorin is set free, the manganese 
 compound being changed to manganous chlorid ; although chlorin 
 should ordinarily chlorinate ferrous salt to the ferric condition, 
 it will not readily in so dilute a solution of the iron salt as must 
 be used in this process. 
 
 Since HCl is a much more convenient solvent of iron pres 
 than H2SO4, the dichromate method, in which the presence of 
 even a large excess of this acid does no harm, is the better one 
 for general purposes. 
 
 In this method the reducing agent used to convert all the iron 
 to the ferrous condition, before the treatment with oxidizing 
 solution, is stannous chlorid ; the excess of it is removed by 
 mercuric chlorid, the presence of a moderate quantity of which 
 in the solution does not affect the result. The chromic acid is 
 Converted in this operation to chromic chlorid. 
 
§128.] IRON AND SULFUR TRIOXID. I37 
 
 The indicator used is potassium ferricyanid. This may some- 
 times contain ferrocyanid, which can be changed to the ferri- 
 cyanid by treatment of the solution with chlorin, the excess 
 of which must be removed by boiling. 
 
 The preparation of .the standard solution. To 5 grams of pure 
 KjCrjO,, approximately weighed on the reagent-shelf scales, add 
 about sperc.c. of water in a beaker, and heat the mixture on the 
 hot plate till solution is complete; cool the solution, transfer it 
 to a one-liter glass-stoppered bottle, fill the bottle up to the 
 shoulder, and mix the contents thoroughly. 
 
 Weigh out two portions of about 150 mgms. of clean plaiio' 1 
 wire, whose contents of pure iron should be determined if not 
 known (ordinarily very nearly 99.6 per cent.), dissolve the wirejn^ 
 small/covered beakers,rin about 40 c.c. of HCl with the aid of 
 a gentle heat; to the hot solution add a little SnClj dropwise and 
 with constant stirring, till the yellow color that may have been 
 present at first is entirely removed, and with care to add only a 
 small excess; dilute to about 150 c.c, cool quickly, add at once 
 HgClj, of which about 20 c.c. will usually suffice ; the precipitate 
 should be white; next proceed without delay with the addition 
 of the KaCn^Oj from a burette, till no reaction appears with the 
 KsFeCye after the test drops have been in contact for half a 
 minute. 
 
 Time will be saved, and some useful practice gained in 
 stochiometrical calculation, by figuring out in advaijce the 
 probable quantity of the standard solution that will be required, 
 and then running the solution in at once up to within 5 c.c. of 
 this amount, with constant and rapid stirring, before making any 
 tests. When first beginning to make the tests, from 0.5 to i c.c. 
 of the standard solution can be added between them; but as the 
 end is approached the quantity should be diminished till, close to 
 the end, it should be only a tenth of a cubic centimeter at once. 
 
 At this part of the operation, also, when the proportion of ferrous 
 iron in the solution has become very small, somewhat larger 
 . drops of it should be taken out for the tests. ,-'" 
 
 To make these tests conveniently, put sa«I&'of the solution of 
 KsFeCye in a test tube, and set this tube in a small beaker of 
 water ; put a drop of the solution under analysis on a porcelain 
 plate, by means of the stirring rod, and with a dropping tube 
 bring a small drop of the indicator in contact with it ; put the 
 dropping tube in the water in the beaker, thereby rinsing it for 
 the next test. In order that the progress of the reaction can b^ 
 
138 ELEMENTS OF CHEMICAL ANALYSIS. [§ 129-130. 
 
 followed, toward the end of the operation, in the gradual weak- 
 ening of the color in the tests, drops as nearly alike in size as 
 practicable should be taken for all tests, except at the close as 
 above noted, from both solutions ; and, in order that the 
 strength of the solution of the indicator in all the drops shall 
 be about the same, the water should be blown out of the drop- 
 ping tube each time before taking up a fresh portion of this 
 reagent. 
 
 When the operation is completed with both solutions of the 
 iron, calculate the value of loo c. c. of the solution in Fe as a 
 factor for permanent use. Two determinations of this factor 
 should agree within 2 mgms., if the work has been carefully 
 done. 
 
 For every determination of iron in a substance make the solu- 
 tion acid with 40 c. c. of HCl, and dilute it afterward as in 
 this operation of standardizing the solution. If it is a ferric 
 compound that is analyzed, more SnCljwill of course be re- 
 quired than in the treatment of the above solution of the iron 
 wire. 
 
 129. Assay of limonite. Supposing the ore to have been pre- 
 viously ignited to remove organic matter, which must not be in 
 the solution, proceed as follows : — 
 
 To a weighed portion of about 3 grams add 100 c. c. of HCl, 
 and boil gently in a covered beaker, in the fume closet, till the 
 residue is entirely changed to a gray sandy' Rinse the cover into ' 
 the beaker^vand make the volume of the solution up to 250 c. c. 
 in a measuring flask (§ iii). Measure out three portions of 25 
 c. c. each into beakers, add to each about 10 c. c. of HCl, and 
 proceed in the same manner as in the standardization ofthe 
 dichromate, beginning with the addition of the SnCljffusethe 
 first determination only as an approximate one, adding a cubic 
 centimeter of the dichromate between each test. Proceed in the 
 same manner with another weighed portion of the limonite. 
 Report the result in Fe, giving the average of the last two 
 determinations on each weighed portion. 
 
 130. The determination of sulfur trioxid. Sulfur trioxid in 
 salts is always determined by precipitation as barium sulfate. 
 One part of this salt requires 400,000 parts of water to dissolve 
 it ; it is appreciably more soluble in acids, even if dilute, and 
 its solubility increases with the strength of the acid. Alkaline 
 nitrates in the solution hinder its complete precipitation. 
 
 The precipitate is very fine, and often causes trouble by pass- 
 
§ I3I-J ACIDIMETRY AND ALKALIMETRY. 139 
 
 ing through the filter, especially if made in a cold solution and 
 filtered at once ; a clear filtrate is more easily obtained if HCl 
 or NH4CI is present in the solution. The precipitate readily 
 carries down with it other substances present in the solution, 
 especially nitrates, and it is almost impossible to remove some 
 of these foreign matters, even with hot water or dilute acids ; if 
 nitrates are present they must first be converted into chlorids by 
 repeated evaporation of the solution to dryness with HCl. 
 
 Barium sulfate can be ignited to redness without change, but 
 if the heat is carried up to whiteness, it loses SOa- At a red 
 heat in the presence of reducing substances it passes readily into 
 the sulfid. 
 
 The operation. To the well diluted solution, acidified with 
 HCl and heated nearly to boiling, add a hot solution of BiClj 
 slowly and with constant stirring, as long as a precipitate is 
 formed, and with tamt- care to avoid any large excess of the 
 
 ' reagent ; let the liquid stand, still kept hot but not boiling, till 
 the precipitate has nearly settled, decant the supernatant liquid 
 into the filter, pour about too c. c. of boiling water over the 
 precipitate, let settle and decant again, and repeat till the wash- 
 ings give no notable reaction for chlorids j then transfer the 
 whole of the precipitate to the filter, complete the washing, and 
 dry and ignite in the usual manner, after careful separation of 
 the precipitate from the filter. When the igniti on is completed 
 and the crucible cooled, m oisten tjii Ii iij _ m"j ilijill, i illT 
 
 ^HaSO,, dry over a very low flame, and then ignite gently. Give 
 the result as SO3. 
 
 CHAPTER XVI. 
 
 ACIDIMETRY AND ALKALIMETRY. 
 
 131. This kind of analysis, as the names imply, is the deter- 
 mination of an acid or an alkaline substance, and as commonly 
 understood it refers to their determination by volumetric methods. 
 It can be directly applied to acids only when in the free state and 
 soluble in water, and only indirectly to their determination in 
 salts. Bases can be determined by the alkalimetric methods, 
 when free, and also when in the form of carbonates. 
 
 The method consists simply in the addition of a standard solu- 
 
140 ELEMENTS OF CHEMICAL ANALYSIS. [§ I3I. 
 
 tion of a base to the solution containing the acid to be deter- 
 mined, or in the addition of a standard solution of an acid to 
 the solution of the base to be determined, till the point of neu- 
 trality is reached ; or the addition of a standard acid in excess 
 to the carbonate, and, when the salt is completely decomposed, 
 determining by means of the standard solution of the base how 
 much acid was used in excess ; this subtracted from the total 
 quantity of acid used gives the quantity required to form a neu- 
 tral salt of the basigenic constituent of the carbonate. 
 
 Any base or acid soluble in water can be used for standard 
 solution. The most convenient solutions for general use are 
 an ^ solution of ammonia, and an y solution of hydrochloric 
 acid. The presence of carbonic acid, dissolved in the liquid in 
 which an alkalimetric or acidimetric determination is made, is 
 usually objectionable, because it may interfere with the distinct- 
 ness of the color reaction of the indicator used to show when the 
 neutral point is reached. Potassium and sodium hydroxids 
 absorb carbon dioxid from the air much more readily than am- 
 monium hydroxid does ; furthermore, they act more rapidly on 
 the glass of the bottles or the burettes. A fifth normal solution 
 of HCl can be heated up to boiling without loss of strength ; 
 even a tenth normal solution of NH3 cannot be heated without 
 escape of ammonia; but as there is never any occasion in this 
 work to heat a solution containing an excess of standard am- 
 monia, this is no objection to its use. 
 
 The indicators most employed are litmus, cochineal, and 
 methyl orange ; as the preparation of a really serviceable solution 
 of litmus is difficult, it is used mostly in cases where the others 
 do not give a sharp reaction, as in the titration of organic acids. 
 
 Although the calculation of an acidimetric or alkalimetric de- 
 termination is somewhat easier if the solutions are exactly one- 
 tenth and one-fifth normal, when but small quantities are 
 required, as for this practice, it is not advisable to take the time 
 for their preparation ; it is more convenient to make solutions 
 approximating closely to the desired strength, by the aid of areo- 
 metric specific gravity determinations, and Tables, and then to 
 determine-their exact strength by other means. 
 
 If, however, it is desired to make a solution whose strength is 
 exactly equal to that of a normal solution, or to some aliquot 
 part of such strength, proceed as follows. Prepare the first, 
 approximately correct solution in such a way that it shall surely 
 be somewhat too strong. Determine its exact strength in 
 
§ 132. J ACIDIMETRY AND ALKALIMETRY. 141 
 
 accordance with the special directions given ; calculate the 
 quantity of the active constituent of the reagent in looo c. c. 
 of this solution ; calculate the number of cubic centimeters of 
 this solution, which really contains that quantity of the aptive 
 constituent of the reagent, required to make looo c. c. of solu- 
 tion of the correct strength ; then looo minus this volume gives 
 the quantity of water that must be added to this quantity of 
 the solution to make looo c. c. of a solution of the correct 
 strength. 
 
 For example : it is desired to make an exactly -I solution of 
 silver nitrate, silver being the active constituent. The first solu- 
 tion is prepared as directed above, and when its strength is 
 determined it is found to contain 22.5 grams of silver per 1000 
 C.C., 21.58 grams being the correct quantity ; the solution is too 
 strong. Then 
 
 22.5 : 1000 ; : 21.58 : 9SI.I. 
 1000 -^951.1 = 48.9. 
 
 Therefore, on adding to 951. i c.c. of the solution, which 
 quantity contains the right quantity of silver for 1000 c.c. of 
 an -g- solution of the nitrate, 4^.9 c.c. of water, we shall have 
 1000 c.c. of an f solution of the reagent. 
 
 Since of these two solutions above mentioned, for alkalimetry 
 and acidimetry, the hydrochloric acid is the more stable one, 
 more care is usually given to the determination of its absolute 
 strength than of the ammonia : the strength of the latter can 
 be verified from time to time by comparison with the acid. 
 
 132. Preparation of the standard solutions. With the aid of 
 the areometer (§ 121), and the specific gravity Tables in 
 Part V, determine the strength of the shelf NH4OH, and the 
 HCl of the laboratory. Then prepare a liter of an approxi- 
 mately one-tenth normal solution of ammonia by measuring 
 out the proper quantity of the reagent with the graduated 
 /cyliHder into a one-liter measuring flask, filling the flask up to 
 the mark with water, and mixing thoroughly by repeated inver- 
 sion of the flask. Transfer this solution to a liter glass stoppered 
 bottle ; the bottle should be rinsed out with distilled water but 
 not necessarily dried before using it. In like manner prepare 
 a liter of an approximately one-fifth normal solution of hydro- 
 chloric acid. 
 
 The determination of the relative strength of the acid and the 
 alkaline solutions. Fill one burette with one solution and 
 another burette with the other ; run 10 c. c. of the acid into a 
 
142 ELEMENTS OF CHEMICAL ANALYSIS. [§ I33. 
 
 ^smaiy beaker, add enough of the indicator (about 0.5 
 of cochineal or litmus, or three or four drops of the methyl 
 orange) to give a decided color to the solution, put the beaker 
 on a large sheet of white paper in a good light, and run in 
 ammonia with constant stirring, till the proper change of color 
 appears, produced by, at the most, two or three drops of the 
 solution ; if it is feared that too much may have been added, 
 0.1 to 0.2 c. c. of acid may be run in to restore the original 
 color ; then add ammonia again. By repeating this operations 
 several timej/fcack and forth, the point of neutralization can Ve 
 very acccurately determined. If-g h arp reoultc arc not obtained 
 with ,nnp indicator, try anothe r. Note the total quantities of acid 
 and ammonia used, and repeat the operation with^^ig^. c. por- 
 tions of acid till closely agreeing results are obtained. Finally, 
 calculate the quantity of acid required to neutralize one cubic cen- 
 timeter of ammonia solution and the quantity of ammonia 
 solution required to neutralize one cubic centimeter of the acid 
 solution. I-f all the preliminary measurements and the rest of 
 the work have been carefully performed, the acid should prove 
 to be very nearly twice as strong as the ammonia. 
 
 133. The determination of the absolute strength of the solution 
 of acid. This determination is made by precipitation with silver 
 nitrate, and weighing the chlorid obtained. 
 
 The precipitate of AgCl is white, and mainly flaky, while a 
 part of it remains quite persistently in a finely divided form that 
 passes easily through the filter ; but on vigorously shaking or 
 stirring the liquid containing the precipitate, the fine portion 
 becomes attached to the flocculent part, and the liquid clears 
 more readily on standing, especially if it is hot and contains 
 AgNOs, in excess, instead of HCl. It is very insoluble in 
 water and in HNO3, soluble in traces in HNO3, more soluble in 
 HCl ; it is appreciably soluble in solutions of other chlo- 
 rids, and of nitrates, including silver nitrate; much excess of 
 this last mentioned reagent should therefore be avoided in the 
 precipitation. 
 
 On exposure to sunlight, and especially the direct rays, it 
 turns violet, losing chlorin, and forming, AgjCl ; the change is 
 superficial, but it may affect the weight of the product if 
 allowed to go too far. When gently ignited it fuses to a yellow- 
 ish liquid, without decomposition. 
 
 The operation. .Procure a 130-150 c. c. Erlenmeyer flask, a 
 good cork that when properly softened fits tightly in its mouth, 
 
§ 1 33- J ACIDIMETRY AND ALKALIMETRY. 143 
 
 and a amafl piece of black cloth to protect the precipitate from 
 the light. To 25 c. c. of the standard solution in this flask, add 
 about I c. c. of HNO3, 75 c. c. of water, and then AgNOj, 
 slowly and with constant agitation of the solution by moving 
 the flask gently in a small circle, while resting on the table, till 
 the reagent is in slight excess. 
 
 Since it is very necessary that this excess of the reagent should 
 be present, and the reaction be completed before the precipitate 
 is collected together in the manner described below, time will 
 be saved by making a preliminary calculation of the quantity of 
 silver nitrate required ; see § 114. This is easily done, since the 
 strength of the standard solution is very nearly known, and that 
 of the reagent is given in § lAjrf The precipitate settles so" 
 slowly'hat it is very difficult to determine in the usual manner ■ 
 when enough of the precipitant has been added. •? 
 
 Cork the flask, wrap it in the black cloth/and shake the con- - 
 tents vigorously for about five minutes ;-Dy this operation the 
 precipitate is flocculated, and it will settle very quickly, leaving 
 a supernatant liquid that must be entirely free from turbidity; 
 if it is not, the shaking must be repeated. The filtration should 
 not be attempted till a perfectly clear supernatant liquid is 
 obtained. 
 
 When all is ready for the filtration, by a quick movement of 
 the flask while held in the. hand, throw some of the clear liquid 
 up against the cork, and repeat this till the particles of the pre- 
 cipitate adhering to the cork and the neck of the flask are com- 
 pletely rinsed down : transfer the precipitate at once to the care- 
 fully prepared and rather thick Gooch filter ; the mass on the 
 filter becomes very compact and somewhat fissured; stir and 
 break it up fine, with the rod, with care not to penetrate so far 
 as to disturb the asbestos, and wash with cold water containing 
 about one hundredth of its volume of HNOs, till fifteen or 
 twenty cubic centimeters of the washings give no turbidity with 
 two or three drops of HCl. If during the washing the wash- 
 water becomes turbid, it must of course be passed through the 
 filter again ; it is well to empty the filtering flask frequently, as 
 mentioned in § 115, so that at no time will it be necessary to 
 filter again more than a small quantity of liquid. If any fissures 
 appear in the mass on the filter during the washing, close them 
 in the same manner as at first. — ^.^ 
 
 Dry the precipitate for two or three hours at iio°-i2o° j/then 
 ignite it, at first very gently for a few minutes, with crucible 
 
144 ELEMENTS OF CHEMICAL ANALYSIS. [§ I33. 
 
 ■ covered, and then more strongly till i t just beging to fuse. This 
 ' last part of the operation should be performed with the crucible 
 e/imcovered, so that its progress can be closely watched ; the cru- 
 cible should be laid as far over on its side as possible, and the 
 
 ■ lamp, with a high flame turned on, should be moved in and out 
 ; under the side of the crucible till fusion begins, not only in de- 
 ' tached portions of the chlorid in that part of the crucible directly 
 
 exposed to the flame, but also on the edges of the main mass of . 
 the substance on the asbestos. 
 
 A better way is to hold the crucible by the tongs, in a still 
 more nearly horizontal position, and by a motion of the hand 
 and arm turn it over and back, so that it will be heated on dif- 
 ferent sides while holding it in the flame ; thus danger of over- 
 heating any portion of the chlorid is more easily avoided. When 
 the crucible is thus heated on its sides and only when in a hori- 
 zontal position, or nearly so, and the flame is not at any time 
 allowed to impinge directly agalinst the bottom, the fused chlorid 
 will not^run through or arpynd^ the_ asbestos to the platinuin 
 disk.(( 
 
 Repeat the operation with 6ther portions of the acid till con- 
 cordant results are obtained.' The fused silver chlorid can be 
 loosened from the asbestos arid the disk of platinum by digestion 
 with HCl while in contact with pieces of zinc."^ 
 
 Now calculate the mgms. of HCl in one cubic centimeter of 
 the standard acid : and, knowing the exact relation between this 
 acid and the standard ammonia, calculate the absolute strength 
 of this alkaline solution, Or the number of milligrams in one 
 cubic centimeter. Next, for practice, calculate the value of 
 one cubic centimeter of the acid in sodium carbonate, potas- 
 sium carbonate and calcium carbonate, and the value of one 
 cubic centimeter of the ammonia solution in sulfur trioxid 
 and nitrogen pentoxid. It now remains to test the accuracy 
 of this work in the preparation of these standard solutions, by 
 tTthe analysis of test substances. 
 
 If the substance is a carbonate, a?hiv.>_vvater, which will 
 dissolve it if an alkaline carbonate; add the . indicator, and 
 ^then standard acid very slowly and with constant stirring, till 
 plainly in excess, with the substance itself entirely dissolved. 
 If it is a carbonate insoluble in water, this solution in the acid 
 will take place rather slowly, especially towards the end, unless 
 a large excess of acid is used, which is unadvisable. 
 
 Before titration back with ammonia in the case of a carbon- 
 
§ 1 34-] LEAD, PHOSPHORUS PENTOXID AND CALCIUM. 1 45 
 
 ate, the solution should be heated just to boiling, in a covered 
 beaker, and^kept boiling gently for about five minutes._) The 
 cover and sides of the beaker are then rinsed down with water, 
 and the liquid cooled. 
 
 In all this work be careful not to dilute the solution of the 
 substance to be determined, too much ; the volume should not 
 exceed loo c. c. when the liquid is ready for the titration, and 
 should be within 75 c.c. if practicable. 
 
 TTHAPTER XVII. 
 
 THE DETERMINATION OF LEAD, PHOSPHORUS PENTOXID 
 
 AND CALCIUM. lODOMETRY. DETERMINATION OF 
 
 ANTIMONY. 
 
 134. The determination of lead. Lead is most conveniently 
 determined as lead sulfate. This salt is nearly insoluble in 
 water, more insoluble in water containing sulfuric acid, much 
 more soluble in HjSOi and HNO3, and in water containing 
 ammonium salts in solution, especially the nitrate, acetate or 
 tartrate ; it is insoluble in alcohol. Ignited, at a red heat it is 
 unchanged, but at a white-heat gives off SOs; it is easily reduced 
 at ignition temperatures in contact with incompletely burned 
 combustion products, the metal separating out ; the filter upon 
 which it has been collected cannot, therefore, be wrapped in 
 platinum wire for the ignition (§ 123). 
 
 The operation. To the solution, which should not be concen- 
 trated, add H2SO4 in slight excess ; if nitric acid or a nitrate is 
 possibly present, evaporate the solution down nearly to dryness 
 on the water-bath, leaving the beaker uncovered ; when taken 
 from the bath, the liquid should not give any odor of nitric acid. 
 If hydrochloric acid or a chlorid is possibly present, the solution 
 must receive the same treatment. These obstacles to complete 
 precipitation of the lead as sulfate being removed, add about 50 
 c.c. of water to the residue in the beaker, and after stirring well 
 add about 100 c.c. of alcohol; let the mixture stand for a few 
 hours, filter, wash with alcohol, and dry. Transfer as much of 
 the precipitate as possible from the filter to a crucible, in the 
 usual manner and ignite gently. Fold the filter up and burn it 
 directly in another crucible, heating at first very gently with the 
 
146 ELEMENTS OF CHEMICAL ANALYSIS. [§ 1 35. 
 
 cover partly on, and complete the ignition in the usual manner ; 
 when the crucible is cool moisten its contents with HNO3, 
 evaporate to dryness at a gentle heat, moisten the residue with 
 H2SO4, dry and ignite gently. Add the two weights of substance 
 obtained and calculate the result as Pb. 
 
 For a somewhat shorter method, requiring but one weighing of 
 substance, and much more careful manipulation, but permissible 
 only where there are no currents of air, see Fresenius, § 52. 
 
 135. The determination of .phosphorus pentoxid. Phosphorus 
 pentoxid is nearly always weighed as magnesium pyropho^hate, 
 MgjPjO,, after precipitation as magnesium-ammonium phosphate, 
 MgNHjPOi.eHjO. This salt forms a white, crystalline powder, 
 slightly soluble in water, easily soluble in acids, less soluble in 
 water containing ammonia, less insoluble if ammonium chlorid 
 is also present, easily soluble in acids. Excess of magnesium 
 sulfate increases the insolubility in ammoniated water, but unless 
 much ammonium chlorid is present, magnesium hydroxid, or a 
 basic magnesium sulfate is liable to be precipitated also \ excess 
 of sodium phosphate diminishes the solubility of the precipitate. 
 
 Heated to 100° the water of crystallization escapes, and on 
 ignition, the ammonia also ; too rapid heating, producing a 
 sudden evolution of the ammonia, may cause a loss of sub- 
 stance mechanically. The pyrophosphate is white or grayish, 
 often quite dark in color, unchanged at a white heat, easily 
 soluble in acids. 
 
 The operation. To the solution containing in 75 c. c. about 
 500 mgms. of phosphorus pentoxid, as nearly as can be esti- 
 mated from previous knowledge of the composition of the sub- 
 stance to be analyzed, add about 5 c. c. of ammonia, or till in 
 excess, and then with constant stirring and care not to touch 
 the side of the beaker with the rod, add the magnesia mixture 
 drop by drop, most conveniently from a burette, at the rate of 
 about a drop per second ; 20 c. c. of the reagent will usually be 
 sufficient, if the quantity of the substance present has not been 
 underestimated. Let the mixture stand three or four hours before 
 filtering. Filter and use water containing one-fourth its volume 
 of ammonia for cleaning the beaker and washing the precipitate ; 
 wash till the chlorin reaction disappears, or is at least no stronger 
 than is given by a few drops of the washing solution added to 
 half a cubic centimeter of silver nitrate acidified with HNO3. 
 
 It is often necessary to complete the ignition over the blast- 
 lamp,, if a nearly white residue cannot be obtained by the 
 
§ 136-] LEAD, PHOSPHORUS PENTOXID AND CALCIUM. 147 
 
 ordinary treatment ; after one ignition over a Bunsen lamp, if 
 the product is not white or nearly so, moisten it with a drop of 
 HNO3, and dry very carefully over a low flame, then ignite 
 strongly over the blast-lamp and weigh ; if the residue is still 
 not nearly white, repeat the treatment with HNO3 and the igni- 
 tion, and weigh again; if the loss in weight is null, or insignifi- 
 cant, do not carry the operation any further, but report the result 
 obtained, with a statement of the condition of the precipitate. 
 Give results as P2O5. 
 
 136. The determination of calcium. For the determination of 
 calcium it is usually precipitated as the oxalate ; with this pre- 
 cipitate four courses may be taken. It may be dried at 100° till 
 the weight is constant, the product then having the composition 
 jjii I II 111 I11111 ; it may be ignited very carefully and weighed as 
 carbonate, or ignited very strongly and weighed as oxid ; its 
 complete conversion into carbonate without carrying a little of 
 it on to the oxid is somewhat difficult ; and it is even more 
 difficult to convert a large quantity of the oxalate completely 
 into oxid. 
 
 Therefore another course, which is open to none of these 
 objections is described here, namely, the volumetric method, 
 with potassium permanganate ; this reagent causes the. conversion 
 of all the oxalic anhydrid into carbon dioxid, as the result of a 
 process of oxidation in the mixture in which the reaction is made 
 to take place. ^P 
 
 Calcium oxalate, CaC204.2H20, forms a white, very fine, 
 crystalline precipitate, insoluble in water, and in s olutions ^ 
 alkaline chlorids, easily soluble in mineral acids; /ignited, it 
 passes into the carbonate at a moderate heat, and into the oxid 
 at a high heat. 
 
 The precipitation. To the hot solution, of about the average 
 degree of dilution, and containing, as near as may be estimated 
 from previous knowledge of the composition of the substanc e to b e 
 analyzed, about 100 mgms. of calcium, add ammonia till in 
 moderate excess, and (NH4)2C20/Vith constant stirring, till no 
 ■ further precipitation takes pla^, and let the mixture stand for 
 several hours in a warm place. 
 
 Decant the clear liquid into a weighed Gooch filter, with as 
 little disturbance of the precipitate as possible, wash several times 
 with hot water by decantation, and finally transfer the precipitate 
 itself to the filter; wash the precipitate till no further reaction is 
 obtained for oxalic acid in a test with 5 c. c. of the washings. 
 
148 ELEMENTS OF CHEMICAL ANALYSIS. [§ 1 3 7. 
 
 Unless a very carefully prepared filter is used, and all these 
 directions are followed, there may be difficulty in getting a clear 
 filtrate. 
 
 Dry the crucible and contents to constant weight, at 100° 
 C, and calculate the result as Ca. 
 
 137. Volumetric determination of the. calcium in this pt\: \ >ipiiatt . 
 Make an approximately ^ solution of KMnO^ (see § 108), 
 and standardize it by means of ferrous oxide in the form of 
 ammonium ferrous sulfate, FeSOj. (NH4)2 SO4 + 6H2O, taking 
 carefully weighed portions of about i gram each. Dissolve 
 the salt in about 200 c. c. of water, add at once about 10 c. c. 
 of H2SO4, and, with the beaker on a white tile or plate, add the 
 permanganate from a glass-stoppered burette, dropwise, and with 
 constant stirring. At first the color of each drop disappears 
 immediately, and then more and more slowly ; towards the end 
 of the operation, add the drops very slowly, with stirring between 
 each, till the color disappears ; the end point is reached as soon 
 as the last drop added gives to the whole of the solution an 
 unmistakable faint reddish tinge. This color may be permanent 
 only for a very few moments, but nevertheless the ferrous iron is 
 completely oxidized, and the reaction is cgttipleted. Repeat 
 till closely agreeing results are obtained. 
 
 The equation is given in the section above referred to, for the 
 reaction betweei^he ferrous oxid and permanganate. In the 
 actual operation](PR ferrous oxid is present in the form of sul- 
 fate, and in the presence of the H2SO4 added we have sulfates in 
 the right-hand member of the equation instead of oxids ; but 
 this does not affect the process of oxidation in any other way 
 than to facilitate it. The equation shows that ten atoms of Fe 
 in the form of ferrous salt are converted into ferric salt by the 
 oxygen yielded by two molecules of KMnOj. 
 
 From the formula of the ferrous salt used, calculate the 
 quantity of Fe in the weight of salt taken, and then from the 
 results of the titration calculate the exact strength of the KMnOi 
 solution. Then calculate the value of one cubic centimeter of 
 this solution in CaCjOij for the equation for this reaction 
 between the KMnOj and CaCjOj, take five molecules of the 
 oxalate and two of the permanganate, with the necessary 
 quantity of H2SO4; the products of the reaction are calcium 
 sulfate, manganese^ sulfate, potassium sulfate, carbon dioxid and 
 water ; then calculate the quantity of calcium in this quantity of 
 calcium oxalate, and thus obtain the value of i c.c. of the 
 
§ 138-] lODOMETRY. 149 
 
 permanganate in calcium. Or the value of the permanganate in 
 Ca can be calculated directly, without first calculating its value 
 in calcium oxalate. 
 
 Now determine the quantity of calcium oxalate in the pre- 
 cipitate obtained artd woighc d above/by the same kind of an 
 operation as that performed in standardizing the permanganate ; 
 to this end, transfer the precipitate with the asbestos to a beaker, 
 add about loo c.c. of water, and 50 c.c. of H2SO4, warm to 
 about 60°, and then titrate with permanganate. 
 
 Give the result in Ca. 
 
 138. lodometry. 
 
 This method of volumetric analysis depends upon the action 
 of iodin as an indirect oxidizing agent. In the presence of 
 water hydriodic acid is formed, while oxygen in its nascent state 
 acts on any oxidizable substances present. 
 
 HjSOj (sulfurous acid) -\-\^-\- H^O = H^SO^, + 2HI 
 K3ASO3 (potassium arsenite) + 12+ HjO = KgAsO^ + 2HI 
 
 If the substance combined with the hydrogen is not readily 
 oxidized it may be set free. 
 
 H3S+l2 = 2HI + S 
 
 Iodin may be set free in a solution of potassium iodid by a 
 
 substance capable of displacing it from its combination with the 
 
 metal. 
 
 KI + CI = KCl + I 
 
 The extreme delicacy of the reaction of free iodin with starch, 
 and the sharpness of its reaction with thiosulfate, give the means 
 for measuring the quantity of free iodin in a solution with excep- 
 tional accuracy. 
 
 The reaction with sodium thiosulfate is as follows : — 
 
 aNajSjOj +12 = Na2S405 (sodium tetrathionate) + 2NaI. 
 
 The preparation of the solutions. 
 
 Iodin in potassium iodid. For 500 c.c. of an — solution dis- 
 solve about 12 gms. of potassium iodid in about 200 c.c. of 
 water ; weigh out about 6 gms. of powdered iodin in a covered 
 watch glass, and at once put it into a glass-stoppered measuring 
 flask, rinsing the glass into the flask with some of the iodid solu- 
 tion ; add the remainder of this solution, and shake up the contents 
 of the flask frequently till the iodin is completely dissolved, using 
 no heat; make the solution up to 500 c.c. with water, and mix 
 
150 ELEMENTS OF CHEMICAL ANALYSIS. [§ I39. 
 
 as usual. If a larger quantity of the solution is made it should 
 be put into a number of 250 c.c. bottles, nearly filled ; in this 
 manner it may be kept unchanged in strength for a long time. 
 
 Sodium thiosulfafe. Dissolve 12.4 gms. of the pure and well 
 crystallized salt in 500 c.c. of water, previously boiled to expel 
 CO2 in solution. If this solution is kept in a cool, dark place, 
 its strength will remain unchanged for a considerable time. 
 
 The starch solution. To about a gram of powdered starch add 
 about 100 c.c. of water with constant stirring, and heat the mix- 
 ture, with continued stirring, to boiling ; let cool, and pour off 
 the nearly clear liquid from the sediment. The solution is not 
 permanent, and should be fresh when used. 
 
 Standardizing the iodin solution against the thiosulfate. To 20 
 c.c. of the latter solution, run from a burette into a beaker, add 
 three to four c.c. of the starch solution, and then iodin solution 
 from a glass-stoppered burette, slowly and with constant stirring, 
 till the whole of the liquid is colored blue by the last drop added. 
 Repeat till closely agreeing results are obtained. 
 
 The standard of the iodin solution. Break up some crystals of 
 pure sodium thiosulfate to a coarse powder, dry this over sulfuric 
 acid for a short time, then pulverize the effloresced residue very 
 fine, and dry it for several days over sulfuric acid, with a watch 
 glass containing pieces of potassium hydroxid to absorb any 
 carbon dioxid that might be present and act on the salt. Take 
 about 200 mgms. of the powder for each test, dissolving it in 
 about 20 c.c. of water. Calculate the iodin in one c.c. of the 
 solution. 
 
 139. Determination of antimony, in the form of antimonous 
 oxid. _ / 
 
 SbjOj 4^Ij -t-^Na,0 = SbjOj -f-^Nal. 
 
 The oxidation must take place in an alkaline solution, and in 
 the presence of a large excess of alkaline carbonates. Fresenius 
 gives the following directions, which are to be found also in 
 Fleischer's Titrirmethoden. 
 
 Dissolve a quantity of the substance containing about 100 
 mgms. of antimony in about 10 c.c. of a solution of tartaric acid 
 (one to ten), add sodium carbonate till the solution is nearly neutral, 
 and about 20 c.c. of a cold saturated solution' of sodium bicar- 
 bonatey then the starch, and finally the iodin solution, dropwise 
 -and with constant stirring, till the whole of the liquid assumes a 
 briefly permanent blue color ; that the color disappears after a 
 
§ 140.] ANALYSIS BY ELECTROLYSIS. 15 1 
 
 little time is not to be taken as an indication that more iodin 
 solution is required. Fleischer commends the usefulness of this 
 determination, since antimony can be precipitated as tersulfid 
 from any of its compounds ; and after dissolving the precipitate 
 in HCl, boiling out the hydrogen sulfid, adding tartaric acid 
 and the alkaline carbonates as above directed, the solution is 
 ready for the titration. 
 
 CHAPTER XVIII. 
 
 ANALYSIS BY ELECTROLYSIS— SEPARATION AND DETER- 
 MINATION OF SILVER AND COPPER. 
 
 140. Method I (Classen's). Silver oxalate, precipitated by 
 (NH4)2C204 is insoluble in excess of the precipitant, while copper 
 oxalate is soluble. The two metals are separated by this reaction 
 and subsequent filtration, the silver oxalate is dissolved in potas- 
 sium cyanid, and each solution is electrolyzed separately. 
 
 The re-solution of the copper oxalate in excess of the reagent 
 is easy, but since the silver oxalate settles very slowly, it is 
 difficult to decide when the precipitation is complete, and when 
 the addition of the ammonium oxalate in excess really begins, or 
 when, in the solution colored bluish-green by the dissolved copper 
 salt, the undissolved residue consists only of the white silver salt. 
 It is better, therefore, to estimate by calculation, or ascertain by 
 experiment, how much of a cold saturated solution of the pre- 
 cipitating reagent is required to effect a complete reaction : any 
 excess of the reagent does no harm. For a solution containing 
 about 500 mgms. of copper and silver together, 60 to 70 c. c. of 
 the saturated oxalate solution will be enough, even if copper 
 predominates very largely ; the larger the proportion of silver, 
 the less oxalate will be needed. 
 
 Classen's arrangement of electrodes consist of a platinum dish 
 for the cathode, with vertical sides, holding about 225 c.c, 
 and for the anode a platinum disk 4.5 cm. in diameter, pierced 
 with several holes 5 mm. in diameter, and fastened to a stout 
 platinum wire. These electrodes are supported on a stand, with 
 a glass post carrying a brass ring for the dish and a short rod 
 for the disk, with binding screws for connection with the bat- 
 tery. The wire fastened to the anode passes through a small 
 
152 ELEMENTS OF CHEMICAL ANALYSIS. [§ I40. 
 
 hole in the centre of a cover-glass ; the platinum dish is filled 
 with the solution to such a level that, when the cover is in 
 place, the lowest part of its convex surface is in contact with the 
 liquid directly over the anode, and for an area a little larger than 
 that of the anode ; thus all spattering of the liquid on to the 
 cover from the bubbles of gas evolved at the anode is avoided, 
 and also the consequent necessity for rinsing the cover into the 
 dish towards the close of the operation. 
 
 The most convenient source of the current is a storage battery. 
 
 The analysis. Dissolve about 500 mgms. of the alloy in di- 
 lute nitric acid, evaporate almost to dryness on the water bath, 
 add 15 c.c. of water, evaporate again almost to dryness, and 
 add 50 c.c. of water to the residue. A clear solution, contain- 
 ing very little free acid, should result. To this add 60-70 c.c. 
 of a cold, saturated solution of ammonium oxalate, allow the 
 precipitate to settle, filter, and wash first with ammonium ox- 
 alate, and then with cold water. 
 
 Dissolve this silver oxalate in a solution of pure potassium 
 cyanid, transfer the solution to the weighed platinum dish, 
 make its volume up as directed above, and precipitate the 
 silver with a current corresponding to 0.2 to 0.5 c.c. of oxy- 
 hydrogen gas per minute. Before disconnecting always ascertain 
 whether the precipitation is complete ; for this purpose add to 
 the contents of the dish enough water to raise the level of the 
 liquid about 2 mm., and then allow the current to flow half an 
 hour longer ; if no silver is deposited on the walls of the dish 
 above the level of the first solution, the precipitation is com- 
 plete. Confirm by testing with HCl. 
 
 Remove the cover-glass and anode, pour out the liquid in the 
 dish quickly, and wash the deposit first with water ; holding a 
 wash-bottle mouth lowermost, and with the outer arm of the 
 mouth tube nearly horizontal and very near the inner rim of the 
 dish, direct the stream of water from the mouth-tube on to the 
 inside of the dish above the deposit, while revolving the dish in 
 such a manner as to bring this impact of the water in an oblique 
 direction against the whole circumference of the rim ; pour this 
 water out, and repeat the operation three times. Then wash 
 three times with strong alcohol in the same manner. Remove 
 the last portions of alcohol by blowing into the dish while held 
 in the haijd, dry for an hour in the desiccator, and weigh. 
 
 Determination of the copper. Evaporate the filtrate and 
 washings from the silver oxalate down to about 150 c.c. if the 
 
§§ I4I-I42-J ANALYSIS BY ELECTROLYSIS. 153 
 
 volume is much larger than this, transfer at once to the weighed 
 platinum dish, add 20 c.c. of a cold saturated solution of am- 
 monium oxalate, and electrolyze with a current of the same 
 strength as above. Test for complete precipitation as directed 
 for the silver determination, and also by taking out about one c.c. 
 of the liquid with a small pipette and applying the ferrocyanide 
 test. When precipitation is complete wash and dry the dish, as 
 directed above, and weigh. 
 
 141. Method 2. Precipitation and determination of the silver 
 as chlorid and the copper by electrolysis. In this method the 
 less expensive platinum foil electrodes can be used, the cathode 
 being about cm. and the anode cm. 
 
 Dissolve a quantity of the substance containing 250 to 300 
 mgms. of the metals in water, or in HNO3 if the substance is 
 metallic. In this last case evaporate the solution down till 
 fumes of nitrous acid are no longer evolved, add about 75 c.c. 
 of water and then HCl as long as a precipitate is formed ; 
 make this addition and carry out the subsequent operations as 
 directed for the estimation of HCl in § 133. The liquid will 
 not clarify so readily as in that operation, HCl being in excess 
 instead of silver nitrate. 
 
 Since the filtrate is to be used for the estimation of the cop- 
 per, none of it or of the washings are to be lost ; as is usual in 
 the separation of substances from one another preliminary to 
 their quantitative estimation, the filtrate and washings must be 
 concentrated by evaporation. 
 
 142. The determination of the copper. The solution must be 
 free from HCl or chlorids, and contain nitric acid as its only 
 free acid, except that a very little free sulfuric acid is permissi- 
 ble. If HCl has been added in any previous operation, or the 
 salt is a chlorid, add to the concentrated solution about 20 c. c. 
 of HNO3 and evaporate to dryness on the water bath. Take up 
 the residue with a little water and about 20 c. c. of HNO3, of 
 1.2 sp. gr., in a beaker of about 250 c. c. capacity, heating a 
 short time if necessary to get complete solution, with the beaker 
 covered, and finally add 180 c. c. of water. 
 
 Shape the electrodes into a curved form so that they will fit 
 evenly against the sides of the beaker containing the solution, 
 clean them of any organic matter by heating to redness for a 
 moment in the lamp-flame, and lay them in the desiccators ; do 
 not handle the broader parts with the fingers after they have been 
 thus cleaned. Only the larger electrode of each pair is to be 
 
154 ELEMENTS OF CHEMICAL ANALYSIS. [§ 142- 
 
 weighed, unless there is reason to suppose that a little lead may 
 be deposited on the other as PbOj, as in the analysis of brass. 
 In weighing, suspend the electrode, by the loop in its platinum 
 wire, on the hook over the balance pan. 
 
 Put the electrodes in the beaker so that they nearly touch the 
 bottom, bend the platinum wires over the edge of the beaker, 
 thus suspending each one in its place, and make the connections 
 with a current corresponding to three to four c.c. of oxyhydrogen 
 gas per minute. Cover the beaker during the electrolysis. 
 
 From twelve to twenty-four hours will be required for the com- 
 pletion of the electrolysis, with 250-300 milligrams of copper in 
 the solution. When the solution appears quite colorless, rinse 
 the cover into the beaker, add a little more water so as to raise 
 the level of the liquid by about half a centimeter, stir gently to 
 mix in the added "water, and after one or two hours observe 
 whether any copper is deposited on that part of the electrode 
 freshly immersed ; if not, confirm the test by adding aaimonia 
 to about five c. c. of the liquid till in slight excess, then acetic 
 acid till acid, and then KjFeCye; there should be no red precipi- 
 tate or coloration. 
 
 The deposition of the copper being complete, slowly raise the 
 electrode out of the liquid while it is still in the circuit, rinsing 
 it off on both sides with water as it is raised, finally leaving only 
 one corner immersed; then lift it quite out, and rinse off this 
 corner ; finally rinse off with alcohol, and dry as directed in 
 Method I. 
 
 In the place of an ordinary beaker, one with a lateral tubulure 
 near the top is often used ; the washing of the electrode is done 
 by conducting a small stream of water to the bottom of the 
 beaker, till the overflow through the tubulure is no longer acid ; 
 then the current can be discontinued without danger of redissolv- 
 ing any of the copper. 
 
PART V. 
 
 LISTS OF APPARATUS AND REAGENTS, SPE- 
 CIFIC GRAVITY AND OTHER TABLES. 
 
 143. The qualitative set of apparatus. 
 
 One apparatus, Marsh (flask, funnel-tube, rubber cork, con- 
 ducting tube, and platinum foil) ; one bottle, glass-stoppered, 
 60 c.c, with AgNOaj one bottle, glass-stoppered, with alco- 
 hol; one crucible, porcelain. No. 8; one evaporator, 
 porcelain, 70 mm. ; one package of 50 filters, 7 cm. ; one 
 package of 100 filters, 9 cm. ; one finger cap, rubber ; two 
 flasks, conical (Erlenmeyer), 60 c.c. ; two flasks, conical 
 (Erlenmeyer), 100 c.c. ; one flask, ordinary, flat bottom, 60 
 c.c; . one forceps; three funnels, 50 mm. opening ; one 
 mortar and pestle; one lamp with 60 cm. of 6 mm. rubber 
 tube; one piece plain glass, 10 x 10 cm. ; one platinum 
 cup and wire; two 10 cm. rods of glass; one sand bath; 
 one spatula of horn ; jju* ipuilgt! ; "" one stand, of iron, 
 withrings; six test-tubes, 10 cm. long ; twelve test-tubes, 
 15 era. long; one test-tube holder; one test-tube rack; 
 one test-tube brush ; three tubes, bulbed for arsenic test ; 
 one tube, dropping, drawn out at one end ; one tube, with 
 loop, for CO2, H2SO3, and HCy tests; one wash-bottle; 
 one watch-glass, 28 mm. ; one wire triangle. 
 
 144. Directions concerning the use of this apparatus. This set 
 of apparatus comprises all that is essential for the work in quali- 
 tative analysis. Some of the pieces will, of course, be broken 
 sooner or later, and may perhaps have to be replaced many 
 times during the term. The student is advised to keep his set 
 always full ; there is nothing superfluous in it, and it is mis- 
 taken economy to attempt to carry on the work with any pieces 
 wanting. 
 
 The Marsh apparatus is used only in the test for arsenic in 
 the course for the tin group. 
 
156 ELEMENTS OF CHEMICAL ANALYSIS. [§ 1 44. 
 
 Use the evaporator only for evaporating liquids ; set it directly 
 over the lamp without the intervention of a sand-bath, not more 
 than a centimeter above the mouth of the lamp tube, and turn 
 the gas down so low that the flame will not rise higher on the 
 outside than the level of the liquid within. 
 
 Use the crucible for heating the residues from evaporations ; 
 see § 47 on ignition. 
 
 "Y^xt finger cap is convenient for protecting the skin from con- 
 tact with corrosive liquids, when it is necessary to close the 
 mouth of a test-tube, to be inverted for mixing its contents. 
 
 Always use smaller filters when only small quantities of a sub- 
 stance are to be filtered out. 
 
 The flasks can be heated- over a direct flame, with the same 
 precautions as given above for heating evaporators. Consult 
 §§ S3> 54) o" digestion and boiling. 
 
 Keep the forceps entirely from contact with solutions that you 
 are analyzing, lest you may report copper and zinc incorrectly. 
 
 To light the lamp, turn on the full flow of the gas, and not 
 till after it is lighted turn it down to the desired point ; a flame 
 from five to seven centimeters high is the most suitable for ordi- 
 nary work, and should always be used except when special di- 
 rections are given for a lower or a higher flame. Be particularly 
 careful in turning the flame down very low, that it does not 
 "strike down" and burn at the little jet by the air inlets; 
 when this has taken place, the gas burns also at the mouth of the 
 tube with a pale, light-colored, slender flame, and not with an 
 almost colorless, somewhat bulging flame, without light, as it 
 should ; when burning in this way the whole lamp may become 
 hot and burn the fingers if touched ; it is to avoid this that the 
 directions are given as above for lighting the lamp. The only 
 way to set the matter right when the lamp is burning in this 
 way, is to shut the gas off' entirely and light it again in the manner 
 directed above. 
 
 Keep your platinum cup bright and clean ; fuse a little potas- 
 sium bisulfate in it, and soak the fused mass off" with hot water 
 when it cannot be cleaned by heating with HCl. 
 
 Do not bring the horn spatula in contact with strong acid or 
 alkaline liquids, or the sponge in contact with strong acids. 
 
 See § 54 about heating liquids in test-tubes. Do not have any 
 acid in the test-tube when cleaning it with the brush. 
 
 Put only sand enough in the sand-bath to fill it about one- 
 third. Put only distilled water in the wash-bottle. 
 
§§ 145-146-] APPARATUS, REAGENTS|, ETC. 157 
 
 145. The apparatus for quantitative work. 
 
 The smaller of the two sets of apparatus given below is issued 
 to students taking only the short course of quantitative work 
 laid out in Part IV, and occupying about one hundred and ten 
 hours of actual practice. The other set is issued to those taking 
 a longer course and working more hours. 
 
 There is occasional use for some expensive pieces of apparatus, 
 especially by students taking the longer course of work, which 
 are not included in these sets. In the author's laboratory these 
 can be obtained, for such temporary use, of the supply clerk, 
 checks being in all cases deposited for each piece ; any piece of 
 apparatus drawn on check is to be returned, as soon as the special 
 work for which it was required is completed, and the check is to 
 be reclaimed. Checks missing at the end of the term may be 
 charged for at a rate much above their actual cost, since, under 
 this system, they may represent apparatus of great value ; there- 
 fore it behooves the student to look after them carefully. 
 
 146. The smaller quantitative set of apparatus. 
 
 * ^wonq ^ apparatus checks; seven beakers (one 30 c.c, four 
 200 c.c, two 300 c.c); six beaker covers (two 62 mm., four 
 80 mm.) ; five bottles (one 60 c.c. with AgNOa, one 250 c.c. with 
 alcohol, two 1000 c.c, flat stoppered, one 500 c.c, wide mouth) ; 
 two burettes, 50 c.c. graduated in -^ c.c, with rubber tube, 
 glass ball, and jet ; two burette floats ; two crucibles, porcelain. 
 No. 7; uiiu eiuLl'IM, - Caldwell Gooch, - with perforated plat i- 
 num dioli ; one crucible tongs; two desiccators, with glass cov- 
 ers and triangles ; t ii vo ' e¥ap 9 ratoi ' 3, 'i ' ia"m m. ; fifty filters (25 
 for quantitative filtration, 25 common) ; tln^ flasks (one 60 
 c.c, Ipwe 250 c.c, conical, with lateral tube and rubber stopper, 
 for suction filtration) ; one forceps ; 4n»e funnels (four, usual form, 
 50 mm., ono cup ohapod fof the Gooch cruciblc j ; one lamp, 
 Bunsen, with 60 centimeters of 6 mm. rubber tube; one sheet 
 glazed paper, cut (see § 119) ; one pipette, 25 c.c, with mark on 
 neck ; one white plate ; four rods of glass ; one spatula, horn V 
 e««i*JwwiwiiW(pr ; two triangles, platinum-wrapped^ one tube, 
 dropping, drawn out at one end ; iTS»ety centimeters rubber 
 tube, 3 mm.; three test-tubes, 10 cm.; one tube, graduated ; 
 one wash-bottle (flask with rubber cork and tubes) ; two watch- 
 glasses, 38 mm. ; one wire, platinum, in glass handle ; -Gse 
 
158 ELEMENTS OF CHEMICAL ANALYSIS. [§§ I47-I48. 
 
 Also, one iron rod with two lamp rings, one rod with funnel 
 holder, and one **Q} burette holder, all for the fixed iron stand 
 on the table. 
 
 147. The larger set of apparatus. 
 
 Twenty apparatus checks; seven beakers (one 30 c.c, four 
 200 CO., two 300 CO.); ten beaker covers (two 62 mm., six 
 80 mm., two 95 mm.) ; -Jen bottles (one 60 c.c. with AgNOs, one 
 250 c.c, with alcohol, one 1000 c.c. with dis t illed water , one 
 500 c.c, wide mouth, two 250 c.c, two 500 c.c, flat stopper, 
 two 1000 c.c, flat stopper); two burettes, 50 c.c. gradu- 
 uated in Jj-, with jet, rubber tube, and glass ball ; two burette 
 floats ; *«o — con e o, — platinum^ — for — suciiuu — flllialiuii ; four 
 crucibles, porcelain (two No. 7 ordinary, two No. 6 Cald- 
 well-Gooch, ' i Tit h p r rfnnt rd plntinnm rli i1-T) ; one crucible 
 tongs; one cylinder, 100 c.c, graduated; two desiccators, 
 with glass covers and triangles ; six evaporators (two no mm., 
 two 145 mm., two 180 mm.); one hundred filters (twenty-five 
 ordinary, twenty-five 7 era., and fifty 9 cm. for quantitative 
 filtration); seven flasks (one ordinary 60 c.c, two 500 c.c. 
 Erlenmeyer, with lateral tubulure for suction filtration, two 
 Erlenmeyer, 250 c.c, two ditto, 400 c.c; one forceps; eight 
 funnels (six ordinary, 50 mm. opening, tjro cup-shape for 
 Gooch crucible ; one lamp, Bunsen, with 60 centimeters of 6 
 mm. rubber tube ; one mortar and pestle ; one sheet paper, 
 glazed, cut (see § 119); four pipettes (one 10 c.c, one 25 c.c, 
 one 50 c.c, each with mark on neck, one 10 c.c, graduated) ; 
 one white plate; eight rods, glass, 15-18 cm. long; one spatula, 
 horn ; one thermometer ; two triangles, platinum-wrapped ; 
 one dropping-tube ; ninety centimeters of 3 mm. rubber tube ; 
 twelve test-tubes (six 10 cm., six 15 cm.) ; one test-tube brush ; 
 one test-tube holder ; one test-tube rack ; one test-tube, gradu- 
 ated; two wash-bottles (one 250 c.c, one 500 c.c.) with rubber 
 corks and tubes complete; four watch-glasses (two 35 mm., 
 two 50 mm.) ; one-pair oLweighirrg ■ttri!res7-ntad>e-fr&m two test- 
 -twbe?; tinr Y ti i br ; one wire, platinum, in handle ; one wire 
 gauze, 10 cm. square ; also, one iron rod with two lamp rings, 
 one rod with funnel holder, and one flf&b burette holder, all for 
 the fixed iron stand on the table. 
 
 148. List of the reagents used in the work described in this 
 book, arranged in the alphabetical order of their full names and 
 
§ 148.] APPARATUS, REAGENTS, ETC. 159 
 
 giving, when practicable, the number of grams to be taken for 
 1000 c.c. of solution. In the case of those given in italics, refer 
 to § 150 for special directions for making the solutions. 
 
 Acetic acid, HC2H3O2. 
 
 Alcohol, C2H5OH or QHeO. 
 
 Ammonia alum. 
 
 Ammonium carbonate, (NH4)jCOs. 250 
 
 Ammonium chlorid, NH4CI. 100 
 
 Ammonium ferrous sulfate (NH4)jS04.FeS04 -(- 6H2O. 
 
 Ammonium hydroxid, NHjOH. 
 
 Ammonium molybdate, (NH4)2Mo04. 
 
 Ammonium oxalate, (NHjjCjOi -f- HjO. 75 
 
 Ammonium sulfid, (NHi)2S 
 
 (or, with excess of sulfur, (NH4)2Sj). 
 
 Aqua regia, 3 HCl, i HNO3. 
 
 Barium carbonate, BaCOs. 
 
 Barium chlorid, BaCl2 + 2H2O. 75 
 
 Barium hydroxid, Ba(0H)2. saturated solution. 
 
 Borax, NajB^O, -f- 10H2O. 
 
 Bromin (solution), Br. 
 
 Calcium carbonate, CaCOs. 
 
 Calcium hydroxid, Ca(0H)2 
 
 (or milk of lime). saturated solution. 
 
 Calcium sulfate, CaSOi -f aHjO. saturated solution. 
 
 Carbon dioxid 
 
 (or carbonic acid), CO2. 
 
 Carbon disulfid, CS2. 
 
 Chlorin (water), CI. 
 
 Chromic acid cleaning mixture. 
 
 Cochineal, tincture of. 
 
 Ferric chlorid, FeClj. 
 
 Ferrous sulfate, FeSO^ + 7H2O. 
 
 Hydrochloric acid, concentrated, HCl. 
 
 Hydrochloric acid, dilute, HCl. 
 
 Hydrosulfuric acid, or hydrogen sulfid, HjS. 
 
 Indigo solution. 
 
 lodin solution. 
 
 Iron filings, Fe. 
 
 Iron wire, piano. 
 
 Lead acetate, Pb(C2H302)2 + sHjO. 100 
 
 Lead acetate and ammonium acetate. 
 
 Lime water. saturated solution. 
 
l6o ELEMENTS OF CHEMICAL ANALYSIS. [§ 1 49. 
 
 Litmus solution- 
 Magnesia mixture. 
 
 Mercuric chlorid HgCl2. 5° 
 
 Methyl orange, indicator. 0.5 
 
 Nitric acid, concentrated, HNO3. 
 
 Oxalic acid, HaQO* + 2H2O. 100 
 
 Phenyl-sulfuric acid. 
 
 Potassium acetate, KC2H5O2. saturated solution. 
 
 Potassium bisulphate, KHSO4. 
 Potassium chlorate, KClOs , 
 
 Potassium chromate, KjCrO^. 100 
 
 Potassium cyanid, KCy, or KCN. 50 
 
 Potassium dichromate, K^CrzO,. 50 
 
 Potassium ferricyanidjKsFeCys, or K3Fe(CN)6. 10 
 
 Potassium ferrocyanid, K4FeCy6 0rK4Fe(CN)6 + 3H2O. 50 
 Potassium iodid, KI. 50 
 
 Potassium nitrate, KNOj. 
 Potassium permanganate, KMn04. 
 
 Potassium sulfate, KjSO,. 100 
 
 Potassium sulfocyanate, KCNS or KCyS. 50 
 
 Silver nitrate, AgNOs- 50 
 
 Sodio-cobaltic nitrite, (NaN02)3 Co(N02)3. 
 Sodium carbonate, NajCOs -|- 10H2O. 200 
 
 Sodium hydroxid, NaOH. 150 
 
 Sodium phosphate, Na2HP04 + 12H2O. 75 
 
 Sodium thiosulfate, NazSjOa. 
 
 Sodium sulfite Na^SOj. 100 
 
 Stannous chlorid, SnCl2. 
 Starch. 
 
 Sulfuric acid, concentrated, H2SO1. 
 Sulfuric acid, dilute, H2SO4. 
 
 Tartaric acid, H2C4H4O6. 100 
 
 Zinc (metallic), Zn. 
 Zinc, sulfate, ZaSO^ + 7H2O. 100 
 
 149. List of such reagents as are usually named only by their 
 formulas, in the description of the analytical work, arranged in 
 the alphabetical order of their formulas. 
 
 AgNOs, silver nitrate. 
 
 BaClj, barium chlorid. 
 
 BaCOs, barium carbonate. 
 
 Ba(0H)2, barium hydroxid. 
 
§ 1 49 -J APPARATUS, REAGENTS, ETC. l6l 
 
 CaCOa, calcium carbonate. 
 
 Ca(OH)2, calcium hydroxid or lime water. 
 
 CaSOi, calcium sulfate, 
 
 QlijOH, or QHeO, alcohol. 
 
 CI, chlorin (water). 
 
 CO2, carbon dioxid, or carbonic acid. 
 
 CSu, carbon disulfid. 
 
 Fe, iron (filings). 
 
 FeCla, ferric chlorid. 
 
 FeSOi, ferrous sulfate. 
 
 HCjHjOz, acetic acid. 
 
 HjCiHjOs, tartaric acid. 
 
 HCl, hydrochloric acid, concentrated. 
 
 HCl, hydrochloric acid, dilute. 
 
 H2C2O4, oxalic acid, 
 
 HNO3, nitric acid, concentrated. 
 
 HNO3, nitric acid, dilute. 
 
 H2S, hydrogen sulfid. 
 
 HaSOi, sulfuric acid, concentrated. 
 
 H2SO4, sulfuric acid, dilute. 
 
 HgClj, mercuric chlorid. 
 
 KC2H3O2, potassium acetate. 
 
 KCl, potassium chlorid. 
 
 KCIO3, potassium chlorate. 
 
 K2Cr04, potassium chromate. 
 
 K^CrjO,, potassium dichromate. 
 
 KCy, or KCN, potassium cyanid. 
 
 KCyS, or KCNS, potassium sulfocyanate. 
 
 KsFeCys, or K3Fe(CN)e, potassium ferricyanid. 
 
 KiFeCys, or K4Fe(CN)8, potassium ferrocyanid. 
 
 KHSO4, potassium bisulfate. 
 
 KI, potassium iodid. 
 
 KMn04, potassium permanganate. 
 
 KNO3, potassium nitrate. 
 
 K2SO4, potassium sulfate. 
 
 NaCjHjOa, sodium acetate. 
 
 NajCOg, sodium carbonate. 
 
 NaaHPOi, sodium phosphate. 
 
 NaNOs, sodium nitrate. 
 
 (NaN02)3Co(NOa)3, sodio-cobaltic nitrite. 
 
 NaOH, sodium hydroxid. 
 
 Na2S03, sodium sulfite. 
 
l62 ELEMENTS OF CHEMICAL ANALYSIS. [§ I50. 
 
 NajSjOg, sodium thiosulfate. 
 
 NH4CI, ammonium chlorid. 
 
 NH4CNS, ammonium sulfocyanate. 
 
 (NH4)2C03, ammonium carbonate. 
 
 (NHijjCjOi, ammonium oxalate. 
 
 (NH4)2 M0O4, ammonium molybdate. 
 
 NH4OH, ammonium hydroxidt 
 
 (NH4)2S, ammonium sulfid. 
 
 (NH4)jSj, ammonium sulfid, with excess of sulfur. 
 
 Pb(C2Hs02)2, lead acetate. 
 
 SnClj, stannous chlorid. 
 
 Zn, zinc (metallic). 
 
 ZnSOi, zinc sulphate. 
 
 150. Special directions for the preparatioti of reagents or solu- 
 tions. 
 
 The strength of the acids. Hydrochloric acid : — Only for the 
 solution of the precipitated sulfids of the metals of the 6th group 
 is acid of full strength (about 1.2 sp. gr.) required. For ordinary 
 use, this acid diluted with its volume of water is sufficiently 
 strong ; this moderately diluted acid is indicated by the heavy- 
 faced symbol HCl, and is about i.i sp. gr. 
 
 For dilute hydrochloric acid, indicated by HCl, add to the 
 fully concentrated acid eight parts of water. 
 
 Nitric acid : — For the concentrated acid for ordinary use, 
 indicated by HNO3, add to the fully concentrated acid its vol- 
 ume of water, making an acid of about 1.2 sp. gr. 
 
 Sulfuric acid: — For the dilute acid, H2SO4, add one part of 
 ordinary concentrated acid, H2SO4, to four parts of water. 
 
 Ammonium carbonate: — Dissolve 250 gms. of the salt in a 
 mixture of 200 c.c. of ordinary aqua ammonia and 800 c.c. of 
 water. 
 
 Ammonium hydroxid : — The solution for laboratory use should 
 have a specific gravity of about 0.96. 
 
 Ammonium molybdate : — For two litres of solution take 1300 
 c.c. of water; to 200 c.c. of NH4OH add 300 c.c. of this water, 
 and dissolve 100 gms. of molybdic acid jn this diluted ammonia. 
 To 500 c.c. of fully concentrated nitric acid add the rest of 
 the water, and to this add the ammoniacal molybdic solution, 
 slowly and with constant stirring ; let the whole stand in a 
 warm place 48 hours, and decant off the clear solution for 
 use. 
 
§ ISO.] APPARATUS, REAGENTS, ETC. 163 
 
 Ammonium sulfid : — Pass HjS through ordinary ammonia 
 water till the solution gives no precipitate with MgSOi, and to 
 700 c.c. add 300 c.c. of NH^OH. For the sulfid indicated by 
 (NH4)2Sj dissolve sulftir in this solution to saturation. 
 
 Brotnin solution : — To a solution of 50 gms7~of potassium 
 bromid in 500 c.c. of water, add bromin till no more is dis- 
 solved when the mixture is well shaken. 
 
 Cochineal, tincture of : — Digest 3 grams of cochineal for a 
 long time in 250 c.c. of a mixture of 3 to 4 parts of water and 
 I part of alcohol, and filter, or decant. If the solution to be 
 titrated is heated when this indicator is used, the presence of 
 free carbonic acid does not appreciably mask the change of 
 color. 
 
 Tke chromic acid cleaning mixture : — To about 150 c. c. of 
 warm water in a beaker add about 40 grams of ordinary 
 powdered KjCr^O, ; when all the salt is dissolved, cool the 
 solution and pour it slowly and with constant stirring into 
 about 230 c. c. of H2SO4. When the mixture is cold transfer 
 it to a 500 c. c, wide-mouth, glass-stoppered bottle; any por- 
 tion of it once used for cleaning can be poured back into the 
 bottle. Shake it up when about to pour it into a vessel to be 
 cleaned, for the red crystals are the most effective part for 
 cleansing purposes. As it is a strongly corrosive liquid, any of 
 it dropped on the table should be at once washed off with much 
 water. It is to be used only for cleaning glass ware that cannot 
 be cleaned by ordinary treatment with water, or with a little hot 
 HCl, and then with water ; it is never to be used for cleaning 
 beakers, flasks, or evaporators, unless they have had some 
 organic matter in them, such as fat or oil, that water will not 
 remove. 
 
 To clean a burette, put it mouth downward into the bottle 
 containing the mixture, and, opening the ball valve in the rubber 
 tube, slowly suck the liquid up, with as much of the red precipi- 
 tate of chromic acid as possible, to within three or four centi- 
 meters of the rubber tube ; on letting the valve close the liquid 
 will stand at that height, and can be left undisturbed as may be 
 desired, with the simple precaution to so support the burette 
 that it cannot upset the bottle by its weight. On rinsing the 
 burette out afterward, take off the rubber tube ; the cleaning 
 mixture should never come in contact with that. 
 
 To clean a pipette, attach a short piece of rubber tubs to the 
 mouth, and with the point in the cleaning mixture in the bottle. 
 
1 64 ELEMENTS OF CHEMICAL ANALYSIS. [§ I50. 
 
 cautiously draw the liquid up to the mark on the neck ; then 
 pinch the rubber tube tight while closing its open end with a 
 short piece of glass rod. 
 
 Ferric chlorid : — For this solution use the ammonio-ferric 
 chlorid, which is not so deliquescent as the ferric chlorid itself, 
 dissolving loo gms. in a litre of water. 
 
 Ferrous sulfate: — This solution should be freshly prepared; 
 or if kept on the shelves it should be acidified with H2SO4 (100 
 gms. FeSOi, 500 c. c. water, 5 c. c. H2SO4), and should always 
 be kept acid, and have a little undissolved iron in it. 
 
 Indigo solution : — To 5 parts of fuming sulfuric acid, add 
 slowly and with constant stirring one part of finely pulverized 
 indigo, in a beaker immersed in cold water ; let the mixture 
 stand 48 hours, the beaker being covered, then pour it into 
 twenty times its volume of water, mix and filter. 
 
 lodin solution: — In 500 c. c. of water dissolve 18 gms. of 
 potassium iodid, and then 7 gms. of iodin. 
 
 Lead acetate and ammonium acetate : — Acidify with acetic 
 acid a mixture of equal parts of solution of lead acetate and a 
 ten per cent, solution of ammonium acetate. 
 
 Litmus solution: — Boil the litmus three or four times with 85 
 per cent, alcohol, and finally filter. Wash the insoluble residue 
 once with a little water, by decantation, and then digest it with 
 hot water and filter. Divide this extract in two portions. Just 
 barely acidify one portion with H2SO4, make the other portion 
 very weakly alkaline with NaOH solution, and mix the two 
 portions together. The solution will keep better if in a loosely 
 stoppered bottle. A few drops of a solution of salicylic acid in 
 20 to 30 parts of alcohol added to 100 c. c. of the litmus solu- 
 tion will preserve it completely from mould. 
 
 Magnesia mixture: — Dissolve 100 grams of MgClj and 200 
 grams of NH4CI in 400 or 500 c. c. of water, add 400 c. c. of 
 ammonia, sp. gr. .96, make the solution up to one liter, let 
 stand several days in a closed bottle, and decant off the clear 
 liquid from any precipitate that may have separated out. 
 
 Phenyl-sulfuric acid : — Dissolve one part of carbolic acid in 
 four parts of H2SO4, and add two parts of water. 
 
 Sodio-cobaltic nitrite: — Dissolve 100 gms. of sodium nitrite 
 in 300 c.c. of water, add acetic acid to feeble acid reaction, and 
 10 gms. of cobaltic nitrate ; let the solution stand for several 
 hours and filter if not clear. Since the reagent decomposes 
 slowly, it is better pot to make a large quantity at once. If it 
 
§ 1 5 O.J APPARATUS, REAGENTS, ETC. 1 65 
 
 loses its precipitating power for potassium, the addition of more 
 sodium nitrite will restore its efficiency. 
 
 Stannous chlorid : — To a saturated solution of tin in hot HCl 
 add four parts of water and a few pieces of granulated tin ; the 
 solution should always have an excess of tin and a slight quantity 
 of free acid in it. 
 
 As to the important matter of the purity of these reagents, pure 
 nitric and hydrochloric acids will be found on the reagent 
 shelves, except that there may be slight traces of sul- 
 furic acid in the latter, and of hydrochloric acid in the 
 former; pure ammonia is supplied also. The quality of the 
 other reagents will be as good as practicable, but the student 
 should form the habit of testing them in cases where any im- 
 purities that they might contain, such as chlorid or sulfate, 
 would affect his results. Fresenius gives, in his works on quali- 
 tative and quantitative analysis, a full account of the tests that 
 should be made. It may sometimes occur that a reagent is not 
 perfectly clear, in which case some of it should be filtered for 
 use, especially in quantitative work. 
 
i66 
 
 ELEMENTS OF CHEMICAL ANALYSIS. 
 
 [§'51 
 
 151. TABLE OF ATOMIC WEIGHTS. 
 
 These atomic weights are taken from a revised table by F. W. Clarke, and 
 issued December 6th, 1890; the rare elements are omitted. The full table, as 
 stated by the revisor, " represents the latest and most trustworthy results, 
 reduced to a uniform basis of comparison with Oxygen = 16." 
 
 Name. 
 
 Symbol. 
 
 Atomic 
 Wkight. 
 
 Name. 
 
 Symbol. 
 
 Atomic 
 Weight. 
 
 Aluminum, . . 
 
 Al 
 
 27. 
 
 Manganese, . . . 
 
 Mn 
 
 55- 
 
 Antimony, 
 
 Sb 
 
 120. 
 
 Mercury, . . . 
 
 Hg 
 
 200. 
 
 Arsenic, . . . 
 
 As 
 
 75- 
 
 Molybdenum, 
 
 Mo 
 
 96. 
 
 Barium, . . . . 
 
 Ba 
 
 137- 
 
 Nickel 
 
 Ni 
 
 S8.7 
 
 Bismuth, . . 
 
 Bi 
 
 208.9 
 
 Nitrogen, . . . 
 
 N 
 
 14-03 
 
 Boron, . . 
 
 B 
 
 II. 
 
 Oxygen, .... 
 
 
 
 16. 
 
 Bromin, . 
 
 Br 
 
 79-95 
 
 Phosphorus, . 
 
 P 
 
 31- 
 
 Cadmium, . 
 
 Cd 
 
 112. 
 
 Platinum, . 
 
 Pt 
 
 195- 
 
 Calcium, ... 
 
 Ca 
 
 40. 
 
 Potassium, 
 
 K 
 
 39" 
 
 Carbon, . 
 
 C 
 
 12. 
 
 Selenium, 
 
 Se 
 
 79- 
 
 Chlorin, . . . 
 
 CI 
 
 35-45 
 
 Silicon, . . 
 
 Si 
 
 28.4 
 
 Chromium, . . 
 
 Cr 
 
 S2.I 
 
 Silver, ... 
 
 Ag 
 
 107.92 
 
 Cobalt, 
 
 Co 
 
 59- 
 
 Sodium 
 
 Na 
 
 23-05 
 
 Copper 
 
 Cu 
 
 63-4 
 
 Strontium, . . . 
 
 Sr 
 
 87.6 
 
 Fluorin, . . . 
 
 F 
 
 19. 
 
 Sulfur 
 
 S 
 
 32.06 
 
 Gold, . . 
 
 Au 
 
 197-3 
 
 Tellurium , . 
 
 Te 
 
 125. 
 
 Hydrogen, . . 
 
 H 
 
 1.007 
 
 Tin 
 
 Sn 
 
 119. 
 
 lodin, . . . 
 
 I 
 
 126.85 
 
 Titanium, . . . 
 
 Ti 
 
 48. 
 
 Iron, 
 
 Fe 
 
 56. 
 
 Tungsten, . . . 
 
 W 
 
 184. 
 
 Lead, ..... 
 
 Pb 
 
 206.9s 
 
 Uranium, .... 
 
 u 
 
 239.6 
 
 Lithium, . . 
 
 Li 
 
 7.02 
 
 Zinc 
 
 Zn 
 
 65-3 
 
 Magnesium, . . 
 
 Mg 
 
 24.3 
 
 Zirconium, . . . 
 
 Zr 
 
 90.6 . 
 
§§ IS 2-1 S3- J APPARATUS, REAGENTS, ETC. 
 
 167 
 
 15a. — Table giving grams of NH3 in 100 c.c. of solution of 
 
 NHjOH, of different specific gravity, at is° C. 
 
 (Lunge and Wernik : Zeit., ang. Cheniie, 1889.) 
 
 Specific 
 
 Grams NH3 
 
 Specific 
 
 Grams NH3 
 
 Specific 
 
 Grams NH3 
 
 Gravity. 
 
 IN 100 c.c. 
 
 Gravity. 
 
 IN 100 c.c. 
 
 Gkavitv. 
 
 ■ IN 100 c.c. 
 
 .960 
 
 9.51 
 
 •932 
 
 16.81 
 
 .904 
 
 2439 
 
 •958 
 
 10.03 
 
 •93° 
 
 17.34 
 
 .902 
 
 24.94 
 
 •956 
 
 IO.S4 
 
 .928 
 
 17.86 
 
 .900 
 
 25^So 
 
 ■954 
 
 11.07 
 
 .926 
 
 18.42 
 
 .898 
 
 26.05 
 
 •952 
 
 11.59 
 
 •924 
 
 18.93 
 
 .896 
 
 26.60 
 
 •950 
 
 12.10 
 
 .922 
 
 19^47 
 
 .894 
 
 27^iS 
 
 .948 
 
 12.62 
 
 .920 
 
 20.0 1 
 
 .892 
 
 27.70 
 
 .946 
 
 13-13 ' 
 
 .918 
 
 20.56 
 
 .890 
 
 28.26 
 
 •944 
 
 i3^65 
 
 .916 
 
 21.09 
 
 .888 
 
 28.86 
 
 •942 
 
 14.17 
 
 .914 
 
 21.63 
 
 .886 
 
 29.46 
 
 .940 
 
 14.69 
 
 .912 
 
 22.19 
 
 .884 
 
 30-14 
 
 ■938 
 
 15.21 
 
 .910 
 
 22.74 
 
 .882 
 
 30.83 
 
 •936 
 
 i5^74 
 
 .908 
 
 23.29 
 
 
 
 •934 
 
 16.27 
 
 .906 
 
 23^83 
 
 
 
 153. — Table giving grams of SO3 in 100 c.c. of solution of 
 
 different specific gravity, at iS° C. 
 
 (Lunge and Isler: Zeit. ang. Chemie, 1890. p. 129.) 
 
 Specific 
 
 Grams SO3 
 
 Specific 
 
 Grams SOj 
 
 Specific 
 
 Grams SO3 
 
 Gravity. 
 
 IN icDO c.c. 
 
 Gravity. 
 
 IN 100 c.c. 
 
 Gravity. 
 
 IN 100 C.c. 
 
 1.08 
 
 10.3 
 
 '■35 
 
 49-4 
 
 I.61 
 
 91.3 •' 
 
 1. 10 
 
 12.9 
 
 i^36 
 
 50.9 
 
 1.62 
 
 93^o 
 
 I. II 
 
 14.3 
 
 ••37 
 
 52^5 
 
 1.63 
 
 94-7 
 
 1. 12 
 
 i5^6 
 
 1.38 
 
 54^1 
 
 I 64 
 
 96.4 
 
 I-I3 
 
 16.9 
 
 1-39 
 
 55^7 
 
 ■ 1.6s 
 
 98.1 
 
 1. 14 
 
 18.3 
 
 1.40 
 
 57-3 
 
 1.66 
 
 99.8 
 
 i.iS 
 
 19.6 
 
 1.41 
 
 58.9 
 
 1.67 
 
 101.6 
 
 1. 16 
 
 21.0 
 
 1.42 
 
 60.4 
 
 1.68 
 
 103.4 
 
 1. 17 
 
 22.4 
 
 1.43 
 
 62.0 
 
 1.69 
 
 io5^3 
 
 I.I8 
 
 23.8 
 
 ••44 
 
 63.6 
 
 1.70 
 
 107. 1 
 
 1. 19 
 
 25^3 
 
 1.45 
 
 65.1 
 
 1.71 
 
 108.9 
 
 1.20 
 
 26.S 
 
 1.46 
 
 66.7 
 
 1.72 
 
 110.8 
 
 1. 21 
 
 28.2 
 
 1.47 
 
 68.3 
 
 ••73 
 
 112.7 
 
 1.22 
 
 29.7 
 
 1.48 
 
 699 
 
 1-74 
 
 1 14.6 
 
 1.23 
 
 31.2 
 
 1.49 
 
 71^5 
 
 '•75 
 
 "6.5 1 
 
 1.24 
 
 32^7 
 
 1.50 
 
 73-' 
 
 1.76 
 
 118.S 
 
 1.25 
 
 34^1 
 
 1.51- 
 
 74.8 
 
 1-77 
 
 120.4 
 
 1.26 
 
 35.6 
 
 1-52 
 
 76.4 
 
 1.78 
 
 122.8 1 
 
 1.27 
 
 370 
 
 '•S3 
 
 78.1 
 
 1.79 
 
 125.2 
 
 1.28 
 
 38.5 
 
 '•54 
 
 79.7 
 
 1.80 
 
 127.7 
 
 1.29 
 
 40.0 
 
 1^55 
 
 81.3 
 
 . ..81 
 
 1 30.5 
 
 1.30 
 
 41.6 
 
 1.56 
 
 82.9 
 
 1.82 
 
 133^8 
 
 I3I 
 
 43^2 
 
 '•57 
 
 84.5 
 
 1.83 
 
 i37^6 
 
 1.32 
 
 44^7 
 
 1.58 
 
 86.1 
 
 1.84 
 
 i43^6 
 
 1-33 
 
 46.2 
 
 '•59 
 
 87.7 
 
 
 
 '•34 
 
 47-9 
 
 1.60 
 
 89^5 
 
 
 
i68 
 
 ELEMENTS OF CHEMICAL ANALYSIS. [§ 154-155. 
 
 154. — Table giving grams of HCl in loo parts of hydrochloric 
 acid of different specific gravity, at 15° C. (Ure.) 
 
 Specific 
 
 Grams HCl 
 
 Specific 
 
 Grams HCl 
 
 Specific 
 
 Grams HCl 
 
 Gravity. 
 
 IN 100 PTS. 
 
 Gratity. 
 
 IN ICXJ PTS. 
 
 Gravity. 
 
 IN 100 ^. 
 
 1.0259 
 
 5-3 
 
 1.0859 
 
 17-53 
 
 I-I473 
 
 29-77 
 
 1.0298 
 
 6.12 
 
 1 .0899 
 
 18.35 
 
 1-1515 
 
 30.58 
 
 10337 
 
 6.93 
 
 1.0939 
 
 19.17 
 
 I-I557 
 
 31-40 
 
 I-0377 
 
 7-75 
 
 1.0980 
 
 19.98 
 
 1.1599 
 
 32.21 
 
 I. 041 7 
 
 8.56 
 
 1. 1020 
 
 20.80 
 
 1.1641 
 
 33-03 
 
 1.0457 
 
 9-38 
 
 i.io6i 
 
 21.61 
 
 1.1681. 
 
 33-85 
 
 1.0497 
 
 10.19 
 
 1.1102 
 
 22.43 
 
 1.1721 
 
 34.66 
 
 I -0537 
 
 1 1. 01 
 
 11143 
 
 23.24 
 
 1. 1762 
 
 3548 
 
 1.0577 
 
 11.83 
 
 1.1185 
 
 24.06 
 
 1. 1802 
 
 36.29 
 
 1.0617 
 
 12.64 
 
 1. 1226 
 
 24.87 
 
 1. 1846 
 
 37-11 
 
 1.0657 
 
 13.46 
 
 1. 1267 
 
 25-69. 
 
 1. 1875 
 
 37-92 
 
 1.0697 
 
 14.27 
 
 1.1308 
 
 26.51 
 
 1.1910 
 
 38-74 
 
 1.0738 
 
 15.09 
 
 I-I349 
 
 27.32 
 
 1. 1946 
 
 3955 
 
 1.0778 
 
 15.90 
 
 1.1389 
 
 28.14 
 
 1. 1982 
 
 40.37 
 
 1. 0818 
 
 16.72 
 
 11431 
 
 28.95 
 
 1.200 
 
 40.78 
 
 155. — Table giving grams of N2O5 and HNO3 in 100 c.c. of 
 
 nitric acid of different specific gravities at 15° C. 
 
 (Lunge and Rey : Zeitschrift fur angewandte Chemie, 1891, p. 16.) 
 
 
 Grams 
 
 Grams 
 
 
 Grams 
 
 Grams 
 
 
 Grams 
 
 Grams 
 
 Specific 
 
 NjOs 
 
 HNO3 
 
 Specific 
 
 NjOb 
 
 HNOs 
 
 Specific 
 
 N2O6 
 
 HNOs 
 
 Gravity. 
 
 IN 
 
 IN 
 
 Gravity. 
 
 IN 
 
 IN 
 
 Gravity. 
 
 in 
 
 IN 
 
 
 100 C.C. 
 
 100 C.C. 
 
 
 100 c.c. 
 
 100 C.C. 
 
 
 100 C.C. 
 
 100 C.C. 
 
 1.02 
 
 3-3 
 
 3-8 
 
 1. 19 
 
 3I-S 
 
 36.7 
 
 1.36 
 
 67.1 
 
 78.3 
 
 103 
 
 4-9 
 
 5-7 
 
 1.20 
 
 33-3 
 
 38-8 
 
 1-37 
 
 69.8 
 
 81.4 
 
 1.04 
 
 ?-^ 
 
 7-5 
 
 1. 21 
 
 35-1 
 
 40.9 
 
 1-38 
 
 72.5 
 
 84.6 
 
 1.05 
 
 8.1 
 
 9.4 
 
 1.22 
 
 36-9 
 
 43-0 
 
 1-39 
 
 75-3 
 
 87.9 
 
 1.06 
 
 9-7 
 
 "•3 
 
 1.23 
 
 38.7 
 
 45.2 
 
 1.40 
 
 78.3 
 
 91-4 
 
 1. 07 
 
 "■3 
 
 13-2 
 
 1.24 
 
 40-7 
 
 47-5 
 
 1.41 
 
 81.6 
 
 95-2 
 
 1.08 
 
 12.9 
 
 15.1 
 
 1.25 
 
 42.7 
 
 49-8 
 
 ..42 
 
 84.9 
 
 99.1 
 
 1.09 
 
 J4.5 
 
 16.9 
 
 1.26 
 
 44-7 
 
 52.1 
 
 1-43 
 
 88.5 
 
 103.2 
 
 1. 10 
 
 16.1 
 
 18.8 
 
 1.27 
 
 46.7 
 
 544 
 
 1.44 
 
 92.1 
 
 107.5 
 
 I. II 
 
 '7-7 
 
 20.7 
 
 1.28 
 
 48.7 
 
 56.8 
 
 1-45 
 
 96.1 
 
 112.1 
 
 I 12 
 
 19-5 
 
 22.7 
 
 1.29 
 
 50.8 
 
 59-3 
 
 1.46 
 
 100. 1 
 
 II6.8 
 
 I-I3 
 
 21. 1 
 
 24.6 
 
 1.30 
 
 52.9 
 
 bi.7 
 
 1-47 
 
 104.5 
 
 121.9 
 
 1. 14 
 
 22.8 
 
 26.6* 
 
 I-3I 
 
 55-1 
 
 643 
 
 1.48 
 
 109.2 
 
 127.4 
 
 I-I5 
 
 24.5 
 
 28.6 
 
 1,32 
 
 57-3 
 
 66.9 
 
 1.49 
 
 U4.4 
 
 '33-5 
 
 1. 16 
 
 26.2 
 
 30.6 
 
 1-33 
 
 59-7 
 
 69.7 
 
 1.50 
 
 121.0 
 
 141^1 
 
 '■'7 
 
 27.9 
 
 32.6 
 
 1-34 
 
 62.1 
 
 72.5 
 
 
 
 
 1. 18 
 
 29.7 
 
 34-7 
 
 '■35 , 
 
 64-5 
 
 75-3 
 
 
 
 
§ IS6-] APPARATUS, REAGENTS, ETC. 
 
 156. Comparison of measures and weights. 
 
 169 
 
 — I 9 
 
 g Directions are often given, especially in the 
 
 qualitative work, to add a certain volume of 
 
 r 
 
 a liquid to a substance or solution under treat- 
 ment. The adjoining figure represents the 
 5 actual size of the 10 centimeter test-tubes usu- 
 ally issued to the students in the author's 
 , laboratory ; with the aid of this graduation 
 
 _ J 
 
 in cubic centimeters, a close" approximation to 
 
 2 any desired quantity of liquid is easily made. 
 1.5 
 
 o.a- 
 
 AppRoxiMATE Relations Between English and Metric Weights and 
 
 Measures. 
 
 I Kilo, equals 
 
 2.2 lbs. av. 
 
 I lb. av. equals 
 
 454 grms 
 
 I Gram " 
 
 15.4 grains. 
 
 I grain " 
 
 64.8 mgms 
 
 I Gram " 
 
 0.03s °^' *v- 
 
 I oz. av. " 
 
 28.35 grros 
 
 I Liter ',' 
 
 2.1 pints. 
 
 I quart " 
 
 946 c.c 
 
 I Liter " 
 
 33.8 fluid oz. 
 
 I fluid oz. " 
 
 30 c.c 
 
 1 Meter " 
 
 39.4 inches. 
 
 I inch " 
 
 2.54 cm 
 
 Inches X 5 _ 
 
 = centimeters. 
 
 Centimeters X 2 
 
 = inches. 
 
170 elements of chemical analysis. [§ 157. 
 
 Course of Laboratory Work in Chemistry. 
 '. 157. The following course of quantitative analytical work, for 
 special students of chemistry at Cornell University, is so planned 
 as to give practice in the greatest variety of manipulation, and 
 also of difficult processes, as is possible in the time allowed for it. 
 It follows the introductory course given in this book. 
 
 (i) Limestone, complete analysis. (2) Sugar by the volumetric 
 and by the gravimetric method. (3) Nitrogen in organic sub- 
 stances, by the Kjeldahl method. (4'fjHi/k, complete analysis : 
 total solids, fat, sugar, proteids, ash.. (e,~)\Butier ; water, vola-' 
 tile and insoluble fatty acids, iodin equivalent, by Hiibl's 
 method, melting point. (6) Water, sanitary examination : total 
 solids, free and albuminoid ammonia, chlorids, nitrates, nitrites, 
 oxygen consumed, oxygen dissolved. (7) Potassium in a salt. 
 (8) Phosphorus pentoxid in a salt, by the molybdate method. 
 (g)l£/rine; urea by hypobromite, phosphorus pentoxid, by the 
 volumetric uranium method, chlorin by Volhar^'s volumetric 
 method. 
 
 (10) Feldspar, complete ; silicic oxide, aluminum oxide, potas- 
 sium oxide, calcium oxide, etc. (11) Nitrogen pentoxid, by 
 modified Kjeldahl method, by method of Pelouze and Fresenius. 
 (12) Organic ultimate analysis; carbon and hydrogen in a solid, 
 and in a volatile liquid ; sulfur, chlorin : nitrogen by the absolute 
 method. (13) Iron and steel ; phosphorus by the molybdate- 
 magnesia method, and by titration of the molybdate precipitate 
 witl) permanganate ; manganese, by the Williams method ; car- 
 bon, by the chromic acid method. (14) Chemical toxicology, 
 inorganic; detection and determination, in a mixture with 
 organic matter, of arsenic, and one other substance from the 
 following list : antimony, lead, copper, mercury, cyanogen, 
 phosphorus. 
 
 (15) Chemical toxicology, organic ; detection, in mixture with 
 organic substance, of two alkaloids selected from the follow- 
 ing list : atropine, aconitine, brucin, coniine, morphine, narco- 
 tine, nicotin, strychnin, veratrin. . (16) Tannin in tanning 
 materials, or indigo, analysis for valuation ; by two methods. 
 (17) Alloys, Jf»f€ itom the following list: type metal, solder, 
 bronze, Wood's metal, tin and lead, bismuth and lead, phosphor 
 bronze. (18) Complete analysis of plfo minerals selected from 
 the following list : beryl, chromite, franklinite, cassiterite, spha- 
 lerite, chalcopyrite, wavellite, celestine, bornite, stibnite, molyb- 
 
§ 1 57- J APPARATUS, REAGENTS, ETC. I71 
 
 denite, lepidolite, rutile, fahleiz, strontianite, wolframite, petalite, 
 boro natrocalcite., 
 
 (j.<)) Separations ; nickel and cobalt; arsenic, antimony and 
 tin. (20) Wine, or tobacco, or food substance^ complete analysis; 
 in wine, alcohol, extract, sugar, free acid, tannin, glycerine; in 
 tobacco, nic6|in, nitrate, ammonia; in food., or fodder, ash, 
 proteids, ether-extract, fiber, nitrogen-free extract, non-albumi- 
 noid nitrogen. (.21) Analysis by electrolysis ; Reparation and 
 determination of copper and manganese, copper and lead, copper 
 and nickel, antimony'^nd tin. 
 
 In connection with this work, and partly following it, instruc- 
 tion is also given in ga^,,analysis, and the use of the micro- 
 scope, spectroscope, colorinieter, polariscope, and refractometer, 
 in chemical analvsis. 
 
INDEX. 
 
 Acetic acid, in qualitative analysis, 58^ 66. 
 
 Acid, defined, 9 
 
 Acidification, operation of, 33. 
 
 Acidimetry, 139. 
 
 Acidigenic elements and groups, list of, 25. 
 
 Acidigens, or acids, notes on the chemistry 
 ot the analysis for, 59. 
 
 Acids, barium group, solubility of com- 
 pounds and reactions, 53 ; analysis of, 61 ; 
 organic group, ditto, ditto, 58, 66 ; oxi- 
 dizing group, ditto, ditto, 58, 66; silver 
 group, ditto, ditto, 56, 63, 
 
 Alkalimetry, 139. 
 
 Alkalization, 33. 
 
 Aluminum in qualitative analysis, 92, 93 ; 
 group of basigens, forms of occur- 
 rence and reactions,. 92; analysis for, 
 92 ; notes on chemistry of analysis for, 
 92: 
 
 Ammonia, standard solution, preparation, 
 141 ; determination of strength of, 144 ; 
 
 solution. Table of specific gravity, 
 
 167. 
 
 Ammonium, in qual. analysis, g8, gg ; 
 
 carbonate, as reagent, 162 ; hy- 
 
 droxid, reagent, preparation, 162 ; 
 
 magnesium phosphate, as quant, ppt., 
 146 ; raolybdate, reagent, prepara- 
 tion, 162 ; sulfid, reagent, prepa- 
 ration, 163. 
 
 Antimony in qual. analysis, 72-7S; deter- 
 mination by iodometry, 154. 
 
 Apparatus, qualitative set, 155; directions 
 
 for use of, 155; quantitative set, 
 
 larger, 15S ; smaller set, 157. 
 
 Aqua regia, oxidation and chlorination by, 
 16. 
 
 Areometer, principle of, 127. 
 
 Arsenic in qual. analysis, 71, 78. 
 
 Asbestos filters, 121. 
 
 Assay : the testing of a metal or an ore to 
 determine the proportion of its valu- 
 able constituents. 
 
 Atomic weights, table of, 166. 
 
 Balance, description and use of, 101-103. 
 
 Barium, in qual. analysis, 94, 97; sul- 
 fate, as quantitative ppt., 138. 
 
 Base, defined, 10. 
 
 Basigenic elements and groups, list of, 25. 
 
 Bismuth in qual. analysis, 79, 83. 
 
 Boiling of liquids, loss in,32 ; how to conduct, 
 36. 
 
 Boric acid, in qual. analysis, 55, 62. 
 
 Bromin, conditions under which set free, 
 
 29 ; -^^ oxidation by, 17 ; solution 
 
 as reagent, 163. 
 
 Burette, calibration, 114; use of, 112. 
 
 Cadmium, in qual. analysis, 79, 83. 
 
 Calcium, in qual. analysis, 94, 97 ; determi- 
 nation of, 147; group, forms of 
 
 occurrence and reactions, 94 ; analysis 
 of 95 ; notes on chemistry of analysis, 
 
 95; oxalate, as quant, ppt,, 147; 
 
 oxidation of by KMnj04, 148. 
 
 Cald well-GoocJi crucible , 121; platinum 
 jacket for, 122. 
 
 Calibration; the determination of the rela- 
 tive values of the different parts of a 
 scale. 
 
 Calibration of graduated instruments, 113. 
 
 Carbonate, analysis of by alkalimetry, 144. 
 
 Carbon dioxid, in qual. analysis, 53, 61. 
 
 Chloric acid, in qual. analysis, 58, 69. 
 
 Chlorination, defined, 11 ; conditions of, 11 ; 
 reactions of, 16. 
 
 Chlorin, conditions under which set free, 28. 
 
 Chromic acid cleaning mixture, 163. 
 
 Chromium in qual. analysis, as acidigen, 54, 
 62 ; as basigen, 92, 93. 
 
 Chromic acid, oxidation by, 18. 
 
 Citric acid in qual. analysis, 58, 67. 
 
 Cleaning mixture, chromic acid, 163. 
 
 Cleanliness in laboratory, 38. 
 
 Cobalt in qual. analysis, 84, go. 
 
 Cochineal tincture, reagent, 163. 
 
 Copper, determination by electrolysis, 153; 
 
 ^-^ in. qual. analysis, 79, 83 ; group, 
 
 forms ot occurrence anci reactions, 79 ; 
 analysis for, 83 ; notes on chemistry of 
 
 analysis for, 80 ; separation from 
 
 silver, 151. 
 
 Cylinders, graduated, 113. 
 
 Decantation, 37. 
 Desiccator, 106. 
 Digestion, 35, 
 
 Electrolysis, determination of copper by, 
 
 153; of silver, 152. 
 
 Eleijients and groups ot same ; basigenic 
 
 and acidigenic, Table of, 25. 
 Effervescence ; foaming or bubbling of a 
 
 liquid, due to the rapid setting free of a 
 
 gas in it. 
 Equation, chemical, correct writing of, 22 ; 
 
 common errors in, 26; signs of, 25. 
 
 Ferric chlorid, reagent, preparation, 164. 
 Ferrous sulfate, reagent, preparation, 164. 
 Ferrous and ferric hydroxids, in quant. 
 
 analysis, 135 
 Filters, quantitative, 117 ; strengthened 
 
 by treatment with HNO3, 119. 
 Filtration, 36 ; quantitative, 117 ; — by 
 
 suction, iig ; in Gooch crucible, 121, 
 
 Fluxing, 31. 
 
 Formulas, graphic or structural, 23. 
 
 Gases, solution of, 7. 
 
 Gooch crucible, 121, 
 
 Gold in qual. analysis, 71, 78. 
 
 Graduated instruments, directions for use 
 of, 115. 
 
 Gravimetric analysis, definition of, 100. 
 
 Grouping of substances, qualitative, 41. 
 
 Groups of elements, acidigenic and basi- 
 genic, 25. 
 
 Hydriodic acid in qual. analysis, 56, 64. 
 
 Hydrobromic acid in qual. analysis, 56, 64. 
 
 Hydrochloric acid in qual. analysis, 57, 65 ; 
 
 determination of, gravimetric, 142 ; 
 
 standard solution of, preparation, 
 
 Z41, and determination of absolute 
 
 173 
 
174 
 
 INDEX. 
 
 strength, 142 ; as reagent, prepara- 
 tion, 162 ; Table of specific gravity 
 
 of, i68. 
 
 Hydrocyanic acid in qual. analysis, 57, 64. 
 
 Hydroferri cyanic acid, in qual. analysis, 
 
 Hydroferrocyanic acid, in qual. analysis, 
 
 57. 65- 
 Hydrofluoric acid, in qual. analysis, 55, 62. 
 Hydrogen, conditions under which set free, 
 
 28. 
 Hydrosulfuric acid, in qual. analysis, 56, 
 
 64. 
 Hydroxids, properties, 44. 
 Hygroscopic, tending to absorb moisture. 
 Hygroscopic substance, weighing of, 104. 
 
 Ignition of residues from evaporation, 32 ; 
 — - of quantitative ppts., 123. 
 
 Indicator ; in volumetric analysis, the sub- 
 stance employed to show when the re- 
 action is completed. 
 
 Indicators, 140. 
 
 Indigo solution, reagent, preparation, 164. 
 
 lodin, conditions under which set free, 29. 
 
 lodin solution, reagent, preparation, 164. 
 
 lodometry defined, 1491; ^^preparation of 
 
 solutions for, 149 ; determination of 
 
 antimony by, 150. 
 
 Iron, in qual. analysis, 84, 91 ; determi- 
 nation of, gravimetric, 135, ditto volu- 
 metric, 136; group, forms of occur- 
 rence and reactions, 84 ; analysis of, 
 
 go ; notes on the chemistry of the 
 
 analysis for, 86. 
 
 Lead, acetate and ammonium acetate mix- 
 ture as reagent, preparation, 164. 
 
 Lead, in qual. analysis, 67, 70 ; determi- 
 nation, 145; sulfate, properties as 
 
 quant, ppt,, 145. 
 
 Limonite, assay of, 138. 
 
 Litmus solution, preparation, 164. 
 
 Magnesia mixture, reagent, preparation, 
 164. 
 
 Magnesium in qual. analysis, 94 97 ; py- 
 rophosphate, as quant, ppt,, 146. 
 
 Manganese, in qual. analysis, 84, gi. 
 
 Manipulations of analytical chemistry, 30. 
 
 Maxims, special, for quantitative work, 132. 
 
 Measuring flask, 113; how to use for 
 
 making certain volume of a solution, 
 115. 
 
 Measurement in volumetric analysis, stand- 
 ard of, 107. 
 
 Measures and weights, comparison of, 169. 
 
 Meniscus ; the curved surface of a liquid 
 caused by capillarity. 
 
 Mercury in qual. analysis, 68, 70, and 79, 
 
 83. 
 
 Metals, solubility of, 6. 
 
 Metathesis, defined, 18 ; kinds of, 21. 
 
 Neutralization, 33, 
 
 Nickel in qual. analysis, 84, 90. 
 
 Nitric acid, in qual. analysis, 58, 66 ; 
 
 oxidation by, 15; as reagent, pre- 
 paration of, i6a ; Table of specific 
 
 gravity of, 168, 
 
 Nitrogen, conditions under which set free, 
 29. 
 
 Normal solution, defined, 108. 
 
 Note-book, quantitative, 130, 
 
 Oxalic acid, in qual. analysis, 54, (2. 
 Oxidation, defined, 11 : conditions of, 
 
 II ; reactions of, 15. 
 
 Oxygen, conditions under which set free, 27 ; 
 
 free, oxidation by, 15. 
 
 Pheynl-sulfuric acid, reagent, preparation, 
 164, . 
 
 Phosphoric acid, in qual, analysis, 55, 63; 
 anhydrid, determination, 146. 
 
 Pipette, J12; calibration of 114; 
 
 measuring out several portions with, 
 115; specific gravity, 128. 
 
 Platinum, in qual.' analysis, 71, 78; 
 
 ware, use and care of, 129. 
 
 Potassium, in qual, analysis, 98, 99 ; 
 
 group, forms of occurrence and reac- 
 tions, 98 ; notes on analysis of, g8 ; 
 
 ■ chlorate, oxidation and chlorina- 
 
 tion by, 17; dichromate, standard 
 
 solution of, 137; permanganate, 
 
 standard solution of, 148. 
 
 Precipitation, 34; quantitative, testing 
 
 for completeness of, 117. 
 
 Precipitates, description of, 34 ; dissolving 
 of, 37 ; washing of, 37, 120. 
 
 Precipitates, quantitative, 117; ignition of, 
 125 ; preparation for weighing, 123 ; 
 removal of from beaker, 118; transfer 
 to crucible, 123 ; washing of, 120. 
 
 Qualitative analysis, order of arrangement 
 of work, 46 ; course of, tabular view, 49, 
 
 Rapidity of work, 38, 133. 
 
 Reaction : the chemical change produced 
 by a reagent. 
 
 Reagent : the chemical substance used to 
 take part in producing some desired 
 chemical change, in chemical analysis. 
 
 -Reagents, addition of in excess, 33; list of 
 in alphabetical order of full names, i5g, 
 ditto in alphabetical order of formulas, 
 160 ; purity of, 165. 
 
 Records of quantitative work, 131. 
 
 Reduction, defined, 13; agents of, 14; 
 conditions of, 13; reactions of, 14. 
 
 Residue; that portion of a substance that 
 is lelt after treatment of it with a sol- 
 vent in some prescribed manner, or 
 after igniting it. 
 
 Results of quantitative determinations : cal- 
 culation, 125; recording of, 130. 
 
 Salt, defined, 10; acid, basic, normal, 
 
 10, II ; solubility in acids, 6. 
 
 Silicic acid, in qual. analysis 55, 63, 
 
 Silver, in qual. analysis, 67, 70; group 
 
 of basigens, forms of occurrence and 
 reactions, 67 ; analysis of, 68 ; notes on; 
 
 the chemistry of the analysis, 68 ; 
 
 chlorid.as quantitative precipitate, 142 
 determination, 152, 153 ; separation from 
 copper, 151, 153. 
 
 Sodio-cobaltic nitrite, reagent, 164. 
 
 Sodium, in qual. analysis, 98, 99. 
 
 Solids, obtained from solutions, by cooling 
 of saturated solutions, 8 ; ditto, by 
 removal of solvent agent, g. 
 
 Solubilities, Table of, 5. 
 
 Solubility of salts in acids, 6. 
 
 Solution, 3; chemical, 4; deter- 
 mination of specific gravity of, 126:—- — 
 
 of gases and vapors, 7; ■ making 
 
 o'l 30; physical, 3; relation of 
 
 specific gravity to amount of substance 
 contained, 126; relation to tempera- 
 ture, 6, 7; of substance for quali- 
 tative analysis, 48; ditto, for quanti- 
 tative analysis, 116. 
 
 Solutions, Tables of relative specific gravity 
 and contents explained, 126. 
 
 Solvents, different solvent power compared, 
 6. 
 
 Specific gravity of solutions, by areometer, 
 126; ditto, by specific gravity pipette, 
 127. 
 
INDEX. 
 
 175 
 
 Stochiometry : the application of the laws 
 of chemical combination in fixed pro- 
 portions, in chemical calculation. 
 
 Standard solutions defined, 108 ; use of, 
 
 112. 
 
 Stannous chlorid, reagent, preparation, 165. 
 
 Strontium in qual. analysis, 94, 97. 
 
 Substance for analysis, quantitative, quantity 
 taken, 104. 
 
 Suction filtration, iicj. 
 
 Sulfids, properties ot, 42, 
 
 Sulfuric acid, in qual. analysis, 53, 61 ; 
 
 as reagent, preparation of, 162 ; — 
 ■ Tables of specific gravity of, 167. 
 
 Sulfuric trioxid, determination of, 150. 
 
 Sulfurous acid, in qual, analysis, 54, 62. 
 
 Tests, final, qualitative, 46. 
 
 Tin, in qual, analysis, 73, 78; group, 
 
 forms of occurrence and reactions, 71 ; 
 
 analysis of, 78 ; notes on the chemistry 
 
 of the analysis, 74. 
 
 Titration: in volumetric analysis, the act 
 of adding the standard solution to the 
 solution of the substance under analysis, 
 for the purpose of determining how 
 much of it IS required to react upon the 
 substance to be estimated. 
 
 Valence of the elements, 23. 
 
 Vapors, solution of, 7. 
 
 Volumetric analysis, definition of, 100. 
 
 Wash-bottle, how to use, 120. 
 Washing, quantitative precipitates, 120. 
 Weighing, directions for, 103-106 : 
 
 records of, 106 ; tubes, 107. 
 
 Weights, atomic. Table of, 166; set 
 
 of, for balance, descAbed, 102 ; and 
 
 measures, compared, 169. 
 
 Zinc, in qual, analysis, 89, gi.