LIBRARY UNIVERSITY OF CALIFORNIA. Received. Accessions No. jj/. Shelf THE LABORATORY GUIDE. THE LABORATORY GUIDE A MANUAL OF PRACTICAL CHEMISTRY FOR COLLEGES AND SCHOOLS SPECIALL Y ARRANGED FOR AGBICULTUBAL STUDENTS BY ARTHUR HERBERT CHURCH, M.A., F.R.S., PROFESSOR OP CHEMISTRY IN THE ROYAL ACADEMY OP ARTS IN LONDON ; SOMETIME PROFESSOR OF CHEMISTRY IN THE ROYAL AGRICULTURAL COLLEGE, CIRENCESTER ', AUTHOR OF " FOOD, ITS SOURCES, CONSTITUENTS, AND USES ", "THE FOOD-GRAINS OF INDIA ", ETC. ETC. SIXTH EDITION, REVISED AND ENLARGED. LONDON: GURNEY AND JACKSON, 1, PATERNOSTER ROW, (SUCCESSORS TO MR. VAN VOOEST.) MDCCCLXXXVIII. [The right of Translation is reserved.] FLAMMAM. PRINTED BY TAYLOR AND FRANCIS, KED LION COURT, FLEET STREET PREFACE THIS little book of directions in Practical Chemistry differs in several particulars from ordinary manuals of labora- tory practice ; otherwise I should not have added to the number. After the lapse of nearly a quarter of a century, it still remains the only English work in which a com- plete course of laboratory practice is provided for the use of agricultural students. The elementary lessons on Manipulation are drawn chiefly from familiar, important, or interesting materials with which every one ought to be acquainted. In the Qualitative Part, not only all the rare elements, but also nearly all those which are not important consti- tuents of any agricultural material or product are omitted, and thus many of the processes of analysis have been sim- plified. As, however, this section of laboratory practice is often felt to be irksome by agricultural students, a judicious teacher may further reduce its complexity by passing over, at least for a time, the less important parts vi PREFACE. of the "Preliminary Examination," as well as those " Reactions " and " Tables " which include what may be called nan-agricultural elements, such as antimony, arsenic, copper, mercury, tin, &c. In giving Quantitative Methods, examples have been selected from the most important substances likely to engage the attention of the agricultural analyst. By reference to the Table of Contents it will be seen that the examination not only of soils, manures, and cattle- foods, but also of dairy-produce, of bread, and of waters, is included. The student who carefully and intelligently carries out the processes described, will be able to extend their application to many materials which are not referred to specifically in the following pages. The various processes given in this volume for the esti- mation of the several constituents of cattle-foods, manures, te., have been personally tested over and over again. They will be found to yield trustworthy results with the expenditure of such an amount of skill, attention, and time as can reasonably be demanded of agricultural stu- dents during their course of scientific training. The rough and inaccurate methods of analysing manures which were too often employed when this Guide was first pub- lished, have been excluded from the present volume. The notation and nomenclature used in the following pages are nearly identical with those employed by the majority of English scientific chemists exceptional usages PREFACE. Vll of terms are in most cases explained or justified. The Centigrade thermometric scale and the metric system of weights and measures have been employed almost ex- clusively ; hut, in a few instances, where comparison with other results, with existing data, or with common stan- dards would have been rendered inconvenient, the grain, the inch, and the gallon have been exceptionally retained. Sometimes, for example, the weight in grams, or a measured volume in cubic centimetres, of a substance with which experiments are to be performed, is followed by a weight in grains, or by a measure in ounces, which is given as a suitable but by no means identical quantity. In preparing the present edition of the Laboratory Guide for the press it has been once again subjected to revision ; fuller explanations, directions, and tables have been in- serted, and some new processes have been introduced. The section of the work devoted to the analysis of milk and dairy-products has been almost entirely re- written. In the previous edition I drew particular attention to the various classes of nitrogen-compounds which occur in vegetable foods, and gave some suggestions as to their discrimination and separate estimation. The first process published in this country for the determination of true albuminoids was that which I called " The Carbolic-Acid Method/' After much experimenting I still place more confidence in the results of this process than in those obtained by the use of tannin, ferric acetate, or lead ace- tate these reagents precipitating, along with the true albuminoids, other nitrogenous bodies of no ascertained PREFACE. alimentary value. The method of separating albuminoids by the use of moist copper hydrate is not faultless, for it yields results which, in the presence of certain nitro- genous acids, are decidedly too high, yet it presents the advantage of permitting the nitrate from the precipitated albuminoids to be tested and further analysed. The use of phosphotungstic acid, as a precipitant for the peptones, which are now known to occur in many seeds, I have not described, because my limited experience of this reagent has not been satisfactory. I have introduced, in deference to the opinion of several correspondents, a slight alteration in the factor used in calculating the albuminoids from the ascertained percentage of nitrogen. This is now given as 6*25 instead of 6*33. Some persons using this manual may regret the absence from its pages of information which they expected to find therein. And, on the other hand, I anticipate that ob- jection will be taken to some of the Lessons in Part I., and to some of the analytical directions given in the succeeding sections of the volume. Yet nothing has been inserted and nothing omitted without careful consideration, nor have I failed to appropriate to the utmost the advice of those teachers who, in many parts of the world, have been in the habit of using the book in their laboratory classes. I trust that, on the whole, the volume as it now stands will be found to merit the increasing favour with which each successive issue has been received. From a small privately printed pamphlet of some forty pages, the Guide has grown, in six subsequent stages, to a volume PREFACE. IX of nearly seven times its original bulk. I have, however, endeavoured to limit the expansion of the work hy keeping continually in view its original scope as set forth in this Preface and in the Introductory Chapter. The Guide was intended primarily for use in the Royal Agricultural College, as a help in carrying out the system of practical instruction of chemistry there pursued. Ex- perience has confirmed my conviction that the publication of the plan of laboratory practice which I had developed at Cirencester would not only be helpful to my own pupils, but would also render a wider service in extending the study of practical chemistry in relation to agriculture. The Laboratory Guide has been adopted as the text-book not only in our Agricultural Colleges at home, but also in Australia, India, Italy, and Japan. It was so long ago as 1864 that my then assistant, Mr. Robert Warington, drew up, at my request, some directions in quantitative analysis which once formed a considerable part of the third division of the Laboratory Guide. During the twenty-four years which have passed since that time, many new processes of analysis have been developed or adopted, and many old processes simplified or improved under my personal supervision. It would be impossible to acknowledge specifically the source of each analytical detail or method ; but the labours of many well- known chemists have been utilized in the preparation of my little volume, and in the improvement of each succes- sive edition. I cannot, however, refrain from expressing X PREFACE. the obligations which I am under for special help accorded to me in the preparation of the present issue by Professor Kinch of Cirencester and Dr. Munro of Downton, who have furnished me with notes, hints, and emendations, suggested by their experience in the use of the book. I am indebted to Mr. E. H. Harland and to the authors of papers in recent volumes of ' The Analyst J for improve- ments in the section " On Dairy Products " the Reports issued by the United States Association of Official Chemists have also been laid under contribution. A. H. C. Kew, June 1888. CONTENTS. Introduction 1 PART I. CHEMICAL MANIPULATION. Setting to work 5 Lesson I. Solution and Filtration 7 n. Crystallization 9 ,, IH. Sublimation 9 IV. Specific Gravity ; 10 V. Washing by Decantatiou 13 VI. Preparation of Hydrogen 14 VH. Preparation of Oxygen 15 ,, VHI. Preparation of Sulphur Dioxide 17 IX. Preparation of Ammonia 19 X. Preparation of Carbon Dioxide 20 XI. Distillation of Nitric Acid 21 XII. Distillation of Acetic Acid 22 ., XHI. Testing of Waters 23 XIV. Detection of Arsenic 25 XV. Examination of Bronze Coin 26 ,, XVI. Examination of Silver Coin 27 XVII. Examination of Capsule Metal 29 XVIII. Examination of Type-metal 30 XIX. Examination of Zinc Alloy 30 XX. Reduction and Oxidation 82 XXI. Manganates and Permanganate.- 33 ,, XXH. Blowpipe Experiments (1) 34 xii CONTENTS. Lesson XXIII. Blowpipe Experiments (2) 35 , XXIV. Manufacture of Superphosphate 37 XXV. Experiments with Lime 39 XXVI. Lime in Soils 41 XXVII. Experiments with Soils 41 XXVIII. Starch and Sugar 43 XXIX. Experiments with Milk, Butter, and Cheese . . 44 XXX. Dextrin and Gum 45 XXXI. Experiments with Bread 46 XXXII. Ashes of Plants 48 XXXIII. Vegetable Colours 49 XXXIV. Experiments with Bone and Flesh 50 XXXV. Experiments with Blood 51 XXXVI. Cotton, Wool, and Silk 52 XXXVII. Wine and Beer 54 PART II. QUALITATIVE ANALYSIS. CHAPTER I. i. Introduction 56 $ ii. Of the Elements 58 iii. Of Reagents and Tests 64 iv. Of Reactions 75 CHAPTER II. i. The Method of Analysis 87 ii. Preliminary Examination 89 iii. Preparation of the Solution 95 iv. Analytical Schemes for the Metals or Basic Radicles 94 Group I. The Insoluble Chlorides 97 II. The Insoluble Sulphides 98 HI. The Soluble Sulphides 102 IV. The Insoluble Carbonates 105 V. The Soluble Carbonates . .107 CONTENTS. Xlll Page T. Analytical Schemes for the Non-metallic or Acid Radicles 108 Group I. Chlorine and other Monad Acid Radicles .... 109 II. Fluorine and the Phosphoric and Oxalic Radicles ............................ 110 III. The Tartaric and Citric Radicles .......... Ill Special Tests for Acid Radicles ............ 112 vi. Analytical Scheme for the Examination of Insoluble Sub- stances .................................... 113, 116 vii. Analytical Scheme for the Examination of Alloys ...... 116 Table of Solubilities .................................. 114, 115 An Example of a Qualitative Analysis ...................... 117 / PART III. QUANTITATIVE ANALYSIS. CHAPTER I. i. Introduction . , ...................................... 121 Chemical Nomenclature ............................ 122 Weights and Measures .............................. 123 Weighing and the Balance .......................... 124 Quantitative Apparatus ............................ 127 ii. Preliminary Instructions in Quantitative Operations ...... 131 Estimation of Lime ................................ 131 Magnesia ............................ 132 Baryta .............................. 133 Phosphorus Pentoxide .................. 134 Potash .............................. 134 Preparation of Standard Acid and Alkali Solutions ...... 135 CHAPTER II. i. Analysis of Manures .................................. 139 Analysis of Bone-dust, Boiled Bones, &c ............... 139 Estimation of Nitrogen ............................ 141 Thiosulphate Method .......................... 145 Analysis of Bone-black, &c ........................... 146 Bone-ash ............. ................ 147 XIV CONTENTS. Page Analysis of Apatite 147 Coprolites 148 Oxalic-Acid Method 150 Determination of Alumina, &c 151 Estimation of Iron by Volumetric Method 153 Analysis of Phosphatic Guanos 155 Fusion Method 155 Analysis of Superphosphates 156 Beet Manure and Dissolved Guano, &c 164 Peruvian Guano, &c 165 Appendix to Analysis of Phosphates : the Gravimetric Uranium Method 168 Volumetric Uranium Method 168 Analysis of Nitrate of Soda or Potash 170 Volumetric Determination of Chlorine 171 Estimation of Nitric Acid 172 Analysis of Potash Salts 173 Common Salt 175 Ammonia Salts 176 Soot 176 ii. Analysis of Soils 177 Mechanical Analysis of Soils 178 Chemical Analysis of Soils 185 Partial Chemical Analysis of Soils 186 Molybdic-Acid Method 189 Citric- Acid Method 190 Complete Chemical Analysis of Soils 193 Analysis of Insoluble Silicates 199 Sulphuric-Acid Method 199 Hydrofluoric-Acid Method 200 Baryta Fusion Method 201 Analysis of Limestone 202 ) iii. Analysis of Waters 204 Total Solid Contents 207 Organic Matter 207 Oxygen taken from Permanganate 208 CONTENTS. XV Page Chlorine 210 Ready-formed Ammonia 211 Ammonia from Organic Compounds 213 Nitrogen as Nitrates and Nitrites 214 Copper-zinc Method , 214 Aluminium Method , 215 Griess's Method (for nitrites) 216 Total and Permanent Hardness 217 Statement of Results 220 iv. Analysis of Foods 223 Analysis of Oilcakes 223 Estimation of Oil 223 Fibre 226 Sulphuric-Acid Method 228 Acid and Alkali Method 228 Potassium-Chlorate Method 229 Estimation of Albuminoids 229 Kjeldahl's Method 230 Analysis of Grain, Straw, Hay 233 Estimation of Starch 233 Analysis of Turnips and other Roots 235 Estimation of Albuminoids 237 Phenol Method 237 Copper-Hydrate Method 238 Estimation of Sugar 239 Starch.. 243 Pectose, &c 244 Analysis of Leaves and Green Fodder 245 Fermented Liquors 248 Ashes of Plants 251 Milk 253 Estimation of Total Solids 254 Solids-not-Fat 254 Fat (Adams's Method) 256 Albuminoids 258 Milk-Sugar 259 XVI CONTENTS. Analysis of Cream 261 Butter 262 Estimation of Fat 264 Koettstorfer's Saponification Method 265 Rapid Saponification Method 265 Keichert's Saponification Method 267 Hehner's Saponification Method 268 Analysis of Cheese 272 Estimation of Fat 274 Analysis of Bread 275 ADDENDUM to " Mechanical Analysis of Soils," pp. 180 and 184. When a soil suffers much change of texture by ignition, or when it contains an appreciable amount of clay, it is better to use for elutriation that portion of earth (passing through a 0'6 millimetre mesh) which has been dried till constant at 100, and not jhat which has been gently ignited. The " coarse sand" and " fine sand " obtained in the operation should be weighed after drying at 100, as well as after ignition ; the differences in the weights will represent " organic matter and combined water." As the total amount of these constituents in 30 grams of soil has been previously determined, the quantity in the "clay, "page 182, may be learnt by difference. THE LABOEATOEY GUIDE, . INTRODUCTION. CHEMISTRY is essentially a science of experiment. The Labora- tory is as important as the Lecture-room. It is not sufficient to have an experiment described, nor even to see it performed; the student must repeat it for himself. And he must apprehend all the conditions of the experiment and the laws which it illustrates. Thus only can the science be thoroughly learnt so as to be of real service in practical life ; thus only can be fully realized its beneficial effects in training the mind to accurate observation and close reasoning. Besides these chief advantages of practical chemical work others may be mentioned. For instance, actual repetitions of leading experiments give sharpness and precision to the memory ; and, at the same time, the unexpected results, and even the mishaps that attend laboratory practice, afford a certain amount of play to ingenuity in contriving new arrange- ments of apparatus and new conditions of experiment. In this way it has happened that the stimulus to original endeavour which accidents give has resulted in discoveries of great scientific or economic importance. But just as lectures may become too theoretical, so laboratory work may become too practical. The student in the laboratory must never forget that the experiment is the means, not the end. An experiment rightly tried is a question properly put to nature ; and though its results may be striking or beautiful, it is to their meaning or interpretation that we look. Merely to make a coloured precipitate or a flash of bright flame is not the end of experimenting, but to identify facts by means of phenomena is. B 2 INTRODUCTION. We read in our text-books that sulphuric acid dissolves zinc and gives off a light and combustible gas ; but it is not till we have watched the bubbles rise from the mixture, collected them, burnt them, arid otherwise tested them, that we realize the properties and relations of zinc and acid and hydrogen. Eat our books tell us something more about this experiment. We not only have to learn how to make it, and the qualities of the materials taken and of those formed, but we see that we have to do with quantities. We learn that 60 parts by weight of zinc will dislodge only 2 parts by weight of the gas hydrogen, yet that these two parts by weight of gas will occupy more than 2300 times the bulk of the solid zinc used. These considerations enable us to divide the work of practical chemistry into 3 sections : 1. Manipulation, which includes the management of apparatus and tests. 2. Qualitative Analysis, by which the constituents of sub- stances are separated and identified by appropriate methods. 3. Quantitative Analysis, by which the quantities of the several constituents of the substance examined are ascertained, either by weighing or measuring. These sections are found in practice not to be absolutely dis- tinct ; indeed, the study of the first of them, Manipulation, in- volves both Qualitative and Quantitative work, while the third necessarily includes the other two. But it is, after all, not only usual, but very convenient to divide Laboratory practice into these sections, and the plan has accordingly been adopted in the pages which follow. For whatever occupation in life a student may be destined, the foundations of his chemical knowledge must be laid in the same -way. Yet there is a mode, and a perfectly legitimate one, of giving a special character even to early scientific instruction. In a medical school the more elaborate illustrations of chemical facts, both in lecture and lesson, may be selected mainly from substances with which the physician or surgeon is more immediately con- cerned, and thus a medical bias be given to the whole course. The great facts concerning the elements and their combinations INTRODUCTION. 3 would be duly explained in all cases but while a subject should be illustrated by potassium iodide or magnesium, sulphate when addressing medical students, potassium chloride or calcium phos- phate should be specially dwelt upon in the case of agricultural students. The latter, too, would have the laws of diffusion illus- trated to him by the processes which go on in the soil and in the plant ; the medical student, on the other hand, would study the same laws as they work in the liquids and gases concerned in the functions of the human body. The agricultural student would devote particular attention to those compounds of nitrogen which are used as manure, while the medical student would make the acquaintance of those which are of importance in the treatment of disease. Both students follow the fortunes of nitrogen till it appears as ammonia, then the former combines it with sulphuric acid, the latter with citric. Both will study analysis, one to detect and estimate phosphoric acid, and the other arsenic. But as the whole of the present volume affords an illustration of this method as applied to agricultural teaching, it is unnecessary further to explain it here. The student using this Guide will do so with the greatest effect if, while he is going through the experiments on manipulation described in Part I., he will attend a course of Lectures on Inorganic Chemistry, and study the corresponding chapters of a text-book of Chemistry. The lessons on Manipulation may then be readily mastered by two or three hours' practice in the laboratory each week during a period of four months; an additional hour or so each week will be requisite for posting up the ' laboratory book ' with the results of the practical work. This time is exclusive of that which lectures require. This Guide can be used without the personal help of a teacher; but the progress of the student will then be less sure and rapid, especially where, as in the processes of analysis, the operations described are very delicate or complicated. When the student has prepared and examined the common gases, hydrogen, oxygen, nitrogen, carbon dioxide, sulphur di- oxide, &c., and has studied, by actual practice on suitable (often B2 4 INTRODUCTION. agricultural) examples, the processes of solution, evaporation, distillation, precipitation, filtration, decautation, crystallization, drying, ignition, and weighing, he must next acquire an exact acquaintance with the various substances with which the analyst is concerned. More than this, he must become familiar with the tests and reagents employed either to separate or discriminate the several constituents of any ordinary solid or liquid material which may be submitted to analysis. By the use of these tests or reagents different effects ensue : gases are evolved, precipi- tates are formed, or colours arc produced ; from these phenomena definite inferences are drawn as to the nature of the substance or substances present. These reagents do not, except in a few instances, separate a body in the elementary or uncombined state, but in some characteristic and easily identified form of combina- tion. As, however, the simple element is occasionally eliminated in the free state, a list of the most salient properties of each important element is given further on : a reference to this list will enable the experimenter to identify any particular element. When the student has become familiar with the behaviour of each metallic or basic, and of each acid constituent, when acted upon by the reagents in use, he proceeds to the systematic part of Qualitative Analysis. This, the method of analysis, consists of the application, in a fixed order, of certain tests. But the schemes which have to be here followed are often modified to suit the particular state and nature of the material to be analysed. When the schemes are mastered, and the student has success- fully analysed the various simple and complex substances that have been selected as examples, he commences the study of the third part of this work, which is devoted to Quantitative Analysis. This section of the Guide commences with minute directions for the estimation of potassium, nitrogen, and other important con- stituents of foods, soils, and manures, and it then gives numerous examples for the practice of quantitative analysis. All these examples are drawn from the produce of the farm, or from those materials which are of the highest importance to the agricul- turist. PART I. CHEMICAL MANIPULATION. THE Lessons which follow have been so devised as to illustrate and confirm some of the chief truths learnt during the course of leitures on Inorganic or Mineral Chemistry, which they are intended to accompany. The usual introductory lectures of such a course will refer to Chemical Physics. The corresponding Lessons are devoted to Solution, Crystallization, Sublimation, and so forth. Next in order, both at lecture and in lesson, come hydrogen, oxygen, and other important non-metals and their compounds : afterwards the chief metals. Here and there throughout the series it will be well to introduce one of the special agricultural lessons, in order to connect, even in the early stages of instruction, chemical science with the commonest and most familiar materials of life on the farm. To show the mode of carrying on a class of practical chemistry in the most effective way a few words of general description are necessary. The lesson having been selected, the teacher will suspend in some conspicuous place in the laboratory a diagram embodying the chief operations to be performed. He will read this, commenting upon it as he reads, and illustrating apparatus and methods by sketches on the black-board, and in many cases by going through the experiment, or making the apparatus to be employed, before the class. This done, the class is told what materials and apparatus will be required. Part of this will belong to the student's set, part will be found on the shelves above his bench, and part will be specially provided for the use of the class, according to the demands of each lesson. Work may now be commenced. 6 CHEMICAL MANIPULATION. The student should bear in mind the great importance of (1) cleanliness, (2) order, (3) quietness, (4) exactness. All apparatus must be made clean before being used, and must be kept clean. A test-tube washed out three times with a little water is really cleaner than if washed once with much. When work is over, put the apparatus away, dry as well as clean. Pour away all residues, unless the contrary be specially directed at the time of the lesson : clean up all messes. As to order, never have anything on the bench which is not required, but never omit anything that is. Arrange your appa- ratus so as to be most convenient for work, so as not to prevent your getting reagents from the shelves, and so as not to be liable to be upset. Hurry and noise prevent the successful performance of ex- periments. Give every experiment time. If you are told to let a liquid cool, give it time to do so. If you are told to heat a substance till it becomes dry, give it time to get so. By exactness, we mean the use of the right materials in the right way. If you are directed to warm a liquid, don't boil it. If you are directed to add five drops of some test, don't let an un- counted number tumble into your test-tube : economy is not only better, it is more successful than waste. Be careful to see that you add the right test : don't use ferrocyanide for ferricyanide, nor sulphate for sulphite. If you are directed to use strong sulphuric acid in any experiment do not spill it about, nor mix it suddenly with any liquid, and above all never allow it to come in contact with hot water, or, if it be itself hot, with hot or cold water. But cleanliness, order, quietness, and exactness will be of small avail unless the student accurately observe the result of each ex- periment, grasp its meaning, and make a full record of all his work. Rough notes should be taken in the laboratory, to be afterwards copied into a book. In making and transferring such notes, remember that the actual results of your own experiments, not the directions given you for carrying them out, are of the first importance. See that you understand the reason of each step taken, of each addition made, and of each change effected : write SOLUTION AND FILTRATION. 7 out the chemical equations for such changes. Be careful to spell chemical words exactly as given in the lessons and on the labels of the laboratory. The names of chemical substances and pro- cesses have been formed (sometimes awkwardly enough) chiefly from Latin and Greek words ; and their derivations as well as meanings are obscured or lost when through inattention a letter is omitted or altered. For instance, never spell chlorine without an A, nor analyse with a z. Seeing now what we have to do, and how to do it, we may begin work. Each of the following lessons will require from one to two hours for its successful completion. LESSON I. SOLUTION AND FILTRATION. Apparatus required. Retort stand ; funnel ; filter-papers ; spirit-lamp ; porcelain bason ; two beakers ; wash-bottle ; scales and weights. Ordinary reagent. Dilute hydrochloric acid (HC1). Special materials. A mixture, in known proportions, of sand and salt, to be labelled A : a mixture, in known proportions, of sand and chalk, labelled B ; a feather. 1. Weigh out 10 grams (or 100 grains) of a mixture (A) of sand and salt. Place the weighed substance on a filter fitted in a funnel and pour water gently into the funnel. The filter- paper used above is folded first into halves along the line a, a, then into quarters from the centre to b, b. It is opened par- tially when in the funnel, so as to bring a and a together and to leave b and b similarly placed. "When the liquid that drops from the funnel (called the filtrate) no longer tastes salt, syringe out every particle of the sand, which alone remains on the filter, into a bason : this washing 8 CHEMICAL MANIPULATION. out the residue on the filter is easily done by the wash-bottle jet being allowed to play upon it, the Fig. 2. funnel being held upside down over the bason. Pour off the water, leaving the sand in the bason. Turn the bason about, so that the wet sand forms a thin layer all over it : then heat it cautiously, to avoid spirting, until the sand is dry ; sweep it, when cold, with a feather into one of the pans of the scales, and weigh it. Its weight, multiplied by 10, if grams have been used, gives you the percentage of sand in the original mix- ture. 2. Weigh out 10 grams (or 100 grains) of a mixture (B) of sand and chalk. Place the weighed substance in a beaker, and pour upon it a little hydrochloric acid : shake the mixture. Continue to add hydrochloric acid, drop by drop, till all frothing (due to the escape of carbon dioxide, C0 2 ) ceases ; shake the mix- ture from time to time. Add water to the residue that has not dissolved, and gently decant it off again. This pouring on and off of water is to be repeated twice, taking care to lose none of the sand at the bottom. The sand should now be syringed, as before described, into a porcelain bason : it is to be dried and weighed as in experiment 1. The student learns by this lesson that substances differ in solubility, some being soluble in water, some in acids, some in- soluble in both. He also learns that a filter separates solid particles from liquids. The only chemical change in these experiments occurs during the solution of the chalk in the hydrochloric acid. It is represented thus : CaC0 8 + 2HC1 = H 2 + CaCl 2 + C0 2 Chalk, insoluble Acid. Water. Calcium chloride, Carbon di- in water. dissolved in the oxide, goes water. off as gas. CRYSTALLIZATION. SUBLIMATION. LESSON II. CRYSTALLIZATION. Apparatus required. Furnace-support ; wire gauze ; spirit- lamp ; wash-bottle ; two porcelain basons ; porcelain crucible ; triangle ; test-tubes ; scales and weights ; filter-papers. Special Materials. Solutions of copper sulphate, sodium sul- phate, calcium chloride, and potassium dichromate ; piece of wire. 1. Evaporate | of a test-tube full of a solution of copper sulphate over the lamp in a porcelain bason until the crystals which form round the margin of the solution cease to dissolve w f hen pushed into it : set it aside to cool. 2. Add 30 drops of sodium sulphate solution to a test-tube about ^ full of calcium chloride solution. The white substance which gradually separates from the mixture will be found to be made up of small crystals which can be seen with a pocket lens. These crystals are calcium sulphate (= gypsum, CaS0 4 , 2H 2 0). 3. Weigh out in a crucible of known weight 2 grams (or 30 grains) of crystals of copper sulphate (CuS0 4 , 5H 2 0), from expe- riment 1. The crystals must first bo pressed between filter-papers, and then lightly powdered in a mortar before weighing. Heat the weighed salt and stir it with a wire ; continue to heat it until its blue colour has entirely disappeared. When the crucible is cold weigh it again. The difference in weight will be the water of crystallization lost by the salt. 4. A solution of potassium dichromate, when evaporated as in experiment 1 above, will deposit on cooling crystals (K 2 Cr 2 7 ) which contain no combined water. LESSON III. SUBLIMATION. Apparatus required. Retort-stand; triangle; spirit-lamp; scales and weights ; porcelain crucible ; test-tubes and stand. 10 CHEMICAL MANIPULATION. Special Materials. Iodine ; pure ammonium chloride ; adul- terated ammonium sulphate. 1. Into a dry test-tube drop a crystal of iodine and gently heat it. Purplish-violet vapours will be produced which will condense on the cooler parts of the tube into small crystals of iodine. This physical change of a solid into a gas, followed by the re-formation of the original solid, is unaccompanied by any chemical change : it is called ' sublimation.' 2. Take 1 gram (or 10 grains) of ammonium chloride (NH 4 C1), place it in a porcelain crucible which has been counterpoised, or the weight of which has been ascertained, and then heat it over the spirit-lamp till no more fumes are given off. When the crucible is cold weigh it again. The salt, if pure, will have left no residue, having been entirely sublimed. A cold surface, say, a test-tube, placed in the fumes will be covered with minute crystals of sublimed and condensed ammonium chloride. 3. Take 1 gram (or 10 grains) of adulterated ammonium sul- phate and heat it exactly as above. , The materials used to adul- terate this valuable salt are generally non-volatile, and will be left behind. The amount of adulteration will be learnt by finding what weights have to be added to the counterpoise in order that it may balance the crucible and the non-volatile residue in it. The student must, however, remember that many substances used as adulterations are volatile. Vegetable and animal sub- stances and water itself are amongst these, and must be looked for in making an analysis of any ammonia salt used as manure. LESSON IV. SPECIFIC GKAVITY. Apparatus required. Scales and weights: a large beaker nearly full of water. Special matwials. Pieces of lead, glass, and iron ; thread ; and a gold or silver coin. SPECIFIC GKAVITY. 11 1. Tie a piece of iron by means of a thread so that it shall hang ahout 3 inches below one pan of the scales. Place weights in the other pan to counterpoise the iron, noting the number of grams or grains required. Now lower the beam of the scales until the piece of iron is wholly immersed in water contained in a beaker, taking care that the iron does not touch the sides or bottom, and removing any air-bubbles that may adhere to it by means of a small brush. Remove weights from the pan till those left again balance the iron. Subtract the second weight from the first ; the difference is the weight of the volume of water displaced by the iron that is, the weight of an equal volume of water. To find the specific gravity of the iron, water being taken as unity, divide the weight in air by the above difference, the quotient will be the Fig. 3. required specific gravity. The following is an example of the working of this problem : Weight in air of a piece of gold (a sovereign) 7'971 grams. in water of the same.. 7'517 Weight Difference '454 gram. This difference, '454 of a gram, repre- sents then the weight of the volume of water displaced by the immersion of the gold that is, the weight of an equal volume of water. We have now no- thing to do but to divide the weight of the gold in air by this difference: 'and the dividend will express how many times the weight of the volume of gold contains the weight of an equal volume of water : 7-971 454 = 17-56, spec. grav. of standard gold. Or wo may express the same facts in another form. We may 12 CHEMICAL MANIPULATION. say that the weights of equal volumes of water and gold are in the ratio of "454 to 7*971 ; and then, assuming the specific gravity of water to be 1, we have the following proportion : 454 : 1 = 7-971 : x Weight of water dis- Spec. grav. Weight of Spec. grav. placed by gold. of water. gold. of gold. The specific gravity of standard gold, which contains 8-33 per cent, of copper, is lower than that of pure gold, which is 19-3. 2. The same experiment is to be tried with a piece of lead, and, 3, with a piece of glass, and, 4, with a silver coin. The specific gravity of a body is the ratio of the weight of any volume of that body to the weight of an equal volume of water. It is expressed by a number which shows how many times the weight of any volume of the body contains the weight of an equal volume of water, e. . Into the remainder of the filtrate drop a piece of blue litmus paper ; if the blue colour becomes reddish, it is a sign of the " sourness " of the soil, and that the application of a base such as lime, will be beneficial to it. 2. Warm 2 grams (or 30 grains) of peat in a flask with enough sodium hydrate solution to cover it. When the mixture has been heated five minutes, add a little water and pour the mixture on a wetted filter. If the filtrate is dark brown and gives a brown flocky precipitate when it is made acid with excess of dilute hydrochloric acid, it is a sign of the presence of certain organic acids (humic &c.), which are nearly insoluble in water, but form soluble salts with alkalies. They are derived from the decay of organic matter. 3. To half a test-tube of water add five drops of ammonium hydrate ; the solution will turn turmeric paper brown. Now fit a filter into a funnel, fill it two thirds full of a loamy or peaty soil, and pour water upon it until drops begin to fall from the funnel below ; now add the weak ammonia solution prepared above, and then some water. Good soils have so strong an absorptive power for ammonia, that when such a solution as that before mentioned is allowed to soak through them, the ammonia is so far removed that the filtrate no longer smells of ammonia, nor turns turmeric paper brown. The ammonia solution, should be returned so as to soak twice or thrice through the soil. 4. Through another portion of the same soil similarly ar- STARCH AND SUGAR. 43 ranged in a funnel, let a decoction of logwood (or other coloured liquid) soak ; the colour will be much reduced, if not completely removed. Liquid sewage and the drainage of manure-heaps lose by the same treatment their colour and odour, owing to the absorptive power of peat. LESSON XXYIII. STARCH AND SUGAR. Apparatus required. Eetort-stand ; spirit-lamp ; test-tubes ; two flasks ; cut niters ; funnels ; pestle and mortar ; wash-bottle. Ordinary reagents. Sodium hydrate solution ; sulphuric acid (H 2 S0 4 ), concentrated and dilute. Special materials and tests. Starch ; a raisin ; the " sugar test ; " tincture of iodine ; cane- or beet-sugar in crystals. 1. Crush a fragment of starch, shake it up in a test-tube half full of water, and boil, constantly shaking the tube. Pour the starch paste thus formed into three test-tubes, , 6, and c. To )IIg 200- 64 QUALITATIVE ANALYSIS, iii. OF REAGENTS AND TESTS. The following is a descriptive list of the reagents and tests employed in the qualitative and quantitative processes given in the present work. The most important impurities are noted, together with the most suitable strength for each solution. In a few instances, however, solutions which are employed for special purposes and of exact strength are described under the headings of those quantitative methods in which they are used. METALS. Copper (Cu). Copper foil or fine wire may be ob- tained nearly pure, and may be rendered still purer by ignition to redness in a stream of hydrogen. Iron (Fe). Some kinds of steel and soft iron wire, notably piano -wire, contain a very small percentage of impurities. Zine (Zn). The most usual impurities of zinc are iron, lead, and arsenic. By distillation it may be freed from lead and iron ; if the distilled zinc be kept fused for some time in an earthen crucible it may often thus be freed from arsenic. NON-METALS. Chlorine (Cl)may bo prepared by gently warm- ing strong hydrochloric acid with manganese dioxide. If a so- lution be wanted, the gas is conducted into very cold water until the latter is saturated. Iodine (I). A saturated aqueous solution of resublimed iodino is to be used ; or the element may be dissolved in water contain- ing 4 per cent, of alcohol. Carbon (C). Charcoal for blowpipe experiments should be of beech or other compact wood, and should be free from bark or knots. Pieces about 1| inch in diameter and 4 inches in length should be sawn lengthwise in two ; the flat surface of the longi- tudinal section thus made will be found adapted for most blowpipe purposes ; occasionally a cross or slant section is to be preferred. POTASSIUM SALTS. Potassium Iodide (KI). Commercial iodide often contains iodate, carbonate, and bromide. The two former im- purities may be removed by digesting the powdered salt with hot -strong alcohol, when they will remain undissolved. Evaporate OF REAGENTS AND TESTS. 65 the alcoholic solution to dryness, and make a 10 per cent. (%) solution of the residue. Potassium Chlorate (KC10 3 ). The commercial salt may be used ; it generally, however, contains sulphate, and occasionally a trace of lead. Potassium Nitrate (KN"0 3 ). Refined nitre is pure enough for ordinary use : the chloride and sulphate which it generally con- tains may be separated by repeated crystallizations. Potassium Cyanide (KCN) . The commercial salt, if kept dry, answers every purpose. Potassium Sulphocyanide (KCNS). The commercial salt may be used : 10 / . Potassium Ferrocyanide (K 4 FeCy e , 3aq.) occurs pure in com- merce : 8 %. Potassium Ferrieyanide (K 3 FeCy 6 ). This salt occurs in com- merce of sufficient purity : dissolved in water, it suffers, after a time, a partial decomposition ; the fresh solution only should be used: 10%. Potassium Sulphide (K 2 S). The commercial salt may be used : 4 / . Potassium Hydrate (KHO). Commercial potash answers well for most analytical operations, but it is well to remember that it contains small quantities of potassium carbonate, chloride, silicate, and sulphate ; alumina is generally and lead sometimes present. If the commercial hydrate be dissolved in alcohol, and the clear liquor evaporated (in the absence of C0 2 ) in a silver dish, the hydrate is obtained nearly pure : 5 / . Potassium and Sodium Carbonates (K 2 C0 3 + Na 2 C0 3 ). The dry salts are mixed in atomic proportions, about 13 parts of the former salt to 10 of the latter. Potassium Dichromate (K 2 Cr 2 7 ). The commercial salt may be purified readily by recrystallization. Potassium Chromate (K 2 Cr0 4 ). It may be prepared from the dichromate. To 100 parts of this salt dissolved in water add 47 parts dry potassium carbonate (K 2 C0 3 ) : crystallize : 5 %. Potassium Permanganate (KMn0 4 ). The crystallized com- 66 QUALITATIVE ANALYSIS. mercial salt may be used : -395 gram is dissolved in 1 litre of water. Potassium Antimoniate (K 2 Sb a 6 , 7aq.). This salt is occasion- ally used as a test for sodium : it is troublesome to prepare. Potassium Acetate (KC 2 H 3 O a ) occurs nearly pure : 25 / . SODIUM SALTS. Sodium Hydrate (NaHO) is used for the same purposes as potassium hydrate. When required pure*, that made from sodium should be employed : 5 / . Sodium Carbonate (Na 2 C0 3 ). The commercial salt generally contains sulphate and chloride, besides excess of C0 2 . Pure so- dium carbonate may be obtained by igniting precipitated and washed sodium oxalate, Na 2 C 2 4 ==Na 2 C0 3 + CO ; or by the ig- nition of the pure dicarbonate ; in the case of the latter salt magnesium should be first looked for : 10 / . Sodium Phosphate (Na 2 HP0 4 , 12aq.). The ordinary phosphate contains sulphate ; it may be purified by recrystallization. The solution of this salt acts powerfully upon porcelain and glass, taking up impurities and losing some of its phosphoric consti- tuent : it should generally be prepared only when required : 10 / . Sodium Borate (Na 2 H 2 B 4 8 , 9aq.), or borax, may be employed as obtained in commerce. Sodium Acetate (NaC 2 H 3 2 , 3aq.). The commercial salt may contain traces of calcium salts, but for ordinary purposes may be used. It should be dissolved in five times its weight of water. AMMONIUM SALTS. Ammonium Chloride (NH 4 C1). The chief impurity of this salt is ferric chloride. To separate this, add a few drops of ammonium sulphide, filter off the iron sulphide, add slight excess of hydrochloric acid to the filtrate, evaporate till all odour of hydrosulphuric acid has ceased, neutralize with ammonia, evaporate and crystallize : 20 / . Ammonium Sulphide ([NH 4 ] 2 S). This salt is obtained in solu- tion thus : Take some solution of ammonia, divide it into two equal parts, saturate one with hydrosulphuric acid, and then add the other part. Ammonia is known to be saturated with the acid in question when it no longer occasions a precipitate in magnesium sulphate. Yellow ammonium sulphide is prepared OF REAGENTS AND TESTS. 67 by dissolving a little sulphur in the ordinary sulphide. The glass of the bottles in which these reagents are kept must not contain lead. Ammonia (NH 3 ). Ammonia-gas dissolved in water is supposed to form ammonium hydrate (NH 4 HO). Commercial liquor am- moniae, if it leave no residue on evaporation, may be used in analysis ; it may be diluted with 4 times its volume of water. Ammonium Carbonate ([NHJ a C0 3 ). The commercial " sesqui- carbonate " appears to yield a solution of this salt when dissolved in hot water. The commercial salt is pure enough for most analytical purposes : 10 / . A solution saturated in the cold, of commercial sesquicarbonate, is also required in analysis. Ammonium Acetate (NH 4 C 2 H 3 2 ). Acetic acid may be satu- rated with ammonium carbonate, and warmed. Ammonium Oxalate ([NHJ 2 C 2 4 , 2aq.); The commercial salt suffices for most purposes; but if pure ammonium oxalate be desired, it may be obtained by saturating liquid ammonia with a solution of sublimed oxalic acid : 1 part of the crystals obtained by evaporating the solution should be dissolved in 25 parts of water. Ammonium Phosphate ([NH 4 ] 2 HP0 4 ). This salt may be ob- tained in commerce quite pure. Ammonium MolybdaU ([NH 4 ] 2 Mo0 4 ). Dissolve 50 grams of the commercial salt in 200 c. c. of ammonium hydrate solution (made by mixing 1 vol. of '88 ammonia with 2 vols. of water) ; pour this into 800 c. c. of dilute nitric acid prepared from equal volumes of strong nitric acid and of water : keep the solution in the dark, and decant it from any precipitate which may form . This reagent may be made from inolybdic acid by dissolving 1 part in 4 parts of ammonia solution of sp. gr. -96, filtering the solution and pouring it, with constant stirring, into 15 parts of nitric acid of sp. gr. 1-2. SILVER SALT. Silver Nitrate (AgN"0 3 ). This is best obtained by dissolving pure silver in nitric acid (H1S"0 8 ) which has been diluted with about its own bulk of water, evaporating the solution to dryness, and gently fusing the residue. The fused mass may be dissolved in water when cold, and then crystallized. It is thus obtained quite free from acid. If silver coin (i. e. silver 68 QUALITATIVE ANALYSIS. alloyed with copper) be employed, it is necessary, after dissolving it in nitric acid, to precipitate the silver as chloride by the addition of hydrochloric acid, to filter it off, and then to wash it till it no longer contains a trace of the soluble copper salt. The silver chloride may then be reduced into metal, either by fusing it with twice its weight of dry sodium carbonate, or by placing it in a dish together with water, a drop or two of hydrochloric acid, and a strip of pure zinc. When the reduction of the silver is complete, the remaining zinc must be removed, the spongy silver warmed with a little dilute hydrochloric acid, and then thoroughly washed, dissolved in nitric acid, and the solution evaporated to dryness. The residue, if gently fused, will be nearly pure silver nitrate; it may be further purified by crystallization : 5 / . BARIUM SALTS. Barium Chloride (BaCl 2 , 2aq.). This salt is generally found in commerce of sufficient purity for ordinary analytical operations. If it contain lead, it may be purified by recrystallization : 10 / . Barium Oxide or Baryta (BaO). Introduce finely powdered barium nitrate, little by little, into a crucible maintained at a bright red heat. After cooling, the crucible is broken, and the fused mass separated from foreign matters and preserved from the air. Barium Hydrate (BaH 2 2 , 2aq.). Boil the oxide in water, filter into a large flask, and allow the filtrate to cool. Crystals of the hydrate will separate ; one or two recrystallizations of these will give a perfectly pure product. Or the commercial crystallized hydrate may be similarly purified. A cold saturated solution may be used in testing : it should be prepared and kept out of contact with the air. Barium Nitrate (Ba2N0 3 ). The commercial salt may be used : Barium Carbonate (BaC0 3 ). Precipitate a warm solution of barium chloride with ammonium carbonate ; wash the precipitate thoroughly. It should be kept moistened with water in a wide- mouthed stoppered bottle. CALCIUM SALTS. Calcium Chloride (CaCl 2 ). This may be OF BEAGENTS AND TESTS. 60 prepared in the purest form by dissolving the finest white marble, or, better still, small crystals of Iceland spar, in hydrochloric acid, the acid not being in sufficient quantity to dissolve the whole of the carbonate : 5 / . Calcium Oxide (CaO). Freshly burnt quicklime just from the kiln should be taken, the white hard pieces being selected, and preserved in a well-stoppered bottle, the stopper having been lubricated with a little vaseline. Calcium Hydrate (CaH 2 2 ), or Lime-water. A cold saturated solution of calcium hydrate is made by shaking some slaked lime with distilled water. The first water is poured away, and a second quantity of water added to the residue : this liquid, when clear, may be decanted for use : it is to be kept out of contact with the air. Calcium Sulphate (CaS0 4 , 2 aq.). The well-washed precipitated sulphate is shaken up with distilled water. The saturated solu- tion (1 in 420 of water) is used. MAGNESIUM SALTS. Magnesium Sulphate (MgS0 4 , 7aq,), The commercial salt (Epsom salts) is of sufficient purity for all ordi- nary analytical purposes : 10 %. Ammoniacal Magnesium Chloride (magnesia mixture). 11 grams of crystallized magnesium chloride and 14 grams of ammonium chloride are dissolved in 130 c. c. of water, and the solution made ammoniacal by the addition of 70 c. c. of ammonium hydrate. The addition of a few drops of chlorine-water, and digestion for some hours in a warm place, will separate any manganese : a little strong ammonia water is again added to the solution, which is then filtered and preserved in bottles of hard glass. IKON SALTS. Arrows Sulphate (FeS0 4 , 7aq.). The best com- mercial salt, known as copperas, green vitriol, and protosulphate of iron, is generally of sufficient purity for use, it being very care- fully prepared for photographic purposes. The crystals should be dissolved in cold water. A piece of iron wire should be kept in the bottle, and an addition of a few drops of dilute sulphuric acid be now and then made to it. This reagent may thus be kept free from ferric compounds any length of time. 70 QUALITATIVE ANALYSIS* Ferric Chloride (Fe 2 Cl 6 ). The salt is also termed eesqui- chloride and perchloride of iron. The commercial preparation may be used ; or the solution may be prepared by dissolving pure iron wire in dilute hydrochloric acid and then passing chlorine through the solution till a drop of the liquid gives no precipitate with potassium ferricyanide. Iron Sulphide (FeS) is most conveniently made by heating a bar of iron to whiteness in a blacksmith's forge and immediately applying to it a roll of sulphur. The fused iron sulphide as it drops from the bar should be received in a vessel of water. COBALT SALT. Cobalt Nitrate (Co2N0 3 , 6aq.). This salt may be purchased fit for use : 15 / . COPPEB SALT. Copper Sulphate (CuS0 4 , 5aq.). The commer- cial salt is usually contaminated with iron and lead sulphates. For analytical purposes, the metallic copper obtained by electro- lysis may be dissolved in hot pure sulphuric acid, or the pure hydrate, oxide, or carbonate may be taken, and heated with diluted sulphuric acid ; the salt should then be crystallized from its solution : 10 %. Sodio-cupric Tartrate, or the Sugar test. Dissolve 34-64 grams of pure crystallized copper sulphate, dried between filter- paper, in about 200 c. c. of water. In another vessel dissolve 173 grams of crystallized potassium and sodium tartrate (Ro- chelle salt) in 480 c. c. of solution of sodium hydrate having the sp. gr. 1'14. Add the former solution to the latter and dilute to 1 litre. Keep the solution in a well-stoppered bottle to prevent absorption of carbon dioxide, which will interfere with the accu- racy of the test : the bottle should be covered with black paper soaked in melted paraffin, or else it should be kept in the dark. The stopper should be lightly smeared with vaseline. LEAD SALT. Lead Acetate (Pb2C 2 H 3 2 , 3aq.), The commer- cial salt, known as sugar of lead, answers : 15 %. MEKCTJRY SALTS. Mercurous Nitrate (Hg 2 2N0 3 ). This salt, sometimes termed the protonitrate, may be prepared by keeping pure mercury in contact with pure cold nitric acid. A saturated aqueous solution may be used, some metallic mercury being kept in the reagent-bottle. OF REAGENTS AND TESTS. 71 Mercuric Chloride (HgCl a ), or mercury dichloride, is met with pure in commerce as corrosive sublimate : 5 / . Potassio-mercuric Iodide, or Nessler's test. This excessively delicate test for ammonia is a solution of HgK 2 I 4 in potassium or sodium hydrate. To prepare it take 3*5 grams of potassium iodide and dissolve them in 10 c. c. of water : dissolve 1-7 gram of mercuric chloride in 30 c. c. of water, and add the latter solution to the former gradually, till a permanent precipitate is produced. Then add a 20 per cent, solution of sodium hydrate till the liquid measures 100 c. c. ; add more mercuric chloride solution drop by drop until a permanent precipitate again forms; allow the solu- tion to rest, then pour off the clear part, and preserve it in a well-closed bottle. MERCURIC OXIDE (HgO). This compound should be prepared by precipitating a saturated solution of mercuric chloride with an excess of sodium hydrate solution. The yellow mercuric hydrate at first thrown down passes, after thorough washing and drying at 100 C., into the oxide. PALLADIUM SALT. Palladious Chloride (PdCl 2 ) is made by dissolving palladium in hydrochloric acid, to which a quarter of its bulk of nitric acid has been added, evaporating the solution to dryness on the water-bath, moistening the residue with hydro- chloric acid, and again evaporating to dryness on the water-bath ; this process is repeated twice or thrice : the residue is then once more dissolved in water. URANIUM SALT. Uranic Acetate may be purchased in a state of purity. It should give no precipitate with hydrosulphuric acid, or excess of ammonium carbonate. TIN SALT. Stannous Chloride (SnCl 2 ), or tin dichloride, may be prepared in solution by digesting granulated tin in a mixture of equal bulks of concentrated hydrochloric acid and water with the aid of heat, the process being stopped before all the metal and acid are consumed : the presence of a strip of platinum foil aids the process of solution. Decant the clear solution into a bottle containing granulated tin, and add a little dilute hydro- chloric acid. 72 QUALITATIVE ANALYSIS. PLATINUM SALT. Platinum Tetrachloride (PtCl 4 ). This salt which is also called platinic chloride, may be obtained tolerably pure ; but it is often purposely adulterated with sodium chloride. It may be prepared from the metal in the same way as palladious chloride. It always contains 2HC1 when dried at 100 C., and is frequently contaminated with Iridium chloride. Gold terchlo- ride may also be made by the same process. ETHYL SALTS. Ethyl Oxide, or Ether ([C 2 H_] 2 0). Commer- cial methylated ether answers most purposes. If required dry, it may be distilled in a water-bath from caustic lime. Ether usually contains, besides water, a considerable quantity of alcohol, from which it may be freed by contact with water in a bottle ; the washed ether may then be freed from water by means of lime. The specific gravity of pure ether is '72. Ethyl Hydrate, or Alcohol (C 2 H 5 HO). Eectified methylated spirit may generally be employed : it may be obtained nearly free from water by distillation from caustic lime. Starch Water (C 6 H 10 5 ). Mix finely powdered white starch with a little cold water, and pour the mixture into boiling water. Allow the liquid to cool before using it. A lump of camphor will preserve starch solution from change for some time. Arrow- root starch may be advantageously employed. 2 grams of starch in 1 litre of water. HYDKOGEN SALTS or ACIDS. Hydrochloric Acid (HC1). Nitric and sulphuric acids, salts of iron, and arsenic trichloride are common impurities of commercial hydrochloric acid; it may, however, be obtained pure in commerce. One part of the strong acid, sp. gr. 1'2, diluted with 4 parts of water is used as dilute hydrochloric acid. Nitric Acid (HftT0 3 ). The commercial acid generally contains a little hydrochloric and sulphuric acid ; it may, however, be purchased pure. One vol. of strong acid, sp. gr. 1-42, is to be mixed with 4 vols. of water to form the dilute acid. Acetic Acid (HC 2 H 3 2 ). This acid is often contaminated with sulphuric acid. The glacial acid prepared for photographic use is pure. It has the sp. gr. 1-048 : to make the dilute acid add OF REAGENTS AND TESTS. 73 3 vols. of water to the strong commercial, or 9 vols. to the glacial acid. Water (H 2 0). This liquid, as it generally occurs, holds vari- ous salts in solution sulphates, chlorides, carbonates. Rain- water collected in the open country is nearly pure. Water may be completely purified by careful distillation after having been rendered alkaline by a little sodium carbonate, the first part of the liquid which comes over being rejected so long as it gives a yellow colour with Nessler's test. Hydrosulphuric Acid, or Sulphuretted Hydrogen (H 2 S). Iron sulphide is to be acted on with dilute sulphuric acid ; the evolved gas is washed by passing it through a wash-bottle containing a small quantity of water. A saturated solution of the gas is much employed in analysis; it should be kept in well- stoppered bottles, the stoppers of which have been smeared with vaseline. Sulphuric Acid (H 2 S0 4 ). The commercial acid, or oil of vitriol, generally contains lead, nitric acid, and arsenic. Lead may be separated by diluting the acid. Arsenic is more difiicult of removal : addition of potassium dichromate and distillation is said to yield a pure product. Nitric acid is expelled by heating with oxalic acid or ammonium sulphate. To make the dilute acid, 1 vol. of oil of vitrol is very gradually and cautiously poured, with constant stirring, into 5 vols. of water : after 24 hours de- cant the clear liquid from the precipitated lead sulphate. Oxalic Acid (H 2 C 2 4 ). The commercial acid usually contains alkalies, lime, and sulphuric acid. It may be purified by subli- mation. The sublimed acid has no water of crystallization ; its formula is given above : 5 / . Phenol or Carbolic Acid (HC 6 H 5 0). The white crystallized car- bolic acid of commerce may be dissolved in distilled water : 4 / . Sulphitidigotic Acid. The solution of 1 part of indigo in 6 parts of fuming sulphuric acid is known by this name. The sul- phuric acid must be free from nitric acid. The blue liquid is diluted before use with 20 vols of water. Tartaric Acid (H,jC 4 H 4 6 ). The commercial acid is sufficiently pure : 10 %. 74 QUALITATIVE ANALYSIS. Citric Acid (H 3 C 6 H 5 7 , aq.) may be obtained pure in com- merce : dissolve the crystals in their own weight of water. Hydrofluosilicic Acid (H 2 SiP 6 ). A mixture of 1 part of sand, 1 part of calcium fluoride (fluorspar), and 6 parts of oil of vitriol is heated in a flask or in an earthenware jar placed in hot water ; the gas evolved is silicon fluoride. If conducted into about 4 parts of water, silica will separate, and the liquid will contain a combination of hydrofluosilicic acid and silicon tetrafluoride, known as hydrofluosilicic acid. The tube which delivers the gas into the water should just dip under the surface of a little mercury, to prevent its opening becoming choked up with the separated silica. The solution is finally filtered for use through a linen cloth. If hydrofluoric acid be required, it is to be made from 1 part calcium fluoride and 6 parts of oil of vitriol, heating the mixture and absorbing the HF evolved in water. In the preparation of this acid vessels entirely made of lead or platinum must be used ; its solution is generally preserved for use in bottles of gutta-percha. TEST-PAPEKS. Vegetable blues, or at least most of them, possess the peculiar property of becoming red when moistened with an acid, i. e. the hydrogen salt of a simple or compound acid-radicle ; while their original colour is restored by an alkaline solution that is, by the solution of a substance whose basic properties are definite. Some of the most delicate vegetable blues or purples even assume a new colour when submitted to an alkaline liquid, becoming a brilliant green. An alcoholic tincture of dahlia-flowers or of the stems of the Coleus verschaffelti may be used as a sensitive test colour. Vegetable yellows, when dipped into alkaline solutions, become red-brown, but are not .influenced by acids beyond the restoration of their original colour (boracic acid being an excep- tion, for it behaves with turmeric like an alkali). These indica- tions, although very valuable, must not be too implicitly relied on, since certain salts which are theoretically neutral produce changes of colour. OF REACTIONS. 75 Blue Litmus Paper. The litmus of commerce should be crushed and mixed with water, and kept, with continual stirring, at a temperature just under that of boiling water for some time. Very dilute sulphuric acid is now added to the filtered solution, until the colour has been changed to a reddish violet ; the blue colour is then just restored by the addition of a small quantity of the original solution. White wove writing-paper, not highly glazed, is then to be painted with the blue liquid on one side only ; and the coloured pieces, when dry, are to be cut into narrow strips for use, and preserved in a well-stoppered bottle. Red Litmus Paper. This may be prepared in the same way as the preceding paper, the blue liquid being in this case first slightly reddened with a drop of dilute sulphuric acid. Turmeric Paper. An alcoholic extract of turmeric-root is of an orange-yellow colour, and becomes reddish-brown when sub- mitted to the action of alkaline solutions : the paper is prepared as above. Phenol-phthalein Paper. Smooth unglazed writing-paper is steeped in a solution of phenol-phthalein. This solution is made by dissolving 5 grams of this substance in 1 litre of proof spirit. Lead-acetate Paper. Strips of paper steeped in a solution of basic lead acetate are very useful in the detection of hydrosul- phuric acid (H 3 S). iv. OF REACTIONS. By the use of the various reagents and tests already described, it is easy to identify or to separate the several constituents of any common substance which may require examination. But before the student can thus analyse (dj/a\vut to the ed. filtrate add NH 4 HO in slight exce ss, then ammonium carbonate, and then boil and filter. The precipitate The fil- is examined trate is for Ba, Sr, tested for Ca, by Table Mg: see for Group p. 107. . IV. p. 106. Notes to Table for Group III. (1) Test this precipitate for Mn also, by fusing a small part with Na 2 CO 3 and KC1O 3 on platinum foil. (2) If P 2 ^s k e absent, this solution may be at once tested for iron by add- ing K 4 FeCy 6 , omitting the citric acid. ANALYTICAL SCHEMES. 105 If P 2 g be absent. To the main portion of the solution add NH 4 C1 NH^HO and then an excess of (NH 4 ) 2 S without filtering off the first precipitate as in the previous Scheme. The mixture is warmed and the precipitate collected on a filter and washed (if black, with weak ~(NH 4 ) 2 S). The filtrate is reserved for Groups IV. and V., while the precipitate is examined for Fe, Mn, Al, and Zn, according to the above Table for Group III. As phos- phates are absent, the precipitate produced by NaHO contains Fe and Mn only. (See note 2 to Table.) A portion of the original solution of the substance may be taken for this group if no precipitate has been obtained in the preceding groups. Much may be learnt as to the metals present by carefully noting the changes produced on adding ammonium hydrate after ammonium chloride. If ammonium hydrate in excess produce no precipitate, manganese and ferrous salts are the only members of the group that can be present. If a white precipitate be pro- duced soluble in excess of ammonium hydrate, zinc is present. If ammonium hydrate afford a permanent white precipitate, either aluminium or phosphates or oxalates of the alkaline earths are present. A red precipitate by ammonia indicates a ferric salt, a dark green a ferrous salt, ferrous oxide being partially precipitated by ammonia when the amount of ammoniacal salt present is small. The knowledge thus obtained will serve greatly to shorten the subsequent operations ; for instance, if no black precipitate be obtained on adding ammonium sulphide, and iron is consequently absent, the precipitate by ammonium hydrate containing manganese and phosphates need not be dissolved and treated with citric acid. GBOUP IV. THE CARBONATES INSOLUBLE IN WATER. Ammonium carbonate gives a white precipitate of the metallic carbonate, in neutral or alkaline solutions of calcium, strontium, and barium salts. Before adding ammonium carbonate, the filtrate from the pre- ceding group (that is, from the precipitate produced by ammo- nium sulphide) is to be treated with hydrochloric acid, and boiled 106 QUALITATIVE ANALYSIS. till all smell of hydrosulphuric acid has ceased ; it is then, if cloudy, filtered. If none of the preceding group-tests has pro- duced a precipitate, the original solution, after addition of am- monium chloride, may be treated at once as under. SCHEME. To the solution add ammonium hydrate in slight excess, then ammonium carbonate, warm and filter ; reserve the filtrate for examination by the Table for Group Y. Wash the precipitate, and then proceed thus : TABLE FOR GROUP IV. The precipitate is to be dissolved on the filter in the smallest possible quantity of acetic acid ; then add potassium chromate in slight excess, warm and filter : Ba. The precipitate is barium chro- mate. For special The filtrate may contain strontium and calcium ; divide it into two portions : tests for barium and the metals of Sr. I. To one portion Ca. II. To the other por- this group, refer add a considerable tion, if strontium has not to Preliminary Examination, p. quantity of solution of calcium sulphate : been found in I., add am- monium hydrate and am- 91. a white precipitate monium oxalate : a white coming down after a precipitate indicates cal- time indicates stron- cium. If strontium has tium. beenfouud in I., evaporate (Calcium sulphate solu- tion produces no pre- cipitate in solutions of portion Il.with a solution of potassium sulphate and boil the dry residue with calcium salts unless water. Filter the extract they are very strong.) thus made ; to the filtrate add ammonium, oxalate, as above directed. Barium chloride is insoluble in alcohol, the strontium chloride soluble : on this fact the following mode of separating barium and strontium (in the presence of calcium) is founded. Add excess of calcium sulphate solution to the hydrochloric acid solu- tion of the Group IV. precipitate ; boil, collect and well wash the precipitated barium and strontium sulphates, then boil them for some time with potassium carbonate solution. The sulphates thus converted into carbonates are washed, and then dissolved ANALYTICAL SCHEMES. 107 in hydrochloric acid, and the solution evaporated to. dryness. The residue, digested with a little strong alcohol, will yield a solution of strontium chloride, which may be warmed and ignited, and the crimson colour of the flame observed. GKOUP Y. THE CARBONATES SOLUBLE IN AMMO- NIACAL SALTS OR WATER. The nitrate from the previous group may contain MAGNESIUM, SODIUM, and POTASSIUM salts. AMMONIUM compounds must be tested for in the original substance. See Preliminary Examina- tion, page 90. Concentrate the nitrate, add to it a few drops of ammonium oxalate, and filter it if necessary. SCHEME. The nitrate is divided into two unequal parts, and thus tested : Mg. I. Smaller portion. Add a little ammonium chloride and ammonium hydrate and some sodium phosphate ; agitate well : a white crystalline precipitate of ammonio-magnesium phosphate, which may form very slowly, indicates magnesium. II. Larger portion. The larger portion is to be evaporated to dryness in a platinum or thin porcelain vessel, and then ignited to expel salts of ammonium. If magnesium has been found in the previous experiment, moisten the residue with ammonium carbonate, evaporate and ignite again. Dissolve the residue in a little hot water and filter : use the filtrate as follows : K. Moisten a platinum wire with it, and ignite in the blow- pipe-flame ; a lilac tint indicates potassium. To another portion of the same solution add an excess of tartaric acid and some alcohol, and agitate well : if potassium be present, a white crys- talline precipitate of hydro-potassium tartrate will be formed. Platinum tetrachloride, a drop of hydrochloric acid, and some alcohol added to another portion of the filtrate will give, on standing, an orange crystalline precipitate of the double chloride of platinum and potassium (K 2 PtCl 6 ). To obtain the precipitates here indicated, it is essential that a concentrated solution should be employed. 108 QUALITATIVE ANALYSIS. Na, The presence of sodium compounds is recognized by the bright yellow tint they impart to the blowpipe-flame. This is so intense as to obscure the violet potassium colour, unless the flame be viewed through dark cobalt-blue glass, which cuts off the yellow sodium rays only. Sodium in sufficient quantity to give the flame reaction distinctly is sure to be present in the fil- trate from the four groups of bases. It is impossible to obtain reagents free from it, or to prevent its introduction in other ways. v. ANALYTICAL SCHEMES FOE THE DETEC- TION OF THE NON-METALLIC OR ACID RADICLES. In the preliminary examination (see Experiments VIII. to XIII.) much information will have been obtained in reference to the acids. The examination of basic radicles, just concluded, will also frequently throw some light on the subject. Thus, if the substance is found to be soluble in water, and to contain certain basic radicles, it is evident that only those acid radicles can be present which form soluble compounds with them : thus the presence of barium excludes that of the sulphuric radicle. With substances insoluble in water similar reasoning will apply. The student will therefore consult with advantage the Table of Solubilities given at pp. 114, 115. The search for the acid radicles may be divided into three parts. We make first of all certain experiments on the original substance, constituting part of the preliminary examination ; then we apply two or three reagents to a prepared solution and examine further the precipitates formed ; and, lastly, we try the action of a few special tests upon this prepared solution. EXAMINATION FOE ACIDS IN A PEEPAEED SOLUTION. If silica in the soluble form be present, it must first of all be separated by evaporation to dryness with excess of hydrochloric acid ; in this case chlorine, iodine, and cyanogen cannot be tested ANALYTICAL SCHEMES. 109 for in the redissolved residue, but must be specially sought for in the original substance. The carbonic, hydrosulphuric, sulphurous, nitric, and acetic radicles will have been detected already in the preliminary examination, and would likewise be lost in the pre- paration of the solution. The sulphuric radicle is sought for in Experiment XIII. p. 94. If no indications of any acid radicles have been obtained in the preliminary examination, the only acid radicles that need be sought for are the phosphoric and oxygen. Before proceeding to the following groups, all basic radicles other than the alkaline metals must be separated. This may be effected by boiling with an excess of sodium carbonate. Where long-continued ebullition with a solution of sodium carbonate does not effect a transference of acid and basic radicles, fusion with the mixed sodium and potassium carbonates will be found to answer the purpose in view (see p. 113). In this case, how- ever, organic acids are, of course, destroyed. If organic matter be present, together with metals of the first three groups, hydrosulphuric acid or ammonium sulphide must be employed to separate these metals : and if the alkaline earths be also present, the solution, after removal of the sulphur, must be finally boiled with sodium carbonate. If hydrosulphuric acid be employed, the arsenious radicle will of course be removed from the solution. The prepared solution (or the original solution, supposing this to contain only alkaline bases) is divided into three portions, which are examined according to the following groups ; if, how- ever, the preliminary examination has proved the absence of organic acids, examination for the third group is omitted. The solution should not be too dilute. GROUP I. CHLOKINE AND OTHEE MONAD ACID RADICLES. SCHEME. To one portion of the solution add dilute nitric acid till the solution is distinctly acid, and then solution of silver 110 QUALITATIVE ANALYSIS. nitrate till no further precipitate is formed. The precipitate may contain silver chloride, iodide, and cyanide. Wash the pre- cipitate, and heat it gently with excess of ammonium hydrate till no more dissolves ; filter. I, The residue, in- soluble in ammoni- um hyd rate, is, if yel- lowish, silver iodide. Confirm the presence of iodine by treating a little of the original substancewithstarch- paste and a drop of chlorine water : a dark blue colour in- dicates iodine. The filtrate may contain silver cyanide and chlo- ride*. Add nitric acid in excess, agitate, wash the precipitate by decantation, dry and heat it to fusion on a piece of porcelain. Boil the residue on the porcelain with nitric acid, dilute, filter. Cl. Any inso- luble residue is silver chlo- ride. Cy. If the filtrate contain any silver, its presence indicates cyan- ogen, for silver cyanide is decom- posed by heat ; and the residue, chiefly of silver, which it leaves, is then soluble in nitric acid. * If cyanogen has not been found in the preliminary examination, further treatment can, of course, be omitted, as the precipitate, on the addition of nitric acid, can then be silver chloride only. GROUP II. FLUORINE AND THE PHOSPHORIC AND OXALIC RADICLES. To another portion of the solution add acetic acid in excess, and divide into two parts. P0 4 . (1) Add ferric chloride solution, drop by drop. A yellowish-white precipitate is ferric phosphate. Confirm by the molybdate test, pages 38 and 104. P. (2) Add calcium chloride solution. A white gelatinous precipitate is calcium fluoride. Confirm by etching glass, as in Preliminary Examination, page 93. C 2 4 . A white crystalline precipitate on the addition of calcium chloride is calcium oxalate. It may be distinguished from calcium fluoride by leaving calcium carbonate on ignition, and then dissolving with effervescence on the addition of acetic acid. If fluorine has been found by its action on glass, and the calcium precipitate after ignition partially dissolves, with evolu- tion of carbon dioxide, in acetic acid, both hydrofluoric and oxalic acids are present. ANALYTICAL SCHEMES. Ill GROUP III. THE TAETAEIC AND CITEIC EADICLES. Another portion of the solution is made exactly neutral. This is effected by adding dilute nitric acid until the solution is very slightly acid, boiling to expel carbon dioxide, and then adding very dilute ammonium hydrate until the solution is exactly neu- tral to test-papers. It is absolutely necessary that the least possible excess of either acid or alkali should be added, as the formation of am- monium salts in any quantity interferes with the subsequent reactions. If ammonia has been found present in the substance in the search for bases, it must be expelled by continued ebulli- tion with caustic soda before proceeding to the examination for the acids of this group. To the neutral solution add calcium chloride, shake well, and filter. CiHiOe- A white precipitate, soluble in ammonium chloride, is calcium tartrate. Calcium phosphate and oxalate, the acid radicles of which have been detected in the previous group, would also ba pre- cipitated here, but may be distinguished from the tartrate by being insoluble in ammonium chloride. C 6 H 5 7 . To infiltrate add a few drops of ammonium hydrate, and boil ; a white crystalline precipitate, so- luble in ammonium chlo- ride, is calcium citrate. Owing to the great similarity between citric and tartaric acid (which have been previously indicated, by blackening with sul- phuric acid, in the Preliminary Examination), the following points of distinction, in addition to the above, should be carefully attended to. Calcium tartrate is soluble in a cold solution of potassium hydrate, and is reprecipitated on boiling, whereas calcium citrate is insoluble in either hot or cold caustic alkali. Silver tartrate, heated with a little ammonium hydrate, pro- duces a metallic mirror of silver in a few minutes, whereas silver citrate requires long boiling for reduction. This experiment is performed as follows : Eemove the preci- pitate of calcium tartrate or citrate (by means of a spatula) to a 112 QUALITATIVE ANALYSIS. test-tube which has been thoroughly cleaned by means of caustic soda and washing with distilled water. Then add a few drops of silver nitrate solution, and only so much of a very weak ammonia solution as shall suffice to dissolve part of the precipi- tate which it first forms. If a mirror appear in the tube on gently warming it, a tartrate was present ; if the mirror form only on boiling for some time, the presence of a citrate is indi- cated. A solution of a tartrate, strongly alkaline with sodium or po- tassium hydrate, heated to boiling, and a few drops of potassium permanganate added, first turns green ; and then a brown preci- pitate falls, the solution becoming colourless. An alkaline solution of a citrate so treated turns green, but no precipitate is produced. SPECIAL TESTS FOR ACID RADICLES. Acetates. See Preliminary Examination, Experiment XI., p. 93. Acetates in a neutral solution give, with ferric chloride, a blood-red colour, destroyed by HC1. Cyanides. Cyanogen is best tested for as follows : Moisten the substance in a watch-glass with hydrochloric acid ; imme- diately invert over it another watch-glass, having its inner sur- face moistened with a drop of yellow ammonium sulphide : warm gently, remove the upper watch-glass, dry it on the water-bath, add a drop of dilute hydrochloric acid and a drop of ferric chlo- ride : a blood-red colour indicates a cyanide. Nitrates. See Preliminary Examination, Experiment X., p. 93. Phosphates. See pp. 38 and 104. Silicates. See pp. 91 and 94. The silicic radicle present in its soluble form may be recognized by evaporating the solution to dryness with an excess of hydrochloric acid, heating the residue for some time to a temperature of about 150 C., and then digesting it in strong hydrochloric acid. An insoluble residue, volatilizing entirely when warmed in a platinum crucible with hydrofluoric acid, is silica. ANALYTICAL SCHEMES. 113 Sulphates. See Preliminary Examination, Experiment XIII., p. 94. All the other acid radicles not included in the three acid groups above will have been identified in the preliminary ex- amination. vi. ANALYTICAL SCHEME FOR THE EXAMI- NATION OF SUBSTANCES INSOLUBLE IN ACIDS. An examination before the blowpipe will in many cases, espe- cially if the substance be a simple salt, prove sufficient for its identification. If the presence of sulphur, carbon, or phosphorus be suspected, the substance is first to be ignited ; if it continue unaltered, or a distinct residue remain, it is to be finely pow- dered, mixed with four times its weight of the mixed potassium and sodium carbonates, and the whole kept in fusion for a quarter of an hour, a platinum crucible being used unless the preliminary examination has shown the presence of an easily reducible metal, when one of porcelain must be employed; in this case traces of silica and alumina will be unavoidably in- troduced into the analysis. The crucible and its contents, when cold, are to be boiled with water, and the solution filtered. The solution in water may contain aluminium, tin, antimonj, the silicic radicle, &c. &c. Divide into two portions. To one add nitric acid in excess and boil ; render the solution slightly alka- line with ammonium hydrate, and filter if necessary ; the filtrate is to be examined for all acids save nitric and the organic acids. The other portion of the solution is to be evaporated to dryness with an excess of hydrochloric acid. Heat the residue to about 150 C. for some time ; when cold, moisten it with strong hydro- chloric acid, and allow it to stand twenty minutes ; then add water, and dissolve. An insoluble residue is probably silica : confirm by special tests. Filter. Examine the filtrate for tin, 114 QUALITATIVE ANALYSIS. TABLE OF Acetate. Arseniate. Arsenite. Carbonate. Chloride. 1 b 3 i > o3 1 >~ w 3 nb A Aluminium .... AT" Ammonium .... Am' Antimony .... Sb'" Arsenic As'" Barium . Ba" S S S s I S I I I S S (S) 8 T S S S s s (ft) S (S) 8 I s I s I s (ft) S 1 Calcium Ca" s T w/ T s (S) s (ft) s Copper Cu" Ferric . . Fe"' s s I I I T I T s s s s I T T I T Ferrous . . Fe" s T T T s s 1 (T) S Lead Pb" s T T T (ft) (S) T (ft) (ft) Magnesium .... Mg" Manganese .... Mn" Mercuric Hg" s s s I I T I I T I 1 T s s s s I S I S I T s s (T) /0\ Mercurous .... Hg Potassium .... K' Silver Ag' (u) s (S) S T 1 S T S T s F s T s T S T S F Sodium Na' s s' S S s S S S S Stannic .... Sn IV s T T s T (ft) Stannous Sn" s T T T s T (ft) Strontium .... Sr" Zinc Zn" s s I T (ft) I T s 8 (I) (ft) s T S T S s S = Soluble in water : (S) Sparingly soluble in water. F= Insoluble in water and acids. I = Insoluble in water, but soluble in HOI, or HN0 3 , or nitrohydro- chloric acid. (I) = Insoluble in water, sparingly soluble in one or other of the above acids. Notes to Table of Solubilities. Arsenic, antimony, tin, lead, aluminium, and zinc oxides or hydrates are soluble in KHO or NaHO. Arsenic, silver, copper, manganese, zinc, and magnesium oxides or hydrates are soluble in NH 4 HO or ammonium salts. SOLUBILITY OF SALTS. 115 SOLUBILITIES. 3 ,2 1 cS -2 1 1 [f -S C3 'I rl & 1 Is o r^ |H 1 43 ~tn H H 19 oj ^ PH GO CO GO i H s I I I F S I I s Aluminium. s s s S S S s s Ammonium. (S) I I S I I I Antimony. , , (S) s I s Arsenic. s I s I I F s I I Barium. s I (S) I I (S) (S) (S) (S) Calcium. s I I I I S I (S) Copper. s s (I) I I s (S) I s Ferric. (S) I I I , . s (S) I (S) Ferrous. s I I I , F I I I Lead. s s I I F S s s s Magnesium. s I I I I s I I (S) Manganese. s I I I s I I I Mercuric. s I I I s I I I Mercurous. s s s s S s s s s Potassium. s I I I (S) I I I Silver. s s s s S 8 s s s Sodium. s s I I s s I s Stannic. s I I I s (S) I (S) Stannous. s I (S) I I F s (S) (S) Strontium. s I I I I S s (S) Zinc. Some salts insoluble in water or acids are soluble in saline solutions, as calcium tartrate in ammonium salts, and lead sulphate in solution of alka- line tartrates or acetates. Some metals (Ag, Ou, Hg, Pb) and alloys not affected, or scarcely so, by HC1, are dissolved by HNO 3 . Many sulphides insoluble in HC1 are decomposed by HNO 3 . HgS, Hg 2 01 2 , Fe 2 O 3 (ignited), &c., scarcely attacked by either HC1 or HNO 3 , are dissolved by nitrohydrochloric acid. Sand, many silicates (pipe-clay), fluor-spar, sulphates of barium, stron- tium (calcium), tin-stone, glass, AgOl, PbSO 4 , carbon and sulphur, chrome iron-ore are not attacked by these acids: and S are recognized by their behaviour when heated ; and the others may, for the most part, be decom- posed by fusion with potassium and sodium carbonates. QUALITATIVE ANALYSIS. antimony, arsenic, and aluminium, according to the schemes for Groups II. and III. The residue, insoluble in water, may contain silicic acid, the alkaline- earthy metals as carbonates, lead oxide, metallic silver, and ferric oxide. "Wash thoroughly, and dissolve in dilute hydro- chloric acid with the aid of heat, or, if the original substance was blackened by ammonium sulphide, in nitric acid. The solution is to be examined for basic radicles according to the plans already given. The residue consists, probably, of silica, or of a portion of the original substance which has escaped the action of the alkaline carbonates. If it is desired to examine insoluble silicates for the alkaline metals, the substance is to be fused with four times its weight of barium hydrate in a platinum crucible, the mass dissolved in dilute hydrochloric acid, and the barium and alkali metals sepa- rated according to the schemes given for Groups IV. and Y. Or the finely powdered silicate may be treated with hydrofluoric acid in a platinum or lead vessel, then with sulphuric acid, the excess of that acid being volatilized by heat; the silica is thus entirely removed : the residue is to be examined in the ordinary way for the basic radicles. The construction and uses of the annexed Table of Solubilities will be readily understood by the student who has followed the instructions in Qualitative Analysis which have been given. vii. ANALYTICAL SCHEME FOE THE EXAMI- NATION OF ALLOYS. The alloy is reduced to a fine state of division by cutting with a knife, filing, or, when brittle, by powdering in a steel mortar. The portion taken for analysis is boiled with nitric acid diluted with. twice its bulk of water, till all action ceases; the solution is then diluted with water. EXAMPLE OF QUALITATIVE ANALYSIS. 117 The solution will contain all metals present in the alloy, save gold, platinum, tin, and perhaps antimony. Examine it accord- ing to the foregoing schemes for the detection of basic radicles. The residue may contain gold, platinum (both greyish black), stannic oxide, and antimony oxide (both white). If large quan- tities of tin be present, traces of other metals may occur in this residue. After thoroughly washing the residue, fuse it with three parts of potassium cyanide in a porcelain crucible ; boil the mass with water, and wash the metallic residue by decantation ; then heat it with concentrated hydrochloric acid. Sn. To a small portion of the clear solution add a drop or two of mercuric chloride ; a white precipitate, becoming grey on boiling, indicates tin. Add a little nitric acid to the rest of the solution and residue, and boil till complete solution is effected : divide into three portions. An. A small portion of the liquid is considerably diluted, and a little stannous chloride and ferric chloride added ; a purplish or reddish coloration proves the presence of gold. Pt. A small portion is treated with ammonium chloride, eva- porated nearly to dryness and treated with alcohol : a yellow crystalline residue indicates platinum. Sb. The rest of the solution is treated with excess of ammonium sesquicarbonate, and then well boiled and filtered. The nitrate is acidified with hydrochloric acid, and hydro- sulphuric acid and water added. An orange-red precipitate indicates antimony. In order that the student of qualitative analysis may see how the methods of examination which we have just described are applied in practice, we proceed to give AN EXAMPLE of the QUALITATIVE EXAMINATION of an unknown mixture of 118 QUALITATIVE ANALYSIS. salts, this mixture occurring as a. dull greenish solution with a white residue or sediment. First of all the solution and residue (after nitration) were separately divided into four portions, the former labelled S 1, S 2, S 3, and S 4, and the latter R 1, E 2, E 3, and B, 4. 1. Preliminary Examination for Bases. S 1. This portion of the solution was cautiously evaporated just to dryness, and tested in accordance with the directions given in the Table of the Preliminary Examination for Bases (pp. 89, 90, 91, and 92), when changes occurred in the follow- ing experiments only : I. a luhite sublimate in tube, and, on further heating, fumes of N0 2 ; II. bluish-green flame ; III. substance deflagrated ; Y. when hot, green ; when cold, blue. Prom these experiments we infer that the following substances are present : NH 4 , Cu, and a nitrate or chlorate. Now, in the first instance we might have argued, from Experiment I., that As and Hg were present as well as NH 4 "; but this could not be the case, since neither globules nor metallic mirror was obtained with the bulb-tube and Na 2 C0 3 , in Experiment I b. B 1. This portion of the residue was tested in the same way as the solid matter obtained by the evaporation of S 1 : changes occurred in the following experiments only : I. a gas, C0 2 , given off-, II. red flame', III. luminous residue and bluish- white malleable globules of metal ; IV. globules as in III. Erom these results we infer the presence of Ca, Ba, Sr, or Mg, and of Pb. 2. Systematic Examination for Bases. S 2. The second portion of the solution was submitted to the action of the group-tests (p. 96) in order, each precipitate ob- tained being further examined according to the Table for the group to which it belonged. In Group II. (pp. 98-102) a brownish- black precipitate, proved by further treatment and special tests to be copper sulphide"; in Group III. (pp. 102-105) a black precipitate was shown to be iron sulphide (the iron was found to exist as a EXAMPLE OF QUALITATIVE ANALYSIS. 119 ferrous salt in the original solution) ; while no other base was detected, [save that in the Experiment I a of the Preliminary Examination (p. 90) ammonia was detected. E 2. This portion of the original residue was found to be altered, but not dissolved completely, by dilute HC1 ; and so dilute HN0 3 was employed instead, when escape of C0 2 took place. The solution thus made could not be mixed with S 2 above without producing a dense precipitate ; and therefore it was analysed separately (though in most analyses such admixture may be made) ; had it been wholly or partially insoluble in acids, it would have been requisite to treat this residue accord- ing to the scheme for the Examination of Insoluble Substances (p. 113). When the HN0 3 solution of E 2 was duly examined by the group-tests, precipitates were obtained in Group I. of lead chloride, in Group II. of lead sulphide, in Group IV. of calcium carbonate ; all these indications were duly confirmed by special tests. 3. Preliminary Examination for Acids. S 3 and E 3. Small portions of the solution and residue were mixed and evaporated just to dry ness ; with the dry material thus obtained the following Experiments (pp. 92, 93, and 94) were performed : VIII. C0 2 evolved ; X. brown ring. 4. Systematic Examination for Acids. S 4 and E 4. With the remaining portions of the original solution and residue mixed together, a "prepared solution" was made (p. 108). With this liquid the systematic examination for acids was conducted, a small portion, however, being used for Experiment XIII. Preliminary Examination, p. 94, when sul- phuric acid was found. In Group I. of the acids chlorine was identified, while no indications were obtained in the other groups. Among the special tests, those for nitric acid gave positive results. Thus from the results of the preliminary and systematic exa- 120 QUALITATIVE ANALYSIS. urinations, we conclude the unknown mixture of salts contained the metals or basic radicles Pb, Cu, Fe, Ca, and NH 4 , and the acid radicles C0 3 , Cl, N0 3 , and S0 4 . From the separate exami- nation of the solution and residue, we conclude that the salts actually present in each were : Copper, ferrous, and^ Lead carbonate, 1 in the re- ammonium chlo- I in the so- Calcium carbonate, J sidue. rides, sulphates j lution. and nitrates, PART III. QUANTITATIVE ANALYSIS, CHAPTER I. i. INTRODUCTION. the student has acquired some skill in recognizing and detecting the common basic and acid radicles, the quantitative estimation of various chemical substances will engage his atten- tion. Scrupulous care and precision, together with manipula- tory adroitness, are here more than ever necessary. The knowledge which he has gained is here applied to deter- mine the quantity of the various constituents of a compound body. The course of practice under this head is necessarily limited in its variety, from the greater amount of time required for the operations of quantitative analysis. Attention is there- fore at once turned to matters of agricultural importance the analysis of manures, soils, feeding-materials, &c. In following the schemes of analysis here described, it should always be borne in mind that they are intended only for the* particular case mentioned, and may consequently fail if otherwise applied if, for instance, other substances be present than those here supposed. To describe processes available under every con- tigency would demand a far larger work than the present. In cases differing somewhat from those described, the student's own knowledge of chemistry must be brought to bear, and he must endeavour to think out a modification of the process suitable to the case. Before proceeding to operate upon the various commercial and 122 QUANTITATIVE ANALYSIS. agricultural products which have been selected as suitable sub- jects of quantitative analysis, the student will find it best to make estimations of the constituents of certain definite and pure chemical compounds. For the determination of water, a weighed quantity of crystallized sulphate of copper may be taken ; for the sulphuric radicle and for calcium, crystallized calcium sul- phate or selenite ; for magnesium, Epsom salts : for potassium, the pure sulphate of that metal ; for iron, crystallized green vitriol ; for aluminium, ammonia-alum ; and so on with the other most important metallic and acid radicles. We proceed to give full directions for the estimation of calcium, barium, magnesium, potassium, and the phosphoric and sulphuric radicles the quanti- tative determination of other ingredients of soils, food, manures, &c. being duly described under the examples in which they severally first occur. It will, however, be well to introduce a word or two now concerning the names of chemical compounds, and concern- ing weights and measures. Chemical Nomenclature. The names assigned to salts and che- mical compounds in this book are mainly those commonly adopted by scientific chemists. But a very rigid adherence to one system has not been observed, and is indeed a matter of minor im- portance, though of considerable difficulty. In the case, for instance, of the substance which is correctly termed sodium nitrate, the terms sodic nitrate and, still more commonly, nitrate of soda, are often employed indifferently. It is of real import- ance nevertheless to know that these three names signify the same compound (NaN0 3 ), a combination of one atom of sodium, one of nitrogen, and three of oxygen. In the case of this com- pound, and of many other common substances, we shall in future use the more familiar along with the accurate names, or even instead of them, on account of the special commercial or econo- mical character of the subjects of which we treat in the third part of this volume. We shall likewise adopt the expressions ammonia, lime, magnesia, &c., and calculate our results into these forms on account of the convenience of comparing our results with published analyses. The acid constituents of salts will appear, in a similar WEIGHTS AND MEASURES. 123 manner, as sulphur trioxide, phosphorus pentoxide, &c., instead of as the corresponding acid radicles, for the same reason. Weights and Measures. The system of weights and measures now in almost universal use for scientific work is the French metrical (decimal) system, founded on the metre or one ten -mil- lionth part of a quadrant of a meridian measured through the poles of the earth. This unit of length, the metre, = 39-37079 inches. The unit of weight is a gramme, written in English gram, which is the weight of a cube of distilled water at its maximum density, viz. 4 C. ( = 39'2F.), the edge of this cube being a centimetre. It is equivalent to 15'432349 grains. The unit of capacity is a litre, or the capacity of a cube whose edge is a decimetre, and is therefore =1000 cubic centimetres. It equals 1-761 33 pint. The decimal multiples of these units are denoted by the Greek prefixes Deka, ten ; Hecto, hundred ; Kilo, thousand ; and the decimal subdivisions by the Latin prefixes Deci, one tenth ; Centi, one hundredth ; Milli, one thousandth. If this system be used, the following weights and measures will be required in the work of quantatitive analysis : 1. A set of gram weights, from 50 grams to 1 gram in brass, and downwards to 5 milligrams in platinum, with a centigram wire " rider " to weigh milligrams and parts of milligrams OP the divided beam of the balance. 2. A litre flask, which, filled so that the lowest point of the meniscus coincides with a mark on the neck, contains 1 litre at 60 P. (15-55 C.). A litre is 1000 cubic centimetres, i.e. strictly the volume occupied by (a kilogram or) 1000 grams oi water at 4 C. ; measurements are, however, for convenience, taken at 15*55 C. (60 P.) ; the actual difference thus made is 2 thousandth parts, equal to a deficiency of 2 grams. 3. A half-litre flask, or one which, filled to a mark on the neck, will deliver 500 c. c. 4. A cylindrical measure graduated to 100 or 200 c. c. 5. A Mohr's burette (with Erdmann's float), graduated to 100 c. c., divided into ths c. c. 124 QUANTITATIVE ANALYSIS. 6. A pipette to hold 20 c. c., either graduated or simply marked to show when it contains the desired quantity. If, however, the English system of weights and measures be used, the student will require : 1. A set of grain-weights, from 1000 to 10 grains in brass, thence downwards to -fa grain in platinum or aluminium, with a ^-grain wire rider. 2. A burette, graduated to 200 septems. A septem is the volume occupied by 7 grains of distilled water at 62 F., and barometer 30 in. ; 10,000 septems therefore equal a gallon. 3. A cylindrical stoppered measure for mixing, graduated to 1 or 2 decigallons. A decigallon = 1000 septems. 4. A cubic-inch pipette. A cubic inch of distilled water, at standard pressure (30 in.) and temperature (62 F.), weighs 252-457 grains : 277'274 cubic inches make 1 gallon. A Centigrade mercurial thermometer ranging from 10 to 300, and having its graduations etched on the glass, will be of service. The conversion of Centigrade degrees into Fahrenheit and vice versd may be accomplished by means of these two equa- tions : (1) (C.X 1'8) + 32 = F.; (2) (F. - 32) 4- 1'8 = C. The balance should be kept in a place not subject to acid fumes, and free from vibration ; a tall jar containing a stick of caustic potash, or else two vessels, one containing oil of vitriol, and the other a lump of quicklime, should be kept in the case to absorb the moisture of the air, and to prevent the rusting of the knife-edges and other steel parts of the balance. The balance must be levelled by means of the three adjusting screws, tfro spirit-levels laid on the floor of the balance- case (one parallel with, and the other at right angles to the beam) being employed for this purpose. In order that the whole case may not shift its position, the lower ends of the levelling screws may be made to rest upon solid disks of vulcanized india-rubber permanently fixed to the table : or three box-wood cups having flanges with screws may be fastened in such positions on the table that their WEIGHTS AND MEASURES. 125 cavities may receive the lower ends of the levelling screws. These cavities should be accurately turned and deep, though rather narrow : they may be filled up with fine graphite powder. When the balance has been made level, the perfect equilibrium of the beam must be secured. When both pans are empty and the beam is released, the pointer should coincide with the zero of the ivory scale, or else it should swing an equal number of degrees to each side. If this be not the case, the little vane over the middle of the beam must be moved towards that end of the beam which is lighter until the adjustment is complete. The weights must next engage our attention. When supplied by a good instrument-maker they are usually sufficiently ac- curate for all ordinary purposes, although when used in original researches they must be severely tested : it is also advisable to examine their condition from time to time. The large chemical weights are usually made of brass, the tenths of the gram being made in platinum, while sometimes the centigrams and lower weights are constructed of aluminium. Brass weights increase by corrosion ; gilt and platinum weights slightly diminish by wear. The following set of weights " of precision " are commonly employed in chemical laboratories : In Brass. In Platinum. In Aluminium. 50 grams *5 gram -05 gram. 20 -2 -02 10 -1 -01 10 -1 -01 5 ,, *'00o 2 *-002 1 gram *'001 1 *'001 1 *-001 The milligram weights (marked *) are seldom used, a " rider " of wire, weighing 1 centigram when in the pan, being em- ployed instead. This rider is made to travel along the divided arm of the beam, gradually diminishing in effect as it approaches 126 QUANTITATIVE ANALYSIS. the fulcrum. The arm is divided into ten parts, so that when the rider is halfway it rests on division 5 and equals 5 milli- grams or -005 gram ; when it has been placed three fourths of the distance from the extremity of the arm, it rests between the division 3 and 2 and is equal to a weight of 2J milligrams, or -0025 gram in the pan. The following directions should be followed in weighing the vessels and substances with which one has to deal in quantitative analysis. 1. Open the balance-case without shaking or displacing the instrument. 2. Release the beam of the balance (by means of the milled head or key in front) gently and steadily, avoiding all jerking motion. 3. Always use the same pan for the weights. 4. Never weigh any crucible &c. after heating until it has cooled down, in the desiccator, to the temperature of the balance- room. 5. The weights should be tried in regular order from the heavier downwards until the object which is being weighed is exactly balanced. The weights are to be read oif when the index swings an equal number of degrees on either side of the zero of the scale. 6. Keep the balance- case closed as much as possible ; this pre- caution is particularly necessary when completing a weighing. 7. Bring the balance to rest, by supporting the beam, exactly at the moment when the index points to zero : this must always be done before adding any thing to, or taking any thing from, either pan. 8. The watch-glass or crucible in which a substance is being weighed should be removed from the pan whenever any thing is to be added to it or taken from it. 9. Bead off the weights used, not only from the marks upon them, but by means of the vacant spaces in the weight-box : then restore them to their places. 10. Particular care should be taken of the smaller weights ; if WEIGHTS AND MEASURES. 127 one of these be lost, immediate search for it should be made, as it would be irretrievably ruined if trodden upon. 11. Weights are to be moved only by the forceps provided for this purpose : they must on no account be touched by the fingers. In measuring liquids in the graduated vessels, the measure must be placed perfectly perpendicular, and the eye must be on a level with the surface of the liquid. The exact level can be conveniently found by means of a small mirror placed close to the vessel on the opposite side ; when the surface of the fluid is in a straight line with the centre of the eye and its reflection, the eye is in the right position. The readings should be taken at the lower line of the dark zone of the surface of the fluid ; this may be made more distinct by placing behind the tube a piece of white paper, on which a strip of black paper is pasted, in such a position that the border line between the black and white is just below the dark zone. Besides the ordinary apparatus employed in qualitative analy- sis, and the measures, weights, and balances just described, a few instruments or special contrivances are requisite for quantitative work. Amongst the most important of these we may here describe : 1. A platinum crucible, about 24 millimetres broad at its base, 34 millims. at top : its height may be 37 millims. ; and its weight, with a flanged capsule cover (of 7 grams) to fit loosely inside the rim, need not exceed 30 grams. The capsule cover or lid is " dished " to a depth of 3 millims., while the breadth of its flange is 2 millims., except in one place, where it is formed into a broad flat expansion. The greatest care must be taken of this crucible ; it must never come in contact with zinc, tin, silver, antimony, or lead ; nor must any compounds of these metals be heated in it. Even alkaline salts in the presence of carbonaceous matter may injure it. For many purposes a crucible of hard Berlin porcelain may be substituted for one of platinum. 2. A platinum spatula, spud-shaped at one end and pointed at the other, of the form and size shown in fig. 10, though not quite so slender towards the pointed end, will be found very useful. The 128 QUANTITATIVE ANALYSIS. weight of this implement (which is made from stout wire) need not exceed 4 grams. Fig. 10. 3. A desiccator, in which the crucible, dish, or other vessel to be weighed is allowed to cool and carried from the laboratory to the balance-room. This contrivance may be made with a heavy thick finger-glass, the upper edge of which is first to be ground on a corundum and shellac hone : a greased ground-glass disk forms a convenient cover. To support the crucible in this glass an iron wire triangle, raised on three legs and with pieces of tobacco-pipe strung on its sides, is constructed : a little piece of cork fixed to the extremity of each leg prevents the triangle from slipping about. The drying or desiccating material to be used is dry calcium chloride in lumps ; it is well to prevent this from touching the bottom of the crucible by means of a piece of mica interposed between them. A still more convenient mode of fitting up a desiccator is thus carried out : The ground finger- glass named above has the upper part of a beaker cemented by means of marine-glue to its interior : within this a neck from a flask is similarly fixed. Into this a tubular support of tin-plate, surmounted by a horizontal portion, drops, this part of the arrangement being used for holding watch-glasses and such drying-tubes as that described on p. 135. A moveable iron wire triangle, mounted with pieces of tobacco-pipe, completes the desiccator. Lumps of calcium chloride are used as the drying material. The annexed diagrams (figs. 11, 12, and 13) will explain the construction of this form of portable desiccator, and illustrate its uses better than further verbal description. A very convenient form of portable desiccator may now be obtained of the dealers in chemical apparatus. In shape it some- what resembles an hourglass, the slightly constricted part in the middle being occupied by a horizontal perforated plate, on which the object to be kept dry is to be placed. Below this, on the QUANTITATIVE APPABATTJS. 129 floor of the lower compartment, some lumps of calcium chloride are arranged, while the upper compartment is closed with a ground-glass plate. Fig. 11. Vertical section of Desiccator. Ground-glass Support for watch- glasses Fig. 12. View of Desiccator from above. Fig. 13. Moveable support for watch-glasses and tubes. 130 QUANTITATIVE ANALYSIS. 4. An iron wire triangle covered with tobacco-pipe, or a plati- num triangle, or one of nickel-wire, is used to support crucibles in a ring of the retort-stand when they are being heated. 5. Besides the ordinary wash-bottle with moveable jet for cold water, a flask similarly fitted for hot water is required for wash- ing many of the precipitates obtained in the processes of quanti- tative analysis. Small washing-flasks or bottles for dilute hydro- chloric acid, for dilute ammonia, and for alcohol and ether should also be at hand. 6. A few funnels having four internal ribs as suggested by Messrs. Hehner and Richmond, will be found very useful for rapid nitration. Amongst the more important general apparatus and fittings of the laboratory for quantitative analysis we may name th e folio w- ing: 1. The water-oven for drying substances previously to analysis should be very capacious. It should be made of copper, and be divided into at least two cupboards. By means of sliding glass screens or shutters in these cupboards the temperature of those parts of them most distant from the doors may be maintained within two or three degrees of 100 C. The steam which serves to heat this water-oven may be advantageously condensed by means of a worm of pure tin or tin-lined pipe, and so yield an abundant supply of distilled water. 2. A hot air- or oil-bath heated by a self-acting gas-regulator. 3. A gas combustion-furnace, constructed according to one or other of the various plans in use. "With due care Griffin's or Erlenmeyer's combustion-furnace answers well. 4. A table-blowpipe, fitted with double-bellows, and a Hera- path blowpipe for glass-working. Fletcher's hot-blast blowpipe and his gas-furnace and muffle will also be found useful. 5. A small hand-mill for grinding samples. 6. A set of cylindrical zinc sieves of graduated fineness, and fitting into one another. 7. An apparatus for filtering under increased pressure. QUANTITATIVE OPERATIONS. 131 For further details concerning laboratory apparatus and fittings, reference may be made to the works of Greville Williams, Thorpe, and Dittmar; but some additional contrivances will be found described further on in the present volume. ii. PRELIMINARY INSTRUCTIONS IN QUAN- TITATIVE OPERATIONS. The details of the quantitative estimations which have to be performed in the analysis of agricultural materials and products are best learned by practice on pure substances of known com- position. For this purpose standard solutions are most conve- nient, for each analysis an accurately measured portion being taken. The quantity to be employed, and the strength of each solution, will be indicated further on. Estimation of Lime. Solution employed, CaC0 3 in HCl=CaCl 2 , containing about a per cent. The solution, about 60 c. c., is to be heated nearly to boil- ing, then add excess of ammonium oxalate and ammonia until the liquid, after stirring, smells strongly ammoniacal ; cover the beaker, and set it aside for twelve hours in a warm place ; decant off the clear liquid through German or Swedish filter-paper, add hot water to the precipitate, allow it to subside, again decant, then add more hot water, and transfer the precipitate to the filter, allowing all the liquid to run through the paper before adding a fresh portion. Remove every particle of the precipitate from the beaker with the aid of a feather or of a rod, one end of which has an inch of india-rubber tubing tightly fitted on to it. Wash the precipitate on the filter with hot water, avoiding using a rapid stream, or some of the precipitate may be driven through the pores of the paper : the precipitate should be carefully washed down from the side of the filter-paper so as to form a compact mass at the bottom of the cone. Dry, transfer the pre- cipitate to a weighed crucible, leaving as little as possible ad- hering to the paper, which is to be tightly folded (in such a way F2 132 QUANTITATIVE ANALYSIS. as to bring the central portion of the filter into the middle of the compact folded paper), and burnt in a coil of platinum wire over a crucible standing upon a sheet of glazed black paper ; add the ashes of the paper and any particles on the glazed paper to the precipi- tate in the crucible, and slowly heat till the bottom of the crucible is just visibly red in the dark, for about ten minutes. When cold, weigh, and then moisten the precipitate with water, and test it with turmeric paper ; if an alkaline reaction be shown, it is due to caustic lime, produced by the application of too strong a heat ; add a little (NH 4 ) 2 C0 3 solution, and evaporate very cautiously, at a temperature below 100 C., to dryness ; ignite as before, being careful not to use too high a temperature. It may be necessary to repeat this treatment. Reactions : CaCl 3 -f (NH 4 ) 2 C 2 4 = CaC 2 4 + 2NH 4 d; by heat, CaC 2 4 = CaC0 3 + CO; the CaC0 3 , if heated too strongly, loses C0 2 , becoming CaO, and necessitating the " carbonating " with (NH 4 ) 3 C0 3 . The resulting CaC0 3 should have the same weight as that originally dissolved in the liquid. Estimation of Magnesia. Solution of magnesium sulphate (MgS0 4 7H 2 0) employed, con- taining about 1 per cent. To the solution (50 c. c.) add ammonium chloride (NH 4 C1) and ammonia (NH 4 HO) ; if the addition of the latter causes a precipi- tate, enough NH 4 C1 has not been added ; therefore add a fur- ther quantity, sufficient to dissolve the precipitate formed. Then add sodium phosphate (Na 2 HP0 4 ) in excess, and stir the mix- ture, avoiding touching the sides of the beaker with the stirring- rod ; cover the beaker, and let it stand twelve hours. Collect the precipitate on a filter, and wash with water containing ammonia (KH 4 HO) in solution (a mixture of 1 part of strong solution of ammonia and 7 parts of water) until a few drops of the filtrate, evaporated on a watch-glass or platinum foil, leave no residue. Dry, ignite the paper scraped as clean as possible, in a coil of in ESTIMATION OF BARYTA. 133 platinum wire, with all the precautions mentioned in the prece- ding account relating to lime, add the ashes to the precipitate in the crucible, and ignite gently at first, and finally before the blowpipe. Reactions : MgS0 4 +Na 2 HP0 4 +NH 4 HO = MgNH 4 P0 4 +Na 2 S0 4 +H 2 ; on ignition, 2Mg(OT 4 )P0 4 = Mg 2 P 2 7 + 2NH 3 +H a O. Magnesium pyrophosphate. Calculation : As molecule Mg2 t P2 7 : molecule MgS0 4 7H 2 = amount 2 Mg 2 P 2 7 found : amount MgS0 4 7H 2 given. : 246 = a : a?. 2 Estimation of Baryta. Solution of barium chloride (BaCl 2 2H 2 0) employed, contain- ing about j a per cent. Make the solution (50 c. c.) up to about 120 cubic centims. (or 4 oz.) with distilled water, add a little HC1, and heat just to boiling ; add dilute sulphuric acid as long as a precipitate forms ; keep the mixture near the boiling-point for some time, allow the precipitate to subside, and decant through a filter of German or Swedish paper ; heat the precipitate twice more with water, then transfer to the filter (waiting after the addition of every fresh portion until the fluid has completely passed through the filter), and continue the washing with hot water until the filtrate is no longer rendered turbid by barium chloride. Dry and ignite, scraping the paper as clean as possible, and burning it in a coil of platinum wire. Reaction : BaCl 2 + H 2 S0 4 = BaS0 4 + 2HC1. Calculation : As molecule BaS0 4 : molecule BaCl 2 2H 2 = amount of BaS0 4 found : amount of BaCl 2 2JFT 2 given. 232-8 : 243-8 = a : x. 134 QUANTITATIVE ANALYSIS. Estimation of Phosphorus Pentoxide. Solution of sodium phosphate (Na 2 HP0 4 12H 2 0) employed, containing about 1 per cent. Add to the solution (50 c. c.) ammonium chloride, ammonia till the smell is strongly ammoniacal, and magnesia mixture (a mixture of MgS0 4 , NH 4 C1, and NH 4 HO, or of the two latter salts with MgCl 2 ; see page 69). Stir the mixture with a glass rod (without touching the sides or bottom of the vessel with the rod), cover the beaker, and let it stand 12 hours ; collect the precipitate on a filter, wash with ammonia water until the filtrate is not rendered turbid by barium chloride. Dry and ignite, at first gently, and finally with the blowpipe. Reactions : As in estimation of magnesia. Calculation : As molecule Mg2 ^ 2 7 : molecule Na 2 HP0 4 12H 2 = amount Mg 2 P 2 7 found : amount of Na 2 HP0 4 12H 2 given. 999 * : 358 = a : x. Estimation of Potash. Solution of potassium sulphate employed (K 2 S0 4 ), containing y 1 ^ per cent. Evaporate the solution (about 50 c. c.) to half its bulk ; add a little HC1 and excess of platinic chloride solution and carry the evaporation nearly to dryness, add strong alcohol and wash the substance by decantation, finally collecting it on a filter dried previously at 100 and weighed till constant. After washing with mor,e strong alcohol, 5 c. c. of ether are passed through, and then the filter and contents are dried for half an hour at 100 and weighed. The salt weighed is PtCl 4 , 2KC1. Reaction : K a S0 4 +2HCl+PtCl 4 = PtCl 4 2KCl+H 2 S0 4 . PREPARATION OF ACID AND ALKALI. 135 Calculation : As molecule of PtCl 4 2E:Cl : molecule K 2 S0 4 = amount of PtCl 4 2KCl found : amount of K 2 S0 4 given. 486-7 : 174-2 = a : x. A short and light test-tube, about | an inch broad and 3| inches long, over which another and rather shorter tube slides somewhat stiffly so as to close its mouth, affords a neat contri- vance for drying and weighing the filter above mentioned. Preparation of the Acid and Alkali Solutions med in the Deter- mination of Nitrogen. Acid. The acid employed may be a dilute solution of sul- phuric acid, of about normal strength, i. e. containing an equivalent or half a molecular proportion of H 2 S0 4 f = =49 j in grams in a litre. Preparation. Take oil of vitriol, of which the percentage of H 2 S0 4 has been approximately ascertained, by taking its specific gravity and then referring to the following Table : Strength of Oil of Spec. Grav. at 15'5. % H 2 SO 4 . 1-839 100 1-840 99 1-841 98 1-841 97 1-841 96 1-839 95 1-837 94 1-834 93 1-829 92 1-824 91 1-819 90 1-813 89 1-807 88 1-887 87 1-792.... .... 86 1-783 85 1-773.. . 84 Vitriol. Spec. Grav. at 15-5. % H 2 S 1-764 83 1-755 82 1-746 81 1-737 80 1-728 79 1-717 78 1-706 77 1-685 ,..76 1-674 75 1-663 74 1-652 73 1-640 72 1-628 71 1-616 70 1-604 69 1-592... 68 1-580., ..67 136 QUANTITATIVE ANALYSIS. The best commercial oil of vitriol has a specific gravity of about 1-840, and contains about 96 per cent, of H 2 SO< : 28 c. c., or 51'5 grams, of this acid, or an equivalent quantity of an acid of other strength, are measured or weighed out in a beaker, diluted with the proper precautions to a litre, the whole well mixed and allowed to stand 12 hours, that the lead sulphate present in ordinary sulphuric acid may entirely separate ; then the clear liquid is decanted and the remainder filtered. The exact strength of the acid must now be ascertained. After agitation to ensure perfect mixture, measure 20 c. c. (or 1 cubic inch) into a beaker with the pipette, dilute with 200 c. c. or 6 ozs. of water, add some hydrochloric acid, and boil. "When the liquid is in ebullition, remove it from the lamp, and add to it gradually, and with constant stirring, a boiling solution of barium chloride till it ceases to cause further precipitation. The liquid is to be kept near the boiling temperature for some time ; it is then allowed to cool till the whole of the barium sulphate has settled to the bottom, leaving the solution perfectly clear : the hot liquid is then to be filtered through German or Swedish paper. The precipitate must be thoroughly washed with hot water ; should it show any tendency to pass through the paper, dilute hydrochloric acid may be used for the first washings. The precipitate is to be dried, burnt, and weighed in the usual manner. The amount of S0 3 per 20 c. c. is to be calculated from the mean of three determinations made as above described ; if the operations are carefully performed, the weights of barium sul- phate will not differ by more than -005 gram. Alkali. The alkali is a weak solution of sodium or potassium hydrate, of which 100 c. c. should exactly neutralize 20 c. c. of the acid. Some analysts prefer solutions of barium hydrate or of ammonium hydrate. The solution may be conveniently prepared from the hydrate of either potassium or sodium. The hydrate employed should be free from carbonate ; if not so, it must be rendered caustic by boiling with fresh milk of lime in a clean iron vessel. The caustic soda made from sodium is the best material to use. PREPARATION OF ACID AND ALKALI. 137 Preparation. Having determined to make a certain volume of the alkali (say 2 litres), calculate the amount of hydrate required; thus, if sodium hydrate be used, and the acid contain exactly 49 grams H 2 S0 4 in a litre='98 gram in 20 c. c., then, since H 2 S0 4 saturates 2JS"aHO, Molecular weight. Molecular weight. H 2 SO 4 NaHO H 2 SO 4 2NaHO in 20 c. c. in 100 c. c. 98 : 80 = -98 : -8. c. c. NaHO c. c. taken. NaHO required. 100 : -8 = a : x. Weigh out the amount calculated, and add to it water to about three fourths the volume it is intended to make ; dissolve and well mix, and then ascertain by experiment how many c. c. and fractions of c. c. are required to neutralize 20 c. c. of the acid, a little litmus solution being added to the portion of acid measured out in order that, by its change of colour to purple, the point of neutralization, when enough soda has been added, may be shown, duplicate determinations being made to exclude error. The alkali should be rather stronger than is required ; but, its volume being known, it is easy to dilute it to the re- quired strength ; thus, if 90 c. c. neutralize the acid, and there are 1848 c. c. made, 90 : 100=1848 : 2060, the number of c. c. to which the alkali must be made up. This is then done and the strength again tested, when 20 c. c. of acid should be exactly saturated by 100 c. c. of the alkali. The solution should be kept in well-stoppered bottles in a cool place, or in a bottle through the cork of which a tube containing a mixture of equal parts of sodium sulphate and quicklime, gently ignited together, is placed ; it may then be kept a long time without deteriorating. The value of each c. c. of the alkali has now to be calculated. Since H 2 S0 4 saturates 2NH 3 , if the strength of the acid and alkali be as above, H 2 S0 4 2NH 3 H 2 S0 4 in 20 c. c. NH 3 98 : 34 cr ' -98 : -34. 138 QUANTITATIVE ANALYSIS. 20 c. c. of the acid are neutralized by 100 c. c. of the alkali ; 34 therefore each c. c. of the latter corresponds to ^^=-0034 gram KE 3 , or -0028 gram N. Suppose that, after a nitrogen combustion, the contents of the bulb are exactly neutralized by 65 c. c. of the alkali, it is obvious that the acid has absorbed ammonia during the combustion equal in saturating power to 35 c. c. of the alkali, since 20 c. c. of the acid were originally taken ; 35 x '0034 ='119, the weight of NH 3 obtained, or 35 x -0028 = -098, the weight of JST, from which the percentage is obtained. If the grain, septem, and cubic inch are the weight and mea- sures used, a cubic inch of acid should contain 8*5 to 9 grains H 2 S0 4 , and 200 septems of alkali should neutralize a cubic inch of acid ; the calculation to find the amount of vitriol of, say, 96 per cent., required to make a certain number of cubic inches of dilute acid, 9 grains per cubic inch, will then be : cub. in. 1 grains H 2 S0 4 . : 9 cub. in. = a l grains H 2 SO 4 . 00 96 !. Oil of vitriol. : 100 grains H 2 SO 4 . = x \ grains oil of vitriol required. : y Determine the exact amount of H a S0 4 per cubic inch in the same way as above given. The calculations for the amount of sodium hydrate required, and for the value of each septem, will be conducted in the same manner as if grams and c. c. were used. The litmus solution used in these experiments to ascertain when neutralization has been effected is made by digesting crushed litmus in twenty times its weight of distilled water for a few hours, decanting, filtering, and dividing the filtrate into two equal portions, adding very dilute nitric acid to one until it is faintly red, and then mixing with the other portion ; the whole will then be violet, neither blue nor red. It should be mixed with alcohol and kept in a bottle, with an open bent glass tube through the cork, as if tightly corked it loses part of its ANALYSIS OF BONES. 139 colour and sensitiveness. Instead of litmus a solution of ' helianthin ' (< methyl-orange ') may be used. This is an orange- coloured compound which becomes purple in the presence of a trace of free acid. Another very good example of a quantitative volumetric esti- mation for practice is furnished by iron. Full directions are given on pp. 153-155. CHAPTER H. i. ANALYSIS OF MANURES. BEFORE beginning the several operations and analyses which follow, the directions given should be carefully read over, in order that a clear idea of the whole plan to be pursued may be first obtained. BONE-DTJST, BONE-SHAVINGS, BOILED BONES, &c. These, and all other forms of unburnt bones, consist of cal- cium phosphate, calcium carbonate, carbonaceous and nitrogenous matters commonly called organic matter, moisture, with sandy impurities and minute quantities of other substances. The analysis for commercial purposes may be conducted as follows. Too much care cannot be exercised in order to secure a fair average sample of the manure. Eight or ten portions from dif- ferent bags are first taken : these are well mixed ; and a part is then reduced, by grinding, sifting, and regrinding, to a moderately fine powder. MOISTTTRE. A convenient quantity, say 3 or 4 grams, is weighed into a watch-glass, and kept in a water-oven, at the temperature of 100 C., till it ceases to lose weight ; the loss is moisture. ORGANIC MATTER. Weigh about 1*7 gram (or 25 grs.) into a platinum crucible, cover it loosely with the crucible-lid, and 140 QUANTITATIVE ANALYSIS. raise the temperature very gradually to low redness. When the mass appears white, and no incandescent particles are ex- posed on gently stirring with a platinum wire, the whole is allowed to cool, and then weighed ; the loss is carbonaceous or organic matter plus combined water and moisture. The percentage of the latter constituent, having been determined in the preceding operation, is to be deducted from this loss (after its conversion into a percentage) the remainder will then repre- sent organic matter and combined water. The heat employed should be as low as possible, to avoid the expulsion of carbonic ac^d from the calcium carbonate. If it be feared that this has occurred, moisten the whole with ammonium carbonate solution, dry on the water-bath, heat to low redness for a few seconds, and again weigh. SAND. The portion just calcined is removed to a beaker, and digested in dilute hydrochloric acid till nothing but the sand remains ; this is collected on a filter, washed, dried, burnt, and weighed. PHOSPHATES. The nitrate and washings from the sand are now diluted to about 300 c.' c. (or 10 ozs.), a very slight excess of ammonia added, the precipitated phosphates allowed to settle and collected on a filter. After two or three washings, the pre- cipitate is rinsed from the filter into a beaker, the paper repeatedly moistened with hydrochloric acid and washed, the acid washings being allowed to run into the beaker containing the precipitate. The precipitate redissolves in the acid thus added (which should be as small a quantity as possible) ; the solution is diluted to about 300 c. c., ammonia in slight excess added, and the preci- pitated phosphates collected, thoroughly washed with water slightly ammoniacal, dried, burnt, and weighed* The object of redissolving the phosphates is to separate the lime mixed with the precipitate ; ordinary washing would fail to effect this : to lessen still further this source of error, precipi- tation is effected in a cold and dilute solution, and with the smallest possible excess of ammonia. These precautions are necessary whenever the calcium phosphate is associated with considerable amounts of other lime-salts. The ignited calcium '/i NITEOGEN DETEEMINATION. 1 ' phosphate should not effervesce with acids ; if it does so, it is evidently contaminated with carbonate, and should be redissolved and again precipitated. N.B. Calcium phosphate is not quite insoluble in water ; in a careful analysis therefore it is well to concentrate the whole of the filtrates and washings to about 150 c. c., add a little acid to dissolve the calcium carbonate deposited, boil to expel carbon dioxide, and finally precipitate with ammonia, collect, and weigh. The amount thus obtained is usually about J per cent. CALCIUM CAEBONATE. This may be estimated in the united filtrate from the phosphates by boiling with ammonium oxalate ; but for commercial purposes this determination is frequently omitted, the amount of calcium carbonate present being suffici- ently indicated by the difference between the sum of the per- centage of the other ingredients and a hundred parts. The precipitation of lime by ammonium oxalate should always bo effected in a dilute and hot solution. In igniting the precipitate the heat should not exceed a very low redness. When long burning has been necessary, it is advisable to moisten the residue with ammonium carbonate, and again ignite it gently before weighing ; see page 132. NITROGEN IN OEGANIC MATTEE. Make a combustion for ni- trogen with about 1*7 gram (or 25 grs.) of the finely powdered substance. Estimation of Nitrogen. All the more common nitrogenized substances likely to be met with, give off, when heated with soda or soda-lime, the whole, or very nearly the whole, of their nitrogen in the form of ammonia. While some of the oxygen of the soda-lime unites with the carbon of the organic matter to form carbon dioxide, the hydrogen unites with the nitrogen to yield ammonia. The nitrogen of substances like hair, wool, albumen, &c. is less completely evolved as ammonia in this way ; they should be mixed with ten times their weight of pure dry starch and be burnt in a longer tube. The soda- lime used may be prepared by adding 750 grams of freshly burnt quicklime in small fragments to a litre of water in which 500 grams of good sodium hydrate and 5 grams of sodium thiosul- 142 QUANTITATIVE ANALYSIS. phate have been previously dissolved. The mixture is effected in an iron pot covered with a sheet of tinned iron. Allow the lime to slake in the soda-solution, and then put the pot over a fire and evaporate the contents, constantly stirring them with an iron spatula until they are apparently dry. The dry mass is next transferred to an iron or Hessian crucible, and exposed to a dull red heat for an hour or two. When nearly cold the dry mass is to be pounded up in a warm iron mortar, and then passed through a wire-gauze sieve of 7 meshes to the linear inch. Separate the product into two grades by means of a sieve having 22 meshes to the linear inch, and preserve separately the fine part or powdery soda-lime and the coarse part or granular soda-lime in a number of well- corked phials. Before commencing an analysis heat a sufficient quantity both of the fine and of the granular soda-lime in separate dishes till dry \ then return the materials to the phials. The phials should have small necks without flanges, and of less diameter than the bore of the combustion-tube. The latter is made from hard combustion-tubing having a bore of about 14 millimetres and a length of 25 to 50 centimetres (9 to 18 inches) ; one end is drawn out obliquely to a strong point or tail. The lower part of the tail of the tube is first of all loosely plugged with a little freshly-heated asbestos ; then a little fine soda-lime is introduced and another dry asbestos plug. Pour in a little more soda-lime, then add about half the substance to be analysed from a previously weighed sample-tube, and introduce some more fine soda-lime. Mix the substance and the soda-lime in the tube by means of a clean iron, brass, or copper wire about 60 millimetres in length, twisted at one end like a corkscrew, and with a ring at the outer end to serve as a handle. This wire is pushed down and rapidly moved about in all directions, until no particles of unmixed substance can be detected. Some more fine soda-lime is introduced now, followed by the remainder of the substance from the weighed sample-tube the latter is put carefully on one side, to be afterwards weighed ; the difference between the original and the second weighing shows the amount NITKOGEN DETEEMIffATION. 143 taken : this should vary from P 7 to 2-7 grams, according to rich- ness in nitrogen. More fine soda-lime is added, and the mixing process repeated. This done, another addition of fine soda-lime is made, and the wire carefully withdrawn. Place the tube in a vertical position and introduce a third plug of asbestos. Fill up the rest of the tube with granular soda-lime and a plug of asbestos ; rap the tube gently on the bench. Pig. 14 shows the arrangement of the combustion-tube when ready for heating, the part of the contents marked A representing fine soda-lime, that marked B indicating the mixture containing the substance, and that marked C being the granular soda-lime ; D is the last asbestos plug : a small space, E, is left free. The tube is finally closed with the cork, F, through which passes the end of the nitrogen bulbs, G. Fig. 14. The bulbs, containing 20 c. c. (or a cubic inch) of the standard sulphuric acid, and attached to a sound perforated cork, should be in readiness previous to the mixing of the substance with the soda-lime. It should be stated here that the amount of any nitrogenous substance taken for analysis must depend upon its richness in nitrogen ; with bone-dust not more than 1 gram (or 15 grains) should be employed. Unless the substance contain ready-formed ammonia .(like guano and ammonium salts) the soda-lime may be introduced warm into the tube. The bulbs are filled by measuring the acid into a beaker, inserting the point of the bulbs into the liquid, and applying suction at the other end ; then wash down the point with a jet from a wash-bottle into the beaker, and set the beaker aside* until the combustion is complete. The combustion-tube is now placed in the furnace; but before being heated it should be ascertained if the apparatus is perfectly air-tight : to prove this, gently heat the bulb nearest the combustion-tube, and expel a few bubbles of air, allow it to 144 QUANTITATIVE ANALYSIS. cool ; then if the acid rises to a higher level on the inside, and remains so four or five minutes, the tube is air-tight ; other- wise the acid in each bulb will return to the same level. The tube is now to be gradually heated, from end to end,, commencing at the end near the bulbs, care being taken that the cork is neither scorched by too great a heat nor moistened by the condensation of liquid upon it. A moveable plate of mica enables one to regulate the temperature of the cork with exact- ness. Too high a temperature must be avoided, or the tube will be fused or blown out ; the operation is over when the closed end has been reached, and no more gas is evolved ; towards the end of the operation the heat must be considerably raised. When the process is completed, the acid in the bulbs will begin to re- cede towards the combustion-tube ; when this occurs, and the liquid in the further bulb is at a lower level than that in the other bulb, the fine point of the tube is nipped off, and air, equal in volume to about four times the capacity of the tube, drawn through the apparatus. Or, in order to avoid this aspiration of air, about 4 centimetres in length of the combustion-tube, at the closed end, may be charged with a mixture of equal parts of zinc-dust and soda-lime. On heating this, at the conclusion of the experiment, hydrogen will be evolved, and will drive out any remaining ammonia. The bulbs are now detached, and the acid liquid is emptied into the beaker containing the residue of the measured quantity of acid, the bulbs being rinsed out re- peatedly with distilled water. Some solution of litmus (or other " indicator," as methyl-orange, cor allin, or cochineal) is added, and the neutralization of the acid completed with the standard alkali ; from the quantity required the amount of ammonia or nitrogen in the substance burnt is calculated as before described (page 138). When a gas combustion-furnace, consisting of a battery of 20 or 30 Bunsen burners, is employed, the flames must never touch the tube itself, which may be further protected by being placed in a trough of brass-gauze, or of sheet-iron lined with a thin layer of asbestos : perhaps asbestos-cloth affords the best protec- tion to the tube. DETERMINATION. 145 It has long been known that the nitrogen of many organic and inorganic substances was not wholly and invariably obtain- able in the form of ammonia by combustion with soda-lime. Nitrates and compounds in which cyanogen or oxides of nitrogen may be assumed to exist, are striking examples of substances which give discordant and imperfect results by the ordinary method. But there are also some albuminoid bodies (some of the nitrogenous constituents, for example, of East-Indian linseed- cake) which do not yield quite the whole of their nitrogen in the form of ammonia when they are burnt with soda-lime. But there are two methods by which the majority of such bodies (and am- monia-salts as well) may be satisfactorily analysed. One of these, known as Kjeldahl's method, will be described further on (p. 230) ; the other is a modification of the soda-lime process, and was intro- duced by Ruffle. We now proceed to describe the latter : Ruffle's Thiosulphate Method. The combustion-tube may have the form adopted in ordinary soda-lime combustions, and should be 20 inches long and of ^-inch bore. A dry, loosely-fitting asbestos-plug is first introduced, and then 1 inch of the thiosul- phate mixture. This consists of equal weights of dry powdered slaked lime and of finely-powdered crystals of sodium thiosul- phate. The weighed portion of the substance to be analysed is intimately mixed with an equal weight of a mixture of equal weights of pure flowers of sulphur and pure finely-powdered wood charcoal, and is then placed (in a mortar or on a sheet of glazed paper) upon enough thiosulphate mixture to fill 10 inches of the tube. Mix thoroughly and introduce by means of a funnel into the tube. Rinse the mortar or paper with a little more mixture, and add the rinsings to the tube, and then fill up the tube with granular soda-lime to within 2 inches of the open end of the tube. Place a second plug of ignited asbestos in the tube, and close the latter with a cork. Rap the tube, held horizontally, so as to form a small channel, along its whole length, above the contents. Place the charged tube in the furnace, withdraw the plain cork and attach the nitrogen- bulbs previously charged with the proper amount of standard acid. Gradually heat the portion of the tube containing the soda-lime, and then that containing the mixture the evolved gases should come off at the rate of 2 or 3 bubbles per second. The rest of the operations are conducted as in the ordinary soda- lime process, a solution of cochineal being used as an indicator in the titration with the standard alkali. A blank analysis will serve to show whether the materials themselves are free from nitrogen 146 QUANTITATIVE ANALYSIS. The use of wrought-iron tubes for nitrogen determinations with soda-lime has been adopted by some analysts. The screw cap with which one end is closed is secured by moistening its thread with hydrochloric acid before screwing it on ; the tube is then heated once with soda-lime alone. The absorption-tube for the evolved ammonia is a U-tube having 3 bulbs, a constriction at the base of the further limb, and a thistle-head prolongation at its summit ; part of this limb is filled with glass beads, but these cannot pass the constricted bend into the nearer limb. This absortion-tube is attached directly to the open end of the iron combustion-tube by means of a cork kept from charring by means of a trickling stream of water directed on to some strands of tow which are wound round it and the contiguous extremity of the tube, and the ends of which hang down below to conduct the excess of water away. NOTE. Bone-dust is not unfrequently adulterated with gyp- sum ; it is then requisite to determine the sulphur trioxide pre- sent, from which the amount of gypsum may be calculated. SULPHUR TRIOXIDE. Digest about 3 grams (or 50 grs.) of the original sample with dilute hydrochloric acid till the phosphates are dissolved ; dilute to about 250 c. c., and boil for half an hour ; filter, wash the residue till sulphur trioxide ceases to be found in the washings, and precipitate the filtrate with barium chloride in the usual way. The barium sulphate should, after ignition, be moistened with a drop of strong nitric acid and again ignited, in order to reconvert into sulphate any barium s'ulphide that may have been formed by the reducing action of the organic matter mechanically carried down with the precipitate. Yegetable-ivory turnings have been found in bone-dust and bone-shavings ; they are of no value as manure. They consist chiefly of cellulose, and may be detected by their microscopic structure or by the action of H a S0 4 of sp. gr. 1/53, which dis- solves them without blackening, and forms a solution which, on warming, diluting with water, and addition of ammonia, gives no precipitate. BONE-BLACK, ANIMAL CHARCOAL, &c. Partially burnt bones are to be analysed in the same way as fresh bone. They often contain a mere trace only of nitrogen. If it be required to determine the carbon present, this may be BONE-ASH AND APATITE. 147 done by digesting 3 grams of the substance with dilute hydro- chloric acid and collecting the residual sand and carbon on a tared filter, and weighing it after drying at 100 C. The carbon and filter-paper may then be burnt away in a crucible. The loss will represent the carbon and filter. BONE-ASH. The organic matter, being very small in amount, may be neglected, and the whole volatile matter estimated together by carefully heating to low redness some of the finely powdered sample ; this should be done in a covered crucible, as decrepita- tion is apt to occur. The analysis is in other respects conducted as with bone-dust. Not more than 1 gram (or 16 grs.) should be taken for ana- lysis. A nitrogen combustion is unnecessary. APATITE, and its numerous varieties, known as phosphorite, osteolite, staffellite, &c., contains a very large proportion of calcium phos- phate associated with calcium chloride or fluoride, and minute quantities of moisture, oxide of iron and alumina, insoluble matter (which, in the case of some apatites, is partly a cerium phosphate called cryptolite), and occasionally calcium carbonate. Fluorine should be first tested for. Some of the powdered mineral is placed in a platinum vessel, moistened with oil of vitriol, and the vessel covered with a plate of glass thinly coated with wax, through which a few fine lines have been traced with a point of wood or bone : the platinum vessel is then very slightly warmed. If on removing the wax the lines are found etched on the glass, fluorine is certainly present. If fluorine is found it must be expelled from the quantity taken for analysis by evaporating the hydrochloric solution with sulphuric acid ; the temperature used must not be such as to volatilize the sul- 148 QUANTITATIVE ANALYSIS. phuric acid. The residue is redissolved by boiling it with water and hydrochloric acid. The CALCIUM PHOSPHATE, and the CALCIUM: of the calcium chloride, fluoride, or carbonate, are determined exactly as in bone-dust ; 1 gram will be sufficient for an analysis. CHLORINE is determined in 3 grams of the substance. It is reduced to very fine powder, dissolved in dilute nitric acid, care being taken to warm the mixture, if at all, as slightly as possible ; if necessary the solution is filtered. Silver nitrate is added to the warm solution as long as it produces a precipitate ; the fluid is briskly stirred, and, if necessary, left in a warm place till the precipitate has thoroughly coagulated : the silver chloride is finally collected on a small filter, washed with cold water, dried, ignited, and weighed. The latter operations require some care ; they are effected as fol- lows : The precipitate is separated from the paper with a pen- knife, and placed in a porcelain crucible ; the part of the paper to which the precipitate adhered is cut into several pieces, and carefully burnt on the lid of the crucible. When cold, the ash is moistened with strong nitric acid,- and the crucible lid placed on the water-bath ; when nearly dry a drop of hydrochloric acid is added, and evaporation allowed to continue : after drying, gently ignite, place the lid on the crucible and heat the silver chloride to incipient fusion, cool, and weigh. COPKOLITES. Coprolites consist chiefly of calcium phosphate and carbonate ; they contain, besides, variable and sometimes considerable amounts of silica, ferrous silicate, pyrites, ferric oxide, and alumina, also a little magnesia, carbonaceous matter, and mois- ture, and frequently fluorine. They are sometimes analysed for commercial purposes in the same way as bone- ash ; the result, however, is not equally satisfactory, chiefly owing to the much larger amount of calcium carbonate present, and to the precipi- tation of calcium fluoride with the phosphate : the percentage of phosphate found is thus always excessive. COPKOLITES. 149 To acquire an accurate knowledge of their value, the phos- phorus pentoxide present must be determined. This, with the determination of lime, silica, and volatile matter, will "be suffi- cient for commercial purposes. Fluorine may generally be detected according to the method for apatite ; this plan, however, may possibly fail if the coprolite contain much silica : if therefore no etching is produced on the glass, a second experiment should be tried in which the glass cover is moistened on the underside in place of being waxed. If after the application of a gentle heat the wet surface becomes opalescent from the deposition of gelatinous silica, fluorine is certainly present. The presence of fluorine in small quantity is not prejudicial to the processes now to be described ; if, how- ever, simple precipitation with ammonia be resorted to, it should be previously removed (see Apatite). If a complete analysis be desired, a determination of carbon dioxide will be necessary ; for this purpose see Analysis of Soil (p. 198). MOISTTJEE AND OEGANic MATTER are determined together, as in bone-ash. SILICIOUS MATTEE. 1 gram of the powdered coprolite is di- gested in a beaker with moderately strong hydrochloric acid. The fluid is finally evaporated to dryness, and the residue gently heated on a sand-bath for some time to render insoluble the whole of the silica. If the sample contains any appreciable amount of iron pyrites, the residue must now be warmed with a little nitro-hydrochloric acid and again dried at a gentle heat. The mass, when cold, is moistened with concentrated acid, and, after standing about twenty minutes, treated with a little water and warmed : more water is finally added, heat again applied, and the insoluble matter (which should appear quite free from iron) collected, washed, ignited, and weighed. If ferric oxide and alumina are to be determined, it is best to take twice the amount of coprolite here recommended, and after removal of silica, as before directed, to divide the solution into two equal portions ; this division is most accurately effected by 150 QUANTITATIVE ANALYSIS. weight. Por this purpose the filtrate and washings are collected in a tared flask, diluted to 200 c. c., well mixed, and the flask with its contents weighed ; it is then easy to transfer to another vessel such a portion of the contents that the remaining part shall be counterpoised by exactly half the weight of the original liquid. The phosphorus pentoxide and lime are now determined by the following process. When, however, the greatest accuracy is desirable, and especially where the material to be analysed contains much carbonaceous matter, the " Fusion Method " described under the head of Phosphatic Guanos (p. 155) should be followed for the determination of the P 2 5 . This constituent may be very accurately estimated by means of the molybdic-acid method (p. 189). Oxalic-Acid Method. LIME. A few drops of very dilute ammonia are first added to the solution, with constant stirring, till a slight permanent opalescence is produced. A little oxalic acid is then added, and, after a few minutes, ammonium oxalate until it ceases to pro- duce a precipitate. The whole is then warmed for some hours, that the calcium oxalate may aggregate ; the precipitate is col- lected on a filter, washed, dried, ignited for some time at a very low red heat, and weighed. Any lime found in excess of that necessary to form tricalcic phosphate with the phosphorus pent- oxide present is calculated as calcium carbonate. PHOSPHORUS PENTOXIDE. The filtrate and washings from the lime precipitate are concentrated to about 60 c. c., some citric acid is added, and then ammonia in decided excess. If a preci- pitate be immediately produced, it is a sign of the presence of lime, iron, or alumina. But if a slight crystalline precipitate come down on standing, this is due to the presence of magnesia in the material taken for analysis, and its presence will not in- terfere with the subsequent operations. The next step is to add, drop by drop, some " magnesia mixture " : of this 10 c. c. will be required for every decigram of P 3 6 present in the solution. After standing twelve hours the precipitate is collected, washed COPEOLITES. 151 with rather strong ammonia water, dried, ignited gently for some time, and afterwards at a very high temperature before the Herapath blowpipe, and finally weighed. The precipitate, as already pointed out, has the formula Mg 2 P 2 7 after ignition; its equivalent in Ca 3 2P0 4 is found by calculation, 1 part of the former salt corresponding to 1-3964 of the latter. Determination of Alumina, Ferric Oxide, <$fc. ALUMINA. The acid solution of coprolite, freed from silica, is precipitated by sodium hydrate, a considerable excess being added and the whole warmed for some time. The solution is next di- luted, the precipitate allowed to subside, and the clear liquid poured on to a filter ; the precipitate is washed with hot water three or four times by decantation, the washings being passed through the filter. The filtrate is warmed, and barium chloride cautiously added till it ceases to produce a precipitate ; this pre- cipitate contains all the phosphorus pentoxide present in the solution. A little sodium carbonate is next added to throw down the excess of baryta, and finally some more sodium hydrate. After digesting a short time, the solution is filtered. The preci- pitate on the filter is washed with water containing a drop or two of sodium hydrate solution. The filtrate and washings are then made distinctly acid with hydrochloric acid, a crystal of potassium chlorate added, and the whole warmed for some time to destroy any trace of organic matter. Ammonium chloride is finally added, and a slight excess of ammonia ; the precipitated alumina is allowed to subside. It. is to be thoroughly washed by decantation before removal to a filter. It is finally dried, ignited, and weighed. Should the sodium hydrate contain either alumina or silica, this will fall with the alumina of the analysis and occasion an excess. The presence of impurities of this kind may be readily detected by neutralizing the soda with acid, adding ammonium chloride with a slight excess of ammonia, and allowing the liquid to stand some hours. If the soda contain silica only, the alumina, after weighing, may be dissolved in the platinum capsule with dilute sulphuric acid, heat being applied till the excess of acid has vola- tilized; the residue is dissolved in water and hydrochloric acid; the 152 QUANTITATIVE ANALYSIS. insoluble matter is collected and weighed as silica. Should the soda contain both silica and alumina, the total amount of impurity must be estimated, and a known volume of soda employed in the analysis. As caustic soda and potash when kept in solution become impure from their action on glass, it is best when a pure article is at hand to use it in the solid state. The caustic soda made from sodium is quite pure. PERKIC OXIDE. This is best determined by the volumetric method presently to be described ; or the following plan may be adopted. The original precipitate by soda is dissolved in hydro- chloric acid, and excess of ammonia added, and, lastly, a consider- able excess of acetic acid. The solution is allowed to stand for some minutes in a warm place : the precipitated iron phosphate having then subsided, the clear liquid is poured on to a filter, and the precipitate well washed with warm water by decantation ; a little ammonium acetate and a drop or two of acetic acid may be added to the water used in washing. The ferric phosphate will still contain a little tricalcic phosphate ; it is therefore treated as follows : The paper-filter is moistened with dilute hydrochloric acid, and finally washed, the washings being added to the pre- cipitate in the beaker. Should the ferric phosphate fail to redissolve in the acid thus added, a little oxalic acid is introduced ; neutral potassium oxalate is lastly added, and the whole warmed to aggregate the calcium oxalate ; this is finally separated by filtration. The clear solution is now treated with a considerable excess of sodium hydrate and boiled for some time ; the solution is then diluted, and the precipitated ferric oxide thoroughly washed by decantation, the washings being filtered as before. The ferric oxide is, lastly, redissolved in hydrochloric acid, precipitated by ammonia, and after washing a few times by decantation, collected, washed, dried, ignited, and weighed. If the operation has been successful, no trace of phosphorus pentoxide will be found on redissolving the weighed precipitate in nitric acid, and applying the molybdic-acid test. The above process is the most strictly accurate ; good results may, however, be obtained by simply redissolving the ferric COPROLITE8. 153 phosphate in hydrochloric acid, adding a few drops of sodium phosphate, and treating with ammonia and acetic acid, exactly as at first. The ferric phosphate thus reprecipitated is to be washed a few times by decantation, and finally collected, dried, ignited, and weighed. Its formula is Fe 2 2P0 4 . LIME may, if desired, be determined in the acetic-acid solution in the usual way ; the small precipitate of calcium oxalate ob- tained on redissolving the ferric phosphate is weighed with the main precipitate. MAGNESIA. The filtrate from the lime is concentrated to 60 or 70 c. c., sodium phosphate and excess of ammonia added. The precipitate, after standing 12 hours, is collected, washed with strong ammonia-water, burnt, and weighed. Lime and magnesia need not, of course, be separated here, unless duplicate determinations are desired. /ron, Volumetric Method. IRON is most speedily and accurately determined by means of a standard solution of potassium permanganate. To effect this, the iron is reduced to the ferrous state, and the permanganate added till the iron is exactly peroxidized, this point being known by the purple colour of the reagent remaining undestroyed : the volume of permanganate consumed indicates the amount of iron present. 10FeS0 4 + 8H 2 S0 4 + 2KMn0 4 = 5(Fe 2 3S0 4 ) + K 2 S0 4 . + 2MnS0 4 + 8H 2 0. The reduction of the iron to the ferrous state and its subsequent estimation are performed as follows : The solution of iron, in which not more than 1 gram of metal per litre must be present, and which must contain a large excess of free sulphuric acid, is placed in a small long-necked flask, fitted with a cork and tube bent at right angles ; a few frag- ments of pure zine are introduced, and the flask placed in an inclined position on a retort-stand, the tube attached bending downwards ; the flask is gently warmed to facilitate the action. As the evolution of hydrogen proceeds, the fluid will become colourless ; when this is perfectly effected, and the zinc all dis- 154 QUANTITATIVE ANALYSIS. solved, the operation is completed ; a drop of the liquid, if with- drawn on a glass rod and mixed with a drop of potassium sulpho- cyanide in a porcelain dish, will give no colour if the reduction of the iron is complete. The end of the bent tube is then immersed in distilled water, and the flask allowed to cool : the water will ascend the tube and enter the flask. "When perfectly cold, the clear solution is transferred to a beaker, diluted, if necessary, to 500 or 600 c. c. with recently boiled, cold, distilled water, some sulphuric acid mixed with it, and the permanganate slowly added from a burette till the fluid is, uniformly slightly reddened, the whole being constantly stirred during the operation. The burette used must be entirely of glass, no india-rubber or other organic matter being allowed to come into contact with the permanganate. The absence of iron in the zinc should always be ascertained by experiment. For this purpose it is digested with sulphuric acid till entirely dissolved ; the solution, when cold, is diluted, and a drop of permanganate added : if the red tint is destroyed, the zinc certainly contains iron. In this case a volumetric deter- mination of iron must be made in a weighed quantity of zinc, and the zinc taken for each subsequent operation weighed previously to use, and the amount of iron it contains calculated and deducted from the amount found. In working with impure zinc it is very necessary, to ensure constant results, that the whole of it should be dissolved, as the impurities are generally the last to disappear. Preparation of the Permanganate Solution. A quinquenormal solution is a convenient strength for the pur- pose. Dissolve 3-162 grams of dry crystals of potassium per- manganate in a litre of water ; keep in stoppered bottle. It will be seen by the equation, p. 153, since 2 equivalents of KMn0 4 have 5 available atoms of 0, thereby peroxidizing 10 molecules of a ferrous salt, that 1 c. c. of this solution should theoretically correspond to -0056 Fe, -0072 FeCJ, or -0080 Fe 2 3 : in practice, as the permanganate is never quite pure, it is better to take rather more than the above quantity say, 3-2 grams instead of 3-162. Its exact strength may be ascertained by dissolving about 1 gram of crystals of the double sulphate of iron and ammonium (FeS0 4 , Am 2 S.0 4 , 6H a O) in water, adding dilute sulphuric acid, and titrating with the" permanganate solution. The double sulphate PHOSPHATIC GUANOS. 155 contains exactly ij- of its weight of metallic iron ; by dividing this amount by the number of c. c. of permanganate used, the value of each c. c. in metallic iron is at once found. If septems be the measure used, 27 grains of potassium permanganate should be dissolved in each 1000 septems (^ gallon) of water ; the value of each septem will then be about *04 grain of metallic iron. If a deposit should form at the bottom of the bottle con- taining the solution of permanganate, it should be decanted, but never filtered through paper ; the strength should also be deter- mined at intervals of a few months, as it is liable to weaken by keeping. PHOSPHATIC GFANOS. Sombrero, or Bock Guano, Navassa and Eodonda Guano, Carolina Phosphate, and many other similar materials are rich in phosphates ; but these often consist in great part of those of iron and aluminium. These substances may be analysed as coprolites : the phosphorus pentoxide may also be determined in them by the process given here, and entitled the Fusion Method. The following is a very accurate method of determining the total phosphorus pentoxide present in phosphatic guanos : it may also be successfully employed in the case of nitrogenous guanos. Weigh out about 2-5 grams of the finely powdered and dried sample, and mix them with 10 grams of a fusion mixture con- taining 2 parts of dry sodium carbonate to 1 part of dry potassium chlorate (or nitrate if much carbonaceous matter is present in the phosphate to be analysed). The mixing of the sample with the alkaline salt is best performed in a capacious platinum cru- cible by means of a glass rod, the end of the rod being wiped afterwards with a small strip of Swedish paper, which is thrown into the crucible. A gentle heat from a small and rather distant flame is first applied to the crucible, so that the oxidation may proceed quietly and without loss. When the mixture has become white, the heat is increased and maintained at full redness, so as to keep the contents of the crucible in fusion for fifteen minutes. 156 QUANTITATIVE ANALYSIS. The crucible, when cold, is placed in a beaker, with about 150 c. c. of water, and covered with a clock-glass. Then 30 c. c. of nitric acid (sp. gr. 1*25) are cautiously poured down the side of the beaker. The mass dissolves easily and completely, unless silica and silicates be present, in which case these substances must be removed in the way described under " Coprolites," p. 148. The solution containing the phosphorus pentoxide &c. is now diluted to 500 c. c., and a portion of it analysed by some appro- priate process ; the volumetric uranium method (p. 168), for instance, being preferably employed if iron and aluminium be virtually absent. The bases present may be determined in the remaining portion of the solution by the processes described under " Coprolites." SUPEKPHOSPHATES contain considerable quantities of three compounds not found in bone-ash or coprolites, namely, phosphoric acid (H 3 P0 4 ), mono- calcic phosphate (CaH 4 2P0 4 *) and calcium sulphate. The other constituents of a superphosphate are insoluble calcium phosphate (Ca 3 2P0 4 ), dicalcic phosphate (CaHP0 4 ), ferric and aluminium phosphates, carbonaceous or organic matter, water, with small quantities of alkaline salts and sand, and, possibly, a trace of free sulphuric acid. If the sample is a dry one, it may be prepared for analysis by lightly rubbing it in a mortar and sifting : if moist, it must be passed through a coarse sieve and well mixed, and then a part must be beaten into a smooth paste. MOISTURE is usually determined by drying a few grams in the water-oven for about 2 hours. But the really free water is probably more nearly estimated by desiccation over a tray of ignited calcium chloride in a fairly good vacuum. For this experiment 2 to 5 grams are taken, spread out as much as possible on a watch-glass, and allowed to remain for 18 to 24 hours under the receiver of the air-pump. * Sometimes called bipliosphate, and reckoned, though erroneously, as Ca2P0 3 (=CaO,P 2 6 ). SUPERPHOSPHATES. 157 ORGANIC MATTER and COMBINED WATER. About 1 gram is gently heated over a burner. The loss, after deduction of the * moisture/ represents approximately, but by no means exactly, these constituents of the superphosphate. SILICIOFS MATTER. About 1 gram gently dried over a lamp, but not ignited, is removed to a beaker, digested with hydrochloric acid and slowly evaporated just to dryness, &c. in order to render the silica insoluble. If iron pyrites be present the evaporation must be repeated with a little nitrohydrochloric acid, and again dried. The mass, when cold, is moistened with strong hydro- chloric acid : after standing some time water is added, and the whole warmed until nothing but the sand remains undissolved. This is collected on a filter, thoroughly washed, dried, and weighed. In the filtrate and washings the total lime and the total phosphorus pent oxide are to be determined according to the directions on p. 150, " Oxalic-Acid Method." Ignition of the superphosphate is avoided in these directions in order to prevent any loss of the phosphoric acid. SOLUBLE PHOSPHORUS PENTOXIDE. Under this designation we may include the P 2 S existing in the monocalcic phosphate and in the free phosphoric acid of the manure. Both these compounds are produced from the tricalcium phosphate from which the superphosphate has been made by the action of the sulphuric acid, and both are freely soluble in water. The phosphoric acid is generally the more abundant of the two, and may be written 3H 2 0, P 2 5 , or H 3 P0 4 ; the monocalcic phosphate is expressed by the formula 2H 2 0, CaO, P 2 5 or CaB: 4 2P0 4 . In order to deter- mine the proportion in which these two soluble compounds, the most important constituents of a superphosphate, exist in a sample, they are estimated together by adopting the following method : 5 grams (=77- 17 grains) of the well-mixed sample are taken ; ^ a litre of water is measured into a wash-bottle ; the superphos- phate is then placed in a mortar and rubbed with a little of the water, grinding being avoided; more water is then added, and, after standing a few moments, the supernatant liquid is poured off into 158 QUANTITATIVE ANALYSIS. Fig. 15. a stoppered bottle (A), a large funnel being placed in the bottle to prevent any loss. The residue in the mortar is rubbed with the pestle, and the washing continued as before, the rubbing and washing being repeated until the whole of the superphosphate taken has been transferred to the bottle. The remainder of the % litre of water is now added, and the bottle shaken at short intervals during three hours. The 100 c. c. required for the deter- mination of monocalcic phosphate may now be filtered off, or the mix- ture may remain at rest 12 hours, and then the 100 c. c. may be, if the liquid is clear, removed from the bot- tle by means of a pipette or of a siphon, as shown in fig. 15. The cork, with its two tubes, having been fitted into the bottle A, the pinch-cock at B is pressed, and enough air blown through the tube to fill the siphon C. By keeping the pinch-cock open, the vessel D may be filled with the clear solution up to the n x ' indicating 100 o. c. If the solution be not clear, 100 c. c. mus^be filtered off through German or Swedish paper. The 100 c. c. are proceeded with exactly according to the directions given under Coprolite, on page 150, and entitled the Oxalic- Acid Method," omitting, however, the weighing of the calcium oxalate precipitate. The magnesium pyrophosphate obtained has now to be calculated into phosphorus pentoxide thus : (a) As eq. of Mg 2 P 2 7 : eq. of P 2 5 =ppt. : as. Now, as 100 c. c. yielding this amount of P 2 5 contained 1 per cent, of superphos- phate, x multiplied by 100 is the percentage of P a 5 in a soluble form existing in the original manure. It is usual to tura this into the corresponding percentage of monocalcic phosphate. This may be done by calculating the following proportion : (6) As eq. of P 2 6 : eq. of CaH 4 2P0 4 =% of x : % of CaH 4 2P0 4 . SUPERPHOSPHATES. 159 1 part of this monocalcic phosphate corresponds to 1-33 part of "bone-phosphate rendered soluble," or to -85 part of the so- called " biphosphate." If, therefore, a sample of superphosphate has been found to contain, by calculation, 20 per cent, of mono- calcic phosphate, this figure may be entered in the column of percentages when the analysis is written out, but, at the same time, the quantity of tricalcic phosphate to which it corresponds, and from which it has been made, namely, 26*6 per cent., should be added. This latter figure, 26 -6, should be enclosed in brackets with its proper designation " bone-phosphate made soluble," not " soluble phosphate," as it is vulgarly named. But as monocalcic phosphate constitutes a part only, and often a small part, of the soluble phosphorus pentoxido of a superphosphate, it is much to be preferred that the percentage of soluble P 2 5 should be entered directly as such, adding in brackets the amount of " bone- phosphate made soluble " to which it corresponds : 1 part of P a 5 corresponds to 2-183 parts of Ca 3 2P0 4 . TRICALCTC PHOSPHATE. The insoluble phosphates of a super- phosphate are regarded as consisting almost entirely of unchanged bone-earth, Ca 3 2P0 4 . In order to determine them, the filtrate and washings, obtained from one gram of the prepared sample in the estimation of the p :li 'cious matter as before described, are to be treated exactly in ^e manner given on p. 149 in the case of coprolites, adopting the "oxalic-acid method," and estimating both the lime and the phosphorus pentoxide as therein directed. The Mg 3 P 3 7 obtained represents the total amount of P 2 0_ in the superphosphate. In order to learn how much of it was in the form of insoluble phosphates, calculate the Hg 2 P 2 T found into P 2 5 and then into a percentage, exactly as directed above, and then subtract from this percentage of total P a O g the percentage of P a O, found in the soluble part (see p. 158) ; then calculate the remainder into tricalcic phosphate, thus : As eq. of P 2 8 ; eq. of Ca 3 2P0 4 = residual / of P 2 5 : Ca 3 2P0 4 . But a simpler plan may be adopted ; in this the residual percen- tage is not converted into its equivalent of Ca 3 2P0 4 but directly entered in the tabulated results. 160 QUANTITATIVE ANALYSIS. CALCIUM SULPHATE. The whole of the calcium present in the superphosphate will now have been weighed in the form of car- bonate. It really exists in the manure in the three states of monocalcic phosphate, tricalcic phosphate, and calcium sulphate. If it be desired to ascertain what amount of this last compound exists in the sample, it is best to make a direct determination of S0 3 in a small separate portion of the manure, by means of barium chloride in the presence of hydrochloric acid. The barium sulphate obtained is calculated into its equivalent of calcium sulphate. This ingredient in a superphosphate is entered in the anhydrous form, but it exists for the most part in com- bination with 1 molecule of water (CaS0 4 , H 2 0), and not as gypsum, CaS0 4 ,2H 2 0. ALKALINE SALTS. Evaporate the filtrate from the ammonio- magnesium phosphate to dryness and ignite till all fumes have ceased ; let the residue cool, dissolve it in water ; precipitate the magnesium present with barium hydrate, filter ; then precipitate the excess of barium with ammonium carbonate and ammonia ; filter, evaporate the filtrate to dryness, and heat the residue very gradually to low redness ; it should be tolerably white. The alkaline salts thus obtained are by no means pure, but their quantity is generally too small to be important. In cases where common salt or sodium nitrate has been added to the superphosphate, and the amount of alkalies is therefore com- paratively large, it is necessary to treat the ignited residue with a little sulphuric acid, to ignite strongly, then to add a few drops of ammonium carbonate solution, and finally to evaporate and ignite the residue again : thus the definite composition of the substance weighed may be ensured. If qualitative testing prove that the superphosphate contain much chlorine, the sodium sulphate obtained should, be calculated into sodium chloride. REDUCED on EETEOGKADE PHOSPHATES. Under this name are included those phosphates which are believed to have once been in the soluble condition, but which are no longer dissolved by water. They consist chiefly of ferric and aluminium phosphates, and may be approximately estimated in superphosphates made SUPERPHOSPHATES. 161 from coprolites in the residue of 2 grams of superphosphate which have beeu exhausted with water, as in the determination of monocalcic phosphate. This residue is to be collected on a filter, care being taken to secure every particle of it. A neutral solution of ammonium citrate is used to extract the reduced phos- phates. This solution is prepared by dissolving 370 grams of pure citric acid in 1050 c. c. of water ; then nearly neutralize with commercial ammonium carbonate, heat to expel carbon dioxide, cool, and add ammonia to exact neutrality. Make up the volume to 2 litres, or so that the sp. gr. of the liquid is 1-09 at 20 C. Of the liquid thus prepared 100 c. c. are introduced into a 150 c. c. flask, and then the filter and contents are dropped in. The flask is corked and digested in a water-bath for 30 minutes at 65 C. with frequent shaking. Filter the warm solution quickly and wash the residue with cold water. Dry the filter and contents at 100, ignite them till the organic matter is de- stroyed, with 10 to 15 c. c. of concentrated hydrochloric acid, and digest until the phosphate is dissolved, dilute to 200 c. c., mix, and pass through a dry filter. Take an aliquot part of the filtrate (usually 50 c. c.) and determine in it the P 2 5 by the "molybdic-acid method," or by the " oxalic-acid method." Cal- culate the amount found into Ca 3 2P0 4 , add this to the " bone- phosphate made soluble " and subtract the sum from the total phosphate ; the remainder represents the amount of " reduced " or " citrate-soluble " phosphate expressed as Ca 3 2P0 4 . NITROGEN. A combustion with soda-lime is made, using about 2 grams of the superphosphate. If the superphosphate be a moist one, the quantity weighed out must be partially dried in the water-oven before mixing it with the soda-lime. Superphos- phates made entirely from bone ash, apatite, coprolites, &c. contain no nitrogen. A few notes on the composition of superphosphates may be found useful in arranging and appreciating the results of an analysis. We name the ingredients which have been determined in the order previously adopted. WATER. If a superphosphate bo dried at 100 C. the loss 162 QUANTITATIVE ANALYSIS. represents not only the hygroscopic moisture of the sample, but also a portion of the water of crystallization of the calcium sul- phate present. At 170 C. it appears that all the water present in any form in the superphosphate is driven off, save, indeed, the constitutional water of the monocalcic phosphate, and of the phosphoric acid. MONOCALCIC PHOSPHATE &c. If the superphosphate be a poor one, or if it contain much aluminium or iron, it should not remain longer than three hours in contact with the 500 c. c. of water, but should then be filtered off without waiting for the settling of the suspended matter. In fact, it is better in such cases to extract the superphosphate continuously with very small portions of cold water, filtering after each addition, and washing the residue on the filter so long as any phosphate is dissolved : the mixed filtrates may be cleared, if necessary, with a drop or two of dilute nitric acid. Hot water must on no account be used in extracting the last traces of the monocalcic phosphate and phosphoric acid. It often yields higher results, but their accuracy and constancy may be seriously impaired. Both dicalcic and tricalcic phosphates are altered by boiling water ; and so an extract of a superphos- phate which has been made first with cold water and then with boiling water, will represent not only the amount of mono- calcic phosphate and phosphoric acid, but a part of the other phosphates present, notably of those which have been called " reduced." REDUCED PHOSPHATES. A process for estimating these has been previously given, but the results are not quite so accurate as one would wish. It is a mistake to regard reduced phosphates as of equal value, in a manurial sense, with those which have been made (and which remain) soluble. They lack that initial diffusive power into the soil which monocalcic phosphate pos- sesses. For, although it may be said that all soluble phosphates do ultimately become " reduced " in the ground, yet, owing to their solubility in soil-water, they will travel further and fertilize more earth before this change has been completed. NITROGEN. As ordinary superphosphates contain either no nitrogen or mere traces of so-called nitrogenous organic matter, we may defer any further directions, as to the determination of nitrogen in manures which have been enriched by artificial additions of ammonia-salts or nitrates, until the process for analysing phospho-guano, &c., bo discussed. ST7PEKPHOSPHATES. 163 Statement of Results. There are in use two ways of stating the results of an actual analysis of a superphosphate. The simpler of these involves fewer assumptions and is sufficient for all practical purposes : In 100 parts MOISTURE 00-00 COMBINED WATER AND ORGANIC MATTER, containing nitrogen equal to '00 ammonia OO'OO TOTAL PHOSPHORUS PENTOXIDE *, including ' Soluble' P 2 5 00-00 ' Seduced' P 2 O 5 O'OO ' Insoluble ' P 2 O OO'OO oo-oo CALCIUM SULPHATE, CaSO 4 OO'OO ALKALINE SALTS, &c., undetermined 00-00 SlLICIOUS MATTER CO'OO The more common way of tabulating the analytical results is given below, the figures inserted being those which were obtained in the examination of an actual sample : In 100 parts MOISTURE, or loss at 100 C 18*46 ORGANIC MATTER AND COMBINED WATER, containing 1 ig-gQ nitrogen equal to '34 ammonia J MONOCALCIC PHOSPHATE, CaH 4 P 2 O 8 , equal to 18-181 21'39 biphosphate or 28 '45 bone-phosphate made soluble J TRICALCIC PHOSPHATE, Ca 3 P 2 O 8 , of which 2'31 was 1 ^ai "reduced" phosphate j CALCIUM SULPHATE, CaSO 4 29'38 ALKALINE SALTS, &c. undetermined 2'62 Silicious matter . . 3'72 100-00 * Often described as " Phosphoric acid " or as " Phosphoric anhydride.' G 2 164 QUANTITATIVE ANALYSIS. BEET MANURE. TURNIP MANURE. CORN AND GRASS MANURE. PSOSPHO-GUANO. SULPHATED GUANO. DISSOLVED GuANO, &C. All manures containing soluble phosphates are analysed as a superphosphate. In some cases nitrogen and potassium com- pounds are present in considerable quantities and must be esti- mated, the nitrogen being usually determined, as before directed, by a combustion according to Ruffle's sodium thiosulphate method. In the case of superphosphates and other manures which can be easily reduced to a paste it is a good plan to grind a weighed quantity of the sample with an equal weight of sodium thiosul- phate crystals, to dry the paste at 200 C., to weigh it again, and to take about 3 grams for the combustion. This is conducted as described on page 145. The potassium is determined as follows. Make a hydrochloric solution of about 1 gram of the manure which has been previously gently ignited to char any organic matter present. Evaporate the hydrochloric-acid solution to dryness, and heat the residue slightly on a sand-bath to render insoluble the whole of the silica. The mass, when cold, is moistened with concentrated hydrochloric acid, treated with water, warmed and filtered. To the filtrate add ammonia and ammonium carbonate in excess, warm and filter. Evaporate the filtrate to dryness, and ignite the residue till all fumes cease. Dissolve the residue in the smallest possible quantity of water, filter, and add HC1 and PtCl 4 in excess to the solution : the rest of the operations have been described under the head of the " Estimation of Potash," p. 134. In analysing dissolved and sulphated guanos, the plan appro- priate to superphosphates will answer well if the determina- tions of nitrogen and potassium mentioned in the preceding paragraph be also made. There is one other determination, that of sulphuric trioxide, which will serve to render the analytical results more satisfactory. This estimation may be made by weighing out a convenient quantity of the manure (not more than 1 gram if dissolved Peruvian guano be under examination), and boiling it with dilute hydrochloric acid. Then the liquid is filtered off, and the residue in the beaker or flask again boiled GUANOS. 165 with water and some dilute hydrochloric acid, and the liquid poured through the same filter as before. This process is re- peated until a drop of the filtrate no longer gives any cloudiness with barium chloride the sulphur trioxide is then estimated in the united filtrates by the process described on page 136. The amount of BaS0 4 obtained is calculated into a percentage of S0 3 , which is set down in that form when the results of the analysis are tabulated. Or, if the nitrogen existing in the manure in the form of ammonia be separately determined in the manner de- scribed further on under Guano, it may be presumed to exist as ammonium sulphate ; and then any surplus S0 3 may be written down as calcium sulphate. It must be remembered that on ignit- ing dissolved guano for the purpose of determining its volatile matter and combined water, the greater part of the sulphur trioxide is usually volatilized ; a separate determination of S0 3 in the ash or residue is therefore requisite, or else some part of this constituent of the manure would be entered twice over. The difference between the total S0 3 and that found in the ash must be deducted from the total volatile matter lost on ignition, and the residue only entered as volatile matter. PERUVIAN GUANO. This valuable manure consists chiefly of the more or less altered carcases and excreta of seals and of sea-birds. It con- tains a large quantity of so-called organic matte i* rich in nitrogen together with ammonium carbonate, oxalate, phosphate, and urate. Calcium, magnesium, and alkaline phosphates are also present, together with moisture and a small quantity of silicious matter. The Peruvian guanos now imported are much poorer in nitrogen compounds and more variable in composition than the old Chincha Islands guano : occasionally cargoes damaged with sea-water are imported ; this injury may be detected by the high percentage of moisture found, and by the presence of common salt, the amount of which may be determined by the process for chlorine given under apatite, p. 148. The adultera- tion of guano with ochre may be detected by the red colour of the ash it leaves ; while the admixture of peat, clay, or sand may be ascertained by the increases in the normal percentages of 166 QUANTITATIVE ANALYSIS. volatile matter, of ash, or of silicious matter which they respec- tively cause. Great care must be taken in order to secure a fair average sample of guano for analysis. Several portions should be taken, well mixed and powdered, and then preserved in a bottle having a good stopper. MOISTUEE is determined at 100 in the usual way. Occasion- ally, especially if the guano be damp, this determination is apt to yield results which are too high, from the volatilization of the ammonium carbonate present, along with the water. The amount of ammonium carbonate lost in the water-bath is easily found by making a second nitrogen combustion in the guano after it has been dried. The percentage of nitrogen (cal- culated from the weight of the guano before drying) is subtracted from the total nitrogen found in the fresh guano ; and the dif- ference, calculated as 2(NH 4 ) 2 0, 3C0 2 , gives the amount lost in the water-bath ; this of course, when deducted from the actual loss, gives the true moisture. OKGANIC MATTER is determined in about 2 grams, exactly as in bone-dust. A genuine guano gives a perfectly white ash. SAND AND CALCIUM AND MAGNESIUM PHOSPHATES are determined as in bone-dust. As calcium salts other than phosphate are seldom present in the ash of a genuine guano, it is unnecessary to make the solu- tion dilute before precipitating by ammonia : the re-solution of the phosphates is for the same reason omitted. ALKALIES. These are for commercial purposes determined by difference ; the phosphorus pentoxide they contain should, how- ever, be estimated, as it is of equal importance with that of the soluble monocalcic phosphate. PHOSPHOEUS PENTOXIDE IN ALKALIES. The filtrate from the phosphates is concentrated, and a little ammonium oxalate added. Should a decided precipitate be formed, phosphoric pentoxide can be present only as a mere trace and need not be further looked for ; the calcium oxalate is in this case collected, burnt, and weighed, the amount found being placed in the analysis as calcium carbonate or sulphate, as a qualitative examination may GUANOS. 167 indicate. If ammonium oxalate produces no precipitate, or a mere opalescence, the solution, filtered if necessary, is treated with a little magnesium sulphate and a considerable excess of ammonia ; the precipitate of ammonium magnesium phosphate is collected, washed, burnt, and weighed. The Mg 2 P 2 7 is cal- culated into phosphorus pentoxide. TOTAL NITROGEN. A combustion is made with about '7 gram of the substance. The undried guano should be weighed in a small corked tube, and mixed with the soda-lime as speedily as possible, in the combustion- tube itself, by means of a wire ter- minating in a corkscrew twist : the bulbs filled with acid should be then at once attached. If these precautions be neglected, ammonia will be lost (see p. 142). NITROGEN EXISTING AS AMMONIA SALTS. If it be desired to ascertain what proportion of the nitrogen in a guano exists in the form of compounds of ammonia, the following plan may be adopted. Into a small retort haying its beak directed upwards, introduce about 1 gram of the guano, a little pure water, and some calcined magnesia. The beak of the retort is fitted with a cork and bent delivery-tube, which latter is connected with a nitrogen bulb containing 20 c. c. of the standard sulphuric acid used for nitrogen-determinations. After boiling for some time all the ammonia present in the guano will have been disengaged and then absorbed by the acid in the bulb, which is then titrated with standard alkali solution in the usual way (p. 138). NITROGEN EXISTING AS NITRATES. Some guanos contain traces of nitrates, while sodium nitrate is often added to mixed manures. In the former case the determination of total nitrogen and of that existing as ammonia will always suffice ; but in the latter case we must determine the total nitrogen by means of a combustion of the manure by KuffiVs thiosulphate mixture as described on p. 145. We then proceed to the determination of the nitrogen existing as nitrate by washing out the contents of the retort (as used in the ammonia estimation described in the preceding paragraph) into a beaker, filtering the mixture, and then determining the ammonia which will be formed from it, as described further on under the head of water-analysis (p. 214), by means of a zinc-copper couple. Care must be taken to use no more of the nitrate solution than can be completely reduced to 168 QUANTITATIVE ANALYSIS. ammonia by the quantity of copper-zinc couple present : about 05 gram of NaN0 3 , and no more, may be employed. Before nesslerizing, the ammonia may have to be distilled off into pure water. The Gravimetric Uranium Method. The following is a speedy arid accurate method for the separa- tion of phosphoric acid from lime, magnesia, and the alkalies. It answers well for the analysis of bone, guano, and other phos- phates free from iron or aluminium. As the uranium precipitate is of great bulk, no more of the substance than will contain about 3 gram of calcium phosphate should be taken for analysis. PHOSPHOKTJS PENTOXIDE. The clear and dilute solution of the phosphate is treated with ammonia in slight excess ; dilute acetic acid is then added in small portions at a time till the precipitate is entirely redissolved. Any great excess of acetic acid is to be avoided. A residue, insoluble in acetic acid, is probably iron or aluminium phosphate, and must be removed by filtration. Ura- nium acetate is now added to the solution, and the whole boiled; sufficient uranium has been employed when a fresh addition produces no further precipitate. The uranium phos- phate is allowed to subside, and then washed by decantation, boiling water containing ammonium acetate being employed. The washings are carefully filtered, and the phosphate finally collected on the same paper, dried, separated from the filter as far as possible, the paper being incinerated alone first, and then the whole is ignited. Before weighing, the uranium phosphate should be moistened with strong nitric acid and again ignited. Its colour after ignition should be a bright canary-yellow. The composition of the ignited precipitate is such that one gram contains -1991 of P 2 5 . LIME AND MAGNESIA. The filtrate is concentrated, and the uranium precipitated by ammonia in the cold, the vessel being kept covered. The precipitate is washed twice by decantation, then boiled with a solution of ammonium chloride and collected on a filter. The lime and magnesia are determined in the filtrate in the usual manner. Volumetric Uranium Method. Instead of weighing the uranic phosphate precipitated in the preceding process, a method of determining the point at which GTJANOS. 169 the whole of the phosphorus pentoxide present has been removed from solution has been devised. It is based upon the reaction which occurs between an uranic salt and potassium ferro- cyanide namely, the production of a reddish-brown coloration, a coloration which occurs only when no P 2 5 remains in the liquid. Three solutions must be made specially for this process : 1. The standard uranium solution is prepared by dissolving about 35 grams of crystallized uranium acetate in 900 c. c. of water : add 25 c. c. of glacial acetic acid. Uranium nitrate (after having been purified by solution in ether, nitration and evaporation of the ethereal solution) may be substituted for the acetate : in this case an addition of 3*5 grams of sodium acetate (instead of acetic acid) should be made to the solution. The liquid should be allowed to rest for a few days before its strength is determined, as a deposit containing uranium slowly forms. 2. A sodium acetate solution is made by dissolving 100 grams of that salt in 900 c. c. of water, and making up the bulk to 1 litre by means of strong acetic acid. 3. The third solution requisite is a standard one of calcium phosphate. To prepare this, dis- solve 4-366 grams of pure calcium phosphate in the smallest quantity of nitric acid necessary to effect solution : then make up to 900 c. c. This solution must be standardized by a direct determination of the phosphorus pentoxide in it by the molybdic- acid method, not by weighing the reprecipitated phosphate. Before using this nitric-acid solution, however, the free nitric acid must be removed by adding a little sodium-hydrate solution until a slight opalescence is produced : then add 10 c. c. of the acidulated sodium-acetate solution, which will clear up the slight precipitate formed, provided no aluminium or iron (or only small quantities) be present. Finally make up the solution to 1 litre with distilled water. Now it is necessary to dilute our uranium solution until 20 c. c. of it are exactly precipitated by 50 c. c. of the phosphate solution. To do this, pour 50 c. c. of the phosphate solution into a beaker, add 5 c. c. of the sodium-acetate solution, and then warm it on the " steamer " to about 80, and maintain it during the process at about that temperature. Now run in, with con- stant stirring, about 10 c. c. of the uranium solution. Next add the uranium solution more slowly in quantities of 1 c. c. or P 5 c. c. at a time, testing the liquid as follows after each addition. Bring a few drops of the turbid but nearly colourless liquid from the beaker on to a porcelain slab which has been previously 170 QUANTITATIVE ANALYSIS. covered with a number of annular grease marks, made by a tallowed cork ring about 1 inch in diameter. Now add a small fragment of a crystal of potassium ferrocyanide ; a reddish- brown colour indicates that excess of uranium solution has been added, and the operations must be recommenced. But if no coloration occur, continue the addition of the uranium solution to the liquid in the beaker until a drop or two of the solution, when tested with ferrocyanide, just indicates excess, by the pro- duction of the characteristic colour : this testing should be repeated in five minutes to see whether the process is complete. It will now be easy to ascertain how much water must be added to the uranium solution in order that 20 c. c. of it shall be exactly equivalent to 50 c. c. of the phosphate solution. This strength corresponds to -005 gram of P 2 0. for 1 c. c. of the standard uranium solution. In applying this volumetric process to the estimation of P 2 5 in a guano, either the filtered acetic acid solution of the ash of the guano may be directly used, or the ash may be treated with hydrochloric acid, &c. in order to render any silica insoluble, and then the acid solution may be first rendered faintly alkaline with soda, and finally acid with acetic acid. In operating then upon a solution however obtained, no free acid save acetic must be present, while the rest of the treatment is conducted with 50 c. c. of the solution in question, exactly as described above. It is scarcely necessary to add that the uranium solution must be standardized by means of repeated trials, and that two or more volumetric estimations should be made in separate portions of each phosphatic solution to be tested. It is necessary that about the same quantity of sodium acetate solution be used in each experiment. Any ferric phosphate which may be precipitated on removal of the free nitric acid from the solution of the guano, &c. by means of sodium acetate may be collected on a filter, washed thrice with boiling water, dried, ignited and weighed. The P ? 5 in it may be cal- culated from its formula, which is approximately Fe 2 3 , P 2 5 . The amount thus found must be added to that obtained in the volumetric determination to represent the total. NITRATE OF SODA OK POTASH. The proportion of real sodium or potassium nitrate in a sample is usually determined by difference, the impurities only being NITRATE OP SODA. 171 estimated; these are generally moisture, sand and insoluble matter, sodium chloride, and sodium or calcium sulphate. The sample is prepared by the usual processes of powdering and mixing. MOISTURE is determined by heating about 5 grams to 130 C. till the weight is constant. SAND AND INSOLUBLE MATTER. About 7 grams are dissolved in water, the residue collected on a counterpoised or weighed filter, thoroughly washed, dried, and weighed. The result is total insoluble matter. The filter may then be burnt ; the inor- ganic residue is sand. SULPHUR TRIOXIDE. The filtered solution obtained from the previous operation is to be largely diluted, boiled, and preci- pitated with barium nitrate, nitric acid being also added. The weight of barium sulphate obtained will be calculated as calcium or sodium sulphate, according to the amount of calcium found. Determination of Chlorine. The chlorine is best determined by a standard solution of silver nitrate, which is added from a graduated vessel to the filtered solution of 7 grams, or of a smaller quantity if much sodium chloride be present (with which a few drops of a solution of neutral potassium chromate have been mixed), till the orange tinge produced by each drop of the silver solution remains just perceptible after stirring. Preparation of the Standard Solution of Silver Nitrate. The most convenient strength is a decinormal solution. Dis- solve 16' 9 7 grams of pure silver nitrate in water, and make up to a litre. Preserve in a stoppered bottle. This solution now contains ^ of the molecular weight of AgN0 3 in a litre: therefore 1 c. c. should correspond to ^~ the molecular weight of Cl=-00355 gram, or of NaCl = -00585 gram, &c. Titrate with pure sodium chloride to find the exact strength. 172 QUANTITATIVE ANALYSIS. If septems be. used, 169*7 grains of silver nitrate should be dissolved in 1000 septems of water ; 1 septem will then =0355 grain Cl. The silver solution must be neutral, and the solution to be tested either neutral or very slightly alkaline with a fixed alkali ; it may also be worked in the presence of a small quantity of acetic acid. The potassium chromate must also be neutral and free from chloride ; it may be conveniently made so by adding nitrate of silver till the red precipitate becomes permanent, and then filtering. LIME is determined in the usual way, in the filtered solution from 7 grams. N.B. Where the necessary appliances are at hand, it is simplest to dissolve 35 grams of the nitre in water, pass the whole through the counterpoised filter, and then divide the filtrate by weight or measure into five equal parts, in which the several determinations are made. Actual Determination of Nitrogen Pentoxide. The amount of nitrogen pentoxide may, if desired, be found with some approach to accuracy as follows, in the absence of organic matter : Mix 1 gram of the finely powdered sample with six times its weight of finely ground silica or quartz ; place the mixture in a platinum capsule, and dry in the water-oven, or, preferably, at 130 C., till it ceases to lose weight ; then raise the temperature to a low red heat for half an hour : the whole of the N 2 5 will be expelled, and its amount found by the loss of weight which the mixture has sustained subsequent to its desiccation in the waterroven. The silica may be prepared by igniting flints, plunging them while red-hot into cold water, and pulverizing the residue. Nitrogen pentoxide may be exactly determined in nitrates by means of the copper-zinc couple method or by the aluminium method as given further on (pp. 214 and 215). POTASH SALTS. .1 >< : , . ,. \\~* JK fc^fy POTASH SALTS. Besides potassium salts, the articles sold under this name aro likely to contain salts of sodium, calcium, and magnesium. As their value depends entirely on the amount of potash present, its determination is all that will be required. The methods here described are equally suited for the analysis of the commercial " sulphate " or " muriate." The sample must be powdered and carefully mixed before analysis. Direct Method of Determining Potash. Weigh out 10 grams of the salt, boil for ten minutes in 200 c. c. of water, and after cooling the solution, but without fil- tering it, make up the bulk to 1000 c. c. and run it through a dry filter. If the sample contain 10 to 15 per cent, of K 2 (kainite), take 50 c. c. of the filtrate, but if less than 5 per cent. K 2 be present 100 c. c. must be used. In any case make up the volume to 150 c. c., heat to 100, and add, drop by drop, with constant stirring, slight excess of barium chloride solution : without filter- ing, add in the same manner baryta water in slight excess. Heat, filter, and wash the precipitate until it is free from chlo- rides. Add to the filtrate and washings 1 c. c. of strong ammo, nia-water, and then a saturated solution of ammonium carbonate until the excess of barium is precipitated. Heat. Add now, in fine powder, '5 gram of pure oxalic acid or *75 gram of ammo- nium oxalate. Filter, wash free from chlorides, evaporate fil- trate and washings to dry ness in a thin porcelain or platinum bason. Hold the dish with crucible tongs over a naked flame, but below a red heat, until all volatile matter has been driven off. When cold, the residue is digested with hot water, filtered through a small filter, and washed with successive small portions of water until the filtrate amounts to 30 c. c. or more. To this filtrate, contained in a porcelain bason, two or three drops of strong hydrochloric acid are added, and then 10 c. c. of a ten per cent, solution of platinic chloride. The rest of the opera- 174 QUANTITATIVE ANALfSIS. tions are conducted precisely as described under the heading " Estimation of Potash," p. 134. But if there be the slightest appearance of white foreign matter in the orange- coloured double chloride of potassium and platinum, it should be washed on the filter with a 20 per cent, solution of ammonium chloride which has been saturated with all the K 2 PtCl 6 it will take up. 10 c. c. of this solution are first run through the filter, and then 10 c. c. more are poured on and returned 5 or 6 times : 10 c. c. more are then used in the same way. Finally, the washings with alcohol and with ether are conducted exactly as described on p. 134. The oxalic acid and the ammonium oxalate used must be quite free from sulphuric acid and from potash. Potash may be tested for by igniting a portion, treating the ash (if any) with water, filtering, and examining the filtrate with platinum tetrachloride as above. Oxalic acid may be purified from sulphuric acid by means of barium chloride, and from alkaline salts by crystal- lization, the first crystals being the most impure. Indirect Method of Determining Potash. Not more than *5 gram of the potassium salt is to be taken. Precipitation with barium chloride &c., and ignition with oxalic acid &c., are to be followed exactly as in the previous process. The residue left on ignition is treated with water, filtered, some ammonium chloride added, the solution evaporated to dryness in a platinum or porcelain vessel, the dry mass continuously heated till all ammoniacal salts are expelled, and the residue weighed. It consists of mixed potassium and sodium chlorides. This is next dissolved in water, and the chlorine it contains estimated by the volumetric method described at page 171. The potassium chloride present is then discovered by the following calculation : The amount of chlorine found is multiplied by 2*1029 ; from the product is deducted the weight of the mixed chlorides; the difference is multiplied by 3-6562. The product is the amount of sodium chloride present ; the remainder is potassium chloride. COMMON SALT. 175 Per chloric- Acid Method of Determining Potash. Potash may be conveniently determined in the form of per- chlorate. The solution to be analysed must be first freed from sulphuric acid by means of the addition of a slight excess of barium nitrate; the mixture is then evaporated nearly to dry- ness, and the residue moistened with nitric acid, these processes of evaporating and moistening with nitric acid being repeated until all hydrochloric acid has been removed. The mixture, having now a volume of about 5 c. c., may receive the necessary addition of pure perchloric acid and then be evaporated to dryness. To the residue a few c. c. of water are added, and the whole once more brought to dryness. Some spirit of wine is now poured on the residue : the perchlorates of barium, calcium, magnesium, and sodium are dissolved, while the barium sulphate and perchlorate remain behind. More alcohol is poured on these, and the mixture is rubbed with the end of a glass rod to break down the potas- sium perchlorate crystals. The alcoholic washings are poured off, and the residue once more moistened with water, evaporated to dryness, and taken up with alcohol. The whole is thrown on a filter ; and when the alcohol has drained away, the residue on the filter is treated with boiling water, which dissolves the potas- sium perchlorate. The filtrate and washings are now evaporated to dryness, heated to 100, and weighed. If the weight found be multiplied by *3398, the corresponding amount of K 2 will be the product. COMMON SALT. The amount of real sodium chloride is determined, as in the previous analysis, by difference. The impurities present are usually moisture, insoluble matter, and calcium sulphate, with magnesium chloride and sulphate in traces ; these are estimated by the processes already given : the moisture being driven off at 130. The sulphur trioxide found is combined with the lime ; if an excess remains this is considered to be in union with soda. 176 QUANTITATIVE ANALYSIS. In waste salt which has been used for curing bacon, potassium nitrate may occur ; its amount may be determined by one of the processes given on pp. 214 and 215. AMMONIACAL SALTS. GAS-AMMONIA. The ammonia present in these substances is usually in the form of sulphate. The impurities are very varied both in nature and amount : they may be roughly classed as water, organic and volatile matters, and iron compounds. In preparing the sample for analysis, it should be reduced to a fine powder, and well mixed. MOISTURE is determined by drying in the water-oven in the usual way. ORGANIC AND VOLATILE MATTERS are estimated by loss of weight on ignition. The ferric oxide, with other inorganic matter pre- sent, remains as a dark-red powder. AMMONIA. A combustion is made with a quantity not exceed- ing '7 gram, all possible precautions to prevent the loss of ammonia during the mixing with soda-lime being carefully attended to. The ammonia found may be calculated into sulphate (NH 4 ) 2 S0 4 . As the whole value of the substance depends on the ammonia which it contains, its determination will be all that is generally required. But if a qualitative examination indicates the presence of sulphocyanogen, the real ammonia should be determined as PtCl 4 ,2NH 4 Cl, the operation being conducted exactly as in the estimation of potash (p. 134), except that the precipitate is to be washed with alcohol and ether only. SOOT. Ordinary soot consists mainly of finely divided carbon : it con- tains, besides, a small quantity of ammonium sulphate and com- plex nitrogenous compounds, with various inorganic substances, ANALYSIS OF SOILS. 177 such as constituents of the fuel-ash or fragments of broken masonry ; its value depends on the amount of available nitrogen present. TOTAL INORGANIC MATTERS. An ash-determination is made in about 3 grams of the sample ; the loss on ignition includes the carbonaceous and nitrogenous matters and the water. NITROGEN. A combustion is made with about 1 gram. The nitrogen is usually calculated as ammonium sulphate, but part of the nitrogen in soot exists in the form of nitrogenous bodies having but a low manurial value. ii. ANALYSIS OF SOILS. The constituents of soil may be looked at from a physical or from a chemical point of view. It will conduce to the clear understanding of the problems which the analysis of soils presents if their physical or mechanical constituents be first enumerated : 1. Water, interstitial, hygroscopic, and combined. 2. Air, both interstitial and absorbed. 3. Stones, remaining on a sieve of 5 mm. 4. Gravel, remaining on a sieve of 3 mm. 5. Gravelly sand, remaining on a sieve of '6 mm. 6. Coarse sand. 7. Pine sand. 8. Clay. 9. Organic matter. It should be noted that the four last-named soil-constituents, associated with much water and air or gases, make up the true soil or " fine earth " in which plants find their immediately avail- able supplies of nourishment. The terms clay, sand, and gravel, as here used, are, however, not to be understood as implying any special chemical characters ; they express simply certain me- chanical conditions. On the proportions in which the several physical constituents above named are present in a soil depend 178 QUANTITATIVE ANALYSIS. many of its most important physical properties. Not only so, but as the several mechanical constituents differ from each other in chemical composition, the results of the chemical analysis of a soil will be greatly affected by the proportion in which the mechanical constituents occur. As a rule, the " fine earth " alone is submitted to minute qualitative chemical examination ; but if it be desired to ascertain what reserve of plant-food be present in any soil, then the gravelly sand, the gravel, and even the stones, as separated during the mechanical analysis, may be likewise analysed. Thus it will be seen that there are many reasons for desiring a mechanical as well as a chemical analysis of a soil. Unfortu- nately most of the physical constituents can never be absolutely determined, it being impossible, for instance, to define where gravel ends and sand begins : the amounts found will be much influenced by minute variations in the plans of analysis adopted, and will not be exactly comparable when soils of different origins are treated even by the same method. MECHANICAL ANALYSIS OF SOILS. SAMPLING. Where the soil of a field is uniformly and distinctly marked out from the subsoil, three or four parcels of earth may be taken from different parts of an acre. The surface vegetation and accidental foreign matter are first cleared from the selected spots : then a trench is dug down to the subsoil, so as to leave a square block, ] 2 or 18 inches square, of the surface-soil intact; from this vertical slices are cut until 5 kilograms (or 10 Ibs.) of earth have been obtained. This material is then placed on a piece of sacking on a wheelbarrow. The same operations are repeated on the other selected spots, and from the united quantities of soi thus obtained, after thorough mixing with the spade, a final sample of about 4 or 5 kilos, is taken. This should be trans- ported to the laboratory in a wooden box, not in a closed metallic or glass vessel. A sample of the subsoil may be obtained from the spots opened in the above operations, the depth to which the subsoil is excavated being at least equal to that of the soil. MECHANICAL ANALYSIS OE SOILS. 179 When the surface of the land shows any kind of inequality to exist in the texture, colour, or other character of the surface- soil, it will be necessary to take a number of representative specimens from places which resemble one another closely, and to mix them together. Then a second series of samples is secured from other places in the field differing from those first selected, but also resembling one another. Of course if three sorts of soil exist alongside of one another a third series of samples will be required. In order to prepare the soil for most of the operations of analysis, whether mechanical or chemical, the sample should be spread out in a warm place on a board or on smooth brown paper to dry slowly ; a sample of 100 grams may, however, be at once taken for the determination of moisture. This should be dried till constant at 100 C. and then at 150 C. The main bulk of the soil, when in a fit state, neither too moist nor too dry, must be passed between the fingers, the clods and lumps being crushed from time to time as the drying proceeds. If by any chance the lumps become too dry, they may be mois- tened with the spray of distilled water, and then again left until they are ready for crushing. When the whole sample has been broken down and reduced to a uniform condition, so far as hand- pressure is capable of achieving this result, then the following operations are carried out. STONES. If large stones be present, the sample of air-dried soil is weighed, the stones (which will not pass through a sieve of 5 mm.) are picked out, weighed, then dried in the water-oven, and again weighed. The remaining soil is then well mixed, and transferred to a stoppered bottle. MOISTURE is determined in the usual way. As the sample is sure to be somewhat rough and uneven, 50 grams should, if possible, be taken for this determination. ORGANIC MATTER. As large a portion of soil as can con- veniently be taken is heated gradually to low redness, and thus maintained till stirring with a platinum wire fails to reveal any black particles. The residue, when cold, is moistened, with am- 180 QUANTITATIVE ANALYSIS. monium carbonate, dried, again ignited for a minute and weighed ; the loss is organic matter plus moisture. GRAVEL. About 600 grams (or 10,000 grains) are sifted through a wire sieve, the meshes of which have a diameter of 3 millims.*, the sieve being fitted with a flat circular revolving brush above, and with a drum below to receive the sifted portion. The gravel remaining in the sieve is examined ; if lumps of soil are visible, these are broken, and the sifting resumed. The sieve, with its contents, is finally ^N placed in a bason of water ; and after soaking awhile, the still adhering soil is washed from the gravel, which is then dried in the water-bath and weighed. If it be mixed with roots or other organic matter, gentle ignition must precede the weighing. The matter removed by washing is to be preserved. ^ GRAVELLY SAND. The portion of sand which passed through the first sieve is now placed in a second, the meshes of which have a diameter of 0-6 millim. The sifting and subsequent washing are conducted exactly as before. The matter removed in washing the gravel is added to the contents of the sieve before \* washing is commenced. The fine gravel, or gravelly sand, when quite clean, is dried, gently ignited, and weighed. COARSE SAND. 30 grams (or 500 grains) of the soil which passed through the last sieve are perfectly dried at 100 C., and then weighed. Another similar -^ quantity is gently ignited, and then weighed. This ^ sample is placed in a bason, four or five times its bulk ^ of distilled water added, and the whole boiled for * The scale at the side of this page will enable the analyst to substitute the corresponding English measures of length for those of the metric system given in the text. MECHANICAL ANALYSIS OF SOILS. 181 Fig. 17. half an hour, with frequent stirring. The last is especially neces- sary if the soil be of a clayey nature, the object in view being the perfect disintegration of the mass. The contents of the bason are then removed to the glass vessel A in fig. 17 (depth 20 centims., width at top 7 millims.), fitted at top with a narrow brass ring, provided with an exit-tube, a. The cistern, C, is now filled with distilled water, and the funnel-tube B (length of tube 40 centims., diameter 7 millims., drawn out at the end to a small orifice, diameter 1^ millim.) attached to the cock with a piece of twine. When all is ready, open the cock of the cistern slightly, and, while water is passing through the funnel, introduce the latter into the vessel A, the height of which is to be so arranged that the point of the funnel is about 3 millims. from the bottom of the vessel. The issue of water from the cistern is now regulated so that the height of water in the funnel is kept 20 centims. above that in the elutria- ting glass, A. The stream should issue steadily against the side of the funnel. The water with suspended matter overflowing from the tube a is collected in a large beaker or bason and pre- served. The operation is completed as soon as the water from the discharge-tube runs almost clear. The funnel is then removed, the fluid in A rapidly decanted from the solid matter, which is then rinsed into a bason, dried, ignited, and weighed. The result is coarse sand. The apparatus here described admits of easy construction. An ale-glass of the required height will form a good elutriating vessel. This (in the absence of the brass ring and tube) may be placed in the midst of a large bason, which, when full, can be connected with other vessels by a small glass siphon. FINE SAND. The washings from the previous operations are 182 QUANTITATIVE ANALYSIS. allowed to stand an hour or two, the liquid then poured off, and the solid residue returned into the elutriating glass. The pro- cess above described is then recommenced ; this time, however, the column of water in the funnel is only 3 cm. above that in the glass. The washing is continued till the water passes off clear. The residue is then collected, dried, ignited, and weighed. CLAY. This is found by difference, and should be entered as " clay, so-called, ignited," but it cannot be regarded, in the majority of cases, as consisting entirely of true clay. A method of washing soils by means of the upward flow of a constant stream of water has been employed by several conti- nental chemists. The essential portions of the apparatus employed in carrying out this operation are represented in the annexed Fig. 18. figure 18. A reservoir of water kept at a constant level by means of a large vessel and tube inverted over the reservoir, in the manner of a bird-fountain, is required : this is not shown in our illustration. The water enters the special washing-apparatus at MECHANICAL ANALYSIS OP SOILS. 183 A, passes downwards through a small glass tube with a stopcock B, the end of which, expanded into a small funnel, and covered with fine cambric, passes first into the cork C, with which the " separator " D is closed : this separator is best made of a paraifin- lamp glass inverted. The upper end of the separator D is closed with a perforated cork through which an equal-limbed siphon, E, passes. That end of the siphon which is in the separator has a small upward bend at its extremity. The method of using this arrangement for separating clay, fine sand and coarse sand, is exactly like that just described, the boiled mixture of soil and water being poured into the vessel D and then a stream of distilled water turned on from the reservoir, so that the water flowing from the siphon shall run by drops and not in a con- tinuous thread into the beaker F. When the difference of water- level in the reservoir and the separator is about 57 centims., and the distance between the inflow and outflow in the separator is 13 centims., the fine sand and the clay will both be found com- pletely driven over into the receiver P after a short time and the use of a comparatively small volume of water. Then the coarse sand should be rinsed out of the separator, dried, gently ignited, and weighed. The fine sand and clay will have to be removed from the beaker F, placed in the separator and washed by means of a more gentle current of water. If the difference of water- level between the reservoir and the point C be reduced to 35 centims., the clay will be washed out while the fine sand will remain in the separator, and can be removed to a dish, dried, ignited, and weighed. The clay is found by difference. In using the process just described, it is a good plan to make a few preliminary trials as to level, rates of flow, and sizes of tubes and vessels ; for different classes of soils demand modifi- cations of arrangement. We may add that a lamp-glass measuring 7 centims. across its broadest part, and having an extreme length of 22 centims., forms a good separator, while the siphon should be so arranged as to admit of being lowered more or less into the liquid in this vessel, which may be Ml. 184 QUANTITATIVE ANALYSIS. Calculation of Results. If the soil is one containing large stones or pebbles, it is best to put down the amount of these separately, it being essentially a variable quantity, and to calculate the other ingredients on the coil remaining after their removal. The percentages are all cal- sulated for the dry soil ; this is easily done, the moisture present having been determined by experiment ; as, however, this deter- mination is made subsequent to the separation of the stones, the percentage of these must be calculated as follows : Subtract from the weight of sample the weight of undried stones ; find the amount of dry soil the remainder is equal to : add to this the weight of dried stones, and calculate from this total the percentage of dry stones. The percentages of organic matter, gravel, and gravelly sand are found in the usual way. The organic matter may perhaps present a difficulty. The loss in the experiment consists of or- ganic matter plus moisture ; if, however, we calculate the amount of dry soil that the quantity taken is equal to, and deduct from this the weight after ignition, the difference is organic matter only ; this is then calculated on the dry soil. The difference between the sum of the three above ingredients and 100 parts clearly represents the joint percentage of the coarse and fine sand and clay. Let this latter sum be b, and let a represent the number of grams of ignited sifted earth (see p. 180) taken for elutriation, and c the weight of coarse or fine sand obtained, then a : c = b : x. The percentage of coarse and fine sand being thus known, the clay is found by difference. The higher its percentage of the more finely divided ingre- dients, the better adapted for the growth of plants the soil will prove, taking for granted, of course, the presence in these fine earthy particles of all the necessary ingredients of plant-food in adequate proportion and in suitable condition. Other physical characters of a soil may readily be determined CHEMICAL ANALYSIS OF SOILS. 185 by experiment. Such are the amount of moisture which 70 grams of perfectly dried soil can absorb from the air, when spread out in a thin layer and shaded from the sun, on an ordi- nary summer day ; the amount of water which the same quan- tity of soil can hold when made perfectly wet by dropping water upon it contained in a funnel ; the rapidity with which the wet soil dries : and the power which the soil has of withdrawing such substances as ammonia, potash, phosphorus pentoxide, colouring matter, &c. from their solutions. The interstitial air of a soil may be extracted by means of a Sprengel pump, mea- sured, and submitted to analysis. CHEMICAL ANALYSIS or SOILS. Soils, as we have just seen, are really mixtures of stones, gravel, and sand of various kinds, with the more perfectly disin- tegrated mould ; each of these physical constituents will possess, to a greater or less extent, a different chemical composition ; a complete statement of the chemical constitution of a soil will therefore include an account of the composition of each of these ingredients. An analysis in such detail, however, will seldom bo required ; the directions here given will therefore apply directly to the analysis of the finer portion of the soil. The processes described will nevertheless, in most cases, be equally applicable to the examination of the stony matters ; occasional hints will be given having especial reference to this part of the subject. The sample is prepared by drying, breaking the clods by the hand, and sifting to remove stones and gravel, the sieve finally employed being that mentioned above, having meshes of *6 of a millimetre in diameter. The prepared sample should be preserved in a tightly closed bottle. If an analysis of the stony ingredients is desired, they are to be freed from the finer parts of the soil by washing, then dried and pulverized the last operation being best effected, when the 186 QUANTITATIVE ANALYSIS. gravel is of a silicious nature, by first crushing in an iron mortar, and afterwards completing the pulverization in one of agate. It is particularly necessary that a very fine powder should be obtained. If the stones are evidently flint or other simple mineral of known composition, their analysis may certainly be dispensed with, while, should they be evidently calcareous, the directions for the analysis of limestone may be made use of. It is always well to ascertain qualitatively of what the stones, gravel, and sand mainly consist, even when quantitative results are not required. The results are best arranged so as to exhibit the composition of the perfectly dry soil. The prepared sample will generally contain a little moisture ; the amount of this is to be determined by drying a small weighed quantity at 100 ; it is then easy to calculate all the results as if obtained in a perfectly dry sample. PARTIAL CHEMICAL ANALYSIS. For most agricultural purposes a partial chemical analysis will suffice. The constituents determined quantitatively are organic matter, matters soluble in water, nitrogen, potassium, and phos- phorus pentoxide. Qualitative testings are likewise made for lime, sulphur trioxide, chlorine, nitrogen pentoxide, and iron in the ferrous condition. ORGANIC MATTER. About 4 grams, are heated gradually to low redness, and thus maintained till all blackening has disap- peared ; the residue, when cold, is moistened with ammonium carbonate, again heated for a minute or two, in order to dry it and drive off excess of ammoniacal salt, and then weighed. The loss is organic matter and combined water. SOLUBLE SALTS. About 10 grams are boiled with 200 c. c. of water in a flask and kept at a boiling temperature, with occa- sional shaking for a quarter of an hour. The mixture may then be allowed to subside, and the supernatant liquid decanted off : this process of boiling is repeated with the residue and another portion of water. The second portion of liquid is decanted off when nearly clear ; and then both it and the first portion are PARTIAL ANALYSIS Otf SOILS. 187 filtered through a carefully washed filter. The filtrate will probably still be turbid ; if so it should be boiled and then again filtered. Finally the clear filtrate thus obtained is evaporated to dry ness, in a weighed dish or beaker, on the water-bath, dried at 100 C. and weighed. If the dry residue amounts to more than *2 gram (2 per cent.), it indicates a rather excessive and possibly injurious amount of saline matters in the soil. The residue should be tested qualitatively for phosphates, nitrates, sulphates, and chlorides. NITROGEN. The nitrogen present in soils is commonly pro- portionate to the amount of organic matter they contain. It is not usually convenient to burn a quantity of the soil containing more than '8 or *9 gram of organic matter; but within this limit the largest possible amount should be taken ; if a sufficiently long tube be employed there is no difficulty in using 25 or even 30 grams of earth : the Ruffle thiosulphate method should be adopted. Determinations of nitrogen existing as ammonia and as nitrates may be made separately if desired. For this purpose a watery extract of the soil must be specially prepared as follows. A funnel 4| inches wide is made by cutting off the top of a Win- chester quart-bottle. This is inverted and a disc of copper- gauze laid over the opening, and on this two discs of filter-paper, the upper one slightly wider than the lower. The filter is moistened and then the soil (previously dried at about 55 as quickly as possible) is carefully spread upon it, from 200 to 300 grams being taken according to the supposed richness of the sample in nitrates and nitrites. The neck of the Winchester has been previously fitted with an india-rubber stopper and glass tube. The latter is put into communication with a strong flask in which has been inserted an india-rubber stopper having two openings. Into the second opening of the latter is fitted a bent glass tube communicating with an exhausting syringe or a pump. Water is poured on the soil, and the air in the flask is partially exhausted. W r hen 100 c. c. of water have passed into the flask it may be concluded that all nitrates and nitrites have been extracted from the soil. Their amount may be determined in 188 QUANTITATIVE ANALYSIS. an aliquot part of this liquid "by means of the " copper-zinc method" given on page 214. If there be any ammonia-salts present they must first be removed by distillation with sodium hydrate. The ammonia in a soil may be determined by distilling a suitable quantity of the dried soil with pure magnesia and water (see page 167). PHOSPHOKUS PENTOXIDE. About 10 grams of the soil are employed for the determination of the phosphorus pentoxide and the potassium. The weighed quantity is to be gently ignited for a few minutes,- the heat being scarcely raised to visible redness, as the object is merely to carbonize the organic compounds, and as an intense heat is prejudicial. The soil, when cold, is removed to a beaker and digested with moderately strong hydrochloric acid (the concentrated acid diluted with its own bulk of water). The digestion should be carried on in a covered vessel, at a temperature a little below boiling, for an hour, or, in the case of a ferruginous soil, until the undissolved residue ceases to appear of a red colour. The whole is then evaporated to dryness and the residue heated for some time at a temperature above 100 C. to render the whole of the silica insoluble. The mass after cooling is to be. moistened with con- centrated hydrochloric acid and allowed to stand 15 minutes or longer; a little water is then added and the whole warmed. If the residue be grey or white, or black through the presence of much carbon, the liquid may be diluted with more water, boiled, and filtered. The residue on the filter, when dried and ignited,, consists of silica and silicates, and may be weighed with the usual precautions. The filtrate and washings of this residue are treated as follows : The liquid is precipitated by a slight excess of ammonia, the precipitate washed with hot water and collected on a filter. In the filtrate the potassium is contained ; in the precipitate the phosphorus peutoxide. To estimate the latter the precipitate is redissolved in a small quantity of nitric acid, and the undermen- tioned process adopted for the treatment of the solution thus PARTIAL ANALYSIS 0$ SOILS. 189 obtained. Should the soil contain but little ferric oxide and alumina it is preferable to use the solution of 10 grams freed as above described from silica, but without precipitating the liquid with ammonia. Molybdic-Acid Method. The success of this process is not interfered with by the pre- sence of much ferric oxide or alumina ; it is peculiarly applicable in cases where the amount of phosphorus pentoxide present is very small, but is the method to be generally preferred in all cases. To the solution about 30 c. c. of an acidified solution of ammo- nium molybdate are added ; the mixture is evaporated to a small bulk on a steamer or water-bath ; the bright yellow precipitate is collected on a filter and slightly washed with a few drops of a solution of ammonium nitrate. The filtrate is then treated with a further quantity of ammonium molybdate, and submitted to a second digestion on the water-bath. Should more of the yellow precipitate be formed, it is collected on the same filter as that first obtained : digestion with ammonium molybdate is repeated until no further formation of a yellow precipitate occurs. The formation of a permanent white precipitate of molybdic acid' is a proof that the solution is saturated with that body, and that, consequently, any further addition of the reagent is unnecessary, digestion in the water-bath being all that is required. The white as well as the yellow precipitates are collected on the same filter. The precipitate is to be washed while on the filter with small quantities of the acidified solution of ammonium molybdate, or with a strong solution of ammonium nitrate. It is then treated on the filter with just enough hot dilute solution of ammonia to dissolve it completely ; to the clear solution, which contains the whole of the phosphorus pentoxide, a few drops of citric acid are added, and finally some magnesia mixture. After 12 hours the precipitate of ammonium magnesium phosphate is collected and treated exactly as before described, p. 134. In all determina- tions of P 2 0. by means of this salt, a small loss occurs, owing to its solubility in water and saline solutions. An approximative 190 QUANTITATIVE ANALYSIS. allowance for the error thus introduced may be made by adding to the weight of the magnesium pyrophosphate obtained -001 gram for every 200 c. c. of washings collected. The phosphorus pentoxide is calculated from the weight of Mg 2 P 2 7 obtained ; it is usually regarded as existing in the soil as tricalcic phosphate, although, in fact, it is much more probable that it occurs wholly, or almost wholly, in the state of aluminium and ferric phosphates. Citric-Acid Method. This method, though less exact than the molybdic-acid method just described, may be used, where but a small amount of ferric oxide or alumina is present in the soil. Its success is interfered with by magnesium compounds, so that it is not a method of general applicability. The hydrochloric solution of the ignited soil, fused from silica as already described on page 188, and not exceeding 60 c. c. in bulk, first receives an addition of a considerable quantity of citric- acid solution. A few drops of the liquid are poured into a test- tube and treated with an excess of ammonia ; if the liquor assume a clear lemon hue or a very pale yellow, sufficient citric acid has been used ; if the colour be red or orange, the testing is returned to the main bulk and some more citric acid added until the liquid, on repeating the testing with ammonia, exhibits the desired hue. A considerable excess of ammonia is then added ; the solution should remain perfectly clear. It is finally treated with ammouiacal magnesium-chloride mixture, of which about 10 c. c. are required fo precipitate '24 gram of P 2 5 . This magnesia-mixture should be added drop by drop and in very slight excess above the quantity which may be calculated as requisite for the complete precipitation of the phosphorus pent- oxide. The precipitate is allowed to stand for 12 hours, collected on a filter, washed with strong ammonia-water, dried, ignited, and weighed. The P 2 5 is calculated from the Mg 2 P 2 7 obtained. POTASSIUM. The filtrate from the ammonia precipitate (see page 188, line 33) is boiled and treated with pure ammonium oxalate as long as a precipitate is produced ; the whole is PAETIAL ANALYSIS OF SOILS. 191 filtered : the LIME may be determined, if necessary, by washing, drying, igniting, and weighing this precipitate of calcium oxalate, the usual precautions being taken. The firtrate is evaporated to dryness, and the residue gently ignited to expel ammonium salts. The mass is then treated with pure oxalic acid (in such quantity as to convert all the bases present, viewed as potash, into the salt known as " quadroxalate "), some water added, and the whole once more evaporated to dryness and ignited. The residue is dissolved in a small quantity of hot water, and filtered : the filtrate, if clear, is treated with hydrochloric acid in slight excess, evaporated to dryness, and gently ignited. In a complete analysis of soil this residue is to be weighed ; the weight is that of the mixed potassium and sodium chlorides. In the present case the mixed chlorides are dissolved in the smallest possible quantity of water, some platinum tetrachloride added and a drop of hydro- chloric acid, and the whole evaporated nearly to dryness on the water-bath. If the solution lose its orange tint during evapora- tion, more of the platinum salt must be added. The moist residue is treated with 80 per cent, alcohol, transferred to a very small weighed or counterpoised filter, and washed with alcohol till the washings are colourless. The precipitate is dried at 100 and weighed. For its composition see p. 134. The potassium in a soil may be calculated, according to circumstances, into K 2 0, KC1, or K 2 S0 4 . . By means of the standard silver solution employed in the estimation of chlorine (see p. 171), we may likewise determine the proportion of potassium to sodium in the dry mixed chlorides which have been weighed as above described. We merely rinse out the chlorides into a flask with water and titrate the solution with silver solution and potassium chromate in the usual manner. Thus we obtain the weight of chlorine present ; and as we already know the weight of the mixed chlorides, we have now merely to calculate in what proportions the potassium and sodium must exist in the total salts in order that the quantity of chlorine found should be combined with its proper proportion of these two metals. 192 QUANTITATIVE ANALYSIS. Let S = the weight of mixed chlorides, and A = the weight of chlorine found ; let oc stand for the' potassium present, and y for the sodium. Cl Now as the ratio of chlorine to sodium, or ^-, is expressed Cl by the number 1*543, and the corresponding ratio, -g, by -908, we may arrive at the values of oc or the potassium, and of y or the sodium present, by means of the following equations : 908 37+ 1-543 ?/ = A, ce+ y=S-A, 1-543 x- -908 *?= 1-5,13 (S-A)-A, 1-543 y- -908 2/=A--908 (S-A), 1-543 (S-A) A r= ^ '- , 635 _A- -908 (S-A) 635 A few qualitative testings form a valuable addition to the partial quantitative analysis of a soil just described. A small quantity of the soil is heated with a little water and stirred : a piece of blue litmus paper is then left on the top of the pasty mixture to see if the reaction of the soil is acid ; car- bonic acid may redden the paper, but in that case the blue tint will reappear on warming the paper. A small quantity of the soil should be gently warmed with dilute nitric acid, filtered, and nitric acid and silver nitrate added to one half the filtrate, the other half being tested for sulphates by the addition of a few drops of barium chloride. A testing for lime should also be made, as already described on p. 41 of this Guide. It is of great importance to ascertain the condition in which the iron of a soil exists. This is accomplished to some extent in the following manner : About 2 grams of the soil, which must not have been dried artificially, are shaken with moderately strong hydrochloric acid in a small flask for some minutes; water is added, and the mixture allowed to rest. The super- natant liquid is to be poured through a filter, and the clear filtrate divided into three portions. To one part add a few drops of potassium permanganate solution : an instantaneous disappearance of the violet colour indicates iron in the state of COMPLETE ANALYSIS OF SOILS. 193 a ferrous salt, the protoxide. To another part of the solution add sodium acetate and potassium ferricyanide ; a dark blue precipitate indicates a ferrous, a green colour a ferric salt. To the third part of the solution add sodium acetate and potassium ferrocyanide ; a blue precipitate indicates a ferric salt. COMPLETE CHEMICAL ANALYSIS. The complete chemical investigation of a soil is seldom neces- sary, and involves, when properly conducted, a very large amount of tedious and difficult work. It would unduly extend the size of the present volume were we to attempt to give full directions for the quantitative analysis of soils. We shall therefore only describe such determinations of their usual con- stituents as are most easily and advantageously made. The directions already given, and those with which we now proceed to supplement them, may, however, be applied to what may be called the " fractional analysis " of a soil, as well as to that of the sample prepared as before directed. In the fractional ana- lysis of a soil, a quantity convenient and sufficient for the several determinations is taken in a finely divided state, but without artificial drying ; and it is shaken up at intervals for some hours in a flask with water containing 5 per cent, of acetic acid. Those ingredients in a soil which are immediately available for plant- food are thus dissolved, and may be separately estimated in the clear liquid which is obtained by filtering the mixture of acidu- lated water and soil above mentioned : the residue on the filter is then analysed exactly as directed in the case of a sample of prepared soil. But if it be desired to effect a further classification of the states in which the various kinds of plant-food exist in the soil, the above residue should be boiled in a flask for half an hour with pure hydrochloric acid of spec. grav. 1*15. The liquid is then filtered off, the residue washed, and then the united filtrate and washings are analysed as hereinafter directed. The constituents determined in the more complete analysis of a soil are organic matter, nitrogen, soluble silica, insoluble silica, ferric oxide, alumina, lime, magnesia, potash, soda, sulphur H 194 QUANTITATIVE ANALYSIS. trioxide, phosphorus pentoxide, carbon dioxide, chlorine, and also, in some cases, manganese dioxide. ORGANIC MATTER may be determined as in a partial analysis ; or that part of it which is of the greater agricultural significance may be dissolved out of 10 grams of the soil (previously deprived of CaC0 3 by means of a dilute HC1) by the action of a solution of ordinary ammonia diluted with its own bulk of water. The liquid is filtered through glass wool after 4 hours' contact with occasional agitation. The filtrate and washings are united, evaporated to dryness in a platinum dish, and weighed. The dish is then heated strongly, and the ash of the organic matter deducted from the first weighing : the difference represents the soluble humus of the soil with some approach to accuracy. The ash of the organic matter always contains some phosphorus pentoxide : this may be estimated in the nitric acid extract of the ash by means of ammonium molybdato. NITROGEN, in its several states of combination, is determined exactly as in the partial analysis. INSOLUBLE SILICA AND SILICATES. About 13 grams of the soil are very gently ignited, and subsequently digested in hy- drochloric acid, precisely as directed in the partial analysis under the head of Phosphorus Pentoxide, p. 188. The acid solution is filtered, the insoluble matter collected, thoroughly washed, dried, ignited, and weighed : it is reserved for further examination. SOLUBLE SILICA. The filtrate is evaporated to dryness, the residue heated for some time, and then redissolved (see p. 188) ; the insoluble matter, which should be perfectly white, is col- lected, washed, ignited, and weighed : it generally represents a considerable part of the soluble silica of the soil. The filtrate and washings from the above are well mixed, and divided by weight or measure into two portions, one containing about twice as much as the other : the larger portion is reserved for the determination of phosphorus pentoxide and alkalies, as already described (p. 188). The smaller is employed for the determination of ferric oxide, alumina, manganese dioxide, lime, and magnesia. COMPLETE ANALYSIS OF SOILS. 195 SMALLER PORTION. Method employed in the absence of Manganese. FERRIC OXIDE. The solution is boiled with a little nitric acid ; when cold it is diluted, some ammonium chloride added, and a slight excess of ammonia : the precipitate is washed by decanta- tion, the washings being filtered ; it should then be redissolved and precipitated again, exactly as before, to free it entirely from adhering lime. The mixed ferric oxide and alumina is next dis- solved in a small quantity of hydrochloric acid, brought to boil- ing, and precipitated by an excess of pure sodium hydrate. The solution is filtered, and the precipitate of Fe 2 3 washed by decan- tation, redissolved in hydrochloric acid, reprecipitated by excess of ammonia, and finally collected, washed, dried, ignited, and weighed. ALUMINA. The filtrate and washings from the precipitate by sodium hydrate are treated with hydrochloric acid in slight ex- cess, a crystal of potassium chlorate added, and the whole boiled ; an excess of ammonia is next added, and the boiling continued for some time, until all but a trace of the ammonia has been volatilized : the precipitate is then allowed to subside, thoroughly washed by decantation, and finally collected, dried, ignited, and weighed. The caustic soda or sodium hydrate used should be that made from sodium, and must be free from silica and alumina. The precipitate weighed as alumina will contain all the phosphorus pentoxide present in the " portion " operated on : its amount is to be calculated when the phosphorus pentoxide determination is finished and subtracted from the gross weight of the alumina precipitate ; the difference will be the alumina itself. N.B. The ferric oxide and alumina may also be very accurately determined by means of the volumetric iron method before de- scribed. For this purpose the ferric oxide and alumina precipi- tated by ammonia are collected, gently ignited, and weighed ; they are then digested in concentrated hydrochloric acid till dis- solved, and a determination of iron in the solution is made 196 QUANTITATIVE ANALYSIS. according to the directions previously given at page 153. The alumina will then be found by difference. LIME and MAGNESIA are estimated in the concentrated nitrate and washings from the original precipitate produced by ammonia. The lime is precipitated by ammonium oxalate ; and in the filtrate and washings from the calcium oxalate the magnesia is deter- mined in the usual way, and with the usual precautions. Method employed in the presence of Manganese. The presence or absence of manganese is easily ascertained in the hydrochloric solution of a soil (prepared from a portion which has been gently ignited) by adding ammonium chloride and ammo- nia, filtering rapidly, and mixing some chlorine- water with the filtrate. The mixture is kept for some time in a warm place ; if a brown precipitate or colouration appear, manganese is present. FERRIC OXIDE and ALUMINA. The solution is peroxidized by boiling with a little nitric acid ; ammonium carbonate is then slowly added with constant stirring, till the liquid is neutralized as far as possible without producing a permanent precipitate ; the whole is then diluted to 300 or 350 c. c., an excess of ammonium acetate added, and the solution well boiled.. The precipitate, which contains all the ferric oxide and alumina, is first washed by decantation, and is best brought to the boiling-point after the addition of each washing water, to which a little ammonium acetate has been added ; it is finally collected, washed with hot water, dried, ignited, and weighed. The weighed precipitate is digested in concentrated hydrochloric acid till dissolved ; the ferric oxide is then determined by the volumetric method : the difference is alumina. MANGANESE DIOXIDE. The filtrate and washings from the above are concentrated to about 180 c. c., a considerable amount of chlorine-water or bromine-water added, and the whole digested for some hours, at a temperature of about 55 C. When the preci- pitate has subsided add some more chlorine-water, and observe if any further darkening takes place ; if this is not the case, the pre- COMPLETE ANALYSIS OP SOtLS. 197 clpitated manganese dioxide may be at once collected. It should be thoroughly washed, first by decantation, warm water being employed. When ignited it is converted into Mri 3 4 ; for this purpose a high temperature is required. In many soils the man- ganese exists in the form of Mn0 2 . LIME and MAGNESIA are determined in the usual manner in the filtrate from the manganese precipitate. LARGER PORTION. PHOSPHORUS PENTOXIDE and ALKALIES are determined exactly as directed in the Partial Analysis, in the larger portion of the filtrate and washings (from the silica determination) reserved for that purpose. When in the estimation of the alkalies there de- scribed the amount of potassium chloride present has been ascer- tained, it is only necessary to subtract this amount from the total weight of the mixed alkaline chlorides to find the amount of sodium chloride : this salt may then be calculated into soda. SULPHUR TRIOXIDE. 10 grams of the dried but unburnt soil are digested in dilute hydrochloric acid, and the whole of the silica rendered insoluble by evaporation to dryness ; the residue is re- dissolved in a small quantity of hydrochloric acid, the solution diluted, boiled, and filtered. The clear filtrate is brought to the boiling-point, and precipitated by barium chloride. The barium sulphate, when burnt, is to be moistened with a drop of strong nitric acid, dried, again ignited, and weighed. CHLORINE. 13 grams of the soil are gently ignited as before directed, and digested with distilled water slightly acidulated with nitric acid, the whole filtered, and the soil washed a few times on the filter. The clear solution is treated with silver nitrate, and the whole allowed to stand twelve hours in a warm place. The silver chloride is collected on a very small filter, and washed with water containing a few drops of nitric acid ; the last few washings, however, should be with plain water. Its weight is determined either by having the filter counterpoised, or by 198 QUANTITATIVE ANALYSIS* ignition in a small porcelain crucible; the latter operation is conducted according to the directions given at p. 148. CAKBON DIOXIDE is determined by the loss of weight which occurs on its expulsion ; the dried, unburnt soil is operated on ; the quantity taken must depend on the amount of carbonates present. The soil is introduced into a small wide flask, and moistened with a little water. A short test-tube, c, is two thirds filled with hydrochloric acid, and carefully introduced so that its top rests against the shoulder of the flask, and that no acid es- capes. A perforated cork with two tubes is then attached. One of these tubes reaches to the bottom of the flask, passes through the cork, and extends 4 or 5 cen- tims. above it ; it is closed by a small cork, b. The other tube, which does not extend much be- low the cork of the flask, is bent thrice at right angles, and is finally fitted into a wider tube, a, 6 or 8 centims. long and drawn to a point at its further end, d. This tube has a plug of cotton at either extremity, the interme- diate space being filled with small fragments of neutral calcium chloride which has been well dried over a Bunsen-burner. The apparatus is now weighed. After weighing, the apparatus is slightly inclined, so that a little acid flows out of the tube ; it is afterwards mixed with the soil by gentle agitation ; this is re- peated from time to time till the soil ceases to effervesce. The flask is then warmed, but not boiled: when nearly cold, the small cork is removed, and air slowly drawn through the appara- tus, by suction applied to a piece of india-rubber tubing attached to the open end of the calcium-chloride tube ; this is continued until the air no longer tastes of carbon dioxide ; the little cork is then replaced, and the apparatus, when quite cold, weighed ; COMPLETE ANALYSIS OF SOILS. 199 the loss in weight is carbon dioxide. Some practice is needed to get fairly exact results with this carbon-dioxide apparatus. Other contrivances, in blown glass, may be substituted for the fitted flask shown in fig. 19 ; the forms devised by Schrotter and by E-ohrbeck leave nothing to be desired. ANALYSIS OF INSOLUBLE SILICATES. N.B. The analysis of the stones and gravelly portion of the soil will fall chiefly under this head, unless, indeed, they are of a calcareous nature, in which case they will be easily decomposed by acid, and are analysed as a limestone. The matter insoluble in hydrochloric acid is examined care- fully; if it appear to be pure quartz-sand, further analysis is superfluous. To make the matter quite certain, a small portion is very finely powdered in an agate mortar, and treated in a pla- tinum vessel with hydrofluoric acid ; a gentle heat is applied till the whole of the fluid has evaporated. If a residue remains, it is once more treated with hydrofluoric acid ; should this fail to volatilize it, the substance is not pure silica, but must be sub- mitted to further analysis. If the insoluble silicates are appa- rently argillaceous, they may be analysed by the following simple process ; if otherwise, the hydrofluoric-acid method, or fusion with baryta, must be resorted to. Sulphuric-Acid Method. The substance is reduced to an impalpable powder in an agate mortar. About 2 grams are treated with an excess of sulphuric acid (oil of vitriol plus its own bulk of water) in a platinum or porcelain capsule : heat is then applied, and continued till the acid has been almost entirely volatilized. SILICA. When cold, dilute with water ; collect and thoroughly wash the insoluble matter ; dry, ignite, and weigh. The sand and silica are left ; and the mixed silica may then be partly dis- solved by digestion with a strong solution of sodium carbonate. The sand when obtained should be tested for purity with hydro- fluoric acid. 200 QUANTITATIVE ANALYSIS. ALUMINA, FEEEIC OXIDE, LIME, MAGNESIA, POTASH, and SODA are determined in the filtrate from the silica by the pro- cesses previously described; the magnesia is to be precipitated by ammonium phosphate. The excess of phosphoric acid may be removed by adding to the filtrate from the magnesia precipi- tate a little ferric chloride, boiling and filtering. The alkalies are obtained as sulphates on ignition. Hydrofluoric-Acid Method. 1*3 gram of the finely powdered silicate is placed in a platinum vessel and gradually mixed with rather concentrated hydro- fluoric acid till a thin paste is obtained. The whole is digested at a gentle heat for some time ; oil of vitriol diluted with its own bulk of water is then added, drop by drop, in quantity suf- ficient to be in excess of the bases present. The vessel is then carefully heated till the whole of the acid has volatilized and a dry residue remains; this is treated with concentrated hydro- chloric acid, and allowed to remain at rest one hour ; water is then added, and the whole warmed. If the operation has been successful, a clear solution, devoid of solid particles, will result ; should a residue remain, it must be separated by de- cantation, and treated again with hydrofluoric acid, exactly as before. Silica is by this method determined as loss, being vola- tilized as silicon tetrafluoride. Before using the hydrofluoric acid for this process its purity should be tested by evaporating in a platinum vessel the quantity required for an analysis, weigh- ing the residue and, if necessary, submitting it to quantitative ALUMINA, FEEEIC OXIDE, LIME, MAGNESIA, POTASH, and SODA are determined as in the preceding method. If the alkalies only should be required, the solution is preci- pitated with a little barium chloride, the filtrate evaporated, the residue ignited, treated with pure oxalic acid, again ignited, and the alkalies estimated as chlorides, exactly according to the directions already given. COMPLETE ANALYSIS OF SOILS. 201 Fusion with Baryta. Either barium hydrate, free from water of crystallization, or barium chloride may be used for this purpose. The purity of the barium salt should always be ascertained by experimentc 3 grams, or more, are dissolved in water, the barium precipi- tated by sulphuric acid, the perfectly clear solution evaporated to dryness in a platinum vessel, and gently ignited : no residue should be left ; if any appears, the dish may be weighed, and the amount of impurity thus found. 1*3 gram of the finely powdered substance is intimately mixed with four times its weight of the barium salt, intro- duced into a platinum crucible, which it should not more than one third fill, a little pure barium carbonate being spread over the surface of the mass. The crucible is covered, and its contents brought to a state of fusion, and thus maintained for a quarter of an hour : the barium chloride will require a higher temperature for fusion than the hydrate; the heat of a good gas furnace will, however, suffice ; if this bo not at hand, the platinum vessel is to be placed in a Hessian crucible, which it is prevented from touching by being imbedded in a little magne- sium carbonate, and the whole exposed to a full red heat in any convenient fire. The fused mass when cold is dissolved in dilute hydrochloric acid ; solution is most conveniently effected by placing the pla- tinum vessel in a beaker. SILICA. When the fused mass is completely disintegrated, the crucible is removed and washed, the whole fluid evaporated to dryness, and the residue heated to render all silica insoluble. The mass is finally redissolved, and the silica collected and weighed. It should be tested for purity with hydrofluoric acid ; if found to contain other matters, the fusion has been imperfect. ALUMINA, FERRIC OXIDE, LIME, MAGNESIA, POTASH, and SOLA. The whole of the baryta is thrown down by sulphuric acid, and the bases estimated as before directed. Another good method for separating the alkalies from in- soluble silicates is to heat the powdered mineral with its own 202 QUANTITATIVE ANALYSIS. weight of pure ammonium chloride and eight times its weight of pure calcium carbonate, at first gently and then at a bright red heat for about three quarters of an hour ; when cold the residue is digested in water, filtered, and the lime in the filtrate separated by ammonia and ammonium carbonate. On filtering, evaporating, and igniting, the residue consists only of alkaline chlorides. LIMESTONE, MAKL, AND SHELL-SAND. The chief constituent of limestone is calcium carbonate (car- bonate of lime) ; in magnesian limestone or dolomite a consider- able quantity of magnesium carbonate is also present. The other constituents are silica, ferric oxide, iron pyrites, alumina, with, in most cases, traces of alkalies, manganese dioxide, sulphur trioxide, phosphorus pentoxide, and organic or bituminous matter. The sample is prepared by being finely powdered, MOISTURE and ORGANIC MATTER are estimated by heating to low redness. If the heat, in consequence of the presence of organic matter, is necessarily prolonged, moistening with ammo- nium carbonate must be resorted to. The crucible should be well covered, as decrepitation is apt to occur. SILICA. About 1 gram is dissolved in dilute hydrochloric acid in a covered beaker, and the silica estimated by the usual process of evaporation to dryness. See Partial Analysis of Soils (p. 188). If iron pyrites be present it will remain with the silica unless-nitro-hydrochloric acid be used as the solvent. In analysing tolerably pure limestones, the best plan is to dis- solve two or three times the amount here directed, and, after separating the silica and feriic oxide, to divide the solution, and determine the lime in a part only. FERRIC OXIDE and ALUMINA are precipitated by ammonia in the filtrate from the silica ; the precipitate is to be collected and washed, and must then be redissolved in acid, and again preci- pitated by ammonia, to free it from adhering lime. It must be remembered that the precipitated ferric oxide and alumiua will LIMESTONE, ETC. 203 generally retain all the P 2 0. of the substance. This ingredient may be determined by the methods described below, while the ferric oxide and alumina may be separately estimated as in the analysis of soils. LIME is precipitated in the united nitrates and washings from the above, by an excess of ammonium oxalate. If the limestone be magnesian, decant the clear liquid from the calcium oxalate on to a filter, wash once by decantation, then redissolve the oxalate in hydrochloric acid, dilute with water, add ammonia in excess, and some ammonium oxalate, and collect and weigh in the usual manner. MAGNESIA is determined by means of sodium phosphate and free ammonia in the filtrate from the lime. If it is desired to determine the amount of alkalies, manganese dioxide, sulphur trioxide, and phosphorus pentoxide present, it may be done as follows. 7 grams, or more, of the limestone are dissolved in dilute hydrochloric acid, and the silica separated by evaporation. The residue is moistened with hydrochloric acid, and, after standing some time, dissolved in water, and the solution boiled and filtered. The residue on the filter will contain not only silica, but iron pyrites and organic or bituminous matter. By treat- ment with nitric acid the pyrites may be dissolved, and then estimated from the amount of S0 3 which it yields. STJLPHUK TKIOXIDE is precipitated from a boiling solution by a slight excess of barium chloride. PHOSPHOKFS PENTOXIDE. The excess of free acid is removed as far as possible by the evaporation of the filtrate ; it is after- wards diluted and treated in the cold with an excess of barium carbonate (used mixed with water to a thin cream), the whole being stirred at intervals during the course of an hour ; the precipitate, which contains the whole of the phosphorus pen- toxide, is collected and washed with cold water. It is finally dissolved in a little hydrochloric acid, boiled, the baryta pre- cipitated by sulphuric acid and separated by filtration ; the filtrate, concentrated if necessary, is treated with citric acid, 204 QUANTITATIVE ANALYSIS. excess of ammonia, and a little magnesia-mixture. The magne- sium and ammonium phosphate is collected and estimated in the usual way. Phosphorus pentoxide is also well determined by the mo- lybdic-acid method. 6 to 12 grams of the limestone are dissolved in acid, the silica separated by evaporation, and the filtered solution treated as directed at p. 189. MANGANESE DIOXIDE. The filtrate from the barium carbonate is acidified with acetic acid, some ammonium acetate added, and a considerable amount of chlorine or bromine water ; the further process is conducted as at p. 196. The washing of the precipi- tate must be continued till no trace of barium is found in the washings. The wash-water may be slightly acidified with acetic acid to facilitate the removal of the barium. ALKALIES. The filtrate from the manganese dioxide is boiled, precipitated by ammonium oxalate, and filtered ; the filtrate is evaporated to dryness, and the residue gently ignited to expel ammonium salts ; pure oxalic acid is then added and a little water, and the whole again evaporated and ignited. The residue is dissolved in a little hot water, and the solution filtered. A little hydrochloric acid is then added and the whole evaporated to dryness, ignited, and weighed. The alkalies are now in the state of mixed chlorides ; for their separation see p. 190. N.B. In an accurate analysis of limestone, a determination of carbon dioxide should be made; for, the silica being in part, though to an unknown extent, combined with lime, the per- centage of C0 2 does not admit of exact calculation from the ascertained percentage of lime. iii. THE ANALYSIS OF WATERS. The impurities present in ordinary well- and spring-waters are principally derived from the soils (also turf and roots) through which the water passes, and from the infiltration of or contact with sewage and other refuse matter. A very small amount of impurity is derived from the gaseous and solid matters WATERS. . present in the air; but the carbon dioxide from that source greatly increases the decomposing and solvent 'action of the water on the rocks and soils through which it passes. Great care must be taken in order to obtain a fair sample of the water to be analysed. Stoppered Winchester quarts which have been thoroughly cleansed may be used for collecting the water : the vessels should be first rinsed out with some of the same water. The quantity of water required will vary greatly according to the object in view : two Winchester quarts will suffice for the partial analysis which is generally requisite. When the dissolved gases of the water are to be determined, suitable arrangements should be made at the spring, where also the evaporation of large quantities of any water for the purpose of obtaining the salts should be conducted, if rare substances present in minute quantities are to be identified and estimated. The description of the processes of gas-analysis, and of the search for rare substances, does not fall within the scope of the present work. The foreign or intruding substances usually occurring in waters may be classed as (1) Mechanical Impurities ; (2) Soluble Impurities. MECHANICAL IMPURITIES, or suspended matters, if any, must be separated by filtration before proceeding to the analysis of the water. Collect them, from a measured quantity of water, on a tared filter, drying it at 100 and then weighing. The nature of the impurities may then be ascertained in the matter thus separated by submitting it to analysis, but it is usually sufficient to burn the filter and residue. The weight thus obtained repre- sents the mineral impurities suspended in the water. Their amount is to be subtracted from the total, the remainder repre- sents organic matter suspended. SOLUBLE IMPURITIES. These are usually calcium and magne- sium salts or hardening impurities ; alkaline salts or non-harden- ing impurities ; organic matter ; and inorganic matter derived from organic and especially from animal substances : among these latter impurities are ammonia, and salts of nitrous and 206 QUANTITATIVE ANALYSIS. nitric acids. The acid constituents of the salts occurring in waters are the sulphuric, carbonic, silicic, and chlorine, with occasionally the phosphoric radicle. Alumina, ferrous carbonate, and, rarely, arsenic, barium, lead, copper, manganese, zinc, &c., are found in some waters. Arsenic, Lead, Copper, Zinc, and Manganese may be tested for qualitatively in a litre or more of the water evaporated to a small bulk. If these metals be present in more than mere traces, they ought to be separated by appropriate reagents (H 2 S, &c.) before the other ingredients are estimated. The taste and smell of a water may be best observed by warming to about 40 C. some quantity of it, about 100 c. c., in a perfectly clean covered wide-mouth bottle standing in a water-bath. The colour of a water should be indistinguishable, or nearly so, from the faint bluish tinge of distilled water. To observe the colour of water two straight tubes of colourless glass are used. These tubes should be about 5 centims. in diameter, and 60 centims. in length. The lower ends are closed with discs of colourless plate glass, covered with white enamel on the upper surface : these discs are cemented on to the ground ends of the tube by means of marine glue or Canada balsam. The tubes are suspended side by side in a well-lighted place ; one is filled with the water under examination, the other with distilled water for comparison. In the clear water the principal matters to be quantitatively estimated are : 1. Total solid contents, or fixed solid residue. 2. Organic matter. 3. Oxygen taken from permanganate. 4. Chlorine. 5. Ammonia, ready-formed. 6. Ammonia producible from organic nitrogen compounds. 7. Nitrogen existing as nitrates and nitrites. 8. Total and permanent hardness. WATEES. 207 1. TOTAL SOLID CONTENTS. Evaporate ^ litre (or T 2 ^j gallon) of the water to dryness in a platinum dish over the water-bath, dry the residue in an oil- or air- bath at 130 C., and weigh. It is as well to evaporate a second | litre, in order to obtain a residue in which qualitative testings for P 2 5 by ammonium molybdate may be made. This second residue should be first moistened with nitric acid and evaporated to dryness to render the silica insoluble. Then it should be taken up with a little nitric acid, water being added, and lastly it should be filtered through a filter-paper which has been washed with nitric acid. The filtrate, which should measure 3 c. c., is mixed with its own bulk of the molybdic test and gently warmed for 15 minutes. A yellow colour may be regarded as indicating traces of phosphates, a yellow turbidity or actual pre- cipitate being respectively reported as heavy traces or very heavy traces. 2. OKGANIC MATTEK. The dry residue is heated to low redness until all blackening has disappeared, a clear mica plate being placed over the dish at the commencement of the heating. The residue is treated with ammonium carbonate, dried, gently ignited, and again weighed ; the loss gives approximately the amount of organic matter. The loss on ignition does not, indeed, in any case, give the exact ponderal expression of the organic matter ; but it offers a valuable criterion of purity. On this point, however, much may be learnt by noting the appearance of the dry residue, and especially its changes during the progress of the heating described above. Bad signs are the deliquescent character or yellow colour of the residue, its considerable blackening when heated, or the sudden disappearance with slight deflagration of the black par- ticles. If any sublimate appears on the mica plate, ammonia salts are indicated : the nature of the fumes and odour evolved should also be observed. 208 QUANTITATIVE ANALYSIS. If 250 c. c. of the water, to which a few drops of sulphuric acid have been added, destroy in fifteen minutes, at 27 C., the colour of more than 2 or 3 c. c. of a solution of potassium per- manganate containing '395 gram of that salt per litre, organic matter is probably present in large quantity. Whether this organic matter is likely to be injurious to health or not is a problem that can be answered with tolerable certainty only when a large number of the indications afforded by analysis are favourable or the reverse. The decolorization of permanganate solution by a water may arise from the presence not only of oxidizable organic matter, but of ferrous carbonate and several other substances. 3. OXYGEN TAKEN FROM PERMANGANATE. If it be desired to obtain more exact notions concerning the amount of organic matter present in a water, through the esti- mation of the oxygen absorbed from permanganate, the following plan may be used. The five solutions needed are : 1. *395 gram potassium permanganate dissolved in 1 litre of dis- tilled water: each c. c. contains *0001 gram of available oxygen. 2. 10 grams pure potassium iodide, recrystallized from alcohol, dissolved in 100 c. c. distilled water. 3. 100 cub. cent, pure sulphuric acid mixed with 300 c. c. of distilled water : then potassium permanganate solution is dropped in until the whole retains a very faint pink tint after warming to 27 C. for four hours. 4. 1 gram of sodium thiosulphate crystals dissolved in 1 litre of distilled water. 5. 1 gram of pure white starch, ground up into a cream with a little water, is to be poured into 500 c. c. of boiling distilled water, kept boiling for 5 minutes, and then filtered. This con- stitutes the " starch water " used in the recognition of free iodine in the titration of the permanganate with sodium thiosul- phate, as mentioned below. Two separate determinations have to be made, viz. the amount of oxygen absorbed during fifteen minutes, and that absorbed during four hours; both are to be made at a temperature of 27 C. It is convenient to make these determinations in 12-oz. stoppered bottles, which have been rinsed with sulphuric acid and then with water. Put 250 c. c. into each bottle, which must be WATERS. 209 stoppered and immersed in a water-bath or suitable air-bath until the temperature rises to 27 C. Now add to each bottle 10 c. c. or 100 grains of the dilute sulphuric acid, and then 10 c. c. of the standard potassium permanganate solution. Fifteen minutes after the addition of the potassium perman- ganate, one of the bottles must be removed from the bath, and two or three drops of the solution of potassium iodide added to remove the pink colour. At the end of four hours remove the other bottle, add potassium iodide, and titrate with sodium thiosulphate (hyposulphite). Should the pink colour of the water in the bottle diminish rapidly during the four hours, further measured quantities of the standard solution of potassium per- manganate must be added from time to time so as to keep it markedly pink. The thiosulphate solution must be standardized, not only at first, but (since it is liable to change) from time to time, in the following way : To 250 c. c. of pure redistilled water add two or three drops of the solution of potassium iodide, and then 10 c. c. of the standardized solution of potassium permanganate. Titrate with the thiosulphate solution. The quantity used will be the amount of thiosulphate solution corresponding to 10 c. c. of the standardized potassium permanganate solution, and the factor so found must be used in calculating the results of the thiosulphate titrations to show the amount of the standard per- manganate solution used, and thence the amount of oxygen absorbed. The difference between the quantity of thiosulphate used in the blank experiment and that used in the titration of the examples of water, multiplied by the amount of available oxygen contained in the permanganate added, and the product divided by the volume of thiosulphate corresponding to the latter, is equal to the amount of oxygen absorbed by the water. After thorough admixture, run from a burette the standard solution of sodium thiosulphate, which may be made of a strength of about 1 in 1000, until the yellow colour is nearly destroyed, then add a few drops of starch water, and continue the addition of the thiosul- phate until the blue colour is just discharged. If the titration has been properly conducted, the addition of one drop of potas- sium permanganate solution will restore the blue colour. If it is desired to estimate the mineral matters other than chlorine and nitrogen-compounds, it may sometimes be necessary, if the water is tolerably pure, to evaporate a larger quantity 210 QUANTITATIVE ANALYSIS. than \ a litre to dryness. When intended for the determination of other matters, the residue, after ignition, is treated as follows. SILICA. The residue is treated with hydrochloric acid in slight excess, loss from effervescence being guarded against ; the whole is evaporated to dryness,- and the silica separated in the usual way. FERRIC OXIDE, ALUMINA, LIME, and MAGNESIA are estimated in the same way as in soils, the magnesium "being precipitated by ammonium phosphate. The ferric oxide, if much be present, will require re-solution to remove adhering lime. ALKALIES. The filtrate from the magnesium precipitate is evaporated to dryness and the residue gently ignited ; it is then dissolved in a little water, a slight excess of baryta-water added, the whole boiled and filtered : the filtrate is boiled, a little sul- phuric acid added, the barium sulphate separated by filtration through Swedish paper, and the clear solution evaporated to dryness, ignited, and weighed. The alkalies are here weighed as sulphates ; for their separation, see p. 190. SULPHUR THIOXIDE is determined by precipitation with barium chloride in J a litre of the water, which should be first acidified with a little HC1 and then concentrated to 100 c. c. 4. CHLORINE is determined by the volumetric method (see page 171) in from 100 c. c. to | a litre of the water. Waters containing an abnormal quantity of chlorine have generally obtained it by contamination with sewage, and must therefore, if intended for domestic purposes, be looked upon with suspicion. But it must not be forgotten that two additional and perfectly innocuous sources of chlorides exist, namely : (1) the sea spray, which is occasionally carried forty miles or more inland, finding its way ultimately to water-bearing strata : and (2) the occurrence of saliferous rocks or saline springs. But such local conditions, influencing the amount of chlorides in well-waters, are easily ascertained. The amount of chlorine in the purest waters scarcely exceeds 1 gram in 100 litres ; in London sewage about 1 gram in 10 litres occurs. WA.TERS. 21 1 5. AMMONIA, ready-formed, is determined by distilling a measured quantity of the water rendered alkaline with sodium carbonate and testing the dis- tillate with Nessler's solution against a solution containing a known quantity of ammonia. The comparison is made by dif- ference in colour ; but it is well to determine roughly the amount of ammonia before distillation ; this may be done in the follow- ing way. Take 50 c. c. of the water and place it in a colourless glass cylinder about 18 centims. in height and capable of holding 100 c. c. Now add 2 c. c. of Nessler's solution, and mix well with a glass rod. A second cylinder of similar dimensions is to have 50 c. c. of distilled water run into it (this water should have been previously freed from ammonia by distillation from a retort with a little sodium carbonate, the distillate having been collected when no colouration was produced in it with Nessler's test : if many estimations of ammonia are being made, it will be found convenient to have a few litres of this water kept in well- stoppered bottles at hand), and then 5 c. c. of standard ammo- nium chloride solution. This solution, which contains -00001 gram of ammonia (NH 3 ) per c. c., is to be mixed well with the pure water by stirring. Place the two cylinders upon a sheet of white paper, and compare the colour by looking down through the liquids ; should the colours appear about the same in each, 500 c. c. of the water are to be taken for the estimation ; but should it be more intense in the cylinder containing the sample of water, then a proportionately smaller quantity should be taken, but its bulk should be made up to 500 c. c. with pure distilled water. A measured quantity of the water, not less than % a litre, is now placed in a 40-oz. stoppered retort, and 1 gram, or enough to render the reaction of the water alkaline, of re- cently ignited sodium carbonate added. Distil rapidly, and collect the distillate in one of the glass cylinders mentioned above until it contains 50 c. c. (which may be easily known by pre- viously marking upon them the level to which they will be filled by 50 c. c.). This cylinder is now set on one side, and another 212 QUANTITATIVE ANALYSIS. put in its place and allowed to fill to the same extent, the lamp being then removed from the retort. The second portion has 2 c. c. of Nessler's test added to it, and is then to be well mixed. A third cylinder is now taken, and as much of the standard ammonium chloride solution added as it is thought will produce about the same tint (this can be easily found with a little prac- tice), the cylinder filled up to the mark with pure distilled water, and the Nessler test added. If it be found that the two do not agree in tint, the cylinder is to be emptied and well rinsed out with water free from ammonia, and the same operation gone through with a different quantify of ammonium chloride until the right tint has been obtained ; if the quantity of ammonia does not exceed *001 milligram, t the distillation need not be continued ; but should it be more than this, another 50 c. c. are to be distilled over, and so on until it does not contain more than this amount. If the amount of ammonia in the second distillate does not exceed 2 c. c. of the ammonium chloride solution, then the first quantity of 50 c. c. that was collected may have its ammonia estimated in the same way ; but should the second be found to contain more than this amount, then the first must be measured and a portion only taken at a time, as it would other- wise be so strong that a very dark colour or precipitate would be produced with the Nessler's test. When the amounts of ammonia in all the distillates are known, they are to be added together, from which total the quantity in 100,000 parts is easily calculated ; it should not exceed -01 part in 100,000 in river waters ; sewage may contain 1000 times as much. The standard ammonia solution is made by dissolving *3147 gram of pure ammonium chloride in a litre of pure distilled water ; from this the working solution is made by taking 100 c. c. and diluting it to 1 litre, when 1 c. c. will be equal to '00001 gram of ammonia. The retort used in distilling the ammonia sbould be connected with a Liebig's condenser, both it and the retort having been thoroughly cleaned with water free from ammonia. If the neck of the retort is of such a small size that it will easily slip into the tube of the condenser, it will be easy to make the con- WATERS. 213 nection between them quite tight by means of a round india-- rubber ring, previously cleansed in soda solution, and a band of tinfoil wrapped round the junction. The standard ammonium- chloride solution should always be added before the Nessler test, otherwise a turbidity will be produced ; of course all the operations must be performed in a room free from ammoniacal fumes. The presence of ammonia in any quantity is indicative of con- tamination of the water with decaying or refuse animal matter, such as sewage, or with the farmyard manure &c., which has been applied to the arable land in the area of country from which the water has been derived. The same origin may be assigned to a large part of the nitrates in deep-well waters. The amount of ammonia in Thames water, as supplied to London, is about *002 part per 100,000, and of 1ST as nitrates and nitrites about *2. 6. AMMONIA producible from organic nitrogen compounds in the water. A good deal of the combined nitrogen occurring in impure waters may exist in the form of nitrogenous organic matter : about | of this nitrogen may generally be obtained in the form of what is called "albuminoid ammonia" by the following process : Prepare an alkaline solution of potassium permanganate by dissolving 4 grams of potassium permanganate and 100 grams of potassium hydrate in 550 c. c. of pure distilled water. Boil the solution until it has been reduced to % a litre, and keep it in a well-stoppered bottle. As soon as the distillation of the water for " ready-formed ammonia " has been commenced, about 25 c. c. of this perman- ganate solution are to be placed in a flask diluted with 100 c. c. of distilled water and kept boiling during the whole time that the sample of water is being distilled. To the liquid remaining in the retort, after the distillation with sodium carbonate already described, add of the above 214 QUANTITATIVE ANALYSIS. diluted permanganate solution enough to make up about 500 c. c. of liquid and distil again. Collect the distillate in portions of 50 c. c., as in the estimation of ready-formsd ammonia, and ascertain their strength by means of Nessler's test. Stop the distillation when the last 50 c. c. coming over contain less than 000001 gram of NH 3 . The amounts of ammonia in all these distillates are to be added together and entered as " albuminoid ammonia," a term which, though inexact, is generally under- stood. The bumping or excessive violence with which alkaline liquids often boil may be mitigated by the addition to the retorts of clean pumice or tobacco-pipe. 7. NITROGEN AS NITRATES AND NITRITES. Nitrates may be detected by evaporating a few ounces nearly to dryness, and applying the indigo or sulphate-of-iron test (see p. 22) ; nitrites, by adding to the concentrated water a clear mixture of potassium iodide, starch-paste, and acetic acid : an indigo-blue tint indicates nitrous acid ; care must, however, be taken that the iodide contains no iodate. The nitrogen present in a water in the forms of nitrates and nitrites may be estimated quantitatively by several processes, most of these demanding a good deal of skill and patience. The mercury and oil-of-vitriol method, Warington's improved indigo method, the aluminium method, and the copper-zinc method are all in use. The last-named process is, however, so simple, easy, and exact that it is generally to be preferred. Copper-Zinc Method. The determination of nitrates and nitrites by this process is to be accomplished in the following way. A wet copper-zinc couple is first of all prepared by washing a strip of clean zinc foil, about 2 inches wide and 3 inches long, with sodium-hydrate solution and then with distilled water, to remove grease, and then placing the metallic strip in a solution of copper sulphate containing 3 per cent, of the pure crystallized WATERS. 215 salt. In 3 or 4 minutes, when an adherent coating of spongy copper will have formed upon the strip, the latter is to be removed from the liquid and thoroughly washed with abundance of distilled water, and then finally with a small quantity of the water to be analysed. The couple is now to be placed in a wide-mouth stoppered bottle of 6 or 8 ounces capacity, together with a care- fully measured quantity of the water under examination ; about 100 to 150 c. c. will generally suffice. A small addition of pure oxalic acid to precipitate the lime and quicken the action should be made before inserting the stopper ; 2 decigrams of oxalic acid will be ample. The water remains in contact with the couple all night in a warm place ; on the following morning the conversion of the nitrates into ammonia will be found to be complete. The next step in the process is the determination of the am- monia present in the liquid. A measured portion is drawn off by a siphon if clear, or, if turbid, is poured through a washed filter. If the liquid be colourless and give no precipitate with the Nessler test, then it may be Ncsslerized without further treat- ment, exactly as described on p. 211 ; only it may need dilution with pure distilled ammonia-free water. But should the liquid show any decided colour in the Nessler glass, or should it become turbid on the addition of the Nessler reagent, then a measured portion must be rendered alkaline with sodium carbonate and submitted to distillation with all the precautions given on pages 211-213. The ammonia found must be calculated into its equiva- lent of nitrogen ; from this the amount of nitrogen existing in the water as ready-formed ammonia must be subtracted ; and then the remaining nitrogen should be translated into N 2 5 . Another method for the estimation of oxidized nitrogen consists in the conversion of the nitrogen into ammonia by the action of aluminium in an alkaline solution. For this purpose 100 c. c. of the water are introduced into a non-tubulated retort, and 50 c. c. of a 10 per cent, solution of pure sodium hydrate added ; about 50 c. c. are then distilled off, or until no ammonia is found in the distillate by Nessler's test. The retort is cooled, and a piece of sheet aluminium introduced, the neck, of the retort 216 QUANTITATIVE ANALYSIS. inclined upwards, and closed with a cork fitted with a small glass tube containing glass beads moistened with dilute hydrochloric acid. This is connected with a second similar tube, containing glass beads moistened with strong sulphuric acid, to prevent ammonia from the air entering the apparatus, which is now allowed to stand for a few hours. The first tube is then rinsed into the retort with pure water, the retort fitted to a purified condenser, and about half its contents distilled into pure water, the end of the retort dipping just below the surface of the water : the distillate is made up to a known volume, and the ammonia estimated by Nessler's test, as above. The soda used must be free from nitrates ; it may be rendered so by dissolving a little aluminium in it and boiling. If more convenient, a litre of the water may be concentrated, and treated in the same way, except that the distillate is to be received into standard acid, and the amount of ammonia found by means of standard alkali. The nitric acid in potassium and sodium nitrates may be con- veniently estimated by this last method, the liquid being prefer- ably first distilled into a small flask, from which it is again dis- tilled into the standard acid, thereby retaining any trace of soda which may have first distilled over. This process is also applicable to the estimation of the nitrates existing in turnips, swedes, beets, and other vegetables. A mixture of zinc and iron filings may be substituted for the aluminium. If the nitrates and nitrites in a water have been determined together by means of one of the above-described processes, it is possible to learn by means of another analytic process the amount of nitrites present. This is done by the use of Griess's meta- phenylene-diamine method. This substance gives no colour with nitric acid, but a yellow with nitrous acid. 100 c. c. of the water are poured into a glass cylinder and then 1 c. c. of dilute (1 of acid to 2 of water) pure sulphuric acid and 1 c. c. of metaphenylene-diamine solution are added. The latter reagent is made by dissolving 5 grams of this base in 1 litre of water and then acidulating the solution with sulphuric acid : the liquid must be colourless. If a red colouration be at WATERS. 217 once produced, a fresh and smaller portion of the water must be taken and diluted with pure distilled water to 100 c. c. The colour should take one or two minutes to make its appearance. It is now necessary to compare the colour produced in the water with that obtained in a precisely similar manner in a standard solution of pure potassium nitrite : this comparison must be made simul- taneously, as the colouration increases on standing. The standard potassium nitrite solution contains '00001 gram of N a 3 in 1 c. c. It is prepared by taking *406 gram of pure dry crystallized silver nitrite, dissolving it in hot water and decomposing it with a slight excess of potassium chloride solution. When cold the solution is made up to 1 litre, and the silver chloride allowed to settle. The clear supernatant liquid is decanted off, and each 100 c. c. of it made up to 1 litre : this solution must be kept in well-stoppered bottles completely full. Coloured waters, previously to being tested in the above manner for nitrites, must be decolourized by alum and sodium carbonate or by a mixture of sodium hydrate and carbonate ; the precipitate formed is to be filtered off. If the N 2 3 found by Griess's method be translated into its equivalent of NH 3 , and this amount be deducted from the amount of NH 3 produced from the associated nitrates and nitrites (in, say, the copper-zinc method), the remainder will represent the NH 3 due to nitrites alone, and may be converted into its equivalent of N 2 5 or Ca2N0 3 . 8. TOTAL AND PERMANENT HARDNESS. The hardness of a water is determined by means of Clark's test, which is a solution of soap in weak spirit (equal parts of spirit of specific gravity -835 and water), of which 14-25 c. c. just suffice to produce a permanent lather when shaken with c. c. of water containing '2 gram of calcium carbonate per litre (-222 gram calcium chloride). The soap test is used as follows : 50 c. c. of the water under examination are placed in a stoppered bottle of about four times this capacity, well agitated, and the carbon dioxide given off is 218 QUANTITATIVE ANALYSIS. sucked out by means of a glass tube. A burette graduated in c. c. is then filled with the soap solution and 1 c. c. added at a Table of Hardness. p*s 00 2j tf o ^i 1^ 5^ C3 g} ) -3 O -*-3 go i g^j si *] o3 If* n ** J Ej fit 7 00 4-6 5-43 8-5 1-05 12-4 17-06 8 16 4-7 57 8-6 20 12-5 22 9 32 4-8 71 8-7 35 12-6 38 1-0 48 4-9 86 8-8 50 12-7 54 1-1 63 5-0 6-00 8-9 65 12-8 70 1-2 79 5-1 14 9-0 80 12-9 86 1*3 95 5-2 29 9-1 95 13-0 18-02 1-4 1-11 5-3 43 9-2 12-11 13-1 17 1-5 27 5'4 57 9-3 26 13-2 33 1-6 43 5-5 71 9-4 41 13-3 49 1-7 56 5-6 86 9-5 56 13-4 65 1-8 69 57 7-00 9-6 71 13-5 81 1-9 82 5-8 14 9-7 86 13-6 97 2-0 95 5-9 29 9-8 13-01 13-7 19-13 2-1 2-08 6-0 43 9-9 16 13-8 29 2-2 21 6-1 57 10-0 31 13-9 44 2-3 34 6-2 71 10-1 46 14-0 60 2-4 47 6-3 86 10-2 61 14-1 76 2-5 60 6-4 8-00 10-3 76 14-2 92 2-6 73 6-5 14 10-4 91 14-3 20-08 27 86 6-6 29 10-5 14-06 14-4 24 2-8 99 6-7 43 10-6 21 14-5 40 2-9 312 6-8 57 10-7 37 14-6 56 3-0 25 6-9 71 10-8 52 14-7 71 3-1 38 7-0 86 10-9 68 14-8 87 3-2 51 7-1 9-00 11-0 84 14-9 21-03 3-3 64 7-2 14 11-1 15-00 15-0 19 3-4 77 7-3 29 11-2 16 151 35 3-5 90 7-4 43 11-3 32 15-2 51 3-6 4-03 7-5 57 11-4 48 15-3 (>8 3-7 16 7-6 71 11-5 63 15-4 85 3-8 29 7-7 86 11-6 79 15-5 22-02 3-9 43 7-8 10-00 11-7 95 15-6 18 4-0 57 7-9 15 11-8 16-11 157 35 41 71 8-0 30 11-9 27 15-8 52 4-2 86 81 45 12-0 43 15-9 69 4-3 5-00 8-2 60 12-1 59 16-0 86 4-4 14 8-3 75 12-2 75 4-5 29 8-4 90 12-3 90 WATERS. 219 time. After each addition the stopper is to be placed in the bottle, which is then to be well shaken : towards the end of the operation smaller quantities should be added, the estimation being finished when an unbroken lather remains permanently for five minutes, the bottle being placed upon its side. The number of c. c. of soap solution is now to be read off, and the hardness found by inspection of the Table on p. 218. Should the water not yield a permanent lather with 16 c. c. of soap test, a fresh experiment is commenced with a smaller portion of the water made up to 50 c. c. with fresh-boiled distilled water, and the number showing the hardness multiplied by the fraction of 50 c. c. used ; thus if 25 c. c. were used, multiply by 2, &c. If magne- sium salts are known to be present in considerable quantity in any water, the sample should be so diluted as to require not more than 7 c. c. of soap test for 50 c. c. of the diluted water. The method given above shows the total hardness ; the per- manent hardness is determined by boiling J a litre of the water in a flask of rather large size, and having a long but broad neck. The ebullition is allowed to go on gently for half an hour, a little boiled distilled water being added now and then to replace in part that lost by evaporation ; then the flask is rapidly cooled, the mouth being covered with a watch-glass, and the volume of water in it again made up, with boiled distilled water, to | a litre, filtered, and the hardness estimated in 50 c. c. as before. The temporary hardness is the difference between the total and permanent hardness. It will be evident from the preceding Table that 50 c. c. of distilled water require nearly f of a c. c. of soap test to produce a permanent lather. For the determination of hardness in water two solutions are necessary one of soap, the other of calcium chloride or sul- phate. The modes of preparing these solutions may be thus conducted. PREPARATION OF STANDARD SOAP TEST. Take 9 grams of lead-plaster (Emplastrum Plumbi, B. P.) and 2*6 grams of dry potassium carbonate : rub these materials together in a mortar with a few drops of rectified spirits of wine of spec. gray. '835 V till a perfect mixture, having the consistence of cream, has been 220 QUANTITATIVE ANALYSIS. effected. When the mass has stood some time, exhaust it with repeated additions of spirit, filter the spirituous solution, and add more spirit till the whole liquid is of the bulk of 600 c. c. ; lastly, add 400 c. c. of distilled water which has been recently boiled to expel carbon dioxide. The strong soap solution thus obtained will now require standardizing by means of a solution of calcium chloride, which is prepared as follows. Weigh out *2 gram of Iceland spar into a clean porcelain or platinum dish, having a clock-glass for a cover, and add dilute hydrochloric acid, a little at a time, until the substance is dissolved. Evaporate the solution, together with the washings from the cover, carefully to dryness, and heat the residue till no more acid fumes are given off. Redissolve the residue in water and again evaporate as below. Now to the residue, which must be wholly soluble in water, add enough pure boiled water to make up the volume to 1 litre. The calcium so- lution may now be used to standardize that containing soap. Pour 50 c. c. of the former liquid into a bottle, and run into it from a burette a few drops of the strong soap solution previously described. This operation is repeated with the usual precautions until a permanent lather is obtained. The soap test will be found too strong and must be diluted with proof spirit until its strength has been lowered to the proper standard : this point is reached when 14*25 c. c. produce a permanent lather with 50 c. c. of the standard calcium chloride a strength which corresponds to 20 parts of CaC0 3 in 100,000. The diluted soap test should be allowed to stand some time, and then filtered, before its strength is finally adjusted to the point just named. The soap solution may be prepared with pure white curd soap ; the calcrum solution may be made with an equivalent weight of pure crystallized calcium sulphate, CaS0 4 , 2aq. STATEMENT OP RESULTS. We have hitherto assumed that all the results of a water analysis are referred to parts in 100,000; if it be desired to convert these into grains per gallon, multiply them by *7. To convert grams per litre into grains per gallon, multiply by 70. The total solid residue left on evaporating a water seldom agrees closely in amount with the total amounts of the several ingredients which have been specially determined. One source WATERS. 221 of this discrepancy lies in the reactions which occur amongst the salts of a water as the liquid becomes concentrated ; another in the partial loss of water of crystallization suffered by the cal- cium sulphate and other salts at the temperature of drying the residue. It is impossible to ascertain the manner in which each sub- stance is combined in the original water ; the best plan therefore is to set down all the items, as deduced from the several analyses, separately, subtracting from the total an amount of oxygen equi- valent to the chlorine found, that element being supposed to be combined with the sodium. The total, thus amended, will be less than the solid contents found, by the amount of carbonic acid present. The sum of the saturating power of the acid oxides should of course be equal to the sum of the saturating power of the bases, if the analysis be correct. The most usual mode of placing the results, however, is to combine the acids and bases ; this is generally done as follows : The sulphur trioxide is combined with lime, the remainder of the calcium being set down as carbonate : the chlorine is com- bined with sodium ; if chlorine still remains, it is combined with potassium ; if still in excess, with magnesium. Magnesia, potash, and soda (when their metals are not combined with chlorine) are united with carbon dioxide. Nitrogen pentoxide, if present, may be combined with lime or potash, ammonium with chlorine. Silica remains uncombined, while ferrous oxide is united with carbon dioxide. Some of these arrangements of acids and bases are known to be merely conventional or artificial, and in particular cases there may be found good reasons for modifying them. For instance, there are natural mineral or medicinal waters in which such compounds as magnesium sulphate, ferrous sulphate, ferric chloride, and even barium chloride are known to occur. In order to render a water analysis more complete and in- structive it is desirable to examine under the microscope the deposit which settles down from the freshly drawn sample of 222 QUANTITATIVE AKALYSIB. water when left to rest for 12 hours ; a l and then a J objective being employed. The action of the water on strips of tarnished and untarnished lead should also be tried. This experiment is to be made in 20-ounce bottles half full, the strips rising above the level of the water. The liquid is to be poured off after 24 hours' contact with the metal and tested for lead in solution. A third experiment consists in ascertaining the number of colonies of organisms which grow in a given time on a nutritive jelly which has been mixed with 1 c. c. of the sample of water. All the apparatus used must be completely sterilized, and every pre- caution taken during the course of the experiment to prevent the entrance of extraneous organisms. For the details of the method reference must be made to special works in which this biological method of examining waters is fully described. The precise value of the indications afforded by this process have scarcely been determined : it requires very elaborate precautions, and the most expert manipulation in order that trustworthy results may be secured. It was devised by Dr. Koch, modified and improved by Dr. P. F. Frankland. When the whole of the above-described qualitative and quan- titative results have been obtained, the figures, which have been calculated into parts per 100,000, or into grains per gallon, together with the miscellaneous observations made, should be recorded in order. The following data at least should always be given : Description and origin of sample. Date when drawn. Temperature when drawn. Appearance in 2-foot tube. Smell when heated to 38 or 40 C. Chlorine calculated as Common Salt. Phosphoric acid. Nitrogen as ready-formed Ammonia. Nitrogen in Nitrates and Nitrites. Nitrogen obtained as ammonia from albuminoid matter. Oxygen absorbed in 15 minutes at 27 C. Oxygen absorbed in 4 hours at 27 C. Total Hardness. Permanent Hardness. Total solid matter, dried at 100 C., in parts per 100,000. Appearance, under the microscope, of deposit. Action of the water on lead. OILCAKE. 223 iv. ANALYSIS OF FOODS. OILCAKE . FEEDING -ME AL. The constituents of oilcake are albuminoids, mucilage and other soluble non-nitrogenous substances, oil, cellulose and fibre, mineral matters, and water. In the case of oilcakes, the sample for analysis should be taken right across the middle of the cake, a strip an inch or two in width being sawn out. The sample is prepared by grinding it in a small hand coffee- or spice-mill, sifting the product, and again grinding the remainder left on the sieve. It will be found that oil and nitrogen can be best determined in a finely ground sample. WATEE is determined by drying 2 or 3 grams in the water- oven until constant. The intervals between the weighings should not be too long, as the substance in most cases begins finally to gain weight from the oxidation of the oil. OIL. From 2 to 4 grams, according to its probable richness in oil, of the finely powdered cake are introduced into the tube C (fig. 20), the small end of which is occupied with carded cotton, somewhat closely packed ; cotton is then placed at the upper end of the tube, and above the cotton a loosely coiled spiral of brass wire. The apparatus is now fitted together, 30 c. c. or a fluid ounce, or somewhat less, of petroleum spirit, redistilled under 60 C., or of ether or of carbon disulphide being placed in flask A. Flask A is now placed over a beaker of hot water (as the water cools it may be plunged a little way, and, finally, immersed in it), and B in a beaker of cold water ; the ether will then distil from A to B. The cork of B should be loosened at the com- mencement of the operation, to allow the escape of expanded air. When about two thirds of the solvent have distilled, flask A is shifted to the beaker of cold water ; a vacuum is thus produced by the condensation of the vapour in A, and the distilled solvent consequently passes up the tube from B, through the cake in C, 224 QUANTITATIVE ANALYSIS. and finally falls into A, carrying with it much of the oil which the cake contained. By tilting the apparatus so as to raise flask B above A, the return of the solvent to the latter flask is Fig. 20. rendered easier and more complete. The operation is repeated eight or nine times : then, while the solvent is returning through the cake into A, the apparatus is disengaged, and a drop falling from the lower end of tube C received on a watch-glass and evaporated by a gentle warmth. If no stain be left, or if, at least, no oil-globules appear, the extraction is complete ; if other- wise, the process is repeated as before. When the oil is all ex- tracted, as much solvent as possible is distilled over into B, the oil with a little solvent remaining in the flask A. This flask, which should be short(7centims. high), wide-mouthed, strong, and not over 18 grams in weight, is then kept for a short time in a warm place (say, on the top of the water-oven), and finally is heated to 100 until its weight is constant. The drying should be conducted without unnecessary delay, in order to avoid the oxidation of the oil and consequent increase of weight. But, OILCAKE. 225 on the other hand, the oil from some meals may be found to di- minish seriously in weight in the water-oven. For instance, the oil from palm-nut kernel meal contains some volatile con- stituent, which will be lost unless the drying be conducted at the ordinary temperature of the air, in vacuo and over oil of vitriol. Where but a small quantity of material is available for an oil determination, it may be mixed with coarse but perfectly pure silicious sand before introduction into the oil- extractor. The whole scale of the apparatus may also be slightly reduced in such cases. The traces of chlorophyll and resin which accompany the oil and fat may generally be disregarded. Sometimes a cylinder of fine platinum gauze, fitting exactly into the tube C, may be used to contain the oily material : this en- ables the exhausted substance to be readily withdrawn without loss at the close of the experiment. A very convenient form of extraction- apparatus has been in- troduced by Soxhlet. A vertical section of its main portion is shown in fig. 21, of one fourth the real size. To complete the apparatus, an upright glass tubular condenser, through which a current of cold water passes, is attached by means of a sound perforated cork to the digesting-tube A. The end of the inner condensing-tube should protrude a little below the entrance of the vapour-tube B. To the base of the apparatus at E a short stout flask, of about 100 c. c. capacity and not weighing more than 20 grams, is fitted by means of a good perforated cork. When the apparatus is thus completed the whole may be slung, by wire or cord, in such a way as to admit of being easily raised or lowered. In order to commence a quantitative estimation of oil in an oil- cake, about 15 c. c. (or half a fluid ounce) of the selected solvent are put into the flask (mentioned in the foregoing paragraph), which is then attached to the Soxhlet extractor. A weighed quantity of the powdered oil-cake, contained in a Swedish filter- paper so folded as to loosely fit the tube, is now dropped into the extractor at D (care should be taken that no particles of the powder can escape from this paper packet). The solvent is now introduced in quantity nearly sufficient to rise to the upper curve 226 QUALITATIVE ANALYSIS. Fig. 21. A B of the siphon-tube C at the side, The vertical glass condenser above is now attached and the current of cold water permitted to flow into it. The flask below is placed in or upon a bath of warm water so as to allow the solvent to boil. The vapour will rise through E, passing into B and thence into the vertical condenser, from which it will drop into A as a liquid. The oil will be dissolved out from the cake, and the solution of it will gradually accumulate until the siphon C can act. When this occurs the extractor will be emptied, the liquid passing through the quill tube which terminates the longer limb of the siphon inside E. By the continuous warming of the receiving flask below E the solvent will repeatedly ascend as vapour through B and descend as liquid through C, until a drop, tested as it falls from E, will no longer contain a trace of oil. The remaining operations are conducted exactly as in the case of the employment of the apparatus repre- sented in fig. 20. The defect of the Soxhlet apparatus, as commonly made, consists in the large quantity of ether or other solvent which is required to work it. But this imperfection is remedied by making the place of exit of the siphon-tube C much lower down the extraction-tube : this change is particularly expedient when but a small bulk of material is to be employed for an oil- determination. EIBKE. The terms fibre and cellulose are often used very vaguely, and include the various compounds containing carbon, hydrogen, and oxygen (other than oil), which are insoluble in cold or hot water. Pure cellulose itself may vary a good deal in its chemical deportment, according to its stage of development E OILCAKE. 227 and its physiological role. The fundamental cellulose of plants is much altered in chemical and physical properties by those in- filtrations and deposits which go on in the tissues of the plant. Thus while pure cellulose, represented by purified cotton, is soluble in oil of vitriol of sp. gr. 1/53, cuticle, cork, and lignin or lignose, the chief constituent of hard woods, are nearly insoluble in this reagent. On the other hand, these latter substances may be readily acted upon by means of a mixture of weak nitric acid and potas- sium chlorate, which leaves the cellulose almost untouched. The boiling of a mixed vegetable tissue with weak acid and then with weak alkali, alters and dissolves some of the softer cellulose, and at the same time removes some of the lignin, &c., of which we have before made mention. As the primary object of making an analysis of an oilcake is to ascertain its feeding value, we may be content with processes which do not effect absolutely perfect separation of the constituents of the tissues known as cellulose and fibre. It might indeed have been assumed that the materials which resist the chemical treatment which has been mentioned, and which we are about to describe, cannot have much alimentary value. But this is not the case, for ruminating animals often digest half the so-called "indigestible fibre "of their food. We give three methods for determining cellulose or fibre : the first process being the easiest, but yielding rather irre- gular and somewhat low results ; and the second process being troublesome in manipulation, yet yielding tolerably constant resi- dues. The third process merely determines the cellulose ; and so the residue in this case cannot be entered as "indigestible fibre," particularly as we know that different farm-animals are able to digest such cellulose, in some of its forms, more or less com- pletely. As the presence of oil in considerable quantity interferes with the determination of fibre, it is advisable to use for this purpose that portion of the sample which has been employed for the estimation of oil, or else to exhaust the dry fibre obtained by one of the processes described below with petroleum spirit or ether and again to dry it, i2 228 QUANTITATIVE ANALYSIS. Sulphuric-Acid Method. 1 gram of the substance is placed in a small wide-mouthed stoppered bottle with 30 c. c. of sulphuric acid having the specific gravity 1*53 ; the substances remain in contact at a temperature not exceeding 18 C. for 36 hours. The mixture is then washed into a beaker, diluted with water, filtered (best through a piece of fine linen), and the residue on the filter washed with warm water. The residue is then washed off the filter into a beaker with a 1 per cent, solution of ammonium hydrate, and allowed to digest in a warm place for one hour. The fibre is then returned to the linen filter, and washed with a 1 per cent, ammonium hydrate solution until the filtrate is colourless. Now moisten the filter with dilute hydrochloric acid, and wash with hot water until a few drops of the filtrate leave no residue on evaporation. Transfer the fibre to a weighed filter ; dry at 100, and weigh. Finally burn the filter and fibre, and subtract the weight of the residual ash, minus that of the ash of the paper, from that of the crude fibre. The residue represents the greater part of the lignose and some of the cellulose of the original cake. Acid and Alkali Method. 3 grams of the coarsely powdered sample are placed in a large beaker (or in an Erlenmeyer flask), 150 c. c. of water added, and the whole brought to a boiling heat, with frequent stirring or agitation to prevent burning : 50 c. c. of dilute sulphuric acid containing 5 per cent, of H 2 S0 4 are then added, and the boiling continued for j an hour, the normal volume 200 c. c. (best marked by an ink line on the beaker) being maintained through- out the operation by the addition of a little boiling water. Collect the residue from the acid digestion on a cambric or fine linen filter, after having siphoned off the clear supernatant liquid. The residue is to be thoroughly washed on the filter with hot water, and then syringed off the linen into the beaker with about 100 c. c. of hot water. 50 c. c. of a 5 per cent, of potassium hydrate (KHO) solution are next added, and the beaker filled up with hot OILCAKE. 229 water to the mark indicating 200 c. c. The mixture is boiled for 5 an hour, some cold water added, and the whole allowed to rest. When the supernatant liquid is clear it is siphoned off and the residue collected once more on the linen filter, washed with a 1 per cent, solution "of ammonium hydrate until the filtrate is colourless, and then syringed out of the linen into a paper filter which has been dried and weighed previously. The remaining steps of the process have been described in the plan previously given. Or, when the fibre has been perfectly washed on the linen filter (the aid of an air-pump is often serviceable here), it is transferred to a platinum or porcelain dish, dried on the steamer and then at 100 till constant, and weighed. Afterwards it is ignited, and again weighed : the second weight of dish and ash having been subtracted from the first gives the weight of fibre. Potassium- Chlorate Method. 2 grams of the dried substance (from which the oil has been extracted) are placed in a wide-mouthed stoppered bottle with 1'6 gram of finely powdered potassium chlorate, and 25 c. c. of nitric acid, having the specific gravity 1*10 : the mixture is allowed to remain at a temperature not exceeding 18 C. for 14 days. Then the contents of the bottle are mixed with cold water, transferred to a filter and thoroughly washed, at first with cold, and then with hot water. When all soluble matters have been thus washed out, the fibre is syringed off the filter and treated with ammonium hydrate solution, exactly in the manner described previously with the sulphuric-acid method. Cellulose prepared as above may be rendered still purer by washing with alcohol and ether, but still retains some nitrogen compounds and ash : if it be desired to make corrections for these impurities, determinations of them must be made in the usual manner. ALBUMINOIDS. A nitrogen combustion is made with about 8 gram of the finely powdered cake : in the case of cakes very rich in nitrogen (such as decorticated cotton cake) not more than 5 gram should be taken ; the tube used should be a tolerably long one. The percentage of nitrogen found is multiplied by 230 QUANTITATIVE ANALYSIS. 6 -25 ; the product is regarded as representing the percentage of albuminoids in the cake ; for the albuminoids of plants contain as an average about 16 per cent, of nitrogen, and 16 x 6-25 equals 100. In the case of some cakes it has been found that the ordinary combustion with soda-lime fails to convert the whole of the nitrogen present into ammonia. East-Indian linseed cake affords an example of this peculiarity. It would seem that the use of Ruffle's thiosulphate mixture as described on page 145 affords results nearly as satisfactory as those obtained when the more troublesome and tedious absolute method of determining nitrogen devised by Dumas is employed. But there is a more recently-invented method of determining nitrogen in organic substances easier of execution and probably quite as accurate as that of Dumas. It is known as KjeldahTs Method. In this method the nitrogen present is converted into ammonia by digesting the substance with strong sulphuric acid, the oxida- tion of the carbon and hydrogen being aided by potassium permanganate, and, usually, by a metallic oxide or salt. One gram of the substance to be analysed is brought into a flask of about 250 c. c. capacity (an oxygen-flask is convenient) along with about 0-7 gram of mercuric oxide which has been prepared by precipitation not the ordinary " red oxide." 20 c. c. of the strongest sulphuric acid free from nitrates and ammonium salts are then added. The flask, placed in an inclined position, is gently heated until violent frothing has ceased, and then the temperature is raised until the acid boils. When the liquid is colourless, or of a pale straw hue, the flask is held upright and powdered potassium permanganate added in small quantities at a time, until its contents assume a permanent green or purple colour. The liquid is allowed to cool, cautiously diluted with pure water and transferred to a flask connected with a condenser. 25 c. c. of a solution of commercial potassium sulphide (40 grams OILCAKE. 231 per litre), a little granulated zinc, and 50 c. c. of a saturated solution of caustic soda (free from nitrates) are added, and connec- tion immediately made with the condenser. The mixture is now to be distilled until it is no longer safe to continue heating it. The distillate is collected in a measured quantity of the standard sulphuric acid used in the soda-lime process (see page 135), the end of the condensing-tube dipping under the surface of the acid. The granulated zinc helps to prevent bumping during the distil- lation of the alkaline liquid. When the operation is completed the unneutralized acid is titrated with the standard caustic alkali solution in the same manner as in the ordinary soda-lime process. In the case of substances containing nitrates 2 grams of salicylic acid are added to the strong sulphuric acid used in the first digestion ; 3 grams of zinc dust and 2 or 3 drops of pla- tinum tetrachloride solution are also introduced cautiously the platinum-salt must be free from nitric acid. The liquid is boiled till the white fumes have ceased, the mercuric oxide is then added, while the rest of the operations are carried out from this point in the way above described. Eut this process is generally regarded as less exact in the case of substances con- taining nitrates or nitrites. ASH is determined in about 3 grams of the sample. A good linseed cake will not leave quite 7 per cent, of ash ; and of this 35 per cent, will be phosphorus pentoxide precipitable by ammonium molybdate from the nitric-acid solution of the ash. The phosphorus pentoxide in the ash may also be estimated by the process described further on under the heading " Analysis of Ashes of Plants." But determinations of the percentage of total ash and of the amount of sand and insoluble silicious matter pre- sent will suffice for most purposes. SAND AND SILICIOTTS MATTER. The ash is digested with dilute hydrochloric (or nitric) acid, and the insoluble matter collected, washed, burnt, and weighed. MUCILAGE, &c. The various non-nitrogenous combustible constituents (other than oil and fibre) of cakes are usually 232 QUANTITATIVE ANALYSIS. determined by difference. They include mucilage, digestible cellulose, pectose, and other less important carbonaceous sub- stances. N.B. A genuine linseed cake contains no starch ; if this be present, bran, rice-dust, or some similar substance has been mixed with the cake. Starch may be tested for by boiling some of the powdered sample in water till it forms a thin paste, filtering this through fine muslin (which has been previously cleansed by boiling with water, &c.), and adding to the filtrate when quite cold a few drops of tincture of iodine ; the forma- tion of a blue colour indicates the presence of starch. Sugar, likewise, does not occur in genuine cakes ; its presence may be ascertained thus : boil *2 or *3 of a gram of the powdered cake in water, filter the solution, and add to the clear nitrate a small quantity of the sugar test and a few drops of a solution of sodium hydrate. On boiling the mixture, cuprous oxide (Cu 2 0) will be more or less rapidly deposited, in greater or less quantity, and with a colour varying from yellow to red, according to the nature and proportion of the sugar present. A very small trace of starch or of sugar may sometimes be due to amylaceous or saccharine weed seeds, which, in the pro- portion of a few per cent., occur in all samples of linseed, how- ever good ; indeed, linseed-sellers reckon upon the presence of 4 / of seeds other than linseed, regarding such admixture as representing the standard of commercial purity. The various kinds of cereal refuse, such as bran, rice shudes, oat husks, which are found in adulterated linseed cakes, lower the normal per- centages of oil and albuminoids, and increase the proportion of indigestible fibre ; on the other hand, the addition of saccharine substances like locust beans, largely increases the soluble non- nitrogenous matters. But it must be recollected that the range of variation as to oil and albuminoids in unmixed cakes is con- siderable, and that the quantities of the adulterating materials added may be so adjusted as to imitate very closely, even as to albuminoids and oil, the composition of the pressed linseed itself. The analyst who wishes thoroughly to master this intricate subject, must not rest content with the indications afforded by chemical analysis. He should learn to identify, by the use of the microscope, the surface-markings, colours, &c. of the various vegetable products which are introduced, through accident or by design, into oilcakes. Such observations should be made first of all with the several adulterating and foreign substances them- GRAIN, STRAW, HAY. 233 selves ; it becomes then easy to recognize the fragments of the same substances when present in oilcakes. There are also special experiments which may be made with different species of cakes in order to discover some particular material likely to render them hurtful to animals. One may search by appropriate methods in any particular instance for poisonous alkaloids and for purgative substances, and for essential oil of mustard in the case of rape- seed and Indian linseed. There is also one test for the goodness of linseed-cake which affords fair indications of quality : it is thus performed : Pour 180 cubic centimetres of boiling water upon 10 grams of finely ground linseed-cake contained in a tall beaker, and stir the mixture. In one hour the whole will have set into a kind of jelly, pleasant in odour and taste, of a straw- colour, and neutral to test-papers. GRAIN, STRAW, HAY. Most kinds of grain, flour, bran, and meal, as well as straw, hay, and other dry fodder, may be analysed as an oilcake. Further on a hint or two as to the case of green fodder will be found. If it be desirable to determine separately the starch contained in any of the above products, one of the following plans may be adopted. STARCH. A quantity of the material is taken for the analysis, so that about 1 gram of starch is present in it : it must be finely ground or in a fine state of division. 100 c. c. of water and 1 c. c. of pure hydrochloric acid (of 1'125 sp. gr.) are placed in a flask and the weighed substance introduced. The mixture is kept on the water-bath at a temperature of 70 C. until a drop of the liquid no longer shows a blue tint when tested with iodine solution. The whole is then thrown on to a filter (previously freed from starch) and the filtrate and washings made up to 150 c. c. This liquid must now be further treated with rather stronger acid to convert any dextrin present into glucose. For this purpose add 20 c. c. of strong hydrochloric acid, and heat the mixture on a boiling water-bath for three hours : an upright condenser should be attached to the flask in which the digestion is carried on. At the expiry of the three hours the flask is allowed to cool, and its contents exactly neutralized with sodium hydrate solution. Finally, the liquid is made up to an exact volume, say 200 c. c., and the glucose in it determined by means 234 QUANTITATIVE ANALYSIS. of the copper test for sugar, as described further on under the heading Analysis of Boots Estimation of Sugar. It must be recollected that *05 gram of glucose corresponds to "045 gram of starch. The defects of this process with acids are two the sugars already existing ready -formed in the vegetable matter analysed are not discriminated from the sugar which the starch is made to produce, but the whole are determined together ; and any dextrin or other bodies capable under the circumstances of yielding sugar will be reckoned also as starch. The former of these defects is obviated by first making a determination of ready- formed sugar in the cold-water extract of the material to be analysed, previously inverting the sugar in this extract by means of acid. Of course in this case the dextrin and any other bodies soluble in cold water and capable of yielding sugar will be reckoned as starch in the second extract. Another method of determining starch involves the conversion of starch into sugar by means of malt extract : in this process also the dextrin will accompany the starch and be converted with it into sugar. The operations are conducted thus : The weighed substance, containing about 1 gram of starch, is boiled with 50 c. c. of water until all starch is dissolved ; the action is more easily completed in half an hour in a closed vessel heated to 115 C. The extract of ground malt has been previously prepared with 100 grams in 1 litre of water, the mixture being shaken at intervals for two hours, and then thrown on a double filter. 50 c. c. of the nitrate (which must be perfectly clear) are now added to the prepared starch solution, and the liquid maintained at 65 C. for one hour, or until no starch can be detected in a drop of the solution by means of the iodine test. The contents of the flask are to be filtered and then made up to 250 c. c. 50 c. c. are taken and heated with 20 c. c. of 5 / sulphuric acid for five hours in a closed vessel at a temperature of 110 to 120 C. Then 50 c. c. of the clear malt extract, diluted with 50 c. c. of water, are similarly treated with sul- phuric acid. Nothing remains but to neutralize the two inverted solutions with sodium hydrate, dilute them to the desired volume, and titrate 10 c. c. of the sugar test with each of them. It then remains to subtract the sugar due to the malt extract only from the larger amount due to the mixture containing the starch also. A third method of determining starch has been devised by Asboth. The starch is dissolved by boiling with water, and then precipitated as a baryta-compound (along with any dextrin present) by a measured quantity of standard baryta-water BOOTS. 235 Some proof spirit is then added, and then the excess of free baryta is titrated by means of decinormal hydrochloric acid, using phe- nolphthale in asindicator, in an aliquot part of the clear liquor from the baryta-starch precipitate. A fourth method for estimating starch in tubers and certain roots will be found on page 243. Brewers' grains require great care in the determination of the water, which often constitutes more than 75 per cent, of their weight, and which escapes rapidly ; a sample for analysis should always be secured at the place and time of delivery. In ana- lysing them such amounts for the various estimations must be taken as have reference to the small quantities of solid and nutritive matters they contain. TURNIPS, MANGOLDS, SUGAR-BEETS, &c. The chief constituents of these plants are water, cellulose, pectose, gum, sugar, albuminoids, and mineral matters; there are also present small quantities of fatty, colouring, and other substances. A separate analysis should be made of leaf and root. If it is wished to ascertain the composition of a crop, plants must be taken from several parts of the field, and all the deter- minations in the analysis made from a mixed sample. The analysis of a single plant will be here described, with occasional hints for the management of a larger quantity. ANALYSIS OP ROOT. After the removal of the leaves, and washing to separate ad- hering soil, and wiping, the root is cut through the middle, from top to bottom, into quarters or other convenient parts. WATER-DETERMINATION. A segment obtained as above, and representing therefore (if cut as directed) the average composi- tion of the root, is weighed (a piece of 130 grams will answer well), cut into thin slices, and then strung on a wire and sus- pended in a warm place ; the whole is dried finally in the water- oven till it ceases to lose weight. The dry matter is reduced to a fine powder and preserved in a well-closed bottle. As the complete drying of these slices is a tedious business, it is better 236 QUANTITATIVE ANALYSIS. to operate upon two separate portions : a small one of 20 grams oeing dried, preferably in a hot air-oven at 100 or 105, till fairly constant, for the water determination ; while a larger quantity of 100 grams is partially dried and used for the other determinations. Of course a calculation must be made to show what relation subsists between the partially dried and wholly dried samples. It must, moreover, be remembered that powdered dry residues of roots are extremely absorbent of water, so that even the partially dried sample used for the several determina- tions is sure to gain water after a time. Fig. 22. A very convenient arrangement for drying slices of roots and tubers, and also succulent leaves, is shown in fig. 22. This apparatus consists of a turned open base of mahogany, having two short pillars screwed into it opposite one another. Each of these pillars has a narrow slit at its summit to receive a platinum wire on which the materials to be dried are strung. It is best to have all the platinum wires for this purpose of such stoutness as to remain unbent with the weight of the slices. They should be pointed at each end, and all of the same weight ; a convenient counterpoise is thus always at hand. The whole apparatus may be introduced into the water-oven during the last stages of the drying process. A clock-glass of suitable size placed below the wire will receive any fragments which may fall during the drying. As the dried substance is very hygro- scopic it will be found a good plan to weigh it, still on the wire, in a beaker, which % is allowed to cool in a desiccator of suitable form. In operating on many roots at a time, an eighth or other like part of each may be taken, the whole weighed, cut HOOTS. 237 into thin slices, the slices threaded on a piece of twine, and hung up in a warm place, the drying being finished in the water-oven. ALBUMINOIDS. A nitrogen combustion is made in about 8 gram, and the percentage of nitrogen multiplied by 6-25; the product, though usually regarded as the percentage of albuminoids, requires a correction for that portion of the nitrogen which exists as nitrates, amides, ammonia salts, and other non- albuminoid forms in the root. The nitrates may be estimated in the duly prepared watery extract of the root, by converting their nitrogen into ammonia by the copper-zinc couple (see p. 214). Other plans of obtaining a fairly accurate approximation to the amount of nitrogen really existing as albuminoid or flesh- forming substances in roots, &c. are the two that follow. Phenol MetJiod. The root is dried in the usual manner ; a weighed quantity, about 2 grams, being then reduced to a moderately fine powder, is covered with a warm 4 per cent, aqueous solution of phenol (carbolic acid), to which a few drops of a freshly-made watery solution of metaphosphoric acid have been added. After 15 minutes a little boiling carbolic solution is added, the mixture being stirred and allowed to cool. The whole is then poured on to a small filter, which is washed with more of the same liquid but cold. The filter and its contents are then thoroughly dried, the dried material being afterwards mixed with soda-lime, and a nitrogen combustion made with the whole of it, the filter-paper itself being cut up into fine shreds and introduced into the com- bustion-tube. In this process the albuminoids, being coagulated and rendered insoluble, remain on the filter, while the nitrates, alkaloids, and other nitrogenous matters, which cannot be regarded as pos- sessed of the characters of true flesh-formers, pass into the filtrate. In the case of starchy meals, &c., an alcoholic solu- tion of carbolic acid may be advantageously substituted for an 238 QUANTITATIVE ANALYSIS. aqueous one in the first instance. A solution of tannic acid yields similar but less satisfactory results. Copper-Hydrate Method. Moist copper hydrate unites with albuminoid substances to form insoluble compounds : it unites also with a part of some nitrogenous acids, but it permits nitrates, ammonia salts, and amides to be washed away. The action of copper hydrate upon peptones seems somewhat variable. - The copper hydrate to be used is prepared by dissolving 100 grams of crystallized copper sulphate in 5 litres of water to which 3 c. c. of glycerin have been added. To this solution 1| litre of very dilute sodium hydrate solution is added, so that the resulting mixture has a faint alkaline reaction. The resulting precipitate is thrown upon a filter, allowed to drain, transferred to a dish or beaker, and washed by decantation with distilled water, containing 5 c. c. glycerin per litre, until the wash-waters are free from the least trace of alkali. The moist mass is now to be transferred to a well-stoppered bottle, syringing it out of the containing vessel by means of a 10 / solution of glycerin : this liquid helps to preserve the copper hydrate from change for a few weeks. When a nitrogen-determination is about to be made, a sufficient quantity of the moist copper hydrate is withdrawn from the store, washed by decantation to free it from the glycerin, and added to the weighed-out substance, which has been just heated to 100 C., with 100 c. c. of water. About -8 gram, or, roughly, one teaspoonful of the copper-hydrate paste suffices for 1 gram of dried and powdered residue of a root. A very brief further warming of the mixture will usually suffice to render the whole of the albuminoids insoluble : the whole is then thrown on to a filter, which, after washing and drying, is cut up and burnt with soda-lime, exactly as in the phenol method just described : or the Kjeldahl method may be used. In the case of seeds or other substances rich in alkaline phosphates a few c. c. of a strong solution of potash-alum should be mixed with the material taken previous to the addition of the copper hydrate. If the total nitrogen in a sample of a tuber like the potato, or a root like the mangold, be determined by the Ruffle method, and then the nitrogen actually existing in the albuminoids, the latter will often amount to no more than half, or even but one third of the former. BOOTS. Yv P*fr & MLNEKAL MATTEK. An ash-determination is made in 2 grams of the dry powder. Some ashes containing much alkaline salt are difficult to prepare. In such cases, char the substance at low redness, extract with boiling water, and separately ignite tli black residue and the evaporated extract. Add their weight together for total ash. CELLULOSE. A segment of the root, precisely similar to that taken for the water-determination, but of about 65 to 100 grams, is reduced to the condition of pulp by rubbing (best from end to end) on a clean grater. The pulp is transferred to a beaker, and weighed ; it is then treated with its own volume of tepid water, well stirred, and poured on to a calico filter. The cellulose left on the filter is folded in the cloth and well squeezed ; it is then returned to the beaker and treated with boiling water ; after a short time it is again transferred to the filter, and squeezed as before : the operation is once more repeated. The cellulose is pressed together on the filter, removed to a capsule, and dried till it ceases to lose weight ; the result is crude cellulose, from which the greater part of the albuminoids, the pectoso, and the salts of the root have been removed. This should be carefully powdered, and nitrogen and ash-determinations made in it. The amounts of albuminoid and mineral matters present being thus known, are subtracted from the weight of crude cellulose ; the difference is regarded as cellulose, but does not represent a pure and definite substance. It is better to regard it as a mixture of most of the innutritious ingredients of the root which are insoluble in water, and in the several reagents used. If a number of roots are operated on, the pulp from all might be mixed, and any convenient quantity taken for analysis. Estimation of Sugar. The " sugar test," made as described at page 70, is used. It should contain -3464 gram of copper sulphate in 10 c. c., corre- sponding to -05 gram of grape-sugar, C 6 H 12 6 ; -0475 of cane- sugar, C 12 H 22 O n ; or -045 of starch, C 6 H 10 5 . If grain weights, &c. are used the solution is prepared by dissolving 346 '4 grains of 240 QUANTITATIVE ANALYSIS. pure copper sulphate in about 200 septems of water, mixing it with a solution of 1730 grains of Rochelle salt in 480 septems of sodium hydrate solution, sp. gr. 1-14, and diluting the whole with water to 1000 septems ; 1 septem will then represent '05 grain of grape-sugar and equivalent quantities of cane-sugar or starch. Previously to use the exact strength of the solution must be found by titration, with a solution of pure sugar diluted to about \ / . The analytical process is conducted as follows : 10 c. c. of the copper solution are measured into a white porcelain bason of about 300 c. c. or 10 oz. capacity, diluted with about 40 c. c. of water,' and brought nearly to boiling. The sugar solution, previously inverted by boiling with sulphuric acid, made alkaline* with caustic soda, and diluted to a known volume, so as to contain between | and 1 / of sugar, is then delivered from a burette, the heat being continued, and the whole stirred well with a glass rod ; when the precipitated cuprous oxide appears of a bright red colour, remove the name, and allow the precipitate to settle as much as possible in one part of the dish ; hold the dish on one side, and if any bluish-green tinge remains some more sugar solution must be added ; if not, filter a few drops of the hot mixture through a very small wetted Swedish paper; make one portion acid with acetic acid, and add a drop of po- tassium ferrocyanide ; a brown colour shows that the copper has not been all precipitated, therefore some more sugar solution must be added ; if no brown colour is produced, test a few drops of the filtered liquid with a drop of the copper solution, and boil, to see if excess of sugar has been added. It is difficult to arrive at the exact point on the first trial ; but it affords a good guide to exact titration the second time. From the amount of the sugar solution required to precipitate exactly the copper in the 10 c. c. of sugar test taken, the total amount of sugar and its percentage are easily calculated. Before using the copper solution, 10 c. c. of it should be diluted and boiled alone ; if any precipitate occur, it may generally be remedied by adding more sodium hydrate. In order to maintain the copper solution in good condition, it ROOTS. 241 is better to keep it in the form of two liquids, one containing the copper sulphate, the other the Eochelle salt and the sodium hydrate. The solutions are mixed in due proportions when wanted, diluted to the proper point, and titrated against a pure sample of the sugar to be sought for. A caution is needed as to the conditions for securing constant results with Fehling's copper solution. If the copper solution or the saccharine liquid be decidedly weaker or decidedly stronger than those here recommended, strictly comparable results will not be obtained. If the Fehling solution be diluted with 4 volumes of water, and the sugar solution do not contain more than 1 per cent, of sugar, while the mode of operating is, in all cases, as far as possible identical, then fairly accurate and constant results are secured. It may be mentioned here that a series of experiments by Soxhlet as to the reducing power of different kinds of sugar upon 10 c. c. of Fehling's solution has given figures which do not exactly correspond with those named above. The differences are not large ; their importance is moreover diminished by the ease with which the results of any given mode of working with the Fehling solution may be checked by direct appeal to special titrations against solutions of pure sugars of known strength. In the experiments just referred to, Soxhlet found, with 1 / sugar solutions, and with Fehling diluted with 4 vols. of water, that 10 c. c. of the latter corresponded to : (a) '04950 gram dextrose. (b) '05155 invert sugar, from cane-sugar. (c) '05376 levulose, calculated from a and b. (d) -06757 milk-sugar. (e) -07353 maltose. It will be seen, on glancing at these figures, that 10 c. c. of Fehling's solution required -00155 gram more (about 1J milli- gram) of the grape-sugar or invert sugar to effect complete re- duction than is usually assumed to be needed. This grape-sugar is made up of equal parts of dextrose and levulose, and is the sugar with which, in the estimations described in this manual, we have to deal. If the correction which this difference involves be accepted, it will correspond to a gain of 3 per cent., that is, 20 c. c. of Fehling equal 103 milligrams of grape-sugar, glucose, or invert sugar, and not 100 only as is commonly stated. When, however, a J per cent, solution of invert sugar is employed, and the Fehling liquid is not diluted at all, 20 c. c. of the latter do 242 QUANTITATIVE ANALYSIS. really correspond almost exactly to 100 milligrams of invert sugar, or 10 c. c. to '05 gram. A few words may here be said as to the method of preparing the extract of a root, so as to obtain the whole of the sugar pre- sent in a convenient form for estimation. The selected and weighed average slices, cut as before directed, may be rasped on a grater, and the juice squeezed from the pulp in a cloth : the residual pulp is then repeatedly exhausted with hot water. The juice and washings are then heated to the boil- ing-point for a few minutes and filtered. The filtrate is treated as above directed. A more exact method involves the use of a Sprengel pump filter, or other contrivance, by which the atmospheric pressure or the weight of a column of liquid is taken advantage of to hasten the otherwise tedious process of filtration. This more effective method is thus conducted. The selected and weighed segments of root are cut into very small and thin pieces, or pulped on a grater and placed in a long funnel which may conveniently be made out of the neck and beak of a large retort ; or an ordinary small paraffin lamp -glass may be used. The narrow lower end of this funnel is fitted with a perforated india-rubber cork ; upon it is placed a piece of muslin and 12 millims. of clean sand ; through the perforation a glass tube passes into a receiver below. This receiver (which may be a wide- mouth Winchester quart, with ground neck and having an india-rubber stopper) is kept partially exhausted of air by being placed in suitable connexion with an exhausting syringe. The funnel is kept supplied with hot water till all the sugar has been thus ex- tracted from the root ; by this means a litre of water will extract the whole of the sugar from 100 grams of beet-root. The whole filtrate is then boiled, when a coagulum is formed, and many im- purities with colouring-matters thus rendered separable by filtra- tion. About 15 c. c. of dilute sulphuric acid are then added, the whole evaporated to a small bulk, boiled for a short time to com- plete the inversion of the sugar, filtered if necessary, sodium KOOTS. 243 hydrate in excess added, and the solution diluted to a known volume. A convenient weight of beet-root to take is 120 grams, one half the evaporated extract from which can then be diluted to a litre ; this will give a solution containing the sugar from 6 parts of beet in 100 of water, and generally the right strength for titration. The remainder of the operations have been already described. The starch in potato tubers, parsnips, &c. may be estimated by rasping a weighed portion of the fresh materials and then wash- ing and squeezing the pulp in a piece of fine cambric. When the water flows through clear, a little sodium hydrate solution may be added, and then the starch be allowed to settle, washed by decantation, collected, and dried in vacuo first, then at 100. In the case of the potato it is possible to obtain an approxi- mation to the percentage of starch present in any sample of this tuber by first determining the specific gravity of an average well- grown sample free from disease, and then referring to a previously constructed table in which the relation between certain specific gravities and the corresponding starch-percentages is shown. The specific gravity is easily ascertained for this purpose by selecting 20 average tubers washed clean and wiped dry, and placing them in a solution of common salt containing about 350 grams per litre at a temperature of 16 C. Water is added with thorough agitation until half the tubers float, and then the specific gravity of the liquid is ascertained by means of a hydrometer. The following table gives the mean results of a large number of experiments with several different varieties of potato. But these figures cannot be accepted as more than rough approxima- tions to the truth, since the same specific gravity, so far from corresponding in all cases to the same starch-percentage, does not by any means always involve even the same percentage of total dry residue. 244 QUANTITATIVE ANALYSIS, Starch in Potatoes. Specific Gravity. Percentage of Starch. Specific Gravity. Percentage of Starch. 1-075 12-9 1-105 19-2 1-080 13-9 1-110 20-3 1-085 H-9 1-115 21-4 1-090 1G-0 1-120 22-5 1-095 17-1 1-125 23-5 1100 18-2 1-130 24-6 In many roots there occur considerable quantities of the sub- stances known as pectose, pectin, and pectic acid. It is rarely necessary to determine them separately ; but they may be converted into pectic acid and precipitated as calcium pectate. The opera- tions to be carried out for this purpose are these : A convenient quantity of the material to be analysed is cut up and immersed in strong methylated spirit for 12 hours. Then it is thrown on to a cambric filter, dried partially, and ground. The ground substance (from 5 to 10 grams in weight) is treated with methy- lated spirit to which one fourth its volume of strong hydrochloric acid has been added. When all calcium has been dissolved out of it, it is washed with methylated spirit to remove every trace of HC1. The next step consists in a treatment with 150 c. c. of spirit containing 1 gram of potassium carbonate dissolved in a little water, the digestion being prolonged with constant agitation for half an hour at a temperature of 75 C. : the flask used should be fitted with a condensing-tube. The next step consists in throwing the contents of the flask on to a filter and washing the matter on the filter with alcohol. The whole of the solid substance is then syringed out of the filter with about 700 c. c. water into a litre flask. The addition of 2 grams of ammonium oxalate for each gram of pectic acid presumed to be present in the substance taken is now made, and the mixture is digested for 2 hours at 35 C. Then the whole is filtered and the residue on the filter washed. The filtrate and washings are made up to 1 litre, and 100 to 300 c. c. taken for the purpose of analysis. The LEAVES. 245 pectose, pectin, and pectic acid are now all in the form of alkaline pectate dissolved in water ; this salt is precipitated along with the oxalate by the addition of a solution of calcium acetate in slight excess. The calcium pectate and oxalate thus thrown down are collected on a weighed filter, washed with water, then with alcohol, dried at 100, weighed, burnt, and the lime weighed as carbonate. As the quantity of pure ammonium oxalate used per 100 c. c. is known, the amount of calcium oxalate which it will yield can be ascertained. Call this a ; let the residual CaO, in excess of that required for the oxalate, be called b ; let A be the total weight of the mixed precipitate of calcium oxalate and pectate from 100 c. c. and dried at 100 C. Then oo, or the weight of pectic acid, may be found by the equation Note that calcium oxalate, after treatment with alcohol and dry- ing at 100, is expressed by the formula C 2 Ca0 4 , H 2 ; and that the pectic acid represented by x is calcium pectate minus lime, and not the true acid or hydrogen pectate. A simpler process for getting at the weight of the pectic acid in the mixed precipitate is to dissolve out all but the pectic acid by means of alcohol rendered strongly acid with hydrochloric acid, and then to wash, dry, and weigh the residue. ANALYSIS OP LEAVES, GKEEJT FODDEK, &c. The constituents of the leaf will be for the most part the same as those of the root ; the sugar, however, will be less in amount, while the matters soluble in ether, including fatty and waxy sub- stances with leaf-green, may prove by no means an insignificant quantity. Oxalates, though not absent from the root, sometimes exist in the leaf to the extent of \ to \ a per cent. ; they are accompanied in all plants by salts of other organic acids acetic, citric, malic, or tartaric sometimes in considerable quantity. Tannic acid is another constituent occurring in important amount in certain leaves, while organic bases or alkaloids (such as 246 QUANTITATIVE ANALYSIS. nicotine) are found in others. It does not fall within the scope of this elementary manual to describe processes for the quanti- tative estimation of organic acids and bases : the instances given below refer to the more easily determined constituents only. But an outline of what may be called the "fractional" analysis of plants may be here given. In this method of treatment, which has been elaborated more particularly by Dragendorff, a weighed quantity of the substance to be analysed is exhausted with a number of solvents applied successively in the following order : 1. Petroleum-spirit, boiling at 45 or under. This extracts fixed oils and fats, wax, essential oils, free fat-acids, together with a part of the chlorophyll and some active principles. 2. Ether, free from alcohol and from water. This extracts resins, some organic acid*, and chlorophyll. 3. Alcohol^ which must be nearly absolute. This extracts tannin, glucosides, bitter principles, and alkaloids. 4. Water. This extracts sugars, dextrin, mucilage, many organic acids and their alkaline salts, calcium sulphate, soluble albuminoids, ammonium salts, nitrates, and amides. 5. Sodium hydrate solution, containing ! to '2 per cent. This extracts albuminoids with some kinds of gummy and pectous bodies. 6. Water at 100. This extracts starch. 7. Hydrochloric acid, dilute, containing 1 per cent. This ex- tracts calcium oxalate, manganese and iron oxides, and some gummy substances. The final residue, remaining after the above treatment, will consist chiefly of cellulose and lignose with silica and other mineral matters. It, as well as the several groups of substances which have been removed by the several solvents successively used, will have to be further examined by special methods. In ordinary cases, where the feeding value of green fodder is the chief point to be ascertained, the determinations described below will generally suffice. WATER* Whole leaves, to the amount of 100 grams, or more LEAVES. 247 if the leaves be large, are dried slowly and carefully on bibulous paper, in a current of warm dry air, if possible. If a large number of leaves have to be dried for any special purpose it will be found convenient to tie them up one by one along strings stretched across a room : a warm temperature and free movement of the air assist the drying process greatly. When the dried leaf is required for the subsequent examination of certain ingredients alterable by light (chlorophyll for instance), the room should be kept as dark as possible. Sometimes leaves may be advanta- geously dried by means of the same arrangement as that pre- viously recommended for sliced roots. NITEOGEN". When the total nitrogen merely is required it may be determined in the dried and powdered leaf by a combustion with soda-lime and thiosulphate in the usual way. If after- wards the ammonia be determined by distillation with magnesium carbonate and Nesslerizing the distillate, if the nitrates be deter- mined by the copper-zinc couple method, and if the true albumi- noids be determined by the phenol or the copper-hydrate method, we are then in a position to calculate the amount of nitrogen existing in the form of amides and other bases and of nitrogenous acids, by subtracting the amounts of nitrogen existing in the three known combinations from the total amount. There will, however, be a difficulty in stating the results in percentages, as we do not know the nature and consequently the centesimal com- position of the amides &c. in question. Were we dealing with asparagine only, it would suffice to multiply the percentage of residual nitrogen by 4*7. ASH may be determined in the dried and broken (but not powdered) leaf in the usual way. Where particular accuracy is desired, the leaves should be calcined by the process described further on under the heading " Ashes of Plants." FAT is to be determined in a rather coarsely powdered sample of the dried leaf by extraction with ether, petroleum-spirit, or carbon bisulphide in the usual way. Much of the matter ex- tracted by these solvents will, however, not be fat, but leaf- green or chlorophyll and xanthophyll. These colouring-maters 248 QUANTITATIVE ANALYSIS. may be removed from the solution by filtering it through freshly ignited animal charcoal. CELLULOSE may be determined by carefully bruising in a mortar about 70 grams of whole leaves till a tolerably smooth paste is formed, and then removing the pectose group and afterwards exhausting with water as before described in the case of roots. A determination of fat, as well as of nitrogen and ash, should be made in the crude cellulose. Beet-root pulp from sugar manufactories or distilleries is analysed as directed for Roots : a sugar determination is some- times requisite. FERMENTED LIQUORS, BEERS, &c. An adequate description of the examination of liquids contain- ing alcohol would occupy too much space in the present elemen- tary volume. "We here confine ourselves to some points to which attention should be chiefly directed. ALCOHOL. This is estimated by distilling a known quantity of the liquid in a suitable flask fitted air-tight to a good con- denser. When the last distillate no longer contains any spirit all the previous distillates are mixed together, heated or cooled, as the case may be, to the temperature of 15-5 C. (60 F.), the total volume measured, and the specific gravity of a portion taken in the proper sp. gr. bottle or tube. A Table showing how much absolute alcohol is contained in distillates of different densities may be found in most manuals of chemistry : we give a few extracts from such a Table here. From the amount of alcohol present in the amount weighed, the amount in the whole measured distillate is calculated. FEKMENTED LIQUORS. 249 Spec. Grav. of distillate at 15-5 0. 9991 % absolute alcohol by weight. 47 % absolute alcohol by volume. 60 % proof spirit. 1-04 9981 1- 1-26 2-20 9973 1-5 1-88 3-30 9965 2- 2-51 4-40 9956 2-5 3-14 5-49 9947 3- 3-76 6-58 9938 3-53 4-42 7-74 9930 4- 5-00 8-77 9922 4-5 5-63 9-86 9914 5- 6-24 10-94 9898 6- 7-48 13-13 9884 7- 8-72 15-27 9869 8- 9-95 17-43 9855 9- 11-17 19-58 9841 10- 12-40 21-73 9828 11- 13-62 23-86 9815 12- 14-84 26-00 9802 13- 16-05 28-13 9789 14- 17-26 30-26 9778 15- 18-48 32-38 9766 16- 19-68 34-50 9753 17- 20-89 36-60 9741 18- 22-09 38-71 9728 19- 23-28 40-80 9716 20- 24-48 42-90 9578 30- 36-20 63-43 9396 40- 47-35 82-88 9182 50- 57-84 101-36 8956 60- 67-69 118-63 8721 70- 76-91 134-84 8483 80. 85-49 149-82 8228 90- 93-29 163-48 7938 100- 100- 175-25 250 QUANTITATIVE ANALYSIS. Absolute alcohol is here taken as having the specific gravity '7938 when compared with water at the same temperature, 15' 5 C. According, however, to the latest researches truly absolute alcohol has the specific gravity '7935 under these conditions : an alcohol of '7938 sp. gr. contains only 99 '9 per cent, of absolute alcohol by weight. The difference which this correction would make if applied to the above Table may be safely neglected. Proof spirit has the sp. gr. -9198 and contains 49-24 per cent, of absolute alcohol by weight ; or, if the new value for absolute alcohol be taken, 49-19 per cent. "When a sample of spirit is said to be 30 over proof, it is meant that 100 measures of it, after dilution with water, would measure 130 of proof spirit. A sample 22 under proof contains in 100 measures 100 22 or 78 measures of proof spirit. The last column of figures in the Table serves to show the volumes of proof spirit to which the several percentages of alcohol correspond. The detection of the higher alcohols (or fusel oil) of potato and grain spirit is easy by the simple test of the odour produced when a few drops of the distilled spirit are allowed to evaporate on the hand or in a 3-foot length of wide combustion tube ; their estimation is a difficult matter. TOTAL NON- VOLATILE MATTEK. By evaporating a given weight of the sample of wine, &c., the water, alcohol, acetic acid, and traces of ethers present are volatilized, while the sugars, the glycerin, albuminoids, colouring-matters, gums, pectin, &c., with . all the organic and inorganic salts, remain behind. The pro- cesses already given in this volume may be easily adapted to the estimation of the sugar, the potash, and the albuminoids in such a residue : of course the total mineral matter or ash may be ascer- tained by mere incineration. Any free acid (save carbonic) in wine, beer, or vinegar, provided it be unmixed with any other acid or acid salt, may be estimated by the standard soda solution used in nitrogen-combustions, and litmus (or methyl-orange, or phenolphthalein, or cochineal, or alizarin). Vinegar, for instance, should always be tested for sulphuric acid before an estimation is attempted of its acetic acid. The following data will be useful in ASHES OF PLANTS. 251 showing the quantities of various acid substances which 1 c. c. of the standard soda solution previously referred to will neutralize : 00766 gram H a S0 4 , sulphuric acid. 00938 C a H 4 2 , acetic acid. 02940 C 4 KH 5 6 , hydropotassium tartrate. 01172 C 4 H 6 6 , tartaric acid. 00703 C 3 H 6 3 , lactic acid. 01047 C A H C K , malic acid. ASHES OF PLANTS. The chief substances to be estimated in the ashes of plants are silica, phosphorus pentoxide, sulphur trioxide, iron and manga- nese oxides, lime, magnesia, and potash. Suitable methods for the determination of all these ingredients have been given under the head of " Soil Analysis." These methods may be easily adapted to suit the present materials ; but a few words as to the incineration of vegetable products may be here given. The material to be burnt should be carefully cleansed from all adhering dirt, dried, and reduced to small fragments, but not to powder. If not too bulky it may be heated in a platinum or por- celain crucible laid obliquely, and with its cover so adjusted as to send a current of air over the heated mass ; stirring is seldom advisable, and the heat must not be so high as to fuse or volatilize the alkalies present : the less bottom heat the better, provided only that the surface of the mass attains a sufficient temperature. When the bulk of material to be used is rather large, it may be burnt on a tray of sheet platinum, having its edges turned up and enclosed in a muffle. This muffle is supported on a fire brick, and heated in a suitable furnace : a pipe at the further end of the muffle passes through the furnace back and leads away the gaseous products of combustion. The heat, whether from solid fuel or gas, is made to play upon the sides and top of the muffle ; the incineration takes place easily and at a low temperature. The ash, however prepared, is collected together, ground and mixed, once more heated to low redness, and preserved in a 252 QUANTITATIVE ANALYSIS. stoppered weighing-tube for the several estimations. In one portion a determination of carbon dioxide (see page 198) may be made : in a quantity of 3 or 4 grams the silica (and carbon if any) may be estimated, while the nitrate from the silica (which has been rendered insoluble by the usual treatment with HC1, and subsequent taking up with HN0 3 ) may be treated as fol- lows. It is divided, by weighing or measuring, into three por- tions, in one of which the sulphur trioxide is determined by means of precipitation with a barium salt ; in another portion the phosphorus pentoxide is estimated by the ammonium molybdate process; while from the third portion the bases are separated by the processes recommended in the case of soils. It should be remembered that some of the sulphur in a vegetable product is always lost during incineration. In calculating percentages from the results of an ash-analysis, any carbon and carbon dioxide found are first deducted. The best process for preparing ashes of plants, so as to avoid to a great extent loss of alkalies or chlorine, involves the use of a tube-furnace and a current of carbon dioxide followed by one of oxygen. The substance is weighed in a platinum boat contained in a sliding glass weigh-tube. A small combustion-furnace with six air-burners will suffice. The combustion-tube should be a wide one of hard porcelain. Near the end where the gas enters is a plug of asbestos, then the boat, and then a caoutchouc stopper and exit-tube, leading under the water in a small bottle or tube serving as an indicator of the rapidity of the current : this end of the combustion-tube inclines somewhat downwards. The operation is commenced by filling the tube with carbon dioxide, previously washed with water and passed through sodium bicar- bonate. Then, in a steady current of this gas, the platinum boat is heated gradually and gently till empyreumatic products cease to distil off. When inflammable gases are no longer emitted from the end of the tube, the current of carbon dioxide is replaced by a slow one of oxygen. When oxygen only passes out at the extremity of the tube, then the combustion is finished. The burners are turned out, and perfectly dry air is passed through the tube as it cools. A triple tube with three stopcocks enables the carbon dioxide, the oxygen, and the dry air to be successively passed over the boat. When the apparatus has MILK. 253 cooled sufficiently the boat is withdrawn with a wire hook, in- troduced into the sliding weigh-tube, and the weight of ash ascertained. A determination of carbon will not be needed ; but the C0 2 in the ash may be estimated in the usual way before proceeding with the further analysis. It is sometimes convenient to char the vegetable matter in the boat at a very low temperature before introducing it into the tube and passing the C0 2 over it. MILK. Genuine cows' milk (to which the following remarks and instructions refer, unless otherwise stated) varies somewhat in composition. The decrease in temperature during the night, and the lessened activity of the animal, often cause the morning milk to be a little more aqueous than that of the evening. The length of time that has elapsed since calving, the character of the food given, the temperature and moisture of the air, as well as individual peculiarities in the animals, are among the chief cir- cumstances upon which depend variations in the amount of solid matter in milk, as well as variations in the nature of that solid matter. The whole day's milk of cows to whose ordinary daily ration a moderate addition of oilcake is made, commonly gives about 13-5 per cent, of solid residue as against 12-3 per cent, when that or a similar addition of rich food has not been made. It may be useful to mention here that 100 c. c. of good milk will weigh about 103'2 grams. The quality of milk may be best determined by means of chemical analysis, the indications of the lactometer and creamo- meter being too often fallacious. With quite fresh milk fairly accurate results, so far at least as regards the percentage of fat, may, however, be obtained by the use of an instrument known as the lactoscojpe, an arrangement of two sliding tubes closed by glass plates. In this instrument the opacity of the milk to the light of a standard candle forms the test of quality ; the better the milk the less is the thickness of the stratum required to ex- clude the light. Milk contains matters in suspension and matters in solution. Of the former, butter or fat t in the form of globules, is the most 254 QUANTITATIVE ANALYSIS.^ important; the latter include casein, lactose or sugar of milk, and mineral matters rich in phosphates. Some of the casein of milk appears to be in suspension, while the phosphates are inti- mately associated with this constituent, being partly precipitated with it when the milk is curdled. Most important indications of the quality of milk are deduced from the determination of water and of milk-fat. When we speak of casein as the nitro- genous constituent of milk, we refer to a mixture of albuminoids and not to a single substance : on this point a note will be found at the end of the directions for the analysis of milk, which we now proceed to give. "WATEE. As it is impossible to secure the perfect desiccation of a considerable quantity of milk, it is best to adopt the plan (first proposed by Doyere in 1851) of using a very small quan- tity for the purpose of ascertaining the amount of water and of total solids present. 5 c. c. of the well-mixed sample of milk are accurately measured from a pipette into a flat platinum or porce- lain bason 2 inches in diameter. The bason is placed on a boiling water-bath or " steamer," where it remains for sixty to ninety minutes. Then it is removed to the water-oven, where it is dried for at least an hour. It is now to be placed in the desiccator and weighed when cold : another hour in the water-oven, fol- lowed by another weighing, will enable the experimenter to make sure that the milk residue is really dry. The weight of this residue may be calculated into a percentage on the volume of the milk, or on the iveiglit, if the weight of 5 c. c. be determined. It will average 13 %, and will rarely fall below 12 / in a genuine milk, while, if the cows be properly and liberally fed, it may even exceed 18*5 / . These numbers represent respectively 87, 88, and 86-5 per cent, of water. SOLIDS-NOT-FAT. The determination of the solids other than fat in the dry residue of a milk furnishes an important means of learning whether the milk bas been watered. This determina- tion may be most accurately made by Adams's Paper-Coil Method ; but the following plan may be adopted when a fairly exact estimation is all that is required. Into a platinum (or MILK. 255 porcelain) dish, about 3 inches in diameter and flat-bottomed, 10 grams of milk are introduced : the dish, together with a small glass stirring-rod, must have been previously weighed. Place the dish on the " steamer " and allow the contents to become nearly dry, stirring them occasionally so as to produce a granular condition. If the drying has proceeded too far, moisten the resi- due with a few drops of absolute alcohol, warm it till the alcohol has almost evaporated, and then repeatedly exhaust the solid matter with dry ether or petroleum-spirit, using the stirring-rod to break up the residue on each exhaustion. After each ex- haustion the solution of the milk-fat is poured down a glass rod into a small tared beaker or wide-mouthed flask. The exhaustion with the solvent must be repeated four times or oftener, in fact until a minute drop of the last washing leaves no perceptible greyish translucent stain when let fall upon a piece of clean filter paper. When the extraction of the milk-fat is complete the dish containing the solids-not-fat is dried on the steamer for one hour, then kept in the water-oven for another hour, and finally weighed. If the milk be of good quality the residue should amount to 9'3 up to 9*6 / . It may usually be concluded that the milk has been watered should this figure fall as low as 9. But, as under certain rare or exceptional conditions, genuine milk would appear occasionally to contain no more than 8-5 per cent, of solids-not-fat, ifc is not usual to condemn a milk unless this degree of poverty is reached. Then the amount of added water is calculated on the supposition that genuine milk should contain at least 8'75 / of solids-not-fat. Suppose, for example, that the analysis of a sample has given but 6'2 / of solids-not- fat, we multiply that figure by 100 and divide it by 8'75, and so obtain 70-8 as the quotient, representing the percentage present of real milk : The sample is therefore calculated to contain 29-2 per cent, of added water. 256 QUANTITATIVE ANALYSIS. By evaporating the milk-fat solution obtained in the preceding determination of solids-not-fat we obtain the milk-fat. The evaporation may be conducted in a tared beaker or small wide- mouthed flask, the temperature not exceeding 45. The vessel is finally dried in the water-oven, cooled in the desiccator, and weighed. But the fat in a milk-residue is best determined by the " coil-method" now to be described. FAT. Of all the methods of determining the fat in milk that of Adams, in which a coiled strip of bibulous paper is used, appears to yield the most precise results. It is conducted as follows : Adams's Paper-Coil Method. Deliver 5 c. c. of the milk, by means of a pipette, on to a strip of demy white blotting-paper, 22 inches long and 2\ inches wide. This strip should have been previously rolled up in the form of a helix, which, if not too tightly coiled, will have a diameter of rather less than one inch. This coil is to be placed upon a sheet of glass ; after a little practice it is easy to secure the absorption of every drop of milk by the paper, the glass plate showing no sign of any loss. The coil, after having been dried in the water-oven for an hour, is introduced into a Soxhlet tube and extracted by ether twelve siphonings at least being neces- sary. Boil off the ether and place the flask (a small and light one should be used) in the water-oven in a horizontal position. When the flask and contents are dry, cool the flask in a desiccator for ten minutes and weigh. Deduct the tare of the flask, the remainder represents the milk-fat in 5 c. c. of the milk taken. As the weight of 5 c. c. has been previously determined, it will be easy to calculate the percentage of fat present in 100 parts by weight of the milk. But before proceeding with this calculation it is necessary to deduct from the fat found the small quantity of matter soluble in ether which is naturally present in the paper- coil. This is done by introducing 2 coils of the regulation size and cut from the same sample of blotting-paper, and dried at 100, into a Soxhlet tube and extracting them with ether, in the manner MILK. 257 above described : half of the small quantity of fatty or waxy substance thus obtained is to be deducted from the total amount found in the experiment with the milk. If a sufficiently absor- bent filter-paper can be obtained it may be used instead of blot- ting-paper : in this case it will probably be found that the matters extracted by ether from the paper-coil are smaller. Some analysts prefer to remove the fat present in each coil before using it. If the total solids and the specific gravity of a milk of fairly normal composition have been ascertained, it is easy to calculate from these data the approximate percentage of fat present. The calculation is based upon the fact that, in accordance with their percentage, the fat present depresses to a definite degree and the solids-not-fat raise to a definite degree, the gravity of the milk. Let, then, T represent the ascertained percentage of total solids, G the figures of the gravity beyond 1000, and F the fat, then the simplest and most easily worked expression for the formula becomes Thus a milk which gave 12-36 % of total solids and had the specific gravity 1032-2 yielded experimentally 3-62 / of fat, while by calculation it was estimated to contain 3*59. For J (12-36 - **-) = 3-59. Another formula for calculating the percentage of fat gives results which average *26 / too low : it is this : 833xT-2-22 x V G J Here T represents the percentage of total solids, G the specific gravity of the milk (water =1), and F the percentage of fat. The specific gravity of milk must be taken with considerable accuracy. For this purpose a lactometer is inferior to a specific- gravity bottle or a Sprengel-tube. But another plan may be adopted, namely, the use of Westphal's Hydrostatic Balance, which affords a ready and accurate method for ascertaining the specific gravity of a sample of milk. In this instrument a counterpoised thermometer, suspended by a piece of thin plati- num wire, is attached, as a plummet, to one end of a graduated lever. On immersing the thermometer in a liquid it loses a 258 QUANTITATIVE ANALYSIS. certain weight. The equilibrium is restored by hanging on the lever a series of riders which are so adjusted in weight as to make the reading of their values very simple. The plummet displaces exactly 5 c. c. of liquid, and hence the weight required to restore equilibrium equals that of 5 c. c. of the fluid of which the density is required. A counterpoised glass rod of known displacement, say 10 c. c., may be used in a similar manner with an ordinary equal-armed balance. On immersing the rod in a liquid it will of course lose a portion of its weight equal to that of its own volume of the liquid employed. Add weights to the pan, below which the rod is hung, so as to restore the equili- brium ; and divide the weight in grams thus required by the volume of the plummet in cubic centimeters the figure thus obtained will represent the specific gravity of the liquid used. Having obtained, by one of the preceding processes, the per- centage of milk-fat present in the sample of milk under exami- nation, it may be used, should it fall below 3, to calculate the amount of milk-fat or of cream which has been abstracted from the milk. Assuming that the percentage of milk-fat found is 1-75, then the calculation will be 1-75 x 100 3-25 = 53 ' 5 ' The sample is thus estimated to have lost by skimming 46-5 per cent, of its cream. MILK-PROTEIDS OK ALBUMINOIDS. The casein and other albu- minoids of milk may be determined in the dry residue of 5 c. c. of the milk by burning it with soda-lime in the usual way. A long combustion-tube should be used. The percentage of nitrogen found may be multiplied by the usual factor, 6'25. Some chemists, however, employ the figure 6'3, and others 6-45, on the supposition that the milk-albuminoids contain less than 16 per cent, of nitrogen, namely, 15'87 or 15-5 / . 'It is probable that the factor 6-3 yields results which are very near the truth. An easier and more rapid but less accurate method of ascer- taining the amount of casein and other albuminoids in milk may now be described. Take the milk residue which has served for the determination of solids -not-fat, and from which, therefore, the milk-fat has been removed ; transfer it carefully and com- pletely to a small filter which has been dried and weighed at MILK. 259 100 C. Wash the substance on the filter, first with boiling alcohol of 75 per cent, to which 4 per cent, of phenol and a trace of metaphosphoric acid have been added : the washing is to be completed with a much weaker spirit, also boiling and containing phenol. By this treatment the sugar or lactose is dissolved along with the soluble salts, while the albuminoids with their associ- ated phosphates are left behind. The filter and contents, dried at 1 00 till constant, must now be weighed : the weight, after deduction of the tare of the filter, represents the amount of crude casein, &c., present in the quantity of residue taken : from this number the percentage in the milk itself may be readily calcu- lated. By carefully burning the filter and contents, the ash may be found ; its amount is to be deducted from that of the crude casein ; the remainder will represent the albuminoid matter itself. MILK-SUGAR. A known weight of the milk, say 10 grams, is to be precipitated with 5 or 6 drops of an acid mercuric nitrate solution, prepared by dissolving mercury in twice its weight of nitric acid of specific gravity 1'42 and adding to the liquid its own bulk of water. After the addition of this mercuric nitrate solution to the milk, the mixture is to be thoroughly shaken and then diluted so as to measure 200 c. c. In this manner the albu- minoids and fat are completely separated, and a clear liquid containing all the milk-sugar is obtained. The precipitate is col- lected on a filter and washed with water until all the milk-sugar has been removed. The filtrate and washings (after having been rendered alkaline by a few drops of sodium-hydrate solution, and filtered, if necessary) are used for the determination of the sugar, an aliquot part, representing 1 or 2 grams of the milk, being titrated with Pehling's solution as directed on pp. 239 to 242. It should be remembered that 10 c. c. of the standard copper-solu- tion used in sugar-determinations correspond to *06757 gram of sugar of milk in its ordinary state (C 12 H 22 O n , H 2 0), but to -06419 gram of anhydrous milk-sugar, in which form this body exists in all milk-residues which have been dried at 100 C. The copper- solution used should be titrated with a standard solution of pure lactose. 260 QUANTITATIVE ANALYSIS. ASH. Milk yields between '7 and f 8 part of ash in 100. The proportion in any sample may be determined by incinerating the total residue from 10 grams of milk, or the solids-not-fat. The incineration should be conducted at as low a temperature as possible, preferably in a muffle. The alkaline chlorides in the ash will be in great measure, if not entirely, driven off by half-an- hour's exposure to a bright red heat. As there is some difficulty in producing a white ash at a dull red heat from an ordinary milk-residue, it is safer to char the residue at first, then to ex- tract the charred mass with water, and finally to burn off the charcoal from the insoluble residue. In this way we divide the ash into two portions, insoluble and soluble, for the latter is obtained by evaporating and igniting the watery extract of the charred residue. The two united constitute the total ash. Its percentage should lie somewhere between -72 and *82, a figure lower than this minimum tending to show dilution, and a figure higher than this maximum indicating the probability that common salt, sodium carbonate, borax, boracic acid, phosphoric acid, or some other so-called preservative substance has been added to the milk. It is desirable to test the milk-ash for alkalinity, and to determine the amount of chlorine present. "Wash the whole of the ash, obtained as previously directed, from the dish into a beaker by means of a little distilled water : test a drop of the solution with litmus paper; it should give a barely alkaline reaction ; an acid reaction indicates the addition of some foreign substance. To the solution add one or two drops of neutral potassium chromate solution and titrate with decinormal silver nitrate (p. 171). Calculate from the silver nitrate used the amount of chlorine, which should not exceed one tenth of the weight of the milk-ash. If any excess over -082 per cent, be found it may fairly be inferred that common salt has been added to the milk. Whey, butter-milk, and skimmed milk may be analysed as milk, but for the milk-fat determinations larger quantities must be taken. CREAM. 261 Milk which is not fresh will have undergone alterations vari- able in character and degree, which render a comparison with the same milk in its original state impossible. No system of allow- ances for such alterations can be applied with success. But milk may be preserved in a fit state for analysis by adding to it when fresh a known volume of ammonia solution. NOTE ox THE ALBUMINOIDS OP MILK. Almost the whole of the nitrogenous matters in milk exist in the form of albuminoids. But casein so-called is not the only albuminoid present, although it constitutes rather more than three fourths of the total. Albu- men is present, while there is a third substance of the same group which remains in solution when the casein and albumen have been removed. The albumen may be separated by concen- trating the clear whey from a known weight of milk which has been curdled by a few drops of acetic acid. To the evaporated liquid a little metaphosphoric acid solution is added, the mixture heated to the boiling-point and the small curd of coagulated albumen collected on a tared filter, dried at 100 and weighed. In the filtrate, further concentrated to a small bulk, a few drops of an alcoholic solution of phenol or of tannin will produce a small precipitate, which is to be collected on a small tared filter, washed with spirit, dried at 100, and weighed. CKEAM. Cream varies much in percentage composition ; when made from milk which is becoming sour, more casein is present than when the milk and the cream both remain sweet. It, however, consists essentially of minute globules of milk-fat intimately mingled with small quantities of the other constituents of milk. It may be analysed as milk, determinations of water, of solid residue, and of ash being generally alone necessary, the albumin- oids and sugar being neglected. The quantities of cream taken for the several determinations should be regulated by the propor- tions of each ingredient usually present. Thus for solid residue and fat less cream will suffice than in the case of milk, but for ash more will be needed. In drying cream it is better to pour 262 QUANTITATIVE ANALYSIS. small quantities at a time into the evaporating-dish. But more exact method involves keeping the weighed quantity of cream upon the steamer for 24 hours. Weigh into an evaporating- dish 25 grams of pure dried sand, pour a weighed quantity of cream, about 5 grams, on to the sand, mix thoroughly by the aid of a stiff platinum wire, which must be left in the dish. After drying for some hours, the dish is removed from the steamer, and the mass of cream and sand carefully broken up by the wire. The dish is now placed in the water- oven for some hours. When taken out, any fragments of sand and cream residue are detached from the wire, and the dish with its contents weighed. The solid matter contained in the cream is deduced from the total weight by subtracting the weight of the sand and of the dish. The mixed sand and residue may then be used for the determinations of casein and of milk-fat. BUTTEB. Butter contains, besides milk-fat, a considerable quantity of water and a little salt : traces of milk-sugar, of casein, and of phosphates will likewise be found in it. The percentage of water in genuine fresh butter varies between 5 and 15, the percentage of salt between -1 and -3. In salt butter the range is more extensive, the salt sometimes rising to 8 per cent., and the water to 28 per cent. : it has been stated that even 50 per cent, of water may be incorporated with butter : a percentage higher than 20 may be regarded as savouring of fraud. WATEE. 2 or 3 grams of the butter are weighed into a small dish, preferably of platinum, and containing some clean dry sand. The dish and contents are dried in an air-oven at 105 C. and weighed. The loss is water. SALT. A fresh quantity of butter, varying in amount according to whether the sample is fresh or salt, is employed for the esti- mation of common salt. The weighed quantity is transferred to a flask of about 250 c. c. capacity, and then about 100 c. c. of boiling distilled water are added. The flask is to be corked, and BUTTER. 263 the contents briskly agitated with a rotatory motion, care being taken to prevent the melted butter-fat from touching the cork. After 2 or 3 minutes' shaking, more boiling distilled water is added, so as to fill the flask up to the base of the neck. The flask is allowed to cool, and, when cold, a gentle shake will detach from it the solid cake of fat ; the solution containing the salt can now be decanted through a filter into a beaker. The cake of fat and the flask should be rinsed with a small quantity of cold distilled water, which is added to the original filtrate. The filtrate or an aliquot portion of it can now be titrated with a decinormal solution of silver nitrate, as described on page 171, 1 c. c. of which solution corresponds to 00585 gram of sodium chloride or common salt. It is advisable to test this filtrate for alkalinity before titrating it, as small quantities of alkaline carbonates are occasionally found in impure samples of butter. ASH Is determined by the ignition of a separate portion of about 5 grams of the sample ; the ignition should be as slow as possible. The ash of genuine butters will frequently be found by titration to be rather lower than the percentage of salt ; this is due to the volatilization of sodium chloride during the com- bustion of the fat ; if the ash fuses in the crucible it is probable that borax, or boracic acid, or phosphoric acid has been added to preserve the butter. A genuine butter leaves no ash other than common salt, with a trace of alkaline or earthy phosphates : any ash insoluble in water indicates the presence of such an adulte- rant as soapstone or steatite, a hydrated magnesium silicate. CASEIN. Probably the simplest plan for determining the casein in butter, when it is not desired to make a direct determination of nitrogen by combustion with soda-lime, is the following : 5 grams of butter are weighed into a tared filter contained in a funnel supported by a triangle on a beaker. The arrangement is placed in a hot drying chamber, when most of the fat will soon filter into the beaker. Then the filter is removed from the funnel, folded so as to prevent loss of curd, and placed in a Soxhlet extractor, where it is exhausted with ether or petroleum spirit. 264 QUANTITATIVE ANALYSIS. The filter and contents are dried in the water-oven until constant and then weighed. Deduct the tare of the filter from the gross weight, the remainder will be the casein and mineral matter. The filter and contents are to be ignited at as low a temperature as possible ; the loss in weight multiplied by 20 gives the per- centage of casein. FAT may be calculated from the amount required to make up 100 parts when the ascertained percentages of water, casein, salt, and other mineral matters, if any, are added together. It is, how- ever, much more difficult, although at the same time much more important, to ascertain whether this fat is genuine butter-fat or the fat known as margarine. As the fatty part of butter is not only its chief constituent, but that in which reside the chief differences between the genuine and the spurious kind, it is to this constituent that our attention is chiefly given. Of all the processes for ascertaining whether the fat of a sample of butter is milk-fat or some other kind, the most certain is known as the saponification process. In this, as in other experiments having the same object, the first requisite is a supply of pure, dry, clarified butter-fat : to secure this a small quantity of the sample of butter is melted in a beaker on a steamer, and then filtered through dried Swedish paper, the filtration being per- formed in a water-oven. Sometimes a perfectly clear sample of fused butter-fat may be obtained without filtration ; but in all cases the fat should not be heated for any length of time, or to a temperature more than a few degrees above its melting-point. When a sufficient supply of the clarified butter-fat has been pre- pared it may be weighed in a small beaker containing a pipette. The quantity required for each experiment may then be removed by the pipette, the beaker, pipette, and remaining fat being after- wards weighed again ; the second weight deducted from the first gives the amount of fat taken for one experiment. We give four methods of applying the saponification process to the detection and estimation of the foreign fat in samples of butter, so-called. The first process, devised by Koettstorfer, is a purely volumetric one : the second process (Hehner's simplified) BTJTTER. 265 may be quickly performed and gives the percentage of " insoluble fatty acids " very accurately. In the third process, originally devised by Keichert and subsequently modified by Meissl and Wollny, the volatile acids are alone determined. The fourth process is that invented by Hehner. Koettstorfer's Saponification Method. 2-5 grams of clarified butter-fat are weighed into a small wide- mouthed flask and 25 c. c. of seminormal alcoholic solution of potassium hydrate added. The mixture is boiled on a water-bath under a vertical condenser for half an hour, 1 c. c. of phenol- phthalein solution added and the solution titrated in the flask, while hot, with seminormal hydrochloric acid, care being taken to avoid access of air, as carbonic acid interferes with the accuracy of the result. The quantity of seminormal hydrochloric acid required to exactly neutralize 25 c. c. of the alcoholic solution of potassium hydrate is ascertained by a blank experiment made under pre- cisely similar conditions. The number of c. c. of seminormal hydrochloric acid used by the butter-fat under examination, deducted from the number of c. c. used in the blank experiment, will give the quantity of semi- normal potassium hydrate solution required for the saponification of the 2-5 grams taken ; this figure divided by 2 will give the number of c. c. of normal alkali, therefore : as No. of c. c. normal alkali : 1000 = 2-5 : x. x = the saturation- or saponification- equivalent, or the number of grams of fat capable of being saponified by 1 litre of normal alkali. The range in butter-fat varies from 241 to 253, in mar- garine from 285 to 290. The result may also be expressed in grams of potassium hydrate required to saponify 1 000 grams of fat, thus : as 2-5 : 1000 = No. of c. c. normal KEO x -056 : x. Butter gives from 221-5 to 232-4 ; margarine from 193-5 to 196-5. Rapid Saponification Method. 5 grams of the clarified fat are weighed into a glass bason QUANTITATIVE ANALYSIS. 4| in. in diameter and melted on the water-bath. About 1 gram of stick sodium hydrate is added and then about 1 c. c. of water. After the lapse of a minute or two 4 c. c. of 60 O.P. alcohol are poured in, and then the contents of the bason are well stirred with a glass rod until the fat has assumed a gelatinous appear- ance. The resulting soap is evaporated to complete dryness with occasionally stirring, to free it from alcohol. The saponifi- cation and subsequent evaporation will occupy about half an hour. The soap is dissolved in the bason with boiling distilled water : the solution should be perfectly clear. Dilute sulphuric acid is added, in quantity sufficient to completely decompose the soap. The insoluble fatty acids will rise to the top in a white semi-solid condition : after a short time they become liquid and are to be decanted on to a tared Swedish filter previously well wetted with boiling distilled water. Great care must be taken to wash the bason and rod free from fat ; this is readily done if abundance of boiling distilled water be used. The washing of the fatty acids on the filter with boiling water is continued until 6 ounces of the filtrate, to which a few drops of phenol-phthalein solution have been added, is coloured by the addition of not more than 0*2 c. c. of a decinormal solution of sodium hydrate. Usually more than a litre of water is required for the complete washing of the insoluble fatty acids obtained from 5 grams of the clarified fat. They are now allowed to cool in the filter, and then the filter with its contents is removed to a small tared glass bason and dried on the water-bath until the melted fat soaks into the filter- paper. To assist in expelling the last traces of water about 4 to 8 c. c. of absolute alcohol are poured over the paper, and the heating is continued on the water-bath until the alcohol has evaporated. The bason and contents are dried in the water-oven until constant in weight, and then they are finally weighed. Prom this weight is deducted the tare of the bason and filter ; the result, multiplied by 20, gives the percentage of Insoluble Fatty Acids yielded by the clarified butter-fat. BTJTIEK. 267 The Reichert-Meissl-Wollny Method. 5 grams of the clear fused butter-fat are accurately weighed into a 300 c. c. flask of globular form and having a neck about 7 or 8 centims. long and two 2 centims. wide, 2 c. c. of a 50 per cent, sodium hydrate solution (which must be preserved and drawn from so that not a trace of carbonic acid can be absorbed) together with 10 c. c. of 96 per cent, alcohol are added to the butter- fat and the mixture is heated, in connection with a reflex con- denser, for 15 minutes on a water-bath. The alcohol is then distilled off, the flask being heated for at least half an hour. With every precaution 100 c. c. of boiling water are added, and the flask is heated until the soap which has been formed is completely dissolved. A few small fragments of tobacco-pipe and 40 c. c. of sulphuric acid (25 c. c. H 2 S0 4 in 1 litre of water) are added ; the flask is at once connected with a condenser by means of a glass tube 7 centims. wide, and having, at a distance of 1 centim. above the cork, a bulb of 2 or 2| centims. in dia- meter. The tube is bent immediately above the bulb upward at an oblique angle, and extends in this direction for 5 centims. ; it is then bent downward, also at an oblique angle, and then is connected with a condenser by means of an india-rubber tube. The flask is heated, by means of a very small flame, until the insoluble fatty acids are completely fused : 110 c. c. are then distilled off into a graduated flask, the distillation lasting 30 minutes ; the distillate is mixed by agitation and 100 c. c. of it are filtered off and transferred to a beaker. 1 c. c. of phenol- phthalein test solution (-5 gram to 1 litre of proof spirit) is added and the titration with decinormal baryta solution proceeded with. To the volume of baryta solution used one tenth is added and the figure obtained in a corresponding blank experiment subtracted the latter should not exceed -33 c. c. It is necessary in order to secure accurate results in this process that carbonic acid should be excluded, particularly from the strong sodium hydrate solution, and that the distillation of the volatile acids should proceed at the same rate and occupy the same time in all experiments. 268 QUANTITATIVE ANALYSIS. Hehner's Saponification Method. This process is conducted thus : 5 grams of the clarified fat are weighed into a glass bason, melted on the water-bath, and 50 c. c. of a semi-normal solution of sodium hydrate in alcohol added. The contents of the bason are stirred with a glass rod, until the fat has assumed a gelatinous appearance and has become a soap. This soap is then treated with enough distilled water to fill the bason two thirds. The mixture is now allowed to evapo- rate on the water-bath. The soap thus freed from alcohol, but con- taining an excess of alkali, is dissolved in hot distilled water, and transferred to a flask of about 500 c. c. capacity. Every particle of soap must be rinsed from the bason and rod ; but the total volume of soap solution and washings should not exceed 300 c. c. The soap solution is heated most conveniently by holding it under a vertical condenser, using an Argand burner as the source of heat, and protecting the hand by a thick glove. When the solution is almost boiling, 27*5 c. c. of normal sulphuric acid are added, and the heating continued, with constant rotatory agitation of the contents of the flask, until the decomposition of the soap is complete : the insoluble fatty acids will now have risen to the surface, and will form a layer above the acidulated liquid. When this oily layer is continuous and complete, the flask is filled up to the beginning of the neck with boiling distilled water, rotated so as to bring the oily matter together, and set aside to cool. "When cold, the insoluble fatty acids will be found as a wax-like cake, which can be detached from the walls of the flask by a slight shake. The soluble fatty acids (characteristic of true butter or milk-fat) and the glycerin are found in the watery liquid. This is decanted through an English filter-paper into a Winchester quart. To wash the cake of solid acids a small quantity of cold distilled water is first poured into the flask, which is to be rapidly, but not violently, shaken for a few seconds ; then this water is to be decanted through the same filter into the large bottle. To the flask containing the greater part of the solid acids some boiling distilled water is now added, and the contents thoroughly agitated, the flask being heated to 80 or 90 C. over BUTTER. 269 a flame. Then the flask is once more filled up with boiling dis- tilled water, allowed to cool, the cake of solid acid detached as before, the water poured off and added to the filtrates, and, finally, the cake rinsed once more with cold water. The insoluble fatty acids will now be partly in the flask and partly on the filter : the flask, which contains the greater proportion, is placed in the drying chamber or water-oven. It should be withdrawn about every hour, and a small quantity of air sucked through the neck by means of a bent tube, so as to remove the watery vapour. After 3 or 4 hours it may be weighed ; and the tare of the flask being deducted, the weight of the larger part of the insoluble acids will be obtained. The filter, with its fatty acids, must be allowed to dry in the air, or over oil of vifcroil in vacuo. Then it is placed on a triangle over a small beaker and put into the water-oven. This beaker serves to catch any drops of melted fatty acids which may pass through the filter. When the filter is quite dry, it is removed from the oven, very thoroughly washed with ether, and the ethereal solution, together with any melted fatty acids that may have previously dropped into the beaker, evaporated at a gentle heat, and the residue and beaker weighed. When from this gross weight the tare of the beaker has been deducted, the weight of the fatty acids caught on the filter will be obtained. This weight, added to that (previously ascertained) of the bulk of these acids in the flask, and the sum multiplied by 20, gives the percentage of insoluble fatty acids yielded by the clarified butter-fat. If this percentage be above 88*8, or at most 89, it is clear that margarine or some similar body has been present in the sample of butter examined. If the proportion reach 93 to 95 the fat must have consisted wholly, or almost wholly, of margarine or of other adulterants. It has been found that 100 parts of the glycerides of which pure milk-fat consists yield, after saponification, from 87-8 to 88-8 parts insoluble fatty acids, and 6 to 8 parts soluble acids. The insoluble acids are stearic, palmitic, and oleic ; the soluble are butyric, caproic, caprylic, and capric,-^the last three in smaller quantities. The soluble acids can be got in mere traces 270 QUANTITATIVE ANALYSIS. from oleomargarine, groundnut-oil, and the other fatty adulterants of butter, which, on the other hand, yield no less than 94 to 95 per cent, of the insoluble acids. There are, however, two reasons why this process, though it yields exact results when due care is taken, must-not be held to decide authoritatively as to admixtures or percentages of margarine of less than 10 / . One of these reasons lies in the natural variations (due to season, food, breed, &c.)in the composition of true milk; the other depends upon the variations in the composition of the adulterants. Nor should it be forgotten that the manufacturers of " butterine," " bosch," and other artificial butters usually add to the clarified animal fat, prepared in America, New York, Vienna, Paris, and other centres of production, a not insignificant quantity of genuine butter and of milk. By churning together GO parts of oleo- margarine, 28 of milk, 10 of genuine butter, and 2 of earthnut-oil (from Arachis liypogcea), a " bosch " is obtained, the clarified fat of which contains between 1 1 and 12 per cent, of genuine milk-fat. For this cause the clarified fat of artificial butter frequently yields 1 per cent, less solid fatty acids than simple oleomargarine. If the solid fatty acids obtained in processes 2 or 4 above have been thoroughly washed so as to be free, not only from the easily soluble butyric acid, but from the difficultly soluble caproic, caprylic, and capric acids, we shall find them to amount to 87*8 to 88*8 parts from 100 parts of pure butter-fat. Anything about 89 per cent, is very suspicious, and indicates probable adulteration : 89*5 is certainly bad. We may take 88'5 as the average percentage of insoluble fatty acids obtainable from the fat of genuine butter, and 95 as that of margarine, the difference between these numbers equalling 6*5. This figure, divided into the difference between 88'5 and the percentage of insoluble fatty acids found in an actual experiment, gives, when multiplied by 100, the percentage of margarine : b'5 A=% of Insoluble Fatty acids in sample under examination. B = / -of Insoluble Fatty acids in pure butter-fat. C = / of Margarine in the clarified fab. We may now return to the filtrate (in Hehner's method) con- taining the soluble acids, which, however, need not be directly determined if the previous results have shown the sample to be genuine. If not, the filtrate is made up to a definite volume, BTJTTEB. 271 and an aliquot part, say J, titrated to find the total acidity. A quantity of the alcoholic solution of sodium hydrate, exactly corresponding to that which was used for the saponification analysis, must be mixed with the same quantity of the same acid as that which was used for decomposition of the soap, boiled and titrated. The figure thus found represents the excess of acidity due to the acid added. Deducting this from the result obtained by the titration of the filtrate, we get an amount of acidity corresponding to the proportion of soluble fatty acids. This may be calculated to butyric acid with an equivalent of 88, and should not fall below 6-5 / . Samples of pure butter kept in well-corked bottles undergo very little change ; but if the butter has been exposed to the air for 6 or 8 months considerable change sometimes takes place. A second process is as frequently used for testing butter-fat as that just described, but it is not so trustworthy. It consists in taking the specific gravity of the clarified fat at a temperature of 37*8 C. (100 Fahr.). It is necessary to use a pear-shaped sp. gr. bottle provided with a very accurately fitting thermometer-stopper. When the exact capacity of the bottle in c. c. of distilled water at 37'8 C. has been ascertained, it is dried and filled with the clarified butter-fat to be tested, which should have been previously melted and raised to a temperature of 35 C. The thermometer- stopper must be loosely placed in the bottle, which is to be plunged up to its neck in a water-bath at a temperature of about 39 C., and to be kept in gentle movement until the tem- perature reaches 37'8 C. Then the thermometer- stopper is pro- perly inserted, the excess of fat at once removed by filter-paper, the bottle dried, and weighed while warm. The observed or " actual density " (as the figure obtained in this determination is called) is found by dividing the weight of the fat by the weight of the water which the same bottle has been ascertained to hold at 37*8. The term actual density, instead of specific gravity, is adopted, because the comparison is made with water at 37*8 in- stead of with water at 15*5. Clarified butter-fat has an actual density of from 910-5 to 911'5, assuming water to be 1000, whereas oleomargarine and most other fats likely to be used as adulterants have actual densities varying between 904" and 907. It may be added that the specific gravity of pure butter-fat at a temperature of 15 0< 5, averages 930*7 when compared with water at the same temperature. The specific gravity of butter-fat, at any temperature above its melting-point, may be taken by means of Westphal's hydrostatic balance (see p. 257). 272 QUANTITATIVE ANALYSIS. Borax and boracic acid are frequently found in samples of fresh butter. They are best tested for in the ash contained in a porcelain bason. To this a little concentrated sulphuric acid is added, and then about 10 c. c. of 60 per cent, alcohol. The bason is warmed on the water-bath, and the flame of a Bunsen- burner of steatite is brought down upon the surface of the mix- ture : if boron compounds be present, the characteristic green flame-colouration will be produced. Or the boric ether evolved may be condensed in the form of a white sublimate upon a clock-glass placed upon the bason as a cover. CHEESE contains the same ingredients as milk, sugar, however, being present in very small proportions. Cheese contains also a variable quantity of common salt, a notable percentage of phosphates, and a little colouring-matter. When undergoing the process of decay, many additional compounds are formed, chiefly from the breaking up of the casein. The only determinations which are necessary in ordinary cheese-analysis are those of water, fat, casein or albuminoids, and ash or mineral matter. Full directions for these estimations will be found on previous pages devoted to the ana- lysis of milk, cream, and butter ; but a few special notes and hints specially applicable to cheese may be serviceable. WATEK. About 5 grams of the cheese, cut, before weighing into thin shavings, or else grated, are dried in a small tared platinum dish in the water-oven till practically constant in weight. It has been found that a small quantity of cheese can be more completely dried than a large one, and that it is better to dry several portions of 5 grams separately for the determination of different constituents rather than attempt to prepare at once a considerable amount of dry residue. In order to obtain the residue in a satisfactory condition for the subsequent operations, it is a good plan to pour about 5 c. c. of absolute alcohol upon each quantity of 5 grams of cheese weighed out, and to leave the mixture for ^ an hour before drying it in the water-oven. FAT. 5 grams of the cheese, prepared and treated exactly as CHEESE. 273 described in the last paragraph, are used for this determination : enclose the weighed quantity in a filter-paper properly folded, and place it in the extractor of Soxhlet's apparatus. Dry ether should be used, the operation of extracting the fat being conducted in the usual manner ; the ether is finally distilled off from the flask, the residue dried in the water-oven and weighed. If petroleum-spirit be used, it should have been redistilled under 60 C. CASEIN. The albuminoids in cheese are estimated in most analyses merely by difference, but they may be determined as in a milk- analysis or else by means of a nitrogen-combustion with soda-lime, not more than '5 gram of the dried substance being taken. In decayed cheese, however, the nitrogen exists in other forms than the albuminoid; it may therefore be desirable to adopt the phenol-method (see p. 237) for determining the true or albuminoid nitrogen. STJGAR. The amount of milk-sugar in ordinary cheeses is not important, but it may be useful to determine its percentage in cream-cheeses. For this purpose the residue remaining in the Soxhlet extractor, after the removal of the fat, may be employed. It should be transferred to a bason, warmed and agitated with water and the whole poured on a plaited filter and washed. In the united filtrate and washings, the lactose is determined by Fehling's solution, as described on p. 239. It has been recom- mended in this case to weigh the copper suboxide produced. LACTIC AND BUTYEIC ACID. The acidity of a sample of cheese may be determined by triturating 5 grams with 10 c. c. of alcohol and a few drops of alcoholic solution of phenol-phthalein and then titrating with the sodium hydrate solution employed in nitrogen determinations until a faint pink colour is produced : 1 c. c. of that solution corresponds to '00703 gram of lactic acid. The acid present is assumed to be lactic although butyric acid is also present in old cheeses. AMMONIA. Besides the albuminoids and certain organic com- p3 unds derived from them (leucine &c.), various salts of ammonia 274 QUANTITATIVE ANALYSIS. occur in old, and especially in decaying cheese. The ammonia in them may he approximately estimated by distilling with magnesia and distilled water a small quantity of the original undried cheese after grating it. The ammonia in the distillate is determined by the Nessler reagent according to the process given under the head of the Analysis of Waters (p. 211). ASH. The residue from 5 grams of cheese, dried, as previously described under " Water," is gently calcined until the mass is thoroughly charred. It is then exhausted with hot water, the liquid being afterwards filtered, evaporated to dryness, gently ignited and weighed. The residue consists of the soluble part of the ash. The insoluble part may be obtained by igniting the charred mass and the filter until they have become quite white. The total ash is obtained by adding together the amounts of the soluble and of the insoluble ash. PHOSPHATES. The most important of the natural constituents of the ash of cheese are the phosphates. These are best deter- mined by the molybdic-acid method in the entire ash of 5 grams of cheese, which, for this purpose, may be directly burnt to a white ash. COMMON SALT. The soluble ash, obtained as previously de- scribed, is dissolved in water, and the solution, after having been stirred up with a little calcium sulphate to remove soluble phos- phates, is filtered and titrated with decinorinal solution of silver nitrate, using potassium chromate as the indicator (see p. 171). The addition of oleomargarine (now legally termed margarine in this country) is frequently made to the curd from which certain American cheeses are manufactured. This adulteration can be detected, and its amount estimated, by a modification of Koettstorfer's method. The first step is to separate, in a pure state, a few grams of the fat from the sample of cheese under examination. To effect this, about 45 grams are melted in a bason on the water-bath, and 8 grams of pure warm sand stirred in. The free acid present is then exactly neutralized with the calculated amount of decinormal sodium-hydrate solution this amount being ascertainable from the datum derived from the de- termination of free acid previously made. 8 grams more of sand CHEESE. 275 are now added, and the whole mixture dried in the water-oven with frequent stirring. When dry the contents of the bason are transferred to a Soxhlet extractor, and the fat extracted with dry ether in the usual way. With the pure dry fat thus obtained a saponification experiment is made. 2 grams of this melted fat are dropped carefully into a tared wide-mouthed flask of rather more than 200 c. c. capacity the fat must all fall on to the bottom of the flask. A blank experiment, without any fat, is made in all respects in the same manner as hereinafter directed. Into each of the flasks (one with, and the other with- out fat) 25 c. c. of a normal solution of potassium hydrate in alcohol of '835 spec. grav. (56-1 grams per litre) are very accurately measured, taking care to drop the alkali straight on to the bottom of the flasks. The mouths of the flasks are closed with watch-glasses, and the contents brought to the boiling-point and kept in gentle ebullition for 15 minutes. 10 c. c. of alcohol with a few drops of alcoholic phenolphthalein solution are added to each flask, and the contents titrated with seminormal hydrochloric acid (18-25 grams of real HC1 per litre) until the colour just changes from pink to yellow. The amount of real KHO con- sumed in saponifying the fat is obtained and expressed in milli- grams for each gram of fat taken the correction derived from the blank experiment having been made. Genuine cheese-fat, that is milk-fat, should consume not less than 22'2 milligrams of KHO per gram of fat. If, however, the KHO consumed lies within this limit, then the soluble and insoluble acids in another portion of the extracted fat should be determined by Hehner's process. This should not yield more than 89 per cent, of inso- luble acids ; but if that limit be distinctly passed, the calculation as to the amount of adulteration should be made upon a basis of 88'5 per cent, (see p. 270). The colouring of cheese is almost always accomplished by means of annatto (from Bioca Orellana} ; to this no objection can be taken. Chrome-yellow (lead chromate) has been occasionally used for colouring the outside of American cheeses ; but it is ex- tremely rare to find it in the body of the cheese, at least in this country. BKEAD. The principal adulterants found in bread are alum, rice, and potato-starch. Eice is frequently used in small quantities in order, 276 QUANTITATIVE ANALYSIS. according to the bakers, to improve the character of the crust ; it is seldom used in excessive quantity. Potato-flour and potato-starch are used to increase the amount of moisture which is retained in the baked bread. It is im- possible to detect an admixture of any small percentage of rice or potato by chemical means after the flour has been made into bread. These adulterations must be searched for by the micro- scope ; and even with this instrument it is often impossible to de- tect them, because the character of the starch- granules is greatly altered by heat. The only adulterant of any serious importance is alum ; and the proportion of this which has been used has to be estimated by the determination of one of its constituents, alumina. The quanti- tative estimation of alumina in bread is a tedious process, especi- ally when only small proportions have been used ; and it is there- fore desirable to employ the following qualitative process when- ever possible. Qualitative process l>y logwood. This process aims simply at proving the absence of alum. In order to carry it out, a tincture of logwood is made by steeping logwood chips or cuttings in 60 O.P. alcohol or methylated spirit, in the proportion of 5 parts of logwood to 100 parts of spirit. This tincture can be kept with- out change if carefully stoppered. To use the test, one part of the tincture is mixed with three parts of a saturated solution of ammonium carbonate, and the mixed solution diluted with 3 times its bulk of water. The diluted solution is poured over the bread to be examined ; this should be free from crust, or if the sample bo very small the crust should be carefully scraped. If the bread contains alum even in such a small proportion as 4 grains to the 4-pound loaf, the sample will, after standing for half an hour, assume a dark violet-blue tinge. If salts of magnesia or certain other earthy salts which are occasionally added to bread be pre- sent the sample will assume a more purple tint ; while if the bread be free from alum and these foreign salts the colour will remain of a full reddish plum-colour, gradually fading to a very dirty pink without any trace of purple or blue. BKEAD. 277 In applying this process to flour it is more convenient to make a small portion of the flour into a thick cream with cold water and then add the logwood tincture and solution of ammonium carbonate so as to reduce the whole to the consistency of thin cream. When it becomes necessary to determine the proportion of alum present, the following process must be adopted: 100 grams of the bread are carefully burnt to ash in a platinum dish. This ash is fused with 3 or 4 times its weight of white flux (mixed car- bonate of soda and potash) which has been previously tested for alumina : the fused mass, when cold, is moistened with hydro- chloric acid and evaporated to dryness, the residue is redissolved in acid and the silica filtered off. The filtrate is treated with ammonia until a slight permanent precipitate is produced, which is then redissolved by a few drops of hydrochloric acid. Ammonium acetate having been added, the filtrate is set aside overnight to precipitate, and is then filtered ; the precipitate contains all the alumina freed from, a large proportion of the foreign matters which would have rendered the estimation untrustworthy : this precipitate after having been washed is redissolved on the filter in hydrochloric acid. The solution is boiled for a few minutes with a solution of sodium bisulphite, caustic soda is added in excess, and the solution boiled again. By this process the iron is separated in the form of magnetic oxide, which is separated by filtration, while the alumina contained in the alum (if any has been added) is retained in solution ; the filtrate is acidified again with hydrochloric acid, ammonium acetate added in slight excess, and the solution allowed again to stand overnight. If any alu- mina is present, a precipitate will form, which will consist of pure aluminium phosphate, formed by the combination of the phos- phoric acid present in the flour with the traces of alumina con- tained in the wheat and the alumina contained in any alum added. This precipitate is filtered off, washed, dried, ignited, and weighed. By multiplying the weight of the precipitate thus obtained by 542 we obtain the number of grains of potash-alum contained in two pounds of the flour examined, or by jmultiplying by 1084 we obtain 278 QUANTITATIVE ANALYSIS. the number of grains of potash-alum contained in a 4-pound loaf, which is the mode in which the results of the analysis are usually reported in this country. The first multiplier (542) is more suitable to flour, and the second (1084) to bread. Note. As a small quantity of alumina is sure to be present in the reagents employed, while further traces will be derived from the glass and porcelain vessels used in the analysis, it is better to make a blank analysis as nearly as possible with the same ma- terials, quantities, and vessels as those employed in the actual analysis. The alumina found in the former determination is deducted from that of the latter : the difference is that due to alum. Note, however, that traces of alumina may be derived from earthy matters adherent to the original corn, or from mineral dust from the attrition of the mill-stones ; but since the general introduction of steel-rollers into flour-mills the last source of aluminous impurity has generally ceased to exist. As, however, the percentage of A1 2 3 in such impurities is very low, any con- siderable trace of this body thus originating will involve the presence of several times its own weight of other mineral matters, which will therefore notably increase the percentage of ash, other than salt, in the bread. It is customary to deduct, from the alum found as above described, 6 grains per 4-lb. loaf, reporting the remainder as added alum. This deduction probably suffices to cover any usual natural or accidental aluminous im- purity. Newly baked bread, when cold, seldom contains less than 40 per cent, of water, often more. The moisture, dextrin, sugar, starch, cellulose, alcohol, and true albuminoids in bread may be readily determined by processes already given in the Guide (see pp. 45-47 and 223-253). INDEX. Acetic acid prepared, 22. tested, 22. Acid, acetic, 72. carbolic, 73, 237. citric, 74. hydric, or water, 23, 73. hydrochloric, 72. hydrofluoric, 74. hydrofluosilicic, 74. hyclrosulphuric, 73. lactic, 273. nitric, 72. oxalic, 73. phosphoric, 150, 157. standard, 135. sulphindigotic, 73. sulphuric, 73, 135. sulphurous, 17. tartaric, 74. Acids, schemes for, 108-112. special tests for, 84, 92, 112. Adams's coils, 256. Albuminoids determined, 229, 230, 237, 247. in foods, 229. Alcohol, 72. absolute, 250. estimated, 248. in wine, 250. percentages, 249. specific gravity, 249. tables, 249. Alizarin, 50. Alkali, standard, 137. Alkalies, 60, 65, 66, 67, 107. AUoy of copper, 26. lead, 29, 30. silver, 27. tin, 26, 29. Alloys, examination of, 116. Alum, 36. in bread, 276. Alumina determined, 151. in flour, 277. in manures, 151. in soils, 195. test for, 276. Aluminium, 59, 83, 104. plate, 92. Ammonia, 19, 67, 90. in guano, 166, 167. in soils, 167, 188. ,, in water, 211. prepared, 19. Ammonium, 60. acetate, 67. carbonate, 67. chloride, 66. citrate method, 160. hydrate, 67. molybdate, 67. oxalate, 67. phosphate, 67. salts, 10, 66, 176. sulphate, 10. sulphide, 66. tests for, 84, 90. Analysis, method of, 87. ,, of insoluble silicates, 113, 199. of insoluble substances, 113. Animal charcoal analysed, 146. Antimonicum, 81. Antimoniosum, 81. Antimony, 59. detected, 26, 30, 101. Apatite analysed, 147. Arsenic, 59, 81. detected, 25, 26, 90, 91, 101. 280 INDEX. Arsenic, Fleitmann's test for, 102. Marsh's test for, 101. mirror, 25. Eeinsch's test for, 102. stains, 26, 101. trioxide, 25. heated, 35. Arsenicum, 81. Ash of plants analysed, 251. examined, 48. prepared, 251. Atomic weights, 63. Balance, 124. weights for, 125. Westphal's, 257. Barium, 60, 83, 106. . carbonate, 68. chloride, 68, 86. hydrate, 68. nitrate, 68. sulphate, 36, 133. Baryta, estimation of, 133. Beer, analysis of, 248. examined, 54. Beet manure, 164. root, 235. sugar, 44. Bias, agricultural, of chemical study, 3. Biphosphate of lime, 156, 159. Bivinculant elements, 61. Blood examined, 52. Blowpipe experiments, 34, 35, 89-92. Bone analysed, 139-146. examined, 51. Bone-ash analysed, 147. tested, 38. Bone-black analysed, 147. Bone-dust analysed, 139. Bone-shavings analysed, 139. Bones, boiled, analysed, 139. Borax, 66. beads, 37, 92. Bread, alum in, 276. analysed, 275. ash of, 278. blue vitriol in, 47. dextrin in, 46. examined, 46, 275. starch in, 47. water in, 46. Brewers' grains, 235. Bromine, 61, 93. Bronze coin, 26. Burette, 124. Butter, analysis of, 262-272. artificial, 264. examined, 45. fatty acids of, 269. fusion-point of, 271. salt in, 262. water in, 262. Calcium, 60, 83, 106. ,, carbonate estimated, 131. chloride, 69, 85. hydrate, 69. oxide, 39, 69. phosphate, 140, 150. sulphate, 40, 69, 106. Capsule metal, 29. Carbolic acid, 73, 237. Carbon, 62, 64. dioxide estimated, 198. in breath, 21. in soils, 185, 198. prepared, 20. Carbonating, 132, 140, 141. Care in testing, 79. Carolina phosphate, 155. Casein, 44, 254, 261, 263, 273. Cellulose changed into sugar, 43. dissolved, 53. estimated, 226, 239, 248. examined, 53. recognized, 53. precipitated, 53. Chalk, action of acids on, 8, 40. Charcoal, experiments on, 36, 91. Cheese, analysed, 272. adulteration of, 274. examined, 45. Chemical dissection, 56. Chlorides in water, 24, 210. Chlorine, 60, 64. estimation of, 148, 171. Chlorophyll, 49, 246. Chlorous elements, 60. Chromates, 32, 65. Chromium compounds, 32. Citric acid, 74. method, 190. Clay heated, 182. INDEX. 281 Clay in soils, 182, 184. ,, separated from sand, 13, 183. Cobalt nitrate, 70. Coin, bronze, 26. silver, 27. Coloured flames, 37, 91. Combustion for nitrogen, 141. Common salt analysed, 171, 175. in butter, 262. ,, in cheese, 274. Copper, 59, 64. ammoniacal solution, 53. hydrate method, 238. prepared, 238. reactions of, 77. special tests for, 77. suboxide, 44. sugar-test, 44, 70. sulphate, 9, 70. zinc-couple method, 214. Coprolites analysed, 148-155. made soluble, 38, 156. superphosphate from, 38, Cotton examined, 53. Cream analysed, 261. Crucible, 127. Crystallization, 9. Cubic centimetre, 123. inch, 124. Dahlia-flowers, 49. Decantation, washing by, 13. Density, 11. Desiccators, 128. Dextrin, test for, 45, 46. Diamond, 62. Dissolved bones tested, 38. Distillation of alcohol, 248. water, 24. Doubtful elements, 63. Dyad non-metals, 61. Elements, 58-64. atomic weights of, 63. symbols of, 63. table of, 63. Elutriation, 181. Equations, 57. modes of writing, 57, 78. Ether, 72. Ethyl acetate, 93. Ethyl hydrate, 72. oxide, 72. Experiments, uses of, 1. Fehling's solution, 70, 239, 259. Ferric chloride, 70. oxide determined, 152. volumetri- cally, 153. Ferricum, 82. Ferrosum, 82. Ferrous compounds in soils, 192. sulphate, 69. as a test, 22, 93. Fibre estimated, 226. Fibres distinguished, 52. Filtration, 7. Flesh examined, 51. Fluorine, 61. detected, 93, 110, 147, 149. expelled, 147. Fur in boilers, 21. Fusion method, 155. with alkaline carbonate, 113. ,, with baryta, 201. Galvanized iron, 31. Gas-ammonia, 176. Gelatin heated, 35. Gold in silver coin, 29. ,, coin, specific gravity of, 11. Grain analysed, 233. measures, 124. weights, 124. Gram weights, 125. Graphite, 62. Gravel in soils, 180. Griess's method for nitrites, 216. Group I. Acid radicles, 85, 109. II. 86,110. III. 86,111. Special tests for, 86, 89-95. Group I. Basic radicles, 80, 98. II. , 81,98. III. , 82,102. IV. , 83, 105. V. 84, 107. Group-tests, use of, 77 87, 97. Guano analysed, 165. fusion method for, 155. Guide, mode of using this, 3, Gum-arabic tested, 46. 282 INDEX. Gypsum, 9, 40. heated, 35. Haemoglobin, 52. Hardness of waters, 217. Hay analysed, 233. heated, 35. Hehner's saponification method, 268. Hour-glass desiccator, 128. Hydrofluoric-acid method, 200. Hydrogen, 58. as reducing agent, 153. prepared, 14. Indigo, dyeing with, 50. ,, test for nitrates, 22. Iodine, 61, 64, 93, 110. Iron, 59, 64, 82, 104. detected, 31, 82, 104. salts, 69. sulphate, 69. sulphide, 70. tubes for combustions, 146. volumetric estimation of, 153. Kainite, 173. Kilogram, 123. Kjeldahl's nitrogen method, 230. Koettstorfer's saponification method, 265. Lead, 59, 80, 98. acetate, 70. ,, heated, 36. action of water on, 222. detected, 30, 98. salts of, 70, 98. tests for, 80, 98. Leaves, analysis of, 245. ash of, 48, 247, 252. > drying of, 246. Lime, experiments with, 39. estimation of, 131, 141. in soils, 41, 191, 196, 203. in water, 24, 210. Limestone, analysis of, 202. Liquors, fermented, 248. Litmus paper, 75. solution, 75. tested, 50. Litre, 123. Loam, 42. Madder examined, 50. Magnesia, estimation of, 132, 153. mixture, 69. Magnesium, 60, 84, 107. and ammonium phos- phate, 132, 134. pyrophosphate, 132. sulphate, 69. heated, 36. Malt extract, 234. Manganates, 33. Manganese, 59, 82, 104. dioxide, 196. hydrate, 34. Mangolds, 235. Manures, analysis of, 139-177. Margarine, 264, 265, 270. Measuring, precautions in, 127. Mercuric chloride, 71. oxide, 71. Mercuricum, 81, 100. Mercurosum, 80, 98. Mercurous nitrate, 70. Mercury, 59. Metals, 59, 64. Method, acid and alkali, 228. Adams's Coil, 256. ,, ammonium citrate, 160. chlorine, volumetric, 171. baryta fusion, 201. citric -acid, 190. copper-hydrate, 238. copper-zinc couple, 214. direct potash, 173. fusion, 155. Griess's nitrite, 216. Hehner's saponification, 268. hydrofluoric acid, 200. indirect potash, 174. iron, volumetric, 153. Kjeldahl's nitrogen, 230. Koettstorfer's saponifica- tion, 265. molybdic-acid, 189. oxalic-acid, 150. perchloric-acid, 175. phenol, 237. potassium-chlorate, 229. Reichert's saponification, 267. Ruffle's nitrogen, 145. 283 Method, sulphurloacid, 199. sulphuric-acid (fibre), 228. uranium gravimetric, 168. volumetric, 168. Metre, 123. Milk, adulteration of, 255. albuminoids of, 254, 258. analysis of, 253-261. ash of, 260. examined, 44. fat of, 254, 256. solids-not-fat, 254. sugar of, 259. total solids, 254. Modes of identification, 56. Molybdic-acid method, 189. Monad metals, 60. non-metals, 60. Monocalcic phosphate, 38, 156, 162. estimated, 157. Mucilage in linseed, 233. Myosin, 51. Navassa guano, 155. Nessler's test, 24, 71, 211. Nesslerizing, 211. Nitrate of potash, 170. soda, 170. Nitrates in soils, 187. waters, 214. Nitric acid prepared, 21. tested, 21. Nitrites determined, 216. Nitrogen, 61. estimated, 141, 187. in guano determined, 167. pentoxide determined, 172, 187, 214. Nomenclature, 122. Oilcake, 223. ,, albuminoids in, 229. ash in, 231. fibre in, 226. ,, impurities in, 232. oil in, 202. starch and sugar in, 232. Organic matter in soils, 186. water, 24, 207, 208. Ossein, 51. Oxalic-acid method, 150. Oxidation, 32, 33. Oxygen, 61. mixture, 16. prepared, 16. taken from permanganate, 208. Palladious chloride, 71. Paper-coils, 256. Peat examined, 42. Pectose determined, 244. Perchloric-acid method, 175. Peruvian guano, 165. Phenol method, 237. Phenolphthalein, 75, 267. Phosphates, estimated, 134, 140, 150, 155, 160. in milk, 254. monocalcic, 38, 156. of alkalies, 166. reduced, 157, 162. soluble, 157. Phosphatic guanos analysed, 155. Phospho-guano, 164. Phosphoric acid, 156. Phosphorus, 61. pentoxide estimated, 134,150,155,157,159, 166, 168, 188, 189, 190, 203. Plants, analysed, 245. ash of, analysed, 251. Plaster of Paris, 35, 40. Platinic chloride, 72. Platinum, 59. and potassium chloride 84, 107. atomic weight of, 59. crucible, 127. spatula, 128. Potash, estimation of, 134, 173, 174, 175, 191. in soils, 190. salts of, 64-66 Potassium, 60, 84, 107. acetate, 66. and sodium carbonates, 65. antimoniate, 66. chlorate, 65. method, 229. chloroplatinate, 84, 107. 284 INDEX. Potassium chromate, 65. cyanide, 65. dichromate, 65. ferricyanide, 65. ferrocyanide, 65. hydrate, 65. iodide, 64. nitrate, 65. perchlorate, 175. permanganate, 65. standard solution of. 154. salts, 64, 173. sulphide, 65. sulphocyanide, 65. ,, tests for, 107. Precipitates, how to burn, 131. Preliminary examination for acids, 92-95. for bases, 89-92. Principles of analysis, 75-78. Proof spirit, 250. Qualitative analysis, 56-75. example of 117- Quantitative analysis, 121. examples of, 131-135. apparatus, 123-130. Quicklime, 39. Eain-water, 24. Eeactions, 56, 75. of acid radicles, 84-86, 92-95. of basic radicles, 80-84, 89-92. study of, 80. use of, 76. Reagents, 64. and tests described, 64-75. Bed lead tested, 36. Reduction and oxidation, 32, 33. of lead, 36. Eeinsch's test, 102. Rodonda guano, 155. Rohrbeck's carbon-dioxide flask, 199. Eoots, analysis of, 235. Ruffle's thiosulphate method, 145. Salt, analysis of, 175. Salts in soils, 186. Sand and chalk separated, 8. , salt separated, 7. , in soils, 180. Saponification method, Hehner's, 268. ,, Koettstorfer's, 265. ,, Rei chert's, 267. Scales, English and French, 123. thermometric, 124. Schrotter's carbon-dioxide flask, 199. Septem measure, 124. Serum, 52. Setting to work, 3. Silica, estimation of, 149, 194, 202. separation of, 149, 199, 200, 201. Silicates, insoluble, analysed, 113, 199-202. Silicon, 62. Silk identified, 53. Silver, 59, 80, 98. chloride of, 28, 148. ignition of, 148. coin examined, 27. nitrate, 28, 67. reduction of, 28. standard solution of, 171. tests for, 80. Soap-test, 217. Soda-lime, 141. Sodium, 60. acetate, 66. borate, 66. carbonate, 66. hydrate, 66. impurities in, 151. standard solution of, 137. ,, nitrate, 170. phosphate, 66. plum bate, 53. tested for, 84. Soils absorb ammonia, 42. analysis of, 177-202. ,, ,, complete chemical, 193. mechanical, 178. partial.chemical, 186. lime in, 41, 191. nitrogen in, 42, 187. IffDEX. 285 Soils tested, 42. Solution, 7. preparation of, for analysis, 95. standard, 135, 137, 154. Sombrero guano, 155. Soot, 176. Soxhlet's fat-extractor,' 225. Spatula, 128. Specific gravity, 10. of alcohol, 249. of roots, 243. ,, of sulphuric acid, 135T Stannicum, 82, 101. Stannosum, 82. Stannous chloride, 71. Starch changed into dextrin, 45. sugar, 43, 233. estimated, 233, 243. in potatoes, 243. in paste, 72. tested for, 43, 232. water, 72. Stones in soils, 179. Straw analysed, 233. Strontium, 60, 83, 106. Stylous elements, 60. Sublimation, 3. Sugar, different kinds of, 44. estimation of, 239. in raisins, 43. of milk, 44, 259. test, 70, 239. Sugar-beets, 235, 242. Sulphate of ammonium, 176. barium, 133. iron and ammonium, 154. magnesium, 69. potassium, 173. Sulphates in water, 24. tested for, 36, 86. Sulphur, 61. dioxide prepared, 17. tri oxide, estimated, 136. Superphosphate, alkalies in, 160. analysis of, 156. calcium sulphate in, 160. calculations, 158, 159, 163. made, 38. Superphosphate, phosphoric acid in, 157. reduced phosphates in, 160, 162. Syntonin, 51. Table for acids, 108. for bases, 97. of solubilities, 114, 115. Testing of waters, 24, 221. Test-papers, blue litmus, 75. Coleus, 75. lead acetate, 75. phenolphthalein, 75. ,, red litmus, 75. turmeric, 75. Tests, general, 76. group, 76. ,, special, 77. Tetrad elements, 59, 62. Thermometric scales converted, 124. Thiosulphate method, 145. Tin, 59, 82, 101. dioxide, 27, 29. reduced, 27, 29. sulphide, 98, 100. Triad elements, 59, 61. Tricalcic phosphate, 159. Trivinculant elements, 59, 61. Turmeric root, 50. Turnips analysed, 235. Type-metal examined, 30. Unmnculant elements, 58, 60. Uranium acetate, 71. method, gravimetric, 168. ,, volumetric, 168. Vegetable colours, 49. ivory, 146. Vinculance, 58. Vitriol, strength of oil of, 135. Volatility, 3. Water, 23, 204. ammonia in, 211. analysis of, 204. bath, 130. biological test of, 222. chlorine in, 210. distilled, 24, 130. hardness of, 217. in soils, 177, 179. 286 IJJJDJSl. Water, metals in, 206. nitrates in, 214. nitrites in, 216. organic matter in, 207. oven, 130. silica in, 206. solid contents of, 207. tested, 23. Weighing, precautions in, 126. tubes, 135. Weights and measures, 123-215. Wine, analysis of, 248. Wine examined, 54. Wood, heated, 35. Wool examined, 53. and silk distinguished, 53. Work, rules for successful, 6. Zinc, 60, 83, 105. action of acids on, 15. alloy with iron, 30. detected, 31, 36, 104. sulphate, heated, 36. APPARATUS. Besides the water- oven, blowpipe-table, sand-bath, accurate balance and gram weights, large glass measures, combustion- furnace, sieves, and a small mill for preparing samples, together with a number of pieces of apparatus and tools of different kinds, mentioned in the pages of this Guide (for the common use of the laboratory), each student will require at the back of his bench a set of ordinary reagents, of which the following is a list : Acetic acid. Hydrochloric acid. Hydrosulphuric acid. Nitric acid. Sulphuric acid. Sodium acetate. Sodium carbonate. Sodium hydrate. Sodium phosphate. Ammonium chloride. Ammonium carbonate. Ammonium hydrate. Ammonium oxalate. Ammonium sulphide. Potassium ferrocyanide. Calcium chloride. Calcium hydrate. Calcium sulphate. Barium chloride. Eerric chloride. The special reagents, tests, and materials should be arranged so as to be readily accessible when required for use. They will be found described on pp. 64 to 75 of the Guide, or under the head of the several operations in which they are employed. Each student will require, for his individual and sole use, the apparatus, reagents, &c. comprised in the following lists, which correspond to the three parts into which the Laboratory Guide is divided : PART I. Chemical Manipulation. Wedgwood mortar and pestle. Earthenware furnace-support. Berlin porcelain basons (3). Berlin porcelain crucibles (3). Test-tube rack. Test-tube cleaners (2). Test-tubes (12). Eunnels (4). German glass flasks (4). Watch-glasses (2). Beakers, nest of 5, small. Wash-bottle. Glass stirring-rods (2). Glass spirit-lamp. APPAKATTTS. Retort, stoppered (6 oz.). Slips of glass. Quill-tubing. Crucible-tongs. Mouth-blowpipe. Platinum foil and wire. Square of wire gauze. Round iron sand-bath. Round file ; triangular file. Pair of scissors. Triangle. Scales with glass pans, and weights. Corks. Sheet caoutchouc. Vulcanized caoutchouc tubing. Test-papers. Packets of cut filters (3), to fit the funnels. Duster. Bottle of lamp spirit. Bottle of cobalt nitrate solution. Bottle of silver nitrate solution. Bottle of platinum tetrachlo- ride solution. PART II. Qualitative Analysis. Beakers, a second small set. Spirit of wine (4 oz.). Bunsen burner and connect- ing tube. Square of dark blue glass. Swedish or German filter-paper. Spatula. PART III. Quantitative Analysis. Mohr's 100 c. c. burette and stand. 20 c. c. pipette. Nitrogen bulbs (2). Combustion-tubing and corks. Soda-lime, fine and granular (of each, 4 oz.). Asbestos (1 oz.). Platinum crucible and cover. Iron-wire triangles covered with tobacco-pipe (2). Filter-stands (2). Beakers, large (3). Funnels, large (4). 500 c. c. measure. Finger-glass (ground edge), with ground glass cover, calcium chloride, and sup- ports for crucibles, &c. Carbon-dioxide apparatus. Wide-mouth corked phials, 2 oz. (4). Clock-glasses (4). Packet of cut filters, large size. ^ cloth, 540 pp., with 1G steel plates, carefully coloured by hand, and numerous woodcuts, 1 Is. FARM I N S E CIS : BEING THE NATURAL HISTORY AND ECONOMY OP THE INSECTS INJURIOUS TO THE FIELD CROPS OF GREAT BRITAIN AND IRELAND, AXD ALSO THOSE WHICH INFEST BARNS AND GRANARIES, WITH SUGGESTION'S FOR THEIR DESTRUCTION. BY JOHN CURTIS, F.L.S., &c. SYNOPSIS OF CONTENTS. TURNIP AND MANGEL-WURZLE CROPS. Beetles, Saw-fly and its Black Caterpillar, Plant Lice, Maggots, Caterpillars of Moths and Butterflies, Weevils, Dipterous Flies and Rove Beetles, Surface Grubs, Wireworms, Skip-jacks, &c. CORN CROPS. Wireworms (so called), Ground Beetles, May Bugs, Caterpillars of Moth and Saw-fly, Larvae of minute Flies, Hessian Fly, Wheat-midge, Barley-midge, Thrips, Wheat-louse, Wheat-bug, Vibrio (Ear Cockle), Weevils, &c. PEAS AND BEANS. Maggots, Bees, Plant-lice, Beetles, Moths, Mole-cricket, &c. CARROTS AND PARSNIPS. 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