THE ASSAYER'S GUIDE; OR, PRACTICAL DIRECTIONS TO ASSAYERS, MINERS AND SMELTERS, FOR THE TESTS AND ASSAYS, BY HEAT AND BY WET PROCESSES, OF THE ORES OF ALL THE PRINCIPAL METALS, OF GOLD AND SILVER COINS AND ALLOYS, AND OF COAL, &c. OSCAR M. 1ATE GEOLOGIST TO THE STATE OF MISSISSIPPI. A NEW, REVISED A$D* E EDITION. PHILADELPHIA: HENRY CAREY BAIRD & CO., INDUSTRIAL PDBLISHERS, BOOKSELLERS AND IMPORTERS, 810 WALNUT STREET. 1907- pv ^x- 0' Copyright by HENRY CAREY BAIRD & Co., 1892. 77V PREFACE TO THE REVISED EDITION. THE "Assayer's Guide" has so steadily main- tnined the popularity and reputation it has en- joyed for many years, and has met with such success, that it has been determined to issue a new edition containing, in addition, numerous re- cent and approved assaying methods. The material for this purpose has been largely drawn from the articles on Metallurgy contributed by Prof. Bruno Kerl and others to the fourth edi- tion of u Muspratt's Theoretische, Praktische and Analytische Chemie," now being published in Germany. While many improvements in the apparatus used in assaying have been made, only a few of the most notable of these novelties have been in- troduced, it being believed that the implements and utensils described and illustrated in the work are sufficient for all practical purposes. . " The book has also been provided with a copious (iii) 255808 IV PREFACE TO THE REVISED EDITION. Table of Contents and a very full Index, which will render any subject easy and prompt of ref- erence. In its enlarged and revised shape, it is hoped that the work will fully maintain its claim to the favor it has so long enjoyed as a complete guide in the art of assaying. PHILADELPHIA, December 1, 1892. PREFACE TO THE ORIGINAL EDITION. IN presenting this little volume to the public, I trust that I am filling a void in our chemical lit- erature. I believe there is no work in the Eng- lish language on assaying which combines with practical usefulness a sufficiently popular charac- ter for those readers who have not made metal- lurgy and its kindred sciences objects of their especial study. My desire is to offer a book which fully treats of all the subjects of assaying, and whose price will yet place it within the reach of all persons professionally interested in this important branch of knowledge. The more compendious works on chemistry, if they allude to assaying at all, give so sparing and incidental remarks, that they do not throw any light upon it for technical purposes, as indeed it does not fall within their province to do. The immense mineral wealth of the United States, to which the discoveries in California have so largely added, makes this art a very desirable acquirement for every one engaged in any busi- ness connected with the metals ; and it would ap- pear indispensable to those desirous of deriving the greatest advantage from a residence in that promising and alluring part of our country. Although these pages principally treat of the processes by heat, I have thought it proper to de- VI PREFACE TO THE ORIGINAL EDITION. scribe also some wet processes, either where they serve as methods to rectify the former, or where no others exist; as, for instance, is the case with platinum. For the coins I have selected those employed at mints, and which are therefore gen- erally considered the most serviceable for the analysis of those alloys. I feel induced here to recommend at least a partial study of blowpipe assaying "to those who may wish to make use of the instructions given in this treatise. This infant branch of chemistry was first created, I may say, in Sweden by Crom- sted, and established more firmly by Gahn and Berzelius, both his countrymen, and has of late been made by Plattner a method even for quanti- tatively ascertaining the contents of most min- erals. The requisite blowpipe utensils for the mere detection of the principal components of ores are so few, can so easily be commanded, and may be so readily carried about one's person, that, at least for the purpose of a prior test, it is very advisable to possess some knowledge of their application, which can be acquired with great facility. I cannot conclude these brief remarks without seizing upon the opportunity of acknowledging the liberality of a distinguished officer at Frei- berg in Saxony, Mr. Fritzsche, chief assayer of that mining district. I have made frequent use of his notes and hints, given me while I had the advantage of a personal intercourse with him. O. M. L. CONTENTS. INTRODUCTION. PAGE Definition of assaying, its object and in what it differs from inorganic analytical chemistry properly so called ' 17 Assaying the foundation of theoretical chemistry ; Antiquity of the art - - - - 18 Agricola and his writings ; What should guide the assayer in his operations - - - 19 I. DESCRIPTION OF THE IMPLEMENTS AND UTEN- SILS USED IN THE COURSE OP ASSAYS BY HEAT. The muffle furnace and the muffle, illustrated and described . - - - . . - - - - - 21 Hessian crucibles, illustrated and described - -22 Furnace for tests of iron ores, lead ores, etc., illus- trated and described - - - - - 27 Portable furnaces - - - - - - - 30 The Battersea fiirnace ; Brecon's portable assay fur- nace ; Other instruments used in the assay of ores 31 The balance, and how weighing is to be effected - 32 Scales for weighing larger quantities - - - 33 Crucibles, cupels or cups, and tongs, illustrated and described -------- Mr. Fritzsche's recipe for the preparation of cupels - Hessian crucibles for the assay of iron ores, illustrated and described 37 Preparation of charcoal for coating crucibles - - 38 Pan for cooling buttons of metal - - - - 39 Tongs, illustrated and described - - - - 40 Mode of introducing the cupels into the muffle - 41 (vii) Vili CONTENTS. Sieves and their use ...... 43 Gas assay -furnaces 44 Fletcher's direct-draft crucible furnace, illustrated and described ; Group of gas furnaces designed by Walter Lee Brown, illustrated and described - 45 " Monitor " furnace, illustrated and described - 48 Manner of operating Brown's group of furnaces 51 Management of the ''Monitor" - - - - 52 II. RE-AGENTS USED IN ASSAYING. Re-agents for dry assays ; Reducing agents - - 54 Composition of black flux, white flux and gray flux 55 List of the reducing powers of various reducing agents 56 Oxidizing agents ; Preparation of litharge entirely free from silver 57 Solvent agents ; Acid solvent agents - - - 58 Basic solvent agents 59 Desulphurizing, or precipitating agents - - - 60 Sulphurizing agents ; Concentrating fluxes ; Decom- posing and volatilizing fluxes ; Air-excluding fluxes (covering agents) - - - - 61 Re-agents for wet assays ; For assays by gravimetric and calorimetric analysis ; For volumetric assays - 62 III. ASSAY OF SILVER ORES BY HEAT CUFELLATION. Occurrence of silver in nature ; Preparation of the ore for investigation - - - - - - 64 Object of the addition of lead to the ore ; Impurity of the lead of commerce - 65 Preparation of pure lead 66 Manner of charging the crucible with the ore to be assayed -------- 67 Advantage of making several assays at one time - 68 Process of melting the assay 69 Pouring out the assay ------ 70 CONTENTS. IX PAGE Separation of the slag from the metallic button ; Crucibles used in making the assay ; Silberblick, (silver gleam) 71 On what the accuracy of the assay chiefly depends - 72 Adage current among German smelters and assayers ; Treatment of the buttons of pure silver - - 73 Unavoidable inaccuracies in the shape of losses - 75 IV. A TABLE TO RECTIFY THE Loss IN- CURRED DURING THE SILVER ASSAY. Difference in the results obtained in Freiberg - - 79 V. GAY-LUSSAC'S PROCESS FOR ASSAYING SILVER ALLOYS. Preparation of the assay - - - - 80 Normal and decinormal solutions of common salt ; Decinormal solution of silver ; Preparation of the assay solution ------- 81 Flasks illustrated and described - - - - 82 Titration of the silver solution and apparatus used - 83 Calculation --------86 Preparation of the normal solutions - - - 88 Gay-Lussac's tables for determining the fineness of silver alloys - - 89 Table for decimal salt solution 91 Table for decinormal silver solution - - - - 94 Whittell's method of saving time and insuring greater facility in making Gay-Lussac's assay - - - 97 YI. ASSAY OF NATIVE SILVER ORES. Lowe's method ; Preparation of the ore - - - 99 VII. ASSAY OF GOLD ORES BY HEAT. Similarity of the properties of silver and gojd, and their ores as regards the process of cupellation - 101 X CONTENTS. PAGE Preparation and melting of the assays ; Manner of ascertaining the percentage amount of .gold in the specimen under examination ; Preparation of per- fectly pure silver - 102 Definition of quartation - - - - - 103 Treatment of the button of gold and silver alloy obtained -----. - 104 Manner of ascertaining the original amount of silver 105 VIII. ASSAY OF GOLD ORES BY AMAL- GAMATION. On what this method is founded ; Purification of mercury ; Definition of the term dokimastic test ; Manner of making the assay .... 106 IX. ASSAY OF GOLD BY WASHING. On what the assay is based ; Its employment in Cali- fornia ; Vessels used 108 Execution of the assay 109 X. ASSAY OF GOLD BY PANNING. The pan or lt batea " used in making the test ; Execu- tion of the assay - - 111 Example of calculating the result of the assay ; Separation of the free gold from the sulphides ; Preparation of an amalgamated pan - - - 114 Klein Schmidt's method of assaying gold by panning 115 Another method ; Australian method - - - 1 1 6 XL ASSAY OF GOLD BY COMBINED DRY AND WET METHODS. Object of these assays ; Manner of obtaining a correct average sample of the ore to be assayed - - 117 Manner of pulverizing the sample - - - -118 Assays by smelting with lead ; Scorification assay - 119 Execution of the assay 121 Crucible assay ; Advantage of this assay - - 124 CONTENTS. XI PAGE Melting earthy gold ores or gold ores containing ferric oxide (also dross or sweepings, slags) - - - 125 Charge for American gold ore - .- - - 126 Melting of sulphuretted ores 127 Fluxes for dross or sweepings 129 Cupellation of the auriferous lead - - - - 1 30 Parting the gold from the silver - - - - 131 Indications by which to judge whether silver has to be added or not when cupelling the auriferous lead button - 132 Examination of black specks remaining behind - 134 XII. ASSAY OF GOLD ORES BY A WET PROCESS. Preparation of the assay - - ; - - - 136 Execution of the assay 137 XIII. ASSAY OF SILVER COINS, OR ALLOYS OF SILVER AND COPPER. Test for ascertaining the probable amount of silver and copper - -/--- 138 Erker's table for regulating the requisite quantity of lead 139 Manner of preparing a sample of the coin ; Execution of the assay 140 XIV. ASSAY OF GOLD COINS, OR ALLOYS CONTAINING GOLD, SlLVER AND COPPER. Touchstone or besanite test - - - -. - 141 Execution of the assay - - - - . - 142 D'Arcet's table for regulating the amount of lead to be used 143 Mint units of the various countries - - 145 Table showing the content, weight, etc., of gold coins of various countries - 146 Table showing the content, weight, etc., of silver coins of various countries - 147 Xll CONTENTS. PAGE Table of base coins 148 XV. To FIND THE PROPORTION OF GOLD IN A MIXTURE OF GOLD AND QUARTZ BY CALCULATION. Specific gravity of gold and of quartz ; Manner of making the calculation - 1 49 XVI. ASSAY OF PLATINUM ORES. Occurrence of platinum in the United States ; Execu- tion of the assay - 1 52 Test for ascertaining the amount of the alloy of gold and platinum - 154 Electrolytic assay of platinum - 156 Separation of platinum from iridium - 157 XVII. ASSAY OF COPPER ORES GERMAN AND HUNGARIAN METHODS. Preparation of the ore - - - - - 158 Black flux and its preparation - 159 Difference of opinion regarding the use of oxide of antimony, arsenic or lead ; Manner of charging the crucible - - - 160 Indications of a good assay 162 Removal of foreign metals from the button - - 163 Indications of the presence of lead in the button - 164 XVIII. ASSAY OF COPPER ORES ENGLISH METHOD. Ores to which this assay is applicable ; Preparation of the ore - - .... 165 Preparation of white flux - - .- - - 166 Treatment of the button of copper alloy ; Test of the purity of the copper - - 167 Method of diminishing the loss of copper - - 168 CONTENTS. xin XIX. WET ASSAY OF COPPER. PAGB Advantage of this assay ; Modified Swedish assay ; Preparation of the cupriferous substance - - 17G Precipitation with iron - - - - - -172 Correction for iron - - 175 Characteristics of pure precipitated copper ; Testing the residue from the solution of the ore for copper 176 Precipitation with zinc free from lead and arsenic - 177 XX. ELECTROLYTIC DETERMINATION OF COPPER. Basis of Classen's method for the electrolytic deter- mination of metals 180 Classen's method of the determination of copper - 181 Arrangement of the apparatus used illustrated and described - 182 Herpin's method of assaying copper by electrolysis, illustrated and described 183 XXI. ASSAY OF LEAD ORES. On what the method of assaying lead ores depends 185 Methods of assaying sulphuretted lead ores which contain few or no foreign sulphides - - - 186 Preparation of black flux - - - - - 187 Substitute for black flux ; Cover of common salt and its object -188 Assays without fluxes in iron vessels ; Assay in iron dishes -------- ]89 Assay in iron crucibles - - - - - -190 Assays with fluxes - - - - - . - 191 Assay in an iron crucible with black flux ' - - 192 Method used in England, Germany, France and Belgium * -' - 193 Proportions of the charge in various countries - 194 Assay in a clay crucible with black flux and iron ; available for ores poor in foreign sulphides, but richer in earths 195 XIV CONTENTS. PAGE Upper Harz potash assay in clay crucibles - - 198 Methods of assaying sulphuretted lead ores, which contain many foreign sulphides - - - - 199 Calcination assay 200 Assay with sulphuric acid ..... 203 Methods of assaying for sulphuretted lead ores, which contain many earthy constituents - ^ 205 Methods of assaying oxidized lead ores and smelting products ; By melting with reducing agents - 206 By melting with reducing agents and iron . - - 208 XXII. ASSAY OF LEAD ORES BY HEAT. Loss incurred in the assay ; Preparation of the charge - - - 210 Execution of the assay 211 XXIII. ASSAY OF LEAD ORES BY A WET PROCESS. Preparation of the ore 213 Constitution of sulphate of lead - - - - 214 XXIV. GRAVIMETRIC ANALYSIS OF LEAD, Method as executed at Bleiberg in Carinthia - - 216 Storer's method 217 XXV. ASSAY OF IRON ORES BY HEAT. Preparation of the ore and mode of charging the crucible - 219 Smelting apparatus used in the iron works on the Harz Mountains 220 Method of obtaining chemically pure iron, according to Karsten Characteristics of the button of pure iron - - 223 XXVI. FUCHS'S PROCESS FOR IRON ORES AND IRON. Ores to which this process cannot be applied - - 224 CONTENTS. XV PAGE Preparation of the ore ; Method of ascertaining the peroxide of iron in the ore ----- 225 Method of finding: the whole amount of iron in the ore - - 226 XXVII. SWEDISH ASSAY OF IRON ORES. Manner of obtaining the yield of crude iron from the ores, as well as the approximate content of iron - 221 Mode of obtaining the assay sample ; The aim in executing the assay ------ 228 Berthier's process for the determination of the earthy matter present - - - - - - 229 Quantities of flux required - - --.'- 230 The character of the slag as a test as to whether the correct proportion of earths has been used - - 231 Formation of a slag recommended by Percy; Suit- able fluxes for ores or metallurgical products - 233 Execution of the dry assay of iron ores ; Preparation of ba^qued crucibles - 235 Crucibles best adapted for the assay - - 236 Characteristics of the iron buttons obtained - - 238 Execution of the iron assay in England ; Proportions of ore and fluxes used 239 Reducing agent employed ; Preparation of the charge 240 Probable result of the operation - 241 XXVIII. ASSAY OP QUICKSILVER ORES. Composition of cinnabar ; Analysis of a specimen of cinnabar from Japan by Klaproth - - - 243 Distillation of quicksilver - 244 Fluxes used in the assay of quicksilver - 245 Precaution as to the heat employed during the assay - - - ; -/ - - - - 246 Berthier's preparatory process in assaying quick- silver - 248 Berthier's treatment of quicksilver ' ore containing arsenic 249 XVZ CONTENTS. Electrolytic determination of quicksilver, Escosura's process _ 250 Classen's process - - - ... . 252 XXIX. DRY ASSAY OF TIN ORES. What the assay proper consists of; Difficulties caused by the behavior of stannic oxide and metal- lic tin at an elevated temperature - - 253 German method of assay 255 Mitchell s process ; Leval's assay with potassium cyanide 256 Winkler's bronze assay 258 XXX. ASSAY OF SULPHURETS IN ORES. Preparation of the charge - - - 260 Volumetric determination of sulphur in ores which contain either sulphur alone, or also sulphates; Weil's method 261 Examination of sulphur in metallic lead - - - 262 Determination of sulphur in pyrites ... 263 Bodewig's method of determining sulphur in pyrites 264 XXXI. MODE OF TESTING THE CALORIFIC POWER OF COAL AND OTHER FUELS. Despretz's experiments ; Rumford's process - - 266 Berthier's process - - - -- . . . 267 Examples of comparison in making the assay - - 268 Table of analyses of different clays from which the most approved crucibles are made - - - 270 Table showing, in degrees of the Centigrade and Fahrenheit thermometers, the amount of heat necessary to melt various substances - - 271 Table of the troy weights used with gold and silver, and platinum , Table of avoirdupois weights used with other metals - 272 Index - - - - ' - ... - 273 THE ASSAYER'S GUIDE, INTRODUCTION ASSAYING is the science which treats of the various methods of ascertaining the amount of one or of several ingredients of a chemical compound, such as an ore or alloy, but is solely intended for practical purposes. For this reason one of its main objects is to be able to attain to a very great accuracy with the smallest and cheapest means, and in the shortest possible time. In this it is con- tradistinguished from inorganic analytical chemistry, properly so called. The aim of the latter is to ascertain all the different composing elements of an inorganic com- pound, and also the exact amount of each, 2 17 18 THE ASSAYER'S GUIDE. and for this reason the chemist should never be deterred by a great waste of time and money, if an accurate result should require extravagant means. As assaying is only an aid to technical operations, and these never can extract the whole amount of a metal or other component part contained in a com- position, (be the latter a natural or artificial Dne,) with true chemical precision, it is self- evident that much time and labour would be unnecessarily lost, if the same attention were devoted to it as would be requisite in an analysis. This, however, also shows that it is utterly inadequate for purely scientific ends. Assaying was the earliest known branch of chemistry, and in fact that one which afterward, through the medium of the various investigations of alchemy, drew attention to theoretical chemistry, and thus founded that science. The art of assaying is so ancient, and it has so constantly and imperceptibly re- INTRODUCTION. 19 eeived new additions and perfections, that its origin is entirely unknown. Agricola of Saxony, who lived in the earliest half of the sixteenth century, was the first to col- lect the facts and write on this subject. (G. Agricola de Ke Metallica, libr. XII. Basil, 1546.) Since then the manifold dis- coveries of more enlightened periods have vastly enlarged and developed this branch of study. It is not by any means always necessary that the same measures be employed foi these tests as are used in the separation of the single constituent from the rest of the compound in large quantities; as, for in- stance, in the processes of smelting and amalgamation, although, if convenient, it it very advisable, as it facilitates the metal- lurgist in the detection of the best fluxes and admixtures to be added to his peculiar ores. The assayer should be guided in his operations by chemistry, and the study of 20 THE ASSAYER'S GUIDE. the latter, particularly as far as regards the principal and more common substances, should never be omitted. In other respects, all that can be recommended to one who desires to perfect himself in assaying, is the most scrupulous cleanliness, order, and pre- cision as regards his assays and implements, and the most unwearying adroitness and attention in performing the manipulations required by his science. 21 Description of the Implements and Utensils used in the course of Assays by Heat AMONG the articles necessary for an assayer's office, of course the first that requires a description is the furnace. For most purposes the muffle furnace suffices, and it is the only one used for gold, silver, and copper ores ; but for iron, lead, &c. we require another, though much simpler one. I shall first describe the muffle furnace, (Plate I. figs. 1, 2, and 3.) The character- istic part, the one from which this furnace derives its name, is the muffle, illustrated on the same plate, in figs. 7 and 8. Both these diagrams give a perspective view, the first a semilateral, the second one from in front. They can be procured in most of our larger cities, and are manufactured in 22 THE ASSAYER'S GUIDE. great quantity in Hessia, of a very firm and fire-proof siliceous clay, the same material as that used for the well-known Hessian crucibles, (Plate II. fig 5.) The one from which the drawing was taken in Plate I. measures eight inches across the bottom from mouth to back outside, and four inches down the back. The holes opening upwards towards the interior measure each an inch and a half lengthways, but their number of course varies according to the size of the muffle, which again should depend on the quantity of assays expected to be performed at once. The back and the mouth of the muffle are equal in size. The muffle furnace is exhibited from in front in fig. 1, in a lateral section in fig. 3. and in a transverse perpendicular section in fig. 2. A scale, showing the proportionate dimensions in English feet, is attached, to facilitate the use of the drawings in build- ing a furnace ; for though very small, they have been made with much care, and, with DESCRIPTION OF IMPLEMENTS. 23 the little sketches attached, are fully capa- hle of being employed to that effect. As will be seen from the first figure, the line A B is seven feet long, while the external width of the furnace, C D, is two feet nine inches. The furnace consists of three chief parts, the chimney, i\ in figs. 2 and 3, (which need only be 3i feet high if it enters the chief chimney of the laboratory, which should then measure at least 9 12 feet,) the part above C D, in fig. 1, containing the muffle, and the part below that, the grate, ashes box, &c., &c. In fig. 1 we see imme- diately below the chimney a representation of bricks, (firebricks, for all in immediate contact with the heat should be of this kind ; the external ones are common burnt bricks.) These, though fastened in tight, are placed so that they can be taken out, to put in a new muffle, or 'make other repairs when necessary. In this brickwork we have two openings, d and a. The former is only a small aperture, for insert- 24 THE ASSAYER'S GUIDE. mg pieces of sheet iron, upon which to dry the cupels. It is, however, not immediately necessary, and, if present, is always closed with a tight brick when the muffle is in use. a is the opening of the muffle, which can be closed by a piece of fire-proof brick repre- sented in fig. 4, having an iron piece pro- truding on the exterior, with a narrow opening, into which fits the handle fig. 5, which we apply on removing it. To the right and a little below the muffle is a loose brick, 6, to be taken out whenever it becomes necessary to remove the fire-proof clay bar, o, which holds the muffle, (vid. fig. 2.) As seen in fig. 3, this bar as well as the three others shown in the little sketch affixed to fig. 2, and of which the centre one is a little the longest, are slightly inclined, thus elevating the back of the muffle an inch above the front, and giving a better circulation of heat, as should be the case where stone-coal or cokes are used. In burning charcoal it may be horizontal, DESCRIPTION OF IMPLEMENTS. 25 although this inclination has another ad* vantage, inasmuch as it enables us to clean out the muffle easier, should a cupel upset, the contents running forward. The three fireclay bars, sss, are loose, while o is inlaid on one side, and on the other fastened in with a loose piece of brick and an iron wedge, which can be removed, as already remarked, through e. On inserting the bars and muffle, the parts where they meet, and where the former touch the other bricks, should be powdered over with bone-ashes, to prevent a possible adhesion from the intense heat. Small cracks in the muffle should be mended with coarsely powdered burnt clay, p, in fig. 2, is the open space left round the muffle about an inch and a half wide, and into which the opening d in figs. 1 and 3 leads. Immediately below C D we have the door b exhibited in all three figures It is for the introduction of fuel, and is just above the grate, x x, in figs. 2 and 3, which consists of six iron bars placed in the same 26 THE ASSAYER'S GUIDE. inclination as the muffle. The door/, fig 1, is of iron, with an inside coating of fire-clay, an inch and a quarter thick, kept in place by iron rivets, thus protecting the assayer from the radiating heat of the iron, which would otherwise soon be white-hot. Below the grate stretches the chamber q, in figs. 2 and 3, both for draught and for the cinders, The plane at the bottom of this is inclined like the grate and muffle, and has the opening c to take out the ashes. To intro- duce a regular and sufficient quantity of atmospheric air, the channel k has to be constructed, which enters q at h, and passing under the floor of the laboratory opens outside at i, fig. 3 : Z is a small piece of sheet iron, by pulling out or pushing in which, we open or close the passage Jc at pleasure, and accordingly as we require a great influx of air or not, for a high or low temperature. The little figure annexed to fig. 1, shows the construction of the little opening and slide in the lower door. It is DESCRIPTION OF IMPLEMENTS. 27 exactly as with a common iron stove, y being the hole, while the slide a /? can be closed over it by means of the handle, or removed, as may be desirable for different degrees of ventilation. This furnace is of the kind proposed by Professor Plattner for the Freiberg assay office for the use of stone- coal and cokes, and where it has been employed to great advantage, as regards economy and practicability in general. Having thus pretty minutely given a description of the muffle furnace, as it can best be constructed when not required to be movable, I shall proceed to the furnace for tests of iron ores, lead ores, &c., also in a shape not intended to be moved, as repre- sented by a lateral section in fig. 6, Plate I. Those parts in immediate contact with the heat should be constructed of fire-proof bricks, which ought to reach some distance up the chimney. The main body of the furnace B and A is either square or round, and twelve inches in diameter. The back 28 THE ASSAYER'S GUIDE. is about three feet nine inches high, while the front measures slightly less, as the top has a little slant, merely for convenience in easier being able to get at the bottom. A is the part where the ashes collect, with a door at H having one or several openings, as is represented in the door g, in fig. 1, for the sake of regulating the ventilation. It this furnace is to be used for iron assays, in which case a very intense heat is requi- site, a similar channel as illustrated in K, fig. 3, should be attached, the longer the better, and, if possible, opening into some cool place, e. g. a cellar, thus creating a stronger current of air, and consequently a better ventilation. Above A are the bars forming the grate FG, which ought to vary in distance from one another according as we use charcoal or stone-coal and cokes, in the former case being closer to one another. B is the part in which the crucibles are placed, as well as the fuel, and which has one opening for the introduction of the same DESCRIPTION OF IMPLEMENTS. 29 with the cover E, suspended, when open, by a chain, but which is shut when the furnace is in use. This cover is commonly ol iron, covered with fireproof clay. C is the channel leading off to the chimney D, which may vary in width from one half to one quarter the width of B. For assays of lead and copper it is not necessary to have the chimney very high, as no very severe draught is required ; but for iron assays it should be about thirty feet. In the assay office in Clausthal it measures forty-eight feet. In this case, of course, if there is also a muffle furnace on the same hearth, it is best to conduct the chimneys of both into one large one. On placing the crucibles in this furnace twelve have room in it at once a piece of firebrick, K in the drawing, is first placed on the grate, which, to avoid adhesion of the crucibles, may be powdered with bone-ashes. This brick is employed to have the crucibles more in the focus of heat, by elevating 30 THE ASSAYER'S GUIDE. them above the coal around it, and also clay being a bad conductor to keep them from immediate contact with the cold blast The fuel should never be heaped above 1, the mouth of the channel C, and large coals should be placed below, to keep the grate from choking. If several crucibles are used at once, they ought to stand sufficiently upart to admit coals between them, as they otherwise might melt partially in the course of the process, and form one compact mass. On the foregoing pages I have furnished Inscriptions and measurements of furnaces, which, as I have already remarked, though easily constructed, are not portable ; and it is proper that, before closing this chapter, I should devote a few lines to the mention of those, which, from their being movable, and thus obviating the difficulty and incon- venience of constructing one, might, in many cases, be preferred, although their smaller dimensions, as a matter of course, make it more difficult to perform good DESCRIPTION OF IMPLEMENTS. 31 assays, and impossible to attend to many at a time. Among these we have both muffle furnaces and wind furnaces such as last de- scribed. Many forms have been manufac- tured, and it is not necessary to enter into detailed descriptions. They can generally be procured at all larger stores of chemical apparatus. The Battersea furnace is of fireclay made in sections and bound with iron bands. Brocoris portable assay fur- nace consists of a sheet-iron frame 27 inches high and 14 inches square, lined with fire- brick, the interior being smooth and straight from top to bottom. The cover is ridged to lessen the danger from cracking. The muffle door is cast iron and is fitted with a circular opening filled with mica, that the operations going on within the muffle may be seen when the door is closed. After having thus given a description of the fur- naces used in the course of the experiments elucidated in the following pages, the reader's attention is called to other instruments usecj 32 in the assays of ores. Among these, probably the balance will appear most conspicuous. There ought to be two in use, one very ac- curate, the other less so, for more common purposes, as weighing off the ingredients or admixtures, such as pure lead, borax, &c. The other one should be made with great care, and only used to weigh off the small buttons of gold and silver procured. Before weighing the balance must be tested as to its equilibrium. The substance to be weighed should be cold, and must not be placed directly upon the scale pan, but upon suitable smaller pans, watch glasses, etc. ; hygro- scopic substances in closed tubes. The bal- ance beam should be raised from the knife every time before a weight is put into or removed from the pan. The weights must not be put in the pan at random, but system- atically, this being the only way of saving time. The highest probable weight should be added first, then the next lowest, and so on until the equilibrium has been established. DESCRIPTION OF IMPLEMENTS. 33 The pans should then be changed in order to test the correctness of the weight. Per- fect equilibrium of the balance is, however, not absolutely essential, as a correct weigh- ing may be obtained by placing the substarice to be weighed in one pan and in the other pan any convenient material as a make- weight, such as tin-foil, shot, granules of lead, etc., until equilibrium is established The balance is then raised, the weighed substance is removed from the pan, and sufficient weights to counterpoise the bal- ance are put in its place. The sum of these will give the correct weight of the sample. It is a good plan to always place the weights in one pan (the right-hand one) and whatever is to be weighed always in the other. In the choice of a scale for weighing larger quantities (fluxes, etc.) much latitude may be allowed. It need not be very deli- cate ; a grocer's scale will do. We must now cast a rapid glance at the 3 34 THE ASSAYER'S GUIDE. smaller and less costly utensils, but all of which are necessary for the accomplish- ment of the operations to be performed a& directed in the following pages. I allude to the crucibles, cupels or cups, and tongs, &c., illustrated in Plate II. The former, figs. 1, 2, 3, 4 and 5, are all of their natu- ral size in the drawings. Figs. 1, 3, and 4, should be made from accurate descriptions by a potter, of a pure clay, containing as little silica mechanically combined as pos- sible, since its presence prevents the ves- sels from being sufficiently porous to allow the oxidizing metals to enter, which would, as will hereafter be seen, become a great drawback to the assay. Some hundreds must always be kept on hand, for they can only be used once, as the lead, almost al- ways present, glazes them immediately. Fig. 1 represents a cupel used in the operation technically termed cupdlation of the gold and silver ores : a shows it froiu above, b from the side. The concave inner DESCRIPTION OP IMPLEMENTS. 35 surface should not be too shallow, thus letting the contents run over ; nor, on the other hand, too deep, in which case too small a surface would be exposed to the oxidizing power of the heat. The line given in b shows the proper inclination within. Fig. 2 is a truncated cone, with a very slightly concave surface at the wider ex- tremity or top. It is made in great part of bone-ashes, being among the most porous substances that can stand a high tempera- ture. I give here a recipe for their pre- paration, furnished me by Mr. Fritzsche. It shows the relative quantity of the ingre- dients as used for these cupels at his office, where they are made by the laboratory servant in wooden moulds, using a rod, shaped like a pestle, to make the hollow at the top. The mass consists of 4 parts of wood-ashes previously freed of the pot- ash by filtration, 1 part of lime, and 1 part of bone-ash. 36 THE ASSAYER'S GUIDE. Fig. 3 shows a flat, shallow crucible made of the same pure clay as that repre- sented in fig. 1 : a is the cup as seen from above, while b gives a lateral view, show- ing also the curve of the inner surface. This vessel is used in the assay of copper, as well as fig. 4. Fig. 3 is termed in Ger- man " Kupfer Garscherbe" from the fact that "with" its use the copper assay is finished. Fig. 4 is a high crucible, as mentioned above, used for copper and lead. It is made of the same material as the former. The reason of its having so great a height compared with its width, and otherwise so peculiar a form, is to concentrate all the heat round about the bottom of the in- terior. In some places, in lieu of better, the Hessian crucible (fig. 5) is used; but No. 4 is much better adapted, from the height of the foot-piece, which also protects the contents from the cooling influence of the iron bars on which they are placed. DESCRIPTION OF IMPLEMENTS. 37 and from a too direct contact with the cold draught. Some assay ers use an extra cover for this crucible, a very superfluous addition, since the bottoms of the old cru- cibles answer admirably as covers to the new. As mentioned before, these also are useless after once having been employed, and before throwing them away it is there- fore well first to break off the feet. Fig. 5 gives a drawing of a Hessian cru- cible, which is used chiefly in the assays of iron ores. These are imported into the United States, and can be procured in al- most every crockery store. Their dimen- sions are very different, and so contrived that one fits into the next in size, being in sets of about a dozen. They are com- monly triangular above, and round below, as shown in the figure; but sometimes they are made round above and below, and where these can be had, they should be preferred. If they cannot be procured, similar crucibles of pure clay may be sub- 38 THE ASSAYER'S GUIDE. atituted, and in fact they are sometimes considered preferable. The latter are then commonly made with a foot-piece, some- what as in fig. 4, though not quite so strongly separated from the main bulk of the vessel. These or the Hessian crucibles, as will be seen hereafter, should be kept constantly on hand thickly coated with charcoal. They are prepared in this man- ner. Charcoal of any oak-wood, except red-oak, which contains much oxide of iron, is the best on account of its density. It should be pulverized with the utmost care, since a coarse powder will never furnish a consistent mass. To this we carefully add water until we procure a tough paste or dough, and with this fill the crucible very tightly, always ramming down every new portion introduced, with a pestle or piece of wood. When the whole interior is filled up, we cut out a hole in the middle with a penknife, leaving a margin of about half DESCRIPTION OF IMPLEMENTS. 39 an inch at least, below and all round. (See Assay of Iron Ores.) Fig. 6 furnishes a sketch of an imple- ment, which, though not immediately ne- cessary, will be found extremely useful, inasmuch as it tends to keep up order and accuracy, great requisites for an able assayer. As will be seen from the dif- ferent views a and &, it consists simply of a piece of sheet-iron, having a wooden handle and several semi-circular cavities, the number of which may vary according to the number of assays expected to be performed at once. If a large muffle is used in the furnace, it is well also to have this large; and, in fact, I would suggest having the number of holes in each row equal to the number of cupels, of the sort illustrated in fig. 1, that can, without col- lision, be placed across the muffle from side to side. (See Silver and Gold Ores.) This pan, or whatever we may otherwise term it, is used to cool the buttons of metal and 40 THE ASSAYEft'S GUIDE. their surrounding slag after having oxi dized part of the lead, &c., and separated the gangue-rock, as is the case with silver and gold (q. v.) The holes should be li inch wide and i inch deep: Figs. 7 and 8 represent two different kinds of tongs. Fig. 7 is only shown in a lateral view, since its characteristics are thus exhibited, while fig. 8 is sketched from above. They are both very necessary in the progress of our investigations. The first is shaped like common fire-tongs, only that the ends, instead of widening into a flat circular lobe, are bent downward like a poker, thus enabling us to handle the crucibles with great care. The .second tongs has each piece ending in a semi- circle, the diameter of which circle, when, united, should be so that it may exactly embrace the lower part of fig. 1. It is used to place those cupels into the muffle, as we are thereby prevented from touch- ing the contents. In using this latter in- DESCRIPTION OF IMPLEMENTS. 41 strument great caution should be taken not to upset the cupels. Let me first remark, that on introducing the cupels into the muffle, we always commence with No. 1, i. e. first assay on hand, behind on the left. It may seem a very superfluous precaution to dwell thus long on so simple a manipu- lation as the one I am now describing; but I know from experience, how many failures carelessness in this procedure oc- casions to the uninitiated. Let us now suppose, that we have the crucible, fig. 1, filled with the powdered mineral to be tested, and the other additions, such as lead or borax. Grasping the cupel firmly at the bottom, we lift it up high, so that, when pushed into the mouth of the muffle, it is a good deal above its floor, and cannot knock against it. As soon as it is within the muffle, without leaving hold of it, and keeping it up high, we hold the side of the tongs up against the side of the muffle to steady them, then run them along quietly 42 THE ASSAYBR'B QUID*. though not too slowly, for that only cause the hand to tremble, until the crucible is just above the spot where we intend to place it, (when once down it should never be moved,) and then slowly lower it, not letting go till it stands secure. These tongs should be made 'light enough conveniently to handle them with one hand. The handles are made of some good firm wood, though No. 8 is general!} 7 held lower down than the handles, and, I may add, never so that the end of the tongs, the handle, passes under the arm. but exactly as the savages hold their darts when about to hurl them. It may seem awkward at first, and yet I know many accidents, as regards the assays, having occurred from not attending to it. The length of the tongs ought to be about three feet. It may be well to supply oneself with a third pair, with straight and rather pointed ends. DESCRIPTION OF IMPLEMENTS. 43 For sifting brass or copper wire sieves are generally used in preference to hair sieves, since the latter deteriorate. Such sieves are furnished of various diameters (6 to 8 inches is a good size). For less valuable ores the sieves have about 35 to 50 meshes to the square inch and for more valuable ores from 70 to 80. The box-sieve of tinned iron consisting of a sieve, of about 80 to 100 meshes to the linear inch, with tightly fitting bottom to catch all the sifted ma- terial, and cover to retain the dust, is a valuable implement. Brittle substances will pass through the sieves without diffi- culty, but those with malleable admixtures will leave behind a flattened residue, as, for example, ores carrying native silver and copper, silver glance, granules of lead in slag and thin matt, sweepings containing gold and silver, etc. In case hard gangue (quartz) is to be sifted, the fine mass which has passed through the sieve is several times rubbed together with the coarse residue re- 44 THE ASSAYER 7 S GUIDE. maining upon the sieve, until everything has passed through. The residue of soft gangue is weighed and at once assayed by itself, and the fine siftings separately also, after they have been mixed upon glazed FIG. A. paper and several times passed through a coarse sieve. The entire yield is then cal- culated by adding the product of both to- gether. Gas assay -furnaces. These furnaces have DESCRIPTION OF IMPLEMENTS. 45 been known and used for some time. The source of heat is our common illuminating gas. Fig. A shows Fletcher's direct-draft crucible furnace. It consists of a fire-clay body held together by sheet-iron bands. The heat and flame pass through the body of the furnace to the chimney. It can be used either for scorifying or cupelling, and by removing the top cover the heat has full play upon a roasting dish placed upon it. Fig. B gives a representation of a group of gas furnaces designed by Walter Lee Brown and described by him as a complete gas-assaying plant.* Its duty is to do roasting, crucible fusion, scorification and cupellation. The furnace at the left is for roasting sulphurets or other ores for experimentation or actual work. It is what is known as a Fletcher No. 163, the same as shown in fig. A. The heat and flame pass from the burner through the * Transactions of 'the American Institute of Mining Engineers, 1884. 4(5 THE ASSAYER'S GUIDE. furnace, and out and up the chimney pipe. FIG. B. The funnel-shaped pipe over the cover is to DESCRIPTION OF IMPLEMENTS. 47 catch and draw the fumes up the chimney. When the burner is lighted a powerful draught ensues, carrying all odors and fumes at once away. Both the pipe and hood are provided with dampers, controlled by small weights. The burner is connected to the gas-tap by stout \ inch rubber tubing. A cast-iron tripod supports one end of the furnace and keeps everything firm. Next in regular order (supposing a sul- phuret ore to be under treatment) is the middle furnace for crucible fusions. This, likewise, consists of a furnace and burner. The latter is a Fletcher No. 15, of the same construction, however, as the No. 16. The furnace proper is made in five parts, the central section (a cylinder of fireclay), the bed-plate upon which it rests and which has an opening for the flame to pass through ; the cover (with handle attached), which also has an opening filled by a plug all of fire- clay ; and finally a plumbago lining. The 48 THE ASSAYER'S GUIDE. rubber tube chimney connections and darn per are like those of the other furnace. Finally at the right is shown the furnace for scorification and cupellation, which the author designates the "Monitor." Fig. C FIG. C. shows it enlarged and uncovered. Its form is almost that of a reverberatory furnace, the movable bricks, when in place, being the roof. Looking at it from another point of view, it may be considered as a muffle DESCRIPTION OF IMPLEMENTS. 49 with the flame as well as the heat inside. Its exterior dimensions are as follows : length 20 inches; width 7 inches; and depth 5 inches. In the interior, upon the bottom, are four little wedge-shaped bridges of fire-clay which are movable; and upon these rests a false bottom or floor, also movable. The latter corresponds to the muffle-bottom of an ordinary furnace, and upon it is done all the work. It is 3i inches wide by 7i inches long and i inch thick, and has a shoulder or bench running across its entire width on the end nearest the burner. The covering bricks, four in number, are each 7 inches long by 21 inches wide and II inches high, each with a slotted bridge for convenient handling. The con- nections are similar to those of the first mentioned furnaces. The 3-inch stove-pipes of all three fur- naces are fitted into one long, horizontal pipe, which fits snugly into the chimney. The bench or table upon which rest the 50 THE ASSAYER'S GUIDE. furnaces described is made of pine, well seasoned and firmly joined, to resist as much as possible the warping influence of heat, and to support the weight of the fur- naces and table-tiles. In dimensions (not figuring on the' top, which overlaps 1 inch all round) it is 4 feet 6 inches long, 1 foot 7 inches wide, and 2 feet 1 inch high, plus the thickness of the top, which is II inches. A double coat of shellac varnish is its sole ornamentation. To the sides and ends of the table-top are firmly screwed four strips of band iron of 24 inches width and 1 inch thickness, and of such lengths as to alter- nately overlap at the angles, making smooth joints. The top of this sort of wall is I inch above the bed of the table. Upon the latter are 114 fire-clay tiles, or, rathei; clamps, such as are used to join house tiles and having the shape of the letter " E " less the middle projection. Their average size is 34 inches by 3 inches across and II inches high. They are so arranged on the DESCRIPTION OF IMPLEMENTS. 51 table as to leave a series of six air tubes or chambers running its entire length. The spaces between the tiles are filled with a mixture of plaster of Paris and Venetian red rubbed up with water. The latter color is also used for the tiles themselves, and somewhat on the fire-clay portions of the furnaces. A t-inch bore gas-pipe, with proper taps and nozzles, is screwed to the front of the table. The manner of operating the furnaces is simple. As regards the roasting-furnace, it is necessary merely to shut off the dampers of the other furnaces, turn on and light the gas and regulate the heat to suit the par- ticular ore. The control of the mixture of gas and air is effected by means of the milled handle at the burner. In using the crucible-furnace, remove cover, turn gas on full at tap, light and regulate by milled handle. Crucibles containing charges that are to be heated gradually can be placed in 52 the furnace as soon as lighted ; others after the lapse of a few moments to allow the furnace to become thoroughly heated, Placing the charges in cold, good fusions of refractory ores have been made in twenty- five minutes from time of lighting. The fur- nace will take crucibles in size up to Bat- tersea "S" (4i inches across by 5 inches deep). To manage the " Monitor," remove the covering bricks, open the .damper and shut those of the other furnaces, turn back the milled handle at the gas-entrance to the burner so as to allow a full flow of gas, turn gas on full at tap, light and put back the bricks into place. In from twelve to twenty minutes, the interior will be hot enough for work. The bricks are then again removed, the charged scorifiers are placed on the false floor, the bricks are re- placed, and the excess of gas is turned off at the burner. When the charges have melted, slide the bricks aside more or less DESCRIPTION UF IMPLEMENTS. 53 principally those nearest the burner to admit air for oxidation. In cupellation, the gas is turned down more than in scorifica- tion. The time of performing either scorifica- tion or cupellation varies according to the nature of the ore, charge, size of button, etc., but is about the same as that occupied in the use of a coke furnace. The con- sumption of gas is not far from thirty cubic feet per hour. It is not intended or claimed that this furnace can take the place of one required to be run from ten to twelve hours per day ; for that, of course, solid fuel will be cheaper. But for short runs of from one to say four hours, it is economical, as are also the others here described. The complete plant, as illustrated, costs about $75.00. The furnaces are manufactured by the Buffalo Dental Manufacturing Com- pany, of Buffalo, New York. II. Re-agents Used in Assaying. Re- agents for dry assays. According to their action they may be divided into : 1. Reducing agents. Wood charcoal, in the form of powder, or of small pieces. One part of ordinary charcoal will reduce from 22 to nearly 32 parts of metallic lead from litharge, according to the purity of the charcoal. When employed in the roasting of antimonial and arsenical gold and silver ores, charcoal exercises a desulphurizing action. Powdered coke, anthracite and graphite may also be used instead'of powdered char- coal, but they are less combustible. Argol (crude bitartrate of potash) yields consid- erable carbon on becoming carbonized, and in consequence exerts a vigorous reducing RE-AGENTS USED IN ASSAYING. 55 effect, but causes refractoriness. For this reason its content of carbon is reduced, if necessary, by mixing it in different pro- portions with saltpetre. The mixture is poured into a red-hot crucible, placed under a well-drawing chimney. The mix- ture deflagrates and emits empyreumatic odors, and a partial oxidation of the carbon taking place, a mixture of potassium car- bonate and carbon is formed. This is known as black flux. For vigorous reduction it is made from 3 parts argol and 1 salt- petre; for less vigorous, either 2i and 1, or 2 and 1 parts respectively. White flux consists of 1 to 2 parts saltpetre and 1 part argol; gray flux of 3 parts argol and 2 saltpetre. On account of the hygro- scopic properties of black flux, a mixture of potassium carbonate or of bicarbonate of soda and flour is used in preference, it being also cheaper. Usually 20 to 25 per cent, of wheat flour is taken, but for more vigorous reductions, 30 to 35 per 56 THE ASSAYER'S GUIDE. cent., and even as much as 50 per cent. Potassium cyanide is an energetic reduc- ing (as well as desulphurizing) agent. It being very poisonous, great care should be exercised in handling it. Potassium ferrocyanide yields, on heating, a mixture of iron carbide, ferrous and ferric oxides, free carbon, and a small quantity of potassium cyanide. It exer- cises also a vigorous desulphurizing action. The following list of the reducing powers of various reducing agents will be found very useful. The values are approximate only, but for air practical assaying they are sufficiently near. will reduce parts 1 part of of metallic lead. Ordinary wood charcoal, 22 to 30 Powdered coke, 24 Powdered hard coal, 25 Powdered soft coal, 22 Wheat flour, 15 Cornstarch, 11 to 13 Laundry starch, 11 J to 13 RE-AGENTS USED IN ASSAYING. 57 will reduce parts 1 part of of metallic lead. Pulverized white sugar, 14 J Pulverized gum arabic, 1 1 Crude argol, 5 to 8J Cream of tartar, 4 to 6 2. Oxidizing agents. Saltpetre. Ordi- nary saltpetre of commerce is used. It should, however, be as free as possible from sulphates. Pulverize finely, and keep dry. Litharge (plumbic monoxide, yellow oxide of lead) exerts an oxidizing effect upon metals and metallic sulphides, as well as upon organic substances. It should be dry, and free from any considerable amount of red oxide of lead, as this causes oxidation .of silver and consequent loss. When the litharge contains silver, white lead not adulterated with heavy spar may be sub- stituted for it. Litharge entirely free from silver may be prepared by oxidizing the purest Pattison or Villach lead by cupella- tion, or bringing such lead, after it has been granulated into fused saltpetre; or by 58 gradually scattering powdered charcoal upon litharge fused in a refractory crucible, whereby some lead will be reduced which, in subsiding, withdraws the silver from the litharge. 3. Solvent agents, a. Acid; such as silica and glass. Silica is best used in the form of pulverized silica, since it is then in a very fine state of division suitable for intimate mixture with ores and fluxes. It should be perfectly dry. Borax-glass. This is produced by fusing borax in a clay crucible, and then pouring it upon a bright metallic surface. It is more fusible than glass, and the boric acid forms combinations with nearly all the bases as well as with silicic acid. Salt of phosphorus (sodium-ammonium- liydrogen phosphate) or microcosmic salt. In the anhydrous state it is a more ener- getic solvent agent than borax. Clay, such as kaolin. Most varieties of clay contain over 50 per cent, of silica. BE- AGENTS USED IN ASSAYING. 59 b. Basic. Potassium carbonate. Ordi- nary carbonate of potash. It should be ground to a fine powder and kept from the air, as otherwise it would rapidly absorb moisture. Sodium carbonate (bicarbonate of soda) acts somewhat less energetically than po- tassium carbonate, and consequently a larger quantity of it must be used. It is less deliquescent, more fusible and cheaper. A mixture of 13 parts of dry potassium car- bonate and 10 of calcined bicarbonate of soda furnishes a very readily fusible flux. Caustic alkalies act more energetically than carbonates, but exert a very injurious effect upon the crucibles. Calcium carbonate, in the form of chalk (or calcite), may be used for smelting oper- ations at higher temperatures (for instance, in assays of iron) . Fluor-spar is more readily fusible than calcium carbonate, and is especially effec- tive for removing silica. It readily fuses 60 THE ASSAYEK'S GUIDE. down with calcium phosphate, heavy spar and gypsum. Lead oxide (litharge, minium, white lead) readily fuses with silica, the alkalies, and most of the heavy metallic oxides, but less so with the earths and alkaline earths. 4. Desulphurizing or precipitating agents. Iron in the form of iron filings and as pieces of wire. Potassium cyanide and potassium ferro- cyanide (see p. 56). Caustic alkalies and carbonates decom- pose metallic sulphides. The metal is sep- arated, and sulphites, hyposulphites, and sulphates of the alkalies, together with alkaline sulphide, are formed. The latter forms a sulphur-salt with one part of the metallic sulphide, which, as a general rule, can be decomposed with iron. Carbon promotes desulphuration (black flux, potassium carbonate and flour). Salt- petre oxidizes metallic sulphides, while the metals are separated. RE- AGENTS USED IN ASSAYING. 61 5. Sulphurizing agents. Sulphur in the form of flowers of sulphur ; or of iron py- rites. 6. Concentrating fluxes. Lead in a granulated form (assay lead). Silver for alloying with gold (quartation). Gold for collecting copper (assay of nickel and cobalt) . Copper oxide for t in . Iron pyrites as collecting agent for copper (assay of matt). 7. Decomposing and volatilizing fluxes. Charcoal and' graphite for decomposing sulphates, arseniates and antimoniates by roasting. Ammonium carbonate for decom- posing sulphates, especially copper sulphate, at red heat, but less completely lead and bismuth sulphates. Common salt for the volatilization of antimony and arsenic in refining black copper according to the Cor- nish method. 8. Air-excluding fluxes (covering agents). Decrepitated common salt, as free from sul- phates as possible, fuses easily and becorn- 62 THE ASSAYER'S GUIDE. ing very thinly-fluid washes down particles of metal adhering to the sides of the assay vessels. Refined slag from charcoal iron blast furnaces. Re-agents for wet assays. The following are principally used : 1. For assays by gravimetric and color i- metric analysis. Acids: Hydrochloric, sulphuric, nitric and acetic; aqua regia. Bases and salts: Caustic alkalies, alkaline carbonates, potassium chlorate, ferrous sul- phate, sodium sulphide, etc. Metals for precipitation : Iron in the form of wire, or in a pulverulent condition, for copper ; zinc in the form of wire or granules, or in a pulverulent state, as a reducing agent for iron solutions, etc. ; copper ; bromine for decomposing sulphurets, compounds of gold, etc. 2. For volumetric assays. Potassium , permanganate ; sodium sulphide ; potassium cyanide ; barium chloride ; potassium iodide, free and with dissolved iodine; sodiurn EE- AGENTS USED IN ASSAYING. 63 hyposulphite ; ferric chloride ; sodium chlor- ide; potassium sulphocyanide, etc. As in- dicators: Litmus tincture, Brazil wood tincture, etc., for acids and alkalies; the salts of iron, nickel and lead, and sodium nitroprusside, for sulphur ; starch-paste for iodine; potassium sulphocyanide, etc., for iron oxide. 64 III. cf Silver Ores by Heat Cupellativn. SILVER occurs in nature chiefly in lead ores, (galena,) and native, as in the Lake Superior copper mines, or less commonly as chloride of silver, as is the case in the extensive mines of Chili. The following directions, however, refer equally to the assays of all. As with all minerals to be investigated by these methods, the ore must previously be reduced to the finest possible powder, for which purpose, where many assays are made, a large iron bowl is used as a mortar, the pestle having a wooden handle attached at right angles to the iron part, enabling us thus to employ a much greater force than if it were straight, as commonly is the case. The usual shape of a mortar. ASSAY OF SILVER ORES BY HEAT. 65 used in kitchens is not so good, for its depth prevents its being cleaned sufficiently to insure accuracy. In lieu of the former, and when small quantities only are de- sired to be pulverized, an agate mortar may suffice. Of the ore we weigh off one part, about 3 grammes, equal to 46 grs. Troy, (say 50 grs.) is a good standard weight, and . mix it with ten parts by weight of pure lead, and from one-tenth to one-tifth part of borax, in the manner de- scribed below. The lead is added to -extract all impuri- ties, such as copper, nickel, &c., and in cases where these occur in great abun- dance, should be used in the proportions even up to fifteen and twenty parts, though it is always injurious, and .tends to create a loss, to add too much. To the rules for testing the quality of alloys of silver and copper, will be found subjoined a table by Erker, to regulate this. The lead of commerce contains many im 66 THE ASSAYEE S GUIDE. purities, iii the shape of other metals, which, since silver always is among thoni, is very injurious to our assays, and it ia therefore necessary to obtain a purer article. At silver furnaces lead is produced as an extra product, sufficiently pure for our pur- poses. That, for instance, thus procured from the smelting works at Freiberg in Saxony, and used there by the assay ers, contains, to 6.40000 parts of lead, from 0.00001 to 0.000015 parts of silver, too slight an impurity to affect the result of the assay. If so situated as not to be able to get it in this manner, the best way is to reduce it by a galvanic process from acetate of lead. This, the sugar of lead of com- merce, we can readily dissolve in luke- warm water, after which we should filter off the solution, and introduce a rod of zinc, by which process all the lead is re- duced and collected round that metal. After some time remove it, and continue in this manner until all the lead is pre- ASSAY OF SILVER ORES BY HEAT. 67 cipitated. It is then to be repeatedly washed with care to remove the acid, and afterward dried between blotting paper. If not in a sufficiently pulverized shape, it need only be shaken a little in a towel and finally sieved. A spoon containing a given amount five parts, equal to 250 grs., is con- venient is used to measure the quantity for each assay, thus avoiding the tedium of weighing each time, a matter of consider- able consequence in an assaying office, where frequently hundreds of assays are made in a day. The vessel into which the mineral, to- gether with the lead and borax, is placed, to be introduced into the muffle of the fur- nace, is represented in fig. 1, Plate II. (See the description given a few pages back.) We first put one-half of the lead to be used in it, and on the top the silver ore, mixing the two with great care, not to spill the least particle, and afterward cover it with the rest of the. lead, and 68 THE ASSAYER'S GUIDE. sprinkle the borax over the whole. The latter is used to facilitate the melting of the lead, and to produce a good slag. When much tin, zinc, or lime is present in the ore, the borax should be increased in quantity up to the largest amount before mentioned. If we desire to test ores containing very little silica, and our crucibles are not as perfect as we might wish them to be, it is very advisable to make use of some quartz or glass-powder, to be added immediately, or, better still, when the slag is forming, and the process of calcining is thus at an end. We should, for the sake of economy with the fuel, make several assays at once, and always five or six of each ore, afterward taking the average, and thus regulating our own labour. After previously firing the furnace, and bringing the muffle to a regular and con- stant red-heat, we may introduce the cru- ASSAY OF SILVER ORES BY HEAT. 69 cibles. To quicken the melting of the lead, we place some pieces of well-dried charcoal, which should always be kept on hand, in front of the crucibles. Yapours will be observed to be emitted, caused by the discharge of volatile substances. The door of the muffle, previously closed, should be kept perfectly open as soon as the operation of calcining or roasting the ore has properly commenced, to admit fresh air, and prevent the heat from in- creasing too much. This process generally lasts about twenty minutes, after which, by introducing fresh coals into the muffle and again closing the door, we raise the heat, and continue it sufficiently long to let the slags collect and flow easily, so as to make a crust round the white-hot metal. When not employing a sufficiently high temperature, the slag will remain thick or tough, and retain the metallic alloy of silver and lead in small particles disseminated throughout the mass. THE ASSAYER'S GUIDE. From the circular portion of argentiferous lead, which appears to be in a constant rotary motion in the centre of the slag, vapours of lead rise incessantly. The time that should be occupied by this process of melting varies much according to the character and quality of the ore, which sometimes, though rarely, may even require something more than half an hour. Gene- rally much less time is wanted with a good fire, and the assayer can always see at what time the encircling slag has been properly separated from the metal, and even with very little practice is enabled to regulate it. We now again open the muffle, and by oxidizing some more lead during the space of ten minutes, cover the metal entirely, and after that, once more apply a strong heat for a few minutes to make the slags flow easy, and then taking out the crucibles, pour the whole contents into the different hollows of the iron plate, illustrated by fig, 0. Plate II. This should be done very ASSAY OF SILVER ORES BY HEAT. 7 1 quickly, for otherwise the lead will not collect in one button, but be distributed in small particles all over the molten slag as above. A little practice will soon accus- tom any one to all these operations. On cooling, with a stroke or two of the hammer we separate the slags from the metallic buttons, and with a few more easily shape the latter into cubes as regular as possible. The crucibles shown in fig. 2, Plate II. come into use at this part of the assay. If well made and dried, they should be very porous, and so friable as to be crushed between the fingers with ease. In these cupels we expose the metal cubes to a moderate red-heat, which we are enabled to regulate by inserting cold pieces of pottery old crucibles will be found very serviceable and leaving the furnace open. The rising vapours are from the lead, and continue until that peculiar bright flash of light is observed, termed silberblick, (silver- 72 TUP: ASSAYER'S GUIDE. gleam,) in German mining and smelting technology, and from which we know that the silver is pure. The utmost attention should be paid to this part of the assay, to ascertain the moment when this occurs. The coolers are then carefully removed, the aperture closed, and the most intense heat possible kept up for a few moments. To do this well is, I may say, the chef tfoeuvre of an assayer, and on it depends, in a great measure, the accuracy of the assay; for the silver, when pure, requires a much greater heat to bring it to the melting point than when it contains even a very small admix- ture of lead ; and for this reason, if we do not instantly elevate the temperature when the ceasing of the rainbow colours and the bright light of the globule of pure silver inform us that all the lead has left, then the silver would cool suddenly, and, of course, quicker at the surface than in the interior or at the bottom, and by this subitaneous contraction cause a spattering ASSAY OF SILVER ORES BY HEAT. 73 motion of the yet unconsolidated particles, and be productive of great loss to the assay. There is an old adage current among German smelters and assay ers, probably known to all who may have had the advantage of studying this art in that country, where it has been brought to such perfection, which, since it is many centu- ries old, shows how long it has been re- garded as the great aim, in this mode of testing silver ores, to keep up a moderate temperature as long as any lead is left, and to apply intense heat as soon as all has de- parted. I insert them here : " Kiihl getrieben, heisser Blick 1st des Probierer's Meisterstiick." In English it would be : To evaporate coolly and to use heat when pure, is the masterpiece of an assayer. When the buttons of pure silver have cooled, we grasp them firmly with a pair of pincers, tight enough to compress the 74 THE A&SAYER'S GUIDE. sides, thus exposing the bottom more, and with a wire brush remove the adhering particles of litharge, and dust of the cupel. Turning them half round so as to make the base a square, we repeat the operation, and then weigh, but only when quite cold, since otherwise the heat, by increasing the bulk, might tend to create a varia- tion. The silver produced in this manner, it should be remarked, is not perfectly pure, chemically speaking, but the slight impu- rities are too insignificant to deserve any attention from an assayer, who has nothing but technical purposes in view, though they might require it from a scientific chemist ; and for this latter reason, -I have thought proper in the fourth chapter to sug- gest a method to ascertain the exact amount of silver in this button, should it be deemed necessary, though, I must add, that such precision can only be required at mints, if the investigations are not con- ASSAY OF SILVER ORES BY HEAT. 75 ducted for science' sake, in which case, the wet process would, of course, be preferred from the beginning. Besides this, small inaccuracies in the shape of losses, as has already been re- marked, cannot be averted, even though the assay be performed with the greatest care, as the evaporating, or rather oxid- izing lead probably carries off small par- ticles of silver, particularly when too much heat is used during that process. It is im- possible to give any perfect rules how to obviate such faults, since so much depends on the care and attention paid, as well as on the acquired practice and innate prac- tical skill of the assayer ; yet, pre-supposing all this as perfect, the Parisian mint has established a table to regulate their assays, which will be found on pages 77 and 78. From this it is seen that the different losses with different quantities of silver vary con- siderably, nor is the loss a per-centage, being greatest where the original or true 76 THE ASSAYER'S GUIDE. amount of silver in the ore or alloy is seven hundred. This table should always be referred to, as it enables us to calculate the true amount of silver, and to rectify those un- avoidable faults which may be occasioned by the lead carrying off portions of the silver entirely, or else drawing them along with it into the pores of the crucible. 77 IV. A Table to rectify ike Loss incurred during tJie Silver Assay. Real amount of sUver. Amount of silver found by the assay. Loss during the procesp. 1000 998-97 1-03 975 973-24 1-76 950 947-50 2-50 925 921-75 3-25 900 896-00 4-00 875 870-93 407 850 845-85 4-15 825 820-78 4-22 800 795-70 4-30 775 770-59 1-41 750 745-48 4-52 725 720-36 4-64 700 695-25 4-75 675 670-27 4-73 650 645-29 4-71 625 620-30 4-70 600 595-32 4-08 575 570-32 4-68 78 THE ASSAYER'S GUIDE. Real amount of silver. Amount of silver found by the assay. Loss during the process. 550 545-32 468 525 520-32 4-68 500 495-32 4-68 475 470-50 4-50 450 445-69 4-31 425 420-87 4-13 400 396-05 3-95 375 371-39 3-61 350 346-73 3-27 325 322-06 2-94 300 297-40 2-60 275 272-42 2-58 250 247-44 2-56 225 222-45 2-55 200 197-47 2-53 175 172-88 2-12 150 148-30 1-70 125 123-71 1-29 100 99-12 0-88 75 74-34 0-66 50 49-56 0-44 25 24-78 0-22 LOSS DUBING THE SILVER ASSAY. 79 Iii Freiberg somewhat different results have been obtained. With refined silver the loss by absorption by the cupel was found to be 0.0015 to 0.0002 ; and in alloys of medium .richness the loss was greater than that stated in the preceding table. For instance, with 750 thousandths and 16 weights of lead, the loss was 5.55 thou- sandths, but with 11 weights of lead it ac- corded with the table, 4.52 thousandths. According to Plattner, fine silver with five times the quantity of lead frequently gives a loss up to 0.009, refined silver with 937 thousandths and five times the quantity of lead, 0.0042 to 0.0059 ; refined silver with 687 to 750 thousandths and 14 times the quantity of lead, 0.0073 to 0.0083. V. Gay-Lussads Process far assaying Silver Alloys. THIS modus operandi is one which, from its very simplicity and shortness, almost necessarily insures success, but it is only intended for alloys, such as coins, and can, therefore, if applied to ores, only be used to ascertain the real amount of silver in the button produced in the last assay, which, as already observed, contains a very minute amount of spurious metals in an alloyed state. It was proposed by Gay-Lussac, and from the indubitableness of its results, has since been introduced in France, and most parts of Germany, to regulate the assays of the mint. They dissolve a given weight of the GAY-LUSSAC'S PROCESS. 81 alloy in nitric acid and precipitate from the solution all the silver as chloride of silver by means of a standard solution of sodium chloride. For this purpose a normal solu- tion of common salt is required, 100 cubic centimeters of which will precipitate 1 gramme of chemically pure silver. There is further required a decmormal solution of common salt, containing but one-tenth the quantity of common salt in solution in the first, and a decinormal solution of silver in nitric acid containing 1 milligramme of sil- ver in 1 cubic centimeter of solution. Preparation of the assay solution. The degree of richness of the silver is approxi- mately determined by a preliminary assay, 4 to 6 thousandths parts the amount of silver found by this assay being added to the result. It is generally preferred to assume the degree of richness a few thou- sandths higher than is actually the case, and to base the calculation for the quantity of assay-sample required upon this, as, to 82 THE ASSAYER'S GUIDE. effect the more rapid settling of the silver chloride, it is more preferable to add, during the titration, a few thousandths from the de- cinormal solution of salt than to be obliged to add from the decinormal solution of sil- ver. The quantity of alloy containing 1 gramme of silver which is to be taken is then calculated (for instance, if the prelim- inary assay gives a content of 897 thou- sandths, then 1.115 grammes of alloy con- taining 1 gramme of silver should be taken, 1000 : 897 = x : 1000). The sample in the form of shavings or granules is placed in a numbered flask, together with 6 to 7 cubic centimeters of nitric acid free from chlorine, and dissolved either on a water or sand bath. The flasks in which the sam- ples are dissolved are from 10 to 15 centi- meters high, and 5 to 5 2 centimeters wide. If several assays are 'to be made, it is ad- visable to dip the flasks, which are arranged upon a stand, Fig. D, into hot water. (A black " residue maybe gold or sulphide of 83 silver; should the latter be the case, some concentrated nitric acid is added and the fluid heated, or sulphuric acid used.) The nitrous acid formed is then driven out of the flask by means of a small bellows with curved extremity, and the contents of the flask are treat- ed with the normal solution. But, as the influence of the temperature upon the volume of the normal solution of common salt must be taken into considera- tion, its liter must always be determined on the same day the assays are to be made, with 1 gramme of pure silver + 1 to 2 cubic centimeters decinormal solution of silver, in order to be able, for the above-mentioned reason, to use decinormal solution of salt for the final tit ration. The silver solution is then titrated by placing the glass flask in the metal cylinder C, Fig. E, standing upon the sliding carriage B (Sire's apparatus). The glass-cock c (a pinch-cock may be used 84 THE ASSAYER 7 S GUIDE. instead) is then opened and. accompanied by the admission of air through a, the nor- mal solution of sodium chloride flows from the vessel A through h, the thermometer FIG. E. tube by and the rubber tube d, into the burette e. It ascends in this, and a sniall quantity reaches the saucer g through the grifice/. The cock c is now closed (h and GAY-LUSSAC'S PROCESS. 85 e may be also directly connected by a rub- ber tube provided with a clip) and the pipette 6, which is now filled, will contain exactly 100 cubic centimeters of liquid. The index finger of the left hand is now placed upon the mouth /of the pipette, the rubber tube d is detached from the lower end of the pipette e, and the sliding car- riage B, upon which stands the metal cylin- der G containing the flask with the solution of silver, is pushed underneath the dis- charge orifice of the pipette. The index finger is now removed from /, and the 100 cubic centimeters of the common salt solu- tion are allowed to run into the flask, care being taken that the pipette does not rest on the neck of the flask. The sliding car- riage is then pushed back, the flask is closed with its ground-glass stopper, and its con- tents are cleared by shaking, which is best done by inclosing it for the purpose in a metal cylinder of proper size. If many 86 assays are to be made, it is advisable to use Gay-Lussac's or Mulder's agitator. One cubic centimeter of decinorrnai so lution is now added to the entirely clear fluid standing over the precipitate of silver chloride, by means of a graduated pipette contained in a flask, Fig. F, whereby the point of the pipette should be placed against the neck of the flask containing the silver solution. If turbidity is produced, the silver solution is agitated until it is again clear, and 1 cubic centi- ^ meter of the decinormal solution of DIG. r. common salt again added, etc., until the last cubic centimeter which is added does not produce any turbidity. This last cubic centimeter is not taken into calcula- tion, and only one-half of the one previously added. (For the reason previously stated, it is more suitable to use decinormal solu- tion of common salt than decinormal solu- tion of silver for the final reaction.) Calculation. Suppose the richness of GAY-LUSSAC'S PROCESS. 87 the alloy was found according to the pre- liminary assay to be 897 thousandths, 1115 thousandths of the sample containing 1.000 gramme would have to be weighed off. 1000 cubic centimeters of the decinormal solution of salt 1 gramme of silver. Now sup- pose 1002.5 cubic centimeters of decinor- mal solution of common salt had been used, 1000 parts of the alloy would therefore con- tain 899.1 parts of silver. In case mercury should be present, so- dium acetate (0.5 gramme to 5 thousandths of mercury) is added, which will prevent the mercury from being precipitated by the sodium chloride solution ; or the mercury is previously volatilized by heating the assay sample in a small graphite crucible in the muffle. For bismuth some tartaric acid is added. In case tin is present, the assay sample is dissolved in sulphuric acid instead of nitric acid. According to Thorpe, only 2 parts of silver chloride freshly precipi- tated, and 0.8 part that has been blackened 88 by exposure to light, are dissolved in 106,. 000 parts of nitric acid. Preparation of the normal solutions. A completely saturated solution of common salt is prepared, of which, if the salt used is entirely pure, 170 cubic centimeters con- tain 54.15 grammes of common salt. These 170 centimeters are diluted to the volume of 10 liters. 100 cubic centimeters of this solution correspond to 0.5415 gramme of common salt, which will completely precipi- tate 1 gramme of pure silver. The true standard is obtained by pouring 100 cubic centimeters of the common salt solution into a solution of 1 gramme of chemically pure silver. This is agitated by shaking until it becomes clear, and the number of thousandths of common salt or silver which remain free are exactly determined by the addition of an observed volume of very dilute salt solution of known strength, or of a decinormal solution of silver, and from this the quantity of water or of common G4Y-LUSSAC ? S PROCESS. 89 salt is calculated which must be added to obtain the correct standard. When this addition has been made, a new test is had with the standard solution and the decinor- mal solution prepared from it, and this is continued until the solution does not show a perceptible variation from the correct standard The decinorinal solution of common salt is prepared by pouring 100 cubic centi- meters of the standard common salt solu- tion into a flask capable of holding 1 liter and filling it with water to the liter mark. For the decinormal solution of silver 1 gramme of fine silver is dissolved in 5 to 6 grammes of nitric acid, which is then diluted with water to 1 liter. When a large number and great variety of silver alloys have to be assayed, the following tables, A and B, calculated by Gay-Lussac for his silver assay, will be found to save much time and trouble in determining the fineness of the alloy. If, 90 THE ASSAYER'S GUIDE. after the addition of the standard common salt solution, no reaction takes place on adding the decimal salt solution or the decimal silver solution, it is an indication that the silver in the alloy assayed amounts to exactly 1000 milligrammes, and it fur- ther indicates that the standard solution is correct. The titer is indicated in the columns by the figure 0. 91 I i ! 00 O O -i-< 05 os os . cp oloo ?O O 06 or? os ^ o *c o p oj 01 as a> oo QO i^ t- cc t cc ic >c i i i iB& O;oiO5Gcoot>.r^ OiClOiO5O5O5Oi iciOTf<-^c i * . . 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O iO O >O O >O O Id O "O O IO O IO O >O co^CiC5OO'- j '^c-ic-icofOTf<-r | ioio T-I i i T-H r-( C-l C-I CI Cl C 1 Cl O1 re copper the alloy contains, the more lead should be used. 140 THE ASSAYEK'S GUIDE. The only way to pulverize a coin or alloy is to file off small portions. About a gramme or fifteen grains of the filings should be carefully weighed off, wrapped in paper, (satin paper is the best, giving little ashes,) to prevent small particles from being lost, and placed in the muffle furnace on the cupel, fig. 2. When the paper is burnt to ashes, the lead is added according to the table. The rest of the assay is exactly as with silver ores. As long as lead and copper are being oxidized, no severe heat should be employed, which is, however, done as soon as the bright flash appears. The alloy or coin may also be treated according to Gay-Lussac's process, already described. Having thus ascertained the amount of silver, we are easily enabled to calculate that of the copper, by subtraction, i XIV. Assay of Gold Coins, or Alloys containing Oold, Silver, and Copper. BEFORE making the regular assay, it is necessary to ascertain the probable contents of the alloy, as with silver. The method commonly used is the touchstone or besanite test, the same employed by goldsmiths when purchasing coin or bullion. A dark fine-grained basalt or siliceous slate is re- quired, and on this a line is drawn with the gold coin. Those whom business has fre- quently brought in contact with such alloys are generally able to judge pretty accurately by this alone, as the purer it is, the brighter the yellow, silver making it whitish, copper of a redder hue. To carry this test out farther, the mark is moistened witb an acid, which, dissolving the baser 142 THE ASSATER'S GUIDE. metals, leaves the gold in its virgin state. This acid consists, in thousand parts, of 784 parts of pure nitric acid, of 1.340 specific gravity, 16 " " " muriatic acid, of 1.173 spec. grav. 200 " " " distilled water. 1000 As with gold ores, several assays should be made at once, to regulate one another. When some of the alloy has been filed off' too small pieces ought not to be taken, on account of their liability to be blown away the&e particles should he carefully brushed, to remove the fine dust, which might otherwise only drop off after weigh- ing, and thus cause a decided loss. For the assays, 5 grains are used in each, and the value of the gold is afterward given in carats fine, pure gold being reckoned at 24 carats fine. In this way an alloy containing 91.666 per cent, of gold will be 22 carats fine, or in other words, it contains S or jj of pure gold to % of the alloyed metal. ASSAY OF GOLD COINS. 14:3 After having weighed off the above quantity of the gold to be tested, three times the weight of the expected amount of gold, as ascertained by the prior inves- tigations, are taken in pure silver. Some deem two and a half sufficient. The gold and the silver are then carefully wrapped in a piece of paper. It is now necessary to ascertain the required quantity of pure lead, which varies according to the per-centage of cop- per in the coin or alloy. As this metal has a much greater affinity for gold than for silver, it is much more difficult to sepa- rate it from its alloys with the former than with the latter, and for this reason the lead used should be about twice as much as would be necessary, were we assaying a coin consisting of silver and copper. The following table is given by D'Arcet to regulate the amount to be used : 144 THE ASSAYER S GUIDE If the contents of gold in the alloy is The quanti- Relative quantity ty of lead re- of lead to the quired is copper. In 1,000 parts. In carats fine. 1.000 24. 1 0.900 21.6 10 100.000 to 1 0.800 19.2 16 80.000 to 1 0.700 16.8 22 73.333 to 1 0.600 14.4 24 60.000 to 1 0.500 12.0 26 52.600 to 1 0.400 9.6 34 56.666 to 1 0.300 7.2 34 48.571 to 1 0.200 4.8 34 42.500 to 1 0.100 2.4 34 37.777 to 1 As with silver assays, if too much be employed, it will produce a loss, while too little would not extract all the copper. The lead is first placed in the cupel, (fig. 2,) and only when the process of oxid- ation has commenced, is the paper contain ing the gold and silver to be added. The rest is performed exactly as with gold ores. The button should be hammered to a very thin sheet, before being submitted to the nitric acid; and to do this well, it should be perfectly cold, JIM otherwise marginal 145 cracks are often produced, which again may be productive of loss. It may not be quite out of place here to give the mint units and the content, weight, etc., of the coins of various countries. Mint -Units. Country. Miut-uiiit. Weight in grammes. Fineness of principal coins. Fine gold. Fine silver. Austria I Gold gulden 0.7258 8.8217 1.3725 0.4032 7.3224 0.29 0.3584 0.29 0.29 0.29 1.1997 0.29 0.066 1.5046 11.11 22.5 4.5 4.5 4.5 4.5 17.9961 4.5 0.998 900 900 900 900 900 900 916.66 900 900 900 900 900 916 66 868.05 900 900 900 900 Brazil Chili I Silver gulden. .. Gold milreis.. Peso (gold) Peso (silver). Krone Denmark, Sweden and Norway England , Pound or sove- reign.. Franc France, Belgium, Switzerland German Empire... (j reece 10 marks Drachme Italy lioumaiiia Russia .. I Lira Lei Gold rouble Silver rouble Dinar Gold piastre Silver piastre Dollar Servia Turkey | United States of North America. JO 146 The following tables show the content, weight, etc., of the coins of various coun- tries. Gold Coins. Weight Fineness Fineness Remedy Remedy Country. Coins. in in thou- in in in gram'es. sandths. gram'es. weight. fineness. 8 Gulden .. 6.4516 900 5.8065 0.002 0.002 Austria... * 4 3.2258 900 2.9032 0.002 0.002 Dukaten... 3.4909 986.111 3.4424 0.00125 0.00175 100 Francs 32.2518 900 29.0323 0.001 0.002 50 " 16.1290 900 14.5161 0.001 France.. 20 " 6.451d 900 5.8065 0.002 10 " 3.2258 900 2.9032 0.002 5 " 1.6129 900 1.4516 0.003 ' 20 Marks.. 7.965 900 0.002 _ German J 10 " 3.9825 900 0.002 _ Empire j 5 " 1.9912 900 0.004 f 5 Sovereigns 39.9403 916.667 36.6119 0.002 0.002 Great 2 " 15.9761 916.667 14.6448 0.002 Britain 1 1 Sovereign 7.9881 916.667 7.3224 0.002 i " 3.9940 916.667 3.6612 0.002 | Imperial 6.5440 916.667 5.9987 0.00679 Russia ... { Imperial ( Dukat... 3.9264 916.667 3.5992 0.00566 f Double United eagle 33.4363 900 30.0926 0.000969 States of Eagle 16.7181 900 15.0463 0.001938 North ' i eagle 8.3591 900 7.5232 0.001938 America, i \ eagle 4.1795 900 3.7616 0.003876 i 1 1 Dollar... 1.6718 900 1.5046 0.00969 147 Silver Coins. Country. Coins. Weight in gram'es. Fineness in thou- sandths. Fineness in gram'es. Remedy in weight. Remedy in fineness. 2 Gulden .. 24.6914 900 22.222 0.003 0.003 1 " 12.3457 900 11.111 0.004 i 5.3419 520 2.7778 0.010 Austria... . 20 Kreuzer 2.6667 500 1.3333 10 " 1.6667 400 0.6667 Maria-Theresa- Thaler... 20.0668 833.333 5 Francs... 25 900 22.5 0.003 0.002 2 10 835 8.35 0.005 0.003 France.., , 1 5 835 4.175 0.005 0.003 50Centimes 2.5 835 2.0875 0.007 0.003 20 " 1 835 0.835 0.010 0.003 German 1 5 Marks... 27.7778 900 25 0.010 0.003 Empire 2 " 11.1111 900 10 0.010 0.003 1 5.5555 900 5 0.010 0.003 50 Pfennig 2.7778 900 2.5 0.010 0.003 20 " 1.1111 900 1 0.003 Great 1 Crown... 28.2759 925 26.1552 0.004 Britain i " 14.1380 925 13.0776 0.004 1 1 Shilling. 5.6552 925 5.2310 0.004 6 Pence.... 2.8276 925 2.6155 0.004 4 " 1.8851 925 1.7437 0.004 1 Rouble... 20. 73 15 1 868.056 17.9961 0.00857 i " 10.3658 868.056 8.9981 0.01286 Russia ... - i " 5.1829 868.056 4.4990 0.01715 I'OKopecks 3.5992 500 1.7996 0.01715 10 " 1.7996 500 0.8998 5 0.8998 500 0.4499 United [ 1 Dollar... 27.2156 900 24.4940 0.00357 0.003 States of * " 12.5 900 11.25 0.00714 North ! i " 6.25 900 5.625 0.01428 America. i " 5. 900 4.5 - 0.01428 ' I 1 Dime 2.5 900 2.25 0.03571 ~ 148 Base Coins. Country. Coins. Weight in gram'es. Composition. Per cent. Remedy in content. l! f 4 Kreuzer 134 1 Austria.. \ 1 " . 3J [Cu 1 i 1 & 1 15 j lOCentimes 10 511 5 0.01 Cu 0.01 France .. - 2u 2 95 Cu 4-4 Sn 0.005 Sn 0.01 1 " 1 + 1 Zn 0.005 Zn 0.015 German 10 Pfennig 5 " 4 2.5 ) 75 Cu + 25 . Ni 1 0.005 Ni 0.05 Empire 1 2 " 3.13 1 t 95 Cu +4 Sn i 0.05 i 1 " 2 J + 1 Zn 0.05 _ 1 Penny 9.4498 !p- r , 1+4Sn Great ! Britain j 5.6699 1 Farthing 2.8349 + 1 Zn 5 Kopecks 16.352 1 3 9.820 2 " 6.532 Russia... . 1 3.244 bronze i " 1.600 i " 0.800 j United States of North ' 5 Cents 3 " 5 1.944 ) 75 Cu + 25 j Ni 1 0.025 0.039 0.066! America [ 1 " 3.944 95 Cu + 5 Sn - and Zn 0.044 143 XV. To find the Proportion of Gold in a mixture of Gold and Quartz ~by Calculation* THE specific gravity of gold = 19.000 The specific gravity of quartz = 2.600 These numbers can be corrected when experiment shows the specific gravities to be different. A. Ascertain the specific gravity of the mixture of gold and quartz. Suppose it to be 8.067. B. Deduct the specific gravity of the *This article is taken from J. A. Phillips's "Gold Mining and Assaying," (London, 1852,) p. 85, a work published since the first edition of this little volume, and one which, like the other productions of its author, it is needless more particularly to recommend to those who pay attention to the recent publications in this department of applied chemistry. 150 THE ASbAiEil'S GUIDE. mixture from the specific gravity of the gold : the difference is the ratio of the quartz by volume : 19.000-8.067 = 10.933 C. Deduct the specific gravity of the quartz from the specific gravity of the mix- ture : the difference is the ratio of the gold by volume: 8.067 - 2.600 = 5.467 D. Add these ratios together, and pro- ceed by the rule of proportion. The pro- duct is the per-centage of gold by bulk : 10.933 + 5.467 = 16.400 16.4 is to 5.467 as 100 is to 33.35 E. Multiply the per-centage of gold by bulk, by its specific gravity. The product is the ratio of gold in the mixture by weight : 33.35x19.00 = 633.65 F. Multiply the per-centage of quartz by bulk, by its specific gravity. The product PROPORTIONS OF GOLD. 151 is the ratio of the quartz in the mixture by weight : ^ 66.65x2.60 = 173.29 G. To find the per-centage of gold, add these ratios together, and proceed by the rule of proportion : 633.65 + 173.29 = 806.94 806.94 is to 633.65 as 100 is to 78.53 Hence, a mixture of quartz and gold, having the specific gravity of 8.067, con- tains 78.53 per cent, of gold by weight. 152 XVI. Assay of Platinum Ores. THIS metal has as yet' occurred in the United States only in gold ores, and even then in the merest traces, and hence, per- haps, it would barely deserve a mention in these pages; but the great interest attached to its occurrence, as so rare a metal all over the world, and its useful application to chemical purposes, has caused me to insert some rules for its assay. If the ore contain platinum in no larger amount than three or four per cent, of the gold, the former, as already observed in Article VII., on quartation, will be entirely dissolved in the nitric acid used on ac- count of the silver. From this solution of the two metals precipitate the silver with common salt, or muriatic acid, as chloride ASSAY OF PLATINUM ORES. 153 of silver; filter and wash until the water dropping from the funnel no longer con- tains any of the platinum solution. This latter evaporate to dryness, after adding sal-ammonia. Wash it with alcohol, (see Gold, art. XII.) and heat the double chlo- ride of platinum and ammonium to red- ness, thus producing a spongy mass of pure platinum. If there be more than three or four per cent, of platinum in the gold, its presence is readily perceived, from various circum- stances : thus, in evaporating the lead a higher temperature is necessary than is commonly the case, to make the metal flow and acquire a round form ; secondly, the bright light cannot be observed; thirdly, the surface of the button is crystalline or rough, and when large, flat and quite ir- regular, besides looking dull and having a more or less grayish colour; fourthly, the nitric acid is frequently discoloured; and fifthly, the little roll of gold is not of a 154 THE ASSAYEL s GUIDE. pure gold yellow, but rather inclining to- wards steel gray. After having thus recognised a larger quantity of this metal, it becomes neces- sary, since copper is frequently present, to make a prior test, to ascertain, by cupella- tion, the amount of the alloy of gold and platinum. After that, two assays should be made; the one, to ascertain the exact conjoint per-centage of the two; the other, inquartation (pure) silver being added, to discover the amount of the gold alone. The difference of the two results gives the amount of platinum. The inquartation silver should not be more than from two and a half to three times the weight of the alloy of gold and platinum ; and it is often well to add a certain, accurately weighed quantity of pure gold at the same time, so that the gold may afterward be procured m one connected sheet or piece. This ought particularly to be done, when there is as much as a third the weight of the ASSAY OP PLATINtM OftES. 155 gold in platinum, as, for instance, in the platinum grains of the Ural Mountains, which contain about 80 per cent. The button is hammered flat, and proceeded with exactly as gold ores, the platinum dissolving with the silver in nitric acid. But as it does not do so as easily as the latter, at least when in large quantities, it is necessary to repeat the process from the quartering on once or twice, using silver and lead over again. This should be done until nothing but the silver used is dis- solved in the nitric acid, or, in other words, until two assays following one another have produced the same results, a thing that may not occur until the fifth time. It should be remarked, that it is neces- sary to add a little more lead for cupella- tion, than .would be done if no platinum were in the ore; and also, that just before the bright flash of light occurs during the operation of quartering, it is well to shake the cupel a little, to make the button 156 THE ASSAYER'S GUIDE. stiffen, as soon as the last lead has entered the former, by which the platinum will be more regularly distributed in the alloy, and cannot so well collect in different uncon- nected lumps, unexposed afterward to the action of the acid. The platinum may then be extracted and reduced from the solution as above. Electrolytic assay of platinum. Com- pounds of platinum are decomposed with the greatest ease by the galvanic current, with the deposition of the metal on the negative electrode. A current of two Bun- sen cells produces decomposition so rapidly that the platinum separates as platinum black and cannot be determined. If one cell is used it separates in so dense a form that it cannot be distinguished from ham- mered platinum. It is possible, in this way, gradually to deposit considerable quan- tities of platinum on the negative electrode without changing its appearance. For the determination of platinum in its salts, the ASSAY OF PLATINUM ORES. 157 solution may be slightly acidified with hy- drochloric acid or with sulphuric acid, or treated with ammonium or potassium oxal- ate, gently warmed and electrolyzed. The platinum separates in a comparatively short time. For example, a solution of platinum chloride diluted to 200 cubic centimetres, containing 0.6 gramme platinum, deposited 0.5 gramme in five hours. Iridium is not reduced from its solutions by a single Bunsen cell. This fact may be used for the separation of platinum from iridium 158 XVII. Assay of Capper Ores German and HUM- garian Method. THIS ore, if a sulphuret, as is very gene- rally the case, should, after having been reduced to the finest possible powder, be submitted to the process of roasting, vul- garly termed calcining. For this purpose one part by weight of the ore is mixed up with one fifth of graphite, (black-lead,) which, consisting of carbon in a more con- densed state than that element occurs in charcoal, is, therefore, so much the more effectual in driving off the sulphur. This mixture of the two should be exposed to an intense red-heat in the cupel, (fig. 1,) (painted over on the inside with red chalk, or Spanish red, to prevent adhesion,) for about twenty minutes, after which it is ASSAY OF COPPER ORES. 159 to be taken out, and stirred up with a small iron ladle to expose the unburnt parts of graphite, when it should again be exposed in the muffle. In about a quarter of an hour we take it out again, pound it over, for the mass is generally clogged, and mix it with about twice its weight of charcoal- dust, after which we continue the roasting for about one-half to a full hour, according as the ore contains a little or much sul- phur, vapours of which may be seen rising during the whole of this process. After this the ore has a reddish, or what is generally called a ferruginous colour, and we now take it from the first crucible, and introduce it into that represented in fig. 4, Plate II., or if not in possession of such, into a Hessian crucible, fig. 5, on the same plate. For this purpose, however, some Hack flux should be provided. It consists of carbonate of potash and lime, and is made by igniting together one part by weight of saltpetre, and two of rural- 160 THE ASSAYER'S GUIDE. mon tartar. The flux produced should be kept carefully corked to prevent the ab- sorption of hygroscopic water. It is still better to make -it only when required for immediate use. If the ore is poor, one tenth part by weight of oxide of antimony, (antimonious acid,) or of arsenic, (arsenious acid,) or if it is richer, fifteen per-cent. of pure lead* are requisite, as will hereafter be seen to make the particles of copper unite. One of these together with three parts of black flux, one half the weight in borax, and two parts of table salt, must then be added to the roast- ed ore, though none except a part of the * Some assayers use neither of these three, on the ground that the arsenic, as occasionally even 40 per- cent, may be taken, is very difficult to separate from the copper, and that the antimony may unite with part of the same, forming an antimoniate. They therefore only employ borax and black flux, in about the same proportions, however, as given above. It is hard to say which is best, and it must be left to the discretion and experience of the assayer to act as may be most suitable co his peculiar ores ASSAY OF COPPER ORES. 161 flux are mixed with the mineral now in- vestigating. The salt is merely used to form a crust over the whole. When all have thus been placed in the crucible, they are covered over with a piece of charcoal, cut to match the size of the vessel ; after which the cover is put on. We then ex- pose it to a white-heat for about one-half to one full hour, as may be most conve- nient, either in the draught furnace, fig. 6, Plate I., or in the muffle furnace; in which latter case, we must allow the longest period of time. The carbon of the flux is intended to reduce the peroxide of copper produced by roasting, while its carbonate of potash unites with the earthy contents of the ore and the oxides of other metals present, such as iron, which would otherwise also be reduced to their metallic state. With these it forms a slag, the borax being added to make it flow easy, and allow the copper to collect in one button. 11 162 On cooling, we break open the crucible, and, on removing the slag, extract a spheri- cal piece of impure or alloyed copper, according as other metals may chance to occur in the ore. If any intermediate crust should have formed between the button and the slag, the ore was not proper- ly roasted, a part of the copper not reduced, and consequently the assay is worthless. In a good assay the slag should be black and vitreous in appearance, never of an earthy texture. If striated or speckled with red, we may know that protoxide of copper is dissolved in it, and again that the whole cannot be productive of an accurate result. Much attention is required during this test, and, as already mentioned under the heads of silver and gold, the final result depends entirely upon the care taken by the assayer. If well managed, however, as here directed, he can hardly fail to be suc- cessful. The button, as remarked above, may ASSAY OF COPPER ORES. 163 vary in purity. It generally contains some iron, and (since these metals frequently exist in copper ores) lead, bismuth, tin, cobalt, nickel, antimony, and arsenic the latter two in particular, if they were added in the process of reduction. Thus it very rarely, if ever, happens, that a copper ore is sufficiently pure to require no third process. The less admixtures the alloy con- tains, the less brittle and the more ductile it is. Nickel particularly tends to harden it. To remove the foreign metals, the button is put in a piece of paper, with sufficient borax to cover it, (one-fourth to one-third part by weight, rather more than less,) and if no lead occur in the ore, with about from live to ten per-cent. of that metal, which amount, however, should increase up to forty, or even more, if there are many impurities in the alloy. Even if this be not the case, it is always safer, and can never produce any bad effect, to add much. A crucible of the kind illustrated in fig. 3, 164 THE ASSAYER'S GUIDE. Plate II., should be brought to a bright white-heat in the muffle. Coals may be placed round to increase the temperature, which should be so great, that the copper, on being introduced, wrapped in paper with borax and lead, may melt in a few minutes. As long as the tongs held over the button are reflected, or rainbow colours are yet seen to flicker over its surface, lead is still present. As with silver and gold, too great heat ought not to be employed. When the lead has left, we immediately take out the crucible, and immerse it in water, to pre- vent any copper from oxidating unneces- sarily. The button of pure copper is then broken out and weighed. A slight loss can- not be prevented, as it is impossible to pre- vent some oxide of copper from being formed, and we must therefore grant a larger per- centage than the assay would direct. At least two assays should be made at once, to compare the results, and take the average. 165 XVIII. At&ay of Capper Ores English Method. AT the copper mines in Cornwall, a mode of assaying, is employed, which in several of its minutiae differs considerably from the one just described. It should be remarked that this method is, properly speaking, ouly applicable to sulphurets, as all copper con- tained in the ore as a pure oxide, or com- bined with an acid, will pass over into the slag during the reduction process ; and that therefore if these latter are present, some means should be employed, as shall be shown hereafter, to extract them from the slags, when the other parts of the assay are concluded. The ore, being a sulphuret, should be roasted as directed in the foregoing Ger- man or Hungarian method, after which it 166 THE ASSAYER'S GUIDE. is mixed with from one to one and a half parts of pounded glass, which should, how- ever, contain no lead or arsenic, from twenty-five to fifty per-cent. of saltpetre, and fifty per-cent. of borax. Together with these, it is exposed to a strong melting heat in a clay crucible. On cooling, the button is removed, as is the case in the other mode t of procedure, more common on the conti- nent of Europe. Having thus reduced the copper, it is ne- cessary to purify it, as was also done in the other assay. I must observe, however, that this part of the Cornwall process, again, can only be applied where very little lead is contained in the copper ore. For this purpose, some white flux should be prepared, which is done by igniting to- gether equal parts of saltpetre and tartar. Being as susceptible to the effects of atmo- spheric moisture as black flux, it requires the same precaution as regards its preser- vation. ASSAY OF COPPER ORES. 167 The button of copper alloy is then ham- mered out flat, to a sheet as thin as it will allow of, without breaking. It is then ex- posed in a crucible, (fig. 3,) already red- hot, and, as soon as it melts, covered with white flux. Some table-salt, from which the water of crystallization has been re- moved by heat, is frequently added to give a covering and protect the copper from too immediate contact with the atmosphere, which, together with the heat, would un- avoidably create a free oxidation. A con- siderable ebullition is produced, on the sub- siding of which, and when therefore the mass flows quietly, the contents of the cru- cible are poured into an iron mould, (fig. 6, Plate II.,) greased over beforehand, from which the mass should be removed with a pair of tongs, as soon as sufficiently consoli- dated, to be dipped in water, which ena- bles us to separate the slag from the copper with greater ease. The purity of the latter is known by its malleability, and by it 168 THE ASSAYER'S GUIDE. not cracking much at the margin, when stretched on the anvil under the blows of a hammer. Should this test prove its yet uncleansed state, it ought again to be sub- mitted to the operation just concluded. Sometimes it is necessary to repeat this several times. It has already been mentioned, that, par- ticularly when not all the copper in an ore is contained in the shape of a sulphu- ret, it is impossible to prevent some of this metal from escaping into the slag; and therefore, to diminish this loss as much as possible, English assayers collect the slags, both of the reducing and of the purifying processes, and, pounding them up together, mix them with an equal quantity of tartar and some powdered coke. This mixture is then melted in a Hessian crucible, after being covered over with com- mon salt. The little button produced in this way is of course impure, and requires the same treatment as the larger one, origi- ASSAY OF COPPER ORES. 1GO nally procured. This second button Is weighed together with the large one, and the result will givp vpry accurately the per-centage of coppei m cne ore. XTX. Wet Assay of Copper. ON account of its greater accuracy and simpler execution, the wet method has, as a general rule, been substituted for the dry assay of copper. Modified Swedish assay. The cuprifer- ous substance is brought into solution with sulphuric or hydrochloric acid (nitric acid must not be used, as the precipitated copper is again dissolved in it), and the copper pre- cipitated with iron or zinc, and determined either as metal or oxide. This plan is not admissible in the presence of metals which are also precipitated by iron and zinc. Such metals, however, can be removed during the operation without injurious effect by igniting the precipitated copper, or by a preparatory roasting at not too high a tern- WET ASSAY OF COPPEIl. 171 perature of the assay-sample, first by itself, and then with the addition of some iron py- rites. Tin and antimony are removed by heating with moderately diluted sulphuric acid, then adding nitric acid, and heating nearly to boiling. If necessary, as in the oase of metallic sulphides, a few drops of fuming nitric acid are added. The solu- tion is then evaporated to dryness until the fuming ceases. The dry mass is dissolved in hot water and filtered, and the solution treated with some hydrochloric or nitric acid, etc. ; or, the antimony is removed by fusing the assay-sample with potassium hydrate or potassium carbonate in a silver crucible, lixiviating the potassium antimoniate and dissolving the residue ; or, the assay-sample is dissolved, neutralized with soda, and di- gested with a solution of sodium sulphide to extract the antimony, arsenic and tin in soluble form. It is now filtered, and the residue washed and dissolved as above. Ores containing bitumen, for instance, cupri- 172 THE ASSAYER'S GUIDE. ferous schists, must be ignited to remove the bitumen, before they are dissolved. a. Precipitation with iron. Into a suit- able flask placed in an oblique position bring, according to the richness of the ore, 1 to 5, generally 2.5 to 5, grammes of the assay- sample, and decompose them by heating with sulphuric acid, adding from time to time some fuming nitric acid or potassium chlorate, until the separated sulphur, in- closing particles of the ore, is oxidized as much as possible. Or, the sample is at once dissolved in aqua regia. It is then evapo- rated to dryness with some sulphuric acid, or until the sulphuric acid vapors appear in the flask. To dissolve the basic salts, add a few drops of sulphuric acid to the dry mass and then, cautiously, water. The fluid, which is now entirely free from nitric acid, is filtered into a flask, and the residue washed until the wash-water no longer pro- duces a red stain upon a piece of bright sheet- iron. Two pieces of iron wire, 3 to WET ASSAY OF COPPER. 173 4 centimeters long, are then added ; or, to shorten the time required for the assay, the fluid may at once be filtered into a porcelain dish in which the iron wires lie, and copper will then be precipitated during filtration. The filtrate is then sufficiently diluted and gently heated until a pointed iron wire dipped into the fluid does not show a red- dish stain of copper. To prevent the sepa- ration of basic iron salts, which are more readily formed by hot water, the copper is twice decanted with cold water into a spa- cious beaker and then three times with boiling water. The flask is then completely filled with cold water, and a flat-bottomed porcelain dish about 20 millimeters high and 80 millimeters in diameter is placed bottom upwards, on top of it. The flask and dish are then inverted. The mouth of the flask is held in an oblique position, and the water allowed to run into the dish until it is nearly full. The flask is left standing in the dish until all the 174 THE ASS AVER'S GUIDE. copper and the iron wires have falter Ir.co the water in the dish. Small particles of carbon separated from the iron will re- main floating on the water for some time. The flask is then gently removed by draw- ing it over the side of the dish, which should be somewhat inclined for the pur- pose. The iron is freed from copper by rubbing with the fingers, which should be rinsed off in the water. The copper is now decanted twice with boiling water. This is poured off as completely as possible from the copper, which is moistened with abso- lute alcohol, and dried on the water-bath until it has assumed a pulverulent condition. It is allowed to cool in the desiccator, and is then brought upon the pan of the balance, or into a tarred porcelain crucible with the aid of a fine brush, and quickly weighed. It is now dried for 10 or 15 minutes more, and again weighed until the results agree ; o?', the copper is spread out upon a roasting dish and ignited in the muffle furnace, and WET ASSAY OF COPPER. 175 the metal calculated from the amount of cupric oxide formed . (100 cupric oxide = 79. 88 copper). If the water used in decanta- tion shows a reddish sediment, it should be filtered, the filter dried and ignited upon the scorifier, and the percentage of copper re- sulting from the cupric oxide should be added to the principal yield. Correction for iron that may be contained in the precipitated copper on account of a deposit of basic iron salts : The precipitated copper is ignited upon the scorifier until it becomes black. The cupric and ferric ox^ ides formed are weighed and dissolved in hydrochloric or sulphuric acid. The ferric oxide is precipitated with ammonia. The solution is filtered upon a small filter of paper. The filter is dried and ignited, and the ferric oxide, which may be found, is de- ducted from the combined weight of the cupric and ferric oxides, and the copper cal- culated from the quantity of pure cupric oxide found. Instead of decanting the pre- 176 THE ASSAYER'S GUIDE. cipitated copper, it may all be filtered, dried, ignited, weighed, and dissolved, as above, for obtaining the content of iron. Pare precipitated copper has a fine copper color. If the solution contains antimony and arsenic, it has first a copper color which later on, by the antimony and arsenic being precipitated, changes to black. The larger portion of the antimony, after the precipi- tate has been evaporated to dryness with sulphuric acid and again moistened with water, remains as basic sulphate of anti- mony, while arsenic passes into solution. The residue from the solution of the ore, etc., is tested for copper by heating it with nitric acid, filtering, and adding ammonia in excess. The appearance of a blue color indicates copper. Instead of two iron wires, a single wire bent into the form of a ring, with one end projecting vertically, may be used. The ring is dipped into the liquid in the beakei glass so that the end projects. When pre- WET ASSAY OF COPPER. 177 cipitation is complete, the copper is rinsed from the ring, decanted, etc., as above. Or, a strip of sheet-iron may be used in place of the wire, but it must be immediately re- moved from the liquid after the precipita- tion of the copper is complete to avoid the formation of basic iron salts. In solutions that are too concentrated, the copper ad- heres too strongly to the iron. b. Precipitation with zinc free from lead and arsenic. Prepare a solution of the as- say-sample with sulphuric acid, as above described, and filter. Then place a strip of zinc in the solution and heat until a bright iron wire held in it shows no copper de- posit; or until a drop of the solution placed upon a porcelain dish is not browned by sulphuretted hydrogen. The strip of zinc is then taken out, and the precipitated cop- per washed off with the wash bottle. It is next filtered until but a small layer of water covering the copper remains. A few drops of warm hydrochloric acid are then -added 12 178 THE ASSAYER'S GUIDE. to dissolve any particles of zinc which ma;y be present. It is now decanted, etc., as in the precipitation with iron ; or it is filtered as soon as effervescence ceases, quickly washed with hot water, and dried. The copper is then detached from the filter, ignited on the cover of a porcelain or plati- num crucible, or upon a roasting dish in the muffle and the oxide quickly weighed The black crust upon the end of the piece of zinc, which has been dipped into the fluid, is a spongy layer of zinc colored by a trace of sulphide of copper. Nickel, which is not thrown down by iron, is precipitated with zinc, but cobalt is not. Granulated zinc may be used instead of a strip, but the granules must be completely dissolved by the time the bubbles cease. The copper is then decanted, etc. The cupriferous fluid may be filtered into a platinum dish, and some hydrochloric acid added to it. Now heat and add a few small pieces of zinc, whereupon the copper will. WET ASSAV CF COPPER. 179 firmly deposit itself on the platinum, but loosely on the zinc. After precipitation is complete, which is ascertained by testing with sulphuretted hydrogen, as above, the copper is rubbed and washed off from the zinc. It is then allowed to settle, decanted, treated with hot water, to which some hydrochloric acid has been added; then quickly washed with hot water by decanta- tion to prevent the loss of copper by solu tion. It is finally moistened with absolute alcohol dried in a water-bath at 230 to 248 F., and the tarred platinum dish, after having been cooled in the desiccator, is weighed. If the utmost accuracy is de- manded, the copper is heated in a current of sulphuretted hydrogen. 180 XX. Electrolytic Determination of Copper. CLASSEN'S method for the electrolytic de- termination of metals is based upon the fact that the separation of the metal is best effected when the oxide is fixed to an acid readily decomposed by the current, so that a secondary reaction cannot take place. Such an acid is oxalic acid, which splits into carbonic acid and hydrogen. Most heavy rnetals give insoluble precipitates with oxalic acid ; their double alkaline salts are, however, readily soluble, and by adding ammonium oxalate in excess the re- action progresses with ease and without the formation of a precipitate. The carbonic acid separated on the positive pole by the decomposition of the ammonium oxalate combines with the ammonium, forming am- ELECTROLYTIC DETERMINATION OF COPPER. 181 monium carbonate. In general the process is conducted by converting the neutral chlorides arid sulphates of the metals into double oxalates by the addition of a large excess of ammonium oxalate, heating the solution and exposing it to the action of a galvanic current, whereby the metals de- posit quickly and in a compact form on the negative electrode. The determination of copper, as is well known, can be very easily effected directly from the acid solution. According to Clas- sen's method the solution (concentrated, if necessary, by evaporation) is heated to boil- ing, and, after adding 3 to 4 grammes of solid ammonium oxalate, subjected to the action of the electric current as soon as everything is dissolved. The copper sep- arates quickly and easily, provided the current is not too weak. With a strength of current corresponding to 300 cubic cen- timeters of oxy hydrogen gas per hour, 0.15 gramme of metallic copper can be separated 182 THE ASSAYER'S GUIDE. in 25 minutes. As the negative electrode, Classen uses a 'platinum dish, and for the positive electrode a disk, 4 to 5 centimeters in diameter, of moderately thick platinum sheet, Fig. G, which is secured by a screw to a medium thick platinum wire. To prevent loss the plati- num dish is covered with a watch crystal perforated in the centre. The entire ar- rangement of the apparatus is shown in Fig. H. The glass cylinder shown in front is the resistance-arrangement recommended by Classen for " --- N. ^ the reduction of more consid- G. erable strengths of current. It consists of a rod b with a zinc pole, which can be moved to and from the zinc pole a until the current reaches the desired strength. The zinc poles must be amai- ELECTROLYTIC DETERMINATION OF COPPER. 183 gamated with mercury and hydrochloric acid, and the contacts at , b kept clean. According to Herpin's method of assay- ing copper by electrolysis, 1 gramme or more of the assay-sample is dissolved in nitric acid. The solution is evaporated FIG. H. nearly to dryness, the residue dissolved in a small quantity of dilute sulphuric acid and the solution diluted to 60 or 70 cubic centimeters. The solution is poured into the platinum dish A, Fig I, and the conduct- ing stand B of the dish is connected with 184 THE ASS AVER'S GUIDE. the negative electrode, the platinum spiral C with the positive elec- trode, and the liquid electrolyzed after the funnel D has been placed in position. When the copper has been precipi- tated, the fluid is poured ] from the dish. The lat- FIG. I. ter is rinsed out first with water and next with alcohol, then dried and weighed, the copper being determined from the increase in weight. 185 XXI. Assay of Lead Ores. THE method of assaying lead ores de- pends on the nature of the ore and chiefly on whether the lead occurs in a sulphur- etted or oxidized state. A. With sulphuretted lead combinations three cases are to be distinguished : a. The galena contains, besides a few earthy con- stituents, none or very few foreign sulphides (copper pyrites, iron pyrites, zinc blende, etc.). b. Many of such sulphides are pres- ent, c. Earthy 'constituents are present in predominant quantity. As a rule, these conditions can be better recognized, when the assay-sample is in pieces than when in the form of a powder.. In the latter case elutriation may, with the assistance of a magnifying glass, give 186 THE ASSAY ER*8 GUIDE. important disclosures regarding the metallic admixtures. 1. Methods of assaying sulphuretted lead ores which contain few or no foreign sul- phides. These methods are based upon the desul- phuration of the galena by iron and alka- lies, or, as is more generally done, simulta- neously- by iron and alkalies, and promoting the reduction of the alkalies by the addition of carbon, or entirely omitting the latter. Too much carbon causes refractoriness. The carboniferous substances also main- tain an oxidizing atmosphere in the cru- cible and prevent the oxidation of the sulphides of iron to oxidized iron, which strongly attacks the sides of the crucible and in pouring out the assay contributes to the retention of particles of lead. Any white lead or sulphate of lead occurring together with the galena are reduced by the carboniferous substances. By the alkalies alone, or the simultaneous use of suitable ASSAY OF LEAD ORES. 187 fluxes, such as glass and borax, the earths occurring in the ores are scorified. If for- eign sulphides, such as copper pyrites, sul- phide of antimony, zinc blende, etc., are associated with the galena, they are also partially decomposed by the alkalies and the iron, and their radicals pass into the lead. They also give rise to the formation of sulphur-salts, which retain sulphide of lead in the slag. Of the alkaline combina- tions potash and dehydrated soda are chiefly used. The carbon is employed either in the form of coal dust mixed with the potash, or still better, in a finely divided state in black flux, or in a mixture of potash and flour. The black flux is prepared by pouring a mixture of 2 parts crude tartar and 1 part saltpetre (crude flux) in a heated clay cru- cible and laying a glowing coal upon the surface; or by gradually introducing the mixture into a glowing crucible. The mass thereby decrepitates, whereby the oxygen 188 THE ASSAYER'S GUIDE. of the nitric acid first oxidizes the hydrogen of the tartaric acid, this being the most readily oxidizable constituent, and then also a portion of the carbon, while, with a cor- rect quantity of saltpetre, another portion of the carbon separates in a finely divided state. By taking too much saltpetre all the carbon is oxidized, and instead of a mixture of potassium carbonate and carbon (black flux) only potassium carbonate (white flux) is obtained, arid with little carbon, gray flux. Black flux has the disagreeable property of readily absorbing moisture, arid, hence, must frequently be prepared fresh. For this reason it is more convenient to use a mixture of 100 parts potash and 10 to 15 parts rye or wheat flour. On heating the mixture the latter carbonizes and finely divided carbon is separated with the evolu- tion of reducing varieties of gas. The fluxes are frequently protected by a cover of common salt. It serves to keep off the air from the melting assay and after ASSAY OF LEAD ORES. 189 it has become thinly-fluid as a wash, bring- ing down from the sides of the crucible ad- hering metallic grains or fluxes. All assays, containing in their charge carbon, puff up in consequence of the for- mation of carbonic oxide, and hence capa- cious crucibles, which should at the utmost be filled I full with the assay-sample, have to be used. The crucibles are heated either in an air-furnace or a muffle-furnace ; a blast-furnace being seldom used. For assaying lead ores of the kind men- tioned under A 1, various methods are in use in different places. a. Assays without /luxes . in iron vessels. These are suitable only for nearly pure galena. a. Assay in iron dishes. Galenas nearly free from foreign admixtures are assayed in England as follows : About 300 grammes of the ore are placed in a red-hot w rough t- irondish. The latter is about 5 to 6 milli- meters thick, 0.127 meter in diameter and 190 0.025 meter deep in the centre. After in- troducing the assay-sample the dish is pro- vided with a semicircular lid of somewhat larger diameter, and the whole heated in a blast-furnace for about 2 minutes. The dish is then taken from the furnace and placed upon a ring. When the matte is congealed, empty the still liquid lead intc a conical bronze mould, melt the matte in the dish once more, using a stronger fire, and then pour all upon a metal plate, whereby a small lead regulus still results. In 5 to 6 minutes two such meltings are finished. Seventy-five to eighty per cent, of lead are in a short time brought out, and these assays are especially used for controlling the reverberatory furnace process, in which nearly the same volatilization of metal takes place. P. Assay in iron crucibles. In South Wales about 80 grammes of galena are melted in an iron crucible, about 72 milli- meters high and 69 millimeters in diameter ASSAY OF LEAD ORES. 191 on the top, in an air-furnace for about 10 to 15 minutes. The yield is 81 to 82 per cent. b. Assays with fluxes. The fluxes, which have to be added to more impure ores, serve either for decomposing the galena or for scorifying oxide and earthy admixtures, or for both purposes. Of silver nearly everything passes into the lead ; with a content of sulphide of iron in the slag more silver is retained than without such a content. Copper is divided between lead and slag. Of zinc only a small portion passes into the lead, that which does not volatilize passing chiefly into the slag. Iron is only found in traces in the lead, but antimony in abundance, while arsenic partially vola- tilizes as arsenic and orpiment, and par- tially yields speiss with iron. Silica pro- motes the scorification of lead more than calcareous spar and heavy spar. If lime and ferric oxide be at the same time present i92 scorification is counteracted. The lead in an impure lead regulus obtained by the dry assay can only be determined by the wet method. With a content of copper, dissolve the regulus in moderately strong nitric acid, evaporate the solution with sulphuric acid until the nitric acid is expelled, dilute with water, bring the sulphate of lead upon a dry, weighed filter, or reduce it with cya- nide of potash and soda in a porcelain crucible. Brittle lead containing antimony is oxidized with nitric acid, the dilute solu- tion digested with ammonia, ammonium sulphide and some sulphur, and the undis- solved sulphide of lead converted into sulphate. According to the quality and quantity of the foreign admixtures, the following methods of assaying may be used. a. Assay in an iron crucible with black flux. With ores as free as possible from copper and poor in earths, this assay in a short time gives the greatest yield (84 i to ASSAY OF LEAD ORES. 193 85 i per cent.), because it is for a shorter time (10 to 15 minutes) in the fire and can be executed with larger quantities of ore, whereby the loss is distributed over larger quantities. The absence of a larger content of earths favors the complete pour- ing out of the contents of the crucible into moulds, while with larger quantities of slag, the latter adheres to the sides of the crucible and mechanically retains lead. This method, which is much used in Eng- land, Germany, France and Belgium, is executed as follows : Heat a wrought-iron crucible in an air-furnace to a red heat, and then charge it with 25 to 50 grammes of lead ore and 12 to 15 grammes of flux (potash, soda, or a mixture of 2 parts salt- petre, 3 argol, and 1 borax). Then add a cover of common salt or powdered glass, place an iron lid upon the crucible and gradually heat during 5 minutes to a red heat, and maintain this temperature for 5 to 8 minutes longer. When all is melted, 13 194 THE ASSAYER'S GUIDE. and any globules of lead appearing on the surface or unmelted masses have been sub- merged with a spatula, take the crucible from the furnace, and, after allowing it to cool somewhat, pour the contents into a warmed ingot-mould painted inside with black lead. The slag may be again melted with some flux (soda or potash and argol) for 10 to 12 minutes. The difference between the quantity of lead obtained by the assay and that actually present in the ore is nearly the same with ores from the highest to 50 per cent, con- tent of lead, but increases with poorer ores. Of 86.81 per cent, actual content of galena 84 i to 85i per cent, is obtained by this assay. The proportions of the charge in various works are as follows : In England : for rich ores, 500 grains (32. 4 grammes) ore, 500 grains soda and 50 grains argol ; for poorer ores, 850 grains soda, 150 grains borax and 50 grains argol ; time for melting, 8 to 10 minutes; entire time, 10 to 15 ASSAY OF LEAD ORES. 195 minutes. At Freiberg : 50 grammes ore, 2 tablespoon fuls flux (3 parts argol, 2 salt- petre, 1 borax) ; time for melting, at a red heat, 12 to 15 minutes; time for heating the slag with potash, 10 to 12 minutes. 0. Assay in a clay crucible with black flux and iron ; available for ores poor in foreign sulphides but richer in earths. At Freiberg this method of assaying is executed as fol- lows: Charge a crucible, first with 3.75 grammes of powdered ore, then, according to its richness, place upon the ore 0.37 to 1.12 grammes of iron wire (a piece 6.5 to 9.8 millimeters long and 4 to 5.5 millimeters thick), spread out upon it 11.25 grammes of black flux, or 8.37 grammes of a mix- ture of potash and flour, cover the latter with 1.12 to 1.5 grammes of borax, and finally add a cover of common salt a few millimeters thick. If foreign sulphides, combinations of antimony or arsenic are present, the ore previously to charging it may be somewhat roasted. 196 THE ASSAYEK'8 GUIDE. With galena ores the charge at Pribram is as follows: 5 grammes ore, 11.5 to 12 grammes black flux (2 parts argol, 1 salt- petre), 1 to 1.2 grammes borax and 2 to 2.5 grammes iron wire. With ores containing blende : 5 grammes ore, 20 grammes black flux, 1 to 1.2 grammes borax and 2 t.o 2.5 grammes iron wire. Some argol is always placed upon the bottom of the crucible and under the common salt serving as cover, 2 to 3 per cent, saltpetre, in order to make the common salt more fluid and retain the lead, which is volatilized, by oxidation. The assay is melted in an air-furnace. When taken from the furnace, the crucible is allowed to cool, the lead regulus is then freed from slag, flattened to remove any adhering sulphide of iron, and weighed. The assay may be considered a success when assay and counter-assay agree, when the lead is at the bottom in one button and the slag uniform in character. By a few ASSAY OF LEAD ORES. 197 blows of the hammer, the iron wire is separated from the adhering lead. . The galena is at first desulphurized by the alkali, alkaline sulphate and potassium sulphide being formed besides lead. The potassium sulphide combines with a portion of still undecomposed galena to a sulphur- salt which passing into the slag at an in- creased temperature hence, towards the end of melting is freed by the iron from its content of lead. The carbon prevents an oxidation of the lead and reduces the alkali. It, therefore, also contributes towards the desulphurization, the potassium formed being closely allied to sulphur. Another portion of the alkali in conjunction with the borax and glass causes the scorification of the earths and metallic oxides contained in the assay-sample. Besides silicates the slag also contains sulphur-salts, especially a double sulphide of potash and iron. The cover of the readily-fluid common salt pre- vents the adherence of lead globules on 198 THE ASSAYER'S GUIDE. the edge of the crucible and shuts out the air. This method of assaying is very simple, readily executed and permits of the best yield of lead for ores of the above-mentioned kinds. From galena with 85.5 per cent, of lead up to 84.85 per cent, is obtained ; with more impure ores, the loss of lead may, however, increase to 10 per cent. v. Upper Harz potash assay in clay cru- cibles. Melt 5 grammes of galena with three times the quantity of potash under a cover of common salt in a crucible under the muffle strongly heated for 15 to 30 minutes or longer until fusion is complete. The following reaction thereby takes place : 4 K 2 C 3 + Pb S = 4- Pb + 3 (K 2 S + Pb S) + K 2 S 4 + 4 C 2 . In order to separate from th sulphur-salt (K 2 S + Pb S) the lead retained by it open the muffle 5 to 10 minutes and moderate the fire, whereby the K 2 S is converted into K 2 S 4 , and the liberated Pb S partially ASSAY OF LEAD ORES. 199 into Pb S 4 . If now the muffle is again closed and after 10 minutes a strong heat is given, the sulphate of lead acts upon the decomposed sulphide of lead, metallic lead being formed, if the proper time has been allowed for the above-mentioned cooling (Pb S + Pb S 4 = 2 Pb + 2 S'0 2 ). If cooling is continued for too long a time, oxide of lead remains in the slag, and if for too short a time, sulphide of lead. The dura- tion of cooling at which the most lead is obtained must be ascertained for each ore. 2. Methods of assaying sulphuretted lead ores which contain many foreign sulphides. The above-mentioned assays are not suit- able for such lead combinations, because the foreign sulphides are decomposed by the alkalies and the iron, their radical passing into the lead button, and an abun- dant formation of sulphur-salts takes. place, which always retain much lead in the slag. For such substances the calcination-assay 200 THE ASSAYER"S GUIDE. and a partially wet assay with sulphuric acid are suitable. a. Calcination-assay. This assay is used for Rarnmelsberg ores whose small content of lead is diminished 5 to 8 per cent, by the presence of considerable quantities of iron pyrites, copper pyrites, zinc blende, antimony and arsenic combinations, as well as earthy substances. Take from a pile of ore, which has previously been roasted, three times, 5 to 10 grammes. Pulverize this assay-sample and thoroughly roast it for 6 or more hours in a more or less shallow crucible about 65 millimeters in diameter, 13 to 16 millimeters deep and painted in- side with reddle or chalk washes. By thorough roasting is understood heating the ore at a gradually increasing temperature and with the access of air, so that no fusion takes place, but the air can exert an oxi- dizing effect upon the sulphides, whereby the latter, with the development of sul- phurous acid, are converted into oxides. ASSAY OF LEAD ORES. 201 In order to effect this as completely as pos- sible frequently turn the crucible around so that the air can act uniformly. After half an hour take the crucible from the furnace, triturate the assay-sample, if it should be slagged together, in a cast-iron mortar, roast again for about half an hour, triturate again, mix coal dust or another carbonaceous substance, for instance, suet, with it and reheat. In roasting, metallic sulphates are also formed from the sul- phides, which by the addition of carbon are to be decomposed so that, with the develop- ment of sulphurous acid, they again form sulphides and then with the repeated access of air are reconverted into oxides and sul- phates. The sulphur can only be removed by repeated triturating and heating of the ore with carbon at a gradually increased temperature. The last portions of it, which remain as sulphates in the roasted powder, are removed by heating the latter with ammonium carbonate, volatile ammonium 202 sulphate being formed. The sulphate of lead formed in roasting the sulphide of lead can in this manner be but incompletely de- composed and hence remains as such in the roasted sample. 'A thoroughly roasted sample has an earthy appearance and shows no odor of sulphurous acid. It is finally taken from the furnace, allowed to cool and, after being charged with suitable fluxes, melted for metallic lead. The roasted sample chiefly consists of the oxides of the lead, iron, copper, zinc, etc., and if it is melted at not too high a tem- perature with reducing agents (black flux, potash and flour) and solving fluxing (borax, glass), the lead oxide is reduced to metallic lead while the metallic oxides, reducible with more difficulty, are scorified. How- ever, with too high a temperature in melt- ing, the latter are also partially reduced and the resulting lead is impure. Too much or too little of solving fluxes causes glorification of lead oxide, or reduction of ASSAY OF LEAD ORES. 203 the foreign oxides if scorifying agents are wanting. The sulphate of lead present is partially decomposed by the acids of the borax and glass and partially reduced to sulphide of lead, from which by the alkali a portion of the lead is separated, while another portion remains as a double sul- phide of potash and lead in the slag. For the decomposition of the latter combina- tion a small addition of iron is recom- mended. Melting is executed by mixing the roasted assay-sample with three to four times the quantity of black flux and an equal weight of borax and glass, bringing the mixture into a crucible, covering it with common salt and. after placing the lid upon the cru- cible, heating it in an air-furnace for about i hour. If the assay has been successful the lead lies on the bottom under the well- fused slag in one button without being en- veloped by brittle sulphides. b. Assay with sulphuric acid. Decom- 204 THE ASSAYER'S GUIDE. pose 5 or 10 grammes of finely pulverized ore in a digesting-glass with nitric acid, evaporate, with the addition of sulphuric acid, the contents of the glass to dryness, moisten the dry mass with a few drops of sulphuric acid, soften it with water, bring it upon a filter, and thoroughly wash the residue upon the latter. Besides insoluble earths, the residue chiefly consists of sul- phate of lead which is with difficulty sol- uble in water, while the sulphates of the metals associated with galena being readily soluble in water are removed after washing the residue. The filter is dried, ignited with its contents and the ignited mass melted with black flux and iron, whereby the sulphide of lead reduced from sulphate of lead is decomposed by the iron, the re- sult being a button of lead. This assay gives a more correct content of lead than the preceding, and is also suitable for lead alloys. On account of the availability of lower temperatures, the ASSAY OF LEAD ORES. 205 assay becomes still more accurate by mix- ing the residue obtained by treating the mass in a capacious porcelain crucible and heating until the free sulphur is volatilized, with about five times the quantity of potas- sium cyanide (with or without soda) and melting in the covered crucible over a small lamp. The cold melt is extracted" with water, and the lead remaining behind in one or more buttons decanted with water containing alcohol, dried and weighed. If a black powder, which, however, contains no sulphide of lead, has been formed, re- move it by washing. In both cases a content of antimony passes into the lead and has to be removed by the wet process. 3. Methods of assaying for sulphuretted lead ores , which contain many earthy con- stituents. In such combinations the con- tent of lead can only be very inaccurately determined by the dry method by melting a larger quantity of assay substance (100 to 500 grammes) with the most powerful 206 THE ASSAYER'S GUIDE. fluxes (caustic alkalies), and the addition of reducing agents, and stirring a piece of sheet iron bent in the form of a horseshoe around in the fluid mass until all the lead is separated. If the content of lead is not too small, not below i per cent., a useful result is also obtained by mixing 10 to 20 grammes of the substance to be assayed in the ordinary manner with potash or black flux, spreading out on top of the mass arv accurately weighed quantity of finely di- vided silver (30 to 50 per cent.), covering the latter with common salt and melting in the usual manner. The increase in the weight of the silver represents the content of lead. B. Oxidized lead ores and smelting prod- ucts may be assayed as to their content of lead by two methods, viz. : 1. By melting with reducing agents when the assay-sample contains free lead oxide (litharge, lead scurn, or skim) or lead oxide fixed on carbonic acid or an organic acid ASSAY OF LEAD ORES. 207 (as white lead ore, lead acetate), or lead oxide combined with fixed mineral acids which cannot be reduced, but combine directly with the alkalies (silicate, phos- phate, tungstate and molybdate of lead ; in chromate of lead, the chromic acid is re- duced to chromic oxide, which passes into the slag). Combinations of the above-mentioned variety are mixed with three or four times their weight of black flux or potash and flour, and melted under a cover of salt in a crucible. The slag must become thinly- fluid, and as this chiefly depends on the nature of the by-constituents, the height of the temperature in melting, and the dura- tion of the latter, must accordingly be modified. To highly silicated lead slags it is best to add a flux of from 20 to 50 per cent, borax, and to very poor slags, con- taining i to $ per cent, of lead, a flux of 15 to 20 per cent, silver for the collection of the lead. Slags containing sulphur are 208 THE ASSAYER'S GUIDE. somewhat roasted, or receive a flux of from 5 to 10 per cent. iron. According to the refractoriness of the slags, melting may last from 1 \ to 2 hours, in order to give the lead an opportunity to thoroughly separate from the very thinly-liquid slag. At Mecher- nich the lead slags are melted with soda and \ borax in an iron crucible at a bright red heat ; result, 0.4 to 0.6 per cent, of lead. Percy recommends the following charges : For white lead ore : 500 grains ore, 500 soda, 100 argol and 30 borax. Time of melting, 20 minutes. For minetite (green lead ore) : besides iron flux, 300 grains ore, 400 soda, 20 coal dust and 30 borax ; or 350 grains soda, 100 argol and 30 borax. Duration of the process from the time of in- troducing the charge to pouring out, 25 to 30 minutes. 2. By melting with reducing agents and iron, when the lead oxide is fixed on sul- phuric acid, arsenious or arsenic acids, as, for instance, in sulphate of lead, in calcined ASSAY OF LEAD ORES. 209 galena and matt of lead, lead smoke, slag- lead, dross, etc. Charge with three to four times the quantity of black flux and 10 to 30 per cent. iron. For slags, an addition of 5 to 10 per cent, iron suffices. 14 210 XXII. Assay of Lead Ores by Heat THERE is no way of assaying lead ores by heat which gives the full amount of the metal, as it is so easily oxidized by a high temperature. Generally, the loss varies from one-sixth to one-twelfth, or yet more commonly is about a tenth; and for this reason, the result of the assay should after- ward be increased by A, on giving the per- centage of lead. The assay is performed in the crucible, fig. 4, or in the Hessian one. The part of ore used ought to be about two hundred grains, as lead ores (galena, a sulphuret of lead is the most common) are very heavy, and therefore are comparatively small in bulk. Three parts, or here six hundred grains, of black flux are mixed up with the ASSAY OF LEAD ORES BY HEAT. 211 powdered ore. A little piece of very thick wire, or of a round iron bar, weighing from thirty to forty per-cent. of the weight of the lead ore, is placed on the top, in the crucible. We then expose the whole to a strong, steady red-heat, for about an hour, in the bellows furnace, fig. 6, Plate I. This is ef- fected by first placing the crucible on the bri^.k, and then making a layer of cold burnt coals, as high as the brick. On this come the live coals, and on them the un- burnt ones up to the top of the furnace. When burnt down, we take out the cruci- bles, and thus obtain a button of pure lead and some slag, besides a remaining portion of the iron. The latter should be added in excess, to insure the entire absorption of the sulphur. Galena contains, in hundred parts, 13.45 parts of sulphur to 86.55 of lead, which would require 22.67 parts of metallic iron to form sulphuret of iron, consisting of 37.23 212 parts of sulphur to 62.77 of iron. If, there- fore, two hundred grains of the ore are used, the iron should weigh from 60 to 100 grains. Filings ought never to be used, as they are always covered, to a smaller or greater amount, with oxide. Besides, it is very difficult to get them as free from im- purities as wire. Weighed pieces of the latter should be kept in some vial or box for this purpose. 213 XXIII. Assay of Lead Ores ty a Wet Process. THIS method will be found much the more accurate of the two, although it may not often happen that a practical assayer has sufficient time for this proceeding. (See Woehler's Anal. Chem.) The ore (galena) should be powdered much finer even than in the assay by heat, after which it is moistened with fuming nitric acid, and digested in the sand-bath, by which process it is entirely changed from the sulphuret to the sulphate of lead. If the mass be diluted with water and filtered, the merest traces only of lead can be found in the solution, quantities toe small to deserve any farther attention. If the ore contain copper, iron, or silver, they will be contained in this filtered solution ; 214 THE ASSAYERi'S GUIDE. the first are then discovered by ammonia, the latter by muriatic acid. Should fuming nitric acid not be at hand, and if therefore a weaker kind is used, a mixture of sulphate of lead and sul- phur is produced, together with a solution of nitrate of lead. From this latter the metal should be precipitated with sulphuric acid. By heating the dried residue, after filtering and washing, by pouring water over it while yet on the filter, sulphur is evaporated and sulphate of lead is retained. In both cases, the lead produced is a sulphate, and in this shape it should be weighed, and from the result the amount of the former alone may be easily calcu- lated, as will be seen from the sequel. Sulphate of lead consists, in 100 parts by weight, of Oxide of lead . 73.56 Sulphuric acid . 26.44 100.00 ASSAY OF LEAD ORES BY A WET PROCESS. 215 and the oxide of lead, again, of Lead 92.83 Oxygen .... 7.17 Hence we say, if 100 parts of oxide of lead contain 92.83 of pure lead, then 73.56 of pure lead contain 68.285748 parts; or, in other words, sulphate of lead consists ol Lead . . . 68.285748 Oxygen . . . 5.274252' Sulphuric acid . 26.440000 100.000000 For this assay about twenty grains only need be taken. A smaller amount might make us incapable of finding the real quan- tity of lead, while a larger one would only give us unnecessary trouble. 216 XXIV. Gravimetric Analyses of Lead Ores. AT Bleiberg, in Carinthia, this method is executed for pure galenas as follows : De- compose 2 grammes of the ore with concen- trated nitric acid, add a few drops of sul- phuric acid, evaporate nearly to dryness, soften the mass in water, wash, digest the contents of the filter (lead sulphates, cal- cium and barium, sulphur, silica) with concentrated soda solution for one hour in order to convert the sulphate of lead into carbonate, filter, wash the filter until a drop of the filtrate no longer shows turbidity with barium chloride, boil the residue with dilute nitric acid or with acetic acid, wash with water until acid reaction ceases, pre- cipitate the lead with as little sulphuric acid as possible (an excess of acid also pre- GRAVIMETRIC ANALYSES OF LEAD ORES. 217 cipitates lime), filter off the sulphate of lead, wash, dry and heat to a red heat, whereby differences exceeding 0.1 per cent, should not occur. In order to avoid with ores poor in lead and rich in lime, bringing from the start too much calcium sulphate amongst the lead sulphate, the evaporation of the nitric acid solution with sulphuric acid is not carried quite so far, arid the so- lution diluted with J liter water before add- ing the sulphuric acid. Storer decomposes 2 to 3 grammes of galena with a regulus of zinc 6 millimetres in diameter and 7 millimetres thick, and 100 to 150 cubic centimetres of hydro- chloric acid diluted with four times the quantity of water, and heated to 122 F. for 15 to 20 minutes. He then decants the metallic lead, separated under the develop- ment of sulphuretted hydrogen, with hot water, cleanses the cylinder of zinc by rub- ing with the finger and rinsing, and dries the lead in a tared porcelain crucible at a 218 THE ASSAYER'S GUIDE. moderate temperature in a current of illu- minating gas, or in the air-bath. In the presence of insoluble gangues the lead is dis- solved from them by means of nitric acid and the residue weighed. Other metals precip- itable by zinc have to be separately deter- mined by special assays, and deducted from the lead. Since the lead sponge is readily oxidizable, Boessler fixes it on a weighed quantity of Wood's metal (1 part Bi, 0.5 Pb, 0.25 Sn, 0.25 Cd), and finds the lead from the increased weight of the regulus. 219 XXV. Assay of Iron Ores by Heat. ONE part of the ore, about a hundred grains, thoroughly pulverized, is mixed with from thirty to a hundred /ains of calcined borax. The quantity of the latter varies according to the purity of the mineral, and increases when it contains many foreign admixtures. If the ore contains sulphur, it ought first to be roasted, as was the case with the assays of other metals already described. A Hessian crucible is then prepared with coal, as already directed in the description of those vessels under the head of Utensils and Implements. Into the hollow in the centre, the mixture of ore and borax is poured, and on that some charcoal powder; after which the cavity is entirely covered 220 THE ASSAYS R'S GUIDE. with a piece of charcoal. The crucible is then closed, the number of the assay being marked on the inner surface of the cover. This is then fastened down air-tight with some putty. The iron ore, after these preliminary arrangements, is to be submitted to a reduc- tion process in the furnace, fig. 6, Plate L, which lasts about three-quarters of an hour. At the extensive iron- works on the Hartz Mountains in the interior of Germany, a very simple apparatus is used instead of the other furnace, of which, on account of its portability, I here give a description. It consists simply of an open cast-iron pot or jar, measuring about a foot across, and one and a half in height, and having a plate of sheet-iron, perforated with many little holes an inch in diameter, instead of a grate. This leaves a vacant space of about two inches below, to receive the ashes. The latter partition has two open ASSAY OF IRON ORES BY HEAT. 221 ; one, the door to take out these cin- ders the other, to introduce the end of the bellows. Above the iron plate, on which the crucibles are directly placed, without any brick, a coating of fire-clay, an inch thick, extends to the mouth of the jar. The latter is furthermore supplied with three or four short legs, and a handle on each side. In this furnace the process lasts about an hour and a quarter, In both cases, the button produced con- tains exactly the same impurities, carbon, earths, acids, or other metals, as pig-iron would, if procured from the same ore, and therefore this assay is only to be used for furnaces. For these it entirely suffices; but to ascertain the true amount of pure iron, the wet analysis should be resorted to, the same as with other ores ; and it is for this that I shall give directions in the next chapter how to discover or calculate the real per-centage of the pure metal, or to 222 THE ASSAYER'S GUIDE,. assay the pig-iron produced in the process by heat. It may not be uninteresting to many, who may honour these pages with their perusal, to become acquainted with a me- thod for obtaining chemically pure iron, as given by Karsten in his famous and voluminous works on this metal. It is described in vol. i., pages 167, 168. He says, to procure chemically pure iron, take the best bar-iron of commerce, e. g. Swedish iron in the shape of small wire ; cut it up in short pieces, and then mixing it with about a fourth part by weight of oxide of the same metal, melt it in a Hessian cru- cible. To cover it, use a compound flux, consisting of pure quartz, pure lime, and equally pure carbonate of potash, in pro- portions capable of furnishing a glass or slag, not flowing too easily, but of rather a tough consistency. For the manufacture of an oxide of iron, free from all admixtures of foreign metals, ASSAY OF IRON UKES BY HEAT. 223 it is best to use small clean wire, oxidizing it by vapours of watei The button thus produced has a re- markably white colour, a strong metallic lustre, and is more ductile than the best varieties of soft bar-iron. Particularly cha- racteristic, however, is its great specific gravity, amounting to 7.9654, while that of wrought-iron is 7.6 to 7.9, and of cast- iron only from 7.0 to 7.5. The only im- purity this metal may be discovered to possess occurs as slight traces of silicium. and therefore it may be considered to be ass pure as it possibly can be made, even by a process conducted only upon the rules and principles of wet analysis, and thus in this shape it is utterly unknown to the mere practical metallurgist or smelter. 224 XXVI. s Process for Iron Ores and Iran. THIS method, though remarkable for ite simplicity, is a very sure one, not only to ascertain the quantity of iron in an ore, but to acquaint us with the peculiar degree of oxidation in which it exists, and also the amount of each oxide, which it is often not only very interesting, but useful to know. Many ores, particularly the magnetic ones, contain both the peroxide and the prot- oxide, and the only ones to which this process cannot be applied are those con- taining arsenious acid, not a very common ingredient. The process discovered or invented by Fuchs is founded on the fact, that chemically pure muriatic acid, when atmospheric air is excluded, is incapable of dissolving anv copper; but that, when peroxide of iron is contained in it, a corresponding quantity of that metal becomes soluble, a muriate or chloride of iron and chloride of copper being thus formed. The ore is dissolved in muriatic acid, and, if necessary, filtered. A small round-bot- tomed vial should be used. Into the solu- tion a clean weighed strip of copper is placed, and the vessel corked, and covered with a piece of bladder, tied down round -* the neck until we are ready to boil it. This is best done in a water-bath, and should last until no more copper is received by the acid. The former is then taken out, well washed in water, dried with a towel, and immediately weighed. The difference in the weight of the copper is all that is required to ascertain the amount of peroxide of iron in the ore, for we need only multiply this by the equivalent of peroxide of iron, which Fuchs takes to be 40, and divide the product by 15* 226 THE ASSAYE?/S GUIDE. 31.7, the equivalent of copper. The quo- tient gives the quantity of peroxide con- tained in the solution or ore. To know the whole amount of iron in it, we need only weigh off another part. (10 15 grs.,) dissolve it in muriatic acid, and then digest with chlorate of potash, to transform the protoxide into peroxide, after which, copper will decompose the whole. Indtead of 40, the equivalent of peroxide of iron, we insert 28, the equivalent of the pure metal, into our calculations. By sub- tracting the amount of the peroxide from the last result, the amount of the protoxide is found. The presence of alumina, silica, &c. has no effect on this assay, though the existence of copper in it would represent the ore as poorer than it really is. The latter, how- evei, rarely occurs in common iron or its ores except in mere traces, and, as such, it produces no material difference. 227 XXVII. Swedish Assay of Iron Ores. THE following dry method of assaying iron ores is still much employed in Swe- dish works, and though the results obtained are less accurate than most of those ob- tained in the wet way, they approximate much more nearly to the economic value of an iron ore when smelted on a large scale. The yield of crude iron from the ores, as well as the approximate content of iron, is obtained by multiplying the weight of the resulting button of crude iron by 0.95. Only iron ores very rich in manganese have to be directly assayed as to their content of iron. The ores delivered at the works are first assayed in the dry way in order to determine the yield of iron, the nature of the iron, the behavior in smelting, etc. 228 THE ASS AVER'S GUIDE. The required assay-sample is obtained by taking pieces up to 200 Ibs. or more in weight from the circumference and interior of the ore-pile and reducing them to pow- der. The powder, thoroughly mixed, is formed into a conical heap, which is divided into several parts. One or two of these parts are then taken and again formed into a heap, which is divided as before. This reduction is several times repeated until finally 2 to 4 Ibs. of the sample remain, which are passed through a sieve having 40 to 60 meshes to the linear inch, and dried at from 230 to 248 F. The aim in executing the assay is to reduce the oxidized iron, to carbonize the reduced iron, and to melt to a slag the admixed earthy matter. To effect the lat- ter, silica, alumina and lime must be brought together in suitable proportion about 56 : 14 : 30 (bisilicate). In order to approximate this proportion, it is best to make a pre- liminary assay in the wet way for the de SWEDISH ASSAY OF IRON ORES. 229 termination of the earthy matter present. For this purpose Berthier recommends the following process : A weighed quantity of the finely pow- dered ore is heated to redness in a porcelain crucible ; the loss of weight gives the amount of water, carbonic acid, and other volatile matters present. Another weighed portion is heated with dilute nitric acid, which dis- solves out carbonates of lime and magne- sium ; the residue contains, under ordinary circumstances, only oxide of iron, clay and quartz, the difference giving the amount of the earthy carbonates. A third portion is treated with strong hydrochloric acid, whereby the carbonates of lime and mag- nesium and the oxides of iron ore are dis- solved out, leaving an insoluble residue of quartz and clay. This is weighed, the oxides of iron being determined from the difference of weight by deducting that of the carbonates previously found. From these results the proportion of fluxes neces- 230 THE ASSAYER'S GUIDE. sary to be added can be approximately de- termined, with a view to produce an easily fusible slag. In many instances, however, this pre- liminary assay can be dispensed with, as a sufficiently good idea of the nature of the fluxes to be added can be determined by the appearance of the ore alone. Calcareous ores effervesce with acids-; clayey ores, when breathed upon, give the characteristic odor of clay and adhere to the tongue, while siliceous ores give sparks when struck with the steel. According to experience, the following quantities of flux suffice in many cases : MATERIALS. Chalk, per cent. Fluor- spar, per cent. China clay, per cent. 10 5 25 20 25 to 30 25 to 30 25 25 25 20 to 25 25 to 30 25 to 30 20 to 25 25 20 to 25 10 to 15 specular iron ore red hematite iron ore brown iron ore argillaceous iron ore spathic iron ore ... 20 to 25 20 to 25 finery cinders . ... .... i SWEDISH ASSAY OF IKON ORES. 231 According to the above table, for siliceous and argillaceous iron ores a flux of 20 to 25 per cent, of chalk and 20 to 30 per cent, of fluor-spar is as a rule sufficient. However, in many cases, especially with poor ores, the flux will have to be increased to 50 per cent, or more. When alumina is wanting, 5 to 15 per cent, of China clay is added. From the character of the slag obtained in melting it can readily be recognized whether the correct proportion of earths has been used. If the slag is translucent, has a gray, yellowish or violet (not green) color, and is enamel-like with conchoidal fracture, lime, clay and silica are in the proper propor- tions. If there is too much silica in the flux, the slag has a greenish tint, is glassy, more or less completely transparent, easily broken with a conchoidal fracture and sharp edges. Should the charge be fritted, pul- verulent, and the iron diffused in minute particles, the flux has been wrongly pro- portioned, or the temperature too low. 232 THE ASSAYER'S GUIDE. This is apt to happen with ores containing a large proportion of lime and magnesium, as they are always refractory, and require the addition of a large proportion of silica and lime. If the slag is but half fused and dark in color, the ore contains an excess of silica or silicates of iron and manganese, which react on the carburetted iron, decom- posing it, forming malleable iron and car- bonic acid, giving it a spongy appearance. In this case lime should be added. The presence of a small amount of manganese is indicated by the amethystine color of the slag ; larger amounts render it olive green, yellowish or brown. Titaniferous ores are apt to render the slag copper-colored by the formation of cyano-nitride of titan- ium. Chromic iron ores produce a resinous and dark-colored slag which is sometimes surrounded with a thin metallic layer. A stony, earthy slag with rough fracture and a gray, yellow or brown color, indicates a large content of bases. With a considerable SWEDISH ASSAY OF IRON ORES. excess of lime the slag on being touched crumbles to a powder. Such basic slags with a stony texture may correctly give the content of iron if the button is not too graphitic. Iron ores containing sulphur may also be intentionally charged so as to obtain a basic slag in order to learn whether the iron button proves to be sufficiently free from sulphur. Thus Percy, for instance, recommends the formation of a slag with 38 Si 2 , 15 A1 2 3 and 47 Ca 0, or nearly 21 parts Si 2 , 1 part A1 2 3 and 3 parts Ca 0. Such slag is almost formed by melt- ing together the following fluxes : l9 i JS10 2 1.75(35 Wass 2* | other constants = A 1 2 O 3 0.75 \ 15 Lime 2.50(50 The following fluxes have also been recommended as adapted to ores or metal- lurgical products, which would be classed under the following several general heads. The proportions given are for 0.65 gramme (10 grains) of ore : THE ASSAYER'S GUIDE. 1. Ores nearly free from gangue, some varieties of magnetite, red and brown hem- atite, specular iron ore and micaceous iron ore : Parts. Parts. China clay 2 Lime 2 to 3 Lime 2 Blast-furnace slag. 5 Sand Otol Fluor-spar 5 Glass 2 to 2 & 2. Ores, etc., containing silica, varieties of limonite or brown iron ore, refinery slag (tap), and flue cinders : Parts. Parts. Glass Ito2 China clay 2 Lime 2i to 4 Lime 3 to 4 3. Ores containing carbonates of lime, magnesia, protoxide of manganese, etc., calcareous hematites, and spathic ores : Parts. Parts. China clay 2 Glass 3 to 4 Lime 1J Lime 1J to 2 Sand.. . 1 SWEDISH ASSAY OF IRON ORES. 235 4. Ores containing silica and alumina, clay iron ores, etc. : Parts. Parts. Glass to 2* China clay to 2 Lime 2J to 3 Lime 2 to 3 5. Titaniferous ores, or ores containing titanium : Parts. Parts. Lime 3 Glass 2 Glass 2 Lime H China clay 2 China clay 1 Lime 2J The dry assay of iron ores is performed as follows : Mix the finely pulverized ore with the required quantity of flux and transfer it to a basqued or charcoal-lined crucible. The basqued crucibles are prepared as follows : The charcoal powder is mixed with just sufficient gum-water or molasses to make it cohere readily. The crucible is gently rammed full of this charcoal, and a cylin- drical cavity of sufficient size to contain 236 THE ASSAYER'S GUIDE. the charge is made in it with a spatula 01 some other boring instrument. The cru- cibles best adapted for this assay are made of a mixture composed of two parts unburnt and one part burnt clay. They are about II inches high and li inches in diameter at the top. As the amount of ore in the charges never exceeds from 0.64 to 0.96 gramme, four crucibles are placed in the furnace at a time. The charges in each are exactly alike, and if there is but a slight variation in the weight of the result- ing buttons, the assay is probably correct; the mean weight of the four should be taken as the result. It is generally best to stand the four crucibles on a half brick, or lute them to it. so that when the fusion is finished all the crucibles can be removed from the fur- nace at one time. Although lids are some- times used to cover the crucibles, it is better, after the charge has been introduced, to stop the cavity with a charcoal plug and to cover the entire top of the crucible with a clay SWEDISH ASSAY OF IRON ORES. 237 luting. The half brick holding the cru- cibles should be placed near or directly upon the fire-bars at the bottom of the fur- nace and the anthracite or coke fire built up around and over the crucibles. When the latter have been in the fire about li to 2 hours, and a white heat has been reached and maintained through a considerable part of this period, the assay may be considered finished and the crucibles removed. When the crucibles are cold they are broken up, the metallic buttons and globules * which may adhere to the charcoal lining and slag are separated out with a magnet. The ap- pearance of the slag, which has previously been referred to, as well as the character of the iron buttons, serve for judging the assay. If the ores are easily reducible and the proper temperature has been reached and maintained in the furnace, the buttons * The formation of these globules is prevented by not allowing any fine particles of charcoal or dirt to 'get into the cavity when it is being charged. 238 should be dark, tough and, if they have not been cooled too quickly, graphitic. As a general thing the iron buttons are dark gray or mottled according to the condition and amount of carbon they contain. If the crucibles are allowed to cool very slowly, the buttons are, as a rule, very graphitic, but if cooled quickly are fine-grained and white, or grayish in color. The presence of phosphorus generally renders the buttons white, hard and brittle ; sulphur produces a mottled or reticulated structure; man- ganese, a hard, white crystalline or close- grained iron ; titanium, a dull, dark-gray button with a crystalline fracture; chro- mium, a well-fused button, with a tin-white, bright crystalline fracture, to a semi-fused, white, or light gray, spongy mass, accord- ing to the amount of chromium in the iron. A content of sulphur may also be recog- nized by the odor of sulphuretted hydrogen, or the brownish coloration of a lead-paper on SWEDISH ASSAY OF IRON ORES. 239 pouring hydrochloric acid over the regulus. By bringing a sheet of silver over a weighed quantity of the button thus treated, the former is colored the darker the more sul- phur is present. By the degree of colora- tion it may, with some experience, be judged whether the iron is suitable for this or the other purpose. In England the assay of iron is also exe- cuted in large unlined crucibles by mixing the ore with the previously mentioned fluxes (glass and lime) and pulverized char- coal, coke or anthracite. The ore and fluxes should be pulverized and passed through a 60-mesh sieve. With a series, of four, the ore and fluxes may be pro- portioned as follows : 1 and 2. Ore 500 grains (32 grammes) Glass 250 " (16 grammes) Lime 300 " (19.2 grammes) 3 and 4. Ore 500 grains (32 grammes) China clay. c*. ..200 " (12.8 grammes) 240 Sand 50 grains ( 3. 2 grammes) Lime 250 " (16 grammes) The reducing agent employed is prefer- ably anthracite, but charcoal or coke may be used. In any case it should be pulver- ized and passed through a 60 mesh sieve. The following amounts are respectively used : 1 . 80 grains (5. 1 2 grammes) 2. 110 " (7. 04 grammes) 3. 1 20 grains (7. 68 grammes) 4. 150 " (9. 60 grammes) Mix the fluxes and reducing agents thoroughly with the ore, transfer to a cru- cible about 4 inches high by li inches in diameter. Lute the cover on with clay, place on a piece of fire-brick and heat in the usual manner for an hour or more. In lifting the crucible out of the furnace, care must be taken to shake it as little as pos- sible in order to avoid disseminating glob- ules of iron in the slag. When cold, break open the crucible, and collect any small buttons or shots of metal in the slag with a SWEDISH ASSAY OF IRON ORES. 241 magnet. Weigh, then fracture the largest button and note the character of the iron. If the above scheme has been carefully car- ried out, using an ordinary hematite or magnetic ore, the results will be something like as follows : 1. Not being sufficient carbon present, the ore is not all reduced ; the reduced and unreduced ore being fritted together with slag in an irregular lump. 2. Ore completely reduced and fused into a button. Iron, gray. Slag, glassy, and transparent, or perhaps dark-grayish, and opaque. 3. Ore completely reduced and fused into a well-melted button. Iron, gray to grayish white. Slag, clear, glassy and trans- parent; color, gray to greenish by trans- mitted light. 4. Ore completely reduced, but owing to the excess of carbon present the metal is disseminated through the slag in small 16 242 shots or globules. Iron, gray. Slag, glassy, opaque or translucent. There should always be present an excess of the amount of carbon necessary to re- duce the ore. 100 parts by weight of sesquioxide of iron require 22 parts of carbon for reduction. Consequently the amount added must be adjusted according to the oxide of iron present. 243 XXVIII. Assay of Quiclmlver Ores. THIS metal is one of those which some- times occur in the virgin state, though by far the most common shape in which it presents itself is the bisulphuret, commonly termed cinnabar, which in its perfectly pure state consists of: Mercury . . -. . 86.287 Sulphur . ... . 13.713 100.000 Its formula being Hg S. A specimen from Japan, analyzed by Klaproth, gave: Mercury . . T .. 84.50 Sulphur . . . . 14.75 99.25 i Which, though it must have contained 244 THE ASSAYEIl'S GUIDE. 0.75 of other ingredients not mentioned in the analysis, shows that it possessed as much as, according to the above-calcu- lated composition, it could be expected to contain. It is not the place here to give the analyses of other casual occurrences of this metal, such as perhaps are only to be found in the cabinet of the mineralogist; and I shall therefore proceed to describe the manner in which the assays of mercurial ores are performed. In all cases the mercury is procured by simple distillation, for which purpose, wher; not originally uncombined, it is necessary first to disengage it. In distilling quicksilver, an iron retort covered outside with a coating of clay is commonly used. The neck should be so contrived that it can be unscrewed, to facilitate cleaning the interior. Retorts or tubes of clay, glazed externally, are also applicable, and are preferred by some; but ASSAY OF QUICKSILVER ORES. 24o those of iron are safer, inasmuch as the vapors of mercury cannot possibly pene- trate and escape through them. To produce the necessary heat, which should not exceed a mild red, any conve- nient furnace, such as the one described on page 220, will answer. Any tumbler or beaker-glass containing cold water may be employed as a condenser. It must, however, be remarked here that the mouth of the retort ought not to be inserted into the water, because in that case, on cooling, the water would rise up into it. To avoid this, and yet to prevent the escape of the mercurial vapors, a wet wrapper of paper or linen is bound round the neck of the retort, protruding sufficiently to permit of the other end being completely immersed in the water. Some assayers employ a little bag tightly attached to the retort. . The fluxes used are various, and, accord- ing to their efficiency, may be enumerated thus, the first being the best : 24f> THE ASSAYER'S GUIDE. Black llux, from one-half to full weight of ore Carbonate of soda or of potash, one-half " " Iron filings, from a quarter to a half " " Carbonate of lime, one-half to full " " With charcoal powder, one-tenth to one-eighth " The black flux produces with cinnabar besides liberating the mercury, sulphuret of potassium, while sulphates of soda and of potash are formed from the carbonates, The iron filings simply cause the formation of protosulphuret of iron, while the quick- silver is disengaged. The alkaline fluxes are chiefly used with the iron retorts. If the quicksilver is known to exist only in its virgin uncombined state, no flux is re- quired, and we may immediately proceed to distil it over. It has been remarked above that the heat employed during the assay should not exceed a moderate red. This point is of great consequence with cinnabar, because this sulphuret is capable of being sublimated in its undecomposed state, if the heat is in creased beyond that temperature. If the ASSAY OF QUICKSILVER ORES. 247 ore contain chloride or bromide of mercury, these, too, will pass over; and, to avoid this, the ore, if their presence is suspected, must first be mixed with soda. To render the mixing more intimate, a little water is em- ployed, which must, however, be removed before placing the ore in the retort. It is also advisable to apply the heat gradually, and, when retorts are used, to be particular that they are everywhere heated equally, as otherwise quicksilver might be condensed in the interior of the retort. When it has Oeen ascertained that drops of quicksilvei are no longer leaving the retort or tube, and therefore that the process is about being completed, it is advisable to fire up a little before removing the receiving vessel, so that particles of the metal condensed in the neck of the retort or in the tube may be forced out , though, to insure this still more, it is neces- sary to brush out the neck of the vessel with a little brush or feather. The quicksilver which has collected ID THE ASSAYER'S GUIDE. the condensing vessel is frequently indis- posed to join and form a connected mass; but this is easily brought about by boiling it in water. Adhering moisture remaining when the water is decanted should be re moved with blotting-paper. From one-half to three pounds of the orf are commonly employed for the assay, de- creasing in quantity as the value of the ore increases. Perfect accuracy can never be attained in the assay of quicksilver ores by heat, neither as regards the perfect chemical purity nor the full amount of the metal pro- duced; but, as the loss and impurity are yet greater with quicksilver produced on a large scale, this method of treating the ore will be sufficient for technical purposes. Berthier, in the Annales des Mines, h se*rie, t. iii. p. 820, suggests that when the ore is a very poor one, and when therefore the large amount it would be necessary to use might be the cause of considerable in- ASSAY OF QUICKSILVER ORES. 249 convenience in the assay, the following pre- paratory process be resorted to. The ore should be digested with aqua regia, the supernatant liquid decanted or filtered off, the residue thoroughly washed with water, and the acid solution, together with the washings, evaporated to dryness. All the quicksilver in the shape of chloride is then contained in the last-dried residue, and can be further treated in the dry way, only that, as above remarked, it is always neces- sary carefully to mix with soda, when choride of quicksilver is present. Before closing this chapter it will be well to describe the treatment necessary when a quicksilver ore contains arsenic. I shall literally translate the remarks of BodemaD in the work quoted in the preface. He says : " An ore from Huanca-Ve*lica, in Peru, containing arsenic (red sulphuret of arsenic, &c.) and cinnabar, having been submitted to Berthier's inspection, he, after various ^"vJ THE ASSAYER S GUIDE. useless experiments, discovered the follow- ing process to be the most adequate for determining the mercury in it. " The ore is mixed with four or five times its weight of litharge, and then heated in a retort. A flowing, slag-like mass is formed by the litharge, sulphuret of arsenic, &c.. while the cinnabar is decomposed into sul- phurous acid and metallic mercury. The quicksilver is completely volatilized by a moderate heat, and collected in the condens- ing apparatus and the farther portion of the aeck of the retort. The only precaution necessary during the operation consists in gradually and but moderately heating the clay or glass retort, to prevent its being perforated by the effects of the litharge be- fore the process is concluded." Electrolytic determination of quicksilver. According to Escosura, 0.5 gramme of the ore is digested with 10 to 15 cubic centi- meters of hydrochloric acid and 20 cubic centimeters of water in a porcelain dish. ASSAY OF QUICKSILVER ORES. 251 After boiling add from 0.5 to 1 gramme of potassium chlorate in small portions. When decomposition is complete, dilute with 50 cubic centimeters of water and expel free chlorine by continued boiling. In order to separate selenium or tellurium, if present, add 20 to 30 cubic centimeters of a sat- urated solution of ammonium sulphate and boil moderately. When the insoluble resi- due has settled, filter, and use the filtrate as the electrolytic bath. The negative electrode should be pure gold, and the posi- ;ive a platinum sheet. The solution is subjected to the galvanic current from 24 to 30 hours. The increased weight of the gold equals the content of quicksilver. Two Bunsen cells are generally sufficient. This assay may also be executed by treat- ing the finely pulverized ore in a platinum dish with hydrochloric acid, ammonium sulphate, and water. Of 10 per cent, ore only 0.2 gramme is used, and .of 0.1 per cent, ore, 10 grammes. The platinum dish 252 serves as the negative pole, and a disk of sheet-gold, about 4 centimeters in diameter, as the positive pole. The current is sup- plied by 6 Meidinger cells, and the quick- silver is precipitated in 24 hours. These determinations are said to be very accurate and are exclusively used at Almaden. From a solution of its salt acidified with nitric acid, mercury is, according to Classen, precipitated on the negative electrode in the form of a mirror, or of small globules, by a current of 0.2 to 0.5 cubic centimeter of oxyhydrogen gas. The metal adheres well and can be washed without loss. The washing must, however, be done without interrupting the current. Insoluble quick- silver compounds may easily be analyzed by suspending them in acidulated water, or in a dilute solution of common salt (1:10) and electrolyzing as usual. 253 XXIX. Dry Assay of Tin Ores. TIN that is to be assayed in the dry way must be present in the form of oxide. The assay proper consists of applying in a cru- cible at a high temperature reducing and fluxing re-agerits which, bring the stannic oxide to the metallic state and convert the gangue into a liquid slag. The behavior of stannic oxide and of metallic tin at an elevated temperature causes, however, cer- tain difficulties, which make the results often less accurate than could be desired. These difficulties are : 1. That some of the resulting metallic tin is liable to be volatilized. 2. That metallic tin decomposes the alkali carbonates used as fluxes forming stannates which enter the slag. 254 3. That at the temperature required to reduce the stannic oxide, other metallic oxides become also reduced to the metallic state and alloy with the resulting tin but- ton, and vitiate the assay. 4. That sulphates are reduced, or, if sul- phides are present, they combine directly with the metallic tin and carry it into the slag. 5. That the gangue in the ore is always siliceous. This causes loss as the stannic oxide, while passing through the interme- diate state of stan nous oxide, combines with silica and silicates. 6. That stannic oxide is liable, before its reduction has begun, to combine with the basic fluxes used in assaying and form stan- nates ; this liability increases as the quan- tity of flux is increased. Thus it will be seen that the results can be too high (as when iron enters the tin button) or too low (as when tin is carried off in the slag as stannate, sulphide, or sili- ASSAY OF TIN ORES. 255 cate), and that all impurities should be re- moved, if possible, before the actual dry assay takes place. The making up of the charge must also be regulated to counteract as much as possible the bad influences of the basic fluxes. The crucibles used in assaying tin ores are the ordinary clay cru- cibles, the plumbago crucible, and the porce- lain crucible. Crucible linings are unneces- sary. German method of assay. Five grammes of ore are intimately mixed with 0.75 to 1 gramme of charcoal dust, and charged into a clay crucible ; on top are placed 12.5 to 15 grammes black flux (or the substi- tute: 2 parts of potassium-sodium-carbonate and 1 part of flour), with 1 to 1.25 grammes borax-glass, then a common salt cover, and fin ally a piece of charcoal. The crucible being covered, heat in a muffle or a pot-fur- nace at a moderate, gradually increasing tem- perature, until the boiling has ceased, and then for from half to three-quarters of an 256 THE ASSAYER'S GUIDE. hour at a white heat. The crucible is then removed from the fire, broken, when cool, and the tin button weighed. Mitchell * mixes 400 grains ore, 100 argol, 300 sodium carbonate, 50 lime, and charges in a crucible so large that.it need only be half filled ; then gives a cover of sodium carbonate and 200 grains of borax, heats gently and keeps' for at least 20 minutes at a dull red heat, increasing the temperature, until tranquil fusion takes place. LevaTs assay with potassium cyanide. A sufficient quantity of powdered potassium cyanide is rammed into a capacious porce- lain or fire-clay crucible to form a layer of from 12 to 15 millimeters thick. Five grammes of the .powdered ore intimately mixed with five times the quantity of potas- sium cyanide are added to that in the cru- cible, and the whole is covered with a thin layer of the cyanide. The charge is then * >Janual of Assaying; New York, 1881, p. 48, DRY ASSAY OF TIN ORES. 257 aeated in a moderate fire until it fuses, and is kept in constant fusion for 10 minutes. The crucible is then taken out and gently tapped to facilitate the formation of a single button, and allowed to cool. The button is then freed from adhering slag by water. In case copper or lead is present, the ore must be freed from them before reduction by treating it with acid. This is the most accurate method of assaying tin (to within one-half per cent.), and can be executed in a very short time. In case the ore is siliceous, a mixture of 10 grammes of ore, 3 to 8 grammes of ferric oxide, and 40 grammes of potassium cyanide, is placed in a crucible lined with charcoal. The mix- ture is first covered with potassium cyanide and then with powdered charcoal. The cover is luted on and the charge heated at a high temperature for one-half to one hour. In any case it is always better to mix a small quantity of powdered charcoal with 17 258 THE ASSAYER'S GUIDE. the charge. One-half of the potassium cyanide may be mixed with the ore and the balance used to cover the charge. Care must be taken not to allow the fire to become too hot or the charge to boil over. After pouring, the mould must not be moved until the slag has set, otherwise it is apt to penetrate into the button. Winklers bronze assay. Five grammes of ore are mixed with 5 grammes of cupric oxide and charged in a clay crucible ; on top are placed 15 grammes of black flux with 1.25 grammes of borax-glass, then a common salt cover, and finally a large piece of charcoal. The crucible is heated in a muffle or pot-furnace, after boiling has ceased, for three-quarters of an hour to an hour at a bright-red heat, finishing the assay at almost a white heat. The result is a white, brittle, tin-copper alloy. With every tin-assay, an assay of 5 grammes of cupric oxide with the same charge is made, and the weight of the resulting button of DRY ASSAY CF TtX ORES. 25 f* copper, subtracted from the bronze-button, gives the weight of the tin contained in the ore. This assay is actually a modification of the German method previously described. Its advantage is that no prills of tin (or, rather, particles of bronze) are found sus- pended in the slag. All the metallic oxides that have been reduced are found collected in one button. It is claimed that more tin is recovered by this method than by the regular German method, and that the but- tons do not differ more than from 0.4 to 0.5 per cent. 2i)0 XXX. Assay of Sulplmrets in Ores. IT is often very necessary to know the quantity of sulphurets contained in ores, to be able to arrange accordingly the processes of smelting them. To one part of ore, 50 to 100 grains, one part of powdered glass and two of borax are required. The borax is first mixed with the ore, and when placed in the Hessian crucible, or in the lead and copper one, fig. 4, Plate II., both are covered with the glass. The crucible is then exposed to a bright red-heat, as with copper and lead, and on cooling the button is broken out, which may contain in the shape of sulphurets, copper, lead, iron, ASSAY OF SULPHURETS IN ORES. 261 &c., according as these exist in the ore, and it may then be examined for these metals by the means already given in their respec- tive assays. Volumetric determination of sulphur in ores which contain either sulphur alone, or also sulphates. Weil gives the following method : Place 1 to 2 grammes of the finely powdered ore in a flask provided with a cork, through which passes a bent tube. The outside end of this tube dips into an ammoniacal solution of copper of known strength. A few small pieces of granulated zinc are placed in the flask, and 75 cubic centimeters of hydrochloric acid poured over its contents; quickly close the flask and heat. The sulphuretted hydrogen de- veloped precipitates an equivalent portion of copper, and, when precipitation ceases, the sulphide is allowed to settle, is filtered and washed. The object of adding the zinc is to dilute the sulphuretted hydrogen with hydrogen, and to carry off the last 262 THE ASSAYER'S GUIDE. traces of it which may remain in the flask and glass tube. The amount of filtrate from the precipitated copper sulphide is carefully measured, and 10 to 20 cubic centimeters of it saturated with from 25 to 50 cubic centimeters of hydrochloric acid. Heat to boiling, and when boiling titrate with a standardized solution of stannous chloride. This quantity multiplied by 0.50393 gives the content of sulphur sought. The zinc added facilitates the ac- tion of the acid upon the ore, and if any galena is present, it is also more readily decomposed ; the chloride of lead formed being reduced to metallic lead by the zinc. Examination of sulphur in metallic lead. Treat 20 to 30 grammes of very fine chips of the lead with a considerable excess of concentrated hydrochloric acid ; sulphur will be set free as sulphuretted hydrogen. Pass this sulphuretted hydrogen, by means of an aspirator, into bromine water, in which it is decomposed, sulphuric acid be- ASSAY OF SULPHURETS IN ORES. 263 ing formed. Determine the sulphur in the latter with barium chloride as usual. The solution of the lead is aided by gentle heat. A large excess of hydrochloric acid prevents the separation of lead ehloride. Determination of sulphur in pyrites. To 1 gramme of the finely powdered ore in a porcelain dish or casserole add a small amount of potassium chlorate, cover the dish with a watch glass, add 50 cubic cen- timeters concentrated nitric acid, and heat to boiling, adding a little chlorate from time to time. When perfectly oxidized, remove the watch glass (and it should be rinsed into the dish), and evaporate to a small bulk on a water bath. Add a little strong hydrochloric acid, and evaporate to dryness, moisten with the same acid, add water, and filter from silica and the gangue. To the filtrate add 1 gramme tartaric acid, heat, add hot solution of barium chloride, drop by drop, boil, let settle, filter and wash well with hot water. 264 THE ASSAYER'S GUIDE. Weigh a clean porcelain or platinum cru- cible, add the filter and precipitate, burn to ashes, cool, and weigh as baric sulphate. After deducting weights of crucible and filter ash, multiply the remainder by 0.1374, and the product by 100 for percentage of sulphur. Bodewig's method of determining sulphur in pyrites. One-half gramme of pyrites is treated in a glass-stoppered vessel of about 100 cubic centimeters' capacity, with 30 cubic centimeters of water and 4 c. c. of bromine. The stopper is quickly inserted, and the vessel shaken for 5 minutes. When oxidation is ended, which is known by the disappearance of all pulverulent sulphur adhering to the sides of the glass, the solu- tion is emptied into a casserole, and most of the bromine allowed to evaporate in the cold. The solution is almost neutralized with ammonia, then poured into an excess of hot ammonia contained in a platinum dish, and digested from 10 to 15 minutes at ASSAY OF SULPHURETS IN ORES. 265 a gentle heat. The sulphuric acid is de- termined in the filtrate from this in the usual manner. The entire amount of bro- mine employed must not be added all at once, as otherwise there may be some loss of sulphur in the form of sulphuretted hy- drogen. Some iron volatilizes as a bromide with the excess of bromine ; hence it can- not be determined in the precipitate made by the ammonia. 266 XXXI. Mode of testing the Calorific Power of Coal and other Fuels.* IT must not be supposed that the amount of heat which a fuel is capable of producing is entirely dependent on its chemical com- position. Different means have been adopted to determine the efficacy of coal as a fuel. Thus, Despretz has made experiments of this kind by discovering the amount of water which a certain quantity of coal will elevate in temperature one degree of the centigrade thermometer. The varying tem- perature of the water, however, must ever prevent an accurate result. Kumford has proposed to determine the same by the * Rarsten's Eiseuhiittenkunde, vol. ii., p. 219, 476. CALORIFIC POWER OF COAL. 267 direct use of a thermometer in a closed vessel. Berthier has, however, proposed one that seems equally simple, and service- able for all practical purposes. According to his proposition, one gramme of the coal (or other fuel; for it is applica- ble to all) should be thoroughly pulverized. All coals are readily reduced to such a state. Wood should be used as shavings, or rasped. The powdered substance is then mixed with some litharge, but more than it is capable of reducing, not less than twenty times its own weight nor more than forty. The quality of the fuel will enable the assay er, after a little practice, to deter- mine d, priori with considerable accuracy what will be the requisite quantity. The mixture is placed in a clay crucible (Plate II., fig. 4 or 5) and carefully covered with about twenty to thirty grammes of litharge. The crucible must not be filled over one- half This is then placed in a heated muffle and covered. The heat should not be too 268 THE ASSAYER'S GUIDE. severe and rapid. The contents will boil up. When the melting has thoroughly taken place, strong heat should be applied for ten minutes, so that the button may collect. The crucible is then taken out and cooled slowly, then broken, and the button extracted and weighed. This process rests upon the fact that the carbon will reduce the litharge; and having, therefore, assumed one number for the amount of litharge reduced, from which to calculate our experiments, it will be easy to compare the different varieties of fuel. When many experiments of this kind are made, the assayer will do well to establish a certain number as the basis. This will vary according to the general character of his coals. This number it will be well to assume as low as possible, to avoid the in- convenience of fractions. He would there- fore adopt a very inferior variety of coal as the one with which to compare the others in the following manner, though CALORIFIC POWER OF COAL. 269 be it remembered I am not now giving results of assays, but only imaginary examples. 1 part bone-coal reduced 10.00 parts by weight of litharge " rough bituminous" 12.50 " " '< " good bituminous " 20.00 " ' " anthracite " 26.00 " II Sis fll .270 inclusive, les in the gland. two fi clays, 1 to 3 sed chiefly for crucib facture of steel in En rst iefl T86 | 5*66 | 0'66 | 9'66 i'OOI O'OOl 1 II From Stourbridge, England, by Ber- thier- Sr OQ b "-.I ill |ii CO 271 Table showing, in Degrees of the Centigrade and Fah- renheit Thermometers, the Amount of Heat necessary to melt various Substances. Centigrade. Fahrenheit Platina.... 2500 4532 1500-1600 2732-3012 Steel 1300-1400 2372-2552 Cast iron, j irav 1200 2192 Do. irhite 1050 1922 Gold 1100-1250 2012-2282 Silver 1000 1832 900 1652 Antimony . 450 842 Zinc 360 680 Lead 330 658 Bismuth... 260 480 Tin 230 446 Alloys of Tin, Lead, and Bismuth. (in parts.) (in parts.) (in parts.) 1 3 289 554 1 1 _ 241 464 3 1 200 892 3 1 _ 186 865 2 _ 1 167.7 333.5 1 _ 1 142.2 283.8 4 1 5 188-9 246.2 ! 3 2 5 100 212 3 5 8 100 212 1 1 4 94 203 109 280 Mercury -39 38 2 e.^ i "2T1 T 2 S (0 HENRY CAREY BAIRD & CO.'S CATALOGUE. 4RMENGAUD, AMOROUX, AND JOHNSON. The Practi- ial Draughtsman's Book of Industrial Design, and Ma- chinist's and Engineer's Drawing Companion : Farming a Complete Course of Mechanical Engineering and Archi- tectural Drawing. From the French of M, Armengaud the elder, Prof, of Design in the Conservatoire of Arts and Industry, Paris, and M. Armengaud the younger, and Amoroux, Civil Engineers. 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The Practical Model Calculator: For the Engineer, Mechanic, Manufacturer of Engine Work, Naval Architect, Miner and Millwright. By OLIVER BYRNE. 8vo., nearly 600 pages. , (Scarce.; CABINET MAKER'S ALBUM OF FURNITURE: Comprising a Collection of Designs for various Styles of Furniture. Illustrated by Forty-eight Large and Beautifully Engraved Plates. Oblong, 8vo. . . . $1.50 CALLINGHAM. Sign Writing and Glass Embossing: A Complete Practical Illustrated Manual of the Art. By JAMES CALLINGHAM. To which are added Numerous Alphabets and the Art of Letter Painting Made Easy. By JAMES C. BADENOCH. 258 pages. I2mo. $'-5 CAMPIN. A Practical Treatise on Mechanical Engineering: Comprising Metallurgy, Moulding, Casting, Forging, Tools, Work* shop Machinery, Mechanical Manipulation, Manufacture of Steam' Engines, etc. With an Appendix on the Analysis of Iron and Iron Ores. By FRANCIS CAMPIN, C. E. To which are added, Observation* at) the Construction of Steam Boilers, and Remarks upon Furnaces used for Smoke Prevention ; with a Chapter on Explosions By R ARMSTRONG, C. E., and JOHN BOURNE, (scarce.) HENRY CAREY BAIRD & CG. S S CATALOGUE. CAREY. A Memoir of Henry C. Carey. By DR. WM. ELDER. With a portrait. 8vo., cloth . . 75 CAREY. The Works of Henry C. Carey : Manual of Social Science. Condensed from Carey's " Principled of Social Science." By KATE McKEAN. i vol. I2mo. . 2.00 Miscellaneous Works. With a Portrait. 2 vols. 8vo. $1000 Past, Present and Future. Svo. .... $2.50 Principles of Social Science. 3 volumes, Svo. . . $10.00 The Slave-Trade, Domestic and Foreign ; Why it Exists, and How it may be Extinguished (1853) Svo. , . . $2.00 The Unity of Law : As Exhibited in the Relations of Physical, Social, Mental and Moral Science (1872). Svo. . . $2.50 CLARK. Tramways, their Construction and Working : Embracing a Comprehensive History of the System. 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A Practical Manual of House Painting, Grain- ing, Marbling, and Sign- Writing: Containing full information on the processes of House Painting ir Oil and Distemper, the Formation of Letters and Practice of Sign- Writing, the Principles of Decorative Art, a Course of Elementary Drawing for House Painters, Writers, etc., and a Collection of Useful Receipts. With nine colored illustrations of Woods and Marbles, and numerous wood engravings. By ELLIS A DAVIDSON. i2mo. $2.00 DAVIES. A Treatise on Earthy and Other Minerals and Mining: By D. C. DAVIES, F. G. S., Mining Engineer, etc. Illustrated by 76 Engravings. I2mo $5.00 DAVIES. A Treatise on Metalliferous Minerals and Mining: By D. C. DAVIES, F. G. S , Mining Engineer, Examiner of Mines, Quarries and Collieries. Illustrated by 148 engravings of Geological Formations, Mining Operations and Machinery, drawn from the practice of all parts of the world. Fifth Edition, thoroughly Revised and much Enlarged by his son, E. Henry Davies. 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I2mo. 427 pp. . . . . . #2.OC GARDNER. Everybody's Paint Book: A Complete Guide to the Art of Outdoor ami Indoor Painting. 38 illustrations. i2mo, 183 pp. . . . $l.oo 3EE. The Jeweller's Assistant in the Art of Working in Gold: A Practical Treatise foi Masters and Workmen. I2mo. . $3- GEE. The Goldsmith's Handbook : Containing full instructions for the Alloying and Working of Gold, including the Art of Alloying, Melting, Reducing, Coloring, Col lecting, and Refining; the Processes of Manipulation, Recovery of Waste; Chemical and Physical Properties of Gold; with a New System of Mixing its Alloys ; Solders, Enamels, and other Useful Rules and Recipes. By GEORGE E. GEE. I2mo. . . 1.25 GEE. The Silversmith's Handbook : Containing full instructions for the Alloying and Working of Silver, including the different modes of Refining ind Melting the Metal; its Solders ; the Preparation of Imitation Alloys ; Methods of Manipula- tion ; Prevention of Waste ; Instructions for Improving and Finishing the Surface of the Work ; together with other Useful Information and Memoranda. By GEORGE E. GEE. Illustrated. I2mo. Si. 25 GOTHIC ALBUM FOR CABINET-MAKERS: Designs for Gothic Furniture. Twenty-three plates. Oblong 1.00 3RANT. A Handbook on the Teeth of Gears : Their Curves, Properties, and Practical Construction. By GEORGE B. GRANT. Illustrated. Third Edition, enlarged. 8vo. $1.00 GREENWOOD. Iron and Steel: Vol. I. Iron : Its Sources, Properties, and Manufacture. By WILL- IAM HENRY GREENWOOD. Revised and Re-written by A. HUM- BOLDT SEXTON. 255pp. Illustrated 12010. . . . $1.00 Vol. II. Steel Its Varieties, Properties,, and Manufacture By WILLIAM HENRY GREENWOOD. 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S. 8vo. . . . $2.50 Hand-Book of Useful Tables for the Lumberman, Farmer and Mechanic: Containing Accurate Tables of Logs Reduced to Inch Board Meas. ure, Plank, Scantling and Timber Measure ; Wages and Rent, by Week or Month; Capacity of Granaries, Bins and Cisterns; Land Measure, Interest Tables, with Directions for Finding the Interest on any sum at 4, 5, 6, 7 and 8 per cent., and many other Useful Tables. 32 mo., boards. I6& pages . . . . . .2$ HASERICK. The Secrets of the Art of Dyeing Wool, Cotton, and Linen, Including B'.eachir.g an/i Coloring Wool and Cotton Hosiery and Random Yarns. A Treatise based on Economy and Practice. By E. C. HASERICK. Illustrated by 323 Dyed Patterns of the Varnt or Fabrics. 8vo #4- 5 HATS AND FELTING: A Practical Treatise on their Manufacture. By a Practical Hatte* Illustrated by Drawings of Machinery, etc. 8vo. . . $1.00 HERMANN. Painting on Glass and Porcelain, and Enamel Painting: A Complete Introduction to the Preparation of all the Colors and Fluxes Used for Painting on Glass, Porcelain, Enamel, Faience and Stoneware, the Color Pastes and Colored Glasses, together with Minute Description ot the Firing ot Colors and Enamels, on tht Basis of Personal Practical Experience of the Art up to Date. 18 illustrations. Second edition. $4.00 HAUPT. Street Railway Motors: With Descriptions and Cost of Plants and Operation of the Various Systems now in Use. HENRY CAREY BAIRD & CO.'S CATALOGUE. 15 HAUPT. A Manual of Engineering Specifications and Con- tracts. By LEWIS M. HAUPT, C. E. Illustrated with numerous maps. 328pp. 8vo $3 oo HAUPT. The Topographer, His Instruments and Methods. By LEWIS M. HAUPT, A. M., C. E. Illustrated with numerous plates, maps and engravings. 247 pp. 8vo. . . . $3.00 HUGHES. American Miller and Millwright's Assistant: By WILLIAM CARTER HUGHES. I2mo. .... $1.50 HULME. Worked Examination Questions in Plane Geomet- rical Drawing : For the Use of Candidates for the Royal Military Academy, Wool- wich ; the Royal Military College, Sandhurst ; the Indian Civil En- gineering College, Cooper's Hill ; Indian Public Works and Tele- graph Departments ; Royal Marine Light Infantry ; the Oxford and Cambridge Local Examinations, etc. By F. EDWARD HULME, F. L. S., F. S. A., Art-Master Marlborough College. Illustrated by 300 examples. Small quarto $1.00 JEKVIS. Railroad Property: A Treatise on the Construction and Management of Railways; designed to afford useful knowledge, in the popular style, to the holders of this class of property ; as well as Railway Managers, Offi cers, and Agents. By JOHN B. JERVIS, late Civil Engineer of the Hudson River Railroad, Croton Aqueduct, etc. i2mo., cloth $1.^0 KEENE. 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I2mo. 1.25 16 HENRY CAREY BAIRD & CO.'S CATALOGUE. KENTISH. A Treatise on a Box of Instruments, And the Slide Ruie ; with the Theory of Trigonometry and Log* rithms, including Practical Geometry, Surveying, Measuring of Tim her, Cask and Malt Gauging, Heights, and Distances. By THOMA' KENTISH. In one volume. I2mo. . . . . $i-O KIRK. A Practical Treatise on Foundry Irons. Comprising Pig Iron, and Fracture Grading of Pig and Scrap Irons; Scrap Irons; Mixing Irons; Elements and Metalloids; Grading Iron by Analysis; Chemical Standards for Iron Castings; Testing Cast Iron; Semi Steel ; Malleable Iron; Etc., Etc. By EDWARD KIRK, Practical Moulder and Melter, Consulting Expert in Melting. Illus trated. 294 pages. 8vo. 1911. #3.00 KICK. Flour Manufacture. A Treatise on Milling Science and Practice. By FREDERICK KICK Imperial Regierungsrath, Professor of Mechanical Technology in th. imperial German Polytechnic Institute, Prngue. Translated from the second enlarged and revised edition with supplement by H. H P. POWLES, Assoc. Memb. Institution of Civil Engineers. Illustrated with 28 Plates, and 167 Wood-cuts. 367 pages. 8vo. . Jgio.OO ^INGZETT. The History, Products, and Processes of th Alkali Trade : including the most Recent Improvements. By CHARLES THOMA* KTVOZETT. Consulting Chemist. With 23 illustrations. 8vo. $2.00 IRK. The Cupola Furnace : A Practical Treatise on the Construction and Management of Foundry Cupolas. By EDWARD KIRK, Practical Moulder and Melter, Con- sulting Expert in Melting. Illustrated by 106 engravings. Third Edition, revised and enlarged. 482 pages. 8vo. 1910. #35 LANDRIN. A Treatise on Steel : Comprising its Theory, Metallurgy. Properties, Practical Working, and Use. By M. H. C. LANDRIN, JR. From the French, by A. A. FESQUET. i2mo. . ::. . . . . . . J&i.oo LANGBEIN. A Ccrr.piete Treatise on the E!ectro-Deposl tion of Metals : Comprising Electro-Plating and Galvanoplastic Operations, the De- position of Metals by the Contact and Immersion Processes, the Color- ing of Metals, the Methods of Grinding and Polishing, as well as- Description of the Voltaic Cells, Dynamo- Electric Machines, Ther. mopyles, and of the Materials and Processes Used in Every Depart- ment of the Art. Translated from the Fifth German Edition ot DR. GEORGE LANGBEIN, Proprietor of a Manufactory for Chemical Products, Machines, Apparatus and Utensils for Electro- Platers, and of an Electro-Plating Establishment in Leipzig. With Additions by WILLIAM T. BRANNT, Editot of ''The Techno-Chemical Receipt Book." Sixth Edition, Revised and Enlarged. Illustrated by 163 Engravings, 8vo , 725 pages (1909) . . . . . $4 oo LEHNER. The Manufacture of Ink: Comprising the Raw Materials, and the Preparation of Wrting, Copyingand Hektograph Inks, Safety Inks. 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New Theorems, Tables, and Diagrams, for thf Computation of Earth-work : Designed for the use of Engineers in Preliminary and Final Estimates of Students in Engineering, and of Contractors and other non-profes- sional Computers. In two parts, with an Appendix. Part I. A Prac- tical Treatise; Part II. A Theoretical Treatise, and the Appendix Containing Notes to the Rules and Examples of Part I.; Explana tions of the Construction, of Scales, Tables, and Diagrams, and z Treatise upon Equivalent Square Bases and Equivalent Level Heights By JOHN WARNER, A. M., Mining and Mechanical Engineer, Illus- t -ated by 14 Plates. 8vo. . . . . . . $3.00 WILSON. Carpentry and Joinery : Bj JOHN WILSON, Lecturer on Building Construction, Carpentry and Joinery, etc., in the Manchester Technical School. Third Edition, with 65 full-page plates, in flexible cover, oblong. . . ( Scarce. ) WATSON. A Manual of the Hand-Lathe : Comprising Concise Directions for Working Metals of all kinds, Ivory, Bone, and Precious Woods ; Dyeing, Coloring, and French Polishing ; Inlaying by Veneers, and various methods practised to produce Elaborate work with Dispatch, and at Small Expense. By EGBERT P. WATSON, Author of "The Modern Practice of American Machinists and Engineers." Illustrated by 78 engravings. $1.00 WATSON. The Modern Practice of American Machinists and Engineers : Including the Construction, Application, and Use of Drills, Lathe Tools, Cutters for Boring Cylinders, and Hollow-work generally, with the most Economical Speed for the same ; the Results verified by Actual Practice at the Lathe, the Vise, and on the floor. Togethei HENRY CAREY BAIRD & CO.'S CATALOGUE. 29 with Workshop Management, Economy of Manufacture, the Steam Engine, Boilers, Geys, Belting, etc., etc. By EGBERT P. WATSON. Illustrated by eighty ~*,ix engravings. I2mo. . . . $2.00 WATT. The Art of Soap Making : A Practical Hand-Book of the Manufacture of Hard and Soft Soaps, Toilet Soaps, etc. Fifth Edition, Revised, to which is added an Appendix on Modern Candle Making. By ALEXANDER WATT. 111. I2mo. $3.00 WEATHERLY. Treatise on the Art of Boiling Sugar, Crys- tallizing, Lozenge making, Comfits, Gum Goods, And other processes for Confectionery, including Methods for Manu- facturing every Description of Raw and Refined Sugar Goods. A New and Enlarged Edition, with an Appendix on Cocoa, Chocolate, Chocolate Confections, etc. 196 pages, 1 2mo. (1903) . #1.50 WILL. Tables of Qualitative Chemical Analysis r With an Introductory Chapter on the Course of Analysis. By Pro- fessor HEINRICH WILL, of Giessen, Germany. Third American, from the eleventh German edition. Edited by CHARLES F. HIMES, Ph. D., Professor of Natural Science, Dickinson College, Carlisle, Pa. 8vo $1.50 WILLIAMS. On Heat and Steam : Embracing New Views of Vaporization, Condensation and Explo- sion. 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