,. ~4 UNWERSiny CALIFORNIA ,1 COLLEGE of MINING |/ | DEPARTMENTAL LIBRARY BEQUEST OF SAMUELBENEDICTCHRISTY PROFESSOR OP MINING AND METALLURGY 1885-1914 QUANTITATIVE ANALYSIS FOR MINING ENGINEERS BY EDMUND H. MILLER, PH.D. ADJUNCT PROFESSOR OF ANALYTICAL CHEMISTRY AND ASSAYING IN COLUMBIA UNIVERSITY NEW YORK : D. VAN NOSTRAND COMPANY 23 Murray and 27 Warren Streets 1904 Entered according to Act of Congress, in the year 1904, by EDMUND H. MILLER In the office of the Librarian of Congress, at Washington, D C. PRESS or THE NEW ERA PRINTING COMPANY, LANCASTER. PA. PREFACE. This small book on quantitative analysis consists entirely of a series of articles which appeared in the SCHOOL OF MINES QUAR- TERLY, Volume XXV. It was written primarily, to furnish the engineering students at Columbia University, particularly the min- ing engineers, with the directions required for their course in quantitative analysis. Also, as so many men now enter the min- ing course with advanced standing from other universities, col- leges and schools, it seemed advisable to show in this way what we require from our mining students in quantitative work. No attempt is made to cover the entire field of inorganic analysis ; but a few important analyses are given in considerable detail ; the aim being to describe these analyses with enough explanation for the student to work understandingly and with an appreciation of the modern theories of chemistry. References will be found at the end of the chapters to books and articles giving additional information on the subjects treated ; and the last chapter is devoted entirely to references on important analyses which are not given in the text or required in the course for mining engineers. In describing some well-known methods, it is not always pos- sible to give to each chemist exactly the credit he deserves in its development, so acknowledgment is made here to all the stand- ard books on the subject, and special references are made to the more recent journal articles. The methods as described in many cases embody the results of investigations, which have been car- ried out in the Havemeyer laboratories by the recent graduates in chemistry. Acknowledgment is made to this work and also to Dr. Morgan, Dr. Sherman and Dr. Joiiet for helpful suggestions and corrections. E. H. M. QUANTITATIVE LABORATORY, COLUMBIA UNIVERITY, Dec. 31, 1903. in TABLE OF CONTENTS. CHAPTER I. PAGE. lONIZATION I Cations, Anions 3 CHAPTER II. MASS ACTION 7 Effects of Mass Action on lonization 9 Mass Action on Indicators II Solubility Product 13 Complex Ions 15 CHAPTER III. THE ANALYSIS OF MAGNESIUM SULPHATE AND THE DETERMINATION OF ALUMINA IN ALUM 16 Crystallized Magnesium Sulphate 16 Determination of Water 16 Determination of Sulphuric Anhydride 17 Properties of Barium Sulphate 18 Determination of Magnesia 20 Properties of Magnesium Ammonium Phosphate 21 Potassium Alum 22 Determination of Alumina 22 Properties of Aluminum Hydroxide 23 CHAPTER IV. COAL ANALYSIS 25 Sampling 25 Proximate Analysis 26 Determination of Sulphur 27 CHAPTER V. FERRIC AMMONIUM ALUM 30 Determination of Ferric Oxide Gravimetrically 30 Determination of Ferric Oxide Volumetrically 32 By Potassium Permanganate 32 By Potassium Dichromate 37 CHAPTER VI. ANALYSIS OF IRON ORE. Determination of Iron 39 Scheme for the Determination of Silica, Sulphur and Phosphorus in one portion 42 vi CONTENTS. Notes, Reasons and Properties of Precipitates 44 Additional References 47 CHAPTER VII. PIG IRON AND STEEL ANALYSIS 48 Determination of Phosphorus 48 Carbon Determinations 50 Sulphur Determination 53 Oxidation Methods 53 Evolution Method.. 55 Silicon Determination 56 Determination of Manganese 57 Additional References , 57 CHAPTER VIII. DETERMINATION OF MANGANESE IN SPIEGEL AND IN MANGANESE ORES. Volhard's Method 59 Chlorate Separation 61 Gravimetric Method for Spiegel 61 Notes on the " Basic Acetate" Separation 62 Removal of Nickel and Cobalt 64 Precipitation of Manganese by Bromine 64 Precipitation of Manganese as Phosphate ... 65 Additional References 66 CHAPTER IX. DETERMINATION OF ZINC IN ORES 67 Volumetric Method by Potassium Ferrocyanide 67 Method for Franklinite , 71 Gravimetric Method 7 2 Precipitation of Zinc as Sulphide 72 Precipitation of Zinc Ammonium Phosphate 73 Additional References 74 CHAPTER X. LIMESTONE ANALYSIS 75 Determination of Silica and Oxides of Iron and Aluminum 75 Precipitation of Calcium Oxalate 77 Magnesium Determination 79 Effect of Barium Manganese or Phosphoric Acid 80 Applications of the " Limestone " Analysis 8l Determinations of Carbon Dioxide, Sulphur and Phosphorus 82 CHAPTER XI. THE DETERMINATION OF COPPER IN ORES AND MATTES 84 Electrolytic Method 85 Iodide Method 90 Potassium Cyanide Method 93 Thiocyanate Method 95 CONTENTS. vii CHAPTER XII. THE DETERMINATION OF LEAD TN ORES 97 Gravimetric as Lead Sulphate 97 Ferrocyanide Method 99 Molybdate Method 101 CHAPTER XIII. THE DETERMINATION OF ANTIMONY IN ORES 103 Gravimetric Method 103 Volumetric Methods 106 Weller's Method 106 Mohr's Method 108 CHAPTER XIV. THE DETERMINATION OF ARSENIC IN ORES no Distillation Method no Precipitation of Magnesium Ammonium Arsenate 112 Separations of Arsenic and Antimony 112 Volumetric Methods 113 Pearce's Method as Modified by Bennet l?3 Sodium Peroxide Method 115 Additional References to both Arsenic and Antimony 117 CHAPTER XV. SLAG ANALYSIS 118 Iron and Manganese Slags 119 Lead and Copper Slags 121 CHAPTER XVI. FLUE GAS ANALYSIS 125 Reagents 126 Sampling 128 Analysis 128 Results 129 CHAPTER XVII. REFERENCES TO ADDITIONAL ANALYSES 131 NOTES ON QUANTITATIVE ANALYSIS FOR MINING ENGINEERS. CHAPTER I. lonization. Chemistry to-day must consider, besides atoms and molecules, ions. Ion was the name given by Faraday to the moving par- ticles in a solution which carried the electric current. Many years later, in 1887, Arrhenius, in attempting to explain the abnormally high osmotic pressures given by many Aqueous solutions, discov- ered that only those solutions which conducted the current gave these high osmotic pressures, and so decided f hat there were pres- ent in such solutions particles other than mMecules, which he designated by Faraday's name of ions. Although there is now abundant evidence of t,.e existence of ions, a few words on osmotic pressure may not be out of place, as it affords one of the most convincing proofs of ionization. It has been shown by experiment that the laws of gases in regard to pressure and temperature apply equally to substances in solution. Here the volume is the volume of the solution, and the pressure is not exerted, as in the case of gases, on the walls of the containing vessel; but requires for its detection a semi-permeable membrane of such a nature that the solvent can pass through, but the dis- solved substance cannot. Such diaphragms were made by Pfeffer in 1877, and with them he showed that the osmotic pressure of such substances as sugar obeyed the gas laws ; that doubling the number of molecules of sugar, dissolved in a given volume of water, doubled the osmotic pressure, and also that increasing the tem- perature increased the pressure in the same ratio as for gaseous molecules. This important agreement having been shown for a number of substances, usually organic, it was found that there were many salts and other inorganic compounds, such as acids and bases, which did not obey the law, but which gave osmotic pressures greater than 2 QUANTITATIVE ANALYSIS. those calculated from the number of molecules present, so that, as the pressure depended on the number of particles, there must be more particles than molecules present. This gave rise to the theory of ionization or electrolytic dissociation which is: that many com- pounds, such as salts, when they are dissolved in water are disso- ciated into ions, and that these smaller particles conduct the electric currentandaretheactive elements in most chemical reactions. When a simple salt dissolves in water, such as sodium chloride,two ions are formed, Na and Cl ; in this case the ions coincide in chemical formula with the atoms,but they differ chemically. If we place the metal sodium, with which we are familiar, in water, an immediate reaction results with the evolution of hydrogen and the formation of caustic soda; and also the familiar chlorine is a gas of disagree- able odor and active properties, which differs entirely from the chlorine ion. The difference between these elements in the ordi- nary and in the ionic condition is one of electric charge. The ions do not always coincide with the atoms, however ; when cupric sulphate is dissolved in water we have Cu and SO 4 ions, the solution being blue on account of the presence of the Cu ions ; if a current of electricity is passed through such a solution the cop- per ions travel to the cathode; and as the positive charges of elec- tricity they carry are neutralized by the negative current, the blue copper ions are converted to the red metallic copper which de- posits on the cathode. The electric charge carried by the equivalent weight in grams of any element or radicle is 96,540 coulombs, so to liberate one gram of hydrogen by the electrolysis of water we must supply 96,540 coulombs of electricity. As in cupric sulphate, copper is a diatomic element, the hydrogen equivalent is one half the atomic weight, so that 96,540 coulombs will deposit 31.8 grams ; or we may say that the cupric ion carries a double charge of electricity. This is designated Cu, to show two positive charges. The importance of this quantity of electric charge, not only from the theoretical, but also from the practical standpoint, is seen when we consider solu- tions of an element in two degrees of oxidation or where the ion has difference degrees of valence or of electric charge. Take, for example, solutions of cuprous and of cupric salts, with the cuprous there is but a single charge of electricity, with the cupric a double; so 96,540 coulombs will deposit from a. cuprous solution 63.6 grams of copper and from a cupric 31.8 : or if we consider the amperage, IONIZATION. $ the same current will in the same time deposit twice the copper from a cuprous that it will from a cupric solution. This shows the intimate connection which exists between the valence of an ion and its electric charge. It is accompanied often by marked physical differences. Compare solutions of potassium manganate * and potassium per- manganate, one green the other purple, but both composed of the same ions, K and MnO 4 . The only difference is that with the manganate we have K, K and MnO 4 , while with the permanganate K and MnO 4 , the anion or negative ion has a double charge in the manganate. Similarly there is a difference between the colors of ferrous chloride and of ferric chloride depending on whether the Fe ion has two or three positive charges. The following list | gives the most important cations and anions : CATIONS. Monwalent. H in acids, K, Na, Li, Cs, Rb, Tl, Ag, NH 4 , Cu (cuprous), Hg (mercurous). Divalent. Ca, Sr, Ba, Mg, Fe (ferrous), Cu (cupric), Pb, Hg (mercuric), Co, Ni, Zn, Cd. Irivalent. Al, Bi, Sb, Fe (ferric). Tetravalent. Sn, Zr. ANIONS. Monavalent. Qn in bases, F, Cl, Br, I,NO 3 , C1O 3 , C1O 4 , BrO 4 , MnO 4 (permanganates) and the anions of all other monobasic acids, t. e. t the acid molecule minus one hydrogen which goes to the kathode. Divalent. S, Se, Te, SO 4 , SeO 4 , MnO 4 (manganates) and the anions of dibasic acids. Tri- to Hexavalent. The anions of tri- to hexavalent acids. Elementary anions with a valence of more than two are not known. The degree of ionization is measured most readily by finding the electrical conductivity of the solution, for this is dependent on the number of ions present and the rate at which they move ; and is more convenient than obtaining the results from the osmotic pressure, on account of the difficulty in making diaphragms which shall resist these enormous pressures and at the same time not let through any of the dissolved substance. In this way it is shown that most organic compounds are practically undissociated into ions. * Add a little alkali to prevent rapid decomposition. | Taken from Ostwald's Scientific Foundations of Analytical Chemistry. 4 QUANTITATIVE ANALYSIS. It is true that organic acids and bases are dissociated in aqueous 'solution, but the great majority of the important organic com- pounds, such as alcohols, ethers, carbohydrates, hydrocarbons, etc., are practically without appreciable ionization. The extent of the ionization of some of the typical inorganic compounds is as follows: In a tenth normal solution most sim- ple salts such as potassium sulphate, sodium nitrate, potassium chloride, ammonium chloride and so on, are almost completely dis- sociated. There are but few exceptions to this statement ; one is the salts of cadmium and another those of mercury, the most im- portant being mercuric chloride, and the fact that the nitrate gives many reactions which are not obtained from the chloride, may be explained by the inertness of the chloride, due to lack of dissocia- tion into ions. With acids the dissociation is into hydrogen ions and negative ions consisting of the negative element or radicle as ft, Cl; H,N0 3 ; H, C 2 H 3 O 2 ; rf, rf,SO 4 ; H, H,C 2 O 4 ,etc. The con- centration of the hydrogen ions measures the strength of the acid In a tenth normal solution the percentage of ionization is as fol- lows : Hydrochloric acid, 99.5 per cent.; nitric acid, 100 per cent.; sulphuric acid, 69 per cent; acetic acid, 1.4 per cent; carbonic acid, 0.174 per cent.; sulphydric acid (H 2 S), 0.075 per cent.; boric acid, 0.013 per cent. These values give definite expression to the ideas concerning the relative strength of acids though they contradict some of the old views : for instance, it has been often stated that sulphuric acid is the strongest, because it will displace other acids from their salts, but it is less ionized than hydrochloric acid, and the fact that when evaporated with sulphuric acid, chlorides are changed to sulphates, is explained by the easy volatibility of hydro- chloric acid and is not a proof that sulphuric is the stronger acid. Similarly the strength of a base depends on the concentration of the OH ions. At a dilution of tenth normal, potassium hy- droxide is IOO per cent, dissociated, sodium hydroxide, 95.3 per cent, and ammonium hydroxide only 1.6 per cent. So that nitric and hydrochloric acids bear almost the same relation to acetic acid as the fixed caustic alkalies do to ammonia. Ionization increases with dilution to a very marked degree so that at an infinite dilution all ionizable substances are completely dissociated. The effect of dilution is shown by the following values for monochloracetic acid: N/2, 5.4 per cent, dissociated; , 10 57 per cent. ; N/^2, 20 per cent. I ON I Z ATI ON. 5 Temperature has but little effect on the degree of ionization, but a very considerable influence on the rapidity with which the ions travel ; so that rise in temperature increases the conductivity of the solution as it increases the rate of migration of the ions, and there- fore must be considered in calculating the ionization from the con- ductivity. So far water alone has been considered as the solvent, as it has the greatest dissociating power ; in other solutions the degree of ionization is much less; but water itself, although usually con- sidered a non-conductor, is dissociated very slightly, and is found to contain one gram of hydrogen ions to twelve million liters. As will be explained later even this infinitesimal ionization makes water a reagent of importance in a number of quantitative reactions. The reaction in neutralizing sodium hydroxide by hydrochloric acid is usually written : NaOH + HC1 = NaCl -f H 2 O. This represents the weights which take part in the reaction and if we evaporate off the water, the calculated quantity of sodium chloride will be obtained. But while in solution these substances are not all present as molecules, and if we perform the neutral- ization with solutions more dilute than tenth normal, so that the ionization of the acid, alkali and salt is practically complete, we shall have : Na|OH + H|C1 = Na|Cl + H 2 O or on both sides of the equation we have Na and Cl ions, but in- stead of H ions and OH ions we have undissociated water. So that the essential part of this and every other reaction of neutrali- zation is the formation of water. This is strikingly confirmed by the fact that the heat of neutralization of equivalent quantities o caustic alkali by different strong acids is the same, 13,700 calories for the equivalent weights in grams. The following may emphasize the importance of considering what is present in a solution instead of what was dissolved to pro- duce it : Suppose the formula weight in milligrams of potassium chloride and the formula weight in milligrams of sodium nitrate are dissolved together in a large volume of water so that the dis- sociation is complete ; and that in another vessel in an equally large volume of water, the formula weights in milligrams of potassium nitrate and of sodium chloride are dissolved. The two solutions are identical for there are present in each the same number of the same four ions Na, K, Cl and NO 3 . 6 QUANTITATIVE ANALYSIS. The characteristic colors of solutions are due either to the color of the ion or the color of the molecule. When solutions of nickel or copper are evaporated to fumes with sulphuric acid, they lose their characteristic colors, for when the water has been removed there is no longer ionization or color. Cobalt chloride dissolved in alcohol is blue, the color of the molecule ; when water is added it becomes pink, showing the color of the ion. In the same way cupric chloride changes from brown to blue. The change in the colors of indicators is due to the passing from an ionized salt of the indicator to an undissociated molecule. While it is not claimed that there is no reaction without ioniza- tion it is certain that in the case of aqueous solutions of inorganic compounds we are dealing with ionic reactions. In quantitative analysis most of the tests are tests for ions, as silver nitrate for the chlorine ion; but if sodium chlorate is dissolved in water and silver nitrate is added, no precipitate of silver chloride is produced; for though there is chlorine present there are no chlorine ions, as the dissociation is into Na and C1O 3 . Also with a solution of sodium chlorplatinate there is no production of silver chloride but a yel- low precipitate of silver chlorplatinate is formed, a test for the PtCl 6 ion. When ammonia is added to a solution of ferric chloride or any other solution containing ferric ions, ferric hydroxide is formed ; but no such reaction takes place when it is added to a solution of potassium ferricyanide, although it contains iron in the ferric con- dition, for the ionization is into K ions and Fe (CN) 6 ions. If a test for the Fe(CN) 6 ion is applied in each case, for example ferrous ions, nothing results with the ferric solution; while with the ferri- cyanide a characteristic precipitate is formed, Turnbull's blue. As inorganic qualitative analysis is made up largely of such tests and separations, there is no lack of further illustrations of the application of the theory of ionization to this important branch of analytical chemistry. MASS ACTION. CHAPTER II. Mass Action. In order to understand the most important effects of ionization on quantitative analysis, the law of mass action must be con- sidered in an elementary way. This will be done by taking it up first in connection with molecular and then with ionic dissociation. Dissociation was the name given originally by Deville to the separation of a molecule into smaller molecules by heat. For in- stance, when hydriodic acid gas is heated above l8oC. it begins to separate into hydrogen and iodine. This decomposition increases as the temperature is raised still further and decreases on lowering the temperature again, so that for hydriodic acid the amount of dissociation is always the same at a given temperature and pres- sure. This is often expressed as follows : 2HI ^"^ H 2 -f I 2 which shows that the reaction may go from right to left or from left to right depending on conditions. Ammonium chloride dissociates readily into ammonia and hydrochloric acid gases, so that when this process is complete, there will be present double the number of molecules and, according to Avogadro's law, double the pressure if the volume is unchanged. This is a disturbing feature in those methods of molecular weight determination which rely on vapor density determinations, for the molecular weight decreases with increasing dissociation as the temperature rises. With sulphur the molecular weight at low temperatures shows eight atoms in the molecule, while at 86oC. there are only S 2 molecules present. Ferric chloride gives values agreeing with the formula Fe 2 Cl 6 at 320-440 but dissociates at higher temperatures. Nitric oxide is a mixture of NO 2 and N 2 O 4 , at ordinary temperatures, but if the the temperature is raised the density diminishes until at 150 it remains constant at 22.9 compared to H 2 as unity, which agrees closely with the calculated weight for NO 2 . In all such cases there is for each condition of temperature and pressure a definite state of equilibrium at which the proportion of the two gases is constant. If " reaction velocity " is considered as the rate at which this condition is approached, then the state of equilib- rium will be that in which the reaction velocities are equal. In the 8 QUANTITATIVE ANALYSIS. reaction N 2 O 4 ^I^2NO 2 . When the state of equilibrium is reached, just as much N 3 O 4 is formed in each second by the combination of NO, as is dissociated into NO 2 . While there is reaction going on, as the two effects are equal in amount and opposite in direction, the effect is nothing and a condition of equilibrium exists. The principle that the reaction velocity at any moment is proportional to the masses of the substances then present, is called the law of mass action. Guldberg and Waage found that the rate of chemical action (reaction velocity) was proportional to the active mass of each of the reacting substances ; that is, to the number of gram molecules or formula weights per liter, whether as a gas or in solution. The following instances illustrate how important the influence of mass is in some familiar reversible reactions : CaCO, ^Ttl CaO -f CO 2 . At high temperature we have the condition of equilibrium dis- turbed, dissociation increases and if the active mass of carbon dioxide is decreased by removing the gas the tendency for the re- verse reaction is checked and the reaction soon proceeds com- pletely from left to right. On the other hand, when carbon diox- ide is passed over cold lime the reverse reaction takes place. When steam is passed over red-hot iron an oxide of iron is formed and hydrogen ; while if the oxide is heated in a current of hydrogen aqueous vapor and metallic iron are produced. The action is reversible, depending on the active mass of the sub- stances present ; in the first case there can be no concentration of the hydrogen as it is constantly displaced by fresh quantities of steam ; while in the second case the concentration of the steam is prevented by the current of hydrogen. In accordance with this law, if to a dissociated substance one or more of the products of dissociation is added, the degree of dis- sociation is diminished, because the active mass is increased and the tendency to the reverse reaction strengthened. When phos- phorus pentachloride is vaporized, it is very largely dissociated into phosphorus trichloride and chlorine, but if vaporized in an atmosphere of chlorine, this is prevented by the mass action of the chlorine and the molecular weight is found to correspond very nearly to that calculated for phosphorus pentachloride, instead of to about half that value. These principles have a most important bearing on analytical chemistry : for instance, lead can be precipitated as sulphide, from MASS ACTION. 9 a solution very slightly acid with hydrochloric acid ; while on the other hand lead sulphide, whether natural or artificial, can be dis- solved readily in strong hydrochloric acid. This is evidently a re- versible reaction. PbS + 2HC1 ^t H 2 S + PbCl 2 . In order to have it proceed from left to right, the active mass of the hydrochloric acid must be large and that of the sulphuretted hydrogen small. This is accomplished by using a considerable quantity of strong acid and allowing the sulphuretted hydrogen to escape from an open vessel, or better by heating. To get the re- verse reaction the concentration of the acid must be reduced by neutralization or dilution, and that of the sulphuretted hydrogen increased by passing a steady stream of the gas through the solu- tion. If the lead is to be precipitated completely the conditions must be such that the direct reaction is entirely prevented, i. e., there must be very little acid present. The same considerations apply to other sulphides, such as that of cadmium, and to other precipitates as well. EFFECTS OF MASS ACTION ON IONIZATION. Just as the laws of gases have been found to apply to ions in solution as well as to gaseous molecules, as is shown by the os- motic pressures of electrolytes, so the law of mass action is found to apply to the ions in solution ; and the effect of mass is the same, whether the dissociation is like that of gases into smaller molecules or in solution of an electrolytic nature into ions. The addition of an ion in common drives back the dissociation. An illustration of this is found in the fact that while aluminum hydroxide is perceptibly soluble in an excess of ammonia, this solubility is diminished by the presence of ammonium chloride or other ammonium salt. As ammonium hydroxide is slightly dis- sociated and ammonium chloride almost completely, the mass ac- tion of the increased ammonium ions drives back the dissociation of the ammonia, and so readily diminishes the concentration of the hydroxyl ions to such an extent that it is too weak an alkali to dissolve aluminum hydroxide. The weakening of acetic acid by the addition of an acetate, or the driving back of the dissociation by the addition of an ion in common, can be very strikingly shown by the following experi- io QUANTITATIVE ANALYSIS. ment: If to a solution of ferric acetate, slightly acid with acetic acid, sulphuretted hydrogen water is added, no black precipitate is found, but only a separation of sulphur due to the reduction of the iron ; but if to another portion of the same solution a considerable quantity of sodium acetate is added and then sulphuretted hydro- gen water as before, a heavy black precipitate of ferrous sulphide will form immediately, because the mass action of the acetions (C 2 H 3 O 2 ) has driven back the dissociation of the acetic acid to such an extent that it can no longer dissolve iron sulphide.* To illustrate this action numerically let : a = the concentration of H ions in gram molecules per liter. b = the concentration of C 2 H 3 O 2 ions in gram molecules per liter. r=the concentration of undissociated acetic acid molecules in gram molecules per liter. k = a constant. The law of mass action states that the product of the concentra- tions of the ionized portion equals that of the undissociated portion times a constant, which is dependent on the nature of the substance, the temperature and the pressure ; or using the letters to designate these concentrations ab = kc. With acetic acid this would mean that the product of the concentrations of the hydrogen ions and the acetions equalled the concentration of the molecules of acetic acid times k. Let us suppose that there are present a weight of acetic acid equal to that of two hundred gram molecules at a dilution nearly tenth normal, that is very nearly 6 grams of actual acetic acid per liter. We shall have dissociation to the extent of about 1 .5 per cent, or three gram hydrogen ions, three gram acetions and one hundred and ninety-seven gram molecules of acetic acid. Substituting these values for a, b and y ammonia, filter, wash. Filtrate. Precipitate in neutral solution. Ppt. CaC 2 O 4 , wash, ignite and weigh as CaO or CaSO 4 , or, titrate the combined oxalic acid by KMn- 4 . twice by (NHJ 2 C 2 O 4 Filtrate. Precipitate theMgasMgNH 4 - PO 4 , ignite and weigh as Mg 2 P 2 O 7 dissolve in HC1 and reprecipitate. This scheme is without the detail which is especially important in this analysis, and is given only to show the relation of the dif- ferent parts of the analysis. DETERMINATION OF SILICA AND OXIDES OF IRON AND ALUMINUM. Weigh out exactly one gram of the finely ground sample, trans- fer it to a small beaker and treat with 20 c.c. of water, 5 c.c. of 76 QUANTITATIVE ANALYSIS. concentrated hydrochloric acid and about I c.c. of concentrated ni- tric acid, cover with a watch glass and heat until no further solution takes place. Filter through a very small paper into a small casserole and wash the residue once or twice with water. Place the filtrate and washings on the water or steam-bath to evaporate. If the limestone contained CaCO s , MgCO s , FeCO 3 and SiO 2 only, the residue, after more careful washing, could be ignited and weighed as silica, as in this form it is insoluble in acids. This is sometimes true and saves much time with the analysis, but if there are present silicates of lime, magnesia, etc., these may be insoluble or may give gelatinous silica which dissolves partly, so to ensure accurate results it is necessary to fuse the residue to decompose some silicates and also to evaporate and dehydrate the solution to obtain the soluble silica. The nitric acid is added to oxidize the iron which may be present as pyrites, FeS 2 , or as siderite, FeCO 3 . While the filtrate is evaporating, dry and burn the filter contain- ing the residue in a small platinum crucible, then add about six times its weight of mixed carbonates and a crystal of nitrate, the size of a pin head, and fuse for about 15 minutes over a Bunsen buner. The fusion should be perfectly liquid ; if it is not, increase the heat or the flux or both until a complete decomposition of the insoluble residue is obtained, bearing in mind the disadvantage of introducing into the analysis large quantities of alkali salts. When cold remove the melt in a cake if possible, dissolve it in hydro- chloric acid and water and add this to the solution which is evap- orating on the water-bath. Continue the evaporation to dryness, stirring with a glass rod, when the salts begin to crystallize ; then transfer to an air-bath and heat at 110 C. until there is no more smell of hydrochloric acid. If the insoluble residue consisted of silicates of calcium, mag- nesium or aluminum after fusion there are present CaCO 3 , Mg- CO 8 , Na 2 Al 2 O 4 , Na 2 SiO 3 and the corresponding potassium salts ; on treating with acid these give CaCl 2 , MgCl 2 , A1C1 3 and H 2 SiO 3 , besides NaCl and KC1. After combining the two solutions we have CaCl 2 , MgCl 2 , FeCl 3 , A1C1 8 , H 2 SiO 8 , NaCl, KC1, HC1. As the cal- cium chloride is the predominating salt, the dehydration of the silica will be easy on account of its great affinity for water (compare action of sulphuric acid in Brown's method for silicon), so that in the analysis of an ordinary limestone it is not necessary to repeat the dehydration. LIMESTONE ANALYSIS. 77 After dehydration treat the mass of salts with hydrochloric acid and water, heat to dissolve the salts of iron and aluminum and filter out the silica, which should be perfectly white. Wash with hot water, being careful to use a wash bottle which gives a very fine stream, so as not to dilute the filtrate to more than 100 c.c. Burn the paper and ignite the silica over the blast-lamp to drive out the last of the water, cool in a desiccator and weigh. Check this by driving off the silica by hydrofluoric and sulphuric acids as already described under iron ore. If there should be a residue it is probably alumina, in any event fuse it with a little mixed car- bonate, dissolve the melt in hydrochloric acid and add this to the filtrate from the silica. To the main filtrate add ammonia in slight excess, and heat to boiling, so that the flocculent precipitate of ferric and aluminum hydroxides collects well. This contains any phosphoric acid present and is probably contaminated by calcium and magnesium hydroxides. Allow to settle, and decant through a filter, leaving all of the precipitate in the bottom of the beaker. Dissolve the precipitate in dilute hydrochloric acid and reprecipitate by am- monia, heat again, filter and wash till free from chlorides by boiling water, avoiding unnecessary dilution of the filtrate. Filter without delay as the alkaline solution will absorb carbon dioxide from the air and so cause contamination due to calcium carbonate. The remedy would be to redissolve in acid, boil out the carbon dioxide and reprecipitate. Burn the paper, etc., moisten the residue with nitric acid and ignite finally by the blast-lamp and weigh the com- bined oxides of iron and alumina. PRECIPITATION OF CALCIUM OXALATE. The filtrate, containing CaCl 2 , MgCl 2 , KC1, NaCl, NH 4 C1 etc., is made decidedly acid with hydrochloric acid ; then enough oxalic acid is added to combine with all the lime and the solution is heated to boiling. To the boiling solution a few drops of methyl-orange are added and then gradually and with frequent pauses dilute ammonia, till the indicator changes color. The neutralization should take half an hour, then a considerable excess of ammonium oxalate is added and the precipitate allowed to stand for four hours. Next filter and wash with a I per cent, solution of ammonium oxalate.* Al- * Richards, Z. Anorg. Chemie, 28, 88. 78 QUANTITATIVE ANALYSIS. though if these conditions are carried out very carefully it is possi- ble to obtain a very complete separation of calcium from magne- sium by one precipitation, it is safer to redissolve the precipitate in hydrochloric acid, after decanting or filtering, and to reprecipitate as before by neutralizing with ammonia and then adding ammo- nium oxalate. The main difficulty in precipitating calcium oxalate is the con- tamination due to magnesium oxalate. Although this is a per- fectly soluble salt it is carried down by the calcium oxalate (adsorp- tion) and not readily removed by washing. An alkaline solution is most favorable to this contamination ; so, if to the acid solution we add enough oxalic acid to combine with the lime and then neutralize gradually, the calcium oxalate will be formed in as acid a solution as possible and also in one in which it is somewhat soluble, hence it will be free from magnesium oxalate and also in large crystals which can be easily filtered and washed. The indi- cator, methyl-orange, turns before an excess of ammonia has been added. If we stopped at this point we would not get complete precipitation of the calcium as there is not yet present any consid- erable excess of ammonium oxalate, so then an excess of ammo- nium oxalate is added, which converts the magnesium largely to oxalate, and by the mass action of the C 2 O 4 ions the solubility prod- uct of calcium oxalate is exceeded, the Ca ions are driven out of solution, and the precipitation of the calcium oxalate is complete. Now that the magnesium is present largely as oxalate, we must not wait too long before filtering, as it has been found that the magnesium oxalate increases on the precipitated calcium oxalate. As the calcium oxalate is very slightly soluble in hot water, it is washed with a solution containing an ion in common, I per cent, ammonium oxalate. If the calcium is to be determined gravimetrically, the ammo- nium oxalate need not be removed ; if a volumetric method (potas- sium permanganate) is to be used this must be washed out with cold water. When calcium oxalate is ignited it gives a mixture of carbonate and oxide ; this can be heated by a blast-lamp for half an hour or more until constant weight is obtained and the resulting calcium oxide weighed. Great care must be observed to expel all the carbon dioxide and to avoid any reabsorption of this or of water from the air, by cooling in a desiccator and weighing quickly. LIMESTONE ANALYSIS. 79 After burning the paper, etc., the residue can be converted to sulphate by moistening with dilute sulphuric acid and heating care- fully over a Bunsen burner (no blast) till the excess is expelled, then weighing when cold and repeating the treatment until a con- stant weight is obtained. When the oxalic acid combined with the calcium is to be ti- trated by permanganate, proceed as follows : Dissolve the pre- cipitate through the filter with the least possible quantity of hot dilute hydrochloric acid into a large beaker, dilute with warm water, add an excess of concentrated sulphuric acid (56 c.c.), ten grams of manganous sulphate, and titrate at about 65 C. Or dis- solve through the paper in very dilute sulphuric acid, add more sulphuric acid, warm and titrate. Besides the properties of calcium oxalate already mentioned, like barium sulphate, when formed in a cold solution, it is very fine and runs through the filter. It is dissolved by mineral acids and is slightly soluble in acetic acid. It should be precipitated in a solution containing no salts other than those of magnesium and the alkalies, as it would be contaminated by barium oxalate, man- ganous oxalate, etc. MAGNESIUM DETERMINATION. The filtrate should be about 200 c.c. in volume, and will contai a large amount of ammonium chloride and oxalate. If the amount of magnesium is considerable (dolomite) it can be precipitated in this solution by adding sodium or ammonium phosphate and then an excess of ammonia, etc., as already explained. After igniting and weighing the magnesium pyrophosphate, it is best to dissolve it in dilute hydrochloric acid and to weigh any residue of silica with the crucible. Then subtract this weight instead of the original weight of the crucible, as the ammonia salts are likely to cause contamination of the precipitate by silica from the beakers. If the amount of magnesia is small, as is usually the case, it will not come down satisfactorily in the presence of the relatively large amounts of ammonia salts. Concentrate the solution as far as possible in a beaker, then transfer to a platinum dish and evap- orate to dryness. If the salts crawl up the sides, heat the upper edge of the dish instead of the bottom, best by putting a top on the burner which gives a number of small flames from the sides. Then ignite to drive off the ammonia salts, take up the residue 8o QUANTITATIVE ANALYSIS. with dilute hydrochloric acid, filter if necessary (to remove dust and silica) and determine the magnesia as usual. A very good method of getting rid of ammonium chloride is to add to the very'concentrated solution in a casserole (just as the salts are beginning to separate) strong nitric acid and continue the evaporation. The ammonium chloride breaks up and is expelled, probably according to the following reaction : NH 4 Q + HN0 3 = HC1 + 2H 2 + N 2 O, while the excess of nitric acid helps to decompose the oxalates. When the oxalates are not destroyed and sodium phosphate is used as a precipitant, the magnesium ammonium phosphate must be washed very thoroughly to remove the sodium oxalate. EFFECT OF BARIUM, MANGANESE OR PHOSPHORIC ACID. If the limestone contained a little barium carbonate and consider- able pyrites, barium sulphate would be formed, which would con- taminate the silica. After driving off the silica, fuse the residue as usual and, if a precipitate is reformed on acidifying, filter and add only the clear solution to the main filtrate. It might happen that the barium carbonate was in excess of the sulphur, so that only a portion would be precipitated as barium sulphate while some would come down as oxalate and the rest as phosphate. In such a case add dilute sulphuric acid drop by drop before filtering off the silica so as to precipitate all the barium, avoiding much excess, so as not to form calcium sulphate which would contaminate it. Then, after driving off the silica, the barium sulphate can be weighed if pure or fused and reprecipitated. Should there be manganese present it will contaminate the am- monia precipitate unless the precipitation is repeated, and also the calcium oxalate. It is possible to precipitate calcium as oxalate in the presence of iron but not in that of manganese (see slag anal- ysis) so that the manganese must be removed before the precipi- tate of calcium oxalate. This can be done as follows : 1. After several ammonia precipitations add bromine water and ammonia, warm and filter out the higher hydrated oxide of man- ganese. 2. Saturate the filtrate, slightly alkaline with ammonia, with hydrogen sulphide and filter out the manganous sulphide. 3. Substitute the basic acetate for the ammonia precipitation and take the manganese out of the filtrate by either bromine or by hy- drogen sulph'de. LIMESTONE ANALYSIS. 81 The determination of manganese has been described. There are cases in which the amount of phosphoric acid is more than enough to combine with the iron or iron and aluminum pres- ent, so that the ammonia precipitate will also contain calcium as phosphate, which can not be removed by solution and reprecipi- tation. In such a case add a known amount of iron as ferric chlo- ride, which shall furnish an excess over that required to combine with the phosphoric acid, and precipitate with ammonia as usual. All the lime will be in the filtrate and the ferric oxide from the iron solution added must be subtracted from the weight of the total alumina and ferric oxide. APPLICATIONS OF THE " LIMESTONE" ANALYSIS. The most important variations when this analysis is to be ap- plied to a rock are : i. Fuse the entire rock with Na 2 CO 3 or NaKCO 3 , because so little will dissolve in acid that the treatment is not advisable. 2.. Dehydrate the silica by evaporation on a water-bath twice, or if very high in silica (acid rock), three times. The reason for this is seen when we compare the composition of limestone with that of rock. Limestone contains perhaps 2-3 per cent, of silica and 45-50 per cent, of lime. Rock, 60 per cent, or even 80 per cent, of silica and a small amount of lime. So that if one hun- dredth of the silica present escapes the first dehydration, the error is 0.6-0.8 per cent. 3. Always look for manganese in a rock, a green fusion due to manganate when nitrate is added to the mixed carbonates in the fusion, but not always formed without it. With clays the treatment is similar to that given for rocks, but here the percentage of alumina is higher and that of lime and magnesia lower, so that the double dehydration of the silica is necessary, and also the refusion of any residue left after driving off the silica, which will usually be alumina, possibly also titanic ox- ide. The aluminum and ferric hydroxides must be very carefully precipitated in the presence of ammonium chloride and with but a slight excess of ammonia. With rock, clay or cement, it is not enough to obtain the com- bined per cent, of A1 2 O 3 and Fe 2 O 3 ; the iron, ferrous or ferric, is also required. This can be done as follows : After igniting and weighing the combined oxides, fuse them for at least forty-five 82 QUANTITATIVE ANALYSIS. minutes at a low heat with 8-10 times their weight of potassium bisulphate or potassium pyrosulphate, then at the end add concen- trated sulphuric acid to reconvert the potassium sulphate to bisul- phate. This changes the iron and aluminum to sulphates and at the same time dehydrates any silica which has previously escaped and has precipitated with the hydroxides. Dissolve the melt in water and sulphuric acid, filter, add the silica to the main portion, reduce the iron in the filtrate bypassing it through a reductor and titrate by permanganate. For cements, which often contain about 22 per cent, of silica and 60 per cent, of lime, two evaporations for silica, and the sepa- rate percentages of oxides of iron and aluminum, constitute the important variations from the " limestone " analysis described. For the best information on rock analysis see Hillebrand, Bulle- tin of the U. S. Geological Survey, No. 176. For cement analysis, report of committee,/. Society of Chemical Industry, Vol. XXL, pp. 12-30, 1902, and Hillebrand, J. AmericanChetn. Soc., XXV., 1180, 1903. This discussion also covers the main portion of slag analysis ; the composition of slag varies within wide limits, and there may be present any of the common or rare elements. But bearing in mind that the fifth and sixth groups are taken out after the silica, and the principles of the "limestone" analysis, the special meth- ods given later for typical slags will easily be understood. DETERMINATIONS OF CARBON DIOXIDE, SULPHUR AND PHOSPHORUS. The other determinations in limestone are made on separate por- tions. Carbon dioxide is either found by loss or by direct weight, the methods are given in the text-books.* A rapid method is to fuse about four grams of borax glass (Na 2 B 4 O 7 ) in a platinum crucible, and when cold weigh ; place about one gram of the dried lime- stone on the top of the borax glass and reweigh. Then fuse with a Bunsen burner till no more gas is given off (no blast), cool and weigh. The loss in weight is carbon dioxide, provided there is no moisture or organic matter present. The method is only approx- imate, as borax glass is slightly volatile and gives total carbon di- oxide, water and organic matter, when the latter are present. * Cairn's "Quantitative Analysis," pp. 33-37. LIMESTONE ANALYSIS. 83 The reaction is Na 2 B 4 O 7 + CaCO 3 = Na 2 B 2 O 4 + CaB 2 O 4 + CO 2 . Sulpliur. Unless barium sulphate is present,.dissolve five grams of a sample in 15 c.c. concentrated hydrochloric acid and 5 c.c. concentrated nitric acid and 15 c.c. of water in a casserole, evap- orate, add more hydrochloric acid and evaporate to dryness to ex- pel the nitric acid and dehydrate the silica ; take up with hydro- chloric acid and water, boil and filter ; neutralize the filtrate with ammonia so that it is just acid with hydrochloric and precipitate the sulphate by barium chloride as usual. If barium sulphate is present, fuse the residue with mixed car- bonates, leach with water, filter out the barium carbonate and add the filtrate to the main solution, dehydrate and precipitate as usual. Phosphorus. Dissolve 5 grams in 40 c.c. of dilute nitric acid, evaporate to dryness, take up with nitric acid and water, filter, neu- tralize the excess of nitric acid by ammonia, and precipitate as am- monium phosphomolybdate, etc.. as in iron ore. If the iron and alumina are low, the molybdate precipitation can be omitted. Dis- solve 5 grams in hydrochloric acid, evaporate, bake, take up with hydrochloric acid and water, filter ; to the filtrate add 2-3 grams of citric acid, to prevent the precipitation of aluminum or ferric hydroxides or calcium phosphate, neutralize with ammonia and precipitate by magnesia mixture direct. Sulphur and phosphorus are objectionable when the limestone is used as a flux for iron ores. 84 QUANTITATIVE ANALYSIS. CHAPTER XL The Determination of Copper in Ores and Mattes. Among the many methods which have been proposed for the determination of copper the electrolytic, iodide and cyanide are of the greatest importance and the thiocyanate and colorimetric methods deserve mention. As the method of solution is the same for all these methods, it will be described first. For ores, weigh out, depending on the richness, from I to 5 grams of the very finely ground sample, so as to obtain about 150 milligrams of copper. Treat this in a covered casserole or Erlenmeyer flask (200 c.c.) with 20 c.c. concentrated nitric acid, 5 c.c. concentrated hydrochloric acid and 5 c.c. concentrated sul- phuric acid ; heat until all the copper has dissolved and then evap- orate to dense white fumes of SO 3 (at this point the blue color will have disappeared, no water being present), allow to cool; dilute with water and heat to dissolve ferric sulphate, etc. ; filter out the residue, which consists of silica, silicates and the insoluble sul- phates of lead, barium, etc., wash this residue with hot water thoroughly, taking care to avoid unnecessary dilution. This treatment will dissolve the copper in all ordinary ores, but if it is present as silicate (chrysocolla or slags) the residue should be fused with mixed carbonates to ensure complete decomposition. For mattes, use 0.25-0.5 gram and half the quantities of nitric and hydrochloric acids and about 4 c.c. of sulphuric acid. Alloys such as brass, german silver, etc., can be treated in the same way when it is desired to separate out the lead as sulphate ; or dis- solved in nitric acid alone, depending on the methods to be used for the subsequent separations. With bronze nitric acid alone is used followed by long boiling in a very dilute solution, so as to separate out the tin as completely as possible, as rnetastannic acid. This often contains copper which is separated from tin by digesting the residue on a water-bath with potassium sulphide (not ammonium sulphide). This also applies to brass and german silver when they contain tin. THE DETERMINATION OF COPPER. 85 ELECTROLYTIC METHOD. The sulphuric acid solution containing CuSO 4 ,Fe 2 (SOJ 3 , etc., be- sides the possible impurities, arsenic, antimony, bismuth, can be electrolyzed directly, provided there is not too great an excess of sulphuric acid present. 23 c.c. of concentrated acid in a volume of about 100 c.c. is a suitable quantity ; if this is exceeded a por- tion can be neutralized by ammonia. If the copper is from a chalcopyrite there will be a considerable quantity of ferric sulphate present, and the separation of copper succeeds best under the conditions given. It is impracticable to precipitate the iron by ammonia before electrolysis as the ferric hydroxide always carries down copper. If difficulty is encountered in depositing the last traces of copper, the solution after electrolysis can be made alka- line by ammonia and when there are only traces of copper pres- ent, the amount held by the precipitate can be neglected. In the filtrate the copper can be determined colorimetrically or the solu- tion made acid again by sulphuric acid and the electrolysis con- tinued. The colorimetric estimation consists in comparing the shade of blue in the ammoniacal solution with the color of standards made up containing known amounts of copper in the same volume and having the same excess of ammonia and at the same temperature. For the details of this method see Heath, J. Am. Chem. Soc. t Vol. 19, p. 24, 1 897, and Smith, Trans. American Institute Mining Engi- neers, 30, 851, 1901. When arsenic and antimony are present in large quantities, the method described, or any other electrolytic method, fails to give accurate results, as some of these impurities are deposited with the copper. This may be remedied by roast- ing the material before dissolving (after weighing), or by repeated evaporations with bromine, or by heating the precipitated sulphides with a solution of sodium or potassium sulphide, filtering and then dissolving the copper sulphide in nitric acid. When the arsenic and antimony are present only in exceedingly small quantities the presence of nitric acid prevents or retards their deposition, so that the best conditions for the electrolysis of a cop- per matte are, as regards acidity, 2-3 c.c. of sulphuric acid 1.84 sp. gr. and 2 c.c. nitric acid 1.42 sp. gr. in a volume of about 150 c.c. Bismuth is the most troublesome metal in connection with all the methods for copper; it is not removed by roasting, and although not easily precipitated completely by the current, it al- 86 QUANTITATIVE ANALYSIS. ways contaminates the copper when present, often without causing any perceptible discoloration of the deposit. If present, dissolve the deposited copper in nitric acid, add ammonia in excess, then ammonium carbonate, dilute to 150 c.c. and boil. The bismuth is precipitated as a basic carbonate, contaminated by copper; by resolution in nitric acid and reprecipitation it can be obtained pure ; then washed, ignited and weighed as Bi 2 O 3 . The calculated weight of bismuth is deducted from the weight of the deposit. When the bismuth is present in large amount, or when it is also to be determined, the method described by Riederer, J. Am. Chem. Soc., Vol. XXV., p. 919, 1903, can be employed. The special apparatus required for the determination of copper cpnsists of platinum electrodes and a suitable stand. The anode is usually made of a stout platinum wire, bent into a spiral when a cylindrical cathode is used or coiled into a disc when a platinum dish is used. The cylindrical cathode is most con- venient when many determinations are made at the same time ; it should be open at the side so as to allow the circulation of the electrolyte. Both electrodes should be thoroughly clean, free from deposited metal, grease or dust. This is obtained by treatment with nitric acid or with alcohol and then drying above the flame of a burner. The cathode is then weighed and connected with the negative pole of the battery or source of electricity, while the anode is con- nected with the positive pole. With cylindrical electrodes the cop- per solution is placed in a small but tall beaker and the cathode adjusted so that about half an inch is out of the liquid, and the beaker covered by a divided watch glass or two pieces of mica to keep out dust and prevent loss by spattering. With a dish, a watch glass with a hole in the center for the anode to pass through, is used as a cover. The area of the cathode should be about ten square inches and the current 1.5-2 volts and 0.1-0.2 ampere. It is turned on and the copper allowed to deposit for from twelve to fifteen hours, then if the electrolyte is colorless the cathode is lowered about one fourth inch so as to expose a fresh surface of platinum for deposi- tion and the electrolysis is continued for an hour longer. When no more copper is deposited, a few c.c. of the solution are with- drawn by a pipette and tested with freshly prepared hydrogen sul- phide water on a white surface. This test is much more delicate than the blue color with ammonia. THE DETERMINATION OF COPPER. 87 As there is nitric acid present the cathode must be removed while the current is still passing, otherwise the nitric acid would immediately begin to redissolve copper. This can be done by siphoning out the contents of the dish and at the same time adding water, until the solution is too dilute to attack the deposit, or if the electrolysis is done in a beaker, the block beneath it can be removed and a beaker of water substituted, then the cathode is allowed to drop into the water. The deposited copper must be dried without oxidation ; so it is next rinsed off with alcohol to displace the water, then, when great precautions are required, with ether and is dried at a very gentle heat such as can easily be borne by the hand so as not to oxidize the deposit. When cold it is allowed to stand in the balance room for about ten minutes and then weighed. For the electrolytic assay as applied to refined copper, see Heath, Trans. A. /. M. E. t July, 1899. The behavior of the elements likely to be present, under the conditions given is briefly as follows : Iron does not interfere unless insufficient sulphuric acid is present. Then the nitric acid be- comes reduced to ammonia, which precipitites ferric hydroxide. In the directions given, the amount of sulphuric acid is sufficient to neutralize all the ammonia formed, even if the nitric acid is com- pletely reduced. Nickel and cobalt do not interfere in a strongly acid solution. They are, however, deposited in an ammoniacal solution, if the cur- rent is strong. Zinc requires the presence of a strong acid to prevent its precipitation, i.e., nitric; it may be deposited in an extremely weak sulphuric acid solution or readily from solutions of organic acids, like acetic, citric, lactic, etc. So that if the elec- trolysis is prolonged and the free nitric acid reduced zinc may be deposited. Manganese does not deposit as metal, but goes to the anode as peroxide ; it is sometimes oxidized higher to per- manganic acid which gives a color to the solution about the anode. Lead in traces escapes precipitation as sulphate and ap- pears on the anode as PbO aV Bismuth contaminates the copper and also goes to the anode~as peroxide. Arsenic and antimony are liable to contaminate the copperas explained. Silver will be removed as chloride, unless the digestion with con- centrated sulphuric acid is very long, then it is partly changed to sulphate. If present, it will deposit completely with the copper; 88 QUANTITATIVE ANALYSIS. but is easily removed by a drop of a chloride. Gold, platinum, etc., would be deposited, but are not likely to be present in suffi- cient quantity to influence the results. In general salts are objectionable, although in some cases they are added. For example, Classen precipitates copper and other metals from a solution containing large amounts of ammonium oxalate. Hydrochloric acid and chlorides should be absent, as they cause the deposit to be spongy. For a detailed discussion of the quantitative deposition of metals by electrolysis see " Electrochemical Analysis," by Prof. E. F. Smith, 1902. It is of the greatest importance that a dense firmly adherent de- posit be obtained, free from impurities ; aside from the chemical conditions, the character of the current has much influence on that of the deposit. To describe the current we must know the voltage and amper- age ; the latter is often given as current density, that is, the num- ber of amperes per 100 sq. cm. of cathode area. ND.ioo = 0.2 means 0.2 amperes for each 100 sq. cm. of the submerged area of the cathode on which metal is deposited. The amperes determine the rate of deposit, according to Fara- day's law, but in quantitative analysis the character is of greater importance than the rate, so for copper a low-current density is used, 0.1-0.15 ampere, because a stronger current (except in special cases) is liable to give a dark, spongy and non-adherent deposit, which is difficult to dry without oxidation, and to weigh without loss. The voltage should also be low enough to overcome the coun- ter-electromotive force of the solution and its resistance ; for copper about 1.5 volts, but not a high voltage, as it tends to increase the impurity of the deposit. The best current for electrolytic work can be obtained from storage batteries, or primary batteries ; but as the lighting circuits are more convenient, they may be used by insert- ing a suitable resistance. The counter-electromotive force necessary to deposit a metal can be calculated from the heat of formation of the molecule, and the results so obtained agree well with those found by experiment. But the question may well be asked, if salts, such as copper sul- phate, are already ionized in solution, why is all this energy re- quired to pull the copper sulphate apart? The answer is found in THE DETERMINATION OF COPPER. 89 Nernst's solution-tension theory. This is, briefly, that each metal has a certain power of forcing its atoms into solution as ions; just as a liquid continues to evaporate at its surface till the pressure of the vapor becomes equal to the vapor-tension of the liquid, so the metal sends ions into solution till the osmotic pressure of these ions becomes equal to the solution-tension of the metal. Therefore, in order to separate out the copper ions in the form of metallic copper, a certain electrical pressure or intensity of current is required, so that the sum of this and the osmotic pressure shall exceed the solution tension. These differences in solution tension for different ions can be found in the books on physical chemistry, and while the results agree well with the old method of calculating counter-electromo- tive force, the modern method is more accurate, as it considers the variation of voltage with dilution. There is therefore a minimum voltage below which any given metal will not be deposited, so that theoretically, if all metals gave soluble sulphates or nitrates, we could apply just voltage enough to overcome the solution tension of the lowest in the series and when that metal was completely deposited, the current would cease to pass; then by raising the current to just above the intensity re- quired for the next metal, that could be deposited and so on. This is evidently not possible in all cases, but it is in some. If there are present in solution copper and silver as nitrates and a current of one volt is passed, only silver is thrown out. If the sulphates of copper and zinc are in solution (containing but a trace of free sulphuric acid) we can by keeping the current between 1.5 and 2 volts deposit only copper ; while by raising the voltage so as to exceed the solution tension of the zinc, we can deposit brass and by varying the voltage, vary the percentage composition of the alloy. To return to the copper, we can prevent some metals from de- positing by the character of the solution, addition of acid, etc., others will not come down in an aqueous solution at all, others can be prevented from contaminating the copper by regulating the voltage so that the counter-electromotive force of copper is just exce.eded. Practically it is often easier to remove the interfering element than to regulate the voltage, and then, when there is no metal present which will come down at a higher voltage, we need only adjust the amperage or current density so as to get a deposit suitable for weighing. 90 QUANTITATIVE ANALYSIS. ADDITIONAL REFERENCES. " The Elements of Electrochemistry," by LeBlanc, translated by W. R. Whitney for the theory, and " Quantitative Chemical An- alysis by Electrolysis " by Classen for other methods. IODIDE METHOD. In an acetic acid solution, potassium iodide precipitates cuprous iodide, with the liberation of iodine, according to the reaction : 2C 4 (C a H 3 2 ) 2 + 4 KI = Cu 2 I 2 + I 2 + 4 KC 2 H 3 2 , or one atom of iodine is liberated for each atom of copper present in the cupric condition. The liberated iodine can be titrated by a standard solution of sodium thiosulphate, using starch solution as indicator, accord- ing to the reaction : 2Na 2 S 2 3 + J f = 2NaI + Na 2 S 4 O 6 . Here copper acts as an oxidizing agent, liberating iodine, which is measured, and so the copper is determined ; a method of indirect titration. It is evidently essential to the success of this method that there should not be present any other oxidizing or reducing agents, for the first would liberate iodine and cause too high re- sults; the latter would be oxidized by the iodine liberated and cause too low results. The indicator is a solution of starch which gives an intense blue color to the solution in the presence of free iodine. The end point is the discharge of this blue color and is extremely delicate when the proper conditions have been observed. The starch solution is made by mixing about one gram of pure starch to a thin paste with cold water and then pouring it into about 200 c.c. of boiling water and boiling for several minutes. It should be allowed to cool and only the clear solution used. This solution does not keep well ; moulds grow in it which split up the starch giving dextrins and other carbohydrates, some of which give reddish colors with iodine. To guard against this a preservative such as zinc chloride or carbon bisulphide may be added. A standard solution of sodium thiosulphate is made by dissojving 19.6 grams of the crystallized salt, Na 2 S 2 O 3 . 5H 2 O, in water and diluting to one liter. Each c.c. will be equivalent to about 5 milli- grams of copper. Standardize as follows : Weigh out two or three THE DETERMINATION OF COPPER. 91 portions of pure bright copper foil of 100-150 milligrams each, taking different weights, as this ensures a really independent de- termination and saves the time required to weigh out an exact amount. Dissolve the copper in small beakers in about 10 c.c. or less of nitric acid 1.2 sp. gr., evaporate until all red fumes and all excess of nitric acid are expelled, best on a steam bath ; redissolve the copper nitrate in a little water, add a few drops of sodium hydroxide, which should give a slight precipitate of cupric hy- droxide, dissolve this in a few c.c. of acetic acid, allow to cool and dilute with cold water to about 50 c.c. Next add three grams of potassium iodide crystals (or in solu- tion), stirring until they have dissolved. The solution now con- tains a precipitate of almost white cuprous iodide and is colored brown by the liberated iodine. Run in the sodium thiosulphate solution from a burette until the brown color is very faint, a light straw color, then add about 5 c.c. of the clear starch solution and continue the titration until the blue is discharged. Near the end the sodium thiosulphate must be run in drop by drop and the solu- tion stirred thoroughly. Titrate the other portions and calculate the value of the solution in terms of copper. The standards should not differ by more than one in the fifth decimal place (third signifi- cant figure). The blue color will return after a time due to oxidation by the air. If the solution remains colorless for two minutes the end has been reached and the titration is satisfactory. If the blue reap- pears almost immediately there is probably some oxidizing agent present and if this continues after the addition . of a couple more drops of thiosulphate solution the determination is useless. After the potassium iodide has been added the solution must be kept cold to avoid loss of iodine and titrated without delay to avoid oxidation by the air. As large amounts of sodium acetate interfere with the end point, by causing a return of the blue color, care should be taken to add only a few drops of sodium hydroxide solution (not carbonate) in neutralizing the nitric acid. Assay. To the sulphate solution of the ore or matte add two pieces of sheet aluminum, one sixteenth inch thick and one and one half inches square, whose corners are bent so that the two pieces only touch at the points and so present a large surface, then about 5 c.c. of strong sulphuric acid. Heat to boiling, cov- ered to prevent spattering, until all the copper is precipitated. Pour 92 QUANTITATIVE ANALYSIS. the solution and that portion of the copper which does not adhere to the aluminum foil into a clean beaker and allow the copper to settle ; then decant through a filter, wash the aluminum foil coated with copper, with water and the copper in the second beaker, pour the washings through the same filter ; remove the vessel contain- ing the filtrate and washings and substitute the other beaker con- taining the non-adherent copper ; to the beaker containing the aluminum foil add $6 c.c. of nitric acid 1.2 sp. gr. and warm till all the copper has dissolved, then pour the acid copper nitrate solu- tion through the filter into the beaker below, which contains the rest of the copper and heat till all the copper has dissolved. If the precipitated copper is red in color and evidently pure, the washings of the beakers and filter can be added at once and the excess of nitric acid expelled and the copper titrated exactly as in standardizing. If the copper is dark, before diluting with the washings add half a gram of potassium or sodium chlorate and boil to oxidize any arsenic which may be deposited with the cop- per, then add the washings and evaporate as usual. When anti- mony is present it will be oxidized by the nitric acid and be almost all filtered out ; the traces which dissolve must be oxidized like the arsenic. It is of the utmost importance that all the chlorate is de- composed and the chlorine and oxides of chlorine boiled out, as these would liberate iodine later on. Bismuth will be deposited with the copper by the aluminum, it will dissolve in nitric acid and unless thrown out as a basic salt when the copper nitrate is dissolved in water, will precipitate as a brown iodide, Bil g . As this is not attended by any liberation of iodine it will not affect the results, but as this iodide is somewhat soluble in potassium iodide a brown-colored solution is produced, which may look like liberated iodine, and so too much thiosulphate solu- tion may be run in before the starch solution is added. In titrating some ores the end point may not be exactly the same as with pure copper, due to impurities, such as bismuth, lead, etc., which give a greenish solution after the starch is added, so that the change is not from blue to white, but from a dirty green to a yel- lowish white. The amount of potassium iodide has been given as three grams ; this quantity is required for the reaction and the excess necessary to hold the liberated iodine in solution. More does no harm, but as the reagent is expensive, it should be used sparingly. The end THE DETERMINATION OF COPPER. 93 point is so sharp that slight variations of the volume or of the amount of copper present have no effect. Ferric salts cannot be present, as they liberate iodine; in the method described they are reduced to the ferrous condition when the copper is precipitated by aluminum and are thrown away in the filtrate. If sodium car- bonate is used instead of hydroxide in neutralizing the copper nitrate solution some copper remains in solution as bicarbonate. Then, when the potassium iodide is added, iodine and carbon dioxide are liberated together, and some iodine is lost by being carried out with the carbon dioxide. It has been proposed recently by Low to neutralize here with ammonia and then to acidify by acetic acid as described : also to oxidize any arsenic or antimony present to the pentad condition by bromine instead of chlorate. For further information on this method see: Low, y. Am. Chem. Soc., 18, 458 and 24, 1082, 1902. Beringer's "Assaying," p. 160. POTASSIUM CYANIDE METHOD. This method is very largely used, as it is more rapid and less expensive than the iodide method. It depends on the conversion of the intensely blue Cu(NH 3 ) 4 ion into a colorless Cu(CN) 2 ion, or practically the measurement of the amount of potassium cyanide solution necessary to decolorize the ammoniacal solution of copper nitrate or sulphate. The reaction for the sulphate is given by Treadvvell as follows : 2 Cu(NH 3 ) 4 S0 4 ,H 2 + 4 KCN = 2Cu(CN) f + 8NH 3 + 2K 2 SO 4 , then the 2Cu(CN) 2 breaks up, giving Cu 2 (CN) and (CN) 2 , and, if sufficient potassium cyanide is present, forms K 4 Cu 2 (CN T ) 6 , while the (CN) 2 reacts on the excess of ammonia, like Cl on KOH, giving NHCN and NH 4 CNO. So the complete reaction is, 2Cu(NH 3 ) 4 SO 4 ,H 2 O + 8KCN = K 4 Cu(CN) 6 + NH 4 CN + NH 4 CNO + 6NH 3 + 2K 2 SO 4 . This is not advanced as a perfect explanation of what takes place, but to show how complex the simplest form of the reaction is. Then if we begin to consider the influence of other salts present and the easy conversion of ammonium cyanate into urea, a large field of possible organic compounds is opened ; so it is evi- 94 QUANTITATIVE ANALYSIS. dent that the reaction must be carried out under identical condi- tions in order to obtain accurate results. The following facts also emphasize this : 1. Increase of temperature decreases the intensity of the blue color. 2. A large excess of free ammonia tends to vary the color and give low results. 3. Ammonium sulphate gives low results. 4. Hydroxides, bicarbonates, sulphites and nitrites affect the results. 5. Salts of silver, zinc, nickel, etc., which react with potassium cyanide must be absent. 6. Ferric or manganese hydroxides should not be present, as they hold copper and mar the end point. The titration must therefore be made in the absence of iron, manganese, zinc, nickel or silver salts, best without ammonia salts, at the same temperature (the lower the sharper the end point), with the same excess of ammonia, with the same volume at the end, and with approximately the same amount of copper present. Make up a solution containing 22 grams of pure potassium Cyanide per liter. Weigh out two or three portions of pure copper about 150 milligrams each; dissolve them in nitric acid, in a beaker capable of holding 200 c.c. easily, with a mark at 150 c.c. ; boil out the oxides of nitrogen ; dilute with cold water to about 80 c.c. ; neutralize with dilute caustic soda solution till a faint permanent precipitate forms ; then add 6 c.c. of strong ammonia (0.9 sp. gr.) and run in the potassium cyanide solution till the blue color is very faint; dilute to the mark (150 c.c.) and continue the titration until the solution is colorless. To apply the method to ores, etc., follow the directions given for the iodide method until the copper is precipitated on aluminum foil, dissolve this in nitric acid and proceed as in standardizing. The method is very accurate after a little experience with the end point, and its most important feature is the necessity of abso- lute uniformity in the conditions of titration. Should great rapidity be required at the expense of accuracy, the ore can be dissolved in nitric acid, an excess of ammonia added, then titrated to a faint blue, the residue ferric hydroxide, etc., filtered out, and the titration finished on the clear filtrate. THE DETERMINATION OF COPPER. 95 The cyanide solution keeps best in the dark, but as it is con- stantly losing hydrocyanic acid it requires frequent standardizing. For further information see: Beringer's "Assaying," p. 154, and H. H. Miller, Irans. A. I. M. ., Nov., 1901. THIOCYANATE METHOD. This method has many modifications and is only recommended for low grade, impure ores or tailings containing less than three per cent, of copper and particularly when the impurities are arsenic and antimony. What follows is taken largely from an article by Guess,* and the thesis of Lindeman, Columbia University, 1903. The essential features of the method are as follows, the prelimi- nary treatment being as already given : The filtrate containing sul- phates is neutralized by ammonia and then rendered acid by either hydrochloric or sulphuric acid (i per cent, of either is sufficient acidity), next a slight excess of sulphurous acid is added and the solution heated, then a decided excess of potassium thiocyanate f is added and the solution stirred vigorously for a couple of minutes on the water-bath ; filtered immediately and washed with hot acid- ulated water several times. The precipitate is treated in the funnel with a hot 10 per cent, solution of sodium hydroxide, giving sod- ium thiocyanate, which is obtained in a clean beaker, and cuprous hydroxide which is left on the paper. This is washed by hot water. The alkaline filtrate is acidified with dilute sulphuric acid and the free hydrothiocyanic acid is titrated (warm) by potas- sium permanganate, according to the reaction, loHSCN -f 12 KMnO 4 4- 8H 2 SO 4 = 6K 2 SO, + i2MnSO 4 + loHCN + 8H 2 O. The theoretical factor for changing the iron standard to the cop- per standard is 0.1920, but it is safer to standardize against cop- per on account of the slight solubility of the cuprous hydroxide in caustic alkali. The results so obtained agreed with a factor of 0.1892. Of the metals likely to be present silver and possibly bismuth are the only ones which give insoluble thiocyanates under the conditions given. The silver would not interfere, for if not thrown out as chloride, the silver thiocyanide would be left with the cuprous hydroxide as it is not easily decomposed by alkali. The bismuth thiocyanate is soluble in acids and will usually be held in solution unless much is present. It is, however, precipi- * J. American Chem. Soc., 24, 708, 1902. f Often called sulphocyanide. 96 QUANTITATIVE ANALYSIS. tated as metallic bismuth if a large excess of sulphurous acid is used in effecting the reduction of the copper. The weak point of the method is the precipitation of the cuprous thiocyanate, which requires careful regulation of the acidity, especially when bismuth is present. The advantages are the large quantity of permanganate used for small amounts of copper and the non-interference of arsenic and antimony. The precipitation of copper as thiocyanate is used in alloys such as german silver, and to separate the bulk of the copper from the impurities in the analysis of pig copper. ADDITIONAL REFERENCES. VAN NAME. American J. Science, 163, 138-144. PARR, J. Am. Chem. Soc., 22, 685, 1900. MEADE. J. Am. Chem. Soc., 20, 610, i THE DETERMINATION OF LEAD. 97 CHAPTER XII. The Determination of Lead in Ores. The well-known inaccuracy of the fire assay for lead has rendered more important the volumetric methods for its determination. The basis for the sale of ores is now, in many cases, the percentage catually present, as shown by wet methods, minus two per cent., instead of the fire assay results.* The methods to be described are: First, the gravimetric, weigh- ing as sulphate ; second, the ferrocyanide ; third, the molybdate. While there are many other excellent methods, notably Koenig's alkalimetric, and the various modifications of the chromate, the three described are sufficient. GRAVIMETRIC AS LEAD SULPHATE. Treat from 0.5 to I gram of the very finely ground ore, depend- ing on the amount of lead present, with 15-20 c.c. of concentrated nitric acid and a few drops of concentrated hydrochloric acid in a small covered casserole or Erlenmeyer flask ; boiling until no further solution takes place and the sulphur (if the ore is a sulphide) is completely oxidized, adding more acids if necessary to complete the decomposition. Allow to cool slightly and add about 10 c.c. of sulphuric acid 1.41 sp. gr. (i part concentrated acid to I of water) and evaporate to copious, dense fumes of sulphur trioxide. All the common ores of lead will be decomposed by this treat- ment, which is carried out as already described under copper. The addition of a little hydrochloric acid is not always required, but usually aids in the solution of the lead. The evaporation should be nearly to dryness so as to ensure the complete conversion of lead to sulphate and also to prevent there being present too great an excess of sulphuric acid after dilution, more than I 2 per cent. Allow the lead sulphate, etc., to cool and add cautiously about 100 c.c. of distilled water and boil for several minutes to dissolve the ferric sulphate, etc., allow to cool and add about 15 c.c. of strong alcohol, stir well, allow to settle and decant through a small filter, leaving as much as possible of the insoluble sulphates and the silicious residue in the casserole or flask. Wash the residue * See lies, SCHOOL OF MINES QUARTERLY, Vol. XV., p. 336, 1894. 98 QUANTITATIVE ANALYSIS. by decantation thoroughly with water containing I per cent, sul- phuric acid and 10 per cent, alcohol. Pouring the washings through the filter, and wash finally with alcohol alone to remove the sulphuric acid. Place a clean beaker under the funnel, dissolve the lead sul- phate from the residue in a strong hot solution of ammonium acetate, slightly acid with acetic acid ; pour this solution through the filter into a clean beaker. Repeat this treatment until all the lead sulphate has dissolved ; then wash the residue onto the filter and wash it finally with hot water. Most of the trouble in the de- termination of lead occurs just at this point; lead sulphate when free from other insoluble sulphates and freshly precipitated dis- solves readily in hot ammonium acetate, but when ignited or if contaminated by barium, strontium or calcium sulphates, boiling for half an hour with a liberal excess of ammonium acetate is abso- lutely necessary for its complete solution. The ammonium acetate is best made by neutralizing acetic acid with ammonia as the crystallized salt is an expensive reagent and has to be used in large quantities. On solution Pb(C 1 H 8 O g ) s and (NH,) 2 Pb(SO 4 ) 2 are formed. The filtrate is acidified with dilute sulphuric acid, which reprecipitates the lead sulphate, alcohol is added as before (about 10 per cent.) and the precipitate filtered and washed; first with I per cent, sulphuric acid and 10 per cent, alcohol and finally with strong alcohol alone, either ethyl or methyl. The ignition of the lead sulphate, when filtered on paper, gives considerable trouble and often inaccurate results because the car- bon of the paper causes reduction to sulphide and sometimes to metallic lead, which requires reconversion, by nitric and sulphuric acids, to lead sulphate, often accompanied by mechanical loss. This difficulty can be overcome by using a Gooch crucible with asbestos alone, or as follows : Cut out two pieces of " acid- washed" filter paper so as to fit the bottom of the crucible accurately (using a 5 -cent piece) and place them on the bottom of the crucible; then on top of these a thin layer of asbestos which has been washed with dilute sulphuric acid, making a layer of about T 3 ^- of an inch ; then, while still wet, suck this down by a strong suction as tightly as possible and dry in an oven to constant weight at 1 10 C. After weighing moisten the filter and then pour in the solution contain- ing the lead sulphate, using a very gentle suction at the beginning; wash as described, dry again at 110 C. and the increased weight is lead sulphate. THE DETERMINATION OF LEAD. 99 This method has been thoroughly tested and will yield results (when properly carried out) which are accurate to within a few hundredths of a per cent. When such accurate work is not required the alcohol may be omitted, but the use of the Gooch crucible is strongly recommended when the necessary suction can be obtained. Lead sulphate is slightly soluble in water and quite soluble in concentrated sulphuric acid ; it is almost insoluble in a I per cent- solution of sulphuric acid and insoluble in alcohol. Besides being soluble in ammonium acetate it is soluble in ammonium chloride and other ammonium salts. Boiling with alkali carbonates con- verts it to carbonate, which can then be readily dissolved in acids. Koenig dissolves the lead carbonate in standard nitric acid and then by titrating back with a standard solution of caustic soda, using methyl orange as an indicator, determines the quantity of acid required to dissolve the lead and so finds the lead present. This method has a great advantage over the other volumetric methods in the end point, which is sharp and satisfactory, while the others are spot tests and an allowance for the excess required must be subtracted, as in the zinc titration by potassium ferrocya- nide. Lead sulphate is not volatilized if present when silica is driven off by hydrofluoric and sulphuric acids.* In some cases it is preferable to precipitate the lead as sulphide and subsequently convert it to sulphate by strong nitric acid. It should be borne in mind that lead sulphide is the most soluble of the fifth- and sixth-group sulphides in hydrochloric acid, so that less than 2 c.c. of concentrated hydrochloric acid should be present in each 100 c.c. of solution. It can also be precipitated from a neutral or alkaline solution, or one slightly acid with nitric acid. This separation is often necessary with alloys containing antimony, tin, etc., where the sixth-group metal is subsequently removed by digesting with fixed alkali sulphide. FERROCYANIDE METHOD. This method is the same as the gravimetric up to the point where the lead sulphate and insoluble residue has been washed free from sulphuric acid. Add to the residue in a flask or casserole at least 15 c.c. of a solution of commercial ammonium carbonate, sat- urated in the cold ; heat to boiling, then allow to cool, and filter through the filter already used to retain any lead sulphate from *Meade,/. Am. Chem. Sec., Vol. XIX.., p. 37, 1897. ioo QUANTITATIVE ANALYSIS. washing the lead sulphate and residue. Wash the flask and pre- cipitate till the washings show no alkaline reaction. Place in the flask 10 c.c. of 50 per cent, acetic acid and about 20 c.c. of water and boil till the lead carbonate has dissolved completely ; dilute to nearly IOO c.c., warm to 60 C, and titrate by potassium ferrocy- anide, using uranium nitrate as an indicator, as with zinc. As in the zinc titration, uniformity in the conditions for titration are essential to correct results. The same standard solution can be used, or better, one half the strength, about 10 grams of crystallized potassium ferrocyanide per liter. With such a solution the allow- ance for the indicator should be about o.S c.c. ; with the stronger solution, of course, it is less. This allowance is a matter of indi- vidual eyesight and should be determined on a blank test made up of ioo c.c. of water and 10 c.c. of 50 per cent, acetic acid at a temperature of 60 C. The standard is obtained by treating portions of pure dry lead sulphate with ammonium carbonate, dissolving the lead carbonate in acetic acid and titrating under the conditions given. The formula of the precipitate is nearly Pb 2 Fe (CN) 6 . It does not vary as greatly with changed conditions as the zinc ferrocyanide does, but as it is much more soluble equal care must be exercised in obtaining just the conditions given. The objectionable fea- ture is the end point. Many other indicators have been tried, but nothing better than uranium salts has been found. The good fea- ture of the method, which is, in fact, the reason for giving it a slight preference over all the others is that the impurities likely to be present are almost without effect. Antimony even if present to the extent of 0.200 gram is absolutely without effect. Bismuth gives results slightly low, but as 0.360 gram only lowers the amount of I per cent, ferrocyanide used by 0.6 c.c. it will not affect results when present in small quantities. Calcium and strontium are without effect. Barium gives slightly low results. These statements are based on a series of experiments carried out exactly as the method is described here, the low results are not to be attributed to the titration but to the barium and bismuth interfering with the con- version of lead sulphate to carbonate, for this reason, in some cases, the amount of ammonium carbonate solution should be increased considerably, even up to 50 c.c., and also the time of heating. The other metals which give insoluble ferrocyanides do not give insoluble sulphates or basic salts, so they pass into the filtrate when the lead sulphate and residue are filtered. THE DETERMINATION OF LEAD. 101 MOLYBDATE METHOD. This is based on the precipitation of lead as PbMoO 4 by a standard solution of ammonium molybdate in a hot solution slightly acid with acetic acid.* The end point is a spot test with tannin solu- tion which turns yellow when the molybdate is in excess. The standard ammonium molybdate is made by dissolving 9 grams of the pure salt in water and diluting to one liter; if the solution is not clear, add a few drops of ammonia. It is standard- ized by weighing out several portions of dry lead sulphate ; dis- solving them in hot ammonium acetate ; adding 2-3 c.c. of acetic acid and titrating at about 90 C. till a drop of the clear solution gives a slight but distinct yellow color with a drop of a freshly pre- pared tannin solution, which contains about I gram to 300 c.c. of water. The most important point is to titrate hot. If the solution has become cool on account of slow work in titration, it should be heated again so that it is hot when the titration is finished. The solution should be decidedly acid with acetic acid. Here and also in the preceding method the plan given under zinc of dividing the solution roughly in half for titration can be utilized. As an allowance must be made for the excess necessary to affect the indicator, uniformity in volume is essential ; 200 c.c. is recommended. With this volume and the conditions given the allowance should not exceed O.8 c.c. Many attempts have been made to obtain a more satisfactory end point for this method but so far in vain. The most satisfactory substitute has been devised by J. L. Danziger. Crystals of stannous chloride are dissolved in acetic acid till a saturated solution is formed; this is then satu- rated with ammonium thiocyanate. The solution so obtained gives a pink color with ammonium molybdate and is about as deli- cate as the tannin reaction. To apply this method to an ore, follow the gravimetric method till the lead sulphate is dissolved in ammonium acetate, acidify with 2-3 c.c. of acetic acid, dilute to 200 c.c., heat to boiling and titrate as in standardizing. Interferences. Antimony and bismuth are without effect. Barium gives very low results: strontium low results: calcium very slightly low results, but not enough to affect ordinary work. As in the ferrocyanide method the action of these alkaline earth sul- phates is to impede the solution of the lead, and the difficulty can * H. H. Alexander, Engineering and Mining Journal, April, 1893, p. 298. 102 QUANTITATIVE ANALYSIS. be entirely overcome by thoroughly washing the lead sulphate and then boiling it repeatedly with sufficient ammonium acetate. For comparative results on these and other methods see Bull, SCHOOL OF MINES QUARTERLY, Vol. XXIII., pp. 348-366, also Z. fur analytische Chemie, Vol. 41, pp. 653-674, 1902. THE DETERMINATION OF ANTIMONY. 103 CHAPTER XIII. The Determination of Antimony in Ores. On account of the great inaccuracy of the fire assay for antimony it has been abandoned and its place taken by a " wet assay." Before describing these methods a short description of the gravi- metric determination will be given and a few of the more important separations of antimony. The important ores of antimony are stibnite Sb 2 S 3 , cervantite Sb 2 O 4 , produced by the oxidation of the sulphide, and mixtures of the two usually containing more sulphide than oxide. As stibnite is soluble in hydrochloric acid containing a few drops of nitric, and cervantite is practically insoluble, we have three classes of ores ; first, the soluble, stibnite and also the rarer oxide, senarmon- tite, Sb 2 O 3 ; second, the insoluble ; third, the partially soluble. They will be discussed in this order. The following method is taken largely from an article by Brown, Journal American Chemical Society, 21, 780, 1899. GRAVIMETRIC METHOD. Soluble Ores. One gram of the finely ground ore is placed in a small beaker, 25 c.c. of concentrated hydrochloric acid added, cov- ered with a watch glass and boiled until the ore is apparently decom- posed, which reduces the hydrochloric acid to about 15 c.c.; about 2 grams of tartaric acid are added and when dissolved 5 or 6 drops of concentrated nitric acid and the boiling continued for several minutes. The nitric acid causes a violent reaction, accompanied by a more complete decomposition of the ore. The solution is allowed to cool, diluted slightly, the residue filtered, and washed with water. The residue should be tested for antimony, unless the ore is known to be completely soluble. The filtrate is diluted to about 250 c.c. and the antimony is precipitated as sulphide by a stream of hydrogen sulphide, which is passed through for an hour. At the end the solution should be warmed to insure the conversion of any basic chloride (formed by the dilution) to sul- phide ; after standing for an hour to allow the precipitate to collect and settle, it is filtered and washed with hydrogen sulphide water. There may be present in the ore, arsenic and also lead and 104 QUANTITATIVE ANALYSIS. other metals of the fifth group ; the latter will be evident from the dark color of the sulphide. If the sulphide is impure, warm it with a strong solution of ammonium sulphide (NHJ 2 S, until the sul- phides of arsenic and antimony have dissolved, then filter. The residue is lead sulphide, etc. ; in it the lead can be found by meth- ods already given. It should be remembered here that copper sulphide is slightly soluble in ammonium sulphide, so if it is pres- ent sodium or potassium sulphide should be used. If mercury should be present and no copper use ammonium sulphide as mercuric sulphide is readily soluble in the fixed alkali sulphides. Tin is not likely to be present; it would dissolve with the arsenic and antimony readily if stannic sulphide, with difficulty if stannous sulphide. The separation of antimony from tin pre- sents considerable difficulty. See the standard works on quanti- tative analysis and for the most recent descriptions of Clarke's method, etc., Rossing, Zeitschnft fur Analytische Chemie, 41, I, 1902, and Henz, Zeitschrift fur anorganische Chemie, 37, 1-58, 1903. The separation of the fifth and sixth groups is also incomplete by the ordinary methods when there are present mercury, copper and antimony, as sometimes happens with tetrahedrite (fahlerz). For this separation see Pretzfeld,y. Am. Chem. Soc., Feb., 1903. To the filtrate containing the arsenic and antimony as sulpho- salts, dilute hydrochloric acid is added in slight excess, then the solution is diluted to ensure complete separation of the antimony sulphide, which is soluble in even moderately strong hydrochloric acid, and the mixture of sulphides of arsenic and antimony and sulphur is filtered on balanced filters, washed with cold water and dried at 110 C. for two hours or more to constant weight. This gives the total weight of the mixture. It is removed from the paper, ground up and mixed in a small glass mortar and an exact weight, about 0.5 gram, is weighed off in a platinum or porcelain boat. This is placed in a piece of hard glass combustion tubing and the excess of sulphur, over that required to form Sb 2 S 3 and the sulphide of arsenic, are driven off by heating in a current of carbon dioxide for 12-15 minutes. A steady stream of carbon dioxide should be passed through the tube to displace the air before the heating is begun, so as to prevent oxidation ; the heating should be gradual and the final temperature about 250 C., considerably below a dull red heat. THE DETERMINATION OF ANTIMONY. 105 From the weight of the residue of black antimonous sulphide, the total antimony in the mixture of sulphides and sulphur is cal- culated and so the antimony in the ore. Should it be impossible to carry out this method, which is the best, the mixture of sulphide, or a portion of it, can be converted to oxide, Sb 2 O 4 by treating repeatedly with strong nitric acid. This method is not recom- mended as it is almost always attended by mechanical loss, but if nothing better can be done, carry it out as follows : Transfer as much as possible of the dried precipitate to a porcelain crucible, dissolve what adheres to the filter in freshly made ammonium sul- phide, using as little as possible, and add the solution to the pre- cipitate in the crucible; evaporate on a water-bath, add fuming nitric acid and allow to stand, carefully covered, for several hours ; then add more nitric acid, evaporate again on a water-bath ; next drive off the sulphuric acid formed and finally heat over a Bunsen burner (no blast), and weigh the Sb 2 O 4 . The arsenic will be volatilized. Insoluble Ores. One gram of the 6re is mixed with 10 grams of flux, made up of equal parts of sodium carbonate and sulphur, in a porcelain crucible and covered by a layer of the same flux. The mixture is fused for about ten minutes, covered, in the muffle of an assay furnace or by a Bunsen burner. The heat should be low at first and gradually raised, but never high enough to volatil- ize antimony. The melt should be greenish; if it is yellow the decomposition is probably incomplete unless there is scarcely any iron present. The melt is treated with hot water and the sulphides of iron, lead, etc. (those which do not form soluble sulphosalts), fil- tered out. In the filtrate the antimony is precipitated as sulphide by hydrochloric acid and the precipitate treated as just described. This is Rose's method of decomposition and it is also efficacious for the breaking up of cassiterite. Partially soluble ores can be treated as insoluble or treated first like soluble ores and the residue fused. Properties of Antimony Sulphide. Insoluble in water and dilute acids ; decomposed by concentrated nitric or sulphuric ; soluble in concentrated hydrochloric ; easily soluble in potassium or so- dium hydroxide and alkali sulphides. Slightly soluble in ammonia and ammonium carbonate. The separation from arsenic by dis- solving the sulphide of arsenic in ammonium carbonate is not quantitative. A better separation is Pattinson's. Obtain the arsenic io6 QUANTITATIVE ANALYSIS. and antimony in solution in the triad condition, add concentrated hydrochloric acid, so that the sp. gr. due to the acid shall exceed 1.17, and then precipitate the arsenic as sulphide. Arsenic sul- phide is insoluble in concentrated hydrochloric acid, while in acid of 1.17 sp. gr. or over no antimony is precipitated. Other methods of separating arsenic and antimony will be given under arsenic. VOLUMETRIC METHODS. WELLER'S METHOD.* The ore is decomposed as already described and the antimony precipitated as sulphide, if arsenic is also present it must be sepa- rated. As tin does not interfere in this method Pattinson's sepa- ration can be used with stannous chloride to reduce the arsenic to arsenious chloride so that it will be promptly and completely separated as arsenious sulphide in the strong hydrochloric acid solution; then, after diluting the filtrate, the antimony is precipi- tated as sulphide, Sb 2 S 3 . Or the arsenic can be distilled off as arsenious chloride according to Fischer's distillation method (see next chapter). The precipitated sulphide of antimony is dissolved in strong hy- drochloric acid and is oxidized to the pentad condition by adding potassium or sodium chlorate in small portions and boiling till the excess of chlorine is expelled and the oxides of chlorine driven out. It is essential that the oxidation shall be complete and all excess of oxidizing agent expelled, as the method depends on measuring the iodine liberated by the pentad antimony; using a standard thiosulphate solution, as with copper. After oxidation the solution is boiled down to very nearly 50 c.c. ; this is ascertained with sufficient accuracy by making a mark on the beaker ; then 20 c.c. of concentrated hydrochloric acid are added and the solution diluted to 600-700 c.c. with recently boiled cold water. Then three grams of potassium iodide are added and after waiting a few minutes for the solution of the potassium iodide and the liberation of the iodine, the solution is titrated by sodium thiosulphate, using starch solution as indicator, till the blue color disappears. The end point is very sharp and satisfactory when these conditions are maintained exactly. It is very important that the amount of hydrochloric acid is kept constant; if too little is *Youtz, SCHOOL OF MINES QUARTERLY, July, 1903. THE DETERMINATION OF ANTIMONY. 107 present basic iodides and chlorides of antimony separate out on dilution ; if too much, the hydrochloric acid itself acts on the potassium iodide in the presence of air and liberates iodine. We obtain this constant quantity, no matter how much may be used in the solution of the sulphide, by boiling down to 50 c.c. ; this will be acid of 20 per cent., the hydrochloric acid of constant boil- ing point. If it was weaker in the beginning, more water boils off, if stronger, more hydrochloric acid, until this strength of acid is reached. So by this means we obtain always the equivalent of 45 c.c. of concentrated hydrochloric acid in a volume of about 650 c.c. The potassium iodide must be three grams, if more is used results which are too high are obtained. The liberation of iodine is not instantaneous so it is advisable to wait several minutes before titrating, otherwise the solution may be decolorized by the thiosulphate and then the blue color suddenly flashes back, because the reaction is not yet complete. When the end point is reached, under the right conditions, the decolorization lasts for several minutes. The sodium thiosulphate solution used for the copper assay can be used here. Theoretically the standard against antimony would be obtained as follows: Copper standard: antimony standard:: atomic weight copper: one half atomic weight antimony. It has, however, been found that while the standards obtained from copper, from potassium dichromate and from iodine agree with each other, that they do not agree, when calculated to antimony, with the results obtained by standardizing with pure antimony. The discrepancy is almost exactly one per cent., under the conditions for titration just given ; so if the antimony standard is to be calcu- lated from any of the others, one per cent, should be added to that standard. If the calculated standard is 0.0062 grams Sb the figure 0.006262 should be used under the conditions given, or if the ore contained by calculation 18 per cent, the percentage of anti- mony is 1 8. 1 8. The true cause of this variation has not yet been explained but the same deviation has also been observed with arsenic. It is more satisfactory to restandardize against antimony if absolutely pure metallic antimony can be obtained. Weigh out about 0.2 gram and dissolve this in about 50 c.c. or more of con- centrated hydrochloric acid with 1-2 c.c. of concentrated nitric acid, then complete the oxidation by adding portions of 0.5 gram of potassium or sodium chlorate, boil out the oxides of chlorine io8 QUANTITATIVE ANALYSIS. and proceed as described. No tartaric acid is used in this method. The reaction may be indicated as follows : Sb 2 5 + 4 HI = Sb 2 3 + 2l 2 + 2H 2 0. The antimony after oxidation is probably present as antimonic acid and after reduction by hydriodic acid it is present partly as antimonious iodide and partly as antimonious chloride, depending on the relative mass of hydriodic and hydrochloric acids. As tin in the stannic condition is not reduced by hydriodic acid, anti- mony can be determined in the presence of tin. This is of im- portance in the analysis of alloys. This method is not free from theoretical difficulties, but it is very rapid and gives excellent practical results when the proper condi- tions are maintained. The same thiosulphate solution can be used as for copper and the end point is sharp. MOHR'S METHOD. This is exactly the reverse of Weller's method. The reactions can be indicated as follows : Mohr s->- -<- Weller Sb 2 3 + 2l 2 + 2H 2 ^t Sb 2 5 + 4 HI. In Mohr's method we prevent the reverse reaction by preventing any concentration of hydriodic acid by having an excess of alkali present. In order not to decompose the starch or absorb iodine this excess of alkali must be bicarbonate, so the exact reaction becomes Na 3 Sb0 3 + I 2 + 2NaHC0 3 = Na 3 SbO 4 + 2NaI + H 2 O + 2CO 2 . The same statement and a similar reaction applies also to arsenic so it is evident that no arsenic can be present. When the antimony is in the pentad condition it must be re- duced by heating with sulphurous acid. To the acid solution add 30 c.c. of sulphurous acid (about 5 per cent. SO 2 ) and boil till most of the sulphur dioxide is expelled, then add a second portion of 30 c.c. and boil out the sulphur dioxide completely, then add about two grams of tartaric acid, to prevent the subsequent pre- cipitation of antimony as hydrated oxide and make the solution alkaline with sodium bicarbonate, add about 20 c.c. of a saturated THE DETERMINATION OF ANTIMONY. 109 solution in excess, cool and titrate with N/io iodine, using starch as indicator, at a volume of about 200 c.c. When the antimony is separated as sulphide, either Sb 2 S 3 or Sb 2 S 5 , it is dissolved in hydrochloric acid. This, by the liberation of hydrogen sulphide, reduces the antimony to antimonious chloride, so that after adding tartaric acid and neutralizing the excess of acid by alkali, and then adding an excess of sodium bicarbonate it is ready for titration. It is advisable to run a blank made by neutralizing the same amount of hydrochloric acid in the same way and adding the same excess of sodium bicarbonate, in order to see whether a small quantity of iodine is required when there is no antimony present. If this amounts to more than o.i c.c. it should be subtracted. This method can be used for arsenic in exactly the same way, omitting the tartaric acid. Conclusion. Formerly antimony was weighed as sulphide, after washing with alcohol, to remove the water, then with carbon bisulphide to take out the free sulphur and drying at 250 C. The results are always high and the method is only to be used for very small quantities, under I per cent. A comparison of results has shown the weighing as oxide to be slightly low and that the Mohr and Weller methods give accurate results. The application of the volumetric methods to insoluble ores con- taining both arsenic and antimony will be indicated in the next chapter. no QUANTITATIVE ANALYSIS. CHAPTER XIV. The Determination of Arsenic in Ores. DISTILLATION METHOD. This method consists in distilling off the arsenic as arsenious chloride, and so affords a most perfect separation from antimony and tin. Although it requires considerable apparatus, it must be regarded as the standard method of separation ; besides being ap- plicable to ores it is even better for material containing only very low percentages of arsenic, pig copper, etc. It was devised by Professor Emil Fischer, of Berlin. Arsenic ores are almost always sulphides, they may be decom- posed by the fusion methods given under antimony, and the arsenic precipitated as sulphide. The original ore, or the sixth- group sulphides, are treated as follows : Place about two grams of potassium chlorate on the bottom of a beaker ; on this place the weighed sample of ore, from o. 5 to 3 grams, depending on the rich- ness, or the precipitated sulphides ; then about a gram more of potassium or sodium chlorate, sufficient to cover the ore ; pour in cautiously little by little a mixture of 30 c.c. of concentrated hy- drochloric acid and 10 c.c. of water, cover the beaker and heat on a water-bath till the decomposition is complete and the oxides of chlorine, etc., driven off so as not to use up the ferrous salt added later. It is very important that the oxidation is complete to H 3 AsO 4 , as the arsenious chloride would be lost by boiling. If antimony is also to be determined, filter off any residue on asbestos, transfer the solution to a distilling flask (about 400 c.c.) using concen- trated hydrochloric acid to rinse out the beaker, etc., add 5 to 20 grams of ferrous sulphate, depending on the quantity of arsenic pres- ent and make the solution up to about 200 c.c. in volume with con- centrated hydrochloric acid. Connect the flask with a short con- denser and under the end place an Erlenmeyer flask, about 250 c.c., containing a little water so as to cover the end of the condenser tube. Heat the flask on an asbestos pad by a burner ; the arsenic acid is promptly reduced by the large excess of ferrous salt and forms arsenious chloride ; this with hydrochloric acid begins to distill over before a temperature of 100 C. is reached. They are THE DETERMINATION OF ARSENIC. in condensed and collect in the Erlenmeyer flask. If this becomes very hot it should be surrounded by ice water. The apparatus should be set up in a place free from draughts so as to avoid back pressure. The distillation is continued until about half the original volume remains. Remove the Erlenmeyer flask and then the burner, when cool aold another 100 c.c. of concentrated hydro- chloric acid and repeat the distillation, catching the distillate as before. This is continued till no more arsenic distills over, which can easily be ascertained by testing a portion of the last distillate with hydrogen sulphide. Unless there is a very large quantity of arsenic present two or at most three distillations are all that are required. The solution in the flask must not be allowed to be- come too small or in other words the boiling point must not be allowed to rise above 107 C. for the temperature of the vapor and 112 C. for the solution ; above this point antimony will be- gin to distill over. The distillation can be hastened by connect- ing the distilling flask with a second flask containing concentrated hydrochloric acid, this is heated so that a stream of hydrochloric acid gas passes in constantly, so that the strength of the acid is maintained and the removal of the arsenious chloride facilitated (like distilling with steam). When the separation is complete, the apparatus is allowed to cool and the antimony from the distilling flask is precipitated by hydrogen sulphide after diluting largely and the antimony sul- phide treated as already described. The arsenic is all in the dis- tillate in the arsenious condition ; it can be determined by nearly neutralizing the large excess of acid by soda, then adding a strong solution of sodium bicarbonate and titrating by Njio iodine, ex- actly as given under antimony. If a gravimetric method is to be used the arsenic is precipitated by hydrogen sulphide after diluting somewhat. Under these con- ditions the arsenic precipitates immediately as arsenious sulphide with very little sulphur, as it is entirely in the triad condition. If the amount is small it can be filtered on a Gooch crucible, washed with alcohol, then with carbon bisulphide and after drying at 1 10 C. weighed as sulphide. The results are slightly high. If the amount of arsenic is considerable, over 20 per cent., the error will increase proportionally and the arsenic must be dissolved, oxi- dized and finally weighed as magnesium pyroarsenate. The siu- phide is dissolved in fuming nitric acid, the excess of acid ana 112 QUANTITATIVE ANALYSIS. oxides of nitrogen removed by boiling (for manipulation compare antimony sulphide when paper is used) ; or dissolve from the Gooch crucible by ammonia, evaporate down on a water-bath and then oxidize, or dissolve through by a small quantity of sodium hydroxide and oxidize by boiling with bromine. PRECIPITATION OF MAGNESIUM AMMONIUM ARSENATE. The conditions for the precipitation of magnesium ammonium arsenate are similar to those for magnesium ammoniun phosphate, but as the precipitate is more soluble and also more easily decom- posed on ignition greater care must be used. When the arsenic is all in the pentad condition neutralize the acid solution with ammonia and add a slight excess. The volume should not exceed 100 c.c.; add magnesia mixture slowly, drop by drop, till in considerable excess, then alcohol equal to one third the volume of the solution and allow to stand in the cold over night. Filter on asbestos in a Gooch crucible and wash with 2^/ 2 per cent, ammonia containing a little alcohol, then with 20 per cent, alcohol alone, dry and ignite very gently to constant weight ; weigh the Mg 2 As 2 O r SEPARATIONS OF ARSENIC AND ANTIMONY. The action of hydrogen sulphide on arsenic and antimony is important but confusing. The following separations are used : Bunsen's Method. When hydrogen sulphide is passed into an acid solution containing pentad arsenic and pentad antimony at the room temperature and then the hydrogen sulphide driven out by a current of air, antimonic sulphide, Sb 2 S 5 , only is precipitated. The hydrogen sulphide reduces the arsenic slowly, and if the ex- cess is promptly driven out when the precipitation is complete, a satisfactory separation is effected. Pattinsoris Method. In the separation described under anti- mony the hydrochloric acid was so strong that no antimony sul- phide could form ; here to get a prompt precipitation of arsenic it should be reduced before passing in hydrogen sulphide. When stannous chloride is used care must be taken to avoid an excess, which would precipitate metallic arsenic. Neher's Method. The solution containing arsenic and antimony, completely oxidized, and at least two volumes of concentrated hy- drochloric acid to one of solution (i. e., 1. 14 sp. gr.), is cooled to zero THE DETERMINATION OF ARSENIC. 113 and saturated by a rapid stream of hydrogen sulphide. The arsenic is completely precipitated as pentasulphide, As 2 S 5 . McCay ob- tains the same result by saturating the solution containing pentad arsenic in the cold with hydrogen sulphide and then heating in a closed bottle (under pressure) in a water-bath. The arsenic can be filtered on a Gooch crucible and weighed as pentasulphide, As 2 S 5 . These separations are in accord with the theory that in a hot solution hydrogen sulphide reduces the arsenic first and then precipitates it as As 2 S 3 mixed with sulphur ; at the ordinary tem- perature this reduction goes on slowly, at zero it is not perceptible. Also as the acid increases the amount of pentasulphide increases. The limit being Neher's method where at oC. and in a strongly acid solution the precipitation is entirely as As 2 S 5 . So under or- dinary conditions we obtain various mixtures of As 2 S 3 , As 2 S 3 and S, depending on the temperature and the acidity. For information on the formation of sulphoxy acids of arsenic, which by breaking up give these sulphides, see McCay, J. Amer. Client. Soc. t 24, 66 1, 1902. And for more information on the separation, see Treadwell's " Quantitative Analysis," pp. 150-154 (German edition). When arsenic is to be removed in the course of analysis with the fifth and sixth groups, it should be reduced by sulphurous acid and the excess expelled. This is accom- plished readily under pressure by heating in a strong bottle in boiling water, wrapped up in a towel to prevent flying glass, in case of an explosion. VOLUMETRIC METHODS. The most important determination of arsenic for mining engi- neers is in ores, where it is present from i-io per cent, and for this determination some modification of Pearce's method is usually employed. The method is not free from objections and gives low results on arsenopyrite. This method and one recently divised by Danziger and Buckhout * which is also applicable to arsenopyrite will be described. PEARCE'S METHOD AS MODIFIED BY BENNET f is based on the following facts. Arsenic when fused with a mixture of potassium nitrate and sodium carbonate is completely oxidized and forms * SCHOOL OF MINES QUARTERLY, April, 1903. \ J. Amer. Chein. Soc., 21, p. 431, 1899. H4 QUANTITATIVE ANALYSIS. sodium arsenate, Na 3 AsO 4 , which is soluble in water, while anti- mony forms a quite insoluble sodium metantimoniate which is left behind when the melt is leached with water, together with oxide of iron, insoluble carbonates, etc. The filtrate contains beside, Na 3 AsO 4 , Na 2 SO 4 , Na 2 SiO 3 , Na 2 Al 2 O 4 and an excess of Na 2 CO 3 ; this is acidified and the carbon dioxide expelled ; then neutralized exactly and the arsenic precipitated as silver arsenate, Ag 3 AsO 4 , by an aqueous solution of silver nitrate. It is this neutralization which has given trouble ; in the original method it was effected by ammonia, but as the precipitate (Ag 3 AsO 4 ) is readily soluble either in nitric acid or ammonia, it was essential to obtain exactly the neutral point. The second plan for neutralizing was proposed by Canby, the addition of a cream of zinc oxide ; this method will give a sufficiently neutral solution if the zinc oxide is allowed to remain in contact with the solution over night. The latest sug- gestion is that of Bennet to use acetic acid and a sensitive indicator like phenolphthalein. The precipitate of silver arsenate is filtered off and the silver in it determined by Volhard's thiocyanate titration using ferric alum as an indicator. The method is therefore an indirect titration of the arsenic, and for three atoms of silver found there must have been present from the ore, one atom of arsenic. So the arsenic value for the thiocyanate solution is obtained from the silver stand- ard by using the proportion, atomic weight silver to one third atomic weight arsenic. Solutions Required. Aqueous nitrate of silver, made by dissolv- ing silver nitrate crystals in water. (The nitric acid solution used to test for chlorides will not do here.) A ten per cent, solution of ferric sulphate or a saturated solution of iron ammonium alum as indicator ; a solution of ammonium thiocyanate containing about 8 grams per liter. This is standard- ized by dissolving portions of pure silver, about 0.2 gram each in nitric acid, 1.16 sp. gr. diluting to about 100 c.c. ; adding 5 c.c. of the indicator and titrating until a faint permanent reddish color is produced. The silver is precipitated as thiocyanate. The end point is the production of red ferric thiocyanate. Both standards should be placed on the bottle as the solution may be used for the determination of silver in alloys, etc. This solution keeps well and therefore does not require frequent re- standardizing. THE DETERMINATION OF ARSENIC. 115 Flux. Make up a sufficient quantity of flux containing two parts of potassium nitrate by weight, to one part of sodium carbonate. Assay. Place a layer of the flux on the bottom of a Russia iron crucible, mix the weighed portion of the ore, 0.25 to I gram, depending on the quantity of arsenic, with 8-10 times its weight of the flux and place this on top of the first layer ; cover this with a layer of potassium nitrate. Porcelain crucibles may be used, but they usually break, owing to the contraction of the flux on cooling. Heat the crucible very gently and gradually, holding the burner in the hand and allowing the flame to heat different parts of the crudible in turn. The heating requires attention or arsenic will be lost with a high-grade ore. There must be no odor or fumes of arsenic at this point. After the fusion has become quiet, the heating is continued for several minutes and the contents caused to rotate to ensure complete fusion and oxidation. Allow to cool and leach with hot water, filter and wash the residue very thoroughly with hot water ; acidify with nitric acid and boil vigorously till all the carbon dioxide is expelled. If any precepitate, such as hydrated silica, forms here it may be filtered out, as it would interfere with the filtration of the silver arsenate, but not with the accuracy of the results. Allow the solution to cool completely ; add a few drops of phenolphthaleine and then dilute sodium hydroxide solution (not ammonia or sodium car- bonate on account of the indicator) till the solution turns pink, then acetic acid drop by drop till the color is discharged, stirring between each addition, so as to stop when there is but a drop of acetic acid in excess. Then, to the cold solution add a slight ex- cess of aqueous silver nitrate, filter the brick-red silver .arsenate and wash it with cold water till free from silver. As silver acetate is sparingly soluble, this must be completely washed out as well as the excess of nitrate. Dissolve the precipitate through the paper with dilute nitric acid into a clean beaker; dilute to about 100 c.c.; add 5 c.c. of the ferric indicator, and titrate as in standard- izing. SODIUM PEROXIDE METHOD. Sodium peroxide has been found to be an admirable reagent for the decomposition of arsenic ores ; its action is the same as the mixture of potassium nitrate and sodium carbonate to form sodium arsenate, but it acts more rapidly and effectively in preventing loss ii6 QUANTITATIVE ANALYSIS. by volatilization with high-grade ores. After destroying the ex- cess of peroxide and filtering off the residue, we have an alkaline solution containing sodium arsenate. There are at least three volu- metric methods by which the arsenic can be determined : (ist) In- directly as silver arsenate as just described, (2nd) by standard alkali. Acidify the alkaline solution with hydrochloric or nitric acid in slight excess, boil out carbon dioxide, then add methyl orange and titrate till the solution turns yellow, with a dilute solution of sod- ium hydroxide. This marks the neutralization of the excess of hydrochloric or nitric acid and of one hydrogen of the arsenic acid ; we have now in solution NaH 2 AsO 4 ; add a few drops of phenol phthaleine, and titrate to a pink color with a standard solution of sodium hydroxide. The amount of alkali used is that required to neutralize the second hydrogen. Hence for each molecule of sodium hydroxide used there is present one atom of arsenic. This method is only outlined as it is not as accurate as the others. Third method : Measuring the arsenic present by the amount of iodine liberated, as in Weller's method for antimony. This gives accurate results when carried out as follows : About half a gram of arsenopyrite or more of an ore containing less arsenic is mixed with 10-15 grams of sodium peroxide and placed in a large nickel crucible, so that it is not more than one third full, with a cover of sodium peroxide on top. The crucible is heated slowly at first, until the mass is fused, then the temperature is raised to a strong red heat for a couple of minutes, the crucible is held by tongs in the flame and the contents caused to rotate.* Allow to cool and leach with about ipo c.c. of hot water, then boil for five minutes, till the excess of sodium peroxide is completely decom- posed, filter and wash with hot water containing sodium carbonate. Acidify with hydrochloric acid, boil out the carbon dioxide and evaporate to about 75 c.c. When cold, add about 75 c - c - of con- centrated hydrochloric acid and allow to cool again, then add 3 grams of potassium iodide and titrate the liberated iodine by a standard sodium thiosulphate solution, till only a faint straw color, due to free iodine, remains ; finish the titration, using starch solution as a spot test on a white tile, till no blue color is pro- duced. The starch does not give satisfactory results when added to the solution, on account of the great quantity of hydrochloric acid, which has to be present to effect the quantitative liberation *This is necessary to obtain complete decomposition of the ore. THE DETERMINATION OF ARSENIC. n/ of iodine. Pink and violet colors are formed which give an uncertain end point. The spot test is not tiresome in this case because it is possible to judge the end within a few drops by the yellow color of the solution. As in the case of the antimony titration, the results, using the standard calculated from iodine or potassium dichromate, are about I per cent. low. So that I per cent, of the arsenic present should be added to the results ; or better, standardize against freshly re- sublimed arsenious oxide, As 4 O 6 , as follows : Weigh out portions of 0.2-0.25 gram of resublimed arsenious oxide into small beakers ; add to each about 0.5 gram of potassium chlorate and about 20 c.c. of concentrated hydrochloric acid and boil till the oxidation of the arsenic is complete and all yellow color has disappeared from the solution ; add water and concentrated hydrochloric acid so that the final bulk is 100-150 c.c. and consists of half concentrated hydrochloric acid and half water (20 per cent, actual HC1). Cool, add three grams of potassium iodide and titrate as in the ore. Calculate the arsenic standard 'from the number of c.c. used. This is another titration where the results are varied by changes in the conditions of titration ; here the important points are the tem- perature, the acidity and the amount of potassium iodide. When uniform conditions are maintained in standardizing and in titrating the results are very exact. It only remains to indicate a procedure for ores containing both arsenic and antimony. Decompose the ore with sodium peroxide, as given, leach, boil, filter and precipitate the antimony by Bunsen's method (page 112), filter out the antimonic sulphide and titrate the arsenic in the filtrate as just described. To obtain the anti- mony dissolve the residue from the fusion in hydrochloric acid, filter, precipitate the antimony in the filtrate by hydrogen sulphide ; add this to the sulphide already obtained : dissolve and titrate by either of the methods given under antimony ore. ADDITIONAL REFERENCES TO BOTH ARSENIC AND ANTIMONY. Review of methods for antimony, Z.fur Analytische Chemie, 38, p. 664, 1899; for arsenic; same, 39, pp. 654-670 and 699-720, 1900. Beck and Fisher, Separation and Estimation of Arsenic and Antimony in Ores, SCHOOL OF MINES QUARTERLY, 20, 372. ii8 QUANTITATIVE ANALYSIS. CHAPTER XV. Slag Analysis. Under the title of Slag Analysis, nearly the whole subject of analytical chemistry and assaying might be discussed, for a great majority of the elements, both common and rare, are to be found in slags. No such attempt will be made here ; what follows is merely a description of the technical analysis of some of the most important types of slags. . For a more detailed and complete dis- cussion of the subject the reader is referred to an article by Dr. Jouet on the Analysis of Slags and Cinders, in the SCHOOL OF MINES QUARTERLY, Vol. XXII., Nos. i and 2. If the sample of slag has been chilled suddenly, it can usually be decomposed by acids, if allowed to cool slowly, a fusion with mixed carbonates is required. The important points to be shown in a technical analysis are : The ratio of bases to silica, the ratio of R 2 O 8 bases to those of the RO type, the quantity of valuable metal present in a slag, from copper smelting, copper, etc. For convenience in treating this subject the following classifica- tion is made ; Iron Slags. The slags from the blast furnace in the produc- tion of pig iron, though containing much less iron than those which follow. They contain roughly 40-50 per cent, silica, I 5- 20 per cent, alumina, etc., 3040 per cent, lime, magnesia, etc., besides iron, manganese, alkalies, sulphur, phosphorus, etc. The slags from basic processes are often rich in phosphoric acid. For this determination see Bulletin 46, Division of Chemistry, U. S. Department of Agriculture or Wiley's Agricultural Analysis, Vol. II. Manganese Slags. The slags formed in the production of Spiegel, lower in silica than the iron slags, but containing up to ten per cent, of manganese. The difficult points in their analysis are the decomposition and the separation of manganese from alumina. Lead Slags. Containing roughly silica 32 percent., iron 28 per cent., lime, etc., 20 per cent., the remainder being lead, zinc, antimony, sulphur, etc. SLAG ANALYSIS. 119 Copper Slags. Similar in composition to the lead slags, but usually without lead or zinc and containing about half a per cent, of copper. These four groups of slags fall naturally into two divisions, the iron and manganese slags and the lead and copper slags. A general scheme will be given for each of these divisions, fol- lowed by a few comments and special precautions and by some separate methods for the determination of particular constituents. The methods will not be given in detail as they have already been discussed in these notes. IRON AND MANGANESE SLAGS. In this scheme (page 1 20) provision has been made for titanium, barium, zinc, nickel and cobalt and also for the removal of the higher groups, although they are not usually present. When these are omitted the analysis becomes quite similar to that of lime- stone. Phosphorus and sulphur must be determined in separate portions. See Iron Ore. In manganese slags, the fusion with mixed carbonates will usu- ally be required to get complete decomposition, using a liberal quantity of flux and a long fusion. In making the basic acetate separation, the excess of acetic acid must be very small in order to get complete precipitation of alumina and must be repeated to remove the manganese which is sure to come down under these conditions. The determinations of greatest importance and in many cases all that is required, are silica, oxides of iron and alumina, lime and magnesia. When the slag is soluble and only approximate results are required the determinations can be made as follows : * Portion for silica and oxides of iron and alumina. Weigh out half a gram of the sample, place this in a casserole, add about 20 c.c. of water and stir well, then 15-20 c.c. of strong hydrochloric acid, heat to boiling, while stirring to break up any lumps ; then evap- orate rapidly to dryness and bake, take up with hydrochloric acid and water, boil and filter, ignite and weigh the silica (impure). In the filtrate the alumina is precipitated, together with ferric hy- droxide, by ammonia and ammonium chloride. This should be reprecipitated, to free it from lime and magnesia, then ignited and weighed as usual. * See also Lord's "Notes on Metallurgical Analysis," p. 201 and seq. 1 20 QUANTITATIVE ANALYSIS. HH ^j ' j c cc S ttl > rs O ""o o en oT '*n 3 il j ^^3 *j O'ua PH ^ M C ji- ^3 ti aj g . ^ ^ rt 3 T3 .- | g rt rt >0 ^ 1 NaKCOj ydrate sil |l 1 5-g ' R |o ; 1 C OT - 3 ^ c ffi 0, ffi" ""OTJ fl 0.^ g rs 0) hk. WA "rt O . II QW / I - <= I s ! ^1:1 > H^^ g B^s g-gts^ . r^j-iJ'S'B-l l^i^ Jc/5^| g<~ ^-3 3 S S38 S IISJ&I cip 4 , weg SLAG ANALYSIS. 123 iron is usually high and no particular difficulties are likely to be met. Sulphur is occasionally determined in lead slags. This is either done by the Fahlberg-Iles method* or as follows:f One gram of the slag is treated in a casserole with a few c.c. of water, 10 c.c. of concentrated nitric acid and finally 20-25 c.c. of concen- trated hydrochloric acid ; boiled for about ten minutes, more hydrochloric acid added, and then evaporated to dryness and baked on a hot plate. When cold it is taken up with concentrated hydrochloric acid and water and boiled thoroughly ; then the free acid neutralized with ammonia and exactly six c.c. of concentrated hydrochloric acid added and the boiling and stirring continued till it is certain that all the iron oxide and lead sulphate are in solu- tion ; diluted to 200 c.c., 25 c.c. of 10 per cent, barium chloride added and the solution boiled for i 5 to 20 minutes, filtered and washed. The precipitate is ignited in a platimum crucible, the silica driven off by hydrochloric and sulphuric acids and the barium sulphate weighed. If the slag is not chilled, it will not be decomposed thoroughly, so the barium sulphate will be impure. With soluble slags this method gives good results and is much shorter than the Fahlberg-Iles. When the results are required in a very short time accuracy must give way to rapidity. So time is saved by working at once on a number of separate portions. (See Furman's " Manual on Assaying.") The following methods are employed for these slags : Silica. Dissolve half a gram in water and hydrochloric acid, filter, ignite and weigh the silica (which is of course impure). Barium. Dissolve half a gram in hydrochloric acid, add sul- phuric acid and evaporate to fumes, neutralize the excess of sul- phuric acid by ammonia, add 6 c.c. of hydrochloric acid, dilute to 200 c.c., boil and filter, weigh the silica and barium sulphate. Iron. i gram is dissolved and the iron titrated by either the dichromate or the permanganate method. Manganese. i gram, using Volhard's method. Zinc. i gram by the ferrocyanide method. *Iles, Decomposition and Analysis of Slags, SCHOOL OF MINES QUARTERLY, V., p. 357- f Miller and Thompson, paper read at N. Y. Section American Chem. Soc. , Decem- ber 4, 1903. 124 QUANTITATIVE ANALYSIS. Copper. I gram or more by the colorimetric method. Lead. i gram or more by volumetric methods or a larger portion by fire assay. Silver is usually determined by fire assay. The other determinations have been indicated under the iron and manganese slags. When ferrous iron is to be determined, Cooke's method, as given by Hillebrand, Bulletin 176, U. S. Geological Survey, p. 92, is to be used. Objection can easily be made to these schemes ; they are in- complete on one hand and too long for some purposes on the other ; but they are given as representing as much as is likely to be required of the mining engineer and as affording plans which can be amplified, modified or shortened to meet special needs. If more complete schemes are desired, they are to be found in the article by Dr. Joiiet already mentioned. As rocks and slags have much in common from an analytical standpoint, Dr. Hillebrand's bulletin on rock analysis will give much valuable information. FLUE GAS ANALYSIS. 125 CHAPTER XVI. Flue Gas Analysis. Any engineer is almost certain to have charge of some kind of a power plant, usually one where the heat of combustion of coal is the source of power ; in order to ascertain the efficiency at which the plant is run, he must know at least the analysis, better also, the calorific power, of the coal, and the composition of the flue gas and the ash the results of combustion. The examination of the ash is for unburned carbon and requires no additional description.* The determinations required in the flue gas are carbon dioxide, carbon monoxide, oxygen and nitro- gen ; the first two are of the greatest importance, as the higher the carbon dioxide and the lower the monoxide, the more efficient is the combustion. If this is obtained by the introduction of an excessive quantity of air, both the carbon dioxide and monoxide will be low. All that is required of the engineer is a knowledge of how to determine these four important constituents, really only three for the nitrogen is determined by difference, in order to ascertain whether the fuel is being used economically. This is obtained more satisfactorily by a number of analyses at frequent intervals, each made with rapidity, than by one analysis made with all the precautions and corrections, on account of the variations in the composition of the gas due to additions of fresh fuel, changing of draughts, etc. Therefore no mention will be made here of the so- called " exact " gas analysis, where all the measurements are made over mercury and allowance made for changes in temperature, barometer, etc., except to refer the reader to Hempel's Gas Analy- sis, recently translated by Prof. Dennis. We need only consider the most simple application of " technical " gas analysis. Gas analysis is a branch of volumetric analysis and the results are always expressed in percentage by volume. Now, as the vari- ation of volume of all gases for temperature and pressure is the same, the percentage by volume at any given temperature and pressure will be the same as under the standard conditions, OC. * See coal analysis. 126 QUANTITATIVE ANALYSIS. and 760 mm, It is therefore only when some particular con- stituent is absorbed and afterwards determined gravimetrically or by titration, that it is necessary in the " technical " analysis to ap- ply the corrections for temperature, pressure and tension of aque- ous vapor. However, variations of temperature or of pressure must be most carefully guarded against while the analysis is in progress, as these would vitiate the results. Whenever possible, the analysis is conducted in a room of even temperature, prefer- ably with a northern exposure. All measurements are made at the atmospheric pressure and over water which has been previ- ously saturated with a gas similar to that under examination. If the temperature remains constant the tension of aqueous vapor is also constant, and when the analysis is conducted rapidly the variations of the atmospheric pressure are not likely to affect the results seriously. So as these conditions are practically con- stant, the results expressed in percentage by volume will agree within an allowable error of say o. I per cent, of the results calcu- lated to the standard conditions. Unless there is a sudden bar- ometric change or by carelessness the gas becomes changed in temperature, the error is likely to be less than the inaccuracy in reading the volumes. Saturating the water over which the gas is measured or kept, and also the reagents, with the gases present, which are not to be absorbed by this particular reagent, deserves special emphasis. All gases are soluble in water] to some extent and as carbon dioxide is soluble to the extent of about one volume of the gas to one volume of water, the error due to this cause may be great. The saturation is easily accomplished by running through one or two analyses of the gas, after the apparatus has been filled with water, reagents, etc., before making the analysis, the results of which are to be used. The Orsat apparatus is the most convenient for flue gas analysis, as it is compact and portable.* It is assumed in these notes that this form of apparatus is to be used. REAGENTS. Carbon dioxide is removed by a strong solution of potassium hy- dioxide, 500 grams of commercial caustic potash to a liter of * A description of this apparatus can be found in the text-books given at the end of this chapter or in the circulars of the dealers in chemical apparatus. FLUE GAS ANALYSIS. 127 water, each cubic centimeter of this reagent absorbs about 40 c.c. of carbon dioxide. This is the first reagent used with the flue gas. Oxygen is absorbed by an alkaline pyrogallate solution, made by dissolving (as far as possible out of contact with the air) 5 grams of pyrogallol, C 6 H 3 (OH) 3 , in 100 c.c. of the potassium hy- droxide given above. Pyrogallol or, as it is frequently termed, pyrogallic acid, is a triatomic phenol, when dissolved in potassium hydroxide the three hydrogens of the hydroxyl groups are re- placed by potassium atoms. When oxygen is absorbed no definite reaction takes place, but acetic acid, and brown humus-like sub- stances are formed. The reagent will be quickly exhausted if ex- posed to the air ; each c.c. absorbs about 2 c.c. of oxygen. This is the second reagent used in the flue gas analysis ; it is evident that as it contains an enormous excess of caustic alkali it would, if used first, absorb carbon dioxide as well as oxygen. Carbon monoxide is absorbed by a hydrochloric acid solution of cuprous chloride, which is made as follows :* Cover the bottom of a large wide-mouthed bottle with black oxide of copper, not necessarily pure, to a depth of about half an inch ; fill nearly full with hydrochloric acid i.i sp. gr.; add about a hundred pieces of stout copper wire, cut in lengths of about six inches, so that they shall reach from the bottom to the top of the bottle ; allow to stand, shaking occasionally, till the solution is colorless ; then withdraw for use. The action is that the cupric oxide dissolves in the hydrochloric acid giving cupric chloride, this in turn dis- solves copper from the wires forming cuprous chloride, the reagent desired. The wires keep up the strength of the solution and reduce any cupric chloride formed by the air back to cuprous. The solution should be nearly colorless when used. The amount of carbon mon- oxide absorbed per c.c. is given variously by different authorities, but it is safe to assume that it will absorb an equal volume of carbon monoxide. The reaction is supposed to result in the formation of an unstable addition product, Cu 2 Cl 2 .CO. As there is usually only a few tenths of a per cent, of carbon monoxide in flue gas, this reagent will last for some time if protected from oxidation or if kept in contact with metallic copper. This is the third and last reagent used with flue gas. * Gill, *' Gas Analysis for Engineers," p. 34. 128 QUANTITATIVE ANALYSIS. SAMPLING. The sample should be taken as close as possible to the point where the flame ends and at the place in the flue of smallest cross- section, to prevent admixture of air and to get a sample of the gas which is really the result of the combustion in progress when the sample is obtained. Tubes are usually inserted in the wall of the chimney or other flue, which should penetrate to the center and contain asbestos to filter out dust, etc. They may be made of hard glass (combustion tubing), porcelain or metal depending on the temperature. Iron tubes are, however, obectionable as they become coated with oxide, which is reduced by the carbon mon- oxide in the gas with an increase in the amount of carbon dioxide. The end of the tube is provided with a cork or rubber stopper through which passes a smaller glass tube, which is connected by a short rubber tube with the sample tube. Many convenient forms of apparatus for samples of gas can be had from the dealers, but all that is necessary is a large pipette, 200-250 c.c., provided with a short piece of rubber tubing at both ends and two clamps. As the draught of the chimney must be overcome in taking the sample, some form of aspirator is needed. Water pumps are con- venient when water pressure is at hand, but a simple and service- able pump * can be made by reversing the valve of an ordinary large-sized bicycle pump. The aspirator is attached to the sample tube and the flue gases drawn through for several minutes to displace the air which fills the tube and connections ; then the ends of the sample tube are closed (by the clamps on the rubber tubes) and the sample is taken to the Orsat apparatus. ANALYSIS. The Orsat apparatus consists essentially of three pipettes con- taining the reagents already described and a measuring tube grad- uated from o to 100 c.c. in tenths, provided with a levelling bottle, so that the pressure of the gas can be made equal to that of the atmosphere. The measuring tube and connections are filled with water by turning a stop-cock and raising the levelling bottle ; then the tube containing the sample is connected by one end, while the other is placed under water, to prevent admixture of air when the sample of gas is removed ; the connections are * Devised by Irving Langmuir. FLUE GAS ANALYSIS. 129 opened and by lowering the levelling bottle a little more than 100 c.c. of the flue gas is drawn into the measuring tube ; the sample tube is then closed and disconnected and the excess of flue gas above 100 c.c. driven out by raising the levelling bottle so that the liquid in the measuring tube and in the bottle shall coincide with the loo-c.c. mark. Then the stop-cock is turned to prevent the escape of gas and the analysis is begun. The gas is run into the first pipette, containing potassium hydroxide. By raising the levelling bottle, the gas displaces the alkali solution, which passes into the rear portion of the pipette, displacing in turn air which expands a rubber bag. In this way the reagents are kept from contact with the atmosphere. In the pipettes are a number of glass rods ; when the reagent is displaced these rods remain wet and so give a large surface for the absorption of carbon dioxide from the flue gas. After three minutes the gas is drawn back into the measur- ing tube, care being taken that the reagent comes back to exactly the point at which it stood before on the capillary tube connecting with the pipette ; and the gas is remeasured at the atmospheric pressure. The decrease in volume gives the percentage of carbon dioxide. In order to ensure the complete absorption of any con- stituent it is well to run the gas over again into the pipette for three minutes and then back and take a second reading ; if more than two treatments are required, the reagent is becoming ex- hausted and should be renewed. When the carbon dioxide has been completely removed, the gas is run into the second pipette, containing alkaline pyrogallate, and the oxygen removed in the same way. As this reagent is likely to become weakened in a very short time several treatments are often necessary. After the oxygen has been removed and the second decrease in volume noted, the gas is run over into the third pipette containing cuprous chloride, for the removal of carbon monoxide ; then back and the final reading taken. The residual gas is considered nitrogen. Great care should be taken when making the readings to have the level in the levelling bottle and the measuring tube the same, so that the gas is under exactly atmospheric pressure each time. RESULTS. While it is not the province of analytical chemistry to discuss the results, it is to be expected that the carbon dioxide will be from 5-12 per cent, the carbon monoxide 0.0-0.4 P er cent., the 130 QUANTITATIVE ANALYSIS. oxygen together with the carbon dioxide should usually be be- tween 20 and 21 per cent., and the remainder nitrogen. While there is some variation in the percentage of oxygen in the air in different places, country and city, streets and parks, it is very slight, and 20.9 per cent, is very close to the correct percentage. Now if we burn carbon in air completely to carbon dioxide, as the volume of carbon dioxide is equal to the volume of oxygen used, according to Avogadro's law, the sum of the percentages of oxy- gen and carbon dioxide should equal that of the oxygen in the air, i. c., 20.9 per cent. But it often happens in the analysis of flue gas that the sum of these two does not equal 20.9 per cent.; for if any carbon monoxide is produced we get two volumes of carbon monoxide for each volume of oxygen, hence the percentage of nitrogen is diminished ; on the other hand if hydrocarbons such as methane, etc., are present, from bituminous coal, we get one vol- ume of carbon dioxide from two volumes of oxygen, as the water condenses, and therefore an increase in the percentage of nitrogen over that in the air. (See also Calculations of Analytical Chem- istry, Chapter VIII.) For further information on flue gas analysis the reader is referred to Gills' " Gas and Fuel Analysis for Engineers " ; Stillman's " En- gineering Chemistry," and Blair's " Chemical Analysis of Iron." For a complete discussion of gas analysis see Hempel's " Gas Analysis " translated by Dennis, and Winkler's " Technical Gas Analysis," translated and enlarged by Lunge. REFERENCES TO ADDITIONAL ANALYSIS. 131 CHAPTER XVII. References to Additional Analysis. The last chapter concluded the descriptions of the analyses re- quired of the mining engineers at Columbia University, but not all those frequently needed in practice ; so this final chapter will contain references to recent reliable descriptions of a number of additional analyses which are often required of mining engineers, metallurgists or chemists. The following abbreviations will be used : Journal of the American Chemical Society, J. Am. C. S. Transactions of the American Institute of Mining Engineers, T. A. /. M. E. School of Mines Quarterly, S. of M. Qly. Chemical News, C. N. Zeitschriftfur Analytische Chemie, Z. A. C. Zeitschrift fur Anorganische Chemie, Z. Anorg. C. Zeitschriftfur Angewandte Chemie, Z. Angew. C. Journal of the Society of Chemical Industry, J. S. C. I. Engineering and Mining Journal, E. & M. J. Alkalimetry and Acidimetry. BUTTON'S Volumetric Analysis, Eighth Edition. MOHR'S Lehrbuch der Titrirmethoden, Seventh Edition. Revised by Classen. JAMES AND RITCHEY. Analyses Required for an Electrolytic Al- kali Works. J. Am. C. S., 24, 469, 1902. Review of Alkali Determinations. Z. A. C, 37, 684, 1898. NORTH AND LEE. On the Estimation of Alkaline Hydrate or Bi- carbonate in the Presence of Monocarbonate. J. S. C. I., 21, 322, 1902. RIEGLER. Zur Titerstellung sowie zur Bestimmung kaustischer und kohlensaure Alkalien. Z. A. C., 38, 250, 1899. Review. Standardizing Acid and Alkali. Z. A. C., 40, 411, 1901. MARSHALL. Preparation of Standard Solutions of Sulphuric Acid. J. S. C. I., 18, 5, 1899. Alkalies in Feldspar, Rock or Slag. See Hillebrand, Bulletin 176, U. S. Geological Survey. 132 QUANTITATIVE ANALYSIS. Alloys. SACK. Bibliographic der Metalllegierungen. Z. Anorg. C., 35, 249, 1903. Type Metals y Bearing Metals, Etc. ANDREWS. On the Analysis of Alloys of Tin, Lead, Antimony and Arsenic. J. Am. C. S., 17, 869, 1895. GARRIGUES. Alloys for Metal Bearings. J. Am. C. S., 19, 934, 1897. WALTERS AND AFFELDER. Analysis of Bronzes and Bearing Metals. J. Am. C. S., 25, 632, 1903. HERZ. Trennung von Antimon und Zinn mittels Oxalsaure. Z. Anorg. C, 37, I, 1903. Bronze, Brass, German Silver. CAIRNS. Quantitative Analysis. TREADWELL. Arialytische Chemie, Vol. II. (now translated by Hall). SMITH. Electrochemical Analysis. RIBAN. Traite d'analyse chimique par 1'electrolyse. Bismuth. RIEDERER. Volumetric Determination of Bismuth as Molybdate and its Separation from Copper. J. Am. C. S., XXV., 907, 1903. WIMMENAUR. Electrolytic Estimation of Bismuth. Z. Anorg. C., 27, I, 1901. CLARK. Separation of Bismuth from Lead. J. S. C. I., 19, 26, 1900. Bismuth in Pig Lead. Furman's Assaying, p. 163. Boric Acid and Borax. THADDEEFF. Bestimung der Borsaure als Borfluokalium. Z. A. C, 36, 568, 1897. GLADDING. Boric Acid Determination. J. Am. C. S., 20, 288, 1898. SARGENT. Determination of Boric Acid in Tourmaline. J. Am. C. S., 21, 859, 1899. Cadmium. BIEWEND. Ueber den Kadmium gehalt der Zinkerze. Berg und Huttenmannische Z., 61, 401. REFERENCES TO ADDITIONAL ANALYSIS. 133 MILLER AND PAGE. Quantitative Determination of Cadmium. S. of M. Quarterly, 22, 391, 1901. Calorific Power of Fuel. ATWATER AND SNELL. Description of a Bomb Calorimeter and Method of its Use. J. Am. C. S., 25, 659, 1903. PARR. The Peroxide Calorimeter as Applied to European Coals and Petroleum. J. Am. C. S., 24, 167, 1902. LUNGE. Ueber das verfahren von Parr zur Bestimmung des Heiz- werthes von Brennstoffen. Z. Angew. C., 14, 793, 1901. KENT. Calorific Value of American Coals. T. A. I. M. E., November, 1897. PARR. Coal Calorimeter. J. Am. C. S., 22, 646, 1900. NOYES, W. A. Determination of the Heating Effect of Coals. J. Am. C. S., 17, 843, 1895. Cement. STILLMAN'S Engineering Chemistry. MEADE. Chemical and Physical Examination of Portland Cement, 1901. CANDLOT. Ciments et Chaux Hydrauliques. 1898, Paris. LUNGE. Chemische-Technische Untersuchungs Methoden. Vol. i> PP. 599-677. HILLEBRAND AND RICHARDSON. Report on Analysis of Materials for Portland Cement Industry. J. S. C. I., 21, 12, 1902. HILLEBRAND. Critical Review of Certain Cement Analyses, etc. J. Am. C. S., 25, 1180, 1903. Chlorates, Etc. SUTTON. Volumetric Analysis, p. 186, etc. Chromium. CAIRNS. Quantitative Analysis. BLAIR. Chemical Analysis of Iron. McKENNA. Complete Analysis of Chrome Ore. Proc. Eng. Soc. of Western Pa., 63, 180, 1897. MAHON. Chromium in Steel. J. Am. C. S., 21, 1057, 1899. Cobalt. CLASSEN. Ausgewahlte Methoden, p 425. 134 QUANTITATIVE ANALYSIS. Cyanide Solutions. EISSLER. The Cyanide Process for the Extraction of Gold, and other books on Gold Metallurgy, Rose, etc. GREEN. Testing Cyanide Solutions Containing Zinc. Institute of Mining and Metallurgy, October 17, 1901. CHRISTY. Electromotive Force of Metals in Cyanide Solutions. T. A. I. M. E., 30, 864. Review of Methods of Analysis. Z. A. C., 38, 792, 1899. SHARWOOD. Notes on the Estimation of Cyanogen, etc. J. Am. C. S., 19, 400, 1897. Copper. FRESENIUS. Hampe's method. Quantitative Analysis, English Edition, 1900, page 405. KELLER. On the Analysis of American Refined Copper. J. Am. C. S., 16, 785, 1894. HOLLARD. Analysis of Commerical Copper by Electrolytic Methods. Bulletin Soc. Chimique, 23, 292, 1900. ULKE. Copper Assaying and Analysis, Commercial Methods. E. and M. J., December 16, 1899. Review of Methods. Z. A. C., 37, 120, 1898. Fluorine. JANNASCH. Praktische Leitfaden der Gewichts Analyse, p. 267. STAHL. Analysis of Commercial Hydrofluoric Acid. J. Am. C. S., 18, 415. Indicators. SUTTON. Volumetric Analysis. Review of Indicators, Z. A. C., 42, 304, 1903. LUNGE. Bericht der Indikatoren-Kommission. Z. Angew. C., 1 6, H5, 1903- GLASER. Ueber Indicatoren. Z. A. C., 41, 36, 1902; also 38, 273, 1899. Lead. Refined Lead. CAIRNS. Quantitative Analysis. Review of Methods, Z. A. C., 42, 628, 1903. Lithium. JANNASCH. Gewichtsanalyse. WALLER. Bei der Bestimmung des Lithiums. Z. A. C., 36, 513, 1897. REFERENCES TO ADDITIONAL ANALYSIS. 135 Mercury. FURMAN. Manual of Assaying. CHISM. Assay for Mercury. E. & M. J., 66, 86. SMITH AND WALLACE. Electrolytic Estimation of Mercury. J. Am. C. S., 1 8, 169, 1896. RISING AND LENHER. An Electrolytic Method for the Determi- nation of Mercury in Cinnabar. J. Am. C. S., 18, 96, 1896. PRETZFELD. Gravimetric Estimation of Mercury and its Separa- tion from Arsenic, Antimony and Copper. J. Am. C. S., XXV., 198, 1903. Molybdenum. KOPP. Molybdenum in Steel. J. Am. C. S., 24, 186, 1902. AUCHY. Molybdenum in Steel. J. Am. C. S., 24, 273, 1902. Nickel. SARGENT. Determination of Nickel in Nickel Steel. J. Am. C. S., 21, 854, 1899. EDWARDS. Nickel Assay. New Caledonia. E. & M. J., May 28, 1898. LANGMUIR. Nickel in Nickel Ores. J. Am. C. S., 22, 102, 1900. HERZ. Nickel Sulphide, etc. Z. Anorg. C., 28, 342, 1901. TAGGART. Electrolytic Precipitation of Nickel from Phosphate Solutions. J. Am. C. S., 25, 1039, 1 93> Oils. GILL. Oil Analysis. ALLEN. Commercial Organic Analysis, Vol. II. LEWKOWITSCH. Chemical Analysis of Oils, Fats and Waxes. Paint. ELLIS. White Paint Analysis (Evanston, 111.). THOMPSON. Analysis of W T hite Paint. J. S. C. I., 15, 432 and 791, 1896. GNEHM. Unorganische Farbstoffe in Lunge's Chemisch-Tech- nische Untersuchungs Methoden, Vol. II., pp. 765804. Phosphates, Etc. WYATT. Phosphates of America. CHATARD. Phosphate Chemistry as it Concerns the Miner. T. A. I. M. E., 21, 160. 136 QUANTITATIVE ANALYSIS. GLADDING. Determination of Iron Oxide and Alumina in Phos- phate Rock. J. Am. C. S., 18, 717 and 721, 1896. Bulletins of U. S. Dept. of Agriculture. Platinum Metals. CLASSEN. Ausgewahlte Methoden der Analytischen Chemie. Vol. I, 1901. ' LEIDIE AND QUENNESSEN. Estimation of Platinum and Iridium in Platinum Ores. C. N., 84, 216, 1901. RICHARDS. Estimation of Platinum, Gold and Silver in Alloys. Analyst, 27, 266, 1902. WILEY. Recovery of Waste Platinum Chloride. J. Am. C. S., 19, 258, 1897. Separations. In general see the works of Fresenius, Classen and Treadwell ; for the halogens and alkaline earths see Jannasch's Gewichts- analyse. Sulphur in Pyrites. LUNGE. On the '"Estimation of Sulphur in Pyrites. J. Am. C. S., 17, 181, 1895. GLADDING. J. Am. C. S., 16, 403, 1894. Tin. Review on Tin, Antimony and Arsenic. Z. A. C., 38, 307-323, 1899. WELLS. Analysis of Tin Ore. S. of M. Qly, 12, 295, 1891. MILLER. Assay of Tin Ore. S. of M. Qly., 13, 369, 1892. Thorium and Other "Hydroxide" Elements. Treadwell's Analytical Chemistry and Classen's Ausgewahlte Methoden. Titanium. Review of the Determination of Titanium. Z. A. C., 40, 799, 1901. BASKERVILLE. On the Analysis of Titaniferous Iron Ores. J. S. C. L, 19, 419, 1900- POPE. Investigation of Magnetic Iron Ores from Eastern Ontario. T. A. I. M. E., 29, 372, 1899. BAIN. The Estimation of Titanium. J. Am. C. S., 25, 1073, 1903. REFERENCES TO ADDITIONAL ANALYSIS. 13? Tungsten. BORNTRAGER. Rasche Wolframprobe und Analyse von Wolfram- erzen, etc. Z. A. C, 39, 361, 1900. Tungsten in Steel : Blair; McKenna, C. N., 67, 1900; Auchy, J. Am. C. S., 21, 239, 1899. Uranium. KERN. Quantitative Separation and Determination of Uranium. J. Am. C. S., 23, 685-726, 1901. FRITCHLE. Analysis of Uranium and Vanadium Ores. E. & M. J., Nov. 10, 1900. Water. MASON. Examination of Water. 1901. STILLMAN. Engineering Chemistry, pp. 42-97. 1900. 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A Text-book for Textile, Trade and higher Technical Schools, as also for self -instruction. Based upon the ordinary syllabus and curriculum of the Imperial and Royal Weaving Schools. Translated from the German by Chas. Sal- ter. 8vo, cloth, illustrated net. $5.00 Catalogue of the Van Nostrand Science Series. are put up in a uniform, neat, and attractive form. J- boards. Price 50 cents per volume. The subjects are of an eminently scientific eharaoter, and embrace a wide range of topics, and are amply illustrated when the subject demands. No. x. CHIMNEYS FOR FURNACES AND STEAM-BOILERS. By R. Armstrong, C.E. Third American edition, revised and partly rewritten, with an appendix on Theory of Chimney Draught, by F. E. Idell, M.E. No. 2. STEAM-BOILER EXPLOSIONS. By Zerah Colburn. Nw edition, revised by Prof. R. H. Thurston. No. 3. PRACTICAL DESIGNING OF RETAINING- WALLS. By W. Cain. Arthur Jacob, A.B. Second edition, revised, with additions by Prof, No. 4. 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GASES MET WITH IN COAL-MINES. By J. J. Atkinson. Third edition, levised and enlarged by Edward H Williams, jun. D. VAN NOSTRAND COMPANY'S No. 14. FRICTION OF AIR IN MINES. By J. J. Atkinson. No. 15. SKEW ARCHES. By Prof. E. W. Hyde, C.E. Illustrated. No. 16. A GRAPHIC METHOD OF SOLVING CERTAIN QUES- TIONS IN ARITHMETIC OR ALGEBRA. By Prof. Geo. L. Vose. No. 17. WATER AND WATER-SUPPLY. By Prof. W. H. Corfield of the University College, London. No. 18. SEWERAGE AND SEWAGE PURIFICATION. By M. N. Baker, Assoc. Ed. Engineering News. No. 19. STRENGTH OF BEAMS UNDER TRANSVERSE LOADS. By Prof. W. Allan, author of "Theory of Arches." No. 20. BRIDGE AND TUNNEL CENTRES. By John B. Mo- Master, C.E. No. 21. SAFETY VALVES. By Richard H. Buel, C.E. Third edition. No, 22. HIGH MASONRY DAMS. By E. Sherman Gould, C.E. No. 23. THE FATIGUE OF METALS UNDER REPEATED STRAINS. With Various Tables of Results and Experiments. From the German of Prof. Ludwig Spangenburgh, with a Preface by S. H. Shreve, A.M. No. 24. A PRACTICAL TREATISE ON THE TEETH OF WHEELS. By Prof. S. W. Robinson. Second edition, revised. No. 25. ON THE THEORY AND CALCULATION OF CON- TINUOUS BRIDGES. By R. M. Wilcox, Ph.B. No. 26. PRACTICAL TREATISE ON THE PROPERTIES OF CONTINUOUS BRIDGES. By Charles Bender, C.E. No. 27. ON BOILER INCRUSTATION AND CORROSIOH By F. J. Rowan. New edition, revised and partly rewritten by F. L. Idell, M. E. No. 28. TRANSMISSION OF POWER BY WIRE ROPES By Albert W. Stahl, U.S.N. Second edition. No. 29. STEAM INJECTORS. Translated from the French oi M. Leon Pochet. No. 30. TERRESTRIAL MAGNETISM, AND THE MAGNET- ISM OF IRON VESSELS. By Prof. Fairman Rogers. 1*0.31. THE SANITARY CONDITION OF DWELLING- HOUSES IN TOWN AND COUNTRY. By George E. Waring, jun. No. 32. CABLE-MAKING FOR SUSPENSION BRIDGES. By W. Hildenbrand, C.E. No. 33. MECHANICS OF VENTILATION. By George W. Rafter, C.E. New edition (1895), revised by author. No. 34. FOUNDATIONS. By Prof. Jules Gaudard, C.E. Translated from the French. No. 35. THE ANEROID BAROMETER : ITS CONSTRUC- TION AND USE. Compiled by George W. Plympton. Eighth edition. No. 36. MATTER* AND MOTION. By J. Clerk Maxwell, M.A. ^Second American edition. SCIENCE SERIES. No. 37. GEOGRAPHICAL SURVEYING: ITS USES, METH- ODS, AND RESULTS. By Frank De Yeaux Carpenter, C.E. No. 38. MAXIMUM STRESSES IN FRAMED BRIDGES. By Prof. William Cain, A.M., C.E. New and revised edition. No. 39. A HANDBOOK OF THE ELECTRO-MAGNETIC TELEGRAPH. By A. E. Loring. New enlarged edition. No. 40. TRANSMISSION OF POWER BY COMPRESSED AIR. By Robert Zahner, M.E. Second edition. No. 41. STRENGTH OF MATERIALS. By William Kent, C.E., Assoc. Ed. Engineering News. No. 42. THEORY OF STEEL-CONCRETE ARCHES AND OF VAULTED STRUCTURES. By Prof. William Cain. No. 43. WAVE AND VORTEX MOTION. By Dr. Thomas Craig of Johns Hopkins University. No. 44. TURBINE WHEELS. By Prof. W. P. Trowbridge, Columbia College. Second edition. No. 45. THERMODYNAMICS. By Prof. H. T. Eddy, University of Cincinnati. No. 46. ICE-MAKING MACHINES. New edition, revised and en- larged by Prof. J. E. Denton. From the French of M. Le Doux. No. 47. LINKAGES; THE DIFFERENT FORMS AND USES OF ARTICULATED LINKS. By J. D. C. de Roos. No. 48. THEORY OF SOLID AND BRACED ARCHES. By William Cain, C.E. No. 49. ON THE MOTION OF A SOLID IN A FLUID. By Thomas Craig, Ph.D. No. 50. DWELLING-HOUSES : THEIR SANITARY CON- STRUCTION AND ARRANGEMENTS. By Prof. W. H. Corfield. No. 51. THE TELESCOPE : ITS CONSTRUCTION, ETC. By Thomas Nolan. No. 52. IMAGINARY QUANTITIES. Translated from the French of M. Argand. By Prof. Hardy. No. 53. INDUCTION COILS : HOW MADE AND HOW USED. Third American, from Ninth English edition. No. 54. KINEMATICS OF MACHINERY. By Prof. Kennedy. With an introduction by Prof. R. H. Thurston. No. 55. SEWER GASES : THEIR NATURE AND ORIGIN. By A. de Varona. No. 56. THE ACTUAL LATERAL PRESSURE OF EARTH- WORK. By Benjamin Baker, M. Inst C.E. No. 57. INCANDESCENT ELECTRIC LIGHTING. A Practical Description of the Edison System. By L. H. Latimer, to which is added the Design and Operation of Incandescent Stations, by C. J. Field, and the Maximum Efficiency of Incandescent Lamps, by John W. Ho well. No. 58- , THE VENTILATION OF COAL-MINES. By W. Fairley. M.E , F.S.S. D. VAN NOSTRAND COMPANY'S No. 59. RAILROAD ECONOMICS ; OR, NOTES, WITH COM- MENTS. By S. W. Robinson, C.E. No. 60. STRENGTH OF WROUGHT-IRON BRIDGE MEM- BERS. By S. W. Robinson, C.E. No. 61. POTABLE WATER AND METHODS OF DETECT- ING IMPURITIES. By M. N. Baker, Ph.B. No. 62. THE THEORY OF THE GAS-ENGiNE. By Dugald Clerk. Second edition. With additional matter. Edited by F. E. Idell, M.E. No. 63. HOUSE DRAINAGE AND SANITARY PLUMBING. By W. P. Gerhard. Eighth edition, revised. No. 64. ELECTRO-MAGNETS. By A. N. Mansfield, S.B. No. 65. POCKET LOGARITHMS TO FOUR PLACES OF DECI- MALS. No. 66. DYNAMO-ELECTRIC MACHINERY. By S. P. Thompson, With notes by F. L. Pope. Third edition. No. 67. HYDRAULIC TABLES BASED ON " KUTTER'S FORMULA." By P. J. Flynn. No. 68. STEAM-HEATING. By Robert Briggs. Third edition, revised, with additions by A. R. Wolff. No. 69. CHEMICAL PROBLEMS. By Prof. J. C. Foye. Fourth edition, revised and enlarged. No. 70. EXPLOSIVE MATERIALS. The Phenomena and Theories of Explosion, and the Classification, Constitution and Preparation of Explosives. By First Lieut. John P. Wisser, U.S.A. No. 71. DYNAMIC ELECTRICITY. By John Hopkinson, J. N. Shoolbred, and R. E. Day. No. 72. TOPOGRAPHICAL SURVEYING. By George J. Specht, Prof. A. S. Hardy, John B. McMaster, and H. F. Walling. No. 73. SYMBOLIC ALGEBRA; OR, THE ALGEBRA OF ALGEBRAIC NUMBERS. By Prof. W. Cain. No. 74. TESTING MACHINES: THEIR HISTORY, CON- STRUCTION, AND USE. By Arthur V. Abbott. No. 75. RECENT PROGRESS IN DYNAMO-ELECTRIC MA- CHINES. Being a Supplement to Dynamo-Electric Machinery. By Prof. Sylvanus P. Thompson. No. 76. MODERN REPRODUCTIVE GRAPHIC PROCESSES. By Lieut. James S. Pettit, U.S.A. No. 77. STADIA SURVEYING. The Theory of Stadia Measurements. By Arthur Winslow. No. 78. THE STEAM-ENGINE INDICATOR, AND ITS USE. By W. B. Le Van. No. 79. THE FIGURE OF THE EARTH. By Frank C. Roberts, C.E. No. 80. HEALTHY FOUNDATIONS FOR HOUSES. By Gleon Brown. SCIENCE SERIES. No. 8z. WATER METERS : COMPARATIVE TESTS OF ACCURACY, DELIVERY, ETC. Distinctive features of the Worth- ington, Kennedy, Siemens, and Hesse meters. By Ross E. Browne. No. 82. THE PRESERVATION OF TIMBER BY THE USE OF ANTISEPTICS. By Samuel Bagster Boulton, C.E. No. 83. MECHANICAL INTEGRATORS. By Prof. Henry S. H. Shaw, C.E. No. 84. FLOW OF WATER IN OPEN CHANNELS, PIPES, CONDUITS, SEWERS, ETC. With Tables. By P. J. Flynn, C.E. No. 85. THE LUMINIFEROUS ^THER. ByProf.de Volson Wood. No. 86. HAND-BOOK OF MINERALOGY; DETERMINATION AND DESCRIPTION OF MINERALS FOUND IN THE UNITED STATES. By Prof. J. C. Foye. No. 87. TREATISE ON THE THEORY OF THE CON- STRUCTION OF HELICOIDAL OBLIQUE ARCHES. By John L. Culley, C.E. No. 88. BEAMS AND GIRDERS. Practical Formulas for their Re- sistance. By P. H. Philbrick. No. 89. MODERN " GUN-COTTON : ITS MANUFACTURE, PROPERTIES, AND ANALYSIS. By Lieut. John P. Wisser, U.S.A. No. 90. ROTARY MOTION, AS APPLIED TO THE GYRO- SCOPE. By Gen. J. G. Barnard. No. 91. LEVELING: BAROMETRIC, TRIGONOMETRIC, AND SPIRIT. By Prof. I. O. Baker. No. 92. PETROLEUM : ITS PRODUCTION AND USE. By Boverton Redwood, F.I.C., F.C.S. No. 93. RECENT PRACTICE IN THE SANITARY DRAIN- AGE OF BUILDINGS. With Memoranda on the Cost of Plumbing Work. Second edition, revised. By William Paul Gerhard, C. E. No. 94. THE TREATMENT OF SEWAGE. By Dr. C. Meymott Tidy. No. 95 PLATE GIRDER CONSTRUCTION. By Isami Hiroi, C.E, Second edition, revised and enlarged. Plates and Illustrations. No. 96. ALTERNATE CURRENT MACHINERY. By Gisbert Kapp, Assoc. M. Inst., C.E. No. 97. THE DISPOSAL OF HOUSEHOLD WASTE. By W. Paul Gerhard, Sanitary Engineer. No. 98. PRACTICAL DYNAMO-BUILDING FOR AMATEURS. HOW TO WIND FOR ANY OUTPUT. By Frederick Walker. Fully illustrated. Ho. oo. TRIPLE-EXPANSION ENGINES AND ENGINE TRIALS. By Prof. Osborne Reynolds. Edited, with notes, etc., by F. E. Idell, M. E. SCIENCE SERIES. No. 100. HOW TO BECOME AN ENGINEER ; OR, THE THEORETICAL AND PRACTICAL TRAINING NECESSARY IN FITTING FOR THE DUTIES OF THE CIVIL ENGINEER. The Opinions of Eminent Authorities, and the Course of Study in the Technical Schools. By Geo. W. Plympton, Am. Soc. C.E. No. 101. THE SEXTANT AND OTHER REFLECTING MATHEMATICAL INSTRUMENTS. With Practical Suggestions and Wrinkles on their Errors, Adjustments, and Use. With thirty- three illustrations. By F. R. Brainard, U.S.N. No. 102. THE GALVANIC CIRCUIT INVESTIGATED MATHEMATICALLY. By Dr. G. S. Ohm, Berlin, 1827. Translated by William Francis. With Preface and Notes by the Editor, Thomas D. Lockwood, M.I.E.E. No. 103. THE MICROSCOPICAL EXAMINATION OF POTA- BLE WATER. With Diagrams, By Geo. W. Rafter. No. 104. VAN NOSTRAND'S TABLE-BOOK FOR CIVIL AND MECHANICAL ENGINEERS. Compiled by Geo. W. Plympton, C.E, No. 105. DETERMINANTS, AN INTRODUCTION TO THE STUDY OF. With examples. By Prof. G. A. Miller. No. 106. TRANSMISSION BY AIR-POWER. Illustrated. By Prof. A. B. W. Kennedy and W. C. Unwin. No. 107. A GRAPHICAL METHOD FOR SWING-BRIDGES. A Rational and Easy Graphical Analysis of the Stresses in Ordinary Swing-Bridges. With an Introduction on the General Theory of Graphi- cal Statics. 4 Plates. By Benjamin F. LaRue, C.E. No. 108. A FRENCH METHOD FOR OBTAINING SLIDE- VALVE DIAGRAMS. 8 Folding Plates. By Lloyd Bankson, B.S., Assist. Naval Constructor, U.S.N. No. 109. THE MEASUREMENT OF ELECTRIC CURRENTS. ELECTRICAL MEASURING INSTRUMENTS. By Jas. Swinburne. METERS FOR ELECTRICAL ENERGY. By C. H. Wordingham. Edited by T. Commerford Martin. Illustrated. No. 1 10. TRANSITION CURVES. A Field Book for Engineers, containing Rules and Tables for laying out Transition Curves. By Walter G. Fox. No. in. GAS-LIGHTING AND GAS-FITTING, including Specifica- tions and Rules for Gas Piping, Notes on the Advantages of Gas for Cooking and Heating, and useful Hints to Gas Consumers. Second edition, rewritten and enlarged. By Wm. Paul Gerhard. No. 112. A PRIMER ON THE CALCULUS. By E. Sherman Gould, C.E. No. 113. PHYSICAL PROBLEMS AND THEIR SOLUTION. By A. Bourgougnon, formerly Assistant at Bellevue Hospital. No. 114. MANUAL OF THE SLIDE RULE. By F. A. Halsey of the American Machinist. Second edition, revised. SCIENCE SERIES. No. 115. TRAVERSE TABLES, showing the difference of Latitude and Departure for distances between i and 100 and for Angles to Quarter Degrees between i degree and 90 degrees. (Reprinted from Scribner's Pocket Table Book.) No. 116. W RM AND SPIRAL GEARING. Reprinted from "American Machinist." By F. A. Halsey. SCIENTIFIC PUBLICATIONS. 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