Cornell XTlnivetsit^ Xibrar^ OF THE IRew l^orFi State College of Hariculturc Q.iMA&.. il Cornell University Library The original of tiiis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924002971772 EXERCISES IN ELEMENTARY QUANTITATIVE CHEMICAL ANALYSIS Cornell University Library QD 101.L73 Exercises In elementary qua^^^^^^^ -y^^y^' THE MACMILLAN COMPANY HEW YORK • BOSTON - CHICAGO SAN FRANCISCO MACMILLAN & CO., Limited LONDON • BOMBAY • CALCUTTA MELBOURNE THE MACMILLAN CO. OF CANADA, Ltd. TORONTO EXERCISES IN ELEMENTARY QUANTITATIVE CHEMICAL ANALYSIS BY AZARIAH THOMAS LINCOLN, Ph.D. ASSISTANT PROFESSOR OF CHEMISTRY, RENSSELAER POLYTECHNIC INSTITUTE AND JAMES HENRI WALTON, Jr., Ph.D. ASSISTANT PROFESSOR OF CHEMISTRY, UNIVERSITY OF WISCONSIN THE MACMILLAN COMPANY 1914 All rights reserved Copyright, 1907, By the MACMILLAN COMPANY. Set up and elcctrotyped. Published December, 1907, Reprinted October, 1908 ; January, 1910. With corrections, ATarch, 1911 ; August, 1912 ; October, 1913. October, 1914. J. S. CuBhlng Co. —Berwick & Smith Co. Norwood, Mass., U.S.A. PREFACE Owing to the growing demand for quantitative analytical chem- istry by those engaged in the study of agriculture, it seemed to the authors that the presentation of the fundamental methods of agricultural analysis as carried out in the laboratories of the American Experiment Stations would be desirable. While this book is designed primarily as an elementary quantitative guide for the use of agricultural students, it may also be used for the work in general elementary quantitative analysis. This text-book is the outgrowth of several years' experience in teaching quantitative analysis to students specializing in Agri- culture, Chemistry, Medicine, and Household Science. No attempt has been made to present a complete treatise on quantitative analysis; but a few typical exercises have been chosen to illustrate the fundamental principles and the most important methods of manipulation. To further the interest in this work, the student should be encouraged to do considerable outside reading, and there should be available for his use a number of the best books of reference. In the Appendix will be found a list of some of the most important works having a bearing on this subject, while throughout the text reference is made to the original literature. The gravimetric exercises and the work outlined under Acidime- try and Alkalimetry, together with the analysis of Milk or Feeding Material and Fertilizer, comprise the work usually accomplished by the agricultural students in one semester. Those students who desire more quantitative analysis complete the remainder of the exercises in another semester. Owing to the importance of the calculation of analytical data, this subject has been treated in considerable detail in Part V (Stoichiometry). The matter presented is arranged to be studied in conjunction with the regular laboratory exercises. In addition to the methods of solving problems, a large number of problems is given for practice. The selection has been made with the idea of emphasizing the fundamental principles brought out in the VI PREFACE laboratory exercises, and many of the problems are taken from the experimental data of the students. Although it will be found convenient to have a certain amount of platinum ware available for these exercises, it is not necessary. Porcelain crucibles and dishes may be used for all the determina- tions, with the possible exception of the alkalies in soils. The notes which are introduced throughout the text emphasize the important points and may serve as the basis of the classroom work, which should be an important feature of instruction in quan- titative analysis. In preparing this manual, free use has been made of the various standard works on quantitative analysis, of the publications of the Association of Official Agricultural Chemists, of the Bulletins of the United States Department of Agriculture, Bureau of Chem- istry, and, particularly, of Leach's excellent treatise on Food Inspection and Analysis. The authors desire to express their gratitude to Mr. J. H. Pettit, Assistant Professor of Soil Fertility, University of Illinois, for many valuable suggestions on the determinations connected with Fertilizers and Soils ; to Mr. Cyril G. Hopkins, Professor of Agronomy, for his help in correcting the proofs of the Analysis of Fertilizers and of Soils ; and to Mr. D. L. Weatherhead, for assisting in solving the problems. A. T. L. J. H. W., Jr. Urbana, Illinois, August i, 1907. CONTENTS PART I INTRODUCTION PAGE General Remarks i Notebooks 2 Reagents 4 Special Apparatus 5 Desiccators ............ 5 iVash Bottles 6 Stirring Rods 6 Operations of Quantitative Analysis 6 Sa!?!pling .... ...... 6 The IVeighing of Sa7nples . .... 7 Solution and Evaporation .... 8 Precipitation ... ..... 10 Conditions ... ....... 10 Enlargement of the Grains of Crystalline Precipitates . . .11 Colloidal Precipitates . . 12 Filtration . . . ..... 12 Washing .... 13 The Drying and Ignition of Precipitates 14 Crucibles . . ■ ■ 14 The Use and Care of Platinum 15 The Balance 16 The Construction of the Balance 17 Position of Center of Gravity 17 Ktiife-edges . 18 Beam 18 The Weights 19 Summary of Precautions to be observed in Weighing . . . .20 PART II GRAVIMETRIC ANALYSIS Exercises with the Balance 22 Exercise I — Determination of the Time of Vibration ... 22 viii CONTENTS PAGE Exercise II — Determination of the Zero Point 22 Exercise III — Determination of the Sensitiveness .... 23 Exercise IV — Weighing by the Usual Method .... 23 Gravimetric Determinations . .... 24 Exercise V — The Determination of Chlorine ... 24 Exercise VI — The Determination of Sulphur in a Soluble Sulphate . 29 Exercise VII — Separation and Determination of Calcium and Mag- nesium in a Mixture of their Carbonates ... . . 32 Exercise VIII — The Determination of Aluminium in a Soluble Salt . 37 PART III VOLUMETRIC ANALYSIS General Discussion 40 Volumetric Apparatus 40 Pipettes . . 40 Cylinders ......... 41 Flasks . ...... 41 Burettes . . 42 Calibration of Graduated Apparatus . . .... -43 Exercise IX — The Calibration of a Burette .... 45 Standard and Normal Solutions 49 ACIDIMETRY AND ALKALIMETRY 5 1 General . . ......... 51 Indicators . ......... 52 Litmus .......... 52 Phenolphthalein -52 Methyl Orange 52 Cochineal . ........ 52 Notebooks . 53 The Preparation of Standard and Normal Solutions ... 54 Methods of Standardization . .... 54 a. By Precipitation . ... ... 54 b. By Titration ... .... 54 c. By the Absorption Method 55 Exercise X — Preparation of an Approximately Half-Normal Hydrochloric Acid Solution . . . . . . -55 Exercise XI — Preparation of an Approximately Half-Normal Potassium Hydroxide Solution ....... 56 Exercise XII — The Titration of the Acid against the Alkali . 56 CONTENTS ix PAGE Standardization of these Solutions 57 Exercise XI II — Standardization of the Hydrochloric Acid Solu- tion . .... . -57 a. By Precipitation of the Chlorine as Silver Chloride 57 b. Against Calcium Carbonate . . . 59 Exercise XIV — Standardization of the Alkali Solution 59 a. Against Pure Chemicals .... 59 b. By the Absorption Method . . 60 Exercise XV — Determination of the Percentage Strength of Acid Solutions ........ 62 Exercise XVI — The Analysis of a Soluble Carbonate . . 63 Exercise XVII — The Determination of Total and Caustic AlkaH in a Mixture of Sodium Hydroxide and Sodium Carbonate . 63 Oxidation and Reduction . . . . 64 General ... .... . 64 Available Oxygen . ... 65 T/ie Permanganate Method . ... -67 Exercise XVIII — Preparation of a Solution of Potassium Per- manganate ...... . . 67 Exercise XIX — Standardization of a Solution of Potassium Permanganate ......... 68 a. By Pure Iron dissolved out of Contact with the Air 68 b. By Pure Iron reduced by Means of the Jones Reductor 69 Determination of the Blank ... 70 Reduction and Titration of the Iron . . 71 c. By Ferrous Ammonium Sulphate . . 71 d. By Means of Sodium Oxalate ...... 72 Exercise XX — The Determination of the Percentage Purity of Oxalates ...... . . . 72 Exercise XXI — The Determination of the Purity of Hydrogen Peroxide . . 73 Exercise XXII — The Determination of Calcium . 73 Exercise XXIII — The Determination of Iron in Siderite 74 The Dichroinate Afethod ... . . 75 Preparation of a Solution of Potassium Dichromate . 76 Indicator ........ . . 76 Exercise XXIV — Standardization of a Solution of Potassium Dichromate .... 76 a. Against Ferrous Ammonium Sulphate . . 76 b. Against Pure Iron ... .... 77 Exercise XXV — The Determination of Iron in Siderite . . 77 Iodimetry . . .... Methods of Determination . a. The Titration of Oxidizable Bodies . b. Bodies which contain Available Oxygen 78 78 78 78 CONTENTS PAGE c. Free Chlorine or Bodies which liberate Chlorine . . 78 Exercise XXVI — Preparation of Solutions ... 79 a. Approximately N/lo Iodine Solution .... 79 b. N/io Sodium Thiosulphate Solution ... 79 c. Starch Solution . . . 80 Exercise XXVII — Standardization of the Iodine Solution . 80 a. Against N/io Thiosulphate ... .80 b. Against N/io Arsenious Oxide .... 80 c. By Means of Standard Permanganate Solution . . . 81 d. By IVIeans of Standard Dichromate Solution . . 82 Exercise XXVIII — Estimation of Available Chlorine in Bleach- ing Powder . ........ 82 Exercise XXIX — The Determination of Available Oxygen in Pyrolusite ...... ... 83 Exercise XXX — The Determination of the Strength of Hydro- gen Peroxide 84 PART IV AGRICULTURAL ANALYSIS The Analysis of Milk . .... 85 General . . 85 Composition . ....... 85 Sampling . . ........ 86 Specific Gravity . ......... 86 Rejtioval of Samples ......... 87 Total Solids ..... . . -87 Ash . . 88 Fat . . 88 a. Adams' Paper Coil Method 88 b. Babcock Method ......... go Total Proteids 94 Kjeldahl Method 94 Determination of the Blank 97 Milk Sugar ......... gg Tabulation of Results . . . . . . . . .100 References ............ 100 The Analysis of Butter 100 General .......... 100 Sampling ........... loi Water ............ loi Fat ............. 102 Casein ............ 102 Ash . . . . . . . . . . . .102 Salt . . .......... 102 CONTENTS xi The Examination of Butter Fat Composition Differences Chemical ....... Physical Preparation of Pure Butter Fat .... Physical Tests Specific Gravity .... Melting Point . ... Chemical Tests ...... Volatile Fatty Acids Reichert-Meissl Method . Soluble and Insoluble Fatty Acids Saponification or Koettstorfer Number . Iodine Absorption Number, Hanus Method Household Tests ...... The Foam Test . ... Waterhouse or Milk Test References . ... The Analysis of Cereals and Feeding Materials Classification ... ... Composition ....... Carbohydrates Fats Proteids . .... Preparalioji of the Sample .... Dry Matter Ether Extract Separation of Carbohydrates, Stone'' s Method Reducing Sugars, AUihn's Method Sucrose, Clerget's Inversion Method Dextrin and Soluble Starch .... Starch, Diastase Method .... Starch, Saliva Method Crude Fiber Total Proteids ....... Ash . . References The Analysis of Fertilizers .... General . . Sampling ........ Dry Matter Phosphorus . . Total Phosphorus Water-soluble Phosphorus .... xii CONTENTS PAGE Citrate-insoluble Phosphorus . . . . 136 Citrate-soluble Phosphorus . • 137 Nitrogen . ... . . . . 138 Total Nitrogen in Absence of Nitrates . . . . . 138 Total Nitrogen when Nitrates are Present . . . . 138 Nitrogen Soluble in Water . • 139 Nitrogen as Ammonium Salts . 140 Potassium ... . 140 Potassium in Mixed Fertilizers . 140 References ... . 142 The Analysis of Soil . 142 Constituents of the Soil 142 Organic Constituents . 143 Collection and Preparation of the Samples . . 144 Moisture . . . . . 146 Volatile Matter . . . . . 147 The Extraction of the Acid-soluble Material . 147 Removal of Soluble Silica from Solution . 148 Insoluble Matter and Soluble Silica . 149 The Determination of the Acid-soluble Substances . 150 Iron, Aluminium, and Phosphorus, collective y . . . 150 Phosphorus . 151 Manganese 151 Calcium . 152 Magnesium . 152 Sulphur 152 Iron • 153 Potassium • 153 Sodium • 153 Separation of Potassium from Sodium . ■ 153 Humus ... 154 Total Nitrogen in tlie Presence of not More than a Trace of Nitrates . 155 Carbon Dioxide ... . . . . 156 Statement of Results . ... 159 References 160 PART V STOICHIOMETRY Empirical Formulas 161 Problems ... ....... 162 Percentage Composition 162 Problems 163 CONTENTS xiii PAGE Gravimetric Calculations ....... . 163 Factors . 165 Problems .... . 166 Indirect MetJiods . 167 Problems . 168 The Volume of a Reagent Necessary for a Given Reaction . 169 Problems . .... 171 Volumetric Calculations ... 171 Acidimetry and Alkalimetry • 171 Problems • 177 Oxidation and Reduction 178 Balancing Equations 178 Oxidizing Agents . . 180 Exercise in Balancing Equations . 181 Permanganate and Bichromate Methods . , 182 Numerical Relations . 182 Questions on Equations . 183 Methods of Solving Problems ... 184 Problems . . . . . . 186 Iodi.metry . . 187 Method of Solving Problems . 187 Questions on Equations 188 Problems . .... 188 Factor Weights .... .... 189 Miscellaneous Problems . 190 APPENDIX Books of Reference . Table I. Desk Reagents . . . . . . Table II. Laboratory Reagents ....... Table III. Apparatus for Desk Equipment .... Table IV. Specific Gravity of Hydrochloric, Nitric, and Sulphuric Acids Table V. Specific Gravity of Ammonia Solutions Table VI. Determination of Lactose by Soxhlet's Method . Table VII. Determination of Dextrose by Allihn's Method . Table VIII. Logarithms .... Table IX. Antilogarithms .... ... Table X. Combining and Atomic Weights Answers to Problems Index . 195 196 196 202 203 205 206 207 210 2 1 2 214 215 217 LIST OF ILLUSTRATIONS FIG. 1 . Sample Pages of Notebook . 2. Desiccator . 3. Wash Bottle 4. Cover-glasses and Clip . 5. Triangle for supporting Cover-glasses 6. Evaporation of Liquid from a Crucible 7. Ignition of Precipitates 8. Half-form Filter . 9. Pipettes 10. Graduated Cylinder 1 1 . Graduated Flask 12. Burettes and Holder 13. Reading Burettes 14. Calibration Curves 15. Recording Volumetric Data 1 5. Gooch Apparatus 17. Absorption Flask 18. Dissolving Iron out of Contact with Air 19. Jones Reductor . ... 20. Apparatus for Determination of Available Oxygen 21. Muffle Furnace . 22. E.xtraction Apparatus . 23. Extraction Battery, heated Electrically 24. Ether Distilling Apparatus . 25. Centrifugal Machine . . . . 26. Digestion and Oxidation Battery 27. Apparatus for Distilling Ammonia in Kjeldahl Determination 28. Specific Gravity Flask 29. Weighing Tube for Butter . 30. Reflux Hopkins Condenser and Flask . 31. Copper Distilling Flask .... 32. Apparatus for Determination of Carbon Dioxide 27 41 42 42 43 48 53 58 61 69 70 83 89 90 91 92 93 95 96 106 109 125 156 157 PART I INTRODUCTION GENERAL REMARKS The knowledge of the amount of a particular constituent in a substance is often of great importance from the commercial as well as from the scientific standpoint. The necessity of being able to answer the question " How much ?" with a high degree of accuracy has led to the development of the important branch of chemistry known as Quantitative Analysis. The methods of quantitative analysis may be classified according to the nature of the operations employed. The most important are the following : General Methods Special Methods Gravimetric Volumetric Electrolytic Gasometric Colorimetric Photometric Attributive In the following pages the gravimetric and volumetric methods only will be discussed. For a description of the other methods the student is referred to the more comprehensive works on quantita- tive analysis, a list of which is given on page 195. In gravimetric methods the constituent is determined by trans- forming it into an insoluble compound, in which condition it can be separated by filtration from the other constituents which were orig- inally present in the substance. This insoluble compound either has a definite chemical composition or it may be changed into a sub- stance of known composition. It is weighed and the amount of the constituent sought calculated. The methods are based, therefore, upon the insolubility of some compound containing the constituent to be determined. No sub- stance is absolutely insoluble, however, and the amount that will dissolve depends upon the prevailing conditions. Consequently, it 2 QUANTITATIVE ANALYSIS is of fundamental importance to obtain and to maintain conditions of such a nature that the precipitate will always be under condi- tions of minimum solubility. The operations employed in gravimetric processes include pre- cipitation, filtration, and washing, and are very similar to those used in qualitative analysis. It is necessary, however, to perform them with much more care, neatness, and completeness, for in the quanti- tative work the entire amount of the constituent must be precipitated, separated from the other substances, and finally weighed. Not only are the operations similar to those employed in the qualitative work, but the methods of separation of the constituents invariably depend upon the same chemical facts. The relations existing between these two branches of analysis cannot be too strongly em- phasized. In order to become familiar with the fundamental clas- sifications, reactions, separations, and specific tests for the identifi- cation of the elements a careful and systematic review of qualitative analysis should be made. To successfully perform quantitative chemical analyses, one must learn to work carefully and intelligently and also to do more than 071C thing at a time. The student can work intelligently only when he has a clear idea of what is to be done and understands thor- oughly the chemistry of the process which he is carrying out. Fol- lowing the directions blindly always brings trouble. Plan the work so that several operations are going on at the same'time ; for exam- ple, while the samples are being weighed, the crucibles may be heating to constant weight; again, while a precipitate is being di- gested, the samples for the next determination may be weighed. Accuracy cannot be attained without neatness. Hence it is necessary to have the desk and apparatus neat and clean at all times and to exercise the greatest care to keep them in this condi- tion. Nothing makes a more unfavorable impression than dirty apparatus ; moreover, the effect on the student himself is often demoralizing. NOTEBOOKS Care and neatness are just as essential in recording data as in their collection. Record all of the data in a permanent form just as soon as they are obtained. Use the notebook provided for this pur- pose and make the entries in ink. Under no circumstances should records be placed on scraps of paper. If at any time the data INTRODUCTION 3 become valueless through accident, do not tear the leaves out of the notebook, but mark " discarded " and make new entries on another page. The student should learn to record his results in a systematic and orderly manner. The method of recording the data success- fully used in the authors' laboratories is illustrated in Fig. i, which represents two pages of the notebook employed. They are 5" x 7 1" and ruled in cross section by lines -5- of an inch apart. '? J 32E l!a:C5ri]D|HS Jf'Tf- ^[iNATf N Of : DHi 11: s r-TT -t ■ ; aq-I L z. _ l; oiljfl' 1 et. 1 -Vlin 4 1 Sf ic e2 11' J - L4aifJ.25 iSL; am n laiu- ?r \'t mIii J I :i SEEoif lUCI TfT (• 7 . ,, rt^yof X=£ Z^Si' A.i; n V/, ii Tiim p <■ 3^ )f A + n f 5^ r n 1 r f :w+. 1 "; •..■ ii^i '',, :x X fii l.kso Mrvf, ;-Mr.hip t I'lri;; (4? 3 ro 2iia_: il!^ Ak'.: mz: < filiJrA.'j- piii . - i 'iiL fih^'?Q-^- - : 2^=15:2^ : 1 ?.o 5 ^ f^ ipir L/t- ■ "SiSaS IT yz sssSia v-i-.T :: aima-: y df ePT lif V f (,'1 iir HP (=,-?! i=;q x = _ij)j5cii + .',-', c fib ^ pji. "";• ■fi -7 1 fi'.'T 1 1 1 ^D* . 6t7|X6'6 ' i 0,?,?,'=>^ .0 cT^^sq :: no : v .'j'cSp.tt t^t ;,r[ fiW «-) 1 (=; f 1 ^'-■^■■'-^ ^ Xi=l. .00 .-. liof^ r 1 ? 51 /Nt of / 1: f;i £ ^it-^- x \ !f-qi ATinMS ! 1 1 L 1 , ^Ljt|Att\l Ti=i=i 1 kpj.O -inrPlrc p ^^ ; . lldC /Ag ; hfJa fJ d n pr*i!!^f nr,(ti rf KOf ^pr 9 t <: Hii^ed rif +rtl if ■ 5=»l\Pi- " 2^iJDIE = Fig. I The right-hand page is for the record of the experimental data and the report of the percentage of the constituent sought. On the left-hand page should be recorded : 1 . The equations representing all of the chemical changes taking place in the process. 2. The calculation of the results from the data collected. 3. A record of any special difficulties encountered and the reme- dies employed. The use of logarithm tables will greatly facilitate the calculations. Too much importance should not be placed on the fact that du- plicates " check," because it sometimes happens that the same error 4 QUANTITATIVE ANALYSIS will be made in each determination, giving results which agree, but which may be several per cent from the true value. There is often a tendency for the student to "begin over" when some little irreg- ularity has been introduced into the procedure. This tendency is the cause of the loss of much time and also results in the student losing confidence in his work. By consulting the instructor and making a thorough study of the conditions, the difficulties may be overcome, the exercise carried out without loss of time and a certain amount of valuable experience gained. Each exercise should bring forth the best efforts of the student. As a last resort " begin over." REAGENTS One of the most important problems with which the analytical chemist has to deal is the purity of the reagents. It is obvious that no matter how good a manipulator the analyst may be, if im- pure reagents are employed, his results will be valueless. Young chemists are frequently deceived by reagents being marked "chemically pure," "for analysis," etc. For accurate work, how- ever, such labels cannot be considered as a guaranty of the purity of reagents. The analyst can be sure of his reagents only by sub- jecting them to thorough chemical tests, similar to those prescribed by Krauch.i Reagents are often tested by making a "blank" determination. Tfiis consists in carrying out the regular determination, omitting, however, the substances to be analyzed. The results of the blank are subtracted from those obtained in the regular determination. Attention should be called to the fact that solutions of ammo- nium hydroxide on standing in certain reagent bottles attack the glass, with the formation of flaky particles, which may result in spoihng an analysis. Distilled water, moreover, should be fre- quently tested, as certain forms of stills occasionally boil over, with the result that "distilled water" is sometimes more impure than the ordinary tap water. When removing the reagent from the bottle, always pour it out and discard the unused portion. In order to insure the purity of the reagents adopt the general principle of never introducing a pipette, spatula, or other piece of apparatus into a reagent bottle and ^ The Testing of Chemical Reagents for Purity, E. Krauch. Translated by Wil- liamson and Dupre. INTRODUCTION 5 never returning the tinuscd portion of the reagent to the bottle. Be very careful when handling the stoppers of the reagent bottles ; do not put them in such a position that the part which fits into the neck of the bottle will touch the desk or anything else. Cultivate the habit of holding the top of the stopper between the fingers while removing the reagent. SPECIAL APPARATUS Desiccators I^ For keeping crucibles, samples, etc., in a dry atmosphere an ap- paratus known as a desiccator is used. For quantitative work the form shown in Fig. 2 is very efficient. It is fitted with a porce- lain plate which is provided with holes for four crucibles. Granu- lar calcium chloride which has been sifted to remove the fine particles is used as the desiccat- ing agent. When sulphuric acid is used for this purpose, the bottom of the desiccator should be covered with a half-inch layer of asbestos fiber, and this should be saturated with concentrated acid. This prevents the acid splashing upon the crucibles, with subsequent damage to the balances. To render the desic- cator tight, the ground part of the cover should be covered with a very thin coating of grease or vaseHne. Trouble is often caused by the introduction of hot crucibles into the desiccator. This results in heating the air, which expands, and if the cover is then put into place, upon cooling a partial vacuum will be formed. Upon removing the cover the sudden rush of air will often blow the precipitate out of the crucible. It is advisable, therefore, to allow crucibles to cool for about a min- ute before placing them into the desiccator, and also to keep them covered. Fjg, 6 QUANTITATIVE ANALYSIS Wash Bottles At least two wash bottles are necessary in analytical work, one to be used for hot and the other for cold water. A form which is in general use is shown in Fig. 3. A 500 or 750 c.c. plain flask makes a wash bottle of convenient size. To facilitate handling the hot water bottle, its neck should be wrapped with as- bestos paper. This is easily done by thor- oughly wetting a piece of asbestos paper and wrapping it about the neck of the flask. Upon boihng water in the flask, the asbes- tos paper will dry and adhere tightly to the neck. Stirring Rods For the removal of precipitates from beakers a stirring rod provided with a rubber tip (a "policeman") is used. At least four stirring rods should be provided, two 13 cm. and two 18 cm. in length. The ends of these should be fused and rounded. Fig. 3 THE OPERATIONS OF QUANTITATIVE ANALYSIS Sampling The analyst very seldom receives substances in a form ready for analysis. It is more often the case that they come to him in the form of tubs of butter, bags of fertilizers, car loads of ore, etc., and he must obtain a sample whose value shall be representative of the entire amount. At first sight this may not appear to present many difficulties, but when one considers the heterogeneous nature of the material, it is evident that the problem of obtaining a fair sample is one of the most difficult with which the analyst has to deal. The methods of sampling vary with many factors, the most important of which are : the nature and uniformity of the original material, the nature of the constituent to be determined, and the size of the original sample. Minerals are often sampled by crushing to a sufficient fineness, piling in a cone, and by means of a shovel removing the diagonally INTRODUCTION 7 opposite quarters of the cone. This removes one half of the ma- terial. The other half is again piled into the form of a cone and the process repeated. This is continued until only a pound or two of the sample is left, which is pulverized to the desired fine- ness and used for the analysis. At any desired stage the sam- ple may be ground. This process is known as sampling by " quartering." Metals such as pig iron are often nonhomogeneous, conse- quently great care must be exercised in obtaining samples. This is usually done by taking drillings from different parts of the'bars by means of a clean steel drill, mixing these drillings, and using them for the analysis. Agricultural products are so diversified that no general method of sampling can be given. For certain substances like butter, flour, bags of ground fertilizers, etc., a long thin tube may be used, which permits the removal of samples from the various parts of the barrel or tub. Vegetables, such as beets and peas, are usu- ally reduced to a state suitable for chemical analysis by passing them through one of the ordinary kitchen grinding machines. Dry cereals like corn and wheat may be very satisfactorily ground in an ordinary coffee mill. Liquids should be thoroughly mixed by shaking before a sample is removed. References on Sampling Lodge, R. W., Notes on Assaying, p. 23. Lord, N. W., Notes on Metallurgical Analysis, p. 9. Wu,EY, H. W., Agricultural Analysis. Consult the chapters on the analysis of the different agricultural products. Weighing Samples The direct and the indirect methods are used in weighing sam- ples for analysis. Weighing by the direct method consists in placing the substance upon the pan of the balance, or upon a cover-glass or other ves- sel of known weight, and adding enough weights to balance the amount of substance taken, or placing the weight upon the pan and adding enough substance to the other pan to just balance it. This method is in general use in analytical chemistry, it being particularly adapted to weighing specified quantities of the sub- stance. Its application, however, depends to a certain extent on 8 QUANTITATIVE ANALYSIS the nature of the substance. Liquids and substances which absorb moisture from the air cannot be weighed in this manner. The indirect method, or weighing by difference, consists in plac- ing the substance into a stoppered tube or flask, weighing, remov- ing some of the substance, and weighing again, the difference between the two weights being the weight of substance taken. This indirect method is used for weighing substances which readily take up or lose moisture, for liquids, and in general when a speci- fied weight of the substance is not necessary. For weighing substances which absorb moisture readily, several devices may be employed. One of the most convenient is to use two cover glasses, the edges of which are ground to fit and held tightly together by a spring clip as illustrated in Fig. 4. The weight of the glasses and clip being known, the substance is placed upon one of the glasses, the other glass placed over this and held in position by the clip. The weight of the substance can then be obtained without danger of absorbing moisture. . To determine the amount of ^-^ \7^^ y^^ substances to be taken for z^-----:'''' // /""""'""''— --^!!^\ analysis requires considerable /'' ^-'' // /'- — -C/ 'N experience and no general rule V^-O::^ // ./'' .--.i :!!— --^/ can be given, as the quantity to ^^^ jL\S:---''S'--''''y' ^,^-^ ^^ weighed out depends upon -.^;i— ^>-^^ so many factors. The amount ^ ^ of the constituent to be deter- FlG. 4 mined is of primary importance, as in some cases, where the percentage is small, 10 grams may be taken for the analysis, while in other cases 0.5 gram may be sufficient. The nature of the precipitate is also an important factor, a bulky gelatinous precipitate being hard to filter and wash. The quantity of the precipitate must not be too small, for a slight loss due to manipulation introduces a large error. Hence, as the beginner in quantitative analysis has not had the necessary experi- ence which will guide him in determining the amount of the sub- stance to be weighed for analysis, it is necessary to state the quantities to be used. Solution and Evaporation The samples for analysis are dissolved in distilled water whenever possible. If acid must be added to aid in the solution, a large excess mTRODUCriON over the amount called for by the directions should be avoided. An excess of acid may dissolve some of the precipitate, or if it must be neutralized later, it increases the volume of the solution by using more ammonium hydroxide and also increases the amount of soluble salts present. In general the analyst should try to find the happy medium between working with a solution which is too concentrated and one which is too dilute. With concentrated solutions the quantitative separation of precipitates is frequently unsatisfactory, because of the occlusion of soluble salts; moreover, the loss of a drop of such a solution occasions a serious error. Ex- tremely dilute solutions, on the other hand, have the disadvantage of being difficult to handle, requiring considerable time for evapo- ration, and the large volume of liquid may dissolve an appreciable amount of the precipitate. Solutions should be kept covered as much as possible to protect them from contamination. It is frequently necessary to evaporate solutions over a flame or on a water bath, and here also the vessel should be kept covered. This is best done by placing a glass triangle, shown in Fig. S, upon a beaker or casserole, and allowing a cover- glass with a diameter a little larger than that of the vessel to rest up- on the triangle. Small glass hooks which are hung over the side of the vessel may also be used to support the cover-glass. It should be remembered that alkaline solutions attack glass appreciably, and therefore should not be allowed to stand for any length of time in contact with glass vessels, but whenever possible should first be made slightly acid. On boihng certain solutions, especially those which contain par- ticles of suspended matter, much trouble is often experienced by a violent agitation of the liquid which is called "bumping." This is caused by the incomplete diffusion of the heat appHed to the solu- FIG. 5 lo QUANTITATIVE ANALYSIS tion. The liquid becomes locally superheated, a comparatively large amount of steam is given off at once, and this is attended by an explosion which may throw the liquid out of the vessel. This may be prevented in several ways. A stream of gas may be passed through the solution which keeps the heat diffused, so that superheating will not occur. If substances with sharp points, such as broken glass or pumice stone, are placed in the solution, the steam will be evolved gradually from these points. For dis- tilling solutions of this kind copper flasks are often used, the copper being such a good conductor that it permits the heat to be uniformly distributed throughout the solution. Precipitation Conditio7is The object of precipitation in quantitative analysis is to change the constituent which is being determined into such a form that it can be easily separated from the solution by mechanical means, or to remove from solution a substance whose presence would cause trouble in the subsequent procedure. The choice of the form in which the substance is precipitated depends upon the following factors : 1. Solubility. The necessity of the most complete separation possible is obvious. In general, it is customary to precipitate a substance in its least soluble form, and to maintain throughout the determination conditions under which the precipitate will remain insoluble. 2. Ease of filtration and washing. The importance of these factors from the standpoint of economy of time is apparent. 3. Stability on drying and ignition and the possibility of change to a more stable form are also important factors which must be taken into consideration. In general the precipitating reagent is added in the form of a solution. The method has several advantages, among which may be mentioned the ease of control of the quantity of the reagent, and also the possibility of detection of particles of insoluble foreign matter present in the solid reagent. In many cases, more- over, a quantitative separation can be obtained only by adding the precipitant in the form of a solution. Whenever it is possible, the INTRODUCTION ii quantity of reagent necessary to precipitate the substance should be calculated. This prevents the addition of an unnecessary ex- cess of the reagent and also permits a correction when a blank determination is made. The solution must always be tested for complete precipitation. This may be done by testing the super- natant liquid, or by filtering and testing a small portion of the filtrate. Many precipitates are less soluble in solutions which contain in common with them an element or radical (ion), therefore an excess . of the precipitating reagent is often added. Thus barium sul- phate is more insoluble in barium chloride solution than in water, consequently in the determination of sulphuric acid, an excess of barium chloride is added to the solution. Precipitates often possess the power of carrying down or occlud- ing foreign substances. Even though the occluded substances are soluble in water, it is often practically impossible to remove them by washing; hence, conditions which favor occlusion should be carefully avoided. The occlusion of the precipitant is often caused by " dumping " a large quantity of the reagent into the solution. By stirring the solution while the precipitant is being slowly added from a pipette or dropper, this source of error may be avoided. Many substances when first precipitated exist in such a physical state that their separation from the solution by means of a filtering medium is almost impossible, owing to their tendency to run through the filter. Methods have been devised by which such precipitates can be changed to forms permitting their removal by filtration. The Enlargement of the Grains of a Crystalline Precipitate Barium sulphate is a crystalline precipitate whose grains are so small that they often run through the filter. The grains may be enlarged by allowing the precipitate to stand for some time in con- tact with the solution at a temperature close to the boiling point. This may also be accomplished by allowing the precipitate to re- main at the ordinary temperature in contact with the solution, but the length of time must be greatly extended. This process is termed digestion. Ostwald ^ gives the following explanation of this phenomenon : 1 W. Ostwald, The Scientific Foundations of Analytical Chemistry, p. 22 (1900). 12 QUANTITATIVE ANALYSIS Since every substance is slightly soluble, a certain amount of the precipitate always remains in solution. On heating, more of the precipitate dissolves and the smaller particles are the first to go into solution ; the solution then becomes supersaturated with re- spect to the large particles and a precipitation on them takes place. As the heating continues, the small particles are dissolved, and the larger particles grow at their expense. This process goes on at the ordinary temperature, but much more slowly. The digestion must be carried on until the particles are so large that they will not pass through the pores of the filter. Colloidal Precipitates Many substances, such as aluminium hydroxide and the metallic sulphides, form gelatinous or flocculent precipitates and cause trouble by running through the filter. Precipitates of this kind, which are called "colloidal," are thrown down by heating the solu- tion, or by adding solutions of salts, acids, or bases. They are usually precipitated from hot solutions. The addition of salts to facilitate the precipitation is seldom necessary, as they are usually present in the solutions in sufficient amount. Filtration The process of filtration has as its object the separation of the precipitate from the liquid. For this purpose a special grade of filter paper is used which has been washed with acids, and which on burning leaves an ash whose weight may be neglected in ordi- nary quantitative work. The size of the filter should be adapted to the amount of precipitate. The larger the filter, the greater the quantity of wash water needed to remove impurities, consequently the filter should be kept as small as possible. The speed of filtration depends upon 1. The filtering medium. 2. The temperature of the solution. 3. The pressure. Paper is most commonly used for filtering, although in many cases asbestos may be used. Rapidity of filtration depends upon the size of the pores of the filter. Since the internal friction of water is less at high than at the INTRODUCTION 13 ordinary temperatures, it is evident that hot solutions will filter more rapidly than those which are cold. Filtration is often accelerated by diminishing the pressure on one side of the filter. This is accomplished most frequently by the use of long narrow-stemmed funnels. The stem of the funnel becomes filled with a column of Hquid, the weight of which draws the solution through the filter. It is apparent that if the filter does not fit the funnel, air will be drawn down between the filter and the funnel and the advantage of a long stem will be lost. Fil- tration may also be hastened by placing the funnel in the neck of a flask and diminishing the pressure in the flask by means of a suction pump. When this method is employed, care must be taken that the filter is not torn. Its point must be supported by means of a well-fitting platinum cone, or by a cone of hardened filter paper. A very serviceable form of filter paper used for this pur- pose is the half form hardened filter, the use of which is described in Part II, under the Determination of Aluminium, page 37. Washing In order to obtain a precipitate in the form of a definite chemi- cal compound, the impurities must be removed. These impurities are usually soluble salts which can be removed by washing. It sometimes happens, however, that a precipitate contains so much impurity that it must be dissolved and reprecipitated. In the second precipitation the greater part of the impurity remains in solution, while that remaining with the precipitate can easily be removed by washing. Whenever possible, precipitates should be washed several times by decantation, as impurities are much more rapidly removed in this way. When washing the precipitate on the filter, the water should be allowed to drain from the precipitate before the next portion of water is added, as the impurities are dis- solved more rapidly and with the use of the minimum quantity of wash water. The fact should be borne in mind that all precipitates are soluble to some extent, consequently a large amount of wash water may dissolve enough of the substance to introduce an appre- ciable error. Enough wash water should be used to remove the impurities, but no more. The washings are usually tested for some specific impurity, and when this is removed, it is assumed that the other substances have also been washed out. In the determina- 14 QUANTITATIVE ANALYSIS tion of chlorine, for example, the precipitate contains silver nitrate and sodium nitrate as impurities. It is washed until free from sil- ver nitrate on the assumption that by that time it will also be free from sodium nitrate. The wash water must always be tested to be sure that the impurities are removed and under no circum- stances may tliis be neglected. Colloidal precipitates on being washed frequently return to the finely divided state, and run through the filter. This may be pre- vented by using wash water which contains a salt which will vola- tilize when the precipitate is ignited. Ammonium nitrate is often used for this purpose. Drying and Igniting Precipitates For the removal of the last portion of wash water, the precipi- tate is usually dried in an air bath which is maintained at a tem- perature of iio°. To prevent contamination from dust, the funnel should be covered with a wet qualitative filter the edges of which are folded down over the edge of the funnel. Gooch crucibles may be conveniently dried by placing them into small covered beakers, and then putting them into a hot closet. Filters are ignited by the following methods : 1. By placing them with the precipitate into a crucible, allow- ing access of air, and heating until the carbonaceous matter is con- sumed. This method is used when the burning filter paper has no action on the precipitate. 2. By removing the precipitate as completely as possible from the filter, igniting the filter paper upon a platinum wire, so that the ash will fall into a crucible, then adding the main part of the precipitate to the ash. This method is employed when the pre- cipitates are of such a nature that the burning filter paper will change their chemical composition. Crucibles For the ignition of many precipitates porcelain crucibles may be used. They have the disadvantage of being easily broken ; more- over, the thickness of the porcelain makes it impossible to heat the precipitate to a high temperature. On the other hand, they are cheap and are impervious to the reducing gases of the burner. For many purposes platinum crucibles are indispensable. Their INTR OD UCTION 1 5 advantages lie in their resistance to the ordinary reagents, also in the fact that they permit the precipitate to be heated to an ex- tremely high temperature. Their use is restricted by conditions described under the following paragraph. The Use and Care of Platinum ' It is important to remember that, although platinum is not oxidized in the air at any temperature, nor attacked by any single acid, yet there are many substances that attack and combine with it at comparatively low temperatures. Platinum should never be used in solutions containing free chlorine, bromine, iodine, or ferric chloride, as it is attacked under these conditions. The caustic alkalies, the alkaline earths, nitrates and cyanides, and especially the hydrates of barium and lithium, attack platinum at a red heat, although the alkaline car- bonates have no effect at the highest temperatures. Sulphur, in the presence of alkalies, has no action, but phosphorus and arsenic attack platinum when heated with it. Organic matter containing phosphorus should not be ignited in platinum dishes, as it affects the platinum seriously. Direct contact of platinum with burning charcoal should be avoided, since the silicon reduced from the charcoal ashes unites with platinum, making it brittle and hable to fracture. Also contact with compounds of the easily reducible metals is especially dangerous at high tem- peratures, as alloys having a low fusing point are readily formed with platmum. This is especially true of lead. Moreover, the red-hot crucible should never be seized with brass crucible tongs, as hot platinum dissolves copper, and the cru- cible is often stained in this way. When gas is used, care should be taken to have the supply of air sufficient to insure complete combustion, since, with a flame containing free carbon, the plati- num suffers deterioration by the formation of a carbide of platinum, which, oxi- dizing later, blisters the metal. For this reason, also, the inner cone or reducing flame should not be in contact with the metal. The loosening effect of the Bun- sen flame upon the surface of platinum exposed to its action produces the familiar gray appearance which cannot be removed except by burnishing. Platinum tri- angles often become gray and very brittle from the same cause. Systematic application of moist sea sand to all articles affected in this way, after use, will keep them in prime condition and materially prolong their life, with but a trifling loss in weight. Hot crucibles should not be plunged into cold water to loosen fusions which they contain, nor should the platinum be worked between the fingers for the same purpose. If possible, each crucible should be provided with a wooden form which will aid materially in keeping it in the proper shape. Every careful analyst of necessity uses clean utensils. The habit of cleaning and polishing platinum dishes immediately after using them is easily formed, and repays the user with increased confidence in his work as well as in the prolonged life of the article. Rubbing the surface of platinum with moist sea sand (round ' From directions furnished by Baker & Co. 1 6 QUANTITATIVE ANALYSIS grains only) applied with the finger, serves to remove most impurities and to pol- ish the metal without material loss. Fusing potassium bisulphate or borax in the platinum vessel and then boiling it in water and polishing it with sand, as above, is recommended by Gmelin. When it is desired to clean the outer surface of dishes in this manner, they must be placed in dishes of sufficient size to allow the fused flux to envelop completely the article to be cleaned. Sodium amalgam possesses the property of wetting platinum without amalgamating with it, even when other metals are purposely added to the amalgam. This substance, therefore, is useful for effecting a quick and thorough cleansing of platinum. The amalgam is gently rubbed upon the metal with a cloth and then moistened with water, which oxi- dizes the sodium and leaves the mercury free to alloy with foreign metals. The mercury is then wiped off, and the dish is cleaned and polished with sand. If the existence of a base metal alloyed with the platinum is suspected, immerse the article in question first in boiling hydrochloric acid for a few minutes, then, after a thorough rinsing with clean water, immerse it in boiling nitric acid free from chlorine. If the dish is unaffected in weight or appearance, and the acid baths fail to give reactions for the base metals, their absence in appreciable quantities is assured. The Balance Quantitative analysis may be said to have had its birth with the introduction of the balance into the chemical laboratory. The bal- ance is, therefore, one of the most important pieces of apparatus which the chemist uses, and in order to do intelligent work a thorough knowledge of the principles of construction and of its essential parts is necessary. The balance is used to determine the weight of substances, and this is accomplished by utiHzing the force of gravity, which acts as parallel forces on the bodies to be weighed. When these forces are equal, the bodies are said to have equal weights. The weight of a body, i.e., the measure of the earth's attraction for it, bears a definite relation to the quantity of matter it contains, that is, to its mass. The process of weighing is, therefore, a determination of the relation between masses. The weights employed are standard masses, and the process of weighing consists in comparing the at- traction of the earth for the standard mass with its attraction for the mass of the substance whose weight is to be determined. The force of gravity is not the same at all places on the surface of the earth, but varies with the latitude and with the elevation above sea level. The mass of a body does not vary whatever its location on the surface of the earth, hence, the standard mass (weight) and INTR on UCTION 1 7 the body to be weighed will be affected alike by a change in location. The Construction of the Balance The usual analytical balance is essentially a lever supported at its middle point on a frictionless fulcrum and resting in a state of stable equilibrium. The lever, which is known as the beam of the balance, is, therefore, divided into two arms which have as nearly as possible the same length and weight. At the ends of the beam are suspended two pans by means of hooks or stirrups which rest on bearings similar to that on which the beam rests. The essential parts of the balance are : 1. The beam. This should be in a state of stable equilibrium and respond readily to small differences in load. 2. The bearings. Both the central and terminal bearings consist of a knife-edge and a plane or concave surface. They should be made of agate. 3. The pans and their supporting devices. They should be made of non-corroding metal and constructed as light as possible. To fulfill the requirements of the chemist, the balance should be accurate and sensitive. The construction of the essential parts of the balance determines its character. Position of the Center of Gravity The condition that the beam be in a position of stable equilib- rium is fulfilled when the center of gravity is below the axis, that is, below the line of contact between the central knife-edge and the plane on which it rests. For, if the center of gravity were in this axis, the condition of equilibrium would be indifferent, and the beam would not oscillate, but would remain in any position in which it was placed. If, on the other hand, the center of gravity were above the axis, the equilibrium would be unstable, and if the beam were once removed, it would not return to its original posi- tion. By sensitiveness is understood the ease with which the beam moves. The sensitiveness of a balance is usually defined as the angle through which the beam will turn for a given difference of load upon the two pans. It depends mainly upon the nearness of the center of gravity to the axis. Every balance is so constructed 1 8 QUANTITATIVE ANALYSIS that the degree of sensitiveness can be regulated within certain limits by adjusting the distance between the two. This is accom- plished by raising or lowering a movable bob upon the pointer, or a nut upon the post above. The time of oscillation increases with the sensitiveness. It is possible for the oscillations to be so slow that a considerable amount of time will be lost in weighing. The time of an oscillation should be from ten to fifteen seconds. The Knife-edges The terminal knife-edges of a good balance should be parallel to each other and to the central knife-edge. They should lie in the same plane with the central knife-edge, or very slightly above it. By loading the pans of a balance there is a change in the po- sition of the center of gravity with respect to the axis, and it has been shown that a change in the relative position of the axis and the center of gravity affects the sensitiveness. If the terminal knife-edges are below the central one, loading the pans lowers the center of gravity still further and thereby decreases the sensitive- ness. The Beam The beam is one of the main factors in establishing the sensi- tiveness of a balance. The beam must be as rigid as possible, for by loading the balance the terminal knife-edges would be lowered if the beam should bend, and consequently the sensitiveness of the balance would be decreased. As no beam is absolutely rigid, it is practicable to place the terminal knife-edges slightly above the central one and so regulate their distance from the axis that the maximum load of the balance cannot produce indifferent or un- stable equilibrium. If the arms of the beam are heavy, it will re- quire a larger weight at one end (ia one pan) to produce a given deflection than if the beam were lighter. Hence, it is apparent that the sensitiveness, which is the angle of deflection, depends upon the weight of the beam — the lighter the beam, the greater the sensitiveness ; therefore, the beam should be constructed as light as possible. It is very evident, from the principles of the lever, that in the case of two levers (other things being equal), the one with the longer arms will be moved by a smaller weight than the one with short arms. The balance with the longer beam will INTRODUCTION 19 have a greater angle of deflection than the short-armed beam ; therefore, the longer the beam, the greater the sensitiveness. But here, too, there is a Hmit, for it is difficult to get a long beam that is sufficiently rigid without giving too much weight ; further, if it is too sensitive, there may be too much time lost in weighing. From these facts, there has grown up the rivalry between the long and short-armed balances. By the introduction of aluminium in the manufacture of balance beams and pans, we are enabled to get a medium length rigid beam that is very light, thus combining the strong points of the other two styles of balances. The pans are suspended from the ends of the beam upon the terminal knife-edges by means of hooks or stirrups, which permit them to hang perpendicularly and thus not increase the length of the beam. Friction at the terminal knife-edges affects very seri- ously the sensitiveness of the balance. The Weights The capacity of the analytical balances is usually 200 grams; i.e., the maximum weight which may be placed on each pan. It is very rarely, however, that the analyst weighs objects having a greater weight than 100 grams. Hence, sets of weights from 50 grams to 5 milligrams, having a total weight of about 100 grams, are usually provided with each balance. The weights from one gram up are made of brass and are often gold plated, while the fractional weights are of platinum made in the form of a square with one edge turned up to facilitate handling. Milligrams and fractions thereof are measured by a small weight called a rider. This is placed upon the beam, which is graduated from the point directly above the central knife-edge out to the point directly above the terminal knife-edge. The number of divisions depends upon the make of the balan>ce, there usually being 50, 60, or 100. When 5, 6, and 10 milligram riders are used respectively, each di- vision will represent -^^ of a milligram. By means of a rod carry- ing a finger the rider can be conveniently placed at will on any division on the beam. Owing to the different graduations on the beams of balances of different makes, much confusion may arise from use of riders obtained from the various manufacturers. Al- ways be sure that the rider employed when placed on the proper division will balance the 5-milligram weight. 20 QUANTITATIVE ANALYSIS Summary of Precautions to be Observed in Weighing 1. Sit directly in front of the center of the balance so as to avoid parallax while observing the movements of the pointer. 2. See that the balance is level. 3. See that the rider will be free from the beam when it is swinging. 4. Release and arrest of the beam and pans. a. Release the beam before releasing the pans. b. Release and arrest the beam with a slow, steady move- ment, avoiding jerky movements which are sure to in- jure the knife-edges. c. The beam should be arrested only when it is in a hori- zontal position. d. Avoid giving the pans a rotatory motion in the horizon- tal direction, and all other motions which would cause the knife-edges to scrape on their bearings. e. If the beam does not begin swinging as soon as it is released, set it in motion by placing the rider on the four or five milligram division and raising it again. 5. Never place an object, not even the smallest weight, upon the pan, or remove one from it, unless the beam and pans are supported, i.e., arrested. 6. Always place the weights and objects to be weighed in the middle of the pans. Long tubes and other objects which cannot be easily centered on the pan, may be suspended from the hooks above the pans. 7. Handle all the weights with the tweezers provided for this purpose, and never use these tweezers for any other purpose. 8. Objects to be weighed must never be placed in direct con- tact with the pans unless they are metallic, glass, or porcelain. Hot objects cannot be accurately weighed, owing to the upward draughts they create about the pan on which they rest. They may also heat the beam and thus produce a change in the relative length of the arms. Hygroscopic and volatile substances, and those that absorb carbon dioxide from the air, should be weighed in closed vessels which must be opened a moment before weighing. g. Weighing is an accurate operation: never do it when in a hurry. INTR on UCTION 2 1 10. Be sure that the reading of the weights is taken correctly. Check by two readings ; first, read the weights from the vacant spaces where they are kept, and, second, read again as the weights are returned to their places. 11. Never leave the beam resting on the knife-edge when not in use, and never leave the weights on the pan, but always return them to their places. PART II GRAVIMETRIC ANALYSIS EXERCISES WITH THE BALANCE Exercise I Determination of the Time of Vibration Procedure. — Dust the beam and pans very carefully with a camel's-hair brush. Cautiously release the beam and then the pans. After the beam has oscillated long enough to recover from the effects of any jar it may have received when released, deter- mine the time required for the pointer to make ten excursions past the central or zero part of the ivory scale. One tenth of this is the Time of Vibration. Determine the time of vibration when the pointer makes long, short, and medium excursions. Note. — Time of vibration varies with the load. It also varies with the length of the beam, — -the shorter the beam, other things being equal, the shorter the time. The time of vibration for a balance with a given load is a measure of the sensitiveness. Much can be learned concerning the quality and condition of a balance by simply determining the time of vibration under different loads. Exercise II Determination of the Zero Point Procedure. — Release the beam and then the pans, and after a few excursions of the pointer, begin to note and record the num- ber of scale divisions the pointer passes over, estimating to tenths of a division. Place the readings to the right in a column headed R, and those to the left in one headed L. Take a number of observations, three or four on one side and a greater number by one on the other side. Add the two columns and divide each sum by the number of observations taken on that side. The re- sults represent the average excursion of the pointer. Now add these two and divide by two and subtract the quotient from the GRA VIMETRIC ANAL YSIS 2 3 greater of the average excursions. The result gives the distance from the center of the scale, on the side of the longer swing at which the pointer would stop if the beam were to come to rest, i.e., the Zero Point. If the zero point is found to be more than half a division from the middle line of the scale, it should be brought nearer by adjusting the nut on the screw projecting from the end of the beam. Exact adjustment is not essential, as the relative length of the arms is constantly changing. Do not adjust the bal- ance, but ask the instructor to do so. Note. — Lack of constancy of the zero point may be due to changes of temperature, defective condition of the knife-edges, or to jarring. Exercise III Determination of the Sensitiveness Procedure. — Determine the zero point without a load. Now place the rider on the one milligram division (the first numbered division) of the arm and again determine the zero point. The dis- tance between these two zero points is usually designated the Sen- sitiveness of the balance. Note. — A balance is sufficiently sensitive for ordinary quantita- tive work when a weight of one milligram changes the zero point three divisions. Exercise IV Weighing by the Usual Method Procedure. — Obtain the object to be weighed and remove any moisture by means of a clean linen handkerchief. Determine the zero of the balance. Place the object in the center of the left pan and in the center of the right-hand pan a weight which is estimated to be approximately the weight of the object. Release the beam until it is evident which way it swings, then slowly sup- port it again. In case the weight added is nearly equal to the weight of the object, it may be necessary to release the pans in order to see which way the beam swings and which is the heavier, the weight or the object. If the weight is too heavy, remove it and add the next lighter weight, following the order in which the weights are placed in the box. When the beam shows that the 24 QUANTITATIVE ANALYSIS weight added is just too light, add to it the next smaller weight. If this is too heavy, remove it and make trials until one is found which again gives a total weight which is just too light. Continue this series of trials until all of the necessary weights from the box have been added, then place the rider at different points on the arm until one is reached at which the zero point is found to coin- cide with that previously found for the unloaded balance. Begin- ning with the largest weight, read them from the vacant spaces in the weight box and record the values, expressing them in grams and decimals thereof. Do not neglect to notice the position of the rider on the beam and include this value. Then check this by reading the values of the weights as they are removed from the balance pan. GRAVIMETRIC DETERMINATIONS Exercise V The Determination of Chlorine Procedure. — Clean a weighing tube thoroughly, be sure that it is dry, and provide it with a well-fitting cork. Take the tube to the instructor's office and obtain the substance to be analyzed. With a clean Hnen handkerchief remove any particles of substance which adhere to the cork and the inside of the tube as far as the cork extends. Clean two No. 3 beakers, mark them i and 2 respectively, and take them and the weighing tube into the balance room. Be sure that the outside of the tube is clean, then weigh it on the balance which has been assigned, and record this weight in the notebook in the manner indicated on page 3. Hold the weighing tube over beaker No. i, carefully remove the cork by a rotary motion, and by rotating the tube introduce 0.2 to 0.4 gram of the substance into the beaker. Tap the tube gently to remove any loose particles, replace the cork, and weigh the tube and its contents. If much more than 0.4 gram has been taken, it will be necessary to weigh out another portion into a clean beaker. Weigh another portion of the substance into beaker No. 2. Be sure that the numbers on the beakers correspond with the proper weights of substances recorded in the notebook. Add to each portion of the substance about 100 c.c. of cold distilled water and a slight excess of dilute nitric acid. This GRAVIMETRIC ANALYSIS 25 should be done by making the sokition just acid with dilute nitric acid. Use litmus paper to test the acidity of the solution and be sure to wash the liquid adhering to the paper back into the beaker by means of water from the wash bottle. Add to the beaker an excess of two or three cubic centimeters of dilute nitric acid. Now add a clear solution of silver nitrate, drop by drop, allowing it to run down the side of the beaker and stirring continuously with a glass rod. Continue this until no more precipitate is seen to form. Stir the solution vigorously until the particles of the precipitate collect in a curdy mass, then test for complete precipi- tation by adding a few drops of the silver nitrate to the solution. Heat the contents of the beaker until the temperature is near the boiling point, and continue the stirring until the liquid is practi- cally clear. Place a 9 cm. ashless filter paper into a funnel, folding it so that it will fit exactly. If the angle of the funnel is exactly 60°, the filter will fit if it is carefully folded in the usual manner. If it does not fit, it will be necessary to adjust it to the funnel by allowing one edge to lap over the other. By holding the filter in place with the finger and wetting it, it will adhere to the side of the funnel. Be sure that the top edge fits snugly to the funnel. Now filter by pouring the liquid down a glass stirring rod, held tightly against the lip of the beaker and reaching nearly to the bottom of the filter. Wash the precipitate by decantation, using portions of about 20 c.c. distilled water acidified with nitric acid. This should be done by stirring the precipitate in order to disintegrate it, allowing it to settle and pouring off the super- natant liquid as described above. Repeat this process three or four times. Replace the beaker containing the filtrate with a clean beaker, and transfer the precipitate to the filter by aid of a stream from the wash bottle which should contain water acidi- fied with nitric acid. This may be accompHshed by holding the beaker in an inclined position with the lip down, with stirring rod pressed firmly against the lip. By means of a jet of water from the wash bottle the precipitate may be washed down the rod and into the filter. If it cannot be entirely removed in this manner, then by means of a stirring rod provided with a policeman the precipitate can be loosened from the beaker and then removed. Be sure that all of the precipitate is completely removed. This may be ascertained by cleaning the outside of the beaker and then 26 QUANTITATIVE ANALYSIS observing it when held toward the light. When the precipitate has been completely removed from the beaker, continue the washing by directing a stream of the cold acidified water from the wash bottle against the top of the filter. Conduct the stream around the edge of the filter until the water has filled it to within one quarter of an inch from the top. Add no more wash water until that in the filter has run through. Continue washing in this way until the impurities are all removed. This can best be ascer- tained by collecting about 3 c.c. of the wash water in a test tube, acidifying with nitric acid, and adding a drop of dilute hydro- chloric acid. If no turbidity results, the washing is complete. Allow the funnel to drain for a few minutes, cover the top with a piece of wet qualitative filter paper, label properly, and place it into a drying closet which is heated to 110°. While carrying out the foregoing steps of precipitation and filtration, the student will find time to prepare in the following manner two porcelain crucibles in which to weigh the precipitates. Clean two porcelain crucibles and covers and mark them i and 2 respectively by means of a blue pencil. Place the crucibles on clean clay triangles which are resting on tripods, and heat them for fifteen minutes to the full heat of the adjustable burner. Remove the burners, allow the crucibles to cool for about a minute, place them into a desiccator, and weigh them after they have cooled to room temperature, which usually takes about fifteen minutes. Heat again and reweigh. Continue this until two consecutive weighings are not more than 0.2 milligram apart. The crucible has now a constant weight. When the contents of the funnels are dry, remove from the hot closet. Place side by side on the desk two pieces of glazed paper about six inches square, the edges of whicH should be smooth. Remove the filter from the funnel by inserting the small blade of a penknife between the paper and the funnel. Carefully invert the filter over one of the pieces of glazed paper. Loosen the precipitate by gently squeezing and rubbing between the fingers. When most of the precipitate is separated, reverse the filter, and loosen any portions of the silver chloride still remaining by carefully rubbing the sides of the filter together. Allow the portion that is thus detached to fall upon the glazed paper and cover with a cover-glass. Fold the filter so that it will form a half circle, place it upon the other sheet of glazed paper, and fold it into a narrow GRAVIMETRIC ANALYSIS 27 flattened roll, beginning with the straight edge. Now bring the two ends together and wrap a platinum wire securely around them. In this way the central parts of the filter, to which small particles of the precipitate still adhere, are thoroughly enveloped by the exterior parts so that in the subsequent burning nothing can be easily lost. By means of the wire hold the filter paper over the proper weighed crucible which has been placed upon the glazed paper, and ignite by means of a small Bunsen flame. Allow to burn quietly until the flame goes out and then use the burner to keep the residue red hot. Shake the ash into the crucible and remove the last portions from the wire with a small brush. Finally transfer any portions of the ash which have fallen upon the glazed paper into the crucible and heat with the free flame to remove the last trace of carbonaceous matter. As silver chloride is volatilized at a compara- tively low temperature the heating should be done very carefully. Hold the burner in the hand and heat only those parts of the crucible which show black particles of carbonaceous mat- ter. As soon as the carbon is all burned remove the burner at once, allow the crucible to cool, place it upon a sheet of glazed paper, and introduce the main portion of the precipitate. Use a small brush to transfer the last portion of the precipitate from the glazed paper to the crucible. At best some of the silver chloride precipitate remaining with the filter paper has been reHuced to silver, and this must be changed to silver chloride by the following method. Add two or three drops of concentrated nitric acid to the crucible, warm, and, after allowing to cool a short time, add one or two drops of concentrated hydrochloric acid. The contents must be evaporated to complete dryness without loss by spattering. This is best accomplished by placing a small iron pan on a tripod, and supporting the crucible about one eighth of an inch above the bottom of the pan by means of a triangle resting on its edges. (See Fig. 6.) Place Fig. 6 28 QUANTITATIVE ANALYSIS under the pan a burner which is so regulated that it will not boil the contents of the crucible. When the contents of the crucible have evaporated, holding the burner in the hand, heat it with the small free flame until the precipitate just begins to fuse. Cool and weigh. Heat again and weigh as described above, until the weight of crucible and contents is constant. From the weight of the precipitate, calculate the weight of chlorine present and the percentage in the substance taken for analysis. For the method of calculation see page 163. Notes. — I. The presence of a sHght excess of silver nitrate in the solution is advantageous because of the fact that silver chloride is more insoluble in water containing a small amount of silver nitrate ; moreover, it helps the particles of the precipitate to become coagulated. 2. Under the influence of Hght the silver chloride changes from white to a violet color. This is caused by a part of the precipitate changing to a lower chloride with the loss of an appreciable amount of chlorine. The chlorine is replaced, however, by the subsequent addition of nitric and hydrochloric acids to the precipitate. 3. Silver chloride is almost completely insoluble in water which contains a little silver nitrate. It is very sHghtly soluble in cold water and in cold dilute nitric acid. It is more soluble in concen- trated nitric acid ; hence, care should be taken that the precipita- tion does not take place in a solution which is strongly acid. The precipitate is also especially soluble in concentrated hydrochloric acid and hot concentrated solutions of chlorides. 4. Hot water dissolves too much silver chloride to permit its use in washing out the impurities. Cold water, on the other hand, causes the precipitate to return to the colloidal state and run through the filter. This is prevented by adding to the water a small amount of nitric acid. 5. Silver chloride fuses at about 460°. At a temperature slightly higher than its fusing point the substance begins to vola- tilize. Considerable care should be exercised, therefore, in heating this substance. 6. The fused silver chloride may be removed from the crucible by placing a small piece of zinc upon the mass and adding very dilute hydrochloric acid. The chloride will be reduced and the metallic silver can then be easily removed. GRA VIMETRIC ANAL Y\ 31 7. The experiment just described is a type o\ o quantitative determinations. With certain modi, and iodine may be determined by this method, moreover, that the method may be reversed and th silver may be determined by the addition of hydroci, a solution of its soluble salt. 8. The determination of the chlorine in the presence ot a heavy metal is complicated by the fact that many metals, like iron, form basic salts under the condition of the precipitation, and these con- taminate the precipitate. In such cases it is best to first remove the metal by means of a suitable precipitant. 9. The filtrate and all silver residues should be placed into the bottles marked " Silver Residues." Refere.mce Fresenius (Cohn), Vol. I, par. 82 b, p. 198. Exercise VI The Determination of Sulphur in a Soluble Sulphate Procedure. — Obtain the substance for analysis from the instructor and weigh two portions exactly as in Exercise V, but take a some- what larger amount, from 0.4 to i.O gram for each portion. Dissolve in 100 c.c. of distilled water, and acidify with 2 or 3 c.c. of dilute hydrochloric acid. Heat the solution to boiling and add, drop by drop, at a rate not exceeding 5 c.c. per minute, about 10 c.c. of a hot solution of barium chloride. The barium chloride is best added by means of a small medicine dropper similar to those used for filling fountain pens. Be sure that an excess of the precipitating reagent has been added to the solution. Keep the solution at a temperature near the boiling point for about an hour, then allow the precipitate to settle. Prepare two filters in the usual way. If the precipitates have been properly digested, and a good grade of filter paper is used, no trouble should be caused by the particles running through the filter. As an extra precaution double filters may be used or a sin- gle filter may be saturated with a hot concentrated solution of ammonium chloride. Decant the hot supernatant liquid upon the filter. Watch the filtrate closely, and if it is turbid, replace the beaker containing the filtrate with a clean one, and pass the filtrate 28 QUANTITATIVE ANALYSIS ''through the filter again. Do not proceed with the filtration until a clear filtrate is obtained. Wash the precipitate three or four times by decantation, using hot water containing a little hydrochloric acid. Replace the beaker containing the filtrate by a clean one, transfer the precipitate to the filter as in the determination of chlo- rine, and wash with hot water from the wash bottle until 3 c.c. of the filtrate give no test for chlorides. Place the funnel and con- tents into the drying closet. When dry, remove the filter from the funnel and fold it in such a way that it can be placed into a previously weighed porcelain crucible. Be sure that the part of the filter paper containing the main portion of the precipitate is placed in the bottom of the crucible. If any of the precipitate has crept over the edge of the filter and adheres to the funnel, remove it by means of a piece of moist ashless filter paper and place this into the crucible with the filter. Place the crucible in a reclining position on the triangle, and only partially cover with the crucible cover so that a current of air will pass over the filter. (See Fig. 7.) Place the burner under the crucible and heat gently with a low flame until volatile matter begins to come off. Do not allow the volatile gases to take fire, as this is attended by mechanical loss of the barium sulphate. If this should happen, extinguish the flame by means of the crucible cover. Gradually increase the flame until the volatile matter is expelled and nothing but a little carbonaceous matter is left with the precipitate. Heat to the full heat of the burner, directing the flame toward the base of the crucible. When the carbon is all oxidized, cool the crucible in the desiccator and weigh. Heat again and repeat until constant weight is obtained. From the weight of barium sulphate calculate the percentages of sulphuric anhydride and of sulphur present in the original sample. For the method of calculation see page 165 Fig. GRA VIiMETRIC A.XAL \ SIS 3 1 Notes. — I. The precipitate of barium sulphate possesses to a marked degree the power of dragging down or occluding other substances which cannot be easily removed by wash water. This may result in either high or low results. In the presence of iron, aluminium, or chromium the precipitate may be contaminated with the sulphates of these metals. On ignition, sulphur trioxide is given off, and the results obtained are low. In the presence of potassium salts low results are obtained owing to the fact that the precipitate is contaminated with potassium sulphate. When nitrates or chlorates are present, the precipitate will con- tain the barium salts of these acids, consequently high results will be obtained. The rapid addition of the precipitating reagent gives high results due to the occlusion of barium chloride. In general, the amount of occlusion is greater in concentrated solutions. From the abo\'e it is obvious that the solution from which the sulphate is to be precipitated must be as free as possible from iron, aluminium, chromium, and potassium salts. Moreover, nitric and chloric acids must be absent. 2. The addition of an excess of hydrochloric acid is to be avoided. Not only does it tend to dissolve the precipitate, but, as has been shown by Richards, it also increases the amount of barium chloride occluded. 3. If precipitated in a cold or very dilute solution, barium sul- phate will be found to be present in a very finely divided state unless allowed to stand for several hours. If precipitated in a boiling solution, and then heated, the particles are larger. (See page II.) 4. The precipitate may be considered as insoluble in water and dilute acids. It is appreciably soluble, however, in concentrated hydrochloric acid and more soluble in either concentrated nitric or sulphuric acids. The presence of either a soluble barium salt or a soluble sulphate decreases the solubility of the barium sul- phate. In this determination, therefore, a small excess of the precipitating reagent is advantageous. (See page 11.) 5. The filter containing the barium sulphate may also be ignited without first drying. In this case extreme care must be used to heat slowly. The filter should be placed into the crucible, which is inclined on a triangle, as described above, and heated with a low flame which is directed towards the top of the crucible. This dries the precipitate from the top downwards, so that there is no danger 32 QUANTITATIVE ANALYSIS of particles being blown out of the crucible by the sudden forma- tion of steam. The final ignition is conducted in the manner already described. 6. If the precipitate is ignited slowly, the filter is easily oxidized. 1-i.apid heating changes it to a form of carbon resembling graphite, which is oxidized with extreme difficulty. 7. By reversing this determination it is apparent that barium may be estimated as the sulphate. This is true of strontium ; and, with certain modifications of the method, lead may also be deter- mined in this way. References Yo'Li'^, Journal of Biological Chemistry, 1, 131 (1906). HuLETT AND DusCHAK, Zeitschrift fur anorgaftische Chemie, 40, 196 (1904). Richards and Parker, Proceedings of the Americati Academy of Arts and Sciences, 23, 67 (1895). Exercise VII Separation and Determination of Calcium and Magnesium in a Mixture of their Carbonates Calcimn Procedure. — Weigh out two portions of the sample of about I gram each into No. 3 beakers, add about 10 c.c. of water and cover with cover-glasses. By means of a stirring rod introduce through the opening between the lip of the beaker and the cover- glass about 20 c.c. of dilute hydrochloric acid. Heat the beaker on an asbestos gauze, and if any of the substance remains undis- solved, add more acid and warm again. Continue heating until all of the carbon dioxide gas is expelled ; wash the cover-glass with a little water in order to recover any of the solution that may have spattered upon it. Dilute the solution to approximately 200 c.c, make alkaline with ammonium hydro.xide, and heat to boiling. To the hot solution add slowly 25 c.c. of a freshly prepared solution of ammonium oxalate, stirring well. Digest at a temperature near the boiling point for an hour, allow the precipitated calcium oxalate to settle, and decant the supernatant liquid through a filter, keep- ing as much of the precipitate as possible in the beaker. Wash the precipitate three times by decantation, using 20 c.c. of hot water each time. Test the filtrate for complete precipitation by GRA VINE TRIC ANAL YSIS 3 3 adding a few drops of the ammonium oxalate solution and allowing to stand. If no precipitate forms, make the filtrate sHghtly acid and evaporate it on the steam bath for the determination of magnesium. Place the beaker containing the calcium oxalate precipitate un- der the funnel, and dissolve the calcium oxalate by pouring suc- cessive portions of warm dilute hydrochloric acid through the filter, washing the filter this way three times. When the calcium oxalate is all dissolved, finally wash the filter with dilute ammonium hydroxide solution. Dilute the solution to about 200 c.c, add am- monium hydroxide in slight excess, then add 5 c.c. of the ammo- nium oxalate solution, and digest as before for about an hour. Filter the calcium oxalate upon the filter which was first used and wash the precipitate with hot water until it is free from chlorides. Add the first three washings to the filtrate, then use another beaker to collect the remainder of the washings. The filtrate should be made just slightly acid with hydrochloric acid, com- bined with the first filtrate, and used for the determination of mag- nesium. (See below.) Dry the precipitate of calcium oxalate in the drying closet and ignite as described in the determination of sulphur. By heating, the calcium oxalate is changed first to calcium carbonate and finally to calcium oxide. Allow the crucible to cool, and very carefully moisten the residue in the crucible after the carbon has all been consumed, first with one cubic centimeter of water, then with a few drops of dilute sulphuric acid. Heat very cautiously to evaporate the excess of acid. When the white fumes cease to be given off from the crucible, add a few drops more of the sulphuric acid and evaporate to dryness. Heat to redness by means of the free flame, cool, and weigh. Repeat the treatment with sulphuric acid until the weight is constant. All of the calcium is thus con- verted into calcium sulphate, in which form it is weighed. From the weight of the calcium sulphate calculate the weight of calcium oxide and the percentage present in the substance taken for analysis. Magnesium Concentrate the slightly acidified filtrate from the calcium deter- mination by heating on the water bath. When the volume is about 200 c.c, cool, add ammonium hydroxide until it is just neu- 34 QUANTITATIVE ANALYSIS tral, or only very faintly alkaline. Add drop by drop 15 c.c. of a solution of sodium ammonium hydrogen phosphate (microcosmic salt). Add slowly to the solution one third its volume of ammo- nium hydroxide (sp. gr. 0.96) with constant stirring. Allow the solution to stand for several hours, then decant the supernatant liquid through a filter and wash the precipitate three times by decantation, using 2-|- per cent ammonia solution and leaving as much of the precipitate as possible in the beaker. [Calculate the amount of desk reagent required to make 500 c.c. of the 2|- per cent ammonia solution and dilute this quantity to the required volume.] Dissolve the precipitate on the filter by pouring small quantities of warm hydrochloric acid through the filter, receiving the filtrate in the beaker in which the precipitation of the magne- sium ammonium phosphate took place. Wash the filter three times with warm, slightly acid water. Dilute the solution to about 200 c.c, and add ammonium hydroxide drop by drop until the solution is shghtly alkaline, stirring vigorously meanwhile. Now add a few drops of the microcosmic salt solution to insure com- plete precipitation. Then add one third the volume of ammonium hydroxide with constant stirring, and allow to stand for several hours. Decant the supernatant liquid through a filter, wash the precipitate three times by decantation, using cold 2^ per cent ammonia solution, then transfer the precipitate to the filter, con- tinuing the washing with the dilute ammonium hydroxide until a few cubic centimeters of the filtrate give no test for chlorides. Dry the precipitate, transfer the main bulk to a glazed paper, and burn the filter separate from the precipitate as directed in the determi- nation of chlorine, but omit the treatrnent with acids. Transfer the precipitate to the crucible, bring gradually to the full heat of the Bunsen flame, and heat until the precipitate is white. Cool in the desiccator, weigh, and heat to constant weight. From the weight of the pyrophosphate calculate the weight of magnesium oxide, and the percentage of magnesium oxide in the substance taken for analysis. Notes. — I. The separation of calcium and magnesium depends upon the different solubilities of the two oxalates. Calcium oxa- late is practically insoluble in hot water, whereas magnesium oxalate is relatively soluble. Magnesium oxalate is, however, much more soluble in water containing an excess of ammonium GRAVIMETRIC ANALYSIS 35 salts. If a large amount of magnesium is present, the precipitate of calcium will contain some magnesium oxalate, and a reprecipita- tion is necessary. 2. The solution should be well boiled to expel the carbon dio;<- ide. If this is not entirely removed, on adding ammonium hy- droxide and ammonium oxalate the precipitate will consist of calcium oxalate and calcium carbonate. As this latter compound is more soluble than the oxalate, it is well to avoid its formation. Ammonium oxalate solution should be freshly prepared. On standing it undergoes decomposition, ammonium carbonate being one of the products formed. 3. Calcium oxalate on gentle ignition below visible redness is changed to the carbonate and as such may be weighed. A tem- perature slightly too high, however, expels some carbon dioxide. The complete conversion to the oxide requires heating in a plati- num crucible at a high temperature. The action of the sulphuric acid on the calcium oxalate, oxide, and carbonate is to convert them into calcium sulphate. This compound will stand the cherry red heat of a Bunsen burner without alteration ; the higher heat of tlie blast will cause it to lose sulphuric anhydride. 4. On concentrating the filtrate from the calcium oxalate, a crystalline precipitate of magnesium oxalate will sometimes settle out. This may be dissolved in dilute hydrochloric acid and added to the solution. 5. The complete precipitation of magnesium as the salt MgNH4P04 takes place only under certain conditions which must be closely observed. Contamination of the precipitate rnay occur : ^ a. When the precipitation takes place in a strongly ammoniacal solution, particularly when the phosphate is slowly added, the pre- cipitate under these conditions always contains some of the normal magnesium phosphate. b. If the precipitation takes place in a neutral or slightly am- moniacal solution in the presence of ammonium salts and ammo- nium hydroxide is afterwards added, the precipitate then always contains some magnesium tetra ammonium phosphate. To insure a pure precipitate, the solution must be neutral, as 1 This discussion of the determination of magnesium follows very closely Treadwell's (Treadwell-Hall, Vol. II, p. 62, ed. 1904) description of the experiments of Neubaucr (Zeit. fiir Angew. Chem. p. 439, 36 QUANTITATIVE ANALYSIS free as possible from ammonium salts, and the ammonium hydrox- ide must be added after the addition of microcosmic salt solution. 6. The solution in which precipitation takes place may be freed from ammonium salts : a. By evaporation of the solution and the ignition of the resi- due, or evaporation to dryness with an excess of nitric acid. b. By first precipitating the magnesium in the presence of the ammonium salts, then dissolving the impure precipitate in a small amount of acid, and reprecipitating. The second precipitation takes place under the specified conditions, and the precipitate is obtained pure. 7. On the addition of a microcosmic salt solution to the neutral solution containing magnesium, 90 per cent of the magnesium present is at once precipitated as magnesium hydrogen phosphate (MgHP04). When ammonium hydroxide is added to the cold solution, this precipitate is changed to the crystalline magnesium ammonium phosphate. The 10 per cent of the magnesium hydro- gen phosphate which remained in the solution is also completely precipitated by this procedure as magnesium ammonium phos- phate. 8. Magnesium ammonium phosphate is appreciably soluble in hot water, but is much less soluble in cold water. It is least solu- ble in a cold dilute solution of ammonium hydroxide. 9. During ignition the magnesium ammonium phosphate loses water and ammonia, and is converted into magnesium pyrophos- phate. If the pyrophosphate appears gray, it may be whitened by moistening with a few drops of concentrated nitric acid and reigniting after expulsion of the excess of nitric acid by heating over a radiator. References Calcmm Fresenius, Quantitative Analysis (Cohn), Vol. I, par. 73, p. 173. Magnesium W- F. HiLLEBRAND, The Analysis of Silicate and Carbonate Rocks, Bull. No. 305, U.S. Geol. Surv., p. 105. Fresenius, Quantitative Analysis (Cohn), Vol. I, par. 74, p. 176. GRA I 'IMETRIC ANAL YSIS 37 Exercise VIII The Determination of Aluminium in a Soluble Salt Procedure. — Obtain a sample containing aluminium and weigh out two portions of about one gram each. Dissolve in lOO c.c. of hot water, add about 5 c.c. of concentrated hydrochloric acid, and then enough of a clear solution of ammonium hydroxide to make the solution slightly alkaline. Test with litmus paper or by odor after stirring thoroughly. Be sure to avoid adding more than a slight excess of ammonium hydroxide. Boil gently until the liquid gives only a very slight odor of ammonia, or shows a slightly alkaline reaction. Allow the precipitate to settle, then filter at once. This filtration can best be accomplished by the use of suction. Obtain from the supply room the apparatus to be used for this purpose, which consists of the following : I filter pump ; 1 glass T-tube ; 2 filter flasks (500 c.c.) ; 2 rubber stoppers (i hole) to fit the flasks; 2 hardened filter cones ; 2 ashless filter papers, 1 1 cm. Attach the filter pump to a water cock. Connect to this, by means of rubber tubing and the glass T-tube, the two filter flasks which carry by means of the rubber stoppers the two funnels. Fold the half form hardened filter into a cone by the method shown in Fig. 8, and place into the funnels. Upon these place the 11 cm. filtpr papers folded in the usual way. Press the papers into position, be sure that the filter paper fits the funnel snugly at the upper edge, and moisten with a little distilled water. Pour the clear supernatant liquid through the filter and wash 38 QUANTITATIVE ANALYSIS the precipitate by decantation, using boiling water which contains a few drops of ammonium hydroxide and two or three grams of ammonium nitrate per liter. Use a gentle suction to accelerate the filtration and always keep some liquid in tlie funnel while suc- tion is being employed. Finally, transfer the precipitate to the filter, wash free from chlorides, dry the filter, and ignite as in the determination of sulphur. After burning the carbon of the filter, heat the precipitate in the flame of a blast lamp until the weight is constant. Calculate the percentage of aluminium oxide present in the sample taken for analysis. Notes. — I. The complete precipitation of aluminium as the hydroxide takes place only in the presence of certain salts, in this case ammonium salts. The ammonium salts have a twofold function, they decrease the tendency of the excess of ammonium hydroxide to dissolve the precipitate, and they also prevent the aluminium hydroxide from running through the filter in a colloidal or semisoluble condition. The presence of the ammonium nitrate in the wash water has a similar effect. 2. Prolonged boiling to expel the excess of ammonia should be avoided, as it may result in the solution becoming acid, with the subsequent dissolving of a part of the precipitate. 3. The aluminium hydroxide should be filtered as soon as pos- sible after precipitation. On standing, it adheres to the beaker and is removed only with great difiSculty. 4. The precipitate should not be allowed to stand in the funnel for any great length of time without washing, as it dries and cracks, and is then almost impossible to wash free from impurities. The washing should be continued until all chlorides are removed, as any ammonium chloride not washed out will form volatile aluminium chloride on igniting the precipitate. 5. When aluminium hydroxide is ignited, water is given off with the formation of AIO(OH), and on further ignition alu- minium oxide is formed. The aluminium oxide parts with the last trace of water with difficulty, so that the final heating must be done with the blast lamp. As the aluminium oxide also absorbs water easily, unless it is weighed quickly a considerable amount of water will be taken up. The weighing is best accomplished by obtaining an approximate weight of the crucible plus the precipi- t^ite, then making a second weighing by placing the necessary GRAVIMETRIC ANALYSIS 39 weights upon the pan, removing the crucible from the desiccator and completing the weighing by means of the rider. 6. Many other metals, such as iron, chromium, nickel, and cop- per are determined by precipitating as the hydroxide in a manner similar to that just described. With the last two metals, potassium hydroxide is usually employed as the precipitating reagent. Reference Fresenius, Quantitative Analysis (Cohn), Vol. I, par. 75, p. 179. PART III VOLUMETRIC ANALYSIS Volumetric analysis comprises those methods wherein the con- stituent of a sample is not isolated and weighed, but determined by allowing a solution of known composition to react with it, either directly or indirectly. From the volume of the solution used, the amount of the constituent can be computed by means of the laws of chemical equivalents. For example, in a solution containing sodium chloride, the amount present can be determined by pre- cipitating the chlorine as silver chloride, by the addition of a solu- tion of silver nitrate of known strength. In order to indicate the point at which all of the chlorine is precipitated, a little potassium chromate is added to the solution. When the silver nitrate has pre- cipitated all of the chlorine as silver chloride, the next drop of the solution added will react with the potassium chromate with the for- mation of a permanent reddish precipitate of the chromate of silver. A substance, such as potassium chromate, which is used to show when a reaction is complete is called an Indicator. It is very easy to detect this point at which all of the chlorine is precipitated, and from the amount of silver nitrate solution added the equivalent quantity of chlorine can be readily calculated. VOLUMETRIC APPARATUS i The ordinary methods of volumetric analysis require the employ- ment of vessels which will contain or deliver definite specified quantities of solutions. The vessels in general use are the follow- ing : Pipettes are used to deliver definite amounts of liquids. They are of two general kinds : Those provided with one mark deliver but one specified quantity of liquid. This form is illustrated by the 1 See report of the committee for cooperation with the National Bureau of Standards, four. Am. Chem. Soc. Proceedings, p. 17 (1904). 40 VOLUMETRIC ANALYSIS 41 V 23" C.C \ / 25 C.C. pipette in Fig. 9. Those with two marks have the interven- -iiig space subdivided and permit the exact measurement of different quantities of liquid. This form is represented by the 10 c.c. pipette in Fig. 9. To fill the pipette the liquid is sucked above the upper mark and is then held in place by placing the index finger over the top. The liquid is lowered to the mark by slowly rotating the pipette between the thumb and middle finger, and is allowed to run out into the desired vessel by raising the index finger. The opening through which the liquid is delivered should be small, since the speed of outflow determines the amount of liquid remaining on the inner surface. In order to re- move a constant quantity of liquid, hold the point against the wall of the receiving vessel during the free outflow and for fifteen seconds thereafter. Graduated Cylinders are of vari- ous sizes, ranging from a few cubic centimeters to a liter or more in capacity. They are usually not graduated in small divisions and are, therefore, employed when liquids are to be measured only roughly. The usual form is rep- resented in Fig. 10. Graduated Flasks are made in sizes ranging from 25 c.c. to several liters in capacity. The general form is illustrated in Fig. II. They are usually provided with two marks, the lower one in- dicating the point to which the flask is to be filled in order to have contained therein the des- ignated amount, while the upper mark indicates the amount which should be placed into the flask in order to remove from it the specified quantity, the difference in the two quantities being the amount of the liquid that will adhere to the inner surface of the flask. Fig, Fig. 10 42 QUANTITATIVE ANALYSIS Q Burettes are long tubes graduated in cubic centimeters and frac- tions thereof, from which Hquids may be conveniently measured. They have capacities ranging as high as too c.c. In the authors' laboratories burettes of 30 c.c. capacity graduated to ^V o^ ^ cubic centimeter have been found to be of convenient size. Two such burettes with a burette holder are represented in Fig. 12. Burettes should be read to hundredths of a cubic centi- meter, and in reading them the exact position of the curved surface of the liquid, termed the ine- niscus, will depend upon the position of the eye. Hence, great care should be exercised to have the eye on a level with the meniscus. Many devices are employed to facilitate reading burettes. That represented in Fig. 13 shows a strip of paper wrapped around the bu- rette by means of which the position of the menis- cus can be accurately lo- cated. The paper should be held in such a position that the upper edge will be about one milli- meter below the lower surface of the menis- cus, and the eye on a level with the two upper edges of the paper. Parallax can also be avoided by providing burettes with marks which extend nearly or quite around them. A method of having burettes con- structed with a white back in the center of which is a blue stripe, has been devised by Shellbach. By this arrangement the menis- cus appears to be divided into two parts which meet in a point in the center, thus giving a sharp definite point, which is very accurately located. Fig. II JjncoIn'sPiiretteHolde; L : 2i Fig. 12 VOLUMETRIC ANALYSIS 43 THE CALIBRATION OF GRADUATED APPARATUS In accurate chemical work the capacity of all graduated apparatus should be carefully tested. This process of testing is known as Calibration. The vessels to be used should all be calibrated among themselves, so that the relation is accurately known. The 25 c.c. pipette should deliver exactly the same amount of a solution as is delivered by the burette when it reads 25 c.c, and this quantity should be -^-^ the amount contained in the 250 c.c. flask, and -^-^ the capacity of the 1000 c.c. flask. It does not make any difference at what temperature these vessels are calibrated, because the meas- urements are only relative. Nor does it make any difference what unit is employed, provided the same one is used for all of the different measuring vessels. The Mohr cubic centimeter has been used ex- tensively as the unit of volume in volumetric work and is defined as the volume of one gram of water at 17.5" weighed in air with brass weights. This is not, however, a true cubic centimeter, which is defined as the volume of one gram of water in vacuum at its greatest density (4° C). The relation between the Mohr cubic centimeter and the true cubic centimeter is (Cr:^ I Mohr c.c. = 1.0023 true c.c. 17 18 20 In other words, 1000 grams of water, weighed \^ in air, would occupy a volume of 1002.3 c.c. at I g 17.5", or the Mohr liter would occupy a greater ^^^ volume than the true liter. For the most accurate work, in which solutions of definite con- centrations are to be prepared, also for the calibration of burettes for measuring gases, the true cubic centimeter should be used as the standard of calibration. Suppose we desire to cahbrate a liter flask in true cubic centi- meters. The dry flask is placed upon the balance pan and suffi- cient weights are added to counterpoise it. Now, as we desire to establish a mark on the flask which represents just one liter or 1000 true cubic centimeters which weigh 1000 grams in vacuum, the 44 QUANTITATIVE ANALYSIS question arises what difference would there be between the weight in air and in vacuum ? How much weight shall be placed upon the pan to represent the looo grams of water in vacuum ? One kilogram of water displaces approximately one liter of air, which under the ordinary conditions of temperature and pressure weighs about 1.2 grams. (One liter at 0° under a pressure of one atmos- phere weighs 1.293 grams.) Just as the weight of a body in a liquid is lighter than its weight in air by the amount of the liquid displaced, so the water is lighter in air than in a vacuum by the weight of the air it displaces. Therefore, one liter of water is lighter by 1.2 grams when weighed in air than when weighed in vacuum. But the brass weights with which it is weighed are also lighter than they would be were they weighed in vacuum ; hence, since brass has a specific gravity of 8.4 (i.e., 8.4 times as heavy as an equal volume of water), a kilogram of brass weights would occupy only — , or — of the volume of the water. These brass 8.4 84 weights would displace — of 1.2, or 0.14 gram of air. The 84 weight of the kilogram of water in air is then decreased 1.2 grams and that of the kilogram of brass weights, 0.14 gram ; hence, the total decrease of the weight of water due to the buoyant action of air will be the difference between 1.2 and 0.14, or 1.06 grams. A kilogram of water, i.e., exactly 1000 grams, weighed in vacuum, will weigh in air with brass weights 1000— 1.06, or 998.94 grams, and will occupy at 4° C, lOOO true cubic centimeters, or one liter. But let us assume we desire to calibrate the flask at 20° C. At 20° C, 1000 true cubic centimeters of water weigh 998.26 grams in vacuum, and the correction for air displacement, as seen above, is 1.06 grams. Then 998.26— 1.06 = 997.2 grams, and represents the weight that must be put upon the pan of the balance to be equal to the weight of the water that occupies the volume of lOOO true cubic centimeters, or one liter, at 20° C. When the calibration is expressed in true cubic centimeters, the weight of the water in vacuum must be calculated because the unit of volume is weighed under these conditions. The following table, which is given to facilitate the calculations involved, contains the weight in air of one true cubic centimeter of water, and the volume in true cubic centimeters corresponding to the weight in air of one cubic centimeter of water at temperatures from 10° to 30°- I 'OL UME TRIG ANAL YSIS 45 Temperature Weight in Air of i c.c. of Water Vi.LuME Corresponding to THE Weight in Air of I Gram of Water 10" 0.9986 gram 1. 0014 C.C. 11° 0.998s 1. 001 5 12' 0.9984 I.0016 13'^ 0.9983 I.0017 14° 0.9982 I.0018 15° 0.9981 1. 00 1 9 1 6° 0.9979 1. 002 1 17° 09977 1.0023 1 8° 0.9976 1.0024 19° 0.9974 1.0026 20° 0.9972 1 .0028 21" 0.9970 1 .0030 22° 0.9967 1-0033 23" 09965 1.0035 24° 0.9963 1.0037 25" 0.9960 1 .0040 26° 0.9958 1 .0042 27° 0.9955 1 .0045 28° 0.9952 1.0048 29° 0.9949 1.005 I 30° 0.9946 1.0054 Exercise IX The Calibration of a Burette Clean the burette thoroughly with the chromic acid cleaning mixture ^ and then with water, so that the water will not stand in drops on the inner surface, but runs down freely. Boil about 500 c.c. of distilled water, cool, and allow to stand until it has acquired the temperature of the laboratory. Take the temperature with an accurate thermometer, read to the closest degree, and record the same. Fill the glass-stoppered burette with this water and starting at the zero mark, run out a portion of about 5 c.c. into a previously weighed 50 c.c. glass-stoppered flask. Read the quantity of water taken to j-^^ of a cubic centimeter and weigh it to one centi- 1 The chromic acid cleaning mixture is prepared by dissolving 25 grams of commercial sodium dichromate in 150 c.c. of water and adding 100 c.c. of concentrated commercial sulphuric acid. This solution should be placed into a glass-stoppered bottle and saved for future use, as it can be used many times. 46 QUANTITATIVE ANALYSIS gram. Introduce into the flask the second portion of approxi- mately 5 c.c, representing the amount of water between the five and ten cubic centimeter marks. Repeat this process by remov- ing and weighing the successive five cubic centimeter portions until the burette is emptied. Now, refill and repeat the calibration until the values are accurately known. From the values given in the table on page 45, calculate the volume in true cubic centimeters of these portions of liquid. Know- ing the volume as represented by the burette reading and the volume in true cubic centimeters as obtained from the weight, the correction is readily obtained by subtraction. Plot the cor- rection curves, using the abscissas for the burette readings and the ordinates for the corrections. Obtain the weight of the successive 5 c.c. portions taken from the pinchcock burette, calculate the volume in true cubic centi- meters, and plot the cahbration curve as in the case of the glass- stoppered burette. The following table represents a method of recording the data for the calibration of a 30 c.c, burette. The headings of the columns are self-explanatory. Calibration of the Pinchcock Burette Temperature of water 21^ Readings c.c. Weight of Water Volume in True Cubic Centimeters Corrections Additive 0.00 21.375 weight of flask 5.00 26.410 weight of flask -I- water 5-035 5.05 -1-0.05 10.00 31.395 weight of flask -f water 4.985 5.00 co; 15.00 36.410 weight of flask -I- water 5.015 5 -OS 0.08 20.00 41.415 weight of flask -1- water 5.005 5.02 O.IO 25.00 46.430 weight of flask -I- water 5.015 5.03 0.13 30.00 51.435 weight of flask -h water 5.005 5.02 0.15 The volume in true cubic centimeters occupied by the different weights of water may be readily calculated in the following man- ner. The weight of the first portion of water between the zero and the 5 c.c. mark was 5.035 grams. By consulting the table, page 45, it will be found that the weight in air of one true cubic centi- meter of water at 21" is 0.997 gram; 5.035 grams -7- 0.997 = 5-05, the number of true cubic centimeters in the first portion. The VOL UME TRIG ANAL YSIS 47 weight of the second portion is 4.985 grams, and in a similar man- ner we iind th^s equal to 5.00 c.c. Continuing this, we obtain the values for the various portions as given in next to the last column. The values given in the last column, representing the additive corrections for the successive S c.c. portions, are to be represented graphically by means of a curve known as the Calibration Curve. The calibration curve is to be drawn so that the corrections can be read to hundredths of a cubic centimeter and so that they are additive. That is, for any reading of the burette, the correction at that point is given for the total amount of liquid that has been re- moved. The curves given in Fig. 14 illustrate this method of drawing caHbration curves. The abscissas represent the burette readings which can be read direct to 0.25, and the ordinates the corrections estimated to 0.0 1 of a cubic centimeter. The data pre- sented in the above table and given in the last column are plotted as Curve i, which represents a convenient size and one which can be pasted upon the inside of the cover of the notebook. Notes. — I. Be sure that all air bubbles are removed from the tips of the burettes. 2. From an inspection of the values given in the table, page 45, it will be observed that the temperature does not need to be read very closely. For example, the difference between 20° and 21° makes a difference in the volume corresponding to a weight m air of one gram of water, of 0.0002 c.c, and for 5 c.c. this would amount to o.ooi c.c, which is much beyond the accuracy with which the burette can be read. 3. In using a burette always run out the liquid slowly and allow a sufficient length of time to elapse to permit the liquid to run down from the sides before taking the reading. About one minute is sufficient when small quantities are delivered, and two minutes when about the total capacity of the burette is delivered. 4. Make the calibration curves of such size that they can be pasted upon the inside of the front cover of the notebook. This is done by using as the scale for the correction ten divisions of approximately one millimeter for o. i c.c, and the same for each 2.5 c.c. of the burette reading. 5. Burettes may be conveniently calibrated against a burette or vessel, the capacity of which has been accurately determined by VOLUMETRIC ANALYSIS 49 weighing. For this purpose, the Ostwald Calibrating Apparatus is frequently employed. 1 For the calibration of burettes and flasks the Morse-Blalock 2 Bulbs are often used, and are excellent when much of this work is to be done. STANDARD AND NORMAL SOLUTIONS A Standard Solution is one in which the contents of a definite volume are accurately known. The strength of a standard solution is expressed in various ways. If 58.5 grams, the molecular weight, of sodium chloride are dissolved and made up to a liter, one cubic centimeter will contain 0.0585 gram, which is the strength of the solution. Such a solution would contain 35.45 grams of chlorine per liter, i.e., 0.03545 gram per cubic centimeter. The strength may be stated either in terms of sodium chloride or of chlorine. The customary way of expressing the strength of a solution is to state it in terms of one of the constituents ; but it may also be stated in terms of the quantity of a substance to which it is chemi- cally equivalent and which is to be estimated by the use of the standard. Sodium chloride reacts with silver nitrate according to the following equation : NaCl + AgNOg = AgCl + NaNOg, i.e., one combining weight of chlorine is equivalent to one combin- ing weight of silver, or 35.45 grams of chlorine are equal to 107.93 grams of silver ; and 0.10793 gram of silver, which is contained in one cubic centimeter of the solution, is equivalent to 0.03545 gram of chlorine. We could slate then that one cubic centimeter of the sodium chloride solution is equivalent to 0.10793 gram of silver. To a special kind of standard solution the term normal solution is applied. If the molecular weight of hydrochloric acid (36.458 grams) be dissolved in water and the solution made up to 1000 true cubic centimeters, we would have a liter of a hydrochloric acid solu- tion which would contain 1.008 grams of replaceable hydrogen, or one combining weight of hydrogen. One half the molecular weight in grams of sulphuric acid would also furnish one combining weight of hydrogen, or 1.008 grams. If this quantity of sulphuric acid were dissolved and made up to one liter, we would have an acid ' Treadwell-Hall, Analytical Chemistry, 11, 417 (1906). 2 Morse, Exercises in Quantitative Chemistry, p. 85 (1905). E 50 QUANTITATIVE ANALYSIS solution of the same strength as the hydrochloric acid solution. These solutions would contain the same number of grams of the replaceable hydrogen per liter. Solutions which contain one com- bining weight of replaceable hydrogen per true liter are termed Normal Acid Solutions. The molecular weight of sodium hydrox- ide would neutrahze the molecular weight of hydrochloric acid ; it follows, therefore, that if the gram molecular weight of sodium hydroxide were dissolved and made up to a liter, that these looo c.c. would neutralize lOOO c.c. of the normal hydrochloric acid solution, i.e., the two solutions would be equal chemically, cubic centimeter for cubic centimeter. The same may be stated concerning a solution lOOO c.c. of which contain the gram molecular weight of potassium hydroxide and the normal solution of sulphuric acid. It is custom- ary to designate alkali solutions which contain the equivalent of one combining weight of replaceable hydrogen per true liter. Normal Alkali Solutions. In solutions used for oxidation processes the oxygen furnished is the important factor, and since one combining weight of oxygen oxidizes two combining weights of hydrogen, these solutions can be conveniently expressed as normal solutions. A liter of a solu- tion of potassium permanganate which furnishes for oxidation purposes 8 grams of oxygen, i.e., 0.008 gram per cubic centime- ter, is equivalent to one combining weight of hydrogen, and, therefore, is a normal potassium permanganate solution. When the molecular weight of the substance is dissolved and made up to a true liter, the solution is a gram molecular solution. In many cases this is the same as a normal solution, as in the case of hydro- chloric acid, sodium hydroxide, acetic acid, and potassium chloride; but in many other cases they are not the same, — for example, sulphuric acid and potassium dichromate. As a result, consider- able confusion has arisen in the literature and unfortunately the terms normal and molecular are not distinguished ; but normal is sometimes used when gram molecular is meant. Normal solutions are usually too concentrated to be conveniently employed and fractional parts of the amount of the substance re- quired to make a normal solution are used instead. If one-half of the molecular weight of hydrochloric acid is contained in a liter, this is a half-normal solution and is expressed as N/2 HCl. If one-tenth the molecular weight is taken, the solution is tenth- normal, N/iO, and so on. VOL UMETRIC ANAL YSLS 5 1 An error sometimes results from using these solutions at tem- peratures different from that at which they were prepared. The so- lutions are usually made up at a certain temperature (about 20° C), and then stored in bottles from which they are removed when de- sired. One such solution of hydrochloric acid was found to have a temperature of 33°, or an increase of 13" over the temperature at which it was prepared. If we assume that the change between 20-30° is the same as that between 15-25°, one liter of this acid would then occupy 1002.42 c.c. If the molecular weight (36.46 grams) of hydrochloric acid were contained in one liter at 20°, at 30° it would be dissolved in 1002.42 c.c, or in the first case, one cubic centimeter would contain 0.03646 gram, and in the second '■ =0.03637. Now, in titrating, if at 20°, 25 c.c. of the solution 1002.42 would be required, at 30° it would take 25.06 c.c. to furnish the same quantity of acid. This difference is greater than the allowable experimental error, as the burette can be read direct to 0.0 1 c.c. The following table^ gives the expansion of 1000 c.c. of various solutions due to a change of temperature from 15° to 25°: Solution Water . . . N HCl . N H^SO< N H^CjO, N NaOH N NajCO,, N NaCl .' N/io NaCl . N/io AgNO, N/io KMnO< Expansion 2.05 2.42 3-oS 2.62 3-iS 3-03 2.12 2.06 2.16 2-13 ACIDIMETRY AND ALKALIMETRY The processes of acidimetry and alkalimetry comprise the deter- minations of acids and alkalies (hydroxides and carbonates). When an acid is to be determined, a standard alkali solution is employed ; and when the sample is analyzed for hydroxides or carbonates, a standard acid is used. The process of bringing the iSchultz, Zeit. fur Anal. Chem., 21, 167. 52 QUANTITATIVE ANALYSIS solutions of the reacting substances together is termed Titration. The neutral point, or, in general, the point which represents the completion of the reaction, is desigated as the End Point. INDICATORS The end of the reaction is made apparent to the eye by means of indicators whose colors in acid and in alkaline solutions are different. These indicators are usually solutions of organic com- pounds which are added directly to the solution to be titrated. There is no substance which can be used as a universal indicator, consequently, different indicators must be used for the titration of the various acids and alkaUes. The following are the most impor- tant indicators used in the determinations of this kind. Litmus. This is a vegetable coloring matter, usually employed in the form of the aqueous extract. It gives a red color with acids, while with alkalies a blue color is produced. Besides its applica- tion' to the titration of the ordinary acids and alkalies, it may also be used for weak acids and in the presence of ammonium salts. Solutions containing carbon dioxide must be boiled, as litmus is not reliable when used in its presence. Phenolpkthalein is an organic compound which is produced synthetically. It is used in the form of an alcoholic solution. In acid solutions this indicator forms a colorless compound, while in alkahne solutions the products are red. It finds special applica- tion with the weak acids, such as hydrogen sulphide and the organic acids. Carbon dioxide must be expelled from the solution by boiling, before the indicator can be used. It is not reliable when used for the titration of weak alkahes like ammonium hy- droxide. Methyl Orange is an organic substance which in aqueous solu- tion produces a red coloration with acids and a yellow coloration with alkalies. In neutral solution there is a rich golden brown tint which can be easily recognized. This indicator is very satis- factory for the titration of the inorganic acids. It is not affected by carbon dioxide nor hydrogen sulphide in cold solution, and con- sequently may be used in their presence. For the weaker organic acids, such as tartaric and oxalic, it is not reliable. It may also be used for the titration of solutions of ammonium hydroxide. Cochineal. This indicator is used in the form of an alcoholic VOLUMETRIC ANALYSIS 53 extract made from the cochineal insect. With acids the color of the solution is red. This turns to a violet color when the solution is made alkaline. It cannot be used in the presence of iron or aluminium or acetates. It is especially valuable for the titration of ammonium hydroxide. Note. — Since the different indicators require different amounts of alkali or acid to produce the change in color, the same indicator should be used in the analysis as in the standardization ; moreover, an excess of the indicator should not be used. A few drops are usually sufficient. NOTEBOOKS The volumetric experimental data should be recorded in a system- atic manner. A satisfactory method of arrangement is represented in Fig. 15. On the right-hand page the readings of the burettes S- 1 -TV X r - ^ i ilir ¥' ^ 1^ a, ()\\ ^ ( 'H' T ,"-1 iAi: (I ' ^±il] Af ar\ /r ' , 1 T ^r;i"R fir ^i> 1 ; M' - + h =^H ( if H ( 10 u rr n jaoA 1 li a a: r ' \~ -4 ■-- £ kh ^7 1 n flh -( K 'II y ^ n ^ f + ■f =<=a-°'\-'\ - 1 n , <0H fjnl = h^ ua-. Ur ^r^- '( h ^ .(•rS r" n \ ■ 1 1 ■ ■ 1 ! 1 - - + \r o.s.d.sa.cf;^!' H = r 4f ' Ir^' IH 1 1 1 . 1 M^ 1 t ' ' ^ ' I 1 f- ; ' I 1 1 ' 1 , - th'p Norrtiolitij ifri ciQjtc rf J 1 "T~r-"r"i 1 '1 — :- \ ' , 1 ' , ' ' 1 ' ! t . 1 ! .J 1 1 i ^ hp 1 ( H ■sjniiifion ^ 04 ^ 7 1 — i il^ 1 ^^-^ ■ 1 1 _ . L 1 ' 1 1 ' ' < i 1. 1 1 ■ r f ■xnrfx^spri in \prm =, n- 1 1 , i 1 ! i' T*l ^".yc\\\\ 1 M 1 . ' 1 j :f H iol, tlo'n ■ 1(» 'Y rtrt 1 i ! ' ' 1 1 1 ! II ! 1 1 1 1 . A h^ LOSS^ ■^ < 1 1 1 1 1 [_ 1 T I 1 1 II 1 ' 1 1 ■ I 1 t 1 i ' ' ' 1 : . ^ _ -4 Fig. 15 and the ratios of the solutions are recorded. Before recording the burette readings make the necessary corrections from the calibration curves and record the corrected readings. On the left- hand page should appear equations representing all of the chemicdl 54 QUANTITATIVE ANALYSIS changes and a clear, concise statement of the calculations, includ- ing all equations upon which these are based. PREPARATION OF STANDARD AND NORMAL SOLUTIONS The ideal method for the preparation of standard or normal so- lutions of alkalies and acids would be to weigh out accurately the calculated amounts of the substances required to make the desired quantities of these solutions, dissolve in water, and make up to the proper volumes at the specified temperature. Unfortunately, there are very few substances of a sufficiently high degree of purity to be utilized in this manner. The usual method of prepar- ing a standard solution is, therefore, to dissolve the approximate amount of the substance in water and make it up to the required volume. The exact strength of the solution can then be ascer- tained in a variety of ways, depending on whether it is a solution of an acid or an alkali. The following are some of the more common methods used for the standardization of solutions : (a) By precipitation. If the solution to be standardized contains a constituent which can be converted into an insoluble compound, the amount of this constituent, and consequently the amount of the compound in which it occurs, can readily be determined. For ex- ample, a hydrochloric acid solution can be standardized by pre- cipitating the chlorine in a definite volume as silver chloride, and from the weight of the precipitate, the hydrochloric acid in one cubic centimeter of the solution can be calculated. Again, a solu- tion of sulphuric acid can be standardized by precipitating with barium chloride, and from the weight of barium sulphate obtained, the amount of sulphuric acid in one cubic centimeter can be calcu- lated. A barium hydroxide solution can be standardized by pre- cipitating as barium sulphate, and from the weight of the precipitate the barium hydroxide in one cubic centimeter of the solution can be readily ascertained. The application of this method is limited. {b') By titration, i. Against a solution that has been standard- ized very accurately by precipitation, such as barium hydroxide, hydrochloric acid, or sulphuric acid. 2. Against the purest chemicals obtainable. For standardizing the alkalies, the substances usually employed are pure oxalic acid, VOLUMETRIC ANALYSIS 55 tartaric acid, acid oxalates, and potassium acid tartrate ; for acids, Iceland spar, pure precipitated calcium carbonate, and pure dry sodium carbonate obtaiqed by heating the bicarbonate. (c) By the absorption method. A known weight of a volatile gas, such as hydrochloric acid or ammonia, is absorbed in water and the solution made up to a definite volume. Exercise X Preparation of an Approximately Half-Normal Hydrochloric Acid Solution Procedure. — Obtain a sample of hydrochloric acid, a 250 cc. graduated cylinder, a hydrometer, and a thermometer. Introduce into the graduated cylinder sufficient hydrochloric acid solution to float the hydrometer. Place the cylinder under the water tap and allow the water to run upon it, making sure that no water runs into the cylinder. If the tap water is not cold enough, use a beaker of ice water for cooling. Stir the acid occasionally by means of the thermometer, and cool to 15° C, then read the hydrom- eter very carefully by noting the place on the hydrometer stem which is on a line with the surface of the liquid. Be sure that the hydrometer is free to move and does not touch the sides of the cylinder. Record the reading, which gives the specific gravity of the liquid. Now consult the table of specific gravities of hydro- chloric acid on page 203, and ascertain the percentage of hydrO' chloric acid corresponding to this specific gravity. From these data calculate the number of cubic centimeters of this solution that will be required to make two liters of a half-normal hydrochloric acid solution. Measure out this quantity by means of the gradu- ated cylinder, pour into a liter flask, fill to the upper mark, and then transfer to a 2\ liter glass-stoppered bottle. Add another liter of water, and shake the contents of the bottle very thoroughly to insure a homogeneous solution. Label the bottle Hydrochloric Acid Solution. Note. — The density of the solution changes with the tempera- ture, hence the necessity of controlling the temperature during the determination of the specific gravity. 56 QUANTITATIVE ANALYSIS Exercise XI Preparation of an Approximately Half -Normal Potassium Hydroxide Solution Procedure. — On the assumption that the sample of potassium hydroxide to be used is 85 per cent pure, calculate the number of grams required to make two liters of a half-normal solution of potassium hydroxide. Weigh out quickly into a No. 4 beaker on the rough balance five grams more than the calculated amount, transfer quickly to a 2\ liter glass-stoppered bottle, containing two liters of water, shake vigorously to insure a homogeneous liquid. Replace the glass stopper by a cork and label Potassium Hydrox- ide Solution. Note. — Solutions of the caustic alkalies should not be kept in vessels having ground glass stoppers, owing to the fact that the alkali attacks the glass and often cements the stopper so that it cannot be removed. Exercise XII The Titration of the Acid against the Alkali Establish the ratio between the two solutions in the following manner : Having thoroughly cleaned the burettes so that when the water is run out there will be no drops remaining on the inner walls, rinse the glass-stoppered burette three times with 5 c.c. portions of the hydrochloric acid solution and fill it above the zero mark. In a similar manner rinse and fill the pinchcock burette with the potassium hydroxide solution. Now run out the liquids from the burettes until the lower surface of the meniscus stands exactly at the zero mark, making S2ire that the tips contain no air bubbles. Into a clean Erlenmeyer flask containing about 20 c.c. of water introduce about 20 c.c. of the acid, add a few drops (three or four) of the methyl orange indicator, and then run in the potassium hydroxide slowly until the solution becomes yellow, shaking it meanwhile. This indicates that the solution is alkaline, and that an excess of the potassium hydroxide has been introduced. Wash down the sides of the flask with distilled water and add acid drop by drop until one drop changes the solution from yellow to a golden brown tint which is the end point. Then record the VOLUMETRIC ANALYSIS 57 readings of the burettes. Since the reading includes all the liquid run out of the burette, the drop remaining on the tip should be re- moved by means of a stirring rod and added to the ilask before the end point is established. Again fill the burettes to the zero mark with their respective solutions and repeat the titration, using a clean Erlenmeyer flask. Make three such titrations and record the individual results. It is a good plan to record them in the same order in which the burettes are placed. If the acid burette is on the right, record the readings of this burette on the right side of the page. (See Fig. 15.) Now calculate the ratio of each of these titrations, expressing it in terms of the number of cubic cen- timeters of the potassium hydroxide solution equal to one cubic centimeter of the acid. These values should not vary more than two-tenths of a per cent of the total ratio. Take the average of the ratios as the true relation between the two solutions. STANDARDIZATION OF THESE SOLUTIONS The relation between these two solutions has been established, but it is also necessary to know their exact strengths, that is, the number of grams of the respective constituents present in one cubic centimeter. Exercise XIII Standardization of the Hydrochloric Acid Solution a. By Precipitation of the Chlorine as Silver Chloride Procediwe. — Measure from the burette into two No. 2 beakers from 10 to 15 c.c. of the hydrochloric acid solution, record the exact amounts taken, and precipitate the chlorine in the manner described in Exercise V, page 24. Filter by means of a Gooch crucible. Preparation of the Gooch Crucible. — Obtain from the supply room two Gooch crucibles with perforated plates, two Gooch fun- nels and lubbers, and the outfit for filtering by suction, consisting of two filter flasks with stoppers, a T-tube, a suction pump, and three pieces of rubber tubing. Place the funnel in the neck of the filter flask by means of the rubber stopper, stretch the rubber band over the funnel, and place the crucible into the opening. Arrange as shown in Fig. 16, and connect with the filter pump. 58 QUANTITATIVE ANALYSIS Pour an emulsion of asbestos (which has been digested with hydro- chloric acid and washed free from the same) into the crucibles so that a layer i to 2 mm. thick will be formed. Place the perforated plates upon this, and wash with hot water to remove any loose fibers of asbestos. Wash finally with alcohol. Too great a suction Fig. i6 should not be used, since it packs the asbestos mat so closely that the filtration takes place slowly. Place the Gooch crucibles into small beakers, cover with cover-glasses, dry at no" for forty minutes, cool in the desiccator, and weigh. Replace in the oven and heat to constant weight. Place them in the funnels again and filter the silver chloride precipitates, holding the stirring rod near the bottom of the crucible while pouring the liquid into it. Remove all the precipitate from the beaker, wash in the usual manner, and finally wash with a few cubic centimeters of alcohol. Place the crucibles into the oven and heat to constant weight. From the weight of silver chloride calculate the amount of hydro- chloric acid in each cubic centimeter of the solution and also the normality factor. Normality f actor ^ ^^'^^^ °^ "^^ ^" ' ^•^- °^ g^^^" ""^^^^"'^ Weight of HClin i c.c. of normal solution VOLUMETRIC ANALYSIS 59 That is, the iionnality factor is the ratio between the number of grams of hydrochloric acid found and the number of grams there should be found if the solution were normal. Hence, to convert the number of cubic centimeters of the given solution used into cubic centimeters of normal solution, multiply by the normality factor. b. Standardization of the Acid against Calcium Carbonate Procedure. — Weigh out three very finely pulverized samples of Iceland spar of about 0.5 gram each into properly labeled Erlen- meyer flasks. Introduce into each flask 25-30 c.c. of the hydro- chloric acid solution, recording the exact amount used. Allow to stand for several hours, and when the sample is completely dis- solved, add methyl orange indicator, and titrate the excess of acid with the alkali solution. Knowing the ratio between the acid and alkali, calculate the number of cubic centimeters of acid required to dissolve each of the samples of Iceland spar. Assuming the Iceland spar to be absolutely pure, calculate the normality factor of the acid solution. Exercise XIV Standardization of the Alkali Solution a. Against some of tlie Pure Chemicals Available for this Purpose Procedure. — Weigh out accurately 7-8 grams of pure oxalic acid (H2C2O4 • 2H2O), or 8-10 grams of tartaric acid (H2C4H^Oe). Dissolve in water, transfer to a 250 c.c. flask, make up to the mark, and shake thoroughly to insure a homogeneous liquid. Fill the glass-stoppered burette with this solution, and run out about 25 c.c. into a 250 c.c. casserole containing about 25 c.c. of water. Heat to boiling, add a few drops of phenolphthalein, and titrate with the alkali solution until the pink color appears. Add one cubic centi- meter of the acid solution and boil for one minute. Then to the hot solution add potassium hydroxide solution until one drop causes the solution to change to a faint pink color which lasts for several minutes. Repeat until the relation between the solutions has been accurately established. Write the equations representing the chemical reaction, and, assuming that this sample of oxalic 6o QUANTITATIVE ANALYSIS acid (or tartaric acid) is absolutely pure, calculate the normality factor of the alkali solution. Using phenolphthalein as the indicator, establish the relation between the standard hydrochloric acid and the potassium hydrox- ide solutions in the manner just described. From this ratio and the value obtained for the alkali and the oxalic acid calculate the normality of the hydrochloric acid solution. Compare this with the values obtained by the two methods for standardizing the acid. Notes. — I. The result obtained when phenolphthalein is used may be slightly different from that obtained with the use of methyl orange. The indicator used in the standardization should be the same as that used in all the determinations. 2. The distilled water may contain carbon dioxide, especially if blown from the wash bottle by air from the lungs. Moreover, the sample of potassium hydroxide may contain a certain amount of carbonate which liberates carbon dioxide when oxalic acid is added. It is, therefore, necessary to expel the carbon dioxide by heating the solution, as it gives an acid reaction toward phenol- phthalein. 3. If the solution is heated in a glass vessel, enough alkali may be dissolved from the glass to make an appreciable error in the determination. It is necessary, therefore, to use porcelain casse- roles, which do not dissolve under these conditions. b. By the Absorption Method Prmciple. — This method depends on absorbing pure hydrochlo- ric acid gas in a weighed quantity of water, which is then weighed and made up to a definite volume. This gives a standard solution which may be employed in the standardization of alkali solutions. Proccdiire. — Obtain two absorption flasks and their correspond- ing drying tubes, which are filled with granular calcium chloride. These are represented by Fig. 17 and are readily prepared from 100 c.c. Erlenmeyer flasks and common calcium chloride tubes. The tube through which the gas enters may be drawn out or blown into a bulb in which a number of perforations are made. After the flasks have been thoroughly cleaned, introduce about 25 c.c. of water into each. This should be sufficient to immerse the end of the delivery tube to the depth of about one centimeter, when the VOLUMETRIC ANALYSIS 6i tube is nearly touching the bottom of the flask. Weigh the flasks in the following manner : Place one flask and drying tube upon the left pan of the bal- ance, and the other upon the right pan. Determine carefully whether the flask on the left pan is heavier ; if not, reverse their :^b Fig. 17 positions, and add enough weights to produce equilibrium. The weights used represent the excess in weight of the heavier flask, which is marked A, over that of the lighter, B. Take A to the hydrochloric acid generator and after removing the sealing plugs a and b, attach it to the hydrochloric acid generator by means of the long delivery tube. Immerse the absorption flask in water and then start the flow of gaseous hydrochloric acid by allowing con- centrated hydrochloric acid to drop slowly into pure concentrated sulphuric acid. Keep a fairly rapid constant stream of gas bub- bling through the concentrated sulphuric acid wash bottles for about 62 QUANTITATIVE ANALYSIS fifteen minutes. Do not allow it to stop, or it may suck back. Dis- connect and insert the plugs a and b, before shutting off the gas. Having wiped the flask dry and allowed it to acquire the same tem- perature as the balance, put it back upon the left pan with B upon the right and add enough weights to produce equilibrium. The increase in the excess of A over B represents the hydro- chloric acid gas absorbed in A. This should not be less than five grams. Leaving A as it is, repeat the absorption manipula- tion with B. Reweigh as before, with B still on the right pan. The decrease in excess of A over B represents the hydrochlo- ric acid gas absorbed in B. Be sure a record has been made of all weights. Now, carefully transfer the solution in A to a 250 c.c. graduated flask. Rinse the flasks and delivery tubes and transfer all of the rinse water to the graduated flask. Finally make up to the mark with distilled water, shake thoroughly to in- sure a homogeneous solution, and determine the ratio between this solution and the potassium hydroxide solution by at least three titrations. Transfer the contents of B to a 250 c.c. graduated flask and proceed as in the case of A. Assuming, upon the basis of the grams of gas absorbed, that each of the hydrochloric acid solutions is an accurately known standard solution, calculate from the ratio determined the normality factor of the potassium hydroxide solution. Note. — For the generation of the hydrochloric acid gas any con- venient form of apparatus may be used. The success of the method described depends to a considerable extent upon the complete dry- ing of the gas. Exercise XV Determination of the Percentage Strength of Acid Solutions Procedure. — Obtain a 250 c.c. graduated cylinder, a thermometer, a hydrometer, and a solution of one of the following acids: hydro- chloric, sulphuric, or nitric. Determine the specific gravity as described in Exercise X, page 55 ; take 25 c.c, transfer to a 250 c.c. graduated flask, make up to the mark, mix thoroughly, and titrate against a standard alkali solution. From the data calculate the percentage of the acid in the solution. VOLUMETRIC ANALYSIS 63 Exercise XVI Analysis of a Soluble Carbonate Procedure. — Obtain in a weighing tube a sample of a soluble carbonate. Weigh in the usual manner 5-10 grams of the sample into a No. 2 beaker, dissolve in about 100 c.c. of water, and introduce into a 250 c.c. graduated flask. Make up to the mark, mix thoroughly, and titrate against a standard acid solution, using the proper indicator. Write the equation representing the chemical reaction. From the ratio established calculate the percentage purity of the sample taken. Exercise XVII The Determination of Total and Caustic Alkali in a Mixture of Sodium Hydroxide and Sodium Carbonate Principle. — When a solution containing sodium hydroxide and sodium carbonate is titrated with an acid, using phenolphthalein as an indicator, the neutralization takes place in the following stages. The sodium hydroxide is first neutralized, then the sodium carbonate is changed to the bicarbonate : NaOH + HCl = NaCl + H^O, Na^COj + HCl = NaHCOg + NaCl. When the above reactions are complete, the addition of more acid liberates carbon dioxide, which decolorizes the solution. If methyl orange is now added, the other half of the carbonate may be titrated. NaHCOj + HCl = NaCl + H^O + COg. The amount of acid used in titrating with the phenolphthalein represents all of the sodium hydroxide, and one half the sodium carbonate ; that used with the methyl orange represents the other half of the sodium carbonate. Procedure. — Weigh into a No. 2 beaker from 5-10 grams of the sample. Dissolve in about too c.c. of water, transfer to a 250 c.c. graduated flask, and make up to the mark at room temperature. Remove by means of a burette or pipette 25 c.c. of the solution, 64 QUANTITATIVE ANALYSIS introduce into an Erlenmeyer flask, and add a few drops of phenolphthalein. Place the flask in ice water and titrate with half normal hydrochloric acid, shaking gently to mix the solutions. The acid should be introduced under the surface of the liquid by ex- tending the tip of the burette by means of a piece of glass tubing of small bore. When the solution becomes colorless, record the amount of acid used, then add a few drops of methyl orange and continue the titration until the characteristic golden brown tint appears. Record the total amount of acid used and add one more drop to prove that the neutral point has been reached. Repeat this until the ratio has been accurately established. During this last titration the solution used need not be kept cold. From the data, calculate the percentage of sodium carbonate, the percentage of sodium hydrox- ide, and also the total alkalinity of the sample expressed as percentage of sodium oxide. Notes. — I. The quantitative formation of the bicarbonate from the carbonate takes place only at o°, hence the solution must be maintained at this temperature during the titration. 2. If the acid is dropped into the solution, some of the carbon dioxide from the bicarbonate will be lost and too much acid will be used before the end point represented by the phenolphthalein is reached. OXIDATION AND REDUCTION In addition to the processes considered under acidimetry and alkalimetry, there is a large class of important volumetric methods which are based upon the oxidation or the reduction of the substance to be determined. Ferrous iron, for example, may be estimated by adding standard potassium permanganate to its acid solution, the reaction taking place according to the equation : 2 KMnOi + ioFeS04 -I- 8 H2SO4 = 5 Fe2(SO,)3 + K2SO4 + 2 MnSO^-hS H2O. Manganese dioxide may be determined by dissolving a weighed quantity in a standard ferrous sulphate solution, MnOa + 2 FeSO^ + 2 H^SO^ = ¥t^{SOi)z + UnSO^ -f 2 H2O, 1 Before taking up this subject the student should thoroughly review the subject of oxidation and reduction, a satisfactory presentation of which will be found in Treadwell's Qttalitative Analysis, pp. 3—9. VOLUMETRIC ANALYSIS 65 and titrating the excess of ferrous sulphate by means of a standard potassium permanganate solution according to the equation already given. This last process is an indirect method frequently used for the determination of substances of an oxidizing nature. It is analogous to the method of determining the purity of calcium car- bonate by dissolving the carbonate in standard acid and titrating the excess of acid by means of standard alkali. It is obvious that these solutions can be standardized by titrating them directly against the substance to be determined; for example, a solution of potassium permanganate can be standardized by titrat- ing it against a solution containing a known amount of ferrous iron. In general, it is advisable whenever possible to use this method, since the conditions during the standardization will then be similar to those existing during the determination, and the results will be more accurate. It frequently happens, however, that a solution is standardized against a substance other than that to be determined. For example, the permanganate solution can be standardized against oxalic acid and employed to determine iron and hydrogen peroxide. Available Oxygen Potassium permanganate completely oxidizes oxalic acid accord- ing to the equation 2 KMnO^ -t- 5 H2C2O4 -I- 3 H2SO4 = K2S04-|-2 MnSO^-l-ioCOa-l-S H2O. From the above equation and that showing the reaction between potassium permanganate and ferrous sulphate, it is evident that all of the oxygen in the permanganate is not used for oxidizing purposes. Two molecules of potassium permanganate react with ten of ferrous sulphate. It is apparent that of the eight combining weights of oxygen, but five are used for oxidation. The potassium permanganate is assumed to split up into the oxides of the metals (which in the presence of acid form salts) with the liberation of oxygen, thus: KMn04 KMnO^ J K2O -f 2 MnO + 5 O. That is, two molecules of potassium permanganate yield five 66 QUANTITATIVE ANALYSIS combining weights of oxygen and are said to have five available oxygens. Therefore, two gram molecules of permanganate (316.6 grams) yield five combining weights (80 grams) of oxygen for oxidizing purposes. To make a normal solution of permanganate, it is evident from the definition that we must have enough available oxygen to react with one combining weight of hydrogen; i.e., eight grams of oxygen per liter. Consequently, for a normal solution we must dissolve in one liter enough potassium permanga- nate to furnish eight grams of available oxygen ; i.e., — of two 10 2 X 158.3 ^^ ^ gram molecules, or = 31.66 grams 01 potassium perman- ganate. When a potassium dichromate solution is employed as an oxidizing agent, it is assumed to break down into the oxides of the metals (which in the presence of acids form salts) with the liberation of oxygen. The process may be represented as follows : KaCrp^ = K2O -I- 2 CrOj. CrOa I = cr„0, + 3 O. Consequently, from one gram molecule of potassium dichromate three combining weights of oxygen (48 grams) are available for oxidizing purposes. For a normal solution, therefore, |(30 = 6H) of one gram molecule of potassium dichromate should be taken for a liter of solution. Some of the principal oxidizing aiid reducing agents used in volumetric processes are : Potassium permanganate Potassium dichromate Potassium bromate Potassium iodate Hydrogen peroxide Chlorine Bromine . Iodine Oxidizing Agents • Reducing Agents VOLUMETRIC ANALYSIS 67 Hydrogen (obtained from the action of acid on zinc) Sulphurous acid Oxalic acid Stannous chloride Ferrous sulphate Arsenious oxide Sodium thiosulphate Hydrogen sulphide THE PERMANGANATE METHOD Solutions of potassium permanganate are intensely colored, but on being reduced a colorless solution is formed. A slight excess of permanganate gives the solution a pink color, so that on reach- ing the end point the permanganate acts as its own indicator. Potassium permanganate may be obtained pure, but since the strength of the solution changes when first prepared, it should always be standardized. This may be done : a. By means of pure electrolytic iron dissolved in sulphuric acid out of contact with the air. b. By means of pure iron, dissolved in acid and reduced to the ferrous state by means of zinc. c. Against pure ferrous ammonium sulphate (Mohr's Salt). d. Against pure sodium oxalate. Exercise XVIII Preparation of a Solution of Potassium Permanganate Procedure. — Calculate the amount of potassium permanganate necessary to make one liter of a solution of such strength that 20 c.c. wpuld be required to furnish the oxygen necessary to oxi- dize 0.1 gram of pure iron from the ferrous to the ferric state. Weigh out approximately this amount, place it into a No. 8 beaker, and dissolve in one liter of water. Allow the solution to stand for a few hours, and filter through a layer of asbestos free from organic matter into a two-liter glass-stoppered bottle. The asbestos filter may be prepared by placing a few short pieces of glass tubing into a Gooch funnel, and upon this a thin layer of asbestos fiber. 68 QUANTITATIVE ANALYSIS Suction may be used to hasten the filtration. Keep the solution in a dark place when not in use. Notes. — I. Distilled water contains small amounts of ammonium hydroxide and organic matter, which decompose the permanganate with the separation of manganese dioxide. It is well to allow the permanganate solution to stand some time in order that these sub- stances may be completely oxidized. The presence of even small quantities of manganese dioxide decomposes the permanganate, with the separation of more of this substance. It is necessary therefore to remove the dioxide by filtration and to keep the solu- tion out of contact with dust and any other organic matter which would reduce it. 2. If potassium permanganate solution is kept out of the Hght and free from organic matter, its strength will remain unchanged for months. 3. The solution prepared as above is approximately tenth-nor- mal. Stronger solutions of potassium permanganate are seldom employed. Exercise XIX Standardization of a Solution of Potassium Permanganate a. By Means of Pure Iron dissolved out of Contact with Air Procedure. — Weigh out three portions of electrolytic iron of about o. I gram each. Dissolve out of contact with the air in the following manner : Provide three Erlenmeyer flasks with well fit- ting stoppers, carrying bent glass tubes, as illustrated in Fig. 18. One end of the tube should extend about 0.5 cm. below the cork. When the cork carrying the tube is in place, the other end of the tube should reach nearly to the bottom of a beaker containing a five per cent solution of sodium bicarbonate. Add to each flask about 30 c.c. of dilute sulphuric acid, then add a piece of sodium bicarbonate about the size of a small pea for the purpose of expel- ling the oxygen in the flask. Immediately introduce one of the weighed portions of iron into each flask, insert the stopper, and warm gently. When the iron has all dissolved, remove the stop- per, dilute with about 50 c.c. of distilled water, and add perman- ganate from the glass-stoppered burette to the cold solution until a- faint pinkish tint is produced which remains for one minute. (Use the upper edge of the meniscus when reading the burette.) w VOL UME TRIG ANAL YSIS 69 From the data obtained calculate the value of one cubic centi- meter of the permanganate solution in terms of iron. Also, cal- culate the amount of oxygen (in grams) available for oxidizing purposes in one cubic centimeter of the permanganate solution. These results of the standardization should agree within two-tenths per cent of the total amount of oxygen present. For method of ^r calculation see page 184. \ 1 Notes. — I . Sulphuric acid must be used for dissolving the iron, as hydrochloric acid reacts with the permanganate, liberating chlorine. It is possible, however, to titrate the iron in the presence of hydro- chloric acid, if the solution con- tains a large excess of manganese sulphate. Upon this fact is based the Zimmerman-Reinhardt method described in the Jour. Am. ChciH. Soc, 17, 405 (1895). 2. The soft iron wire sometimes recommended for this method of standardization should not be used. It contains carbonaceous matter, which is liberated when the iron is dissolved in acid, with the result that some of the permanganate is used to oxidize the hydro- carbons formed and high results are obtained when expressed in terms of iron. 3. Electrolytic iron which has not been annealed dissolves very readily in acids. 4. Since permanganate solutions attack organic matter, the glass-stoppered burettes must always be used. 5. The formation of a brown turbidity or precipitate during the titration indicates insuiScient acid. It consists of the oxides ot manganese. b. By Pure Iron reduced by Means of a Jones Rcductor In this method the iron is dissolved in acid and reduced to the ferrous state by running the solution through a tube containing granulated zinc. The zinc is amalgamated to prevent its being consumed too rapidly. The tube containing the zinc is known as the Jones Reductor. 70 QUANTITATIVE ANALYSIS -4 This is illustrated in Fig. 19. The large tube has an outside di- ameter of about three quarters of an inch. At the bottom of this are placed some glass beads upon which rest a layer of glass wool, then a thin layer of asbestos, and a column of amalgamated zinc about ten inches in length. Upon the zinc is placed a layer of glass wool about two inches in length. The zinc should be of such size that it will pass through a 20 mesh, but not through a 30 mesh sieve. It is best amalgamated by the method given by Lord.^ Moisten a quantity of the zinc with dilute sulphuric acid (about 3 c.c. concentrated acid to 100 c.c. of water), add a small drop of mercury, and stir until the zinc shows uniformly the white mercury color. Avoid an excess of mercury. One half gram is sufficient for 150 grams of zinc. Wash the zinc free from acid and put it into the tube. Determination of the Blank Since the reagents after passing through the reduc- tor will almost invariably consume some permanga- nate due to impurities in the zinc, etc., blank determinations should be made until concordant results are obtained. Fig. 19 Connect the reductor with the filter pump, using an intervening Wolff bottle to prevent the water from the tap running back into the flask. Run through the tube about 300 c.c. of hot (70°-8o°) dilute sulphuric acid (about 50 c.c. of concentrated sulphuric acid in a liter) by filling the funnel, turn- ing on the suction, and opening the stopcock wide enough to allow the acid to run into the filter flask at a rate not greater than 40 c.c. per minute. Be sure to leave the funnel partially filled. Follow the acid with 100 c.c. of distilled water, leaving a little in the funnel. Titrate the solution in the filter flask with the potassium permanganate. Repeat the above operation until two consecutive blanks check. 1 Lord, Notes on Metallurgical Analysis, p. 36 (1903). VOLUMETRIC ANALYSIS 71 Reduction and Titration of the Iron Procedure. — Weigh out into No. 3 beakers three portions of iron of about 0.1 gram each. Dissolve them in about 100 c.c. of dilute sulphuric acid, of the concentration used in the blank determi- nation. Pour the hot solution through the reductor at a rate not exceeding 40 c.c. per minute, follow it with 200 c.c. of the warm dilute sulphuric acid, some of which should be used to rinse out the beaker containing the solution of iron, and then with 100 c.c. of distilled water. Cool the solution and titrate in the filter flask mth the permanganate solution. Deduct the blank from the amount of permanganate used and from the data calculate the value of permanganate in terms of iron and also the available oxygen per cubic centimeter. Note. — Besides zinc, sulphur dioxide and hydrogen sulphide may be used to reduce the iron to the ferrous condition. The excess of these reducing agents, however, must be removed from the solution before titration, by means of a current of carbon dioxide. Zinc has the disadvantage of always containing a certain amount of iron. c. By Ferrous Ammonium Sulphate (FeSO,(NH,)2SO, -eHjO) Procedure. — Weigh out upon cover-glasses three separate por- tions of pure ferrous ammonium sulphate of about 0.7 gram each. Place about 25 c.c. of water and 15 c.c. of dilute sulphuric acid into each of three Erlenmeyer flasks, add a piece of sodium bicar- bonate the size of a small pea, and immediately introduce one por- tion of the ferrous ammonium sulphate into each flask. When all of the substance has dissolved, titrate with the permanganate as in the previous methods of standardization. Calculate the number of grams of available oxygen per cubic centimeter of perman- ganate solution, also the value of one cubic centimeter of the per- manganate in terms of iron. Notes. — I. Ferrous ammonium sulphate may be obtained very pure by recrystaUization, and is a very satisfactory substance to use for the standardization of permanganate. 2. In the presence of an excess of sulphuric acid ferrous sul- phate is oxidized but very slowly by the oxygen of the air. 72 QUANTITATIVE ANALYSIS d. By Means of Sodium Oxalate (Na^QO,) Principle. — Sodium oxalate on being dissolved in water and acidified with sulphuric acid can be titrated with potassium per- manganate solution : 5 NaaCaO^ + 2 KMnO^ + 8 H2SO4 = 5 Na^SO^ + K2SO4 + 2 MnSO^ + 8 H2O + 10 COj. The solution must be heated to about 70°, as the reaction takes place very slowly at the ordinary temperature. Procedure. — Weigh out about one gram of the sodium oxalate, dissolve in about 100 c.c. of hot water, transfer to a 250 c.c. flask, cool, and make up to the mark. Run into an Erlenmeyer flask about 25 c.c. of the oxalate solution, add 10 c.c. of dilute sulphuric acid, heat to about 70°, and titrate with the permanganate solution until the solution assumes a pink tint that remains for a few minutes. Repeat the titration until concordant results are ob- tained. Calculate the value of one cubic centimeter of the per- manganate solution in terms of iron and also the available oxygen per cubic centimeter. Note. — Potassium permanganate may also be standardized against other oxalates or oxalic acid. Many of these compounds contain water of crystallization, a part of which may easily be lost. Pure sodium oxalate may be readily prepared and kept, and is an excellent substance for standardizing the permanganate. The method of preparing pure sodium oxalate is described by Sorensen, Zeit. fiir Anal. Chem., 36, 639 (1897). Exercise XX Determination of the Percentage Purity of Oxalates One of the following oxalates may be analyzed : — Potassium oxalate .... KgCgO^ • HgO Ammonium oxalate .... (NH4)2C20^ • H2O Potassium acid oxalate .... KHC2O4 • H2O Potassium tetra oxalate . . . KH3(C204)2 • 2H2O VOLUMETRIC ANALYSIS 73 Procedure. — Weigh out from two to three grams of the sample, dissolve in hot water, and make up to a volume of 250 c.c. Titrate portions of the solution as in the standardization of the permanganate by means of sodium oxalate. Calculate the percentage purity of the substance analyzed. Exercise XXI Determination of the Purity of Hydrogen Peroxide Principle. — This determination is based upon the fact that in an acid solution hydrogen peroxide reacts with permanganate with the evolution of oxygen according to the equation : 2 KMn04+ 5 H2O2 + 3 H2SO^=K2S04 + 2 MnSO^ + S H2O+ 5 O^. Procedure. — Introduce 10 c.c. of the peroxide solution into a 250 c.c. graduated flask, make up to the mark, and mix thoroughly. Measure out 25 c.c. of this solution into an Erlenmeyer flask, dilute to 100 c.c, add 10 c.c. of dilute sulphuric acid, and titrate with the standard permanganate until a faint pinkish tint remains. Repeat until the ratio between the two solutions is estabhshed. From the data calculate the percentage purity of the sample, assuming the specific gravity to be one. Calculate also the avail- able oxygen in one cubic centimeter of the sample. Exercise XXII Determination of Calcium Principle. — The calcium is precipitated as the oxalate and dissolved in dilute sulphuric acid according to the equation : CaCaO^ + H2SO4 = CaSO^ + H2C204- By titrating the oxalic acid with a standard permanganate solution, the amount of calcium present can be determined. Procedure. — Weigh out from one to two grams of the sample, dissolve in a covered beaker in hydrochloric acid, and heat to drive off the carbon dioxide. Transfer to a 250 c.c. graduated flask and make up to the mark. Take two portions of 100 c.c. each, and precipitate the calcium as described in Exercise VII. After washing the precipitate free from ammonium oxalate, place the 74 QUANTITATIVE ANALYSIS beaker in which it was precipitated under the funnel and dissolve the oxalate by pouring upon the filter 30 c.c. of dilute sulphuric acid. Wash the filter finally with boiling water. Titrate the hot solution of oxalic acid with the standard permanganate solution. From the data calculate the percentage of calcium oxide in the sample taken for analysis. Note. — The wash water from the calcium oxalate may be tested for ammonium oxalate by acidifying a few cubic centi- meters, and adding to the hot solution a drop of very dilute per- manganate solution. If the color is not discharged, the washing is complete. Exercise XXIII Determination of Iron in Siderite Procedure. — Weigh out into porcelain crucibles three portions of the finely ground sample of about 0.25 gram each. Heat the crucibles in the hottest flame of an ordinary burner for about ten minutes. Cool, transfer the contents of the crucibles to 250 c.c. casseroles, cover with a cover-glass, add 10 c.c. of concentrated hydrochloric acid, and heat until the iron is in solution. Elevate the cover-glass by means of a glass triangle (see Fig. 5), add 20 c.c. of sulphuric acid (sp. gr. 1.4), and heat until the dense white fumes of sulphuric acid begin to be evolved. Cool the solution, dilute to 100 c.c, heat to dissolve any iron salts, and run the hot solution through a clean Jones reductor as in the stand- ardization of the permanganate. A white flocculent residue may be disregarded, as it is silica, and will be removed by the glass wool in the reductor. Wash the reductor with 200 c.c. of the warm dilute sulphuric acid (50 c.c. concentrated acid in one liter) and 100 c.c. of distilled water. Titrate the cold solution with per- manganate and calculate the percentage of iron, also the percent- age of ferrous oxide in the sample taken for analysis. Notes. — I. Siderite is a native carbonate of iron, containing sihca, organic matter, and various other impurities. Since the organic matter would consume some of the permanganate, it must be destroyed by heating (roasting). 2. Iron ores frequently contain appreciable quantities of tita- nium. In this case a certain amount of the titanium is dissolved, VOLUMETRIC ANALYSIS 75 and is partly reduced by the zinc from the oxide TiOa to TigO^. On titrating the latter compound, it consumes some of the per- manganate, being changed back to TiOg. It is obvious, there- fore, that when titanium is present zinc cannot be used for the reduction of the iron. THE DICHROMATE METHOD This method depends upon the fact that in acid solutions ferrous salts can be completely oxidized by dichromate solutions, the reaction taking place according to the equation : KjCrjO, + 6 FeCl2+ 14 HCl = 6 FeCl3+ 2 CrCl3+ 2 KCl -f 7 HjO. Potassium dichromate does not react with the hydrochloric acid present, consequently it may be used in this class of analyses. The complete reduction of the iron to the ferrous condition is accompHshed by the addition of an excess of stannous chloride (2 FeCl3+ SnCl2 = 2 FeCl2+ SnCl4). As the excess of the stan- nous chloride would react with the dichromate, it is oxidized by the addition of an excess of mercuric chloride solution, according to the following equation : SnCl^ + 2 HgCIa = SnCl^ + 2 HgCl. The mercurous chloride forms a white precipitate which is not oxidized by the dichromate. If a large excess of the stannous chloride is present, and if the solution is warm, a grayish precipi tate composed largely of mercury may be formed. SnCla + HgCla = SnCl^ -|- Hg. Since the mercury' is oxidized by the dichromate, these conditions must be avoided. When the dichromate is reduced according to the equation given above, the solution turns green from the formation of chromic chloride. This prevents the determination of the end point b)- placing an indicator in the solution. It is necessary, therefore, to remove drops of the solution and bring them into contact with the indicator outside of the solution. Potassium ferricyanide (K3Fe(CN)g), which gives a blue color (Turnbull's blue) with ferrous salts, is employed as the indicator. je QUANTITATIVE ANALYSIS Preparation of the Dichromate Solution Obtain a sample of pure potassium dichromate and calculate the amount necessary to make a liter of a solution of such strength that 20 c.c. will oxidize o. i gram of iron. Weigh out this amount approximately, dissolve in water, and make up to one liter. The solution will keep indefinitely without changing. Note. — The dichromate may also be weighed out accurately, as it can be prepared very pure. The Indicator Dissolve a piece of pure potassium ferricyanide about the size of the head of a pin in about 20 c.c. of water. Notes. — I. The solution must be prepared fresh, as it is reduced on standing. It must be dilute, or its own color will interfere with the end point. 2. Potassium ferricyanide which is free from ferrocyanide must be used, as this compound reacts with ferric iron with the for- mation of a blue color. Exercise XXIV Standardization of the Solution of Potassium Dichromate a. Against Ferrous Ammonium Sulphate Procedure. — Weigh out three portions of the pure salt of about 0.7 gram each and dissolve them in flasks containing 100 c.c. of water and 10 c.c. of concentrated hydrochloric acid. The air should be expelled from the flask by means of a small piece of sodium bicarbonate as in the standardization of the permanganate. The ferrous ammonium sulphate is very nearly one-seventh iron. Hence, if exactly 0.7 gram were weighed out, this would be the equivalent of o. i gram Fe and 20 c.c. of the solution would be used in the titration. Introduce into the flask one cubic centime- ter less than the calculated amount of the dichromate necessary to oxidize the iron in the sample, stir well, then, by means of a stir- ring rod, bring as small a drop of the solution as possible next to a drop of the ferricyanide indicator which has been placed on a white porcelain tile or titration plate, and allow the two drops to VOLUMETRIC ANALYSIS 77 run together. A blue coloration at the junction of the two drops indicates the presence of ferrous iron, and that not enough of the dichromate solution has been introduced to oxidize the iron. Add a few drops more of the dichromate solution, and with a cleatt stir- ring rod test for the presence of ferrous iron as just described. When near the end point, a pale blue color will be developed. Now add the dichromate a drop at a time, until a point is reached when no color can be seen, after the solution stands for one minute. Read the burette and from the data calculate the value of one cu- bic centimeter of the dichromate solution in terms of iron and also of the available oxygen. A^ote. — The formation of a brown precipitate on bringing the solution and the indicator together shows that the solution of the indicator is too concentrated. b. Against Pure Iron Procedure. — Dissolve three accurately weighed portions of pure iron of about o. i gram each by placing into Erlenmeyer flasks containing 25 c.c. of concentrated hydrochloric acid and heating. Add to the hot solution stannous chloride solution drop by drop until one drop causes the liquid to become colorless. Dilute with 100 c.c. of distilled water and to the cold solution add 25 c.c. of mercuric chloride solution and stir. A white precipitate should form. In case the precipitate is gray, discard the solution. After three or four minutes, titrate the solution with the dichro- mate in the manner already described. Calculate the value of one cubic centimeter of the dichromate in terms of iron and of avail- able oxygen. Note. — Zinc cannot be used for the reduction in this case, as it would form an insoluble white precipitate with the ferricyanide and obscure the end point. Exercise XXV Determination of Iron in Siderite Procedure. ■ — Weigh out the samples and roast as described un- der Exercise XXIII. Dissolve in hydrochloric acid, reduce, and titrate with potassium dichromate solution as just described. Calculate the percentage of iron present ; also, of ferrous oxide. 7S QUANTITATIVE ANALYSIS Note. — The dichromate method finds frequent application in the analysis of iron ores, since hydrochloric acid is the best solvent for this class of ores. lODIMETRY In neutral or acid solutions iodine is an indirect oxidizing agent. In the presence of a reducing agent it may be assumed to react with the water present and liberate oxygen for the oxidation. For example, sulphurous acid is oxidized by iodine according to the equation : NaaSOg + I2 + H2O = NaaSO^ + 2 HI. Iodine cannot be used in the presence of caustic alkalies or the normal carbonates as it reacts with these substances. Its use in alkaline solutions is made possible by the fact that it does not re- act with the bicarbonate; consequently, this substance is used in making determinations which must be carried out in alkaline. solu- tions. The indicator used in determinations of this kind is starch, which in solution forms a blue compound with iodine. The methods of determination in iodimetry may be divided into three general classes : 1. The titration of oxidizable bodies, i.e., reducing agents. The titration of an antimonous compound serves as an illustration. NagSbOg + I2+ 2 NaHCOg = NagSbO^ + 2 Nal 4- H2O + 2CO2. 2. Bodies wliich contain available oxygen, i.e., oxidizing agents. In this class of reactions, iodine is set free and may be titrated by means of a suitable reagent. H2O2 + 2 KI + HaSO^ = I2 + K2SO4 + 2 H2O. The iodine liberated is titrated direct by a standard reducing agent. For this purpose, a solution of sodium thiosulphate may be employed, which is oxidized by means of iodine to the sodium salt of tetrathionic acid. 2 Na2S203 + I2 = Na2S406 + 2 Nal. 3. Free chlorine or compounds which can liberate this substance. In methods of this class the chlorine is brought into contact with potassium iodide solutions, iodine being set free according to the equation : CI2 + 2 KI = 2 KCl -f \. VOLUMETRIC ANALYSIS 79 The iodine may then be titrated with standard thiosulphate solution. From the equation which represents the oxidation of sulphurous acid, H2SO3 + I2 + H2O = H2SO4 + 2 HI, it is evident that one molecule of iodine (I2) furnishes one combining weight of oxygen for the oxidation of the sulphurous acid. One combining weight of iodine (126.97 grams) would consequently be equal to 8 grams of oxygen and, therefore, equivalent to a combining weight of hydrogen. A normal solution of iodine, therefore, contains one combining weight of iodine per liter. Since one gram molecule of sodium thiosulphate (248.3 grams) reacts with one combining weight of the iodine, a normal solution of the thiosulphate will contain 248.3 grams in a liter. Exercise XXVI Preparation of Solutions a. Approximately N/10 Iodine Solution. — Weigh approxi- mately 6.3 grams of resublimed iodine into a No. 3 beaker. Place into the beaker about 10 grams of potassium iodide. Mix it with the iodine and dissolve in as little water as possible. Transfer to a half liter graduated flask and make up to the mark. Notes. — I. Iodine is very slightly soluble in water. It dissolves in a solution of potassium iodide, forming KI3, which is easily de- composed with the formation of potassium iodide and iodine which is available for oxidation. 2. The iodine solution changes on standing, especially if exposed to the light. Hydriodic acid is one of the products of decomposition. 3. Iodine attacks organic matter, consequently the glass-stop- pered burette must always be used. b. N/iO Sodium Thiosulphate Solution. — Weigh into a No. i tared beaker exactly 24.83 grams of pure recrystaUized sodium thiosulphate (NagSgOg- 5 HjO). Dissolve it in water which has been boiled to expel the air, transfer to a liter flask, and make up to the mark with the boiled distilled water. Note. — If made up under these conditions the thiosulphate will remain unchanged for months. The presence of carbon dioxide in the solution decomposes the thiosulphate with the separation of sulphur. 8o QUANTITATIVE ANALYSIS c. Starch Solution. — Make a paste by grinding about one gram of starch in a mortar with 5 c.c. of water. Pour this into 200 c.c. of boiUng water and stir well. Allow to settle and decant the clear liquid, which is to be used in the subsequent titrations. Use about 2 c.c. for each titration. Notes. — I. The solution does not keep well. Moulds grow in it, and starch is spht up into dextrin and other carbohydrates, some of which give reddish-colored solutions with the iodine. It is best to prepare a fresh solution each day. 2. A form of starch which is soluble in water and known as soluble starch may conveniently be used for the preparation of the indicator. Exercise XXVII Standardization of the Iodine Solution This may be done : Directly, by titrating against solutions of thiosulphate or arse- nious oxide of known strength ; Indirectly, by titrating the iodine with thiosulphate solution and standardizing the thiosulphate by means of an oxidizing agent of known strength. By using pure thiosulphate for the standard solution, a double check on the iodine solution is obtained. a. Standardisation of the Iodine Solution against N/io Thiosulphate Procedure. — Place some of the iodine solution into the burette with the glass stopcock, and fill the pinchcock burette with the thiosulphate solution. Run into an Erlenmeyer flask about 25 c.c. of the thiosulphate solution, add about 2 c.c. of the starch solu- tion, dilute with 50 c.c. of water, then titrate with the iodine solu- tion until a blue coloration just appears. Repeat this until the ratio is established between the two solutions. Express the ratio in terms of one cubic centimeter of the thiosulphate solution. Calculate the grams of iodine per -cubic centimeter of the iodine solution. b. Against N/io Arsenious Oxide Solution Principle. — This method depends upon the fact that in an alkaline solution sodium arsenite may be titrated with iodine solution according to the equation : NagAsOg 4- 12 + 2 NaHCOg = NagAsO^ + 2 Nal -1- 2 CO2 + HgO. VOLUMETRIC ANALYSIS 8i Procedure. — Weigh 2.475 grams of pure arsenious oxide into a No. 3 beaker. Dissolve in the least possible amount of warm 10 per cent sodium hydroxide solution. Wash the contents of the beaker into a 500 c.c. measuring flask, add a drop of phenolphtha- lein, then add dilute hydrochloric acid until the solution is color- less. Dissolve about 10 grams of pure sodium bicarbonate in a little water, filter if necessary, and add the solution to the contents of the flask. If the solution is alkaline, add a few drops of the dilute acid until it is decolorized. Make the solution up to the mark with distilled water. Titrate portions of this solution against the standard iodine solution until the ratio is established. From the data calculate the number of grams of iodine in each cubic centimeter of the iodine solution. Notes. — I. Arsenious oxide is much more easily soluble in sodium hydroxide solution than in a solution of the bicarbonate. From what has already been said, it is evident that the excess of caustic alkali must be removed. This is done by neutralizing with acid. Since the titration must be carried out in an alkahne solu- tion an excess of sodium bicarbonate is then added. 2. The reaction between arsenious oxide and iodine takes place in acid solution. Under these conditions, however, the reaction is reversible : AsjOg -V 2 H2O -I- 2 I2 r§: 4 HI + AsgOg. If the hydriodic acid is removed from the solution as fast as it is formed, the arsenious oxide will be completely oxidized to the arsenic oxide. The function of the sodium bicarbonate, therefore, is to remove the hydriodic acid as rapidly as it is formed. c. By Means of Standard P ermanganate Solution Principle. — Potassium permanganate reacts with an acid solu- tion of potassium iodide, liberating iodine quantitatively according to the equation : 2 KMnO^ + 10 KI + 8 H2S04= 5 I2 + 6 KaSO^ + 2 MnSO^-f 8 H,,0. The iodine may be titrated by means of standard thiosulphate. Procedure. — -Introduce 25 c.c. of the standard permanganate solution into an Erlenmeyer flask which contains 10 c.c. of dilute sulphuric acid and one or two grams of potassium iodide. Add 82 QUANTITATIVE ANALYSIS lOO c.c. of water and titrate the liberated iodine with thiosulphate solution until the solution has changed to a straw color, then add about 2 c.c. of the starch solution. Continue the titration until the solution changes from blue to colorless. From the available oxygen in 25 c.c. of the permanganate solution calculate the num- ber of grams of iodine liberated, and the strength of the iodine solution in grams of iodine per cubic centimeter. d. By Alcaus of Standard Diclironiatc Solution Principle. — The method is based upon the fact that a solution of potassium dichromate liberates iodine from an acid solution of potassium iodide, the equation being KXraO^ + 6 KI + 14 HCl = 8 KCl + 2 CrClg + 7 Hp + 3 I^. The iodine liberated is titrated with sodium thiosulphate solution. Procedure. — Place 25 c.c. of the standard dichromate solution into a 500 c.c. Erlenmeyer flask containing 5 or 6 c.c. of concen- trated hydrochloric acid and about two grams of potassium iodide dissolved in 25 c.c. of water. Mix thoroughly. Dilute to about 250 c.c. and run in sodium thiosulphate solution as in the stand- ardization by means of permanganate. In this case the transition is from blue to a pale green. From the data, calculate the strength of the iodine solution in terms of grams of iodine per cubic centimeter. Exercise XXVIII Estimation of Available Chlorine in Bleaching Powder Procedure. — Weigh about 10 grams of bleaching powder into a porcelain mortar, pulverize thoroughly in the presence of a little water until the mixture is of the consistency of thick cream. Add more water, allow to settle, and decant into a Hter flask. Grind the residue with a Uttle water, and continue the process until the last trace has been introduced into the flask without loss. Make up to the mark and shake thoroughly. From the well-mixed milky solution remove 25 c.c. by means of a pipette and introduce it into an Erlenmeyer flask. Dissolve two grams of potassium iodide in 25 c.c. of water, add it to the solution, and acidify with acetic acid. Titrate the iodine Hberated in the usual manner with sodium thio- sulphate. Repeat, and when the ratio between this solution and VOLUMETRIC ANALYSIS 83 the sodium thiosiilphate is established, calculate the percentage of available chlorine in the sample. Xotcs. — I. Commercial bleaching powder is usually a mixture of calcium hypochlorite, calcium chloride, and hydroxide. The true bleaching agent is the hypochlorite. In general, it is valued and sold by the percentage of chlorine available for oxidizing purposes. 2. Chlorates are sometimes present in bleaching powder, owing to faulty manufacture. In the presence of acetic acid, these chlorates do not liberate iodine. Exercise XXIX The Determination of Available Oxygen in Pyrolusite Principle. — When manganese dioxide is heated with hydro- chloric acid, chlorine is liberated. The chlorine may be con- ducted into a so- lution of potas- sium iodide, and the liberated io- dine titrated with thiosul- phate. Procedure. — Set up an appa- ratus similar to that shown in Fig. 20. Use a 75 c.c. glass- stoppered retort and a 250 c.c. ^"^- ==° flask which should be so arranged that a stream of cold water flows upon it. Introduce into the flask about 10 grams of potas- sium iodide dissolved in 150 c.c. of water, which should entirely cover the end of the retort when it is in place. Weigh into the retort 0.5 gram of finely pulverized pyrolusite and add 30 c.c. of concentrated hydrochloric acid. Add two or three pieces of mag- nesite the size of a pea and place the stopper in the retort. Heat the contents of the retort to boiling, using a small flame, and distill 84 QUANTITATIVE ANALYHI^ about one-half of the Uquid over into the flask. In order to pre- vent the iodine solution from being drawn back into the retort, withdraw the delivery tube from the potassium iodide solution before removing the flame. Wash off the end of the delivery tube. Transfer the contents of the flask to a 250 c.c. graduated flask, make up to the mark, mix thoroughly, and titrate 50 c.c. portions with the thiosulphate solution until concordant results are obtained. From the data calculate the percentage purity of the pyrolusite and the available oxygen in one gram. Notes. — I. The available oxygen in chromates, lead peroxide, red lead, and certain other oxidizing substances may also be esti- mated in this way. 2. The magnesite dissolves slowly in the hydrochloric acid, and the carbon dioxide liberated prevents the liquid from drawing back. 3. The receiving flask should be cooled to prevent the loss of iodine by volatilization. 4. The apparatus designed by Bunsen can also be employed for such determinations. Exercise XXX Determination of the Strength of Hydrogen Peroxide Procedure. — Dilute 10 c.c. of the hydrogen peroxide solution to 250 c.c, mix thoroughly. Introduce 25 c.c. of this solution into an Erlenmeyer flask in which one gram of potassium iodide dis- solved in a little water and 30 c.c. of dilute sulphuric acid have been placed. After five minutes dilute to 100 c.c. and titrate with the standard thiosulphate in the usual manner. Repeat, and from the data calculate the percentage of hydrogen peroxide in the sample, assuming the specific gravity to be one. Calculate the number of grams of available oxygen in each cubic centimeter of the original peroxide solution. Note. — The stated order of adding the reagents must be followed, as potassium iodide when added to a neutral solution of hydrogen peroxide decomposes it catalytically, with the evolution of oxygen. PART IV AGRICULTURAL ANALYSIS THE ANALYSIS OF MILK Milk is the natural secretion of the mammary glands of female mammals for the nourishment of their young. The milk of the cow is of most importance and has been studied in greatest detail. Whole A/ilk is the lacteal secretion obtained by the complete milking of one or more healthy cows, properly fed and kept, ex- cluding that obtained within fifteen days before and five days after calving. ^/a«(/(?/v/ J////& is milk containing not less than 12 per cent of total solids and not less than 82- per cent of solids not fat, nor less than 3^ per cent of milk fat. Fresh cow's milk is amphoteric, that is, if tested with blue litmus paper it reacts acid, while with red litmus it reacts alkaline. On standing it becomes distinctly acid, and the acidity increases as the milk sugar is changed by bacterial action into lactic acid. Composition The constituents of milk are water, fat, proteids, milk sugar (lactose), and inorganic salts. The lactose, albumin, and certain salts are present in solution. The casein does not form a true solution, but is present in a colloidal form in combination with calcium phosphate. The fat is present in minute globules which are suspended in the liquid. Milk from other animals contains the same constituents as cow's milk, but in different proportions. The following table, compiled by Konig, gives the composition of some of the different kinds of milk : 85 86 Q UANTITA TIVE ANAL YSIS No. OF Analyses Sp. Gr. Water Ca- sein Albu- min Total Pro- TEIDS Fat Milk Sugar Ash Cow's Milk . 800 Minimum . . 1.0264 ' 89-3- 1.79 0.25 2.07 1.67 2. II 0-35 Maximum 1.0370 90.69 6.29 1-44 6.40 I 6 47 6.12 ■ 1. 21 Mean . I.03I5 87.17 3.02 0-53 3-55 3-64 4.88 0.71 Human Alillc . 200 Mean . 1.029 87.41 1.03 1.26 2.29 378 6.21 0.31 Goat's Milk . . 200 Mean . . 1.0305 85.71 3.20 1.09 4.29 4.78 4.46 0.76 Sampling To insure a representative sample, the milk should be thorough!}' mixed by pouring from one vessel to another. Where this is im- possible, a Scovell sampling tube, which permits samples to be removed from any part of the container, may be used. The samples taken in this way are mixed and used for the analysis. It will be found best to prepare apparatus so that the various determinations can all be started at once. The following appa- ratus will be necessary in addition to that supplied for the ordinary quantitative work : 2 aluminium dishes,- 2||" diameter. 2 strips of fat-free paper. 2 Babcock test bottles. I pipette, 17.6 c.c. I cylinder, 17.5 c.c. Clean the aluminium dishes and two Erlenmeyer flasks (125 c.c.) and heat them at ioo°-iio° in the air bath until the weight is constant. Heat two porcelain dishes over the flame of a Bunsen burner, cool, and weigh. Repeat until the weight is constant. Thoroughly clean two Kjeldahl flasks, a 500 c.c. graduated flask, and the two Babcock test bottles. Specific Gravity Obtain a sample of milk, a thermometer, a hydrometer, and a 250 c.c. graduated cylinder. Thoroughly mix the milk by pouring it from the cylinder into a beaker and back again, three or four AGRICULTURAL ANALYSIS 87 times. Now cover the cylinder with a small beaker, place it under the tap, and allow water to run upon the side until the milk is cooled to 15.6° C, at which temperature determine the specific gravity with a delicate hydrometer (lactometer). Xotcs. — I. The specific gravity of milk may be taken by means of an ordinary hydrometer. Hydrometers for use with milk are known as lactometers and are graduated variously. The following lactometers are in general use : The Ouevenne lactometer is graduated from 15" to 40°, and corresponds to specific gravities from 1.015 to 1.040. The New York Board of Health lactometer has an arbitrary scale, divided into 120 equal parts, the zero being equal to the specific gravity of water, while 100 corresponds to a specific gravity of 1.029. 2. The specific gravity of milk depends upon two factors, the percentage of fat present, and the percentage of solids other than fat. The removal of fat raises the specific gravity ; and as the specific gravity may be brought back by the addition of water, it will be seen that, considered by itself, specific gravity gives no indication of the purity of milk. 3. The temperature, 1 5.6° C. (60° F.), is the standard temperature for taking the specific gravity of milk. Instead of cooling the milk to this temperature, the specific gravity may be taken at the ordinary temperature, and by means of tables calculated to the temperature 15.6°. (See Vieth's tables in Leach's Food Analysis, P- 97-) Removal of Samples While the milk is at the temperature at which the specific gravity was determined, remove all of the samples required for analysis as soon as possible, and proceed with the respective analyses as described below. Total Solids Procedure. — Place into each of the weighed aluminium dishes 5 c.c. of milk, evaporate to dryness on a water bath, and dry in the water oven for exactly one hour, at the temperature of boiling water. Cool in the desiccator, and weigh rapidly to avoid the absorption of hygroscopic moisture. Heat in the water oven again 88 QUANTITATIVE ANALYSIS for exactly thirty minutes, cool, and weigh. Calculate the percent- age of total solids in the sample. Note. — The total solids consist of sugar, fat, proteids, and inor- ganic salts. As certain of the milk constituents undergo decompo- sition when heated above ioo°, the water oven and not the air bath should be used for drying the soHds. A darkening of the solid matter indicates decomposition. Ash Procedure. — Place 25 c.c. of milk into each of the weighed por- celain dishes, add 5 c.c. of concentrated nitric acid, evaporate to dryness on the water bath, and then burn at a low red heat in the mufifle furnace (see Fig. 21) until the ash is free from carbon. Heat to constant weight and calculate the percentage of ash. Azotes. — I. The ash from a large number of samples on analy- sis gave the following composition : Potassium oxide Sodium oxide . Calcium oxide . Magnesium oxide Iron oxide . Sulphur trioxide Phosphorus pentoxide Chlorine 25.02% 10.01 20.01 2.42 0.13 3-?4 24.29 14.28 100.00 2. The ash should not be heated higher than a dull red heat, as there is considerable danger of volatilizing the sodium and potas- sium chlorides which form a large percentage of the inorganic constituents of milk. Fat Adams' Paper Coil Method Procedure. — Suspend strips of fat-free paper from the edge of the desk and deliver evenly upon each exactly 5 c.c. of milk from a pipette. Allow the paper to dry partially, then roll into a coil, bind with a clean tinned iron wire, place both coils into a small beaker, and dry in the water oven at 100" C. for two hours. Place the coils into large inner extraction tubes over the ends of which Fig. 21 ( 90 QUANTITATIVE ANALYSIS /:^=^=:i- A r^ Fig. 22 pieces of hard fat-free filter paper have been fastened by means of tinned iron wire (see Fig. 22, A). Place the inner extraction tubes inside two Soxhlet extractors, attach to the Hopkins conden- sers, connect with clean weighed Erlenmeyer flasks into which 50 c.c. of dry ether have been placed, and extract for two hours. The arrangement of the apparatus is shown in Fig. 22. The Erlen- meyer flask is best heated by means of an electric air bath as illustrated in Fig. 23. Connect the flasks containing the ether with condensers which are set up for this purpose, and recover the ether by distillation. The distil- lation apparatus is shown in Fig. 24. Dry the flask and fat in the water oven to constant weight and calculate the percentage of fat in the milk. Babcock Method Procedure. — Measure out 17.6 c.c. of milk with a Babcock pi- pette, transfer to a Babcock test bottle, and add in small portions 17.5 c.c. of commercial sulphuric acid, shaking the flask after each addition. Thoroughly mix the acid and the milk, until the curd which separates at first is com- pletely dissolved. Prepare dupli- cates at the same time. Imme- diately place the bottles into the centrifugal machine (Fig. 25) AGRTi Y7 I'L'K. If. , /.\V// ) :v/.v 91 opposite oach other, replaee the cox'ei-, and turn the niaeliine at a hii;-h speed for fi\-e niiiuites. Now lill the bottles with \ery hot distilled water to ahi.ut the 7 per eent mark. Turn the maehine Fm;. 23 for one minute mm-e, remove the bottle, and immediately, while still hijt, determine the pereentage of fat b)- measuring the length of the fat column with a pair of dividers. The graduation of the neck of the flask reads percentage of fat direct. The test Ijottles are so made that the length of the fat column is ivad fron) the 92 {> I 'AX TIT A TI I 'E AXAL \ 'SIS bottom of the lower meniscus, which should be nearly flat, to the point at which the upper meniscus meets the side of the neck. Notes. — I. Milk fat is a mixture of glycerides of which palmi- tin, olein, nnristin, and butyrin are the most important. The de- termination of fat by the Adams method is based upon the fact Fic that it is soluble in ethci', while the other solids are insoluble. The fat must be thoroughly dried before it can be extracted ; this is best accomplished by distributing it upon a strip of fat-free paper, allowing most of the water to evaporate in tlie air, and removing the last portion by heating in the water oven. The greater part of the fat is left on the surface of the paper, so that it is easih' extracted with ether. On heating the flasks to constant weight, care should be taken that the fat is not heated too long nor at too high a tem]")erature, inasmuch as on one hand \'olatile fatty acids may escape, causing a Ljss, while on the other hand an increase in A\'eight may take place due to oxidation. 2. In the determination of fat bv the Babcock method, sul- .4 6Vv' ICLLTL R. IL .L\J/.) 'SIS 93 phuric acid dissol\-os the casein and yets tlie fat fr-'e in a pure state. li_\' rotatiii-- in the ceiUiifugal tiie fat is collected in tlie nei k ot tlie flaslv. Since tlie \a)lunie of fat contracts on Cdolini;', the readini; should be taken while it is liquid. l"he colnr of the fat slmuld lie )-el]o\v. If the acid used is too dilute, wliite ixarticles of casein will be mixed with the fat ; if too concentrated, the fat will contain Fig. 25 charred matter due to the action of concentrated acid on the or- ganic matter present in the milk. The sulphuric acid used should have a specific gravit)' between 1. 82 and 1..S3 at 15.0" C. 3. Based on the close relationshi|") between the fat, the specific gravit\', and the solids not fat, formulas ha\"e been derix'cd h\ which, if two of these factors are known, the third ma\' be calcu- lated. The formula in common use in this coimtr}' is that pro- posed by l^abcock.' r- 1 ■ 1 ^ c u ( 1 00 .S — FS , Solids not fat = — I ) ( 100 Vioo — 1. 0753/' .S /■) 2.5. 5' is the specific gra\'it\' and F the percentage of fat, 1 U. S. Liept. iifAgric, Div. uf riicni., lUil, 47. ].. 12;. 94 QUAN riTATIVE ANALYSIS Total Proteids Dctcrniination of Total Nitrogen by tlie KjeldaJil Method Principle. — The determination of the proteids is based upon the fact that about i6 per cent of proteid matter is nitrogen. The nitrogen in the proteids can be changed completely to ammo- nium sulphate by digestion with concentrated sulphuric acid, and the ammonia in this compound distilled into standard acid and determined volumetrically. From the amount of ammonia, the nitrogen, and consequently the amount of proteid matter, can be calculated. Proeednre. — Measure carefully 5 c.c. of milk into a 500 c.c. Kjeldahl digestion flask, taking care that the milk does not get upon the neck of the flask. Add 25 c.c. of pure concentrated sulphuric acid and about 0.65 gram of metallic mercury. Take into the digestion room, incline the flask on a stand (see Fig. 26) at an angle of 30°, and commence heating, watching closely at first, as there is danger of foaming during the first five to ten minutes ; after that the acid may be brought to boiling.^ Con- tinue the digestion for two hours, or until the liquid is colorless, keeping the acid boiling briskly all the time. See that all charred particles are washed down by the acid. After heating for two hours, if the solution is not clear, finish the oxidation by the careful addition of a little powdered potassium permanganate and allow the contents of the flasks to cool. During the digestion obtain the condenser, stands, and other parts of the distilling apparatus, and arrange them as represented in Fig. 27. Place about 200 c.c. of nitrogen-free water into each of two other Kjeldahl flasks, attach to the condensers and distill over without condensing the steam, thus cleaning out the condens- ers thoroughly. Allow the contents of the flasks in which the digestion took place to cool, add 200 c.c. of nitrogen-free water and 25 c.c. of potassium sulphide solution, shaking thoroughly after the addition of the latter solution. Add three or four small 1 A convenient form of digestion apparatus was devised at the Connecticut Experi- ment Station and is sliown in Fig. 26. To avoid the fumes from digestion, the necks of the flasks are inserted into a lead pipe through openings in the side. The lead pipe is connected with a flue having a good draft. A detailed description of this apparatus can be found in the Twenty-first Annual Report of the Agricultural Experiment Station, University of Wisconsin, pages 361-362 (1904). 96 Q UANTITA TIVE ANAL \ 'SIS pieces of granulated zinc. Measure carefully into 250 c.c. Erlen- meyer flasks 30 c.c. of standard sulphuric acid, label the flasks properly, and add to each a few drops of methyl orange indicator. Connect the flasks containing the standard acid with the con- FlG. 27 densers. Then incline the digestion flask and pour 70-80 c.c. of sodium hydroxide solution (600 grams per liter) down the side of the neck, being careful not to mix the alkaU with the acid con- tents. Wash the neck of the flask free from alkali with a little nitrogen-free water, and connect it immediately with the proper condenser. Be sure that the tips of the delivery tubes are AGRICULTURAL ANALYSIS 97 immersed in the standard acid and that the water is running through the condenser ; then mix the contents of the digestion flask thoroughly. Heat very carefully at first and distill over 175-200 c.c. of the Hquid, taking about an hour for the distillation. Watch the solution throughout the distillation, as there is danger of foaming and bumping. Disconnect the flasks before removing the burners and wash off the deUvery tubes into the Erlenmeyer flasks with distilled water. Titrate the excess of acid in the receiving flasks with a solution of standard ammonium hydroxide. (This should be standardized by titrating against the same standard sulphuric acid that was used in the receiving flasks.) From the data calculate the number of cubic centimeters of the standard acid which have been neutralized by the ammonia distilled over. Subtract from this the number of cubic centimeters of the standard sulphuric acid solution neutral- ized by the ammonia from the blank determination described below. The difference gives the number of cubic centimeters of the standard acid neutralized by the ammonia formed from the milk proteids. From this value and the strength of the standard acid (see factor on the bottle) calculate the amount of nitrogen formed from the milk proteids, and then calculate the percentage of nitrogen in the sample. The percentage of nitrogen multiplied by the factor 6.25 gives the percentage of proteids. For the method of calculation see page 175. Determination of the Blank The reagents used in the Kjeldahl process almost always contain small amounts of nitrogenous compounds. This is particularly true of sulphuric acid. It is always necessary, therefore, to make a "blank" to correct for the nitrogenous constituents in the re- agents. This is done by adding the usual amount of sulphuric acid to one gram of sugar, and digesting in a Kjeldahl flask with mercury, carrying out the rest of the determination as in the deter- mination of the milk proteids. The correction found by the blank is conveniently expressed in terms of the number of cubic centi- meters of the standard acid necessary to neutralize the ammonia present in the reagents. Notes. — I. The total proteids in milk have the following com- position : 98 Qi'AA'IITATIVE ANALYSIS Casein 80% Lactalbumiii 15 Traces of other nitrogenous substances 5 Casein is a white odorless and tasteless substance which is sparingly soluble in water, readily soluble in dilute alkalies, and insoluble in alcohol and ether. Strong acids dissolve it, but its nature is changed. 2. Sulphuric acid at a high temperature acts as an oxidizing agent, oxidizing the organic compounds present in milk to carbon dioxide and water. The nitrogen present forms ammonium sul- phate. The mercury is dissolved, forming mercuric sulphate, its function being to make oxidation take place more rapidly. A sub- stance acting in this way is called a "catalyzer." Mercury salts form complex compounds with ammonium salts from which the ammonia may be liberated only with difficulty. It is necessary, therefore, to break up these complexes. This can be done by the addition of potassium sulphide. 3. If the sodium hydroxide solution is mixed at once with the contents of the Kjeldahl flask, the solution will become so hot that there will be danger of loss of ammonia by volatilization. Great care should be exercised at this point, and the flask should be con- nected with the condenser as soon after the addition of the alkali as possible. As there is danger of " bumping " when the flasks are heated, a few pieces of granulated zinc are usually added just before the addition of the alkali, which prevent bumping by dissolving in the alkali with the liberation of hydrogen, which keeps the solution stirred. Fragments of ignited pumice stone will also prevent bumping. 4. In the determination of the blank, the function of the sugar is to reduce any nitrates which might be present in the reagents. 5. The Kjeldahl method for the determination of nitrogen finds wide apphcation in the analysis of agricultural products. For the determination of nitrogen in nitrates, the method cannot be used in the form described. For this purpose a modification of the process is used, in which the nitrates are first reduced to ammonium com- pounds. 6. Potassium sulphate is often added to the digestion flask with the sulphuric acid, in the presence of which it forms potassium acid sulphate. This raises the boiling point of the solution and makes the oxidation take place more rapidly. AGRICULTURAL ANALYSIS 99 7. The term " protein " is often used to designate the results obtained by multiplying the total nitrogen by the factor 6.25. Milk Sugar by Soxhlet's Method Principle. — The determination of lactose depends upon the fact that in an alkahne solution certain sugars, among which are lactose, dextrose, and levulose, together with some other organic compounds, have the power of reducing the copper in copper tartrate to the cuprous state, cuprous oxide being precipitated. The amount of cuprous oxide formed depends upon the nature of the reducing agent, the concentrations of the substances in solution, the tem- perature of the solution, and on the length of time the solution is heated. In the determination of lactose certain standard conditions have been adopted in which the concentrations of the reagents, the tem- perature, and the length of time the solution is heated are the same in every determination. A definite amount of cuprous oxide, therefore, always corresponds to a definite amount of milk sugar, and a table has been prepared, which gives for any amount of cuprous oxide, obtained under these conditions, the equivalent amount of lactose. Procedure. — Place 25 c.c. of milk into the 500 c.c. measuring flask, add 400 c.c. of water, mix, then add 10 c.c. of the Fehling's copper sulphate solution and 8.8 c.c. of N/2 potassium hydroxide solution. Fill the flask to the mark, thoroughly mix, allow the precipitate to settle, and filter through a dry ribbed filter, discarding the first 10 c.c. of the filtrate. The filtrate should have an acid reaction and contain copper in solution. In the solution thus pre- pared determine the milk sugar as follows: Place 25 c.c. of the standard copper sulphate solution and 25 c.c. of the alkaline tartrate solution into a 250 c.c. casserole and heat to boiling. While boil- ing briskly, add lOO c.c. of the milk solution and boil vigorously for six minutes. Filter immediately without diluting, through a quantitative filter paper. Be sure that the filtrate is perfectly clear ; if not, refilter. Wash immediately with boiling distilled water until the wash water no longer reacts alkaline. Transfer filter and con- tents to a weighed crucible and dry carefully. When dry, ignite the precipitate at red heat for about 20 minutes. Transfer quickly to the desiccator, cool, and weigh. Ignite to constant weight. As lOO QUANTITATIVE ANALYSIS cupric oxide is somewhat hygroscopic, weigh as quickly as possible. From the weight of the cupric oxide obtained, calculate the amount of copper. Obtain the weight of milk sugar equivalent to the weight of copper from Table VI on page 206. Calculate the percentage of lactose in the sample. Notes. — I. Since the casein in the milk reduces the alkaline copper tartrate to a certain extent it must be removed. This is done by precipitating copper hydroxide in the solution, the precipitate car- rying down with it all the casein, which is then removed by filtration. 2. The alkaline solution of copper tartrate is known as " Feh- ling's solution." It is usually prepared at the time of using by mixing a solution of copper sulphate and a solution of sodium potassium tartrate containing sodium hydroxide. If kept mixed for any length of time, Fehling's solution undergoes a change, so that on boiling cuprous oxide is precipitated even when no lactose is present. Tabulation of the Results Collect the results obtained in this analysis and neatly tabulate them on one page of the laboratory notebook. References Farrington and Woll, Testing Milk and its Products (1904). Richmond, Dairy Chemistry (1899). Leach, Food l7ispection and Analysis, Chap. VI, p. 88 (1904). THE ANALYSIS OF BUTTER Butter is the clean non-rancid product made by gathering in any manner the fat of fresh or ripened milk or cream into a mass, which also contains a small portion of the other milk constituents, with or without salt, and contains not less than 82.5 per cent of milk fat. By acts of Congress approved August 2, 1886, and May 9, 1902, butter may also contain added coloring matter.^ The following results of a large number of butter analyses by Konig show that the composition may vary within wide limits. 1 U.S. Dept. of Agric, Office of the Secretary, Circular No. 19 (1906). AGRICULTURAL ANALYSIS lOI Water Fat Casein Lactose Lactic Acid Salts Minimum . Maximum . . Mean . . . 4-IS 3S-IS 13-59 69.96 86.15 84-39 0,19 4.78 0.74 0.45 1. 16 12 0.00 1.16 0.12 0.02 15.08 0.66' On exposure to light and air butter fat acquires a disagreeable smell and taste ; it is said to become rancid. The quantity of free fatty acids is greatly increased ; the volatile acids are liberated and their odor can be detected in the rancid butter. Certain oxidation products are also formed. In regard to the changes which take place during this process, but little is known. During the last few years processes have been perfected by which rancid butter is melted and treated in such a way as to remove the objectionable odors and give the product the appearance of pure butter. This product is known as " process," or " renovated," butter, and is at present manufactured on a large scale. Standard renovated butter contains not more than 16 per cent of water and at least 82.5 per cent of milk fat. Sampling Place from 200 to 300 grams of the sample to be analyzed into a glass-stoppered, salt-mouthed bottle and melt the butter at as low a temperature as possible. When melted place the bottle into ice water or under a stream of cold tap water and shake vio- lently until the mass is homogeneous and sufificiently solidified to prevent the separation of the water and salt. Nearly fill a glass- stoppered weighing tube with the butter and keep in a cold place until analyzed. The Determination of Water Procedure. — Dry from 1.5 to 2.5 grams of the sample to constant weight at the temperature of boilingwater in a weighed, flat-bottomed dish, or beaker, which has a surface of at least 20 square centime- ters. From the loss of weight calculate the percentage of water present. If a round-bottomed dish is used, the complete expulsion of the water will be accomplished with difficulty, owing to the depth of the layer of fat. In this case a small stirring rod about 2^ inches long should be weighed with the dish and the butter fat stirred occasionally during the heating. 1 Many of the samples were unsalted, hence the low mineral content. 102 QUANTITATIVE ANALYSIS The Determiaation of Fat Procedure. — Dissolve the dry butter left from the determination of water in absolute ether, and with the aid of a glass-stoppered wash bottle containing ether transfer the contents of the dish to a prepared and weighed Gooch crucible. Wash with ether until free from fat and heat the crucible and contents in the water oven until the weight is constant. Calculate the percentage of fat from the data obtained. Note. — Place the ether residues into a bottle provided for that purpose. The Determination of Casein and Ash Procedure. — Cover the crucible containing the residue from the fat determination, and heat in the ash muffle, gradually raising the temperature to just below redness. Remove the cover and continue the heating until the contents of the crucible are white. The loss in weight of the crucible and contents represents casein, while the residue in the crucible is mineral matter. Note. — If lactose is present, it will be burned and calculated as casein. By obtaining an aqueous extract of a separate portion of butter, the lactose may be determined by means of Fehling's solu- tion, and the proper correction made. The Determination of Salt Principle. — When a silver nitrate solution is added to a neutral solution of an alkali or an alkahne earth chloride, silver chloride is formed. If a small amount of potassium chromate is present, a reddish brown precipitate of silver chromate will be formed, which disappears on stirring, owing to the fact that it is decomposed by the alkali chloride, according to the equation : Ag2Cr04 -h 2 NaCl = 2 AgCl -|- NaaCrO^. After the chlorine is all precipitated, however, the next drop of silver nitrate precipitates silver chromate, which colors the solution a permanent reddish brown. Procedure. — Weigh into a tared beaker about ten grams of the sample. Place the butter into the beaker in portions of about one gram, removing them from different parts of the sample by means AGRICULTURAL ANALYSIS 103 of a spatula. Add about 25 c.c. of boiling water to the beaker, and after the fat has melted pour the liquid into a separatory funnel, and rinse the beaker with several portions of hot water. Shake the funnel and allow it to stand until the fat has collected, then draw off the underlying aqueous solution into a 250 c.c. graduated flask. Add about 20 c.c. of hot water to the funnel, extract again, and re- peat the extraction until about 225 c.c. have been collected in the graduated flask. Cool the contents of the flask to room temperature and make the volume up to 250 c.c. Place 50 c.c. of the salt solution into a casserole and add one cubic centimeter of potassium chromate solution. Add from a burette a solution of N/20 silver nitrate until the solution changes from yellow to brown. The end point may be observed more easily if a casserole containing 50 c.c. of water and one cubic centimeter of the indicator be placed beside the one containing the salt solu- tion and the colors of the two solutions compared during the titra- tion. A blank experiment should be made to determine how much of the silver nitrate solution is necessary to produce the brown color with the indicator when no chloride is present, and this amount should be subtracted from that used in the analysis. From the results of the titration calculate the percentage of sodium chloride in the butter. Note. — Instead of potassium chromate, sodium arsenate solution may be used as an indicator, as recommended by Lunge. This has the advantage of changing the solution from colorless to red- dish brown, making the end point easier to detect. The Examination of Butter Fat The foregoing tests with butter are of value in showing whether or not the butter contains an excessive amount of salt and water. They give no idea, however, of the possibility of the presence of animal fat which may have been used to adulterate the butter. For this purpose an examination of butter fat must be made. Composition of Butter Fat Butter fat is a complex mixture of glycerides which are present in varying amounts. Its separation into the various constituents presents many difficulties, and the results obtained by different in- I04 QUANTITATIVE ANALYSIS vestigators show wide variations. An investigation by Browne^ shows these glycerides to be present in the following proportions : Per cent Present Formula of Acid from which Glvceride is Formed Dioxystearin . . 1.04 Ci7H33(OH)2COOH Glycerides of non- volatile acids in- . soluble in water Olein .... Stearin . Palmitin . . . Myristin 33-95 1. 91 40.51 10.44 C17H33COOH C17H36COOH CisHsiCOOH C13H27COOH ^Laurin 2-73 C11H23COOH Glycerides of vola- tile acids soluble ■ in water Caprin .... Caprylin Caproin . . Butyrin . . . 0.34 0-S3 2.32 6.23 C9H19COOH C7H15COOH CsHuCOOH CsHjCOOH Olein, stearin, and palmitin are the most common of the insoluble glycerides. Butyrin is the most important of the soluble glycerides. In the subsequent discussion these glycerides will be used as types of their respective classes. The most frequent form of butter adulteration consists in replac- ing the fat, either entirely or in part, by certain other fats. Butter which has been adulterated in this way is known as oleomargarine or biitterine. The principal substance used in the manufacture of oleomargarine is oleo oil, a product obtained from the fat of beef cattle, which is essentially a mixture of olein and palmitin. The oleo oil is usually churned with neutral lard, milk, and a small amount of butter. Coloring matter is often added at this stage. The whole mass is then cooled, the fat separated from the liquid, salted, worked, and treated similarly to butter. Oils of vegetable origin, such as cotton seed, peanut, and sesame, are occasionally mixed with the oleo oil. Blyth gives the following proximate analysis of commercial oleomargarine : Per cent Water Casein Salt . Fat . 12.01 0.74 5-23 82.02 Per cent 22.32 46.94 30.42 Palmitin Stearin Olein Butyrin Caproin .Caprylin J 1 Browne, /oar. Am. Chem. Soc, 21, 823 (1899) Insoluble non-volatile acids. 0.32 Soluble and volatile acids. AGRICULTURAL ANALYSIS 105 There are certain important fundamental differences between butter fat and the fat found in oleomargarine, which may be briefly stated as follows : — I. Chemical Differences 1. About 5 per cent of the fatty acids in butter fat are soluble in water and volatile with steam. In oleomargarine these soluble volatile fatty acids form a much smaller part of the fat, never more than one per cent. 2. From the above it follows that the percentage of insoluble fatty acids in butter fat will be several per cent less than that found in the fat of oleomargarine. 3. Butter fat in general contains a smaller percentage of unsatu- rated fatty acids than oleomargarine. 4. In the saponification of equal amounts of butter fat and oleomargarine a larger quantity of the alkali is required for the butter fat. II. Physical Differences 5. The index of refraction of butter fat is always appreciably lower than that of oleomargarine. This is the most important of the physical differences. 6. The specific gravity of butter fat at 37.8° C. is always above 0.910, that of oleomargarine rarely above 0.904. 7. The melting point of butter fat is usually somewhat higher than that of oleomargarine. It is on these differences that the methods for the identification of these fats are based. It is obvious, however, that if a large amount of butter fat is mixed with the oleomargarine, the values of the constants will approach those of pure butter. Preparation of Pure Butter Fat Melt about 100 grams of the butter in a beaker by allowing it to stand in a dry warm place at about 60°. When the water and curd have entirely settled, pour off the clear supernatant fat through a dry filter paper placed in a jacketed funnel containing boiling water. If the melted fat after filtering is not perfectly clear, it must be filtered a second time. Preserve the fat in a stoppered bottle which should be kept in a cool dark place. Note. — By exercising care, the fat may also be filtered through clean, dry absorbent cotton. io6 QUANTITATIVE ANALYSIS Phvsical Tests The Determination of the Specific Gravity of Butter Fat Procedure. — Clean a specific gravity flask of 25 c.c. capacity (see Fig. 28) by washing thoroughly with hot water, alcohol, and ether. Dry the flask and stopper, cool in a desiccator, and weigh accurately. Fill the flask with cold, recently boiled, distilled water. Insert the stopper and allow to stand for 30 minutes in a bath of distilled water kept at 37.8°. Remove the flask from the bath, wipe dry, and after it has cooled nearly to room temperature, place it in the balance case and weigh when the balance temperature has been reached. Rinse the flask with alcohol and ether, dry thoroughly, and fill it with the freshly filtered fat from a vessel which has been standing in the bath at 37.8°. Replace the flask in the water bath, main- tain for fifteen minutes at the tempera- ture 37.8°, and proceed as with the water. The weight of the fat having been deter- mined, the specific gravity is obtained by dividing it by the weight of water previously found. Notes. — I. At the temperature 35° C. it has been found that the difference between the specific gravity of butter fat and certain other fats is greater than at any other temperature. A sample of butter fat at 100° C. gave a specific gravity of 0.8672, oleomargarine 0.8598, a difference of 0.0074. At 35° the specific gravity of the same butter fat was 0.9121, the oleomargarine 0.9019, a difference of 0.0102. The temperature 37.8° (100° F.) has been selected for this determination, because at this temperature all the fats used for the adulteration of butter remain liquid. At a lower temperature there is danger of solidification. In some laboratories it is customary to carry out this determina- tion at 100° C. 2. A number of tests carried out by J. Bell show the values of the specific gravities of butter and certain other fats. His results are incorporated in the following table : Fig. 28 AGRICULTURAL ANALYSIS 107 KiNu 01-" Fat Butter fat (113 samples) Oleomargarine (mean) Mutton suet . Beef suet . Fine lard . Specific Grwity at 37. 8' ■ o. 911-0.913 09039 0.90283 0.90372 o.903;-;4 It is obvious that an oil with a high specific gravity such as cocoanut oil (0.9167 at 37.8°) could be mixed with oleomargarine, and the adulteration could not be detected in this manner. The Determination of the Melting Point ( Wiley's Method) Apparatus and Reagents. — Obtain an accurate thermometer which reads easily to tenths of a degree, a tall beaker about 35 cm. high and 10 cm. in diameter, two test tubes about 30 cm. long and 3.5 cm. in diameter. Place the beaker upon an asbestos gauze which is supported by the ring of an iron stand. By means of a clamp suspend the test tube so that it extends to within a few centimeters of the bottom of the beaker. Suspend the thermometer in such a way that it can be easily lowered into the test tube. Arrange a bent glass tube so that it will extend to the bottom of the beaker, and make possible the agitation of the liquid by blowing air through the tube. Procediire. — Pour freshly boiled hot water into the test tube until it is nearly half full. Nearly fill it with hot freshly boiled alcohol which should be carefully poured down the side of the inclined tube to avoid too much mixing, and place into a tall beaker con- taining ice water. Prepare several disks of fat by allowing the melted and filtered fat to fall from a dropping tube from a height of 1 5-20 cm. upon a smooth piece of ice floating in recently boiled distilled water, forming disks from i to 1.5 cm. in diameter. By pressing the ice under water, the disks are made to float on the surface, from which they can be removed easily with a cold steel spatula. Drop the disk of fat into the test tube. When it has come to rest, place the test tube into the beaker on the stand and lower the delicate ther- I08 QUANTITATIVE ANALYSIS mometer until the fat particle is even with the center of the bulb. Nearly fill the beaker with distilled water, and heat the water slowly, keeping it stirred by occasionally blowing through the bent tube. When the temperature of the mixture rises to about 6° below the melting point, the disk of fat begins to shrivel, and gradually rolls up into an irregular mass. The rise of temperature should be so regulated that the last two degrees of increment require about ten minutes. As soon as the mass of fat forms a sphere, read the temperature, remove the test tube from the bath and place it into the beaker of ice water. A second tube containing alcohol and water should be placed at once into the bath and the determination repeated. As this test tube has been standing in ice water, its temperature is low enough to cool the bath sufficiently. Triplicate determinations should be made and the second and third results should agree within 0.2". Notes. — I. If the alcohol is added after the water has cooled, the mixture will contain air bubbles which will gather on the disk of fat as the temperature rises and may finally force it to the top. 2. The edge of the disk should not be allowed to touch the sides of the tube. If this happens, a new determination should be made. 3. In general the melting point of butter is several degrees higher than that of oleomargarine, although artificial butters may be made which have the same melting point as butter. Con- sequently, this determination is not of itself conclusive evidence of the purity of the sample, but is of value only when used to sup- plement other tests. The following table gives the melting points of some of the more common fats : Fats Butter . . . Oleomargarine (mean) Oleo oil . . . . Beef tallow . . . Mutton tallow Lard Melting Point 28- -33° c. 26 33- -39 42- -49 44- -50 36-46 AGRICULTURAL ANALYSIS 109 Chemical Tests It will be found advantageous to weigh out at the same time samples for the following determinations : volatile acids, saponi- fication number, insoluble acids, and iodine absorption. Obtain a tube of the form shown in Fig. 29 for weighing samples 25. 20. 15. 10. 5Jl. Fig. of butter fat. Nearly fill it with clear molten fat, weigh, and re- move samples by blowing the fat into the proper receptacle as with a wash bottle. In order to prevent moisture from the breath entering the tube, place on the short tip the mouthpiece A, which is filled with soda lime. Remove the mouthpiece and reweigh. Take all of the samples in this manner. no QUANTITATIVE ANALYSIS The Determination of the Volatile Fatty Acids (^Reichert-Meissl Method) Principle. — If a fat or oil is heated with an alkali, the glycerides present are broken up, with the formation of glycerin and the alkali salts of the fatty acids. These salts are known as soaps, and the process is called saponification. The following equation shows the reaction by which stearin is saponified : stearin sodium stearate glycerin (Ci,H35COO)3C3H6 + 3 NaOH = 3 Ci^Hg^COONa + C3H5(OH)3. The addition of dilute sulphuric acid to the soap solution liberates the fatty acids. stearic acid 2 CiTHggCOONa + H2SO4 = 2 C17H35COOH + NaaSO^. On adding water and distilling, the volatile fatty acids pass over with the steam, are condensed, and may be estimated by titration with a standard alkali. The number of cubic centimeters of N/io sodium hydroxide solution equivalent to the soluble fatty acids distilled from five grams of the fat under the conditions of the experiment is known as the Reichert-Meissl Number. Procedure. — Weigh samples of 5 grams of the fat into two 250 c.c. Erlenmeyer flasks, in the manner above described. Add 10 c.c. of 95 per cent alcohol and 2 c.c. of sodium hydroxide solution ( I : I ), attach a reflux condenser, consisting of a glass tube about one meter in length, to the neck of the flask by means of a rubber stopper, and heat on the water bath with occasional shaking until the saponification is complete. This is shown by the clearness of the solution and its freedom from fat globules. Evaporate the alcohol by removing the condenser and heating the flask on the steam bath. The last traces of alcohol vapor may be removed by waving the flask briskly, mouth down, to and fro. Dissolve the soap by adding 132 c.c. of recently boiled distilled water to the flask and warming on the steam bath, with occasional shaking, until solution is complete. When the soap solution has cooled to about 60°, set the fatty acids free by adding 8 c.c. of dilute sul- phuric acid solution (200 c.c. of concentrated sulphuric acid in 1000 c.c. of water). Connect the flask with the reflux condenser AGRICULTURAL ANALYSIS ui and heat in the water bath without boiling, until the fatty acid emulsion forms an oily layer on the surface of the liquid. Cool the flask to room temperature and add a few pieces of pumice stone to prevent bumping. The pumice stone is prepared by throwing it, at a white heat, into distilled water, and keeping it under water until used. This treatment expels the air from the pores of the pumice stone, so that it will sink when added to the liquid. Connect the flask with a glass condenser and distill at such a rate that no c.c. of the distillate will be collected in thirty minutes. Collect the distillate in a no c.c. graduated flask, in the neck of which is a short funnel provided with a loose tuft of absorbent cotton to serve as a filter. Pour the distillate into a beaker, add 0.5 c.c. of phenolphthalein solution, and titrate with N/io sodium hydroxide solution until the red color produced re- mains unchanged for two or three minutes. Calculate the Reichert- Meissl number. Note. — I. The volatile acids are defined as those which pass over with steam, irrespective of the boiling point of the acid. The entire amount of the volatile fatty acids is not obtained in the above process ; moreover, the quantity varies with the amount of distillate, the concentration of reagents used, and other factors. 2. The alcohol added assists in the solution of the fat and con- sequently gives a more rapid saponification. 3. A study of the errors of the Reichert-Meissl process has been made by Wollny. He has found them to be : a. The absorption of carbon dioxide during saponification. b. The formation of volatile ethers during saponification. Bu- tyric acid, for example, reacts with alcohol to form volatile ethyl butyrate : C3H7COOH + C2H5OH = C3H7COOC2H5 -f H2O. The escape of the ethyl butyrate is prevented by the reflux con- denser and it is finally saponified. c. The formation of ethers during the distillation. d. The retention of some of the volatile acids, owing to cohesion of the fatty acids. e. Variation in the fraction of the volatile fatty acids distilled, owing to size and shape of the distilling vessel, and to the length of time of the distillation. 112 QUANTITATIVE ANALYSIS By the adoption of standard methods of procedure, the above errors have either been minimized or made constant, so that uniform results may be obtained, which permits the use of this method as one of comparison. 4. The determination of the volatile acids is one of the most common and the most important methods for the determination of the adulteration of butter with foreign fats. Not only does it serve for their detection, but it is also of use in the estimation of the amount of foreign fat which has been added to the butter. The following table, compiled by Blyth, shows the Reichert-Meissl number of butter fat compared with other fats : Kind of Fat Reichert-Meissl Number Butter fat 24-32 26.8 18,0 17.4 7.0-8.0 0.8-3.0 0.4-0.6 0.6 Butter fat + 10 per cent cocoanut oil Butter fat + 50 per cent cocoanut oil Butter fat 50 per cent] Cocoanut oil 22.5 per cent . . Oleomargarine 27.5 per centj Cocoanut oil .... . . Oleomargarine . . .... .... Lard ... Olive oil . ... The Determination of the Soluble and the Insoluble Fatty Acids Prittciple. — The fatty acids in the butter fat may be set free by saponification and treatment of the soap with a known amount of standard acid, as in the determination of the volatile acids. On melting the fatty acids, leaching with water, and cooling to zero degrees, the insoluble acids adhere and form a solid cake from which the soluble fatty acids may be separated by filtration, and determined by titration. The insoluble acids may be weighed directly. Soluble Acids Procedtcre. — Place two 5 gram samples in 250 c.c. Erlenmeyer flasks, add from a pipette 50 c.c. of alcoholic potash solution (40 grams of potassium hydroxide in one liter of 95 per cent redistilled alcohol), and saponify as in the determination of volatile acids. Two A GRICULI'URAL ANAL YSIS 1 1 3 blank experiments should be conducted at the same time. After complete saponification remove the condensers from the flasks and evaporate the alcohol by further heating. Titrate the blanks with half normal hydrochloric acid, using phenolphthalein as an indica- tor. Run into each of the flasks containing the saponified fat one cubic centimeter more of the half normal hydrochloric acid than was found necessary to neutralize the alkali in the blanks. Connect with the reflux condenser, and heat on the steam bath until the separated fatty acids have collected in a layer,. Cool the flask in ice water until the fatty acids have solidified, then decant the Hquid through a dry filter, taking care not to break the cake. Add about 200 c.c. of water to the flask, insert the cork with the condenser, and heat on the steam bath until the cake of acids is thoroughly melted. During the process the flask should occasionally be agitated with a circulatory motion in such a way that its contents are not allowed to touch the cork. When the fatty acids have again separated into an oily layer, cool the flask and contents in ice water, and filter the liquid through the same filter into the liter flask as before. Repeat the treatment with hot water, followed by cooling and filtration of the wash water, three times, adding the washings to the first filtrate. Make up the wash- ings with water to the liter mark, mix, and titrate 100 c.c. portions with N/iO sodium hydroxide solution, using the proper indicator. Calculate the amount of alkali equivalent to the total amount of solution. This represents the volume of N/iO sodium hydroxide neutralized by the soluble fatty acids of the butter fat, plus that corresponding to the excess of one cubic centimeter of N/2 hydro- chloric acid used. Deduct from the total amount the number of cubic centimeters of the standard alkali equivalent to this excess of acid, and from the corrected volume of standard alkali used calculate the percentage of soluble fatty acids in the butter fat as butyric acid. Insoluble Acids Procedure. — Allow the flask containing the cake of insoluble acids and the paper used for the filtration of the soluble acids to drain for twelve hours, than transfer the cake with as much of the fatty acids as can be removed from the filter paper to a weighed glass evaporating dish. Place the filter in the Erlenmeyer flask and wash it thoroughly with strong alcohol, transferring all the washings to 114 QUANTITATIVE ANALYSIS the dish. Evaporate the alcohol by placing the dish upon the water bath, dry the dish in the water oven for two hours, cool in the desiccator, and weigh. Heat again for half an hour, cool and weigh. If a considerable loss in weight is found, heat for an additional half hour. From the data calculate the percentage of insoluble fatty acids in the butter fat. Note. — The above determination gives a valuable indication of the presence of foreign fats in butter, since the fats used for the purpose of adulteration contain a high percentage of insoluble acids. Blyth gives the following results of analyses which show the relative amounts of soluble and insoluble acids in pure and adul- terated butters. Percentage OF Fatty Acids Kinds of Butter Soluble Insoluble ri 5.92 87.86 Genuine II 5.76 88.10 Butters Ill 5-37 87.68 [iv 4-77 88.44 Adulterated Butters | jjj ' 1.98 2.34 0.58 93-30 93-82 95-51 Saponification or Koettstorfer Number Principle. — The amount of alkali necessary to saponify any fat depends upon the glycerides which compose the fat. In the case of the pure glycerides, the smaller the number of carbon atoms present in the acid, the more alkali will be required for saponiiication, as may be seen from the following equations : butyrin (C3H7COO)3C3H5 + 3 KOH = 3 C3H7COOK + C3H5(OH)3. (mol. wt. 302) (3 X m. w. = 168) One gram of butyrin requires 0.556 gram of potassium hydroxide. (Ci,H35COO)3C3H5 + 3 KOH = 3 C17H35COOK + C3H5(OH)3. (mol. wt. 891) (3 X m. w. = 168) AGRICULTURAL ANALYSIS 115 One gram of stearin requires 0.189 gram of potassium tiy- droxide. From the above, it is obvious that a fat like butter, containing a considerable quantity of glycerides with a small number of carbon atoms, will require more alkali for saponification than a fat which is composed of the higher glycerides. The number of milligrams of potassium hydroxide necessary to completely saponify one gram of the fat is called the Saponifica- tion Number. To determine this value a definite amount of the fat is heated with standard alkali, and after the saponification the excess of alkali is determined by titration with standard acid. Procedure. — Place samples of one or two grams of the butter fat into Erlenmeyer flasks, add 25 c.c. of alcoholic potash solution (40 grams of potassium hydroxide in one liter of 95 per cent redistilled alcohol), connect with a reflux condenser, and saponify by heating on the water bath. Two blank experiments should be conducted at the same time. As soon as saponification is complete, remove the flasks from the bath, cool, and titrate the samples and also the blanks with half-normal hydrochloric acid, using phenol- phthalein as an indicator. Subtract from the number of cubic centi- meters of acid used to titrate the blank that necessary to titrate the excess of alkali from the saponification. This gives the num- ber of cubic centimeters of acid equivalent to the alkali used for the saponification. Calculate the saponification number. Notes. — I. The following are the values of the saponification number of some of the more common fats : Saponification Number Butter fat 220-233 Oleomargarine (mean) . . 195.5 Cocoanut oil 257.3 Tallow 196.8 Commercial lard .... 195.0 2. It has been suggested by Allen that the results obtained by the above method be expressed in terms of the " saponification equivalent." This is the number of grams of fat which react with one gram molecule of the alkali used, and is really an expression of the mean molecular weight of the fat. The saponification equivalent has the advantage that it is independent of the kind of alkali used for saponification Ii6 QUANTITATIVE ANALYSIS 3. The alcoholic potash used in the saponification undergoes changes other than that represented by its reaction with the fat. For example, some of it reacts with the glass vessel in which the reaction takes place. For this reason, the solution used for deter- mining the strength of the caustic potash must be subjected to exactly the same treatment (length of time of heating, etc.) as the alkali used for the saponification ; hence the necessity of the blank. The Determination of the Iodine Absorption Number {Hanns Method^ Principle. — This determination is based on the fact that unsatu- rated fatty acids react with the halogens to form addition products. Olein, for example, reacts with iodine according to the equation olein di-iodo-stearin (Ci,H33COO)3C3H5 + 3 I2 = (Ci,H33l2COO)3C3H5. Since different fats and oils contain different amounts of the unsaturated compounds, the determination of the amount of halo- gen absorbed is of value as a means of identification. The method in outline consists in adding a definite amount of the halogen to a solution of the fat, and titrating the excess after standing for a definite length of time. In the Hanus method the halogen used is a solution of iodine monobromide. The amount of halogen absorbed is calculated as iodine. The number of grams of iodine absorbed by 1 00 grams of the fat is called the Iodine Absorption Number. Reagents Preparation of iodine monobromide solution. Dissolve 13.2 grams of pure resublimed iodine in one liter of pure glacial acetic acid (99 per cent), heating the solution if necessary. To the cold solution add 3 c.c. of liquid bromine. This reagent remains un- changed for months. Sodium thiosulphate solution. — Standardize an approximately N/io sodium thiosulphate solution against a standard solution of potassium dichromate in the manner described in Exercise XXVII, page 82. Starch Solution. — Prepare according to directions given on page 80. AGRICULTURAL ANALYSIS wj Procedure. — Place two portions of 0.7-1 gram of the butter fat into narrow-mouthed bottles of about 250 c.c. capacity, which are provided with well-ground glass stoppers. Dissolve the fat by adding 10 c.c. of chloroform, and after solution has taken place, add 30 c.c. of the iodine monobromide solution (accurately meas- ured), place the bottle in the dark, and allow to stand for about forty minutes. Two blanks should be carried on at the same time and under the same conditions as the above determination. On account of the high coefficient of expansion of acetic acid, the iodine solution should be measured at the same temperature for the blanks as for the determination. If the deep brown color should be discharged on standing, 25 c.c. more of the iodine solu- tion should be added. Add to the bottle 100 c.c. of distilled water, and 20 c.c. of potassium iodide solution (150 grams per liter). Any iodine which may be noticed on the stopper of the bottle should be washed back into the bottle with the potassium iodide solution. Titrate the iodine in the bottle with sodium thiosulphate solu- tion, running it in gradually with constant shaking until the yel- low color of the solution has almost disappeared. Add a few drops of starch solution and continue the titration until the solution is colorless. Towards the end of the reaction the bottle should be stoppered and violently shaken, so that any iodine re- maining in solution in the chloroform may be taken up by the po- tassium iodide solution. The number of cubic centimeters of thiosulphate solution used in the blank minus that used in the de- termination gives the thiosulphate equivalent to the amount of iodine absorbed. From the data calculate the iodine absorption number. Notes. — I. It is customary to calculate the absorption in terms of iodine, although it is obvious that the bromine may take an equally active part in the reaction. 2. The absorption of iodine and bromine is due mainly to their addition to the unsaturated acid. Certain secondary reactions oc- cur, however, in which the halogens are used up. Chief among these is the substitution of the iodine or bromine in the chains of the fatty acids. This determination is, therefore, not an exact quantitative measure of the unsaturated acids. 3. The following table shows the iodine absorption numbers of 1 1 8 Q UANTITA TIVE ANAL YSIS some of the more common fats. The majority of these numbers were determined by Tolman and Munson. Kind of Fat Iodine Number Butter fat 26-38 Oleomargarine . 52-65 Oleo oil 43-3 Olive oil 84.6 Linseed oil 171-178 Household Tests Certain simple household tests for the identification of butter have been found after a little practice to give reliable results and have consequently been introduced into food laboratories. 77^1? Foam Test This is used to distinguish pure butter from process butter and oleomargarine. Procedure. — Place from 3 to 5 grams of the sample into a test tube, or a large spoon, and heat over a low Bunsen flame, stir- ring constantly. If more convenient, the spoon may be held above the chimney of an ordinary kerosene lamp, or over an ordinary gas jet. If the sample is fresh butter, it will boil quietly with the evolution of many small bubbles throughout the mass, which pro- duce a large amount of foam. Oleomargarine and process butter foam either very slightly or not at all, and sputter and crackle like hot grease containing water. Another point of distinction is noted if a small portion of the sample be placed into a small bottle and set into a vessel of water sufficiently warm to melt the butter. The sample is kept melted from half an hour to an hour, and then examined. If renovated butter or oleomargarine, the fat will be turbid ; while if genuine fresh butter, the fat will almost certainly be clear. The Waterhouse or Milk Test This serves to distinguish oleomargarine from fresh and process butter. It is based on the fact that molten butter fat, if added to milk and cooled, will be found diffused with the milk fat, owing to AGRICULTURAL ANALYSIS 119 its similarity to the latter. Oleomargarine, on the contrary, being made from foreign fats, will not diffuse under these conditions, but will remain in a mass. Procedure. — Place about 50 c.c. of well-mixed sweet milk into a beaker, heat nearly to boiling, add 5 or 10 grams of the sample, and stir with a splinter of wood until the fat is melted. Place the beaker into a dish of ice water and begin stirring before the fat starts to solidify, which takes place in ten or fifteen minutes, and continue until the fat becomes solid. If the sample is butter, either fresh or renovated, it will be solidified in a granular condi- tion, and distributed through the milk in small particles. If the sample consists of oleomargarine, it solidifies practically in one piece, and may be Hfted from the milk by means of the stirrer. The nature of the sample under examination may be deter- mined by these two tests. The first distinguishes fresh butter from renovated butter and oleomargarine, while the second dis- tinguishes oleomargarine from either fresh butter or renovated butter. References Leach, A., Food Inspection and Analysis^ Chapter XII, p. 368. Lewkowitsch, J., Chemical Analysis of Oils, Fats, and Waxes. THE ANALYSIS OF CEREALS AND FEEDING MATERIALS These food stuffs may be conveniently classified as follows : 1. Cereals, occurring in the natural state, of which corn, oats, and wheat are types. 2. Cereal products, obtained from cereals by a certain amount of preparation. To this class belong flour, breakfast foods, etc. 3. Feeding materials, including such substances as hay, silage, also oil cake, dried sugar-beet pulp, and other industrial by- products. Composition Vegetable foods, in general, contain high percentages of car- bohydrates and comparatively low percentages of proteids and fats. There are certain exceptions, as in the case of leguminous foods such as peas and beans, which contain high percentages of proteid matter. Moreover, cotton, rape, and certain other seeds contain large amounts of fats and oils. I20 QUANTITATIVE ANALYSIS The following table shows the composition of some of the more common vegetable foods : Water Proteids Fat Sugar Gum and Dextrin Starch Crude Fiber Ash Quaker Rolled Oats . 9.40 I7-5S 7.20 61.56 1 2.40 1.89 Oats Wheat . Corn . . . Peas 12.37 I3-<5S 13.12 12.40 10.41 12.3s 9-85 20.68 5-32 1-75 4.62 1.31 1.91 ^■45 2.46 1.79 2.38 3-38 54.08 64.08 62.57 58.52^ II. 19 2.53 2.49 4.21 3.02 1. 81 I-5I 2.88 Beans . Cotton-seed meal 15-25 8.20 19.63 42.30 1.72 13.10 56-77^ 23.60 1 3-54 5.60 3-29 7.20 Sugar-beet pulp 2 . S8.53 9-45 0.68 62.62 1 22.40 4-85 ^ Nitrogen-free extract, obtained by difference. 2 Dry matter basis Carbohy drates The food values of the carbohydrates present in vegetable foods depend to a great extent upon their solubilities or ease of con- version to soluble forms. The carbohydrates may be classified according to these properties : 1. Those soluble in water, of which the sugars and dextrin are the most important. 2. Those which are not easily soluble in water, but which are made soluble by the action of certain ferments or by hydrolysis with acid. Starch is the most important member of this class. 3. Carbohydrates which resist the action of the usual reagents. They are not hydrolyzed either by acid or alkali, but remain as fiber in the residue after treating the substance with these reagents. Cellulose is a type of this class. 4. Certain insoluble carbohydrates, which on being hydrolyzed with an acid yield sugars. The members of this class are often called " hemicellulose." The greater portion of these insoluble carbohydrates are pentosans. The class is of comparatively small importance. In the analysis of agricultural products the carbohydrates are often determined by difference, being included in what is known as the Nitrogen-free Extract. This is the residue left after the determination of proteids, ether extract, ash, moisture, and crude fiber. Since it contains such substances as gums, resins, etc., it approximates but roughly the total carbohydrates present. AGRICULTURAL ANALYSIS 121 The following table, containing the results of a series of analy- ses by Stone, shows the percentages of the various carbohydrates in certain of the more common cereals and cereal products: Wheat flour . . . Corn . Sugar beet . Bread (wheat) . Corn cake (maize). Sucrose 0.18 0.27 8.38 0.05 0.16 Invert Sugar 0.00 0.00 0.07 0.32 0.19 Dex- trin o.go 0.32 0-35 0.68 0.00 Soluble Starch 0.00 O 00 0.00 1-37 2.80 Normal Starch 46.19 42.50 0.00 2793 40-37 Pento. SANS 0.00 5.14 4.89 4.16 3-54 Crude Fiber 0.25 1.99 1. 00 2.70 2.22 Fats. — The fatty material present in vegetable foods is a complex mixture of glycerides. Olein, stearin, and palmitin are always present to a greater extent than the other glycerides. Proteids. — The proteids of the vegetable foods vary considerably both as to character and to the amount present. For the classifi- cation and general methods of separation of the various proteids, the student is referred to the more comprehensive works on the analysis of foods and to the original literature. Preparation of the Sample Grind the material in a coffee or spice mill until the powder will pass through a sieve with circular holes i mm. in diameter. Dry Matter Procedure. — Weigh two samples of the substance of about 5 grams each into weighed cover-glasses which are provided with covers and spring clips as shown in Fig. 4, page 8. Heat for five hours in the water oven, place the covers on the cover- glasses, and weigh. Heat again for periods of one hour until the weight is constant to 2 mgms. From the loss of weight calcu- late the percentage of dry matter. Save the residue for the determination of the ether-soluble matter. 12: QUANTITATIVE ANALYSIS OUTLINE FOR THE ANALYSIS OF FEEDING >LVTERIALS. Determination of Dry Matter^ Ash, Proteids, Ether Extract, Reducing Sugars, Sucrose (Dextrin + Soluble Starch), Starch, and Crude Fiber. Determine proteids and ash in separate portions of the substance. The moisture, ether extract, and carbohydrates are determined as follows : Weigh out sample, dry at iio°, reweigh. Calculate dry ?natter. Residue A Extract with dry ether. Residue B Extract with boiling alcohol. Ethereal solution («) contains fats, oils, and various other substances. Evaporate the ether and weigh the crtide fell. Alcoholic solution (b) contains sucrose and reducing sugars. Evaporate alcohol, make to known volume with water, remove two aliquot parts (l) and (2). Solution (i) Determine reducing sugars by Allihn's method. Residue C Digest with cold water. Solution (2) Invert by heating with acid. Determine re- ducing sugars by Allihn's method. Subtract reducing sugars found in (i). Calculate sucrose present. Filter. Solution (^) contains dextrin and soluble starch. Hydrolyze by boiling with HCl. Determine dextrose by Allihn's method. Calculate dextrin plus soluble starch. Residue D Boil with water to gelatinize starch. Convert starch to dextrin and maltose by means of malt extract. Filter. Residue E Boil with dilute H2SO4. Solution (rf) contains maltose and dextrin. Hydrolyze by boiling with HCl. Determine dextrose in aliquot part by Allihn's method. Calculate the starch present. Filter. Residue F Boil with dilute NaOH solution. Filter. Solution {e) discard. Residue G Filter on a Gooch. Weigh. Ignite and reweigh. Loss is weight of criide fiber. Solution (/) discard. . AGRICULTURAL ANALYSIS 123 Ether Extract Procedure. — Obtain two large and two small extraction tubes and fasten hardened fat-free iilter paper securely over one end of the large tubes by means of tinned iron wire. Provide the small extraction tube with a double layer of filter paper, using ordinary quantitative filter paper for the inside layer and hardened paper outside. Place the residues from the determination of dry matter into the small extraction tubes, place these inside the large tubes, and introduce into a Soxhlet extractor. Pour 50 c.c. of dry ether into each of two weighed flasks of 125 c.c. capacity, attach the flasks to the extraction apparatus as in the determination of milk fat by the Adams method, and extract for sixteen hours. Remove the ether by distillation and dry the flasks and contents to constant weight in the water oven. Calculate the percentage of ether- soluble matter in the substance. Notes. — I . The term ether extract is used for the constituents of the food which are soluble in ether. Besides fats and oils the ether extract may contain waxes, resins, chlorophyl, coloring matters, and in some cases bodies containing nitrogen and phosphorus. 2. Care should be taken not to extract the material for too long a period, as there is danger of the oxidation of the fats and oils. For the same reasons the flasks should not be allowed to stand in the water oven for an unnecessary length of time. If pos- sible, they should be heated to constant weight in an atmosphere of hydrogen. Separation of Carbohydrates By Stone's Method Procedure. — Use the residue left from the determination of the ether-soluble matter. Connect the Soxhlet extractor with a 250 c.c. Erlenmeyer flask which contains 150 c.c. of 95 per cent alcohol and extract for three or four hours. Evaporate the alcohoHc extract nearly to dryness, add water, transfer to a 100 c.c. gradu- ated flask, and fill to the mark. Use this solution for the determi- nation of reducing sugars and sucrose, filtering if necessary. Note. — Besides the sugars hot alcohol dissolves certain waxes. On evaporation of the alcohol and the addition of water to the extract, these are precipitated. 124 QUANTITATIVE AAAIYSIS Reducing Sugars By Allihns IMcthod Principle. — This determination is based upon the same chemical facts as the determination of lactose ; the concentrations of the solutions and other details are slightly different. Procedure. — Place 30 c.c. of the copper sulphate solution and 30 c.c. of Allihn's alkaline tartrate solution into a casserole, add 60 c.c. of water, and heat to boiling. Add 25 c.c. of the filtered solution containing the sugars, and boil for two minutes. Filter immediately without diluting, and wash with hot water until the filtrate no longer gives an alkaline reaction. Dry the precipitate, ignite, and weigh as cupric oxide. Calculate the amount of copper in the precipitate and consult Allihn's table on page 207 to find the amount of dextrose equivalent to this amount of copper. The percentage of reducing sugars in the sample is expressed as dex- trose. Notes. — I. The filtrate should be examined carefully for cu- prous oxide, as the precipitate has a tendency to run through the filter. 2. In this determination, as in the determination of lactose, the conditions prescribed should be closely observed. The solution analyzed should not contain more than one per cent of reducing sugars. Sucrose By Clerget's Inversion Method Principle. — By heating in the presence of an acid, sucrose is hydrolyzed and forms a mixture of equal amounts of dextrose and levulose. .Sucrose Dextrose Levulose C12H22O11 + H2O = CgHi^Og + CgHj^Oe- The reducing sugars thus formed can be determined by Allihn's method and the amount of sucrose calculated. Procedure. — Place 50 c.c. of the solution containing the reduc- ing sugars and sucrose into a flask marked at 50 and 55 c.c. Fill to the upper mark with pure concentrated hydrochloric acid (sp. gr. 1.20) and mix well. Place in water and heat until a thermora- AGRICULTURAL ANALYSIS 125 eter held with the bulb near the center of the sugar solution reads 68°, consuming about 15 minutes in raising it to this tem- perature. Remove the flask from the bath, cool, and determine by Allihn's method the reducing sugars in 25 c.c. of the solution which have been made neutral by the addition of solid sodium carbonate. Calculate the amount of reducing sugars in the sub- stance. This gives the reducing sugars formed by the inversion of the sucrose, plus the reducing sugars originally present. Sub- tract the amount of reducing sugar in the original sample and calculate the weight and percentage of sucrose present. The reducing sugars should always be calculated as dextrose. Notes. — I. In the above process the hydrochloric acid acts as a catalyzer, accelerating the rate at which the sucrose is inverted. 2. The details of the Clerget method of inversion should be observed closely. If the length of time of heating is too short, the in- version will be incomplete. If the heating is prolonged or the temperature of 68° ex- ceeded, some of the levulose will be de- composed. Dextrin and Soluble Starch Principle. — These substances are hydro- lyzed by heating with an acid, forming dex- trose. The dextrose is estimated in the usual way, and the sum of the dextrin plus soluble starch calculated. Procedure. — Place the residue from the al- coholic extraction into a beaker, add 100 c.c. of water, and allow to stand from eighteen to twenty-four hours with frequent agitations. Filter on a washed linen filter which is placed on a Buchner funnel arranged for filtering with the aid of suction, wash the residue with cold water and evaporate on the steam bath until the volume of the solution is about 60 c.c. Boil the solution gently for two hours with one Fio. 30 tenth its volume of hydrochloric acid (sp. gr. 1.125), using a reflux Hopkins condenser as illustrated in Fig. 30. Cool the solution, neutralize 126 QUANTITATIVE ANALYSIS with solid sodium carbonate, make up to lOO c.c, and determine the dextrose in 25 c.c. by AUihn's method. From the amount of dextrose calculate the percentage of dextrin plus soluble starch in the substance. Note. — Starch which is dissolved by water is called soluble starch. It gives the characteristic blue color with iodine in dis- tinction from some of the other products formed from starch, like dextrin, which does not give the blue color when tested with iodine. If the material which is being analyzed has been sub- jected to heat or friction, as in the grinding of corn or flour, or to the action of acids, then a portion of the starch may have been changed to the soluble form and will be found in the aqueous extract with the dextrin. Starch Diastase Method Principle. — Starch may be completely separated from the other insoluble carbohydrates by the action of diastase, which converts it to maltose and dextrin and has no action on the other insoluble carbohydrates, which can be removed by filtration. By hydrolyzing with an acid the maltose and dextrin are then converted to dextrose. Maltose C12H22O11 + ^26= 2 CgHj20g. Dextrin Ce^ioOg-f H20 = CgHj206. From the amount of dextrose formed the starch present can be calculated. Procedure. — Wash the residue from the alcoholic extraction in the above determination into a 250 c.c. flask with hot water, immerse the flask in boiling water, and stir the contents until the starch gel- atinizes. This usually takes about thirty minutes. Cool to 55° C, add 30 to 40 c.c. of malt extract, measured accurately, and main- tain at 55° until the solution no longer gives the starch reaction when tested with iodine solution. Two or three hours should be sufficient for this purpose. The detection of small quantities of starch is best accomphshed by adding a few drops of iodine to a small quantity of a solution on a glass and examining it by means AGRICULTURAL ANALYSIS 127 of a microscope. The blue color if present can be seen distinctly. Heat the solution to boiling, filter through a linen filter, and wash the residue thoroughly with hot water. Make the filtrate up to 200 c.c, add 20 c.c. of hydrochloric acid (sp. gr. 1.125), connect with a reflux Hopkins condenser, and heat in a boiling water bath for two and one half hours. Nearly neutralize while hot with solid sodium carbonate and make up to 500 c.c. Mix the solution well, pour through a dry filter, discarding the first 10 c.c, and determine the dextrose in 25 c.c. of the filtrate by Allihn's method. Correct for the copper reducing power of the malt extract. Calculate the percentage of starch present. Preparation of Malt Extract. — Pulverize about 20 grams of malt and allow it to stand for several hours with 100 c.c. of water. Shake the solution occasionally. Filter and add to the solution two or three drops of chloroform to prevent the growth of fungi. Deter- mine the amount of soluble carbohydrates in the malt extract by proceeding as follows : take an amount of the solution equal to that used in the determination of starch, dilute to 200 c.c, hydrolyze by heating with hydrochloric acid, and determine the amount of dextrose in 25 c.c. by Allihn's method. In determining starch, make the proper correction for the cuprous oxide reduced by the malt extract. Azotes. — I. When barley is exposed to moist warm air, the grains sprout. The starch present is converted to dextrin and dextrose, and a ferment known as diastase is formed. Diastase has the power of converting starch into dextrin and maltose, the latter being the chief product when the temperature is kept at 50-60°. At higher temperatures there is a larger yield of dextrin. The diastase is soluble in water and consequently may be extracted from the malt and preserved in aqueous solution. 2. As all starches are not affected in the same manner or to the same degree by the action of diastase, it may be necessary in some cases to subject the material to the action of the diastase for a longer time. Saliva Mctliod Principle. — Saliva contains the ferment ptyalin, which possesses the power of bringing starch into solution by converting it first into dextrin and finally into maltose. Eventually dextrose is formed. Procedure. — Collect about 30 c.c. of saliva by chewing a piece 128 QUANTITATIVE ANALYSIS of pure parafifin. Filter and make exactly neutral to litmus paper by adding a 0.2 per cent hydrochloric acid solution drop by drop. Bring the gelatinized starch solution, obtained as in the determina- tion of starch by the diastase method, to 40°. Add about 15 c.c. of the saliva and allow the solution to remain at 40° until a drop of the liquid gives no test for starch with the iodine solution. Filter the solution on a washed linen filter, make up to 200 c.c, hydrolyze with acid, and proceed as in the determination of starch by the diastase method. Notes. — ^_i. The above method for the determination of starch may be advantageously employed when only a few determinations are to be made. Saliva has the advantage over the malt extract in that it contains no soluble carbohydrates and consequently requires no blank determination. 2. The action of normally alkahne saliva is increased by neu- tralization. An excess of acid must be avoided, since as small an amount as 0.003 per cent of hydrochloric acid not only greatly checks the action of the ferment, but also tends to destroy it. The most favorable temperature for the action of the ptyalin is 40". 3. Starch is sometimes determined by heating the residue from the aqueous extraction with dilute hydrochloric acid, and estimat- ing the dextrose formed. By this method the pentosans and cer- tain other carbohydrates are also converted to reducing sugars and consequently are calculated as starch. If the other insoluble carbohydrates are absent, the method gives satisfactory results. Crude Fiber Principle. — Upon boiling the residue from the starch determina- tion with dilute acid, the pentosans and gums are changed to solu- ble reducing sugars and certain nitrogenous bodies are dissolved. Hot dilute sodium hydroxide solution removes other albuminous matter and products of decomposition. The residue is crude fiber. Proccdia'c. — Crude fiber may be determined in the residue from the determination of starch, or in case the carbohydrates were not separated, in the residue from the determination of ether-soluble matter. Wash the residue into a 500 c.c. flask with hot 1.25 per cent sulphuric acid. Add enough of the acid to bring the volume of the solution to 200 c.c, connect the flask with a Hopkins con- denser, boil at once, and continue the boiling for thirty minutes. AGRICULTURAL ANALYSIS 129 Filter through a linen filter and wash with boiling water until the washings are no longer acid. Rinse the substance back into the same flask with 200 c.c. of boiling 1.25 per cent solution of sodium hydroxide, which should be as free as possible from sodium car- bonate. Boil at once and continue the boiling for thirty minutes. Filter on a Gooch filter which has been prepared with a thin layer of asbestos and wash with boiling Water until the washings are neutral. Dry at 110°, weigh, incinerate completely, and reweigh. The loss of weight is crude fiber. Notes. — I. Crude fiber is not in any sense a chemical compound, but is a mixture and includes the substances which make up the framework of vegetable compounds. It consists for the greater part of cellulose, together with Ugnin, pentosans, and a certain amount of proteid matter. 2. Instead of using a Gooch crucible, the crude fiber can be filtered on a tared filter, washed free from alkali, dried at 110°, weighed, ignited, and reweighed. The loss of weight gives the crude fiber plus the filter. A blank should be run with another filter to show the loss caused by treatment with alkali, and the proper correction made. Total Proteids Procedure. — Weigh from i to 2 grams of the substance into a Kjeldahl flask, add 0.65 gram of mercury, 25 c.c. of pure con- centrated sulphuric acid, and digest until the solution is colorless or of a light straw color. Dilute with nitrogen-free water and determine the nitrogen present by distillation as in the determina- tion of proteids in milk. Calculate the percentage of proteids present in the sample. Note. — For some of the more common cereals the factors for the conversion of the nitrogen to proteids are : Wheat, 5.70 Rye, 5.62 Oats, 6.31 Corn, 6.39 Barley, 5.82 The factor 6.25 should be used when other factors are not given. Ash _ Procedure. — Weigh from 2 to 3 grams of the substance into a porcelain crucible, char in the ash muffle, then burn to 130 QUANTITATIVE ANALYSIS whiteness at the lowest possible red heat. If a white ash can- not be obtained in this manner, extract the charred mass with water, collect the insoluble residue on a filter, burn, add this ash to the residue from the evaporation of the aqueous extract, and heat at a low redness until white. Calculate the percentage of ash in the sample. References Leach, Food hispedion and Analysis, Chapter IX, p. 213. Sherman, Jour. Am. Chem. Soc, 19, 291 (1897). Stone, Jour. Am. Chem. Soc, 19, 193 (1897). THE ANALYSIS OF FERTILIZERS Fertilizers are those materials which are added to soils to supply supposed deficiencies in plant foods, or to render more available the stores already present (Wiley). The most important elements present in fertilizers and those most often estimated are nitrogen, potassium, and phosphorus. These elements are used directly as plant food and are conse- quently of great commercial importance. Certain substances, however, may be used as fertilizers which in themselves are of only small value as plant food. Lime, for example, has great value as a fertilizer entirely independent of the fact that growing plants require some calcium as a food. It causes chemical changes in the soil, rendering certain of the constituents available to the plant. For example, feldspar and certain other rocks con- tain potassium in a form which is inaccessible to the plant. The lime acts chemically on these rocks, changing the potassium to a form in which it can be used. Besides the nitrogen, potassium, and phosphorus, then, there are often present in fertilizers certain substances which have an indirect value, and which are of great scientific and often of great commercial interest. The analyst is, therefore, often called upon to estimate organic and volatile mat- ter, Na, Ca, Mg, Fe, Al, Mn, Si, S, CI, Fl. It is of great importance to the analyst to know the origin of the fertilizer, as the methods for the determination of an element differ with the state of chemical combination in which the element is present. For example, in determining the nitrogen in such sub- stances as leather scraps, ammonium sulphate, and sodium nitrate, quite different procedures are followed. .4 GRIt ■ L 'L TL 'R. iL ANAL I .SV.V 131 Fertilizers are obtained either from natural sources or from waste materials. They are used in the raw state and also after being subjected to various forms of treatment to render their con- stituents more available. They are often mixed with other sub- stances in order to furnish a product which contains all three of the essential elements, nitrogen, potassium, and phosphorus. These are known as mixed fertilizers. The natural fertilizers are deposits of plant food which have been brought together during the various geological epochs through which the earth has passed; some of these deposits are the Stassfurt salts, rock phosphates, and Chili saltpeter. The waste materials from factories, slaughter- houses, blast furnaces, etc., have come into general use. Some of the most important of these are blast furnace slag, dried blood, manure, sewage, bones, horns, hoofs, and a great deal of organic refuse. The following table gives the composition of some of the fertilizers which are in general use. The Composition of Typical Fertilizers Nitrogen Phosphorus Citrate- soluble Total Potassium Dried Blood 14.10 Tankage. . 6.70 2.38 5.20 Ammonium Sulphate 20.50 Tobacco Stems 2-35 0.30 6.80 Wood Ashes 0.75 4.20 Kainit . II.OI Raw Bone Meal 4-34 2.S3 9-55 Acidulated Bone .... 2.60 5-94 7.48 Steamed Bone ... 2,64 5.03 12.4S Raw Phosphate Rock 0.72 12.97 Acid Phosphate Rock 6.37 6.58 " Corn and Wheat Grower " 1.70 4.26 5-31 2-35 " Onion, Potato, and Tobacco " - 1-57 4-33 5-37 6.89 Sampling Obtain a representative sample from the total amount of ferti- lizer, mix it thoroughly, grind finely if necessary, and pass the sample for analysis through a sieve having circular openings i mm. in diameter. Mix thoroughly and transfer about 30 grams of the sample to a weighing tube. For special methods for sam- pling manures, etc., see Wiley's Agricultural Analysis, Vol. 11. 132 QUANTITATIVE ANALYSIS Dry Matter Procedure. — For potassium salts, sodium nitrate, or ammonium sulphate, weigh out 2-3 grams upon a cover-glass and heat in the air bath at 130° for one hour. Remove from the bath, cool, and weigh. Heat again for thirty minutes. Cool and weigh. Re- peat until a constant weight is obtained. For all other ferti- lizers heat the sample for five hours at 100° in the water oven. For this determination it is best to use cover-glasses with ground edges and provided with a clip. From the weight of the residue calculate the percentage of dry matter. Note.^-\n the analysis of many fertilizers the determination of hygroscopic water is a matter of extreme difficulty, owing to the decomposition of the fertilizer by heat. Hence, the loss in weight on heating may be due not only to hygroscopic water, but also to chemically combined water, organic matter, ammonia, etc. PHOSPHORUS Phosphorus is found in fertilizers in a state of organic combina- tion, as in tankage, oil cake, and other organic materials ; and in phosphoric acid, either in the free state or combined with certain bases, as in superphosphates and steamed bone. In general, the methods for the determination of phosphorus are the same in both cases ; the methods of destroying the organic matter, however, may differ considerably. Phosphoric acid is present in fertilizers in several different states of combination, which will be more easily understood if the method of manufacturing these fertilizers is considered briefly. Finely ground rock phosphate, Q,2ir^(^0^^, is treated with sulphu- ric acid in lead tanks, the object usually being to produce the soluble monocalcium phosphate. The nature of the product obtained, however, varies with certain factors, such as the purity of the rock phosphate, the quantity of sulphuric acid used, and the tempera- ture at which the reaction takes place. The changes may be represented by the following equations : (dicalcium phosphate) CagCPOi)^ H- H^SOi = CaaHaCPO^)^ + CaSO^. AGRICULTURAL ANALYSIS 133 (monocalcium phosphate) Ca3(P04)2 + 2 H2S04= CaH^(P04)2 + 2 CaSO^. (ortho-phosphoric acid) CagCPO,)^ + 3 H2SO, = 2 H8PO4 + 3 CaSO^. Monocalcium phosphate on standing in contact with tricalcium phosphate undergoes a change, or reversion, which may be shown by the following equation : CaH,(P0,)2 + CagCPO^)^ = 2 Ca^H^CPO,)^. The dicalcium phosphate formed in this way is known as " reverted phosphate." The phosphates in fertilizers may be classified according to their solubilities : Soluble in cold water. Readily available for plants. Free phosphoric acid. Monocalcium phosphate. Monomagnesium phosphate. 2. < Soluble in weak acids and in solutions of certain salts (ammonium citrate) called the citrate-soluble. Readily available for plants. Dicalcium phosphate. Soluble in strong acidsl Tricalcium phosphate, ^ only. lalso phosphates of aluminium and Slowly available for plants.] iron. Total Phosphorus Principle. — The organic matter present is oxidized by means of aqua regia, the phosphorus remaining in solution as phosphoric acid. This is separated from the bases present by precipitating with ammonium molybdate solution, as the ammonium phospho- molybdate. The ammonium phosphomolybdate is dissolved in ammonium hydroxide and the phosphorus precipitated as magne- sium ammonium phosphate. 134 QUANTITATIVE ANALYSIS Procedure. — Weigh 2-3 grams of the sample into a No. 4 beaker and add to it 25 c.c. of strong hydrochloric acid (sp.gr. 1.20) and 10 c.c. of strong nitric acid (sp. gr. 1.40). Cover the beaker with a glass and heat gently until all the organic matter is destroyed. Repeat the treatment with aqua regia if necessary. Cool the solution, dilute it to exactly 250 c.c, mix thoroughly, and filter through a dry filter, discarding the first 10 c.c. of the filtrate. Remove exactly 50 c.c. of the filtrate with a pipette, neutralize carefully with ammonium hydroxide, and add a few drops of nitric acid to dissolve any precipitate which may have been formed. Dissolve 15 grams of pure ammonium nitrate in 25 c.c. of warm water, and add it to the solution. To the warm solution add 75 c.c. of the ammonium molybdate solution and digest at about 65° for an hour. Filter and wash the precipitate with a solution of ammonium nitrate (100 grams per liter) until 5 c.c. of the wash water give no test for chlorides. The yellow precipitate need not be completely removed from the beaker. Test the filtrate for complete precipitation by the addition of 10 c.c. of the molybdate solution and renewed digestion. A white precipitate may be disregarded. Molybdic acid is an expensive reagent ; consequently all resi- dues from this determination should be placed in a bottle provided for them. Dissolve the yellow precipitate by pouring a solution containing equal parts of ammonium hydroxide and hot water through the filter, receiving the solution in the beaker in which the first precip- itation took place. Wash the filter several times with hot water and ammonium hydroxide. Do not allow the total volume of the filtrate to amount to more than 100 c.c. Nearly neutralize the solution with dilute hydrochloric acid, then cool and add mag- nesia mixture (10 c.c.) from a burette, letting it run in at the rate of one drop per second, and stirring the solution vigorously at the same time. After fifteen minutes add 30 c.c. of ammonium hydroxide (sp. gr. 0.96) and fillow to stand for several hours. Filter and treat the precipitate as in the determination of mag- nesium. Exercise VII. From the weight of the magnesium pyro- phosphate calculate the weight of phosphoric anhydride and the percentage of the latter in the sample taken. Calculate the per- centage of phosphorus. AGRICULTURAL ANALYSIS '55 A\Hcs. — I. Organic matter in a fertilizer may also be destroyed and the phosphorus brought into solution by any of the follow- ing methods : a. Ignition and solution of residue in hydrochloric acid. b. Digestion with concentrated sulphuric acid and potassium nitrate. c. Evaporation with concentrated magnesium nitrate solution, ignition, and solution of the residue in hydrochloric acid. 2. The residue left from the treatment with aqua regia generally consists of insoluble mineral matter such as siHca and silicates, these substances being originally present in the mineral phosphate. 3. Under certain conditions phosphorus may be precipitated from an acid solution as ammonium phosphomolybdate, separating it from any bases which may be present in the solution. Arsenic and silica, however, if present, must be removed, as they precipi- tate from the solution with phosphorus. The composition of ammonium phosphomolybdate is not con- stant, but varies with the conditions under which it is precipitated. When precipitated under the above conditions and dried at 130^, the precipitate has the composition (NH4)3P04-i2 MoOg.'- It is usually not practicable to weigh the phosphorus in this form, although this is done by some analysts. It is more satisfactory to redissolve the precipitate in ammonium hydroxide, precipitate the phosphorus as magnesium ammonium phosphate, and weigh it a? magnesium pyrophosphate. 4. The following conditions should be observed in order to obtain the complete precipitation of phosphorus as ammonium phosphomolybdate : Organic matter must not be present. The phosphorus must be present as ortho-phosphoric acid. The precipitate is less soluble in solutions of ammonium nitrate and ammonium molybdate than in water. These salts should, therefore, be present in excess. The presence of ammonium nitrate, moreover, makes the precipitation take place more readily. The solution should be acid with nitric acid, but with only a slight excess, as the precipitate is appreciably soluble in concen- trated acids. It is most soluble in hydrochloric acid, less soluble in sulphuric acid, while nitric acid exercises the least solvent action. The precipitate forms much more readily at 65° than at the 136 QUANTITATIVE ANALYSIS ordinary temperature. A higher temperature is attended by the precipitation of molybdic anhydride ( M0O3). The precipitation is also hastened by agitating the solution. 5. The yellow precipitate is dissolved in ammonium hydroxide with the formation of ammonium phosphate and ammonium molyb- date. 6. Under certain conditions the precipitate may be dissolved in standard alkali according to the equation (NH4)3P04-i2 M0O3 + 23 NaOH = II Na^MoO^ + CNHJaMoO^ + NaNH^HPO^ + ii HgO and the excess of alkali titrated with standard nitric acid. This method is used extensively when a large number of determinations must be made. 7. The addition of a large excess of the magnesia mixture should be avoided, as it tends to throw down magnesium hydroxide and may also cause molybdic anhydride to separate with the precipitate. Molybdic anhydride may also separate if the solution is too con- centrated. Water-soluble Phosphorus Procedure. — Place about two grams of the fertilizer upon a 9 cm. filter, add a little water from a wash bottle, let it run through the filter, add more water, and repeat this treatment until the filtrate measures about 225 c.c. Be sure to allow each portion of water to pass through the filter before more is added. Save the washed residues for the determination of the citrate-insoluble phosphorus. If the filtrate is turbid, add a little hydrochloric acid. Make the filtrate up to 250 c.c. and mix thoroughly. Now measure out 50 c.c, add 75 c.c. of ammonium molybdate solution, and proceed as in the determination of total phosphorus. Save the remainder of this filtrate for the determination of soluble nitrogen. Citrate-insoluble Phosphorus Procedure. — Heat 100 c.c. of strictly neutral ammonium citrate solution (sp. gr. 1.09) to 65° C. in a 200 c.c. Erlenmeyer flask placed in a bath of warm water, keeping the flask loosely stop- pered to prevent evaporation. When the citrate solution in the flask has reached 65", drop into it the filter containing the AGRICULTURAL ANALYSIS 137 washed residue from the water-soluble phosphorus determination, stopper tightly with a smooth rubber stopper, and shake violently until the filter paper is reduced to a pulp. Place the flask back into the bath and maintain the water in the bath at such a temper- ature that the contents of the flask will stand exactly at 65°. Shake the flask every five minutes. At the end of exactly thirty minutes from the time the filter and residue were introduced, re- move the flask from the bath and filter as quickly as possible upon a 1 5 cm. filter. Use a filter pump and support the filter with a cone of hardened paper. Wash thoroughly with water at 65° until a few cubic centimeters of the filtrate give no test for phos- phorus with ammonium molybdate solution. It is essential that the digestion with ammonium citrate takes place precisely as di- rected and also, that at the end of the half hour's digestion the liquid be filtered immediately. Transfer the filter and contents to a small porcelain dish, ignite in the ash muffle until all organic matter is destroyed, add 25 c.c. of concentrated hydrochloric acid and 10 c.c. of concentrated nitric acid, and digest until all the phosphate is dissolved. Dilute the solution to 250 c.c, mix thoroughly, and filter through a dry filter. Take 50 c.c, add about 15 grams of dry ammonium nitrate and 75 c.c. of the ammonium molybdate solution, and proceed as in the determination of total phosphorus. Notes. — I. The above procedure is to be followed in the analy- sis of acidulated samples. For non-acidulated samples treat 2 grams of the phosphate material, without previous washing with water, precisely in the way above described, except that in case the substance contains much animal matter (bone, fish, etc.) the residue insoluble in ammonium citrate should be digested in a Kjeldahl flask with concentrated sulphuric acid and potassium nitrate until the organic matter is destroyed. 2. The determination of this form of phosphorus is essentially conventional, and the results obtained are of relative value only. Citrate-soluble Phosphorus The sum of the water-soluble and citrate-insoluble phosphorus subtracted from the total gives the citrate-soluble. Express the results as percentage of phosphoric anhydride and also as per- centage of phosphorus in the sample. 138 QUANTITATIVE ANALYSIS NITROGEN Nitrogen may be present in fertilizers in any or all of the follow- ing forms: (i) in animal or vegetable substances, in which it is present in a state of organic combination — dried blood, cotton-seed meal, etc.; (2) as ammonia or its combinations — ammonium sulphate; (3) in a more highly oxidized state as salts of nitrous or nitric acid — Chili saltpeter. Total Nitrogen in the Absence of Nitrates In case no nitrates or nitrites are present, the ordinary Kjeldahl method as described' under the analysis of milk may be employed, using from one to two grams of the sample for analysis. Many mixed commercial fertilizers, however, contain nitrates, so that the process must be modified to meet this condition. Total Nitrogen when Nitrates are Present Principle. — The method depends on the reduction of the nitrates to ammonia, the digestion with sulphuric acid to oxidize any or- ganic matter, and the distillation of the ammonia in the usual way. Procedure. — Introduce from i to 2 grams of the sample into a clean Kjeldahl flask, being careful that none of the substance re- mains on the neck. Add 30 c.c. of concentrated sulphuric acid containing 2 grams of salicylic acid, then add gradually 2 grams of zinc dust, shaking the contents of the flask at the same time. Place the flask on the digestion stand and heat over a low flame until all danger from frothing has passed. Increase the heat until the acid boils briskly and continue the boiling until white fumes cease to come off, which should take from five to ten minutes. Add 0.65 gram metallic mercury and continue the boil- ing until the liquid in the flask is colorless or nearly so. In case the contents of the flask are solid before the digestion is complete, add 10 c.c. of sulphuric acid. Complete the oxidation with a Httle potassium permanganate in the usual way and proceed with the determination as described in the directions for the analysis of milk. In case more than 25 c.c. of the sulphuric acid were used in the digestion, the amount of sodium hydroxide used in neutrali- zation should be increased proportionally. Calculate the percent- age of nitrogen in the fertilizer. AGRICULTURAL ANALYSIS 139 Notes. — I. The salicylic acid which is added in this determina- tion facilitates the reduction of the nitrate by forming with it a nitrophenol, a compound in which the nitro group is easily reduced. The change may be represented by the equation : (salicylic aciil) 2 CgH^^^^Qj^ + 2 NaNOg + H2SO, nitrophenol = 2C6H4^Q +Na2SO^+2C02 + 2H20. The nitrophenol thus formed is then reduced by hydrogen formed by the action of sulphuric acid on zinc dust. amidophenol C6H4j^Q +3 H.j = CsH^j^j^ +2H2O The amidophenol is oxidized by digestion with sulphuric acid, the nitrogen being left in the solution in the form of ammonium sulphate. 2 CgH^^JJ 4-27 H2SO4 = (NHJaSO^ + 12 CO2 + 30 H2O + 26 SO^. The above reactions are stated to make more apparent the func- tions of the various reagents in the change of the nitrate to ammonium sulphate. They do not represent all the chemical changes which take place during this process, as there occur many other reactions of a complex nature. 2. Foaming during the distillation of the ammonia may be pre- vented by the addition of a small piece of paraffin to the contents of the Kjeldahl flask. 3. A blank determination should be carried out with the reagents used in this analysis, and the proper corrections made. Nitrogen Soluble in Water Procedure. — Measure 50 c.c. from the water solution prepared for the determination of soluble phosphorus and determine the nitrogen present by the modified Kjeldahl method used for the determination of nitrogen in the presence of nitrates. I40 QUANTITATIVE ANAIYSIS Nitrogen as Ammonium Salts Procedure. — Weigh 1.5 to 3 grams of the substance to be ana- lyzed into a 500 c.c. Kjeldahl flask, add 300 c.c. of nitrogen-free water, and about 5 grams magnesium oxide free from carbonate. Distil 150-200 c.c. of the liquid into a flask containing a measured volume of standard acid. Titrate the excess of acid with standard alkali and calculate the percentage of ammonia and nitrogen present. Note. — In the absence of organic nitrogen caustic soda may be used instead of magnesium oxide. The use of caustic soda in the presence of organic nitrogen is prohibited by the fact that it de- composes the organic matter with the formation of ammonia. POTASSIUM Potassium may be found in fertiHzers in organic combination, as in tobacco waste and cotton-seed hulls, and in inorganic salts, as carbonate in the ash obtained from burning plants of all kinds, or as chloride or sulphate in certain mineral deposits, such as the Stassfurt salts. The preliminary treatments of the various substances containing potassium differ considerably ; however, the final method of precipitating and weighing the potassium is the same in all cases. For the determination of potassium it is essen- tial that all organic matter be destroyed, and that the potassium be brought into a soluble form. Potassium in Mixed Fertilizers Principle. — This determination is based upon the fact that po- tassium chlorplatinate is insoluble in strong alcohol, whereas cer- tain other elements which might be present, such as sodium, form easily soluble salts. Before precipitating the potassium it is necessary to remove calcium, aluminium, etc., by precipitation with ammonium hydroxide and ammonium oxalate. All platinum residues and washings from this determination should be saved. Procedure. — Weigh a sample of 10 grams of the material and boil in a casserole with 300 c.c. of water for thirty minutes. Without filtering, add ammonium hydroxide in slight excess to the hot solution, then add slowly a sufficient quantity of ammonium AGRICULTURAL ANALYSIS 141 oxalate solution to precipitate all the calcium present. Cool the solution, make up to 500 c.c, mix thoroughly, and filter through a dry filter, discarding the first 10 c.c. of the filtrate. Place 50 c.c. of the filtrate into a porcelain dish, evaporate nearly to dryness, add I c.c. of sulphuric acid (sp. gr. 1.4), and evaporate to dry- ness, taking care that the solution does not spatter. Ignite the residue until it is white. As the potassium is all in the form of the sulphate, no loss from volatilization need be apprehended. Dissolve the residue in about 20 c.c. of hot water. If the solution is perfectly clear, add a drop or two of hydrochloric acid and a slight excess of platinic chloride solution (2-5 c.c). If the solution is not clear, filter through a small filter, then add a few drops of hydrochloric acid, and then the platinic chloride solution. Evapo- rate the solution in a small dish to a thick paste and add 40 c.c. of 80 per cent alcohol. Cover the dish with a glass and allow to stand for an hour or two in a place which is free from the fumes of ammonia. At the end of that time examine the supernatant liquid. If it has not a deep yellow color, it is proof that an in- sufficient amount of platinic chloride has been added. When the precipitate has settled, pour off the clear liquid through a prepared and weighed Gooch crucible, and wash the precipitate by decanta- tion with 80 per cent alcohol. Bring all of the precipitate upon the filter and wash with alcohol until the filtrate is colorless. Then wash three times more. Now run through the filter 10 c.c. of the concentrated ammonium chloride solution which has been saturated with potassium chlorplatinate. Repeat this treatment with the ammonium chloride solution five times. Wash the precipitate thoroughly with 80 per cent alcohol, heat for forty minutes at 135° in the air bath, cool, and weigh. Heat and weigh again. When the weight is constant, calculate the weight of potassium oxide from the weight of potassium chlorplatinate. Calculate the per- centages of potassium and potassium oxide present in the fertilizer. Notes. — I. When it is desired to determine the total amount of potassium in organic substances, such as cotton-seed meal, tobacco stems, etc., saturate 10 grams of the sample with strong sulphuric acid, evaporate to dryness, and heat at a low red heat until the organic matter is destroyed. Add a little strong hydrochloric acid, warm slightly in order to loosen the mass from the dish, and pro- ceed as above. 142 QUANTITATIVE AAALYSIS 2. The ammonium hydroxide and ammonium oxalate com- pletely precipitate all of the bases present with the exception of magnesium. Owing to the difficulty of complete volatilization, a large excess of ammonium oxalate should be avoided. 3. Precipitates of aluminium and iron hydroxide have a marked tendency to occlude potassium salts. This may be avoided by adding the precipitating reagent slowly and with stirring. 4. Ammonia forms insoluble ammonium chlorplatinate in the presence of platinic chloride. It is therefore necessary to protect the solution from the fumes of ammonia. For the same reason the platinic chloride should be completely washed out of the pre- cipitate of potassium chlorplatinate before the washing with ammonium chloride solution begins. 5. If the potassium is precipitated from too concentrated a solu- tion, the precipitate will contain water which will be removed with great difficulty. The precipitation should take place in a fairly dilute solution. 6. Potassium chlorplatinate is somewhat soluble in ammonium chloride solutions. Consequently this solution must be saturated with potassium chlorplatinate before using. The ammonium chlo- ride solution removes any magnesium salts which may be present with the precipitate. References Snyder, Soils and Fertilizers (1905). Wiley, Principles and Practice of Agricultural Analysis, Vol. II, Fertilizers. THE ANALYSIS OF SOIL Soil may be defined as that portion of the earth's surface which permits, under proper climatic conditions, the growth and nourish- ing of plants. The soil proper, or top soil, may extend from two or three inches to as many feet below the surface of the ground, the portion below this being known as the subsoil. The subsoil differs from the soil in physical properties, also in its chemical composition. It may consist of rock matter, layers of sand, clay, etc. Constituents of the Soil Soil is a heterogeneous mixture composed of disintegrated rock, organic matter of animal and vegetable origin, water, occluded AGRICULTURAL ANALYSIS 143 gases, and certain living organisms which exert a considerable in- fluence upon vegetable growth. Of the total number of elements there are only about twenty found in soils to any appreciable extent. These are the elements found in the common forms of mineral matter, and those which are present in organic substances. From the standpoint of their values as plant foods, the elements in soils may be arranged in the following classes : ^ I. Essential elctncnts most liable to be deficient. Nitrogen, potassium, phosphorus. These may be present in the following forms : Nitrogen : organic nitrogen, ammonium salts, nitrates. Potassium : silicates, such as orthoclase, mica, and granite. Phosphorus : phosphates and in combination with organic matter. II. Essential elements nsually abundant. Iron, magnesium, calcium, and sulphur. Iron : silicates and oxides. Magnesium : carbonate and silicates. Calcium : carbonate, silicate, phosphates, and sulphate. Sulphur: principally as sulphates. III. Unnecessary and accidental eleinents usually abundant. Aluminium, iron, silicon, etc. Organic Constituents Besides the soil constituents which are present as the result of the disintegration of mineral matter, a certain amount of organic matter is always present and, as in the case of peaty soils, may even be the predominating constituent. This organic matter is a mix- ture of substances of animal and vegetable origin and exists in various stages of decomposition. The decaying organic matter plays an important part in crop production. The active principle of the organic matter is called humus. In genera] this may be considered as the intermediate decomposition products of the organic material. Since the organic constituents present in soils may differ greatly both as to origin and chemical composition, it is obvious that the term humus is indefinite. Among the organic decomposition products are certain substances having acid properties which combine with basic materials in the soil and form organic salts which are known as humates. Some of 1 This classification is essentially that proposed by Snyder. 144 QUANTITATIVE ANALYSIS the important humates are those of potassium and calcium, which are known as potassium and calcium humates respectively. The following table, which contains the results of the analyses of several typical soils, illustrates the marked differences in their chemical composition : Ultimate Analysis of Type Soils of Illinois (Composite Samples) Dry Basis. Surface Soil, Top Seven Inches Early Early Early Peaty Wisconsin Wisconsin Wisconsin Sandy Soil Swampy Glaciation ; Glaciation ; Glaciation; Soil Yellow Silt Bkown Silt Black Clay Loam Loam Loam (Timbkk) (Prairie) (Prairie) Nitrogen .052 3-58 .099 .266 •399 Phosphorus . . . .038 .191 .040 .059 .096 Potassium .... 1.24 .289 1.58 1.78 1.65 Calcium . . .509 .299 .622 .556 1.27 Magnesium . .185 .628 •390 .470 .716 Organic carbon . .642 41.21 1. 10 3.20 4-44 Inorganic carbon .012 .005 .026 Iron . . ... ■835 1.07 1.78 2.57 2.42 Aluminium 2.26 1.06 4.78 5.98 6.29 Sodium . . . . 1.64 1-39 .856 •549 .678 Silicon 42.29 4.48 37-77 34-13 31-77 Oxygen, Hydrogen, Sulphur, Manganese, By differ ence Titanium, etc. . . J The complete examination of a soil includes its study from chemical, physical, and biological standpoints. The chemical ex- amination will be discussed in the following pages, as it alone falls within the scope of this book. The Collection and Preparation of the Sample Remove all surface accumulation of decaying leaves and other foreign matter and then remove a layer of the soil of uniform thickness from the surface to the desired depth. In order to eliminate the effects of accidental variations in the soil, select specimens from five to six places in the field and remove from each place several pounds of the soil, to the depth of six inches, or AGRICULTURAL ANALYSIS 145 Outline for the Analysis of a Sample of Soil Volatile matter 1 Carbon dioxide I Determined in Humus f separate samples. Nitrogen j Determination of Acid-soluble Substances Digest 10 grms. of soil with HCI at 100° for 10 hours. Filter. Solution (to be analyzed for FcjOa, AI0O3, MnO, CaO, MgO, NajO, K2O, SiOa, l'2'Oc, SO3). Add HNO3, Evaporate to dryness, dehydrate silica at 100°. Dissolve bases in HCI. Filter. Solution. Evaporate to dryness and dehydrate. Dissolve and filter. Solution. Make up to a volume of 500 c.c. Label " Solution A." Residue (il. Silicates, organic matter, etc. Residue (2). SiO^ (traces of AI2O3+FC3O3). Residue (3). S1O2, with traces of FejOa and AlgOg. Unite residues i^ 2, and 3, ignite to constant weight, and calculate percentage of insoluble matter + soluble silica. Analysis of Solution A 1 2 Determination of CAI2O3+ FeaOa+PaOo) Determination of SO3, FeaOg, MnO, CaO, and MgO Use 100 c.c. of solution A. Make alkaline with NH4OH. Filter. I Filtrate. NajO and KjO. Concentrate 100 c.c. of solution A, add BaClj. Filter. Boil with Br water. Acidify with acetic acid. Filter. Ppt. Ignite and weigh AljOa+FejOa+PjOs. Filter. Determine AljOs by difference after determining FejOs and PjOj. Filtrate. Add NHjOH. Filtrate. Add NH4OH and (NH,)jC20,. Dissolve ppt. in Ppt. MnOj. Ignite and weigh MnaO,. HCI and re-ppt. with NH40H. Filter. I Filtrate. Ppt. CacA. Ppt. MgNHjPO, in Ignite. Change the usual manner, to CaSO^ and Ignite and weigh weigh. MgjPjO,. Filtrate. Evaporate to dryness to expel ammonium salts. Add Ba(OH)j. Filter. Filtrate. AddNH40H + (NH,)jC03. Filter. 1 Ppt. BaSO^. Ignite and weigh. Determination of PjOg. Concentrate aoo c c, of Solution A, Ppt. the P as (NH4)sP04 . 12 MoO,. Dissolve and ppt. as MgNH4p04. Weigh P as MgjPjO,. Ppt. ofFe(OH)3, Al(0H)3, etc. Dissolve in HCI. Determine Fe by titration with KaCrjO,. Ppt. ofMgCOH),. Disca rd. Filtrate. Evaporate to dryness, expel ammon urn salts and weigh NaCl+ KCl. Dissolve mixed chlorides in water. Add PtCl^ solution and alcohol. Filter on a Gooch crucible. Ppt. ofBaCOg. Discard, Filtrate. Piscard, Ppt. KaPtClfl. Weigh and calculate NaCT by difference. 146 QUANTITATIVE ANALYSIS to the change between the surface soil and the subsoil, in case such change occurs between the depth of six and twelve inches. In no case should the sample be taken to a greater depth than twelve inches. If the surface soil extends to a greater depth, a separate sample below the depth of twelve inches should be taken if a thorough study of the soil is desired. If the surface soil ex- tends to a depth of less than six inches, and the difference between it and the subsoil is unusually great, a separate sample of the sur- face soil should be obtained besides the one to the depth of six inches. Mix all the samples of the surface soils thoroughly, remove all stones, shake out roots and foreign matter, and expose the soil in thin layers in a warm room until thoroughly air dry, or dry it in an air bath at 40°. The soil should be dried rapidly, but it should not be heated above 40°, because of the danger of breaking up the ammonium compounds or making some of the compounds present more insoluble. After drying, all lumps should be finely pulver- ized, the soil thoroughly mixed, spread out upon a clean paper and 200 grams taken from different parts of the sample and sifted through a sieve with circular openings \ mm. in diameter. If necessary, rub the soil gently in a mortar with a pestle until the fine earth has been separated as completely as possible from the particles that are too coarse to pass the sieve. Mix the fine soil which passes through the sieve, place in a tightly stoppered bot- tle, and use for the analysis. The coarse part should be weighed and bottled. Note. — As a result of bacterial action certain constituents of the soil are constantly undergoing changes. The organic nitrogen, for example, is continually being oxidized to the more available forms, nitrates and nitrites. This change is termed nitrification. Because of these changes it is necessary to avoid prolonged dry- ing. Moisture Procedure. — Place from two to four grams of the air-dried soil into a weighed porcelain dish and heat for five hours at 100°. Cool in a desiccator and weigh rapidly to avoid absorption of mois- ture from the air. Repeat the heating, cooling, and weighing at intervals of two hours until constant weight is found, and estimate the moisture by loss of weight. AGRICULTURAL ANALYSIS 14; Volatile Matter Procedure. — Heat the dish and dry soil from the above determi- nation to full redness, until all organic matter is burned. If the soil contains any carbonates, the contents of the dish, after cooling, should be moistened with a few drops of a saturated solution of ammonium carbonate, dried and heated to dull redness to expel ammonium salts, cooled in the desiccator, and weighed. Notes. — I. The addition of ammonium carbonate changes any calcium oxide formed during the ignition back into the carbonate. 2. The loss in weight in the above determination is due to the following causes : (rt) The ignition of the organic matter. {U) Volatilization of ammonium salts and of water of combina- tion. {c) The decomposition of magnesium carbonate with the forma- tion of magnesium oxide, which is not readily changed back to the carbonate, also the fact that the calcium originally present as the humate is changed to the carbonate. 3. A certain increase in weight is caused by the oxidation of any ferrous iron. This tends to counterbalance some of the above-mentioned losses. 4. Because of the variety of factors to which the loss on ignition is due, it is evident that this determination gives but an approxi- mate idea of the amount of organic matter present. The determina- tion of the total organic carbon has recently been used for the estimation of the organic matter in soils. The method is described by Pettit and Schaub, Jour. Am. Chem. Soc., 26, 1640 (1904). The Extraction of the Acid-soluble Material It is well known that the materials present in soils are not all available as plant food. Potassium, for example, may exist as the easily available carbonate, or it may be present as a feldspar which is of little immediate value in aiding the growth of plants. It is, therefore, the usual practice, when analyzing a soil, to deter- mine the amount of available plant food rather than its total quan- tity, although this latter determination is often of value. Numerous solvents have been suggested for the extraction of the plant food from the soil, but none of them imitates the extraction under 148 QUANTITATIVE ANALYSIS natural conditions. The following method, recommended by the Association of Official Agricultural Chemists, in which hydrochloric acid is used as a solvent, is of value in showing approximately the limit of the solvent action of the roots of plants. Procedure. — Place ten grams of the air-dried soil into an Erlen- meyer flask of about 200 c.c. capacity, add 100 c.c. of pure hydrochloric acid of specific gravity i.iiS, insert a rubber stopper carrying a hard-glass condensing tube about \ inch internal diameter and about 30 inches long. If sulphuric acid is to be determined in the solution, a flask with a ground-glass stopper carrying a con- densing tube must be used. Place the flask in a water bath, being sure that it is immersed in the water at least to the level of the acid and that the water is kept boiling during the digestion. Di- gest continuously for ten hours at the temperature of boiling water, shaking once each hour. Decant the clear liquid from the flask into a medium-sized casserole and wash the residue out of the flask with distilled water upon a filter, adding the washings to the acid liquid in the casserole. Thoroughly wash the residue free from acid and then dry it and save it for ignition as directed below. Notes. — I. The amount of material dissolved by the acid varies with the length of time of heating, the temperature and the strength of the acid employed, and the fineness of the material. Conse- quently, the directions given above should be closely followed. 2. By the action of the hydrochloric acid solution on the soil, the following constituents are dissolved : ferrous and ferric oxides, ferrous carbonate, manganese oxides, calcium and magne- sium carbonates, calcium sulphate and phosphates, and certain silicates, such as those of aluminium, calcium, and potassium. Certain forms of organic matter are also dissolved. 3. The residue is composed for the greater part of crystallized and amorphous silica and silicates of Fe, Mn, Al, Ca, Mg, K, Na. Certain forms of organic matter are also present in the residue. Removal of Soluble Silica from Solution Principle. — On evaporating a solution of silicic acid to dryness and heating at 100° it is dehydrated and rendered insoluble in dilute acids. AGRICULTURAL ANALYSIS 149 Procedure. — Add about 5 c.c. of concentrated nitric acid to the filtrate from the insoluble matter in order to oxidize the organic matter present and evaporate to dryness on the steam bath until no more fumes of hydrochloric acid are given off, the residue being left in the form of a dry, dark-brown powder. Add 5 c.c. of con- centrated hydrochloric acid to the casserole, allow to stand for a few minutes to insure the solution of the basic salts, and add 100 c.c. of distilled water. Heat to boiling, filter through an ashless filter, wash with hot water containing a little hydrochloric acid, and wash finally with hot water alone until the residue is free from chlorides. Evaporate the filtrate to dryness and treat exactly as before, using, however, a new filter for the filtration. Cool the filtrate, make up to 500 c.c, and label the solution "A." Notes. — I. For the complete removal of silica from solution, the following conditions should be closely observed: a. Two dehydrations of the silica should be made, since it has been found that only 95 per cent of the silica present is removed by one dehydration. An intermediate filtration between the two dehydrations has been found pecessary. b. The silica may be completely dehydrated on the water bath, although many chemists prefer to heat finally at 110° or 120°. Heating above 120° renders insoluble appreciable amounts of alumina and ferric oxide which cannot be dissolved by long diges- tion with hydrochloric acid. Moreover, at higher temperatures magnesia recombines with silica with the formation of magnesium silicate, which is decomposed by hydrochloric acid with the for- mation of soluble silicic acid. 2. The precipitate should be first washed with hot water acidi- fied with a few cubic centimeters of hydrochloric acid. This will prevent the separation of insoluble iron salts, which would take place if hot water alone were used. Insoluble Matter and Soluble Silica Procedure. — Add the silica residues from solution " A " to the main insoluble residue, ignite in the blast the combined residues together with the filters in a large weighed porcelain crucible and weigh. Heat to constant weight. From the weight of this resi- due calculate the percentage of insoluble matter plus the soluble silica. ISO QUANTITATIVE ANALYSIS The Determination of the Acid-soluble Substances Iron, Aluminium, and Phosphorus Collectively Procedure. — To lOO c.c. of solution "A" add ammonium hy- droxide until the solution is slightly alkaline, observing the pre- cautions given under the determination of aluminium, page 37. Drive off the excess of ammonia by boiling, allow the precipitate to settle, and decant the clear solution through a filter. Add 50 c.c. of hot distilled water, boil, allow to settle, and decant as before. After pouring off all the clear solution possible, dissolve the resi- due with a few drops of nitric acid, and precipitate again with ammonium hydroxide as before. Wash by decantation, transfer all the precipitate to the filter, and wash with hot distilled water containing a Httle ammonium nitrate, until the washings are free from chlorides. Dry the filter and precipitate, separate the pre- cipitate from the filter, burn the filter and add to the ash the precipitate, ignite the crucible to bright redness, cool in a desicca- tor, and weigh. The weight of the ignited precipitate minus the weight of the iron oxide and phosphorus pentoxide (found in separate determinations) represents the weight of the aluminium oxide. Notes. — I. The separation of iron and aluminium from the divalent metals is not complete by one precipitation, a small amount of magnesium invariably precipitating at the same time. It is necessary, therefore, to make a second precipitation. 2. The ammonium hydroxide used must be free from the car- bonate, which would precipitate some of the calcium with the iron and aluminium. 3. If the precipitate is not washed completely free from chlo- rides, there is danger of volatilization of the chlorides of iron and aluminium upon ignition of the precipitate. To facilitate the removal of the chlorides, the precipitate is redissolved in nitric instead of hydrochloric acid. 4. In the presence of hot carbonaceous matter, ferric oxide is partially reduced to the magnetic oxide (Fe304), which cannot be completely changed back to the ferric oxide, even by treatment with oxidizing agents. To avoid this reduction, it is necessary to ignite the filter separate from the precipitate. AGRICULTURAL ANALYSIS 151 Iron See the determination of sodium and potassium on page 154. Phosphorus Procedure. — Evaporate 200 c.c. of solution " A " to about 75 c.c, nearly neutralize with ammonium hydroxide, and add about 10 grams of pure crystalUzed ammonium nitrate. Add gradually about 20 c.c. of ammonium molybdate solution and digest at 40° When the precipitate has settled, remove with a pipette about 5 c.c. of the clear liquid and test it by allowing it to run into 5 c.c. of warm molybdate solution. If any precipitate is produced, the test liquid should be returned to the main portion, more molybdate solution added, and the digestion continued. After standing from eight to twelve hours at a temperature not above 40°, filter the ammonium phosphomolybdate and determine the phosphorus as magnesium pyrophosphate, as described under the determination of the total phosphorus in fertihzers, page 1 34. Express the re- sults as phosphorus and phosphorus pentoxide. Manganese Principle. — When bromine water is added to an alkaline solution of a manganese salt, upon boiling, the manganese is precipitated as a hydrated manganese dioxide. Upon ignition the manganese dioxide is changed to Mn304. 3 MnOa (ignited) = MngO^ + O2. Procedure. — Concentrate the filtrate from the determination of iron, aluminium, and phosphorus to about 75 c.c, make alkaline with ammonium hydroxide, add bromine water, and heat to boiling, keeping the beaker covered with a cover-glass. When most of the bromine has been driven off, allow the beaker to cool some- what, add more ammonium hydroxide and bromine water, and heat again. Continue this process until the manganese is completely precipitated, which requires from fifteen to thirty minutes. Acid- ify the solution with a few drops of acetic acid, filter while still hot, wash the precipitate with hot water, dry, ignite, and weigh as MngO^. Compute the percentage of manganese in the soil. Note. — By strong ignition manganese dioxide is converted to mangano-manganic oxide Mn304. The exact composition of the 152 QUANTITATIVE ANALYSIS ignited precipitate varies with the conditions under which the igni- tion takes place. With small quantities of manganese the varia- tion is so small that it may be neglected. Large precipitates of manganese dioxide should be redissolved in a solution of sulphu- rous acid, precipitated from an ammoniacal solution as manganese ammonium phosphate and weighed as manganese pyrophosphate. Calcium Procedure. — Evaporate the filtrate from the manganese deter- mination to about 50 c.c, make slightly alkaline with ammonium hydroxide, and precipitate with ammonium oxalate. Heat to boil- ing, digest, and decant the clear solution upon a filter. Pour from 15 to 20 c.c. of hot distilled water upon the precipitate, and again decant. Dissolve the precipitate in the beaker with a few drops of hydrochloric acid, add a little water, and reprecipitate. Filter through the same filter as before, wash the precipitate free from chlorides, dry, ignite, convert to calcium sulphate, and weigh. Calculate the percentage of calcium in the soil. Note. — Read the notes on the separation of calcium and mag- nesium, page 34. Magnesium Procedure. — Shghtly acidify the filtrate and washings from the determination of calcium with hydrochloric acid, concentrate to about 50 c.c, and make slightly alkaline with ammonium hydrox- ide. Add 10 c.c. of microcosmic salt solution, allow to stand for a few minutes, then add one-third the volume of ammonium hydroxide solution. Allow to stand for twelve hours ; filter off the magnesium ammonium phosphate. Dissolve the precipitate in hydrochloric acid and reprecipitate. Ignite the precipitate and weigh as magnesium pyrophosphate. Express results as mag- nesium. Sulphur Procedure. — Evaporate lOO to 150 c.c. of solution "A"nearlyto dryness on a water bath, then add 50 c.c. of water and determine the sulphur by precipitating and weighing as barium sulphate as described under Exercise VI, page 29. Note. — The precipitate is appreciably soluble in concentrated hydrochloric acid, hence the necessity of expelling the excess of acid by evaporation. AGRICULTURAL ANALYSIS 153 Iron, Potassium, Sodium Procedure. — Add ammonium hydroxide to the filtrate from the determination of sulphur, and precipitate exactly as in the deter- mination of iron, aluminium, and phosphorus collectively. Wash the precipitate free from chlorides, dissolve it in hydro- chloric acid and estimate the iron present by titrating with standard dichromate solution. Calculate the percentage of iron in the soil. Evaporate the filtrate and washings from the precipitate to dryness on the water bath in a small casserole, heat cautiously for an hour at 1 10°, to avoid decrepitation due to incomplete drying, then heat at a low red heat until the ammonium salts are expelled, holding the casserole in the hand. Dissolve the residue in about 25 c.c. of hot water, add 5 c.c. of a saturated barium hydroxide solution and heat to boiling. Allow the precipitate to settle and test the supernatant liquid for complete precipitation with a few drops of barium hydroxide. When no further precipitate is pro- duced, filter, and wash thoroughly with hot water. Add ammonium hydroxide and ammonium carbonate, to precipitate the barium. Allow to stand a short time on the water bath, filter, wash the precipitate with hot water, and evaporate the filtrate and washings to dryness in a casserole. Expel the ammonium salts as before by first heating at 110°, then over the flame at a low red heat, dissolve the residue in a little water, add a few drops of ammonium hydroxide and a drop or two of ammonium carbonate solution, let stand on the water bath for a few minutes, and filter into a weighed platinum dish. Evaporate to dryness on the water bath (heat at iio°-i20° for half an hour) and heat with a free flame at a dull red heat until the ammonium salts are expelled and the residue just begins to fuse. This part of the procedure must be carried out with extreme care. The burner should be held in the hand, the flame continually moved about the bottom of the plati- num dish in order to prevent the volatilization of the alkali chlorides. The weight of the residue represents potassium and sodium chlo- rides. Separation of Potassium from Sodium Principle. — If an excess of a solution of platinic chloride is added to a solution of sodium and potassium chlorides and alcohol then added, potassium chlorplatinate is precipitated, while sodium 154 QUANTITATIVE ANALYSIS chlorplatinate remains in solution. Since sodium chloride is insol- uble in alcohol, it is necessary to add enough of the platinic chloride to change both the sodium and the potassium chlorides to the chlorplatinates. Procedure. — Dissolve the combined weighed chlorides in about 10 c.c. of water. If they do not go completely into solution, filter, wash, evaporate the filtrate in a platinum dish as before, and weigh again. The solution in water must be complete. When the com- bined chlorides dissolve completely, transfer the solution to a small porcelain dish. Add enough platinic chloride solution (containing O.I gram of platinum per cubic centimeter) to combine with the residue to form the chlorplatinate, assuming that this residue is composed entirely of sodium chloride. Evaporate to a pasty consistency on a water bath, then pour into the dish about 50 c.c. of 80 per cent alcohol and heat the dish and contents for two or three minutes upon the water bath. Stir well and then allow to stand for at least two hours in a cool place, inverting a beaker over the dish, or by some other means protecting it from possible access of ammonia vapors. Pour off the clear liquid through a weighed Gooch crucible, filter and wash the precipitate by decantation, using small quantities of 80 per cent alcohol. Bring the potassium chlorplatinate upon the filter and wash completely by applying repeatedly small quantities of the alcohol. Dry the filter and con- tents to constant weight at 1 3 5". Calculate the weight of the potas- sium chlorplatinate to potassium chloride. Deduct the weight of the potassium chloride from the weight of the mixed chlorides. From the weights of the chlorides calculate the percentages of potassium oxide and sodium oxide in the soil, also the percentages of potassium and sodium. Humus Principle. — The soil is leached with cold dilute hydrochloric acid, which dissolves calcium and magnesium salts. By the re- moval of these substances, the humus is left in a form which is easily changed to a soluble ammonium compound. It is washed out of the soil by means of dilute ammonium hydroxide, the solution is evaporated to dryness, weighed, ignited, and the loss of weight calculated as humus. Procedure. — Place ten grams of the sample in a prepared Gooch crucible, extract with one per cent hydrochloric acid until the AGRICULTURAL ANALYSIS 155 filtrate gives no test for calcium, and remove the acid by washing with water. Wash the contents of the crucible (including the asbestos filter) with four per cent ammonium hydroxide into a 500 c.c. glass-stoppered cylinder, make up to the mark with the ammonium hydroxide and allow to remain, with occasional shaking, for twenty-four hours. During this time the cylinder should be inclined as much as possible without bringing the contents in con- tact with the stopper, thus allowing the soil to settle upon the side of the cylinder and exposing a large surface to the action of the ammonium hydroxide. Place in a vertical position for twelve hours to allow the sediment to settle, then filter the supernatant liquid through a dry filter. Evaporate 100 c.c. of the filtrate to dryness, dry to constant weight at 100°, ignite in the ash muffle, and weigh. The difference in weight between the dried and the ignited residues is humus. Notes. — I. The chemical nature of humus is very imperfectly known. Several distinct bodies having acid characters have been obtained from the humus, but very little is known of their compo- sitions or properties. 2. The ammonium compound of humic acid is very soluble in water, while the calcium compound is insoluble. Total Nitrogen in the Presence of not More than a Trace of Nitrates Procedure. — Place from 7 to 14 grams of the soil in a 500 c.c. Kjeldahl digestion flask, add 30 c.c. of strong sulphuric acid or more if necessary, and about 0.65 gram of mercury. Digest for an hour and if necessary oxidize the residue with potassium per- manganate in the usual way. Cool, add to the flask about 100 c.c. of nitrogen-free water, shake vigorously, allow the sediment to subside, and filter through ignited asbestos into an 800 c.c. Kjeldahl flask, or proceed according to Note 2. The filter is easily prepared by placing a few short pieces of glass tube into the bottom of a Gooch funnel and covering them with a thin layer of the ignited asbestos. The filtration may be accelerated by fitting the funnel by means of a two-hole cork in the neck of a Kjeldahl flask and connecting with the suction. Wash the residue in the flask at least a dozen times with portions of 25 c.c. of hot nitrogen-free water, and determine the ammonia by distilling in the usual manner Calculate the percentage of nitrogen in the soil. IS6 QUANTITATIVE ANALYSIS Notes. — I. If the soil contains more than a trace of nitrates, the modified Kjeldahl process described under the determination of the total nitrogen in fertihzers, page 138, must be used. 2. If the solid residue left after digesting the soil is not removed, on distilling the ammonia violent explosions will be caused by " bumping." The bumping may also be prevented by transferring the entire contents of the digestion flask to a copper distilling flask (see Fig. 31) and proceeding as usual. Carbon Dioxide The Apparatus. — For this determination the apparatus shown in Fig. 32 has been found to give satisfactory results. It consists essentially of a flask C, into which the sample is placed. This is provided with a two-hole rubber stopper which carries a Hopkins condenser D, and a dropping funnel B by means of which dilute acid can be introduced into the flask. The carbon dioxide gas evolved first passes through the condenser, then through the U-tube E which contains glass beads and a few cubic centimeters of sul- phuric acid (sp. gr. 1.4) saturated with silver sulphate, the function of which is to remove hydrochloric acid gas. It is dried by passing into the U-tube /^ which is filled with calcium chloride, and is finally absorbed in the weighed Geissler bulb G which is filled with potassium hydroxide solution. The last traces of carbon dioxide are expelled from the apparatus by replacing it with air which has been freed from carbon dioxide by passing it through the soda-lime tube A. To draw the air through the apparatus, water is allowed to run from the bottle K into Z, which should be placed about five feet lower than K. This process is termed Aspiration. Procedure. — Weigh out two samples of from five to ten grams of the soil into clean dry flasks of 250 c.c. capacity. Fill two Geissler potash bulbs with a solution of potassium hydroxide (350 grams per liter) so that the bulbs are two-thirds full, and fill the drying tubes with fresh granular calcium chloride. Provide the open ends- of the bulbs with caps made of short pieces of rubber tubing about I ] inches long, closed with a short piece of glass rod. Put these caps in place, wipe the bulbs with a clean cloth, and allow them to stand AGRICULTURAL ANALYSIS 157 158 QUANTITATIVE ANALYSIS in the balance case for twenty minutes. Remove the caps to equalize any pressure on the inside of the bulbs, replace them and weigh accurately. Attach the potash bulb to the apparatus as shown in the figure, then place the soda-lime tube H between the absorption bulbs and the aspirator, which should be full of water. Be sure that all rubber connections are tight. Examine the stem of the dropping funnel for drops of acid which might fall into the flask, wipe it dry if necessary, and attach the flask. Test the apparatus for tightness by closing the cock in the drop- ping funnel and opening the pinchcock_/ which connects with the aspirator. If the apparatus has no leaks, bubbles will pass through the absorption bulb for a minute or two and then cease. When it is evident that the apparatus is tight, close the pinchcock on the aspirator tube and equalize the pressure in the flask by carefully opening the cock in the funnel. Disconnect the aspirator from the guard tube. Close the funnel cock, place into the funnel 50 c.c. of hydrochloric acid (sp. gr. 1.12), put the guard tube/i in place, and allow two or three drops of hydrochloric acid to run into the flask. Carbon dioxide gas will be evolved and bubbles will be forced through the absorption bulbs. The bubbles should pass through the bulbs at a rate not greater than three per second. When the evo- lution of gas slackens, add a few more drops of acid, but not enough to cause a rapid evolution of the gas. Proceed in this way until all of the acid has been added, then close the cock in the dropping funnel. Be sure that the water is running through the condenser, then heat the flask with a low flame, regulating the heat so that there will be no rapid evolution of gas. Finally heat to boiling and boil for three minutes. Remove the burner and immediately open the stopcock carefully to admit air and prevent the potash solution from being drawn back. Allow the apparatus to cool for two or three minutes, then connect with the aspirator and draw air through for thirty minutes. Detach the absorption apparatus, place the caps on the ends, allow it to stand in the balance case for twenty minutes, and weigh as before. From the increase in weight calculate the per- centage of carbon dioxide in the sample. Notes. — I. The U-tube for drying the gas should be filled with the granular and not the fused calcium chloride, which contains calcium oxide and consequently absorbs carbon dioxide. Even with the granular calcium chloride when the tube is first filled, a stream of AGRICULTURAL ANALYSIS 159 carbon dioxide should be passed through it for half an hour to neutralize any lime which might be present. The excess of car- bon dioxide must be removed by a current of air. 2. Sulphuric acid should not be used to dry the carbon dioxide passing into the absorption bulbs, because it dries gases more thor- oughly than calcium chloride. On leaving the bulb, the gas passes over calcium chloride, therefore, if it were first dried by means of sulphuric acid, it would leave the absorption apparatus carrying more moisture than when it entered. The result would be a loss of water from the absorption bulb. 3. The Geissler potash bulb may be used until a white precipi- tate of potassium bicarbonate in the first bulb shows that the liquid is saturated. 4. The guard tube //prevents carbon dioxide or moisture passing back into the absorption apparatus. It can be used for a large number of determinations without refilling. 5. The above apparatus may be used for the determination of carbon dio.xide in carbonates, baking powder, etc. Statement of Results as Oxides All results of the soil analysis should be calculated as per cent of the soil dried to constant weight in the water oven, and stated in the following order : Insoluble matter \ Soluble Silica ... J Potash (K,0) Soda (NajO) Lime (CaO) . . Magnesia (MgO) . . . Manganese Oxide (MnO) Ferric Oxide (FeaOi) Alumina (AljOs) Phosphorus Pentoxide (PaOs) Sulphur Trioxide (SO3) Carbon Dioxide (CO2) Volatile matter Total Humus ... • • Also calculate the following statement of results : i6o QUANTITATIVE ANALYSIS Statement of Results as Elements Insoluble matter . . \ Soluble Silica ... ) Nitrogen Phosphorus . ... Potassium Calcium . Magnesium Iron . . . . Sulphur Sodium . . . Aluminium . ... . . Manganese . . . . . . . . .... Inorganic Carbon . . ... .... Oxygen equivalent of above elements (except > Nitrogen) .... .... \ Volatile matter (less Nitrogen) . . ... Total ... . ... Humus ... ... .... Note. — If the organic carbon is added to the above list of determined elements, the remaining " volatile matter " consists chiefly of organic hydrogen and oxygen, combined water (as in hydrated silicates), and errors due to unavoidable changes in mineral com- I pounds during ignition. References Snyder, Soils and Fertilizers. \Q\iJK\, Agricultural Analysis, V o\. I, Soils (1906). PART V STOICHIOMETRY EMPIRICAL FORMULAS The Law of Definite Proportions states that chemically homo- geneous substances — chemical compounds — always have the same composition. Common salt, the chloride of sodium, is always found upon analysis to contain chlorine and sodium in the same proportions by weight. The elements in any chemical compound are always found in a certain definite ratio, and it is by means of this ratio that we are often able to identify a compound. In the case of silver chloride it has been found by analysis that there is 24.74 per cent of chlorine and 75.26 per cent of silver; that is, in 100 grams of silver chloride there are 24.74 grams of chlorine and 75.26 grams of silver. If the combining weight of chlorine is 35.4s grams, there will be as many combining weights of chlorine in 24.74 grams of chlorine as 35-45 is contained in 24.74 which is 0.69. Similarly, if the combining weight of silver is 107.93 grams, in 75.26 grams of silver there are 0.69 combining weights. Hence, in 100 grams of silver chloride there are 0.69 combining weights of chlorine and 0.69 combining weights of silver ; that is, they are present in the ratio of 0.69 Ag to 0.69 CI, or 1:1. The simplest formula for silver chloride, therefore, is AgCl, and is known as the Empirical Formula. In a similar manner, the empirical formulas of more complex compounds may be calculated. A substance on analysis gave the following percentage composition : Pb, 68.31; S, 10.54; O, 21.15. What is the empirical formula } 68.31 20^^=0-330,-0.330=1.00. S = T^ = 0.329, H- 0.330 = 0.997. 32.06 O = ^^ = 1-320, -f- 0.330 =4.00. 16.00 M j6i 1 62 QUANTITATIVE ANALYSIS The ratio of the combining weights as found above is 0.330 : 0.329 : 1.32. Dividing by the greatest common divisor gives the ratio in whole numbers, as i : 1:4. The empirical formula, therefore, is PbSO^. Because of unavoidable errors in the analysis, the values of the percentages almost always vary from the theo- retical value. Although this makes a slight variation in the ratio as seen in the case of sulphur in the problem above, the value is so close that it may be taken as unity. PROBLEMS Calculate the empirical formula from the percentage composition of each of the following compounds : 1. Na, 43.45; C, 1 1. 31; O, 4S-24. 2. K, 16.12; Pt, 40.10; CI, 43.78. 3. K, 40.28; Cr, 26.80; O, 32.92. 4. N, 14.29; H, 4.11; Mo, 48.96; O, 32.64. 5. C, 31.99; H, 4.03; O, 63.98. Percentage Composition The calculation of the percentage composition of a substance from its empirical formula is the reverse of the foregoing. In magnesium sulphate (MgSO^), the molecule is composed of com- bining weights of magnesium, sulphur, and oxygen in the ratio 1:1:4. The molecular weight will then be the sum of these com- bining weights. Mg= 24.36 S = 32.06 4 O = 64.00 120.42 In one gram molecule of magnesium sulphate (120.42 grams) there are 24.36 grams of magnesium, 32.06 grams of sulphur, and 4 X 16 (64) grams of oxygen. Therefore, Per cent Mg = ^^^ = 0.2023 X 100= 20.23 120.42 S = -^^^^ — = 0.2662x100= 26.62 120.42 = ^=0.5315x100= 53.15 120.42 -2J_^ 100.00 STOICHIOMETR Y 1 63 In a similar manner the percentage of any combination of ele- ments may be calculated, as, for example, MgO and SO3 in magne- sium sulphate. Per cent ■.. r\ MgO 40.36 ^gQ= A/rg^ ^ =0.3352x100= 33.52 MgS04 120.42 C/^ SOo 80.06 ^^ o ^^ r> SOo= ^, j^ = = 0.6648 X 100 = 66.48 ^ MgSO. 120.42 =^ "^ * ^ 100.00 PROBLEMS Calculate the percentages of the constituents from the empirical formulas in the following problems : 6. The empirical formula of zinc sulphate is ZnSO^. Calculate the percentages of Zn and ZnO. 7. The empirical formula of ferrous ammonium sulphate is FeS04(NH4)2S04 • 6 H2O. Calculate the percentages of Fe, FeO, S, SO3, and HgO. 8. The empirical formula of zinc pyrophosphate is Xn^^O-j. Calculate the percentages of ZnO and P2O5. 9. The empirical formula of calcium silicate is CaSiOg. Calcu- late the percentages of CaO and SiOg. GRAVIMETRIC CALCULATIONS There are a few isolated cases in gravimetric analysis in which the substance to be determined is weighed in the form in which the result is to be expressed. This is true in the determination of nickel, which is sometimes weighed as the metal, in which case the percentage is easily calculated. Weight of constituent sought X 1 00 ^ percentage of constituent. Weight of substance taken In the majority of cases the compound weighed contains other elements besides the one to be determined, as in the determination of silver, in which case the substance is weighed as silver chloride. The amount of silver present is calculated from the percentage composition of silver chloride. One gram molecule of silver chloride (143.38 grams) contains 1 64 QUANTITATIVE ANALYSIS one combining weight of silver (107.93 grams). If the precipitate weighs 0.2 gram, then letting x equal the weight of silver, AgCl Ag wt. of ppt. 143.38 : 107.93 : : 0.2 gram : x. x = o.\ 506 gram of silver. When barium, barium oxide, or sulphur are to be determined, they can be weighed in the form of barium sulphate and the con- stituents calculated in a manner similar to that given above. In each case, let x equal weight of constituent sought. {a) BaS04 : Ba \b) BaS04 : BaO \c) BaSO^ : S (wt. of ppt.) : x; (wt. of ppt.) : x; (wt. of ppt.) : X. If we wish to calculate the potassium chloride in a precipitate of potassium chlorplatinate (KgPtClg), it is evident that two mole- cules of KCl will be formed from one molecule of the precipitate. KaPtClg : 2 KCl : : (wt. of ppt.) : x. Potassium is often calculated as the oxide, and it is then necessary to express the KgPtClg in terms of this compound. It is evident that for potassium the following relation holds true : KaPtClg : 2 K : : (wt. of ppt.) : x (wt. of K). Now, two combining weights of potassium (2 K) form one mole- cule of potassium oxide (KgO). Consequently, 2 K : K2O : : x :j)/ (wt. of KgO). Expressing these proportions in the form of equations, we have: KgPtClg _ wt. of ppt. . 2K ~;ir(wt.of K)' 2K _ ^(wt. of K) K2O y (wt of K2O) ■ Multiplying the two equations, KgPtClfi ^ 2 K ^ wt. of ppt. ^ X (wt. of K) 2 K K2O X (wt. of K) y (wt. of KgO)' STOICHIOMETRY 165 Canceling, we have, KaPtClfi ^ wt. of ppt. K2O ^(wtofKaOy Expressing as a proportion, KaPtClg : K2O : : wt. of ppt. : j (wt. of K^O). Or, since in KjPtClg there are two combining weights of potas- sium, K, we have enough to make two molecules of KCl or one molecule of KjO. Therefore K2PtCle=K20. Hence KjPtClg : K2O : : wt. of ppt. : wt. of KjO. Factors The amount of the constituent in the substance weighed is often determined by means of factors. In the foregoing examples the sulphur in barium sulphate was calculated by the expression BaS04 : S : : (wt. of ppt.) : x (wt. of S present). 233.5 : 32.06 : : (wt. of ppt.) : x Solving for x we have : ^2 06 x= -^-^ — X (wt. of the precipitate). 233-5 02 06 It is evident that the value -^-^ — = 0-i373. which represents the 233-5 amount of sulphur equivalent to one gram of barium sulphate, is a constant quantity. Therefore, the sulphur in any quantity of barium sulphate may be determined by multiplying its weight by this value, which is called \h.& factor for the conversion of barium sulphate to sulphur. Other factors may be similarly calculated. Barium oxide in barium sulphate : BaSO^ : BaO : : wt. of ppt. : x. 1 66 QUANTITATIVE ANALYSIS BaO ^1534^0.6571, factor. BaSO, 233.S Potassium in potassium chlorplatinate : KaPtClg : 2 K : : wt. of ppt. : x. KgPtCle V 485.8 J Potassium oxide from the potassium chlorplatinate : KjPtClg : KgO : : wt. of ppt. : x. K,0 f94:2o\ ^^_,^,^ factor. KaPtClg V 485-8 7 From these calculations it will be readily seen that the factor may be considered as the weight of the constituent sought in one gram of the substance. PROBLEMS 10. Calculate the factors for the following substances: a. FeO in Fe203. b. P2O5 and P in MgaPgO^. c. ZnO in ZnNH^PO^. d. SO2 in PbSO^. e. PbO in PbSO^. /. MnOa from Mn304. 11. What is the weight of calcium oxide in 1.25 grams of CaCjOi .? 12. What weight of pyrite (FeSg) must be taken to furnish enough sulphur to make 1.6 grams of barium sulphate.-' 13. A substance containing 15 per cent MgO, on being analyzed gave 0.2240 gram of magnesium pyrophosphate. How much of the sample was weighed out for the analysis ? 14. What weight of magnesium ammonium phosphate will yield on ignition 0.5 gram of magnesium pyrophosphate? 2 MgNH^PO^ = MgaPgO^ + 2 NH3 + HgO. 15. 1.2 grams of an alloy containing 80 per cent silver and 20 per cent copper are dissolved in nitric acid. To the solution 0.3 STOICHIOMETRY 167 gram of pure dry potassium chloride is added. What percentage of the silver remains in solution ? 16. A sample of 0.3 gram of bauxite (AIO(OH)) gave a precipi- tate equivalent to 0.25 gram of aluminium oxide. Calculate the percentage purity of the bauxite. 17. The zinc in 2.5 grams of a sample of zinc ore was precipitated as the carbonate. On being ignited to constant weight the precipi- tate lost 0.2 gram of COj. ZnC03=ZnO + C02. Calculate the percentage of zinc in the sample. 18. One gram of a sample of rock on analysis gave 0. 15 gram of the mixed chlorides of sodium and potassium. The potassium was precipitated as the potassium chlorplatinate (KaPtClg), a pre- cipitate of 0.120 gram being obtained. Calculate the percentages of sodium and potassium in the sample. Indirect Methods In a solution containing the chlorides of sodium and potassium the amount of each salt may be determined by evaporating the solution to dryness, weighing the mixed chlorides, dissolving them in water, and determining the total chlorine present as silver chlo- ride. This is a type of the class of indirect methods. The data are best calculated algebraically, the method being illustrated by the following example. The weight of the mixed chlorides of sodium and potassium is 0.3 gram, and the weight of the silver chloride is 0.6323 gram. Cal- culate the weights of sodium chloride and potassium chloride in the mixture. Let X = wt. of KCl ; Then, (0.3 -x) = wt. of NaCl. (The weight of AgCl from x) + (weight of AgCl from (0.3 — x)) = 0.6323 gram. AgCl : KCl : : (AgCl from x) : x. Therefore, (AgCl from x) = ^ x. 1 68 QUANTITATIVE ANALYSIS AgCl : NaCl : : (AgCl from (0.3-.!)) : (0.3-^). Therefore, AgCl from (0.3 - x) = -^c\ (°-3-^)- 1.922 X -\- 2.451 (0.3 — x) = 0.6323. — 0.529^ = — 0.1030. X = 0.1946, wt. of KCl. (0.3 — x) = 0.1054, wt. of NaCl. A mixture of BaCOg and CaCOg weighed a grams. On conver- sion to the sulphates a weight of b grams was obtained. Calculate the weights of BaO and CaO in the original mixture. Let X = wt. of BaO. y = wt. of CaO. BaCOo CaCOg n3a(r" + -cacr-^ = " BaSO. CaSO, , -B^" + 'CaO--^=^- 197.40 100.10 ^' X + —. y = a. 153.40 56.10 ■" 233.46 136.16 , ^^^ X + -^ y ^ b. 153.40 56.10 -^ The equations are then solved for the values of x and y as shown in the last problem. PROBLEMS 19. A mixture of the carbonates of calcium and magnesium weighs 1.2 grams. The carbon dioxide obtained from this mixture weighs 0.58 gram. Calculate the weights of calcium and magne- sium. 20. In a mixture of 2.3 grams of the sulphates of lead and barium there is 0.675 gram of SO3. Calculate the weights of PbO and BaO present. STOJCHIOMETRY 169 21. A mixture of bromide and chloride of silver weighs 4 grams. The bromine is replaced by chlorine, and the mixture then weighs 3.8 grams. What is the percentage of bromine present .■' The Volume of a Reagent Necessary for a Given Reaction The amount of a reagent necessary to bring about a given reaction must often be calculated. The following examples are types of this class of calculations. How many cubic centimeters of a barium chloride solution con- taining 50 grams of the crystallized salt (BaClj • 2H2O) per liter will be necessary to completely precipitate the sulphuric acid in a solution containing 0.25 gram of potassium sulphate .' From the equation, K2SO4+ BaCla • 2 H2O = BaSO^ + 2 KCl + 2 HgO, it is evident that one gram molecule of barium chloride (244.3 grams) is equivalent to one gram molecule of potassium sulphate (174-4 grams). Then, K2SO4 BaCl2 • 2H2O wt. of K2SO4 wt. of BaClj • 2 HgO 174.4 : 244.3 :: 0.25 : x. ;ir=o.350i gram of BaClj • 2 H2O necessary to precipitate the sulphate. I c.c. barium chloride solution = o.os gram BaClg • 2 HjO. 0.3501 0.05 - = 7 c.c. of the solution. The other type of problem involves the use of the specific gravity of the solution used. . . Weight of volume of liquid " ° ■'^ Weight of same volume of standard This ratio gives the number of times the liquid is heavier than the same volume of the standard. The standard which is used is the weight of one cubic centimeter of water at its greatest density, 4° C. Therefore, Weight of I c.c. liquid Specific gravity = Weight-^TF^cTVater- I70 QUANTITATIVE ANALYSIS And since the weight of one cubic centimeter of water is one gram, we have Weight of I c.c. liquid Specific gravity = * — . ° -^ I gram or Specific gravity = Weight of i c.c. of the liquid. In determining the specific gravity it is not always convenient to measure the volume of substances at 4° C, but at more conven- ient temperatures, such as 15° or 20° The value of the specific gravity is expressed in terms of the standard at 4° C. and is written i5°/4°, which signifies that the substance was measured at 15° and compared with water at 4°, i.e., the ratio of weights of equal volumes of the liquid at 1 5° and of the standard at 4° ; 4V4° signifies that the weight of equal volumes are compared at the same tem- perature, 4" ; likewise, 20°/20° signifies the temperature was 20° when the weights were compared. How many cubic centimeters of hydrochloric acid (sp. gr. 1.04) containing 8.16 per cent of HCl are necessary to completely pre- cipitate the silver from 1.5 grams of silver sulphate.' AggSO^ -I- 2 HCl = 2 AgCl -f- H2SO4. From this equation it is evident that one gram molecule(3i 1.9 grams) of silver sulphate is precipitated by two gram molecules (72.92 grams) of hydrochloric acid, and the amount of the acid necessary to precipitate the silver in 1.5 grams of silver sulphate would be AggSO^ 2 HCl wt. of AgSO^ wt. of HCl 31 1.9 : 72.92 :: 1.5 : x. ;r=o.35o6 gram HCl necessary to precipitate the silver. I c.c. of HCl (sp. gr. 1.04) = 1.04 grams. It contains 8.16 per cent HCl by weight. Therefore, I c.c. of HCl =(0.0816 X 1.04) gram HCl = 0.0849 gram HCl. To furnish 0.3506 gram HCl, "•3506 _ 5:^8^ -4-13. STOICHIOMETR Y 171 Therefore, 4.13 c.c. of the solution will be required to precipitate the silver. PROBLEMS 22. How many cubic centimeters of silver nitrate solution (100 grams of AgNOg per liter) will be necessary to completely pre- cipitate the chlorine from 0.22 gram of BaCla • 2H2O.'' 23. How many cubic centimeters of sodium ammonium hydrogen phosphate solution (microcosmic salt, NaNH^HPO^ 4H2O) con- taining 1 5 grams of the salt per liter will be necessary to precipitate the magnesium from 1.2 grams of a substance containing 40 per cent magnesium oxide? 24. A sample of i gram of barium carbonate, the only impurity in which is 3.5 per cent SiOj, is dissolved in hydrochloric acid. How many cubic centimeters of sulphuric acid solution (sp. gr. 1. 10) containing 14.35 per cent H2SO4 by weight will be neces- sary to completely precipitate the barium as barium sulphate ? 25. How many cubic centimeters of ammonium hydroxide (sp- gr. 0.96), containing 9.91 per cent NHg, would be necessary to completely precipitate the iron in a solution containing 1.3 grams of ferric chloride ? VOLUMETRIC CALCULATIONS ACIDIMETRY ,\XD ALKALIMETRY A normal acid solution contains one combining weight, or 1.008 grams of replaceable hydrogen, in one true liter. One combining weight of hydrogen is furnished by one gram molecule of hydro- chloric acid ; hence, it is necessary to have one gram molecule of hydrochloric acid, i.e., the molecular weight in grams (36.46) dis- solved in one liter, to have contained therein 1.008 grams of hydrogen. One gram molecule of sulphuric acid, HgSO^, contains two combining weights of hydrogen, or 2. 016 grams. Hence, to obtain i .008 grams per liter, one gram molecule of sulphuric acid would have to be contained in two Hters, or one-half of it in one Hter ; therefore, two liters of a normal solution can be made from one gram molecule of sulphuric acid. According to the equation HCl 4- KOH = KCl + H2O, I gram mol. of HCl (36.46 grams) = I gram mol. of KOH (56.16 grams). 1/2 QUANTITATIVE ANALYSIS Since, looo c.c. normal hydrochloric acid solution = 36.46 grams HCl, 1000 c.c. normal HCl = 56.16 grams of KOH. If 56.16 grams of potassium hydroxide are dissolved and made up to one liter, we have one liter of a normal potassium hydroxide solution. Hence, 1000 c.c. N. KOH = 56.16 grams of KOH. Therefore, lOoo c.c. N. HC1= 1000 c.c. N. KOH, or, I c.c. N. HC1= I c.c. N. KOH. From the equation H2SO4 + 2 NaOH = NagSO^ + 2 HjO, one gram molecule of sulphuric acid neutralizes two gram molecules of sodium hydroxide. That is, I gram molecule of HgSO^ = 2 gram molecules of sodium hydroxide, (98.08 grams) (2 x 40.06 grams) but, I grammoleculeof H2S04 = 2000 c.c. N. HjSO^, (98.08 grams) hence, 2000 c.c. N. HgSO^ = 2 gram molecules of NaOH, (2 X 40.06 grams) or, 1000 c.c. N. H2S04= i gram molecule of NaOH. (40.06 grams) If 40.06 grams of sodium hydroxide are dissolved and made up to 1000 c.c, we shall have one liter of a normal sodium hydroxide solution. Hence, 1000 c.c. N. NaOH = 40.06 grams NaOH. Therefore, 1000 c.c. N. NaOH = 1000 c.c. N. HgSO^, or, I c.c. N. NaOH = i c.c. N. HgSO^. It, therefore, follows that I c.c. N. HCl = I c.c. N. H2SO4, 1 c.c. N. KOH = I c.c. N. NaOH, I c.c. N. HCl = I c.c. N. NaOH, I c.c. N. H2SO4 = I c.c. N. KOH, STOICHIOMETRY 173 or, in general, one cubic centimeter of any normal acid solution is equivalent to one cubic centitneter of any normal alkali solution, or normal solutions of acids and alkalies are equal, cubic centimeter for cubic centimeter. The following typical exercises will emphasize these fundamen- tal principles and illustrate the relations between the volumetric solutions employed in acidimetry and alkalimetry, as well as the methods of calculation : 9.2637 grams of a sample of KOH were dissolved in 250 c.c. of water; of this solution 25.45 c.c. were equivalent to 14.90 c.c. of N. acid. Calculate the percentage of KOH. Since, 25.45 c.c. KOH solution = 14.90 c.c. N. acid, I c.c. KOH solution = 14:22= 0.5855 c.c. N.acid, 25.45 and 250 c.c. KOH solution = 250 x 0.5855 = 146.37C.C. N.acid. HCl + KOH = KCl + H2O. From which it follows that 1000 c.c. N. HCl = 56.16 grams KOH. Hence, 1000 c.c. N. HCl: 56.16 grams KOH : : 146.37 c.c. N. acid -.x grams KOH. Solving, X = 56.I6 x 146.37 _ 3.220 grams KOH. 1000 Hence, 8.220 grams of KOH were furnished by 9.2637 grams of the sample. What percentage of the sample is pure potassium hydroxide ? grams sample grams KOH 9.2637 : 8.220 :: 100 per cent : .r per cent. Solving, 8.220 X 100 x = 9.2637 = 88.73. Therefore, 88.73 per cent. This same result may be obtained by finding the relation of the alkali in terms of the normal acid. It is sometimes preferable tf 174 QUANTITATIVE ANALYSIS express the relation of the solutions in terms of the standard solution. 14.90 c.c. N. acid = 25.45 c.c. KOH solution. I c.c. N. acid = 1.708 c.c. KOH solution. Since 1000 c.c. N. acid = 56.16 grams KOH, I c.c. N. acid = O.05616 gram KOH, then, 1.708 c.c. KOH solution = 0.05616 gram KOH. Hence, 1.708 c.c. KOH solution : 0.05616 gram KOH : : 250 c.c. KOH solution '.x grams KOH. „ , . 0.05616 X 250 o „ ^rr\XJ Solvmg, X = — 2 5_ = 8.220 grams KOH. 1.708 The percentage is found as above. 50 c.c. of a sample of nitric acid of a specific gravity 1.176 were diluted to 250 c.c. Of this solution 33.10 c.c. were neutralized by 35.55 c.c. of N. KOH. Calculate the percentage of nitric acid in the sample. 33.10 c.c. HNO3 solution = 35.55 c.c. N. KOH, I c.c. HNO3 solution = 1.074 c.c. N. KOH, then, 250 c.c. HNO3 solution = 268.50 c.c. N. KOH. Since, HNO3 + KOH = KNO3 + H2O, 1000 c.c. N.KOH = 1000 c.c. N.HNO3 = 63.02 grams HNO3. Therefore, 1000 c.c. N.KOH : 63.02 grams HNO3 : : 268.50 c.c. N.KOH :;r grams HNO3. C 1 • 63.02 X 268.50 ^ TT1VT/-V Solvmg, x=-=^ ^—= 16.92 grams HNO3. The specific gravity of the nitric acid is 1.176, i.e., i c.c. weighs 1. 176 grams, then 50 c.c. will weigh 50 x 1.176 or 58.80 grams, which is the weight of the sample employed in the analysis. STOICHIOME TRY 175 Therefore, 58.80 grams sample : 16.92 grams HNO3 : : lOO per cent. : x per cent HNO3. e I • 16.92 X 100 o o Solvmg, X = — 2 = 28.78. ^ 58.80 ^ Therefore, 28.78 per cent of HNO3 in the sample. A sample of corn weighing 2.0894 grams was taken for analysis and the nitrogen determined by the Kjeldahl process with the following results : 30.00 c.c. of N/3 acid (HCl) were placed in the receiving flask and after distillation 22.39 c.c. of a standard am- monium hydroxide solution (i.o c.c. = 1.004 c.c. N/3 acid) were required to neutralize the excess of acid. Calculate the percent- age of nitrogen and the percentage of total proteids. Proteids are 6.25 times the nitrogen. If 1.0 c.c. NH^OH solution = 1.004 c-c. N/3 acid, then, 22.39 c.c. NH^OH solution = 22.39 x 1-004 = 22.48 c.c. N/3 acid ; therefore, there were 22.48 c.c. of the standard N/3 acid not neu- tralized by the ammonia distilled over. 30.00 c.c. N/3 acid introduced into the flask, 22.48 c.c. N/3 acid in excess in the flask, 7.52 c.c. N/3 acid is amount neutralized by the am monia distilled over. HCl + NH4OH = NH^Cl + H2O, then, 1000 c.c. N. HCl = i gram molecule of NH4OH. But, I gram molecule NH4OH = NHg = N, 35.05 grams = 17.03 grams = 14.01 grams, therefore, 1000 c.c. N. HCl =014.01 grams nitrogen, 1000 c.c. N/3 HCl = Mi_l _ 4.670 grams nitrogen, 3 and I c.c. N/3 HCl = 0.004670 gram nitrogen. 1/6 QUANTITATIVE ANALYSIS Then, 7.52 c.c. N/3 acid = 0.004670 X 7.52 = 0.03512 gram nitrogen, and the percentage this is of the original sample is found by the following proportion : 2.0894 grams sample : 0.035 12 gram nitrogen : : 100 per cent : x per cent. c 1 ■ 0.03512 X 100 ^o 4. Solvmg, x= — ^^ = 1.68 per cent. ^ 2.0894 ^ Therefore, 1.68 per cent of nitrogen in the sample, and 6.25 x 1.68 = 10.50 per cent of total proteids. A sample of calcium carbonate weighing 0.6759 gram was dis- solved in 44.50 c.c. of 1.005 N/2 acid (HCl), and the excess of acid neutralized b}' 18.21 c.c. of a standard alkali, i.oo c.c. of the acid being equal to 1.031 c.c. of the alkali. Calculate the purity of the calcium carbonate. 1.03 1 c.c. of the alkaU= i c.c. of acid, T 8 2 T and 18.21 c.c. of the alkali = — '- — = 17.66 c.c. acid. 1.031 44.50 c.c. of 1.005 N/2 acid used 17.66 c.c. of 1.005 N/2 acid remaining 26.84 c.c. of 1.005 N/2 acid used in neutralizing the CaCOg. Since the acid is 1.005 times as strong as N/2 acid, 26.84 c.c. will equal 26.84 x 1-005 = 26.97 c-c. N/2 acid. CaCOg + 2 HCl = CaClg + CO^ + HjO. I gram molecule of CaCOg, i.e. (loo.i grams) = 2000 c.c. N. HCl = 4000 c.c. N/2 HCl. Therefore, 4000 c.c. N/2 HCl : 100. 1 grams CaCOg : : 26.97 cc. N/2 HCl : x grams CaCOg. Solving, X = loo-i X ^^-97 = 0.6750 gram CaCOg. 4000 Then, 0.6759 gram of sample : 0.6750 gram CaCOg : : 100 per cent : x per cent. 3* STOICHIOMETRY 177 Solving, ^^0.6750x100^ 0.6759 Therefore, 99.87 per cent of the sample is CaCO; PROBLEMS 26. 11.2798 grams of NaOH were dissolved and diluted to 250 CO., 36.15 c.c. of which were equivalent to 37.40 c.c. N. acid. Calculate the percentage purity. 27. 6.5563 grams of NaKCOg were dissolved and diluted to 250 c.c, 42.88 c.c. of which were equivalent to 17.71 c.c. of N. acid. Calculate the percentage purity. 28. 0.7752 gram of calcium carbonate was dissolved in 32.00 c.c. N. acid ; the excess of acid required 16.52 c.c. N. KOH for neutralization. Calculate the percentage purity of the calcium carbonate. 29. 9.41 16 grams of a mixture of sodium hydroxide and sodium carbonate were dissolved and made up to 250 c.c. ; 40.85 c.c. of this solution required 24.32 c.c. N. acid when phenolphthalein was used as an indicator, and 30.56 c.c. when methyl orange was used. Calculate the percentages of sodium carbonate and sodium hydrox- ide. Calculate the percentage of total alkalinity expressed as sodium oxide. 30. 24.84 c.c. NH4OH, the specific gravity of which was 0.944, were diluted to 250 c.c, and 28.50 c.c. were equivalent to 22.71 c.c. N. acid. Calculate the percentage of ammonia in the sample. 31. 15.00 c.c. of H2SO4 solution, the specific gravity of which was 1.624, were diluted to 250 c.c, and 25.55 c.c. of this solution were equivalent to 35.25 c.c. of N. KOH. Calculate the percent- age of acid in the sample. 32. 25 c.c. of a sample of HCl, the specific gravity of which was I.I 16, were diluted to 250 c.c. ; 20.54 c.c of this solution were equivalent to 14.30 c.c. N. KOH. Calculate the percentage of HCl in the sample. 33. 23.12 c.c. of HNO3 solution, specific gravity 1.19, were diluted to 250 c.c. ; 25.00 c.c. of this solution were equivalent to 12.92 c.c. N. KOH. Calculate the percentage of nitric acid, in the sample. N 178 QUANTITATIVE ANALYSIS 34. How many cubic centimeters of 0.9 N. HgSO^ solution are required to precipitate the barium from 0.25 gram BaCl2- 2 HgO ? 35. In the absorption method for standardizing the KOH solu- tion 7.9284 grams HCl gas were absorbed and diluted to 250 c.c. ; 24.89 c.c. of this solution were equivalent to 21.65 c.c. of the KOH solution. Calculate the normality of the KOH solution. 36. 25.00 c.c. of a standard acid were diluted to 250 c.c. and 25 c.c. of this solution^were treated with AgNOg. The silver chloride from the same weighed 0.3505 gram. What was the normality of the standard acid } 37. A solution of KOH requires 27.00 c.c. of a standard HCl ( I c.c. of which = 0.022 gram CaCOg) for neutralization. What is the weight of potassium hydroxide in the solution .■■ 38. One gram of silver is dissolved in nitric acid. To the solu- tion 8 c.c. of N. HCl are added. What percentage of the silver remains in solution .' Oxidation and Reduction Balancing Equations In writing the equations representing oxidations and reductions, considerable difficulty is experienced owing largely to the fact that the elements undergo a change of valency. These equations can be balanced only when all of the reacting substances and products are known. The numerical values can be readily obtained and the reactions more easily understood if they are represented as taking place by stages, the final result being expressed as the sum of the various steps. A few specific examples will illustrate the method by means of which the equation may be readily balanced. If the reacting substances are nitric acid and metallic copper, the products of the reaction will be copper nitrate, nitric oxide, and water. The usual action of an acid on a metal is attended with the evolution of hydrogen, Cu -f 2 HNOg = Cu(N0g)2 + H2, which in the presence of nitric acid will be oxidized. The nitric acid may be assumed to break up as follows : 2 HNO3 = H2O -I- 2 NO + 3 O, STOICHIOMETRY 179 and the hydrogen oxidized by the oxygen, 3H2+30 = 3H,0. The first equation must be multiplied by three in order to provide enough hydrogen to combine with the oxygen from two molecules of nitric acid. Multiplying by three and collecting the equations we have, 3 Cu + 6 HNO3 = 3 Cu(N03)2 + 3^2 2 HNO3 = H2O + 2 NO + ji) 3^2+>0 = 3H,O 3 Cu + 8 HNO3 = 3 Cu(N03)2 + 2 xNO + 4 H2O. Adding and simplifying gives the above. In the oxidation of ferrous chloride by potassium dichromate in the presence of hydrochloric acid, the products of the reaction are ferric chloride, chromic chloride, potassium chloride, and water. The potassium dichromate may be conceived as splitting up in the following manner : KaCraO^ = KgO + CrgOj + 3 O. The oxides react with hydrochloric acid, K2O + 2 HCl = 2 KCl + H2O, Cr203 + 6 HCl = 2 CrCIg + 3 H2O. The oxygen and hydrochloric acid react with the liberation of chlorine, 6HC1+3 = 3H20 + 6C1. The chlorine reacts with ferrous chloride, oxidizing it to ferric chloride, 6 FeCla + 6 CI = 6 FeCla. Adding and simplifying we have : ^45 + 2 HCl = 2 KCl + H2O Q^^ + 6 HCl = 2 CrCl3 + 3 H2O 3^+6HCl = 3H20 + ^ 6 FeCla + ^^ = 6 FeCl3 KjCrjO^ + 14 HCl + 6 FeCl^ = 2 KCH- 2 CrClg + 6 FeCl3 + 7 H^O. i8o QUANTITATIVE ANALYSIS The reduction of potassium permanganate by potassium iodide (hydriodic acid) in the presence of sulphuric acid may be illus- trated in a similar manner. The potassium permanganate may be conceived as breaking down in the following manner : 2 KMnOi = K2O + 2 MnO + S O. The oxides react with sulphuric acid, forming salts, K2O + H2SO4 = K2SO4 + H2O ; 2 MnO + 2 H2SO4 = 2 MnS04 + 2 H2O. The oxygen reacts with the hydriodic acid, 10 KI 4- s H2SO4 = 10 HI + s K2SO4; 10HI + 5O = 5 H2O + 5 la- Adding and simplifying we have : 2 KMnO^ + 10 KH- 8 H2SO4 = 2 MnS04 + 6 K2SO4 + 5 12 + 8 HjO. The oxidation of arsenious oxide by chlorine (iodine or bromine) is another example. 2 CI2 + 2 H2O = 4 HCl +^2 AS203+^2=AS205 AS2O3 + 2 CI2 + 2 H2O = As2< )5 + 4 HCl. Oxidizing Agents The following compounds are some of the more important oxi- dizing agents from the standpoint of analytical chemistry. Their method of breaking up when acting as oxidizing agents is illus- trated. ■ 2 KMnO^ = K2O + 2 MnO -f 5 O (in acid solution). 2 KMnO^ = K2O + 2 MnOa -|- 3 O (in alkaline solution). Potassium permanganate. Potassium dichromate. K2Cr20^ = K2O + Cr203 -f 3 O. Potassium chlorate. KCIO3 = KCl -f 3 O Nitric acid. 2 HNO3 = HgO + 2 NO -f 3 O. STOJCHIOMETR Y 1 8 1 Sulphuric acid H^SO^ = H^O + SO^ + O. (hot concentrated). Manganese dioxide. MnOj = MnO + O. (in acid solution). Sodium peroxide Na^Oa = NaaO + O. (fusion). Hydrogen peroxide. HjOj = HjO + O. . ■ I The halogens oxidize by decomposing water with the romme. f ]jj3eja,tion of oxygen. HjO + CI2 = 2 HCl + O. It should not be forgotten that oxidizing agents are reduced to dif- ferent compounds under different conditions, as may be seen in the case of potassium permanganate in acid and alkaline solutions. Balance the following equations : 1 . Fe2(S04)3 + H2SO4 + Zn = FeSO^ + ZnSO^. 2. KNO3 + FeClj + HCl = KCl + NO + FeClg + H2O. 3. KCIO3 + FeSO^ + H2SO4 = KCl + Fe2(S04)3 + HjO. 4. K2Cr207 + H2SO4 + Zn = Cr2(S04)3 + K2SO4 + ZnS04 + HjO. 5- Mn02 + H2SO4 + H2C2O4 = MnSO^ + CO2 + H2O. 6. As203 + Cl2+H20 = H3As04+HCl. 7. K4Fe(CN)g + H2S04+KMn04 = K2SO4 + MnS04 + K3Fe(CN)g + H2O. 8. MnOa 4- KOH + KCIO3 (fusion) = K2Mn04 + KCl + H2O. 9. Cr2Cl8 + NaOH + NaClOg (fusion) = NaCl + Na2Cr04 + HjO. 10. Cr2(0H)g + Na202 (fusion) = Na2Cr04 + NaaO + HgO. 11. K2Cr207-t-HCl + C2H60H = CrCl3+KCl+C2H40 + H20. 12. H2S04+Ci2H220„=S02+C02+H20. 13. KI03 + KI-I-H2S04=K2S04+ I2+H2O. 14. KC10 + HI = KCl-l-H20 + l2. 15. Mn02+HCl = MnCl2+H20 + Cl2. 1 82 QUANTITATIVE ANALYSIS i6. Pb02+HI = Pbl2 + H20 + l2. 17. KBrOg + KH- H2SO4 = KBr + K2SO4 + Ij + HjO. 18. KC103 + KI + HCl=KCH-H20 + l2. 19. K3Fe(CN)6+KI = K4Fe(CN)g + l2. 20. Ca(OCl)2CaCl2 + HCl + KI = CaCla + KCl + I2 + H2O. Permanganate and Bichromate Methods Numerical Relations The quantitative relations between certain oxidizable substances can be determined by finding their values in terms of oxygen. Potassium permanganate oxidizes ferrous sulphate to ferric sul- phate. It also oxidizes oxalic acid to carbon dioxide and water. What is the relation between these two reducing agents and what are their values in terms of oxygen .'' The ferrous sulphate is oxidized to ferric sulphate, this being equivalent to oxidizing ferrous oxide to ferric oxide. FeOl P^Q} + = Fe20, That is, one combining weight of oxygen will oxidize two mole- cules of ferrous oxide, which is equivalent to 2 FeS04 or 2 Fe. Similarly, oxalic acid is oxidized by one combining weight of oxygen to carbon dioxide and water. H2C2O4 -H O = 2 CO2 + H2O. Therefore, f H2C2O4 [2 Fe O = or =2 FeO [h2C204-2H2 [aFeSO^ or expressing the relation in grams: 16 g. of oxygen = • 90.03 g. oxalic acid = 126.06 g. crystallized oxalic acid = 1 1 1.8 g. of Fe 143.8 g. of FeO 303.9 g. of FeSO^ If the strength of a solution is given in terms of either of these substances, it stands in a simple ratio to the other substances. STOICHIOMETRY 183 If I c.c. of KMn04 = o.03 gram of oxalic acid, what is its strength in terms of FeO and oxygen? H2C2O4 2 FeO 90.03 : 143.8 : : 0.03 : x. .r= 0.04782 gram, the value of i c.c. in terms of FeO. HaQO, O 90.03 : 16 : : 0.03 -.x. x = 0.00533 1 gram, the value of i c.c. of the permanganate in terms of oxygen. In the case of potassium dichromate, since, K2Cr2 0,= 3 and O =2 FeO =2.YtZQ>^ =2Fe KjCraO^ =30 =6 FeO =6FeS04 =6Fe 294.5 grams = 48 grams = 43i.4 grams = 9ii.7 grams = 335.4 grams. QUESTIONS ON EQUATIONS Equation i, page 181. How many gram molecules of ferric sulphate take part in the reaction .-' When ferric sulphate acts as an oxidizing agent, how many grams of available ox}gen are contained in one gram mole- cule .■" How many gram molecules of ferrous sulphate can be ob- tained by the action of one combining weight of zinc' How many grams, by one gram of zinc .'' Equation 3. One gram molecule of potassium chlorate contains how many grams of available oxygen.'' One gram molecule of potas- sium chlorate will oxidize how many grams of FeS04 ■'' ^^ FeSO/NHJ^SO^-eH^O. Equation 5. How many gram molecules of manganese dioxide and oxalic acid take part in the reaction .'' Considering the oxalic acid as crystalline, how many grams are equivalent to one gram of man- ganese dioxide ? Equation 7. How many grams of potassium ferrocyanide will reduce the 1 84 QUANTITATIVE ANALYSIS same amount of permanganate as one gram of hydrogen ? As one gram of ferrous sulphate ? Equation ii. Calculate the weight of alcohol necessary to reduce two grams of KgCrgO^. If the specific gravity of the alcohol used is 0.8043, how many cubic centimeters will be required ? Methods of Solving Problems A solution of potassium permanganate was standardized by (a) pure iron, {b) ferrous ammonium sulphate, and {c) sodium oxalate. In each case calculate the number of grams of oxygen in one cubic centimeter of the permanganate and also the amount of iron equivalent to one cubic centimeter of the solution. a. 0.1 1 04 gram of electrolytic iron was dissolved, out of contact with air, and required 22.30 c.c. of the permanganate solution to oxidize the ferrous iron to the ferric condition. We saw above that 16 grams of oxygen are equal to 11 1.8 grams of iron, then i gram oxygen = 6.988 grams of iron; therefore, 0. 1104 gram of iron will require 0.1 104 ,0 c ^ = 0.01580 gram of oxygen. Since this quantity of oxygen is furnished by 22.30 c.c. of per- manganate, then, 22.30 c.c. KMn04 = 0.01580 gram oxygen. I c.c. KMn04 = ^ — - — = 0.0007085 gram oxygen. 22.30 Therefore, i c.c. KMn04 furnishes 0.0007085 gram of oxygen for oxidation. Since 22.30 c.c. KMn04 = 0.1 104 gram iron, I c.c. KMnO^ = 0.004950 gram iron. b. 0.8350 gram of ferrous ammonium sulphate was dissolved and oxidized by 24.01 c.c. of the permanganate solution. Since, FeS04(NH4)2S04 ■ 6 HjO Fe wt. of sample wt. of Fe. 392.26 grams : 55.9 :: 0.8350 : x. STOICHIOMETRY 185 Solving, 55-9x0.8350 = 0.1 190 gram 392.26 ^ ^ of iron equivalent to this quantity of ferrous ammo- nium sulphate. Now, knowing the grams of the iron and the amount of perman- ganate solution required to oxidize it from the ferrous to the ferric condition, the results can be calculated in the manner illustrated in the preceding example. c. 1. 401 grams of sodium oxalate were dissolved and made up to 250 c.c. ; 26.50 c.c. of this solution were oxidized by 25.08 c.c. of the potassium permanganate solution. 5 Na2C204 -f 2 KMnO^ + 8 H2SO4 = 2 MnSO^ -h 5 NagSO^ + K2SO4 + 10 CO2 + 8 H2O. 26.50 c.c. oxalate solution = 25.08 c.c. KMnO^, I c.c. oxalate solution = 0.9464 c.c. KMn04, 250 c.c. oxalate solution = 236.61 c.c. KMnO^. From the above equation 5 NagCaO^ = 2 KMn04 = 5 O, or, Na2C204 = O, i.e., 134.1 grams = 16 grams of oxygen. Hence, 134. 1 grams '^■Lfl^^: 16 grams oxygen : : 1. 401 grams Na2C204 .Jtr grams oxygen. Solving, 16 X 1.401 „ --_ ^ x= — = 0.16716 gram oxygen. Since 236.61 c.c. of KMn04 furnished 0.16716 gram of oxygen, one cubic centimeter would furnish — — - — = 0.0007065 gram of oxy- 236.61 gen for oxidizing purposes. Since, I gram oxygen = 6.988 grams iron, 0.0007065 gram oxygen = 0.0007065 x 6.988 = 0.004937 gram iron. Therefore, I c.c. KMn04 = 0.004937 gram iron. 1 86 QUANTITATIVE ANALYSIS PROBLEMS 39. From the following data calculate the number of grams of available oxygen in one cubic centimeter of a potassium perman- ganate solution and also the number of cubic centimeters of this solution required to oxidize 0. 10 gram of iron. a. 0.0946 gram of metallic iron required 10.78 c.c. KMnO^ solution. b. 1.14S grams of ferrous ammonium sulphate required 18.70 c.c. of the permanganate solution. c. I.S477 grams of crystallized oxalic acid were dissolved and made up to 250 c.c. ; 25.25 c.c. of this solution were equivalent to 15.76 c.c. of the permanganate solution. Write the equations representing the reactions in each case. 40. 3.7613 grams of ammonium oxalate ((NH4)2C204 ■ HgOjwere dissolved in water and made up to 250 c.c. ; 10.00 c.c. of which were equal to 20.33 c.c. of KMn04 solution. If i c.c. of the KMn04 is equivalent to 0.000830 gram of oxygen, calculate the percentage purity of the sample. 41. Calculate the percentage purity of KH3( €204)3 • 2H2O, if 1. 1 88 1 grams were dissolved and made up to 250 c.c, and 25.10 c.c. of this solution were equivalent to 17.58 c.c. of KMn04, I c.c. of which is equivalent to 0.000851 gram of oxygen. 42. 1. 61 24 grams of a substance containing calcium were dis- solved and made up to 250 c.c. The calcium was precipitated from 50 c.c. of this solution as calcium oxalate, washed thoroughly, and then dissolved in dilute sulphuric acid. This solution was then titrated with a KMn04 solution, i c.c. of which furnished 0.000830 gram of oxygen. 55-88 c.c. of this KMn04 were re- quired to oxidize the oxalic acid liberated. Write equations repre- senting all of the reactions and calculate the percentage of calcium oxide in the sample. 43. A solution of KgCrjO^ was standardized with the following results : (a) 0.771 gram of ferrous ammonium sulphate required 19.80 c.c. of the K2Cr207 solution. (i>) 0.430 gram of metallic iron was dissolved and made up to 250 c.c; 50 c.c of this solution required 15.45 c.c of the K2Cr207 solution. STOICHIOMETR Y 187 Write the equations representing all of the chemical changes. Calculate the number of grams of available oxygen in each cubic centimeter of the dichromate solution and the number of cubic centimeters of the solution equivalent to o.i gram of iron. 44. 10.00 c.c. of hydrogen peroxide solution were diluted to 250 e.c, and titrated against a potassium permanganate solution. 25.00 c.c. of the diluted peroxide were equivalent to 19.71 c.c. of the permanganate, i c.c. of which contained 0.00070 gram of oxy- gen. Calculate the number of grams of oxygen furnished by each cubic centimeter of the original peroxide solution. Calculate the percentage purity of the hydrogen peroxide, assuming the spe- cific gravity to be one. lODIMETRY Method of Solving Problems. In the solution of problems in which a number of equations are involved, short cuts in the calculations are often made possible by equating the values in such a way that the intermediate calcula- tions may be omitted. If 25 c.c. of a solution of potassium permanganate (i c.c. = 0.004 gram Fe) are added to an acid solution of potassium iodide, how many grams of sodium thiosulphate (NagSaOgS HgO) will be oxidized by the iodine liberated .'' Since I c.c. KMnO^ solution = 0.004 gram Fe, 25 c.c. KMn04 solution = o.ioo gram Fe. Two combining weights of iron are equivalent to one combining weight of oxygen, or 2 Fe = O, and one of oxygen is equivalent to two combining weights of iodine, O = 2I. Two combining weights of iodine will oxidize two gram mole- cules of sodium thiosulphate, 2 I =2Na2S203-5H20; therefore, 2 Fe = 2 NagSgOg • 5 HgO. That is, 55.9 grams Fe = 248.3 grams NagSgOg S H.3O. 1 88 QUANTITATIVE ANALYSIS It follows then that 55.9 grams Fe : 248.3 grams NagSgOg • sHjO : : o. 100 gram Fe : x grams NajSjOg • 5 HgO. Solving, 248.3 X 0.1 ^ , . .^ x= -i — ^ = 0.4442. 55-9 Therefore, 0.4442 gram of sodium thiosulphate will be oxidized by the iodine liberated. This exercise illustrates the common method employed in the solution of problems in iodimetry. It is obvious that the method may be applied to the solution of other classes of problems of oxi- dation and reduction. QUESTIONS ON EQUATIONS Equation 13, page 181. How many grams of potassium iodate will be required to furnish one combining weight of iodine .■■ One gram of iodine .■" Equation 15. How many gram molecules of chlorine are liberated ? How many grams of iodine are equivalent to the available oxygen in one gram molecule of MnOg ■'' To one gram of chlorine } Equation 17. How many grams of iodine are equivalent to the available oxy- gen in 50 c.c. of a solution containing one gram molecule of KBrOg in a liter .' How many grams of KBrOg should be dis- solved in a liter to make a half-normal solution .'' Equation 19. How many grams of potassium ferricyanide are necessary to liberate one combining weight of iodine.'' How many grams of the ferricyanide should be dissolved in a liter of water to make a normal solution .' PROBLEMS 45- 3-035 grams of arsenious oxide were dissolved and made up to 500 c.c. ; 25.70 c.c. of this solution were equivalent to 37.70 c.c. of an iodine solution. Calculate the grams of iodine in one cubic centimeter of the iodine solution. 46. An iodine solution was found by titration to be exactly equivalent to a thiosulphate solution which was standardized by a standard potassium permanganate solution, according to Exercise STOICHIOMETRY 189 XXVII, c. If one cubic centimeter of the permanganate solution was equivalent to 0.000707 gram of oxygen and 28.50 c.c. were equivalent to 26.00 c.c. of the thiosulphate solution, calculate the number of grams of iodine in one cubic centimeter of the iodine solution. Express the normality factor of the iodine solution. 47. 7.0799 grams of bleaching powder were taken for analysis, dissolved and diluted to looo c.c. 50 c.c. of this solution were treated with potassium iodide and acetic acid and the iodine liber- ated, titrated against N/io thiosulphate solution, of which 24.45 c.c. were required. Calculate the percentage of available chlorine in the sample. 48. 0.7697 gram of pyrolusite was treated, as described in Exercise XXIX, with concentrated hydrochloric acid, and the lib- erated chlorine passed into a solution of potassium iodide. This solution was diluted to 500 c.c, and 50 c.c. of it titrated against N/io thiosulphate solution of which 11.90 c.c. were required. Calculate the percentage purity of the pyrolusite. 49. An iodine solution was standardized by means of a standard dichromate solution (i c.c. =0.000848 gram oxygen) according to the method described in Exercise XXVII, d. 28.29 c.c. K2Cr20Y liberated enough iodine to oxidize 30.05 c.c. sodium thio- sulphate, I c.c. of which = 1.206 c.c. of the iodine solution. Cal- culate the normality of the iodine solution. Factor Weights In order to facilitate the calculations, it is frequently of value in volumetric determinations to so adjust the weight of the sample to the strength of the solution that each cubic centimeter used in the titration will represent a definite amount of the constituent. Suppose a permanganate solution is standardized and each cubic centimeter found to be equivalent to 0.0045 gram of iron. If in the analysis 0.45 gram of the sample is weighed out and 22.30 c.c. used in the titration, the percentage of iron found would be 22.30x0.004"; . ■^ ^^ X 100 = 22.3 per cent. 0.45 For this particular weight of substance, therefore, each cubic centimeter of the solution used would indicate one per cent of the constituent sought. I90 QUANTITATIVE ANALYSIS If 0.90 gram of the sample were taken, each cubic centimeter would read 0.50 per cent; if 0.2250 gram, 2 per cent; and so on. In gravimetric processes, the weight of the sample may also be so selected that each milligram of the precipitate will represent a definite amount of the substance sought. How much pyrite must be taken for analysis in order that each milligram of BaSO^ shall represent o. i per cent of S.-" I mg. of BaS04 = 0.1373 mg. of S. 0.1373 mg. of S is o. I per cent of 0.1373 gram. If 0.1373 gram of sample is taken, therefore, each milligram of the precipitate will represent o. i per cent of sulphur. PROBLEMS 50. How much limestone must be taken for analysis for each milligram of calcium sulphate to represent o. i per cent of calcium oxide .•" 51. How much barite must be taken for analysis in order that each milligram of barium sulphate shall represent 0.20 per cent of BaO.? 52. One cubic centimeter of a solution of KMnO^ = 0.00075 gram of oxygen. How many grams of limestone should be weighed out in order that when titrating the calcium as the oxa- late each cubic centimeter of the permanganate solution used cor- responds to 0.5 per cent CaO .-" 53. How much of a feeding material must be taken for analysis by the Kjeldahl method in order that each cubic centimeter of N/4 HCl used to titrate the ammonia distilled over shall represent 0.5 per cent of proteid matter. Use 6.25 for conversion of nitro- gen to proteid matter. MISCELLANEOUS PROBLEMS 54. A mixture of the sulphates of sodium and potassium weighs I.I grams. It is dissolved in water and barium chloride solution added, a precipitate of BaS04 weighing 1.699 grams being obtained. Calculate the weight of each sulphate in the original mixture. 55. How many grams of a sample of fertilizer should be taken for analysis in order that each milligram of MggPgOy shall repre- sent 0.1 per cent of P? 0.2 per cent of P2O5.'' STOICHIOMETRY 191 56. A mixture of equal parts of sodium chloride and potassium chloride weighs 0.30 gram. How many cubic centimeters of platinic chloride solution containing o. i gram platinum per cubic centimeter will be necessary to completely change the sodium and potassium chlorides to the chlorplatinates ? 2 KCl + PtCl^ = KjPtCle. 57. 10 grams of a sample of soil were fused with sodium car- bonate, dissolved in hydrochloric acid after the removal of the silica, and the solution made up to 500 c.c. The phosphorus in 200 c.c. of the sample was precipitated and gave on ignition 0.072 gram of MggPgO^. lOO c.c. of the solution were titrated with dichromate solution for iron, 8.23 c.c. of the dichromate solution being used, (i c.c. KgCrgO^ = 0.00072 gram oxygen.) The iron, aluminium, and phosphorus in 100 c.c. of the solution were precipi- tated with ammonium hydroxide, and on ignition weighed 0.380 gram. Calculate the percentages of FcjOg, AlgOg, and P in the soil. 58. 1.2 grams of a silver coin were dissolved in nitric acid, and the silver precipitated with normal hydrochloric acid, 9.10 c.c. being used. What percentage of silver was in the coin 1 59. To a solution of Glauber's salt N/io BaClg solution was added until no more precipitate was formed, 14.70 c.c. of the solu- tion being used. Calculate the number of grams of anhydrous sodium sulphate in the solution. 60. 13.48 c.c. of a solution of standard hydrochloric acid were necessary to dissolve one gram of pure calcium carbonate. How many cubic centimeters of this solution must be taken to make a liter of normal acid .'' 61. How many cubic centimeters of N/2 HCl would be neces- sary to dissolve 0.3 gram of witherite (BaCOg) which contains as an impurity 7 per cent of quartz .'' 62. How many cubic centimeters of 5.5 normal ammonium hydroxide solution would be required to precipitate the aluminium in one gram of potassium alum } 63. How much NaOH, 85 per cent pure, must be added to 2 liters of a NaOH solution, i c.c. of which is equivalent to 0.041 gram HjSO^, in order to make the solution normal .' How much water should be added to make it N/3 .' 192 QUANTITATIVE ANALYSIS 64. 1.2 grams of pure ammonium chloride were dissolved ir water and heated with an excess of sodium hydroxide solution. The ammonia gas was conducted into water and neutralized with standard sulphuric acid, 18.30 c.c. being used. What was the normality of the sulphuric acid 1 65. A standard solution of HCl is analyzed by precipitating with AgNOgj 10 c.c. of the acid solution gave 0.22 gram AgCl. What is the normality of the acid .? What weight of calcite con- taining 0.3 per cent SiOg as an impurity will be dissolved by 50 c.c. of the acid .' 66. The total phosphorus in a sample of 0.22 gram of fertilizer was precipitated as ammonium phosphomolybdate. The precipi- tate was dissolved in 40 c.c. of N/3 potassium hydroxide solution and the excess of alkali titrated with standard nitric acid (i c.c. = 1. 021 c.c. of N/3 KOH), 14.20 c.c. being used. Calculate the percentage of phosphorus in the sample. 2(NH^)3PO^- 12M0O8+46KOH = 2 (NHJ2HPO4 + (NH J2M0O4 + 23 K2M0O4 + 22 HgO. 6^. A sample of 1.5 grams of feeding material was weighed out for the determination of total proteids by the Kjeldahl method. The ammonia was absorbed in 25.00 c.c. of N/2 HCl. The excess of acid in the absorption flask was neutralized with 12.00 c.c. of standard ammonium hydroxide solution (21.20 c.c. = 18.00 c.c. N/2 H CI). Calculate the percentage of total proteids in the sample. Use 6.25 as the factor for the conversion of nitrogen to proteids. 68. In the determination of the Reichert-Meissl number for butter fat as described on page no, a sample of 5.023 grams was taken for analysis. The total distillate containing the volatile acids was no c.c; 100 c.c. of this solution required 12.50 c.c. of KOH (i c.c. = 1.092 c.c. N/io KOH) for neutralization. Calculate the Reichert-Meissl number. 69. In the determination of the saponification number of butter fat, as described on page 115, 1.740 grams of the sample were taken for analysis. On titrating the blank, 69.70 c.c. of HCl were used, while the sample required 46.75 c.c. HCl. i c.c. HCl = 0.01014 gram of HCl. Calculate the saponification number. 70. A sample of 9.200 grams of butter fat was used for the de- termination of salt, which was extracted with water (see page 102) STOICHIOMETRY 193 and the solution made up to 200 c.c. 50 c.c. of the salt solution re- quired 14.40 c.c. of N/20 AgNOg solution for titration. Calculate the percentage of salt in the butter. 71. A sample of 0.5 gram of siderite (FeCOg), the only impurity in which is 3.5 per cent quartz, is dissolved out of contact with the air. How many cubic centimeters of permanganate solution (i c.c. =0.008 gram of H2C2O4 ■ 2 HgO) will be required to oxidize the iron t 72. 0.5 gram of a sample of ferrous ammonium sulphate which had been heated, was dissolved and titrated with N/io KMnO^, 16.80 c.c. being required. What percentage of the water of crystallization had been lost .'' 73. A sample of 0.5 gram of an iron ore was titrated for iron with N/io KMnO^ solution, 27.80 c.c. being used. If the student neglected to apply the calibration correction of +0.14 c.c, what would be the error in the percentage of iron as reported .'' 74. One cubic centimeter of a solution of KMn04 contains 0.00042 gram of available oxygen. How much oxygen will be available when the permanganate is used for titration in a neutral solution } 2 KMnO^ = K2O + MnOa + 3 O. 75. What weight of iron wire 99.7 per cent pure will be oxi- dized by the potassium dichromate formed from 0.35 gram of chrome iron (FeO • Cr203) the only impurity in which is 4.5 per cent silica .' 'j6. 25.00 c.c. of a solution of potassium permanganate, on being added to a solution of potassium iodide in sulphuric acid, liberated 0.33 gram of iodine. To what volume should one liter of the solu- tion be diluted to make it exactly tenth normal } yy. Some crystallized sodium thiosulphate (NajSgOg • 5 HgO) was exposed to the air and lost water of crystallization. A sample of 0.62 gram was dissolved in water and titrated with an iodine solution (i c.c. = 0.0049 gram AsjOg), 28.10 c.c. being used in the titration. What percentage of the water of crystallization had been lost.' How many grams of the sodium thiosulphate should be weighed out for a liter of N/io solution? 78. A sample of 0.5347 gram of pyrolusite was weighed out for analysis, into a retort. It was heated with hydrochloric acid and 194 QUANTITATIVE ANALYSIS the chlorine evolved passed into a solution of potassium iodide. The iodine solution was diluted to 250 c.c, and 100 c.c. titrated with N/io NagSgOg solution of which 21.90 c.c. were used. Cal- culate (a) the purity of the pyrolusite ; (5) the oxidizing power of one gram in terms of iron and crystallized oxalic acid. 79. In the determination of the iodine absorption number by the Hanus method described on page 117, 0.7380 gram of butter fat was taken for analysis. On titrating Blank required 32.40 c.c. NagSgOg solution, Sample required 11.30 c.c. Na2S20g solution. 20 c.c. K2Cr207 solution are equivalent to 16.20 c.c. Na2S20g. I c.c. of the K2Cr207 contains 0.00387 gram of the dichromate. Calculate the iodine absorption number. 80. Cupric salts in a solution of potassium iodide containing acetic acid are reduced to cuprous salts with the liberation of iodine. The iodine can then be titrated in the usual way with sodium thiosulphate solution. 2 Cu(C2Hg02)2 + 4 KI = CU2I2 + 4 KC2H3O2 + I2. How many grams of copper will furnish the iodine necessary to react with 18.00 c.c. of N/io Na2S203 solution 1 APPENDIX BOOKS OF REFERENCE Agricultural Analysis Allen, A. H. Commercial Organic Analysis. 4 Vols. Blythe, a. W. Foods, Their Composition and Analysis. 5th Edition (1903). Ingle. H. Manual of Agricultural Chemistry (1902). Jago, W. The Science and Art of Bread Making. Chemistry and Analysis of Wheat, Flour, etc. (1895). KoNiG, J. Untersuchung Landwirtschaftlich und Gewerblich Wichtiger Stofit (1906). Leach, A. E. Food Inspection and Analysis (1904). Leffman and Beam. Select Methods of Food Analysis (1905). Richmond, H. D. Dairy Chemistry. Sherman, H. C. Organic Analysis (1905). Snyder, H. Dairy Chemistry (1906). Contains an excellent Bibliography, page i6i. Soils and Fertilizers (1905). United States Department of Agriculture, Division of Chemistry, Bulletin No. 46 (1898), Methods of Analysis adopted by the Association of Official Agricultural Chemists. United States Department of Agriculture, Bureau of Chemistry, Bulletin No. 65 (1902), Provisional Methods for the Analysis of Foods adopted by the Association of Official Agricultural Chemists. Wiley, H. W. Foods and their Adulteration (1907). Principles and Practice of Agricultural Analysis. Vol. I. — Soils (1906). Vol. 2. — Fertilizers (New Edition in Press). Vol. 3. — Agricultural Products (1897). General Quantitative Chemical Analysis Classen, A. Ausgewahlte Methoden der Analytischen Chemie. 2 Vols. (1901). COHN. Indicators and Test Papers (1899). Fresenius. Quantitative Chemical Analysis. 2 Vols. Translated by Cohn (1904). Hillebrand, W. F. The Analysis of Silicate and Carbonate Rocks. United States Geological Survey, Bulletin No. 305. Julian, F. Quantitative Chemical Analysis (1902). Olsen, J. C. Quantitative Chemical Analysis (1904). Sutton, F. Volumetric Analysis, 9th edition. Treadwell-Hall. Analytical Chemistry, Vol. II, Quantitative Analysis. '95 196 QUANTITATIVE ANALYSIS The Application of the Modern Theories of Chetnistry to Quantitative Analysis Abegg, a. The Electrolytic Dissociation Theory. Translated by von Ende. BOTTGER, W. The Principles of Qualitative Analysis from the Standpoint of the Theory of Electrolytic Dissociation and the Law of Mass Action. Translated by Smeaton. OSTWALD, W. The Scientific Foundations of Analytical Chemistry. Translated by McGowan. Talbot and Blanchard. The Electrolytic Dissociation Theory. TABLE I Desk Reagents The reagents placed on the students' desks have the following concentrations. When concentrated and dilute acids are referred to in the procedure, these acids should be used. contains 23.82 per cent HCl. contains 8.16 per cent HCl. contains 69.80 per cent HNO3. contains 32 36 per cent HNO.,. contains 15.71 per cent H2SO4. contains 9.91 per cent NH,. HCl HCl HNO3 HNO3 H,SO., NH^OH concentrated sp. gr. 1. 12 dilute sp. gr. 1.04 concentrated sp. gr. 1.42 dilute sp. gr. 1.20 dilute sp.gr. I. II sp. gr. 0.96 TABLE n Laboratory Reagents Name Descrip- tion Formula Molecu- lar Weight Grams per Liter Specific Gravity at 15° C. Remarks, Preparation, etc. Acid, acetic HC2H3O2 60.03 99.S per cent. (Glacial) Acid, acetic Solution I.0412 30 per cent. Acid, hydro- Solution HCl 36.46 469.00 1.20 39.11 per cent. chloric Acid, hydro- 267.00 1. 12 23.82 per cent. 3 vols. chloric of acid sp. gr. 1.20 to 2 vols, water. Acid, hydro- Solution 2S5-0O I. IIS 22.86 per cent. chloric Acid, hydro- Solution 85.00 1.04 8.16 per cent. chloric Acid, liydro- Solution 18.23 N/2 chloric Acid, hydro- Solution 9.12 N/4 chloric APPENDIX 197 TABLE \\ — Continued Name Descrip- tion Formula Molecu- lar Weight Grams per Liter Specific Gravity at 15° c. Remarks, Preparation, etc. Acid, nitric HNO3 63.02 991.00 1.42 69.8 per cent Acid, nitric Solution 388.00 1.20 32.36 per cent. Made by diluting 2 vols. of sp. gr. 1.42 with 3 vols, of water Acid, oxalic [H,C204 • 2H,0] 126.05 Acid, salicylic [CeH^COH) COOH] 138.05 Acid, sulphuric H2SO4 98.08 1759.00 1.84 95.6 per cent H2SO4 Acid, sulphuric 1.82 Commercial — for Babcock test Acid, sulphuric Solution 702.00 1.40 50.11 per cent H2SO4 Acid, sulphuric Solution 175.00 I. II 15.71 per cent H2SO4 Acid, sulphuric Solution 12-5 1.25 per cent — for crude fiber Acid, tartaric H2C4H40e 150.05 Alcohol CjHsOH 46.05 0.8164 95 per cent by volume Alcohol Solution 0.8639 80 per cent by volume Ammonium car- [(NH4)2C03. I14.I bonate H2O] Ammonium NH4CI 53-49 chloride Ammonium Solution 200.00 Saturated with chloride KaPtCle- See page 201 Ammonium Solution [(NH4)3Ce 243-17 1.09-20° For preparation of citrate H6O7] solution see page 201 Ammonium Solution NH4OH 35-05 0.96 9.91 per cent NH3 hydroxide Ammonium Solution [(NH4)2Mo 196.08 6ogrs. For preparation of molybdate O4] MoOs solution see page 201 Ammonium NH4NO3 80.05 nitrate Ammonium Solution lOO.O nitrate Ammonium Solution [(NH4)2Q 142. 1 42.00 Saturated solution at oxahite Oj • H2O] 15° Arsenious oxide AsaOg 198.00 Asbestos For Gooch crucibles. For preparation see page 201 Barium chloride Solution [BaClj . 244-33 122.00 Barium hydrox- Solution [Ba(0H)2. 315-5 50 Saturated solution ide 8H2O] at 20° 198 QUANTITATIVE ANALYSIS TABLE II — Continued Name Descrip- tion Formula Molecu- lar Weight Grams per Liter Specific Gravity at 15° c. Remarks, Preparation, etc. Bromine water Solution Bra 15992 Water at room tem- perature saturated with liquid bromine with a few drops of bromine in the bot- tom of the bottle. Calcium carbon- CaCOs 100. 1 For standardizing so- ate lutions. Iceland spar, or the pure precipitated sub- stance Calcium chlo- CaCla III.OO Granular. For ab- ride sorbing moisture Chloroform CHCI3 119.36 Copper sulphate [CUSO4 • 5H2O] 249,74 Ether, ethyl (C2H5).20 74.08 For extracting fats. Dry. Distilled fi-om sodium FehUng's copper Solution 69.27 grams CuS04- solution 5 H2O per liter Fehling's alkali Solution 356 grams Rochelle solution, for salts and 100 grams lactose, by NaOH in one liter S oxh 1 e t's method Fehling's alkali Solution 356 grams Rochelle solution for salts and 250 grams use in Allihn's KOH in one liter method for dextrose Ferrous ammo- [FeS04 392.20 nium sulphate (NH,)2S04. 6H2O] Iodine I2 253-94 Iodine mono- Solution I Br 206.93 For preparation of so- bromide lution see page 116 Iron Fe 55-9 Pure, electrolytic Litmus paper Magnesite MgCOs 84.36 Magnesium mix- Solution [MgCl2-|- Dissolve no grams ture NH^Cl-f- NH4OH] of crystallized mag- nesium chloride (MgCl2-6H20)and 50 grams of am- monium chloride in 1500 c.c. of water, add 200 c.c. am- monium hydroxide (sp. gr. 0.96) and make up to two liters with water. APPENDIX TABLE \\ — Continued 199 Name Descrip- tion Formula Molecu- lar Weight Grams per Liter Specific Gravity at 15° t. Remarks, Preparation, etc. Magnesium ox- ide MgO 40.36 Malt extract Solution For preparation, see Mercury Mercuric chlo- ride Solution Hg HgClj 200.00 270.9 50.0 page 127 Methyl orange (orange No. Ill) Molybdic oxide Paraffine Solution M0O3 144.00 1. 00 Dissolve I gram in one liter of water Phenolphthalein Solution 5 -00 Dissolve 5 grams in one liter of 60 per cent alcohol. Filter Platinic chloride Solution ptcu 336-6 172.8 I c.c. of solution con- tains o.i gram of Potassium chro- mate Solution K2Cr04 194-4 100.00 platinum Indicator for determi- nation of chlorine Potassium di- K^Cr.iOr 294-S chromate Potassium ferri- cyanide Potassium hy- K3Fe(CN)e KOH 329.42 56.16 droxide Potassium hy- Solution KOH 40.00 Dissolve in one liter droxide of redistilled 95 per cent alcohol Potassium io- KI 166.12 dide Potassium io- Solution KI 150.00 dide Potassium per- KMnOi 158.IS manganate Potassium sul- Solution K.,S 110.36 40.00 phide Pumice Ignited at red heat and plunged into cold water. Kept under water Rochelle salt Silver nitrate Silver nitrate Solution Solution [KNaCiHi Oe^HaO] AgNOg 282.3 169.94 100.00 8.499 N/20 — for determina- tion of salt in butter Sodium acid NaHCO, 84.06 carbonate 200 QUANTITATIVE ANALYSIS TABLE II — Continued Name Descrip- tion Formula Molecu- lar Weight Grams per L,icer Specific Gravity at Remarks, Preparation, etc. Sodium ammo- Solution [NaNH4 209.16 100.00 nium hydro- HPOi • gen phosphate 4H2O] (microcosmic salt) Sodium carbon- NajCOg 106.10 ate Sodium dichro- [NaaCraOy- 29833 Commercial. For mate 2H2O] cleaning solution. See page 45 Sodium hydrox- NaOH 40.06 ide Sodium hydrox- Solution One part sodium hy- ide droxide to one part "■ of water Sodium hydrox- Solution 600.00 600 grams of commer- ide cial (Greenbank) alkali dissolved in one liter of water Sodium hydrox- Solution 20.03 N/2 ide Sodium hydrox- Solution 4.006 N/io ide Sodium hydrox- Solution 12.5 1.25 per cent. For ide crude fiber deter- minations Sodium oxalate NajCjOi 134.10 For preparation, see page 72 Sodium thiosul- [NaaSaOs • 248.30 phate 5H2O] Stannous chlor- Solution SnCla 189.9 Dissolve 30 grams of ide tin in 125 c.c. of HCl (sp. gr. 1.20). Dilute to 250 c.c. and filter. Add 250 cc. HCl (sp. gr. 1.12) and make up to I liter with water. Add a few pieces of granulated tin Starch (CeHi„05)„ For indicator, see page 80 Sugar (sucrose) Cl2H220n 342.18 Water — n itr o- H2O 18.016 See page 201 gen-free Woo], glass Zinc Zn 65-4 Dust Zinc Granulated Zinc For Jones Reductor APPENDIX 20 r Ammonium Citrate Solution Dissolve 370 grams of commercial citric acid in 1 500 c.c. of water ; nearly neu- tralize with ammonium hydroxide ; cool, add ammonium hydroxide until exactly neutral (tested with a saturated alcoholic solution of corallin) and dilute the vol- ume to 2 liters. Determine the specific gravity, which should be 1.09 at 20°. For another method of preparing this solution, see U.S. Department of Agricul- ture, Bull. No. 46, page 11. Asbestos for Gooch Crucibles Select a grade of asbestos having long fibers, soak it with water, shred it in a porcelain mortar. Treat it with hydrochloric acid (sp. gr. 1.12) for twelve hours, wash it by decanting with distilled water several times, allowing the fine particles of fiber to be decanted with the distilled water. Filter, wash well, dry, and ignite in a platinum dish with the blast lamp. Ammonium Chloride Solution saturated with Potassium Chlorplatinate Dissolve 100 grams of ammonium chloride in 500 c.c. of water, add from 5 to 10 grams of pulverized potassium chlorplatinate, allow to stand for six or eight hours, shaking at intervals. Allow the mixture to .settle overnight, then filter. The residue may be used for the preparation of a fresh supply. Ammonium Molybdate Solution Dissolve 100 grams of molybdic acid (M0O3) in 417 c.c. of ammonium hydrox- ide (sp. gr. o.g6) and .slowly pour the solution thus obtained into 1250 c.c. of nitric acid of specific gravity 1.20. Keep the mixture in a warm place for several days or until a portion heated to 40° deposits no yellow precipitate of ammonium phosphomolybdate. Preparation of Nitrogen-free Water Add to a carboy of ordinary distilled water enough bromine water to give it a distinct color. Allow to stand for a day or two, then add an excess of sodium carbonate and distill in a room free from ammonia fumes. The distillate will be ammonia-free. 202 QUANTITATIVE ANALYSIS TABLE III Apparatus for Desk Equipment Beakers, nests 0-6 .... Bottles, glass-stoppered, 2j liter Brush, camel's-hair Burette, glass stopcock, 30 c.c. Burette, pinchcock, 30 c.c. Burette holder Burners, adjustable Casseroles, 250 c.c. Cover-glasses, 50 mm. Cover-glasses, 75 mm. Cover-glasses, 125 mm. Crucibles, porcelain, No. 00 Cylinder, graduated, 50 c.c. Desiccator, for four crucibles Dishes, porcelain evaporating, 5 cm. diam. ... File .... Filter papers, ashless — 9 cm. Filter papers, ashless — 1 1 cm. Filter papers, qualitative, 9 cm. Filter papers, hardened, half form Flasks, Erlenmeyer, 250 c.c. Flasks, Jena Erlenmeyer, 125 c.c. Flasks, Kjeldahl, 500 c.c. . Flasks, plain. 250 c.c. . . . Flasks, plain, 500 c.c Flasks, volumetric, glass-stoppered, 250 c.c. .... . . Flasks, volumetric, glass-stoppered, 500 c.c ... Flasks, volumetric, glass-stoppered, 1000 c.c. ... .... Forceps, steel, 130 mm. Funnels, 75 mm., stem 200 mm. . Funnels, 25 mm., stem 50 mm. Indicators, 50 c.c. flasks of . . . I 10 25 4 4 2 2 2 2 Lock and key i Matches — boxes i Notebook i Pan, 15 cm. diameter .... i Paper, sheets of glazed .... 4 Pinchcock . . 1 Pipettes, 5 c.c I 10 c.c I 10 c.c. graduated i 25 c.c I 50 c.c. .... I 100 c.c. .... I Policemen, rubber . . .2 Reagent bottles, 30 c.c. for silver nitrate . . . ... I Rod, glass, feet of ... 2 Sponge I Stand, filter i Stands, iron, with two rings each .... . . . "> Stopper, rubber, No. 5 . . . . I Tongs, brass . . . . i Towel . . ... I Triangles, pipe stem, new form . 2 Tripods 2 Tubes, inner extraction, length 85 mm., diam. 25 mm 2 Tubes, inner extraction, length 70 mm., diam. 18 mm 2 Tubes, weighing, with corks . . 3 Tubing, glass, j" diam., feet 3 Tubing, rubber, J" diam., feet 6 Tubing, " -jiijj" diam., foot i Wire gauze, asbestos center . . 2 Wire, platinum, inches .... 3 APPENDIX 203 TABLE IV Specific Gravity of Hydrochloric, Nitric, and Sulphuric Acids G. Lunge Specific Si )ecific Gravity Per Cent by Wei ;lu Gi avity Per Cent by WciEht =""f a '¥ '> 7 320 240.0 342 257.4 364 275-3 386 294.2 299 223 5 321 240.7 343 258.2 36s 276.2 387 388 389 295.1 296-0 296.8 297-7 298.5 299.4 300.3 300 301 224 225 4 2 322 323 241.5 242.3 344 345 259.0 259.8 366 367 277.1 277.9 302 225 9 324 243.1 346 260.6 368 278.8 390 39' 392 393 303 226 7 325 243-9 347 261.4 369 279.6 304 227 S 326 244.6 348 262.3 370 280.5 305 228 3 327 245.4 349 263.1 371 281.4 394 301. 1 306 229 I 328 246.2 35° 263.9 372 282.2 395 302.0 3°7 229 8 329 247.0 351 264.7 373 283.1 396 302.8 308 230 6 330 247.7 352 265.5 374 283.9 397 303-7 309 231 4 331 248.5 353 266.3 375 284.8 398 304.6 310 232 -> 332 249.2 354 267.2 376 285.7 399 305-4 3" 232 9 333 250.0 355 268.0 377 286.5 400 306.3 TABLE VII Determination of Dextrose by Allihn's Method' Milli- grams of copper Milli- grams of dextrose Milli- grams of copper Milli- grams of dextrose Milli- grams of copper Milli- grams of dextrose Milli- grams of copper Milli- grams of dextrose Milli- grams of copper Milli- grams of dextrose 10 6.1 19 10-5 28 15.0 37 19.4 46 23-9 II 6.6 20 II.O 29 15-5 38 19.9 47 24.4 12 7-1 21 II. 5 30 16.0 39 20.4 48 24.^1 13 7-6 22 12.0 31 16.5 40 20.9 49 25-4 14 8.1 23 12.5 32 17.0 41 21.4 50 = 5-9 15 8.6 24 13.0 33 17-5 42 21.9 51 26.4 16 9.0 25 13-5 34 18.0 43 22.4 52 26.9 17 9-5 26 14.0 35 .8.5 44 22-9 53 27.4 18 lO.O 27 14.5 36 18.9 45 23-4 54 27-9 '^Principles and Practice of Agricultural Analysis, Vol. Ill, pp. 156-158. 208 QUANTITATIVE ANALYSIS TABLE N\\ — Continued Milli- Milli- Milli- Milli- Milli- Milli- Milli- Milli- Milli- Milli- grams of grams of grams of grams of grams of grams of grams of grams of grams of grams of copper dextrose copper dextrose copper dextrose copper dextrose copper dextrose 55 2S.4 96 4S.9 137 69.8 178 91. 1 I 219 112. 7 56 28,8 97 49-4 138 70.3 179 91.6 220 113.2 57 293 98 49.9 139 70.8 180 92.1 22 t II3-7 58 29.8 99 50.4 140 71-3 181 92.6 222 II4-3 59 30-3 100 50.9 141 71.8 182 93-1 223 II4.8 60 30. 8 lOI 51.4 142 72-3 183 93-7 224 II5-3 61 31-3 102 51.9 143 72.9 184 94.2 225 115.9 62 31.8 103 52.4 144 73-4 185 94-7 226 116.4 63 32-3 104 52.9 145 73-9 186 95.2 227 116. 9 64 32.8 105 53-5 146 74-4 187 95-7 228 II7-4 65 33-3 106 54.0 147 74-9 18S 96-3 229 iiB.o 66 33-8 107 54-5 148 75-5 189 96.8 230 118. 5 67 34-3 108 55.0 149 76.0 190 97-3 231 119. 68 34-8 109 55-5 150 76.5 191 97.8 232 119. 6 69 35-3 no 56.0 151 77.0 192 98.4 233 1 20. 1 70 35-8 III 56.5 152 77-5 193 98.9 234 120.7 71 36-3 112 57.0 153 78.1 194 994 235 121. 2 72 36.8. "3 57-5 154 78.6 195 100. 236 121.7 73 37-3 114 58.0 155 79.1 196 100.5 237 122.3 74 37-8 "5 58.6 156 79.6 197 lOI.O 238 122.8 75 38.3 116 59.1 157 80. 1 198 101.5 239 123.4 76 38.8 117 59.6 158 80.7 199 102.0 240 123.9 77 39-3 118 60.1 159 81.2 200 102.6 241 124.4 78 39-8 119 60.6 160 81.7 201 103. 1 242 125.0 79 40-3 120 61. 1 161 82.2 202 103.7 243 125.5 80 40.8 121 6r.6 162 82.7 203 104.2 244 126.0 81 41-3 122 62.1 163 83-3 204 104.7 245 126.6 82 41.8 123 62.6 164 83.8 205 i°5-3 246 127. 1 83 42.3 124 63.1 165 84-3 206 105.8 247 127.6 84 42.8 125 63.7 166 84.8 207 106.3 248 128. 1 85 43-4 126 64.2 167 85-3 208 106.8 249 128.7 86 43-9 127 64.7 168 85.9 209 107.4 250 129.2 87 44.4 128 65.2 169 86.4 210 107.9 251 129,7 88 449 129 65.7 170 86.9 211 108.4 252 130-3 89 45-4 130 66.2 171 87.4 212 109.0 253 130.8 90 45-9 131 66.7 172 87.9 213 109.5 254 1314 91 46.4 132 67.2 173 88.5 214 IIO.O 255 131-9 92 46.9 133 67.7 174 89.0 215 no. 6 256 132.4 93 47-4 134 68.2 175 89.5 216 III. I 257 '33-° 94 47-9 135 68.8 176 90.0 217 in. 6 258 133-5 95 48.4 136 69-3 177 90.5 218 112. 1 259 1 34- 1 APPENDIX 209 TABLE VII- - Continued Milli- grams of ! copper Milli- grams of dextrose Milli- Trams of copper Milli- ;rams of dextrose Milli- 2:rams of copper Milli- grams of dextrose Milli- jrams of copper Milli- grams of dextrose Milli- jrams of copper Milli- grams of dextrose 260 134.6 301 I57-I 342 179.8 383 203.1 424 226.9 261 •35-1 302 157.6 343 180.4 384 203.7 425 227.5 262 135-7 303 158.2 344 180.9 385 204.3 426 228.0 263 136-2 3°4 158.7 345 181. 5 386 204.8 427 228.6 264 136.8 305 159-3 346 182. 1 387 205.4 428 229.2 265 137-3 306 159.8 347 182.6 388 206.0 429 229.8 266 137-8 307 160.4 348 183.2 389 206.5 430 230.4 267 138-4 308 160.9 349 183-7 39° 207.1 431 231.0 231.6 268 138.9 309 161.5 35° 184-3 391 207.7 432 269 139-5 310 162.0 351 184.9 392 208.3 433 232.2 270 140.0 311 162.6 352 185.4 393 208.8 434 232.8 271 140.6 312 163. 1 353 186.0 394 209.4 435 233-4 272 141. 1 313 163-7 354 186.6 395 210.0 436 2339 273 141-7 314 164.2 355 187.2 396 210.6 437 234-5 274 142.2 315 164.8 356 187.7 397 211. 2 438 235-1 275 142.8 316 165-3 357 188.3 398 211. 7 439 235-7 236.3 236.9 276 143-3 317 165.9 358 188.9 399 212.3 440 -77 143.9 318 166.4 359 189.4 400 212.9 441 278 144.4 319 167.0 360 190.0 401 213-5 442 237-5 238.1 238.7 279 145.0 320 167.5 361 190.6 402 214. 1 443 280 U5-5 321 168.1 362 191. 1 403 214.6 444 281 146. 1 322 168.6 363 191. 7 404 215.2 445 239-3 282 146.6 323 169.2 364 192.3 405 215.8 446 239-8 283 147-2 324 169.7 365 192.9 406 216.4 447 240.4 284 147-7 325 170-3 366 193.4 407 217.0 448 241.0 241.6 285 148.3 326 170.9 367 194.0 408 217.5 449 286 148.8 327 171-4 368 194.6 409 218. 1 450 242.2 242.8 287 149.4 328 172-0 369 195. 1 410 218.7 451 288 149.9 329 172-5 370 195-7 411 219.3 452 243-4 289 150.5 330 173-I 371 196.3 412 219.9 453 244.0 244.6 290 151. 331 173-7 372 196.8 413 220.4 454 291 292 293 294 151. 6 152.1 152.7 '53-2 332 333 334 335 174.2 174-8 175-3 175-9 373 374 375 376 197.4 198.0 198.6 199.1 414 415 416 417 221-0 221-6 222.2 222.8 455 456 457 458 245.2 245.7 246-3 246.9 295 296 297 298 299 153-8 154-3 154-9 155-4 156.0 336 337 338 339 340 176.5 177.0 177.6 178. 1 178.7 377 378 379 380 381 199.7 200.3 200.8 201.4 202.0 418 419 420 421 422 223.3 223.9 224-5 225-1 225-7 459 460 461 462 463 247.5 248.1 248-7 249-3 249-9 300 156-5 341 179-3 382 202.5 423 226.3 2IO QUANTITATIVE ANALYSIS TABLE VIII Logarithms 7435 7513 7664 7738 7443 7520 7597 7672 7745 7451 7528 7604 7679 7752 7459 7536 7612 7686 7760 7466 7543 7619 7694 7767 7474 7551 7627 7701 7774 7 7 7 7 7 60 61 62 63 64 7782 7853 7924 7993 8062 7789 7860 7931 8000 8069 7796 7868 7938 8007 8075 7803 7875 7945 8014 8082 7810 7882 7952 8021 8089 7818 7889 7959 8028 8096 7825 7896 7966 8035 8102 7832 7903 7973 8041 8109 7839 7910 79?o 8048 8116 7846 7917 7987 8055 8122 2 2 2 2 2 3 4 3 4 3 3 3 3 3 3 4 4 4 4 4 5 5 5 S 5 6 6 6 S 5 6 6 6 6 6 65 66 67 68 69 8129 8195 8261 8325 8388 8136 8202 8267 8331 8395 8142 8209 8274 8338 8401 8149 8215 8280 8344 8407 8156 8222 8287 8351 8414 8162 8228 8293 8357 8420 8169 8235 8299 8363 8426 8176 8241 8306 8370 8432 8182 8248 8312 8376 8439 8189 8254 8319 8382 8445 2 2 2 2 2 3 3 3 3 3 3 3 3 2 3 4 4 4 4 4 5 5 5 4 4 5 5 S 5 5 6 6 6 6 6 70 71 72 73 74 8451 8513 8573 8633 8692 8457 8519 8579 8639 8698 8463 8525 8585 8645 8704 8470 8531 8591 8651 8710 8476 8537 8597 8657 8716 8482 8543 8603 8663 8722 8488 8549 8609 8669 8727 8494 8555 8615 8675 8733 8500 8561 8621 8681 8739 8506 8567 8627 8686 8745 2 2 2 2 2 2 3 2 3 2 3 2 3 2 3 4 4 4 4 4 4 4 4 4 4 5 5 5 6 5 5 S 5 77 78 79 8808 8865 8921 8976 f^56 8814 8871 8927 8982 8762 8820 8876 8932 8987 8768 8825 8882 8938 8993 8774 8831 8887 8943 8998 8779 8837 8893 8949 9004 8785 8842 8899 8954 9009 8791 8848 8904 8960 9015 8797 8854 8910 8965 9020 8802 8859 8915 8971 9025 2 2 2 2 2 2 3 2 3 2 3 2 3 2 3 3 3 3 3 3 4 4 4 4 4 5 5 5 5 S 80 81 82 83 84 9031 9085 9138 9191 9243 9036 9090 9143 9196 9248 9042 9096 9149 9201 9253 9047 9101 9154 9206 9258 9053 9106 9159 9212 9263 9058 9112 9165 9217 9269 9063 9117 9170 9222 9274 9069 9122 9175 9227 9279 9074 9128 9180 9232 9284 9079 9133 9186 9238 9289 2 2 2 2 2 2 3 2 3 2 3 2 3 2 3 3 3 3 3 3 4 4 4 4 4 5 S 5 5 5 85 86 87 88 89 9294 9345 9395 9445 9494 9299 9350 9400 9450 9499 9304 9355 9405 9455 9504 9309 9360 9410 9460 9509 9315 9365 9415 9465 95'3 9320 9370 9420 9469 9518 9325 9375 9425 9474 9523 9330 9380 9430 9479 9528 9335 9385 9435 9484 9533 9340 9390 9440 9489 9538 2 2 2 3 2 3 2 2 2 2 2 2 3 3 3 3 3 4 4 3 3 3 5 5 4 4 4 90 91 92 93 94 9542 9590 9638 9685 9731 9547 9595 9643 9689 9736 9552 9600 9647 9694 974' 9557 9605 9652 9699 9745 9562 9609 9657 9703 9750 9566 9614 9661 9708 9754 9571 9619 9666 9713 9759 9576 9624 9671 9717 9763 9581 9628 9675" 9722 9768 9586 9633 9680 9727 9773 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 4 4 4 4 4 95 96 97 98 99 9777 9823 9868 9912 9956 9782 9827 9872 9917 9961 9786 9832 9877 9921 9965 9791 9836 9881 9926 9969 9795 9841 9886 9930 9974 9800 9845 9890 9934 9978 9805 9850 9894 9939 9983 9809 9854 9899 9943 9987 9814 9859 9903 994S 999' 9818 9863 9908 9952 9996 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 3 4 4 4 4 4 212 QUANTITATIVE ANALYSIS TABLE IX Antilogarithms 10 •A Proportional Parts h 1 2 3 4. 5 6 7 8 9 5 1 ~ - 4 5 6 7 8 9 .00 1000 1002 1005 1007 1009 1012 1014 1016 1019 1021 I 2 2 2 OI 1023 1026 1028 1030 1033 1035 1038 1040 1042 1045 I I 2 2 2 02 1047 1050 1052 1054 1057 1059 1062 1064 1067 1069 I 2 2 2 03 1072 1074 1076 1079 1081 1084 1086 1089 109 1 1094 I 2 2 2 04 1096 1099 1 102 1 104 1 107 1109 III2 1114 H17 1119 2 2 2 2 05 1122 1125 1127 1 130 1132 "35 II38 1140 "43 1 146 2 2 2 2 06 1148 "5' "53 1156 "59 1161 1 164 1167 1169 1 1 72 2 2 2 2 07 1175 1178 1 180 1 183 1186 1189 1191 "94 "97 "99 2 2 2 2 .08 1202 1205 1208 1211 1213 1216 1219 1222 1225 1227 2 2 2 3 09 1230 1233 1236 1239 1242 1245 1247 1250 1253 1256 2 2 2 3 .10 1259 1262 1265 1268 1271 1274 1276 1279 1282 1285 2 2 2 3 II 1288 1 291 1294 1297 1300 ^y^i 1306 1309 1312 "315 2 2 2 2 3 12 1318 1321 1324 1327 1330 1334 1337 1340 1343 1346 2 2 2 2 3 13 1349 '352 1355 1358 1361 ■365 1368 1371 1374 1377 2 2 2 3 3 14 1380 1384 13S7 1390 1393 1396 1400 1403 1406 1409 2 2 2 3 3 15 1413 1416 1419 1422 1426 1429 1432 ■435 1439 1442 2 2 2 3 3 16 1445 1449 1452 1455 1459 1462 1466 1469 1472 1476 2 2 2 3 3 17 1479 1483 i486 1489 1493 1496 1500 i5°3 1507 1510 2 2 2 3 3 18 1514 1517 1521 1524 1528 1531 1535 1538 1542 IS45 2 2 2 3 3 '9 1549 '552 1556 1560 1563 1567 1570 1574 1578 1581 2 2 3 3 3 20 15S5 1589 1592 1596 1600 1603 1607 1611 1614 1618 2 2 3 3 3 21 1622 1626 1629 1633 1637 1641 1644 1648 1652 1656 2 2 2 3 3 3 22 1660 1663 1667 1671 1675 1679 1683 1687 1690 1694 2 2 2 3 3 3 23 1698 1702 1706 1710 1714 1718 1722 1726 1730 1734 2 2 2 3 3 24 '738 1742 1746 1750 '754 1758 1762 1766 1770 1774 2 2 2 3 3 25 1778 1782 1786 1791 1795 1799 1803 1807 1811 1S16 2 2 2 3 3 26 1820 1824 1828 1832 1S37 1S41 1845 1849 1854 1858 2 2 3 3 3 27 1862 1866 1871 1875 1879 1884 1888 1S92 1897 1901 2 2 3 3 3 28 1905 1910 1914 1919 1923 1928 1932 1936 1941 1945 2 2 3 3 4 29 1950 1954 •959 1963 1968 1972 1977 1982 19S6 1991 2 2 3 3 4 30 1995 2000 2004 2009 2014 2018 2023 2028 2032 2037 2 2 3 3 4 31 2042 2046 2051 2056 2061 2065 2070 2075 2080 2084 2 2 3 3 4 32 2089 2094 2099 2104 2109 2113 2118 2123 2128 2133 2 2 3 3 4 33 2138 2143 2148 2153 2158 2163 2168 2173 2178 2183 2 2 3 3 4 34 2188 2193 2198 2203 2208 2213 2218 2223 2228 2234 2 2 3 3 4 4 35 2239 2244 2249 2254 2259 2265 2270 2275 2280 2286 2 2 3 3 4 4 5 36 2291 2296 2301 2307 2312 2317 2323 2328 2333 2339 2 2 3 3 4 4 5 ^l 2344 2350 2355 2360 2366 237' 2377 2382 23S8 2393 2 2 3 3 4 4 5 38 2399 2404 2410 2415 2421 2427 2432 2438 2443 2449 2 2 3 3 4 4 5 39 2455 2460 2466 2472 2477 2483 2489 2495 2500 2506 2 2 3 3 4 5 5 40 2512 2518 2523 2529 2535 2541 2547 2553 2559 2564 2 2 3 4 4 5 5 41 2570 2576 2582 2588 2594 2600 2606 2612 2618 2624 2 2 3 4 4 5 5 42 2630 2636 2642 2649 2655 2661 2667 2673 2679 2685 2 2 3 4 4 5 6 43 2692 2698 2704 2710 2716 2723 2729 2735 2742 2748 2 3 3 4 4 5 6 44 2754 2761 2767 2773 2780 2786 2793 2799 2805 2812 2 3 3 4 4 5 6 45 2818 2825 2831 2838 2844 2851 2858 2864 2871 2877 2 3 3 4 5 5 6 46 2884 2891 2897 2904 291 1 2917 2924 2931 2938 2944 2 3 3 4 5 5 6 47 2951 2958 2965 2972 2979 2985 2992 2999 3006 3013 2 3 3 4 S 5 6 48 3020 3027 3034 3041 3048 3055 3062 3069 3076 3083 2 3 4 4 S 6 6 •49 3090 3097 3'o5 3112 3"9 3126 3'33 3141 3148 3155 2 3 4 4 5 6 6 APPENDIX 213 TABLE IX — Coniimteti s X Proportional Parts H 1 2 3 4. 5 (t 7 g 9 < 1 2 1 3 2 4 S 3 4 6 4 1 5 8 6 9 •50 3162 317° 3177 3'84 3192 3'99 3206 3214 3221 3228 7 51 3236 3243 3251 3258 3266 3273 3281 3289 3296 3304 2 2 3 4 S 5 6 7 5- 331 1 3319 3327 3334 3342 3350 3357 3365 3373 3381 2 2 3 4 5 5 6 7 53 3388 3396 3404 34>2 3420 3428 3436 3443 3451 3459 2 2 3 4 5 6 6 7 54 3467 3475 3483 3491 3499 3508 3516 3524 3532 3540 2 2 3 4 S 6 6 7 55 354S 3556 3565 3573 3581 3589 3597 3606 3614 3622 2 2 3 4 5 6 7 7 56 3631 3639 3648 3656 3664 3673 3681 3690 3698 3707 2 3 3 4 5 6 7 8 57 3715 3724 3733 3741 3750 3758 3767 3776 3784 3793 2 3 3 4 5 6 7 8 .58 3802 381 1 3819 3828 3837 3846 3855 3864 3873 3882 2 3 4 4 5 6 7 8 59 3890 3899 3908 3917 3926 3936 3945 3954 3963 3972 2 3 4 5 5 6 7 8 60 3981 3990 3999 4009 4018 4027 4036 4046 4055 4064 2 3 4 5 6 6 7 8 61 4074 4083 4093 4102 4111 4121 4130 4140 4150 4159 2 3 4 5 6 8 9 .62 4169 4178 4188 4198 4207 4217 4227 4236 4246 4256 2 3 4 5 6 8 9 63 4266 4276 4285 4^95 4305 4315 4325 4335 4345 4355 2 3 4 5 6 8 9 64 4365 4375 4385 4395 4406 4416 4426 4436 4446 4457 2 3 4 S 6 8 9 65 4467 4477 4487 4498 4508 45'9 4529 4539 4550 4560 2 3 4 5 6 8 9 66 4571 4581 4592 4603 4613 4624 4634 4645 4656 4667 2 3 4 5 6 910 67 4677 4688 4699 4710 4721 4732 4742 4753 4764 4775 2 3 4 S 8 g'lo 68 4786 4797 4808 4819 4831 4842 4853 4864 4875 4887 2 3 4 6 8 9 10 .69 4898 4909 4920 4932 4943 4955 4966 4977 4989 5000 2 3 s s 8 9 10 .70 5012 5023 5035 5°47 5058 5070 5082 5093 5105 5"7 2 4 5 6 8 911 •71 5129 5140 5152 5164 5'76 5188 5200 5212 5224 5236 2 4 5 6 8 10 II .72 5248 5260 5272 5284 5297 5309 5321 5333 5346 535S 2 4 5 6 9 10 11 73 537° 5383 5395 5408 5420 5433 5445 5458 547° 5483 3 4 5 6 8 9 10 II 74 5495 5508 5521 5534 5546 5559 5572 5585 5598 5610 3 4 5 6 8 9 10 12 75 5623 5636 5649 5662 5675 5689 5702 5715 5728 5741 3 4 S 7 8 9 10 la 76 5754 5768 5781 5794 5808 5821 5834 5848 5861 5875 3 4 5 7 8 9 II I? 77 5888 5902 5916 5929 5943 5957 5970 5984 5998 6012 3 4 5 7 8 10 II 12 78 6026 6039 6053 6067 6081 6095 6109 6124 6138 6152 3 4 6 7 8 10 II 13 79 6166 6180 6194 6209 6223 6237 6252 6266 6281 6295 3 4 6 7 9 10 II 13 80 6310 6324 6339 6353 6368 6383 6397 6412 6427 6442 3 4 6 7 9 10 12 13 8i 6457 6471 6486 6501 6516 6531 6546 6561 6577 6592 2 3 5 6 8 9 XI 12 14 82 6607 6622 6637 6653 6668 6683 6699 6714 6730 6745 2 3 5 6 8 9 II 12 14 83 6761 6776 6792 6808 6823 6839 6855 6871 6887 6902 2 3 S 6 8 9 II 13 14 84 6918 6934 6950 6966 6982 6998 7015 7031 7047 7063 2 3 5 6 8 10 II 13 15 ll 7079 7096 7112 7129 7145 7161 7178 7'94 721 1 7228 2 3 5 7 8 10 12 13 15 86 7244 7261 7278 7295 73" 7328 7345 7362 7379 7396 2 3 5 7 8 10 12 13 15 87 7413 7430 7447 7464 7482 7499 75'6 7534 7551 7568 2 3 5 7 9 10 12 14 16 88 7586 7603 7621 7638 7656 7674 7691 7709 7727 7745 2 S 7 9 II 12 14 16 89 7762 7780 7798 7816 7834 7852 7870 7889 7907 7925 2 5 7 9 II 13 14 16 90 7943 7962 7980 7998 8017 8035 8054 8072 8091 8110 2 6 7 9 II 13 15 17 91 8128 8147 8166 8185 8204 8222 8241 8260 8279 8299 2 6 8 9 II 13 15 17 92 8318 8337 8356 8375 8395 8414 8433 8453 8472 8492 2 6 8 10 12 14 15 17 93 8511 853' 8551 8570 8590 8610 8630 8650 8670 8690 2 6 8 10 13 ■4 16 18 94 8710 8730 8750 8770 8790 8810 8831 8851 8872 8892 2 6 8 10 12 14 16 18 95 8913 8933 8954 8974 8995 9016 9036 9057 9078 9099 2 6 8 10 12 15 17 19 96 9120 9141 9162 9183 9204 9226 9247 9268 9290 93" 2 6 8 II 13 15 17 19 97 9333 9354 9376 9397 9419 9441 9462 9484 9506 9528 2 7 9 II 13 15 17 20 98 9550 9572 9594 9616 9638 9661 9683 9705 9727 9750 2 7 9 II 13 16 18 20 ■99 9772 9795 9817 9840 9863, 9886 9908 9931 9944 9977 2 7 5 II 14 i6 18 20 214 QUANTITATIVE ANALYSIS TABLE X Combining and Atomic Weights 1907 = 16. 0=16. Aluminium . . . Al 27.1 Neodymium . . . . Nd ■143.6 Antimony . . . . Sb 120.2 Neon . . . . Ne 20 Argon . . . A 39-9 Nickel . . . . Ni 58.7 Arsenic . . . . As 75.0 Nitrogen . . N 14.01 Barium .... . Ba 1374 Osmium . . . . Os 191 Bismuth . . . . Bi 208.0 Oxygen . . . . 16.00 Boron . . . B II.O Palladium . . Pd 106.5 Bromine . Br 79.96 Phosphorus . P 31.0 Cadmium . Cd 1 12.4 Platinum . . . Pt 194.8 Caesium . . Cs 132.9 Potassium . . K 39-15 Calcium . . . Ca 40.1 Praseodymium Pr 140.5 Carbon . . C 12.00 Radium . . Rd 225 Cerium .... . Ce 140.25 Rhodium . . . . Rh 103.0 Chlorine . . . . CI 35-45 Rubidium . . . . Rb 85.5 Chromium . . . Cr 52.1 Ruthenium . . . Ru 101.7 Cobalt . . . Co 59-0 Samarium . . . . Sa 150-3 Columbium . . . Cb 94 Scandium . . . . Sc 44-1 Copper. . . . Cu 63.6 Selenium . . . . Se 79.2 Erbium . . . . Er 1 66 Silicon . . . . . Si 28.4 Europium . . . . Eu 152 Silver • • Ag 107-93 Fluorine . . . F 19.0 Sodium . . . . Na 23-05 Gadolinium . . . . Gd 156 Strontium . Sr 87.6 Gallium . Ga 70 Sulphur . S 32.06 Germanium . . . Ge 72.5 Tantalum . . Ta 181 Glucinum . . Gl 9.1 Tellurium . . Te 127.6 Gold . . . . Au 197.2 Terbium . . Tb 159.2 Helium . . . . He 4.0 Thallium . Tl 204.1 Hydrogen . . . H 1.008 Thorium . . . . Th 232.5 Indium. . . . . In "5 Thulium . . . . Tm 171 Iodine .... . I 126.97 Tin . . . Sn 1 19.0 Iridium . . . . Ir 193.0 Titanium . . . . Ti 48.1 Iron . . . . . Fe 55-9 Tungsten . . W 184 Krypton . . . . Kr 81.8 Uranium . . . . U 238.5 Lanthanum . . . La 138.9 Vanadium . . V 51.2 Lead .... . Pb 206.9 Xenon . . . . Xe 128 Lithium . . . . Li 7-03 Ytterbium . . . . Yb 1730 Magnesium . . • Mg 24.36 Yttrium . . . . Yt 89.0 Manganese . . . Mn 55.0 Zinc .... . . Zn 65.4 Mercury . . . ■ • Hg 200.0 Zirconium . . . Zr 90.6 Molybdenum . . . . Mo 96.0 ANSWERS TO PROBLEMS 1. NaaCOs. 2. KaPtCle. 3. K.CrOi. 4. (NH4)2Mo04. 5. CiHeOs. 6. Zn 40.51 per cent. ZnO 50.41 per cent. 7. Fe 14.25 per cent. FeO 18.33 PS'' cent. S 16.35 P^"^ cent. SO3 40.83 per cent. H2O 27.56 per cent. 8. ZnO 53.41 per cent. P2O6 46.59 per cent. 9. CaO 48.15 per cent. SiO.2 51.85 per cent. 10. a. 0.8999 grani. b. 0.6376 gram. 0.27S4 gram. c. 0.4562 gram. d. 0.21 14 gram. «• 0.7357 gram. / 1. 1397 grams. 11. 0.5475 gram. 12. 0.41 13 gram. 13. 0.5412 gram. 14. 0.6169 gram. 15. 54.79 per cent. 16. 98.02 per cent. 17. 11.90 per cent. 18. K 1.93 per cent. Na 4.46 per cent. 19. Ca 0.2257 gram. Mg 0.1840 gram. 20. PbO 1.0637 grams. BaO 0.5613 gram. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31, 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 215 8.98 per cent. 3.06 c.c. 165.83 c.c. 3.04 c.c. 4.30 c.c. 91.87 per cent. 96.23 per cent. 99.93 per cent. Na20 61.70 per cent. NaOH 47.07 per cent. Na2C03 43.06 per cent. 14.47 P^r cent. 69.43 psr cent. 22.74 per cent. 29.59 per cent. 2.27 c.c. Normal. 0.9778 Normal. 0.6665 gram. 13.66 per cent. u. 0.001256 gram; 11.37 c.c. b. 0.001249 gram; 11.46 c.c. c. 0.001259 gram; 11.370.0. 99.61 per cent. 99.63 per cent. CaO 50.43 per cent. u. 0.0007943 gram; 18.02 c.c. b. 0.0007966 gram; 17.97 c.c. a. 0.0138 gram of Oxyg^ per c.c. b. 2.93 per cent H2O2. 0.01061 gram. li. 0.01230 gram. b. 0.09687 Normality Factor 24.48 per cent. ;cn 2l6 ANSWERS 48. 67.25 per cent. 49. 0.0105 1 gram. 0.08275 Normality Factor. 50. 0.4120 gram. 51. 0.3285 gram. 52. 0.5259 gram. 53. 0.4378 gram. 54. K0SO4 0.3543 gram. Na2S04 0.7457 gram. 55. For 0.1 per centP, 0.2784 gram. For 0.2 per cent P2O6, 0.3195 gram. 56. 4.46 CO. 57. FeO 2.66 per cent. AI2O3 14.89 per cent. P 0.501 per cent. 58. 81.85 per cent. 59. 0.1045 gram. 60. 674.7 c.c. 61. 5.65 c.c. 62. 1. 15 c.c. 63. a. 15.45 grams. b. 3016.5 c.c. 64. 1.226 Normality Factor. 65. a. 0.1534 Normality Factor. b. 0.3851 gram. 66. 5.21 per cent. 67. 43.23 per cent. 68. 14.95 Reichert-Meissl Number. 69. 206.0 Saponification Number. 70. 1.83 per cent. 71. 26.05 P^"^ cent. 72. 87.50 per cent. 73. 0.16 per cent too low. 74. 0.000252 gram per c.c. 75. 0.5018 gram. 76. 1039.6 c.c. 77. a. 28.21 per cent. b. 22.289 grams. 78. a. 44.54 per cent. b. 0.5724 gram Fe. 0.6453 gram Oxalic Acid. '9- 35'35 Iodine Absorption Number. 80. 0.1 145 gram. INDEX Acidimetry, 51. Acids, specific gravity, tables of, 203. Adams paper coil method for fat in milk, 88. Alkalimetry, 51. Aliihn's method for carbohydrates, 124. Alummium, determination of, 37. in soils, 150. Ammonia, specific gravity, tables of, 205. Answers to problems, 215-216. Antiloyarithms, talile of, 212-213. Available oxygen, 65. Babcock method for fat in milk, 90. Balance, 16-20. exercises with, 22-23. Balancing equations, 178. Bleaching powder, estimation of available chlorine in, 82. Books of reference, 195. Bumpinj,'. 9, 156. Butter, analysis of, 100-118. Calcium, determination of, 32, 73, 152. separation from magnesium, 33. Calibration, of burettes, 45. curve, 48. Carbohydrates in cereals, 120, 123. Carbon dioxide, determination of, 156. Caustic alkali, determination of, 66. Cereals, 119. Chlorine, determination of, 24, 82, 102. Clerget's inversion method for sucrose, 124. Crucibles, 14. Gooch, 57, 58. Desiccatc^rs, 5. Desk, equipment, 202. reagents, .concentration of, 196. Dextrin, determination of, 125. Dextrose, determination of, 124, tables for 207, 209. Diastase method for starch, 126. Empirical formula, 162. End point, 52. Factor weights, calculation of, 189. Factors, 165. Fat, in milk, 88, 92. in butter, composition of, 103. Fatty acids, determination of, no, 112, 113- Feeding materials, analysis of, 119, 122. Fertilizers, analysis of, 130. Filtration, 12. by means of suction, 37. Gravimetric analysis, 22. calculations for, 163. Humus, 154. Hydrogen peroxide, purity of, 73, 84. Indicators, 52. Indirect methods, calculation for, 167. lodimetry, 78. calculations for, 187. Iodine absorption number, determination of, u6. Iron, determination of, 74, 77, 150, 153. Jones reductor, 70. Kjeldahl method for nitrogen, 94, 129, 138. Lactometers, 87. Lactose, by Soxhlet's method, table for, 206. Logarithms, table of, 210— 211. Magnesium, determination of, 33, 152. Manganese, determination of, 151. Milk, analysis of, 85. Nitrogen, determination of, 138, 155. Normal solutions, 49, 50. 217 21i INDEX Normality factor, 59. Notebooks, 2, 53. Oleomargarine, 105, 115, 118. Operations of quantitative analysis, 6-14. Oxalates, determination of purity of, 72. Oxidation and reduction, calculations for, 178-185. Oxidation processes, 64. Percentage composition, calculation of, 162. Phosphorus, determination of, 132, 136, 150, 151. Platinum, care of, 15. Potassium, determination of, 140, 153. Precipitates, colloidal, 12. crystalline, n. drying and ignition of, 14. Precipitation, 10. Problems, J62, 163, l66, 168, 171, 177, 186, 188, 190. Proteids, 94, 129. Pyrolusite, determination of available oxy- gen in, 83. Questions on equations, 183, 1S8. Reagents, 4. laboratory, table of, 196-201. Saliva method for starch, 127. Sampling, 6, 86, loi, 121, 131, 145. Saponification numbers, 114. Siderite, determination of iron in, 74, 77. Silica, 148. Sodium, determination of, 153. Soil, analysis of, 142. constituents of, 142, 145. Solutions, normal, 49. preparation for iodimetry, 79. for oxidation and reduction, 67, 79. standard, 49. Specific gravity, 170. of butter fat, 106. Standardization of solutions, acid, 57, 62. alkaU, 59. iodine, 80. methods of, 54. potassium dichromate, 76. potassium permanganate, 68. Starch, 125, 127. Stirring rods, 6. Stoichiometry, 161. Stone's method for carbohydrates, 123. Sucrose, 124. Sulphur, determination of, 29, 152. Titration, 52. of acid against the alkali, 56. Volumetric analysis, 40. apparatus, 40, 41. calibration of, 42. calculations, 171. Wash bottles, 6. Washing of precipitates, 13. Weighing, precautions in, 20. T HE following pages contain advertisements of books on kindred subjefts. STANDARD BOOKS ON CHEMISTRY PUBLISHED BY THE MACMILLAN COMPANY ABEGG AND HERZ. Practical Chemistry : An Experimental Introduction to Labo- ratory Practice and Qualitative Analysis from a Physico-Chemical Standpoint. By R. Abegg and W. Her?,, of the University of Breslau. Authorized translation by H. B. Calvert, B.Sc. (Vic), A.I.C. With Three Tables. 12 + I iS pages, j2mo, cL, $r.jo net ARRHENIUS. Immunochemistry. The Application of the Principles of Physical Chemistry to the Study of the Biological Antibodies. By Svante Arrhenius. xi -\- jog pages, indexes, j 3nio, cl., $i.6o net BAILEY. A Text-Book of Sanitary and Applied Chemistry; or, The Chemistry of Water, Air, and Food. By E. H. S. Bailey, Ph.D., Professor of Chemistry, Uni- versity of Kansas. 20 + j^5 pages, i2mo, cl., S1.40 net BEEBE and BUXTON. Outlines of Physiological Chemistry. By S. P. Beebe, Ph.D., Physiological Chemist to the Huntington Fund for Cancer Research, and B. H. Buxton, M.D., Professor of Experimental Pathology, Cornell Medical College. ^95 P^S^^f I37H0, cL, $1.^0 net BEHRENS. A Manual of Microchemical Analysis. By Professor H. Behrens, of the Polytechnic School in Delft, Holland. With an Introductory Chapter by Pro- fessor John W. Judd, F.R.S., of the Royal College of Science. With 84 Illustrations, drawn by the Author. 11 + 2.^6 pages, i2mo, cl., S^-S^ net (^postage Sc.) BLOUNT. Practical Electro-Chemistry. By Bertram Blount, F.I.C, F.C.S., Assoc. Inst. C.E., Consulting Chemist to the Crown Agents for the Colonies. Second Impression. COHNHEIM. Chemistry of the Proteids. By Dr. Cohnheim. Prepared from the Second German Edition by Dr. Gustav Mann, Author of " Physiological Histology." 8 + boo pages, 8vo, $3.73 net COMEY. A Dictionary of Chemical Solubilities, Inorganic. By Arthur Messinger Comev, Ph.D., formerly Professor of Chemistry, Tufts College. 20 + j/J pages, Svo, cl., Sj-oo net FLEISCHER. A System of Volumetric Analysis. By Dr. Emtl Fleischer. Trans- lated, with Notes and Additions, from the Second German Edition, by M. M. Pattison Muir, F.R.S.E., Assistant Lecturer on Chemistry, The Owens College, Manchester. ig \ 274. pages, isino, il., cl., $2.00 net GATTERMANN. The Practical Methods of Organic Chemistry. By Ludwig Gat- termann, Ph.D., Professor in the University of Freiburg. Authorized Translation by William B. Schober, Ph.D., Instructor in Lehigh University. Second American from Fourth German Edition. '5 + 359 P<^S"> '^"'o, ''■. <^l-t $i.(>o net I STANDARD BCX)KS ON CHEMISTRY — Cbn«naecf HEMPEL. Methods of Gas Analysis. By Dr. Walther Hempel, Professor of Chem- istry in Dresden Technische Hochschule. Translated from the Third German Edition and Considerably Enlarged by L. M. Dennis, Professor of Analytical and Inorganic Chemistry in Cornell University. New Edition. i() + ^90 pages, i2mo, il., cL, $2.2^ net HERTER. The Common Bacterial Infections of the Digestive Tract, and the Intoxications Arising from Them. By C. A. Herter, M.D., Professor of Phar- macology and Therapeutics in Columbia University, Consulting Physician to the City Hospital, New York. X -\- j6o pages, index, 8vo, cl., $1.^0 net; by viail, $1.62 net HILLYER. Laboratory Manual : Experiments to Illustrate the Elementary Principles of Chemistry. By H. W. Hillyer, Ph.D., Assistant Professor of Organic Chemistry in the University of Wisconsin. 6 + 1^8 pages, 8vo, cl., go cents net JONES. The Theory of Electrolytic Dissociation and Some of its Applications. jz + 28g pages, i2mOyCl., $1.60 net Elements of Physical Chemistry. Elements of Inorganic Chemistry. Principles of Inorganic Chemistry. / / -)- 565 pages, 8vo, cl., $4.00 net '3 + 343 pages, Svo, cl., $1.25 net 20 + ^21 pages, $3.00 net All by Harry C. Jones, Professor of Physical Chemistry in the Johns Hopkins University, Baltimore. LASSAR-COHN. A Laboratory Manual of Organic Chemistry. A Compendium of Laboratory Methods for the Use of Chemists, Physicians, and Pharmacists. By Dr. Lassar-Cohn. Translated from the Second German Edition by Alexander Smith, , B.Sc, Ph.D. ig + 20^ pages, Svo, cl., $2.2^ net LEBLANC. The Elements of Electro-Chemistry. By Max LeBlanc, Professor of Chemistry in the University of Leipzig. Translated by W. R. Whitney, Instructor of Chemistry in the Massachusetts Institute of Technology, Boston. New Edition, revised from the Third German Edition. JO + 2S2 pages, i2mo, cl., $r.^0 net LENGFELD. Inorganic Chemical Preparations. By Felix Lengfei.d, formerly Assistant Professor of Inorganic Chemistry in the University of Chicago. g -\- S5 pages, i2mo, cl., bo cents net LEWKOWITSCH. Chemical Technology and Analysis of Oils, Fats, and Waxes. Third Edition. Entirely Rewritten and Enlarged. Eighty-eight Illustrations and Numerous Tables. Two Volumes. lb -\- J2 -\- I IJ2 pages, Svo, il., cl., $12.00 net LEWKOWITSCH. Laboratory Companion to Fats and Oils Industries. By Dr. J. LEWKOWITSCH, M.A., F.I.C., Examiner in Soap Manufacture and in Fats and Oils to the City and Guild of London Institute. 12 + igy pages, Svo, cl., $i.go net 2 STANDARD BOOKS ON CHEMISTRY — Cbnfmuerf LIVERSIDGE. Tables for Qualitative Chemical Analysis, Arranged for the Use of Students by A. Liversidge, M.A., LL.D., F.R.S., Professor of Chemistry in the University of Sydney. Second Edition. 12b pages^ 8vOf cl,, $i.^0 7iet LUPTON. Chemical Arithmetic. With Twelve Hundred Examples. By Sydney LupTON, F.C.S. 12 + ly I pages, ibmo, cL, $i.io net MENSCHUTKIN. Analytical Chemistry. By N. Menschutkin, Professor in the University of St. Petersburg. Translated from the Third German Edition, under the Supervision of the Author, by James Locke. 13 + ^12 pages, 8vo, cL, $4..oo net MEYER. History of Chemistry from the Earliest Times to the Present Day. By Ernest von Meyer, Ph.D. Translated by George MacGowan, Ph.D. 8vo, cl., $4.Jo net MILLER. The Calculations of Analytical Chemistry. By Edmund H. Miller, Ph.D., Professor of Analytical Chemistry in Columbia University. Third Edition. Revised and Enlarged. 10 + 201 pages, Svo, cl., $i,^o tiet MORGAN. Qualitative Analysis as a Laboratory Basis for the Study of General Inorganic Chemistry. By William Conger Morgan, Ph.D. (Yale), Assistant Professor of Chemistry in the University of California, (c.) 14 + 3'S P'^g^^i ^'""t '^-t '^'i $i'9o net NERNST. Theoretical Chemistry from the Standpoint of Avogadro's Rule and Thermodynamics. By Professor Walter Neknst, Ph.D., of the University of Gottingen. Revised by the Fourth German Edition. 24. + yy I pages, Svo, cl., $3.7 J net NOYES. Qualitative Chemical Analysis, with Explanatory Notes. By Arthur A. Noyes, Ph.D., Professor of Theoretical Chemistry in the Massachusetts Institute of ■ Technology. Third Revised and Enlarged Edition. Sg pages, Svo, cl., $1.2^ net OSTWALD. The Scientific Foundations of Analytical Chemistry Treated in an Elementary Manner. Translated by George MacGowan, Ph.D. jy + Tgg pages, Svo, cl., $2.00 net Manual of Physico-Chemical Measurements. Translated by James Walker, D.Sc, Ph.D. 12 + 2 j; J pages, il., cl., $2.2 j net The Principles of Inorganic Chemistry. Translated with the Author's Sanction by Alexander Findlay, M.A., B.Sc, Ph.D. With 122 Figures in the Text. 2y + ySj pages, Svo, cl., $6.00 net All by Wilhelm Ostwald, Professor of Chemistry in the University of Leipzig. REYCHLER. Outlines of Physical Chemistry. By A. Revchler, Professor of Chemistry in the University of Brussels. Authorized Translation by John McCrae, Ph.D. (Heid.). With 52 Illustrations. Second Edition. 16 Ar 368 pages, cl., $1.00 net 3 STANDARD BOOKS ON CHEMISTRY. Continued ROLFE. The Polariscope in the Chemical Laboratory. An Introduction to Polar- imetry and its Application. By George William ROLfE, A.M., Instructor in Sugar Analysis in the Massachusetts Institute of Technology. 7 + J30 pages, i2mo, il., cl.. Si. go net ROSCOE AND SCHORLEMMER. A Treatise on Chemistry. By Sir Henry E. ROSCOE and C. Schorlemmer, F.R.S. Vol. I — The Non-MetalUc Elements. New Edition. Completely Revised by Sir H. Roscoe, Assisted by Drs. Colman and Harden. 12 + g;^ I pages, 8vo, cl., Sj-OO net SCHXABEL. Handbook of Metallurgy. By Dr. Carl Schnabel, Konigl. Preuss. Bergrath Professor of Metallurgy. Translated by Henry Louis, M.A., A.R.S.M., F.I.C., etc.. Professor of Mining at Armstrong College, Newcastle upon-Tyne. Second Edition. Vol. I — Copper, Lead, Silver, Gold. Illustrated with 715 Figures, (c.) 20 + 112^ pages, 8vo, il,, cl., Sd.^o net SCHULTZ and JULIUS. A Systematic Survey of the Organic Colouring Matters. Founded on the German of Drs. G. Schultz and P. Julius. Second Edition. Re- vised Throughout and Greatly Enlarged by Arthur G. Green, F.I.C., F.C.S. 10 + 280 pages, imperial 8vo, cl., S7.00 net SHERMAN. Methods of Organic Analysis. By Henry C. Sherman, Ph.D., Adjunct Professor of Analytical Chemistry in Columbia University. 24^ pages, Svo, cl., $1.75 net (^postage 14c.') TALBOT. An Introductory Course of Quantitative Chemical Analysis, with Ex- planatory Notes and Stoichiometrical Problems. By Henry P. Talbot, Ph.D., Professor of Inorganic and Analytical Chemistry in the Massachusetts Institute of Technology. ^53 pages, 8vo, cl., S^.SO net TALBOT and BLANCHARD. The Electrolytic Dissociation Theory. With Some of its Applications. An Elementary -Treatise for the Use of Students in Chemistry. By Professor H. P. Talbot and Arthur A. Blanchard, both of the Massachusetts Institute of Technology. 4 + 84 pages, Svo, cl., $i.2j net THORP. Outlines of Industrial Chemistry : A Text-Book for Students. By Frank Hall Thorp, Ph.D., Assistant Professor of Industrial Chemistry in the Massachu- setts Institute of Technology. Second Edition. Revised and Enlarged, and Includ- ing a Chapter on Metallurgy by Charles D. Demond, S.B., Testing Engineer of the Anaconda Mining Company. 26 -I- 618 pages, 8vo, il., cl., $S-75 "'t WALKER. Introduction to Physical Chemistry. By James Walker, D.Sc, Ph.D., F.R.S., Professor of Chemistry in University College, Dundee. Fourth Edition. 12 -H 387 pages, 8vo, cl., S3.2J net YOUNG. Fractional Distillation. By Sydney Young, D.Sc, F.R.S. With 72 Illustrations. 12 ■\- 284 pages, i2mo, il., cl., $2.00 net THE MACMILLAN COMPANY PUBLISHEES, 64-66 PIFTH AVENXTE, NEW YORK