UNWERSTTYgrCALIFORNIA COLLEGE of MINING DEPARTMENTAL LIBRARY * BEQUEST OF SAMUELBENEDICrCHRlSTY PROFESSOR OF MINING AND METALLURGY 1885-1914 AT WORK. 8. B. CHRISTY MANUAL OF ASSAYING GOLD, SILVER, COPPER, AND LEAD ORES. WITH ONE COLORED PLATE AND NINETY-FOUR ILLUSTRATIONS ON WOOD. BY WALTER LEE BROWN, B.Sc M SECOND EDITION. THOROUGHLY REVISED, CORRECTED, AND AUGMENTED. CHICAGO:. PUBLISHED BY E. H. SARGENT & CO. 1886. T /V 37 . f MININC* t COPYRIGHT, BY WALTER LEE BROWN. A.D. 1886. I KNISHT & LEOKARU " EXTRACT FROM PREFACE TO FIRST EDITION. WHEN I entered upon the task of preparing this book, it was with the idea of furnishing a guide to those, who, having had no previous technical or es- pecially scientific education, desired to learn some- thing of the practical assaying of gold and silver ores, and in whose hands I could place no work that could give them this information in a clear, simple and thor- oughly detailed manner, and unburdened with un- necessary matter. This intention I have tried to adhere to all the way through, and while I have added other information which was pertinent, I have kept such increase in an appendix, so that the body proper of the work con- tains the real subject matter. It is my sincere belief that there is no book in the English language on the subject of assaying which occupies the space that this little manual tries to fill. A number of such publications fail to meet the want, on account of their antiquity, they having been written some thirty years ago ; hence their methods, apparatus, etc., are not suited to the assayers of to- day. Others are either more suitable as books of reference, or do not give sufficient detail for the inex- perienced. It is this latter fault I have carefully endeavored to avoid, and perhaps have gone to the other extreme. At all events, I have tried to give here in print the PREFA CE. precise instruction which I have previously imparted orally to my students. Those who may choose to criticise, will remember for whom this hand-book is written. I wish to publicly thank the following gentlemen who have very kindly aided me in my work with valuable information: Mr. S. A. Reed, Irwin, Colo.; Mr. A. H. Low, Assayer of the Boston and Colorado Smelting Works, Argo, Colo.; Mr. C. Boyer, Assayer of the U. S. Branch Mint, Denver, Colo.; Mr. M. G. Nixon, Engineer, and Mr. R. G. Coates, both of Chicago. March, 1883. PREFACE TO THE SECOND EDITION. So many words of praise, both from the press and private individuals, greeted the first edition of this work, that I feel encouraged to put forth a second and greatly improved edition, which will not contain the faults that have been pointed out to me as existing in the first. The salient features of the new comer are increase in matter from 318 to 488 pages; the stating of all charges in assay tons, grammes, and grains ; detailed charges in the scorification process ; full notes on the colors and appearances of the scorifiers (with a col- ored plate) and cupels after work ; the expansion of the crucible process from nine to almost ninety pages ; more complete articles on the assay of gold and silver bullion, and the volumetric analysis of copper ores ; and, finally, the issuance of the book in flexible covers. For the idea of the oxidizing powers of ores which I have developed in the notes on the crucible process, I am indebted to Aaron's Assaying. Whatever appears in this edition extracted from the following authorities, is given with the full and written permission of the authors, editors, or owners of the copyright, as the case may be : Mitchell's Manual of Assaying, Kustel's Roasting of Gold and Silver Ores, Aaron's Assaying, Chapman's Furnace Assay, and Hank's Fourth Annual Report as the State Mineralo- gist of California. Besides for that which I have incorporated from the 8 PREFACE. above-mentioned sources, I wish to give thanks to the following gentlemen : to Mr. J, C. Jackson, my suc- cessor in business in Chicago, for illustrations of a permanent furnace, and particularly for the neat and characteristic frontispiece ; to Mr. F. E. Fielding, As- sayer, Virginia City, Nev., for valuable notes on the assay of gold bullion and volumetric analysis of cop- per ores ; and to Mr. G. H. Ellis, for the careful work- ing out of the qualitative schemes. WALTER LEE BROWN. Aurora, 111., Oct. i, 1886. CONTENTS. PART I. APPARATUS AND RE-AGENTS. CHAPTER I. APPARATUS USED IN ASSAYING. IMPLEMENTS FOR PULVERIZING, SAMPLING, ETC., . . 20 SCALES AND BALANCES, .__..__ 36 WEIGHTS, . _ . 59 FURNACES, 64 FURNACE TOOLS, ........92 APPARATUS USED IN THE FURNACE, .... 102 APPARATUS OF GLASS AND PORCELAIN, . . . _ in MISCELLANEOUS APPARATUS, . . . . . . 116 CHAPTER II. RE-AGENTS USED IN ASSAYING. DRY RE-AGENTS FOR ASSAYING, ..... 128 WET RE-AGENTS FOR ASSAYING, ..... 142 RE-AGENTS FOR ANALYSIS, _..... 144 MISCELLANEOUS, 152 CHAPTER III. TESTING OF RE-AGENTS. I. TESTING OF LITHARGE FOR SILVER, .... 154 II. TESTING OF GRANULATED LEAD FOR SILVER, _ . 158 III. TESTING OF SHEET LEAD FOR SILVER, ... 160 9 IO CONTENTS. IV. DETERMINATION OF THE REDUCING POWERS OF REDUC- ING AGENTS, __.._.. 161 V. DETERMINATION OF THE OXIDIZING POWER OF NITRE (NITRATE OF POTASH), 162 PART II. ASSAYING. . CHAPTER I. GOLD AND SILVER ORES. OCCURRENCE, _.._.... 167 ASSAY, 170 I. PREPARATION OF THE SAMPLE, ... 171 II. SCORIFICATION PROCESS, ..... l8l a. Preparation of Charge, 183; b. Scorification, 194; c. Cupellation, 200; d. Weighing the Gold and Silver Bead, 209; e. Parting, 210; f. Inquartation, 214; g. Weighing the Gold Residue. 215; h. Calculations, 216. III. CRUCIBLE PROCESS, 217 Preliminary, 217; Roasting, 259; Methods of the Crucible Assay, 264; Preparation of the Charge, 267; Running the Crucibles in the Fire, 273; General Charges, 276; Special Charges and Directions, 282. CHAPTER II. COPPER ORES. OCCURRENCE 304 ASSAY. 305 I. METHOD FOR NATIVE COPPER, .... 306 II. METHOD FOR OXIDES AND CARBONATES OF COPPER, 307 III. METHOD FOR SULPHIDES OF COPPER, . . . 307 CONTENTS. I I CHAPTER III. LEAD ORES. OCCURRENCE, ..._.._. 311 ASSAY, 312 I. METHODS FOR GALENA, . 312 II. METHODS FOR OXIDES AND CARBONATES, . . 320 APPENDIX. SECTION I. SPECIAL METHODS. I. ASSAYING OF THE VARIOUS MINERALS CONTAINED IN AN ORE, _ 327 II. ASSAYING OF ORES CONTAINING FREE GOLD OR FREE SILVER, _ 329 III. ANALYSIS OF COPPER ORES, . 333 IV. AMALGAMATION ASSAY OR LABORATORY MILL RUN, 351 V. PAN TEST FOR GOLD (" PANNING "), _ 355 VI. CHLORINATION ASSAY OF GOLD ORES, . . _ 364 VII. CHLORINATION TEST FOR SILVER, .... 367 VIII. -THE ASSAY OF GOLD BULLION AND SILVER BULLION, 369 IX. THE ASSAY OF BASE BULLION, .... 404 X. QUALITATIVE TESTS; CARBONATES, SULPHATES, SUL- PHIDES, TELLURIDES, COPPER, IRON, LEAD, MAN- GANESE, SILVER, ....... 408 XI. BRIEF SCHEME FOR SILICA, IRON, AND MANGANESE, 413 XII. DETERMINATION OF MOISTURE IN AN ORE, 415 XIII. DETERMINATION OF SULPHUR IN PYRITES, . . 416 SECTION II. LISTS AND REFERENCES. LIST OF THE PRINCIPAL GOLD MINERALS FOUND IN THE UNITED STATES, 417 1 2 CONTENTS. MINERALS LIKELY TO CARRY GOLD, .... 418 LIST OF THE PRINCIPAL SILVER MINERALS FOUND IN THE UNITED STATES, 418 MINERALS LIKELY TO CARRY SILVER, . . . .421 LIST OF THE PRINCIPAL COPPER MINERALS FOUND IN THE UNITED STATES, 422 LIST OF THE PRINCIPAL LEAD MINERALS FOUND IN THE UNITED STATES, 425 LIST OF USEFUL BOOKS ON SUBJECTS MORE OR LESS CON- NECTED WITH ASSAYING: GENERAL SCIENCE; GENERAL CHEMISTRY; CHEMICAL TECHNOLOGY; REFERENCE BOOKS ON CHEMISTRY; TEXT-BOOKS ON THEORETICAL CHEMIS- TRY; GENERAL QUALITATIVE ANALYSIS; GENERAL QUAN- TITATIVE ANALYSIS; SPECIAL QUANTITATIVE ANALYSIS; VOLUMETRIC ANALYSIS ; LABORATORY MANIPULATION ; GEOLOGY; MINERALOGY; BLOW-PIPE ANALYSIS; METAL- LURGY AND MINING; ASSAYING; METRIC SYSTEM WEIGHTS AND MEASURES; MINING LAW, ... 428 PLAN FOR ASSAY LABORATORY, ' 437 FORM FOR CERTIFICATE OF ASSAY 438 OUTFIT. ASSAYING, . .. . . . - 439 OUTFIT, BLOW-PIPE, - 44* SECTION III. TABLES. MULTIPLICATION TABLE FOR GOLD AND SILVER, _ . 443 TABLE OF VALUES OF GOLD AND SILVER, .... 444 TABLES OF WEIGHTS: AVOIRDUPOIS; TROY; APOTHECARIES'; FRENCH OR METRIC SYSTEM, . 445 EQUIVALENTS OF SOME OF THE ENGLISH AND FRENCH WEIGHTS - 449 ASSAY -TON EQUIVALENTS IN GRAMMES, TROY GRAINS, AND TROY OUNCES, 45 INDEX, 461 INTRODUCTION. In our present state of knowledge we be- lieve all matter to be composed of one or more elements or original simple substances. These elements are considered to be sev- enty in number. Certain of them have what we may call a commercial importance. (See Introduction to Attwood's Blow-pipe Assay- ing.) They are as follows, the metals being in italics: 1. Aluminium. 16. Gold. 2. Antimony. 17. Hydrogen. 3. Arsenic. 18. Iodine. 4. Barium. 19. Iridium. 5. Bismuth. 20. Iron. 6. Boron. 21. Lead. 7. Bromine. 22. Lithium. 8. Cadmium. 23. Magnesium. 9. Calcium. 24. Manganese. 10. Carbon. 25. Mercury. n. Chlorine. 26. Molybdenum. 12. Chromium. 27. Nickel. 13. Cobalt. 28. .Nitrogen. 14. Copper. 29. Oxygen. 15. Fluorine. 30. Palladium. 14 INTRODUCTION. 31. Phosphorus. 39. Tin. 32. Platinum. 40. Titanium. 33. Potassium. 41. Tungsten. 34. Silicon. 42. Uranium. 35. Silver. 43. Vanadium. 36. Sodium. 44. Z/MT. 37. Strontium. 45. Zirconium. 38. Sulphur. Some of the above are valuable in them- selves, others in combination. The remainder of the elements, which have no especial value excepting perhaps as curi- osities, are : 1. Ccesium. 14. Rhodium. 2. Cerium. 15. Rubidium. 3. Columbium. 16. Ruthenium. 4. Davyum. 17. Samarium. 5. Decipiiim. 18. Scandium. 6. Didymium. 19. Selenium. 7. Erbium. 20. Tantalum. 8. Gallium. 21. Tellurium. 9. Glucinum. 22. Thallium. 10. Indium. 23. Thorium. n. Lanthanum. 24. Ytterbium. 12. Norwegium. 25. Yttrium. 13. Osmium. Besides the seventy elements above enu- merated, there are some ten or more ex- tremely rare metals (actinium, gadolinium, germanium, helium, holmium, idunium, ilme- IN TR OD UC TION. I 5 nium, mosandrium, neptunium, philippium, terbium, thulium, etc.), whose existence is not yet quite satisfactorily proven. In order to ascertain the value of an ore, it is necessary to determine the percentage of the metal or metals which it contains. This is the first thing to be done an after consideration is the question of the presence of other ingredients which may injuriously affect the value of the ore or product. There are two general methods, known respectively as assaying -&K& analysis, whereby we may test an ore to learn its composition. A comprehensive definition of assaying is to call it that branch of exact science which enables us to find out of what a substance is composed and the proportions, by means of dry re-agents and heat. On the other hand, analysis is that branch which effects the same results mainly by the use of wet re-agents, with or without the aid of heat. In spite of this distinction, wet assays, as opposed to dry or fire assays, are continually spoken of ; still, to be as consistent as possi- ble, the terms assaying and analysis, as defined above, will be used throughout this work. j 6 IN TR OD UC TJON. The greater number of the processes given in this little book come under the former heading, while analysis proper is employed in only a few cases. The following metals are sought for in ores by assaying : antimony, bismuth, cobalt, cop- per, gold, iron, lead, nickel, platinum, silver, tin and zinc. It is the object of this manual to treat only of gold, silver, copper and lead. For informa- tion concerning the assaying of the remaining metals just mentioned, the student must seek it on page 434, among the various works on assaying there quoted. PART I. APPARATUS AND RE-AGENTS. MANUAL OF ASSAYING, PART I. APPARATUS AND RE-AGENTS. CHAPTER I. APPARATUS USED IN ASSAYING. IT is as true of the art of assaying as of any other, that "good work requires good tools." While many of the latter can be dispensed with by the skilled assayer, it is often convenient, if not absolutely necessary, for the unskilled to have the best utensils for the work required. I shall therefore give an exhaustive list of apparatus needed for the processes herein described, but shall try to avoid mentioning many implements which are not essential. 2Q MANUAL OF ASSAYING. IMPLEMENTS FOR PULVERIZING, SAMPLING, ETC. Iron Mortars and Pestles. Two sizes of mortars are handy, a large one 1 1 inches in diameter, and weighing with pestle about 35 pounds (2 gallons capacity),, and a smaller one of 5 inches diameter and 7 pounds weight gallon capacity). Instead of both, a medium size, 8 inches diameter, in weight about 19 pounds (i gallon capacity), may be employed. They may be either bell or urn-shaped. FlG - * Care should be taken to remove all ore from the mortars after grinding. Gen- erally an old towel, rag, or even paper, will suffice to do this, but occasionally washing must be resorted to. Dry thoroughly after the latter operation. Triturating with dry sand often answers the purpose. When not in use let the mortars rest mouth downward. Mortars of various sizes can also be obtained with two oppo- FIG. 2. sitely situated projections, to serve APPARATUS USED IN ASSAYING. 21 either as handles for carrying, or as trunnions for turning over and dumping contents. Fig. 2 represents this pat- tern. To ease the labor of lifting a heavy pestle, an arrange- ment similar to that shown in fig. 3 is recommended. This particular form is that which was in use in my own lab- oratory, where it al- ways gave satisfac- tion. The spring does not perceptibly add to the force required to strike a crushing blow, but does ma- . FIG. 3. terially aid in lifting the pestle. It (the spring) is 1 8 inches long (when unstretched) 22 MANUAL OF ASSAYING. in coils of if inches diameter, made of the best steel of \ inch diameter, and painted with asphalt black as a protection against rust. It is connected to the bracket by a strong and flexible cord. The supporting bracket or hook is of \ inch malleable iron. The distance of the eye from the wall I have made 13 inches, but it can, of course, vary to suit the circumstances. When not in use do not keep the spring taut, but let the lower end be hung loosely from a hook in the wall. Instead of the above contrivance, a spring- board of hickory, 3 inches wide, \ to i inch thick, and 10 feet long, the further end firmly fastened, the free end connecting by a strong rope with the pestle, will do. Any assay laboratory, whether permanent or transient, will require at least one of the three sizes of mortars specified. For fixed laboratories, and where the quantity of ore to be crushed is considerable, a very large mor- tar, 1 8 inches deep and 12 inches wide (weight about 150 pounds), to stand on the APPARATUS USED IN ASSAYING. 2$ floor, is very valuable. The pestle accom- panying it is 3 feet long, and weighs about 1 8 pounds. The striking end is usually flat- tened out to a width of from 4 to 6 inches to cover more ore at a blow, and also to prevent the flying out of the crushed material. To use, the assayer stands over the mortar, grasping the pestle with both hands. The spring or spring-board arrangement can likewise be applied to the pestle of this mortar. To prevent pieces of ore which are being crushed in the mortar from flying out, it is a good plan to cut a piece of wood, pasteboard or tin of a circumference somewhat larger than that of the top of the mortar, with a hole in the centre large enough to admit of a little play to the pestle, and to lay this on top of the mortar while at work. Crushers. These are intended to take the place of the mortar and pestle for crushing comparatively large quantities of ores. For small samples the mortar will do very well, MANUAL OF ASSAYING. but for say 20 pounds and upward, some sort of a crusher will be a desideratum. Espe- cially will it be needed in a large assay labo- ratory. There are quite a number of hand crushers in the market intended solely for laboratory purposes, such as the Alden, Blake, Forster, Lipsey, etc. FIG. 4. Among the best is the Lipsey, which is represented in full in fig. 4, and in section in APPARATUS USED IN ASSAYING. Fie, 5. fig. 5. It can be turned either by hand or power. For laboratories where say half a ton or so of ore is frequently to be crushed, I can heartily recommend Krom's Laboratory Crusher, shown in fig. 6. It requires power. To insure its cleanliness, run through it, just 26 MANUAL OF ASSAYING. FIG. 6. APPARATUS USED IN ASSAYING. 2J before using, a lot of old crucibles and scori- fiers, or some worthless ore or rocks. Fig. 7 illustrates the Bosworth Crusher for laboratory use, and which runs by either hand or power. It has been highly praised. The value of whatever crusher is employed will depend mainly upon the ease, rapidity, and thoroughness with which it can be cleaned. Certain special apparatus, as hand-stamps and pulverizers, must be left to the necessi- ties and preferences of the individual assayer. 28 MANUAL OF A SSA YING. Pulverizing Plate and Rubbers. These are so useful and convenient that they can hardly FIG. 8. be dispensed with ; in fact, if much assaying is to be done, they will become absolutely necessary. They are represented in fig. 8. The iron plate, which should be perfectly true and have a smooth surface, is made of varying dimensions, as 12x12, 18x24, 23x24, 24x24, 24x30 and 24x36, in inches. It is made with no protecting rims, or with rims at the sides only (as figured), or with a rim at each side and at one end, leaving one end open. In some cases the side rims gradually shallow APPARATUS USED IN ASSAYING. 29 from the back to the front. The size I use, and with which I have no fault to find, is 18x24 inches (inside measurement); thickness of bottom, i inch ; rims, f inch wide and i-J- inches high ; weight, 150 pounds. (The only improvement I can suggest would be to have the back corners rounded instead of being right angles, in order to facilitate the removal of pieces of ore and the dust. Or the rims might be cast at an angle of say 30 instead of being perpendicular to the surface.) The rubber, rocker, pulverizer, grinder, muller, bucking-hammer (by which various names it is known), to go with above plate, is 8 inches long and 4 wide ; thickness at ends, i^ inches; in centre, 2-J- ; surface true and smooth ; weight about 14 pounds. Other rockers made are, in general dimensions, 4x5, 4X5-J-, 4x6, 6x7 an d 8xio inches. An axe-handle is fitted into .the socket on top of rocker, and then it is ready for use. The operation of grinding, or rubbing, or 30 MANUAL OF ASS A YING. pulverizing is described under the treatment of the ores in Part II. When a very hard ore is to be pulverized, it can much more quickly be finished with an 8X10 rocker, weight 60 pounds. The addi- tional weight and greater width have a marked effect. An intermediate size of about 30 pounds' weight would not be amiss. The plate can be placed upon a stout table, but it will be better in the long run to have constructed for it a special and substantial frame-work, as the long continued rubbing on the plate will eventually dislocate any ordi- nary table. The frame can have vertical legs as shown in the cut, or can have them set with an angle of a few degrees' spread at the floor to which they should be firmly screwed, using L-shaped plates of iron as the holders. Additional strength may be secured by insert- ing a thick shelf at about six inches from the floor, and this can serve as a resting place for the mortars where they will be out of the way. In Mr. S. A. Reed's laboratory the plate is APPARATUS USED IN ASSAYING. 31 set at an angle inclining toward the operator so as to allow of more effective pressure at the bottom, and slipped under the front end of the plate is a trough or gutter of sheet-tin or zinc, as shown in the figure. Its object is to catch any particles that may roll down the plate, and after the sample has been pulver- ized, the whole of the powder is brushed down into it. The trough is easily detached from the plate and its contents can then be brushed into a sieve. This simple device may replace one of the zinc sifting pans spoken of else- where. Sample Shovels. A pitch-fork with each tine transformed into a narrow trough would give a fair idea of the appearance of one of these shovels. A better form consists of two troughs from four to six inches deep united, with a space between, and provided with a long han- dle. These implements are more needed in sampling works proper than in the ordinary laboratory. Samplers (also known as dividers). One 32 MANUAL OF ASS A YING. form of these is shown in fig. 9, and consists of a frame with partitions running lengthwise FIG. 9 . it- at equal distances apart, and having each alternate space covered at the bottom. It is made of tin or copper, and it is well to have three sizes. A second pattern is represented in fig. 10. The first form, however, is preferred, as being FIG. 10. more durable. To use either, sprinkle over and across the broken ore to be sampled, and retain that which catches in the troughs, A pulp is sometimes sampled by the use of a sampler of tin, having troughs \ inch in dia- meter and T 3 T inch apart. To use, sprinkle the sample across, over a piece of clean paper, and separate that which goes between the troughs from that which catches in them. Af- ter putting aside the latter portion, sprinkle across the sampler the former portion, and so APPARA TUS USED IN ASS A YING. 33 continue until a quantity is obtained about sufficient for assay. Fig. 1 1 illustrates the Richards Pulverizer or laboratory "arrastre." It may be used in place of the grinding plate, or for the amal- gamation of small quantities of ores. (See, FIG. ii. in appendix, " amalgamation assay.") It is of cast iron, and is simply a mortar with its pestle revolving on a spindle and turned by a crank. The mortar has a trunnion attach- ment to aid in dumping its contents. Its diameter is 8^ inches, weight 65 pounds, and 34 MANUAL OF ASSAYING. price $10. The same apparatus, without the trunnion attachment, is also procurable. Sieves. A sieve of 80, 90 or 100 meshes to the linear inch is necessary. Such sieves are furnished of 5, 6, 7, 8, 9, 10, 12 and 15 inches diameter (6 to 8 inches is a good size), of copper or brass wire in a wooden frame. Those composed of horse hair are apt to deteriorate. The box-sieve of tinned iron, consisting of a sieve (of 80 to 100 mesh) with tightly fitting bottom to catch all the sifted material, and cover to retain the dust, is a valuable implement. A sieve which is better than the ordinary wood-bound pattern is one that is pressed or moulded out of the sheet gauze, and with no wooden rim to retain pieces of an assay which may afterward fall out to contaminate a suc- ceeding assay. It would require but little of a rich ore to make a worthless one appear valuable by the above acci- dent. Fig. 12 shows the idea. If the system of sieving and sampling that APPARATUS USED IN ASSAYING. 35 I speak of under the sampling of ores is adopted, there will be required a further set of four sieves of 2, 4, 8, and 16 meshes re- spectively, each 10 inches in diameter, and with frames of wood 3^ inches deep. A 4O-mesh sieve is useful for sieving cer- tain chemicals, and two common flour sieves are wanted for bone-ash and granulated lead. Zinc Sifting Pans. Fig. 13. These will be FIG. 13. found convenient, and are better than paper for sifting over. A pair is necessary, the material sheet zinc. Length in full 31 inches, of body 25 inches, of neck 6 inches, width of body 12 inches, of neck 2 inches, height of rim 2f inches, with upper edge turned over heavy iron wire. Spatulas and Spoons. By a spatula we mean an instrument shaped somewhat like a 36 MANUAL OF ASSAYING. table-knife (fig. 14), and used for mixing paints, ores, charges, etc. It may be of iron, steel, copper, platinum, silver, ivory, horn, porcelain or glass. A large one of steel or iron (such as painters use), length in full loj inches, blade 5! inches long by i^ wide, is a very good size for mixing ores and crucible charges. For weighing out ores FIG. 14. and mixing scorification charges, a smaller one of steel, length 6 inches, blade 3X| inch is useful. Two or three horn spoons, with or without handles, are serviceable for various purposes. SCALES AND BALANCES. Two balances will be sufficient for the ordinary work of the assayer ; a small one for weighing fluxes, ores, lead buttons, cupels, etc., and a more delicate one for very accu- APPARATUS USED IN ASSAYING, 37 rately weighing the gold and silver beads and gold residues. FIG. 15. Scales for Pulps and Fluxes. Considera- ble latitude can be allowed in the choice of such scales. Balances can be procured carry- ing 2, 5, 10, 20 or 30 ounces and upward, and ranging in delicacy from -^ of a grain to i 38 MANUAL OF ASSAYING. grain. For descriptions, illustrations, and prices of these and others, see the lists of the various manufacturers. Not wishing to puzzle the student too much, I specify but four : Fig. 15 represents as satisfactory a pair as can be wanted. It has a spirit level and two thumb-screws, movable scale-pans (3^ inch diameter), and when it is to be transported, all the parts on the box can be packed in the drawer. Its capacity is 10 oz. (about 311 grammes), and it is sensible to -fa of a grain (about 3^ milligrammes). Its cost is $22.00. (See Becker's list, No. 19.) A glass case in which to keep the scales is a good thing to have, and costs $6.00. Troemner makes a similar balance, capaci- ty 16 oz., sensibility -fa grain, diameter of pans, 4 inches, price $18.00. (See Troem- ner' s list, analytical scale No. 2, fig. 22.) A still cheaper but satisfactory balance, similar to the preceding, is likewise furnished by Troemner, capacity 8 pz., sensibility -fa APPARATUS USED IN ASSAYING. 39 grain, diameter of pans 3^ inches, price $15.00. It is represented in fig. 16. The FIG. 16. objections to it are that it lacks the spirit level and adjusting screws, so that it is not always easy to get it into perfect equilibrium. Directions for Setting-up and Testing. The various parts of the scales shown as fig. 15 come wrapped and packed in the drawer beneath. They should be carefully un- wrapped, rubbed a little, if necessary, with some soft, clean and dry buck or chamois skin, and put into place in the following order : A brass wire, somewhat U-shaped, is to be 4O MANUAL OF ASS A YING. run up from the under side of the top of the box stand through two holes. The ends of this wire pass through two holes in the base of the pillar (which is now standing on the box), and are there held by two screws, shown in the cut. Next the swinging needle (also variously known as the index needle, needle indicator, indicating rod, index pointer or pointer) is firmly screwed on to the centre of the beam, and the latter placed on the knife edges in the socket on top of the pillar. Upon the knife edge at each end of the beam is placed one of the little frames or stirrups having a knife edge and hook, the latter to point forward. It will be observed that each end of the beam and each stirrup is marked with one or more dots. They must, therefore, be put together appropriately, that is, the stirrup with say two dots is to be placed on that end of the beam which also has two dots, and so on. The wire frames that support the scale pans are now taken, the brass piece at bottom of each swung out APPARATUS USED IN ASSAYING. 41 at right angles to the wires, and the frames suspended from the hooks at end of beam. The pans can then be placed in their proper positions. The leveling screws, shown at the front corners of the box, are now put in place, and the scale is ready for testing and after- ward for work. To test, turn the leveling screws until the bubble of air in the spirit level is at rest in the centre of its circular case ; push down the lever shown in front of the graduated scale, thus allowing the pans to swing freely, and gently vibrate the needle by directing a slight puff of wind from the hand upon either pan. The needle should vibrate to the same distance on either side, less a small fraction every time due to the decreasing momentum, and when it has finally come to a condition of perfect rest it should be exactly in front of the central division of the gradu- ated ivory scale. If the scales are not in good order there are no means of adjusting or correcting (save 42 MANUAL OF ASSAYING. such as the natural mechanical ability of the owner may suggest), and the best plan would be to exchange them for a more perfect pair. This is not likely to be the case, however, more especially since such scales are not required to be very delicate. The directions I have given above for the setting up of the scales shown as fig. 15 will apply, slightly modified, to any other and similar pairs. Whatever pair be used, it is advisable to take two large watch glasses, in diameter a trifle less than that of the scale pans, and file down one or the other till they balance each other perfectly. Weigh all charges in these, thus avoiding any danger of corrosion or at- trition of the scale pans. A soft brush should be employed to brush out the contents of the glasses. 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 case many crucible assays are to be made APPARATUS USED IN ASSAYING. 43 (requiring the weighing of many fluxes), a great deal of wear and tear of the balances described can be avoided by substituting hand-scales, which are cheap and serviceable. They are made with brass beam, from which horn scale pans are suspended by means of silk threads (fig. i 7). They can be se- FIG. 17. lected irom a dozen sizes, the length of beam ranging between 4 and 12 inches (7^ or 8| is best prices $2.75 and $3.00). Support them on a nail by the ring at the top, and use them for any and all weighings save those of the ores. Of course no watch glasses need be used with these scales. Their sensibility is from -fa to iro rain - Occasionally it becomes necessary to weigh large quantities (pounds) of ores, fluxes, etc. 44 MANUAL OF ASSAYING. Use whatever scales are easiest obtained ; I need not go into detail concerning them. Balances for Weigh ing Gold and Silver Beads. Here likewise is a range of choice, and per- sonal preference comes largely into play. When the assayer intends to travel consid- erably, the balance now spoken of will be the most suitable. Length 9 to 9^ inches, height Q| inches, width from 3 to 4 inches. It packs into a light box, and by means of a strong leathern strap can be carried by the hand. Total weight, boxed, about 4^ pounds. With the proper weights, this balance will weigh Y 1 ^ milligramme, and by use of the swinging needle and ivory scale will indicate -fa milli- gramme. It is made both by Becker (No. 2 of his list) and Troemner the prices, with weights (i gramme down to y 1 ^ milligramme), being $75 and $65 respectively. When the balance is not liable to be moved around very often, that shown in fig. 18 will serve nicely, and is considerably cheaper. The APPARATUS USED IN ASSAYING. 45 needle indicates \ of a milligramme, and each pan can bear a load of 25 grammes. Price FIG. 18. $55.00 of either Becker (No. i) or Troemner (No. i). A similar but larger and somewhat more o delicate balance is made by Becker (No. 3 price $78.00). The needle indicates 10 divis- ions on the scale for i milligramme. The greatest objection to all of the preceding bal- ances lies in the fact that they have no grad- uated beam to carry a rider to show the weight below 10 milligrammes, but instead indicate o 4 6 MANUAL OF ASSAYING. it by the deviation of a needle. The follow- ing possess this advantage. Fir.. 19. Troemner's No. 2. (fig. 19 of this book) is a fine balance. The beam at the right is divided into tenths, each tenth numbered and corre- sponding to i milligramme, and furthermore each tenth is subdivided into tenths, so that by means of the movable rider carried by the rod (seen in the upper right portion of the engraving), a button of -^ milligramme can easily be weighed. And more ; since the spaces between the ^ milligramme divisions are appreciable, by placing the rider half-way APPARATUS USED IN ASSAYING. 47 between any two, a weight of ^V f a gramme can be determined. Price of this balance, $80.00. FIG. 20. There is a still larger balance (Becker No. 5, Troemner No. 3 price $95.00) which is more delicate and better firiished than the preceding. 48 MANUA L OF A SSA YING. Fig. 20 is a good illustration of Troemner's " Extra Fine " new balance (No. 5), which is noticeable in having its beam of aluminium. Has a double column, with improved new ec- centric lift, that works smoothly and regularly ; beam divided on both ends ; glass case large and roomy, with heavy plate-glass bottom ; needle indicates forty full divisions for one milligramme. Price $175.00. Oertling, of London, furnishes a most ex- quisitely delicate and accurate balance (No. 12), represented in fig. 21, which is regarded as the best made. It is expensive ($175.00), but where very delicate work is required, as in weighing the gold residues from small quantities of low-grade ores, it is indispensable. Notes on Setting-lip the Oertling Balance. In mounting this balance, after the mechan- ism below the floor has been connected with the beam supports, and the standards (or cen- tral pillars) have been screwed in position with the thumb screw provided, the beam (with its index pointer) is put in its place. This APPARATUS USED IN ASSAYING. 49 must be done from the top, and care should be taken that the pointer is not bent in so doing. MANUAL OF ASS A YING. Now adjust the capstan-headed screws on top of the standards in such a manner that, when the beam is raised by turning the thumb screw in front, each screw will touch the beam at the same moment, and with the V-shaped support raise the beam uniformly. The pointer must also coincide exactly with the zero point of the ivory scale. A small APPARATUS USED IN ASSAYING. 51 pin is furnished with the balance for turning the capstan screws. Now the pans may be placed in position and each pan support adjusted in height by means of its screw so as just to touch the pan, when the beam has been raised from its bear- ings. Fig. 22 represents the Ainsworth balance, a recent but worthy rival to the Oertling. In general, it is similar to the latter, but is so constructed that any possible warping of the case will not affect the working of the bal- ance. The rider attachment is so arranged that any lost motion can be taken up. A magnifying glass is adjusted in front of the needle to show the slightest deviation. Sen- sitive to the T ^Q part of a milligramme. Price $175.00. See the price lists of the manufacturers quoted. It will be seen from an examination of the preceding illustrations that all the delicate assay balances are alike in their general con- 52 MANUAL OF ASSAYING. struction. Each consists of certain charac- teristic parts, as herewith described. First, a central pillar, or twa pillars, firmly attached to the floor of the enclosing case. Upon the top of the pillar or pillars is a plane bearing a V-shaped crotch lined with polished steel or agate (preferably the latter, in which rests the beam by means of a steel or agate knife edge. At each end of the beam is fixed a steel or agate knife edge, from which hangs a little frame with a steel or agate plane, and from the frame is sus- pended, by a long and thin wire, the stirrup carrying the detachable scale pan. From the centre of the beam depends a long, delicate index needle, which swings in front of a graduated ivory scale. From the right-hand side of the balance case of the Becker and Troemner balances, and from both sides of the Oertling and Ainsworth, extends inward a movable rod, controlled outside the case by a milled screw head. This rod manipulates a fine " clothes APPARATUS USED IN ASSAYING. 53 pin" of wire known as a " rider," which can be placed on any point of the graduated beam. By the employment of a simple mechanism the beam can be raised from its agate bear- ings to avoid unnecessary and wasteful fric- tion or injury by sudden shocks. This is done by turning the milled screw head shown in front. The scale pans are supported when the beam is raised by two little disks coming up from below. On the top of the index needle is a minute ball, which, by being either screwed up or down, raises or lowers the centre of gravity of the balance, and so either increases or diminishes its sensitiveness. At each end of the beam of the Becker and Troemner balances is a very small milled screw head which can be screwed in or out, and by them the beam is balanced. On the Oertling and Ainsworth, instead of these screws, a fine piece of wire is twisted around the little ball on top of the beam, and points 54 MANUAL OF ASSAYING. forward, and by turning it a little one way or the other the same object is accomplished. A circular spirit level, or two tubular ones at right angles to one another, at the base of the central pillar or pillars, will indicate whether the balance is or is not level ; the milled screw heads under the corners of the case are to do the regulating. The whole mechanism of the balance is contained in a wooden frame with glass on the four sides. Both the front and back win- dows slide up and down, and are locked with the same screw or key which controls the beam. Special Directions. The workmanship of a fine balance is as delicate as that of a watch, consequently the greatest care should be used in setting it up and in handling its various parts. Many excellent balances have been ruined or greatly injured by pure careless- ness, as by striking the knives, or by letting the beam fall suddenly on the central agate bearing, which will destroy the delicately APPARATUS USED IN ASSAYING, 55 ground knife edges, and, as a consequence, the high sensitiveness is lost. The agate hangers should be placed on the beam so that the marks on each corre- spond that is, each hanger or stirrup has a mark corresponding to one on the knife end of the beam to which it belongs, and, as the hangers are not made interchangeable, cor- rect placing should be observed. Care must also be used in handling the pointer or needle, that it is not bent. Should it scrape against the ivory scale when oscil- lating, lift off the beam, taking hold of it at the ends, and lay the pointer on a smooth, flat surface and gently bend the pointer down- ward; then replace the beam and note any improvement. If it still scrapes, remove beam again and repeat the operation, and continue this until the needle will oscillate perfectly freely. It is not advisable to have the pointer too far away from the ivory scale, as it makes it so much more difficult to read the result. 56 MANUAL OF ASSAYING. It must be remembered that all of the bal- ances described are very delicate pieces of apparatus, and should be guarded with the utmost care. They should be placed far from the heat of the furnace, and even away from the rays of the sun, tending to unequal ex- pansion and subsequent contraction. Shocks must be avoided and even continued gentle agitation, and they should be kept away from acid fumes (particularly those of nitric acid), and out of moist atmospheres. By having a small vessel filled with dry fused calcic chloride always inside the case of the balance, the moisture present will be absorbed by it, and thus prevent, in a measure, the rusting of the steel parts of the balance. When saturated replenish. These balances are provided with steel knives and agate bearings, spirit level and set-screws. By means of the latter and by observing the spirit level, the balance can be placed in a v state of perfect equilibrium, and it should always be kept in such. To ascer- APPARATUS USED IN ASSAYING. 57 tain whether it is in adjustment, throw the rest down, thus leaving the pans free, and vibrate the needle by a puff of wind from the hand. The needle should go to the same distance on either side, less a very small frac- tion due to the decreasing momentum. If it does, the balance is in equilibrium ; if it does not, adjust the difference by means of a little screw at one end or the other of the beam, or arrow in the centre. To test its sensibility place a one-centi- gramme weight in each pan and a rider at equal distances on each side of the beam, and see if in balance. If not, adjust as before. Now move one of the riders one of the small- est divisions the balance should respond quickly and distinctly, also with one-half of the smallest divisions (representing with a five-milligramme rider -^ milligramme). When not in use, the rest should not be left down, and on the other hand, when using the balance, it should not be brought up when the needle is vibrating, as this tends to throw 58 MANUAL OF ASSAYING. the knives off the agate bearings, and so work injury. With these balances, as with the ore scales, put the weights always in one pan, the mate- rial to be weighed in the other. Since the rider in most balances is used on the beam at the right, it is better to employ the right- hand scale pan for the weights. Do not leave the weights on the pan for too long a time. In high, dry altitudes, use care in wiping the glass doors of the balance, as electrical action can be excited which may affect the accuracy of the weighing. Particularly should any rubbing be avoided just before using the balance. Cover the balance when not in use with a thick woollen cloth, or heavy pasteboard box lined with flannel or similar material ; this to keep out dust. A very soft and fine camel's hair brush may be employed to cleanse the scale pans or other parts from dust. APPARATUS USED IN ASSAYING. 59 Finally, never use these balances for any other purposes than for weighing gold and silver beads, small pieces of silver or gold, etc. WEIGHTS. The assayer needs three sets : i st. A set in the French or metric system, ranging from 50 grammes down to i centi- gramme (10 milligrammes). Since they are not to be used for very accurate work, but only for weighing fluxes, lead buttons, and other comparatively rough purposes, they need not be very expensive ($5.00 to $6.00). 2d. A second set of metric weights, to be very accurate, their range from i gramme to Y 1 ^ milligramme, their use for weighing gold and silver beads. Such a set is included in the price given for the assay balance for gold and silver beads first men- tioned. Separately, they will cost $8.00 to $10.00. Fig. 23 represents a box of these weights. FIG. 23. 6O MANUAL OF ASSAYING. 3d. A set of assay ton weights. These are important, and should be very accurate. Their range is from ^ to 4 A. T., and price about $6.00. These weights are simply invaluable on account of their use requiring no calculations beyond a few multiplications or divisions. But this assay ton system of weights seems to be one of the bug-bears surrounding the art of assaying to many beginners, especially those advanced in years and opposed to prog- ress, and whose knowledge of weights is based entirely upon the arbitrary systems known as the troy, apothecaries', and avoirdupois. There is no difficulty in understanding it, and I think my explanations will make the matter clear to all. The assay ton system is not restricted to any one system of weights it can be applied to any, be it in use in whatever country. First, then, to illustrate its use : An assayer weighs, of an ore to be tested, \ A. T. (assay ton). As a result he obtains a bead APPARATUS USED IN ASSA YING. 6 1 of silver weighing 10 milligrammes. If ^ A. T. produces 10 mgrs. (milligrammes), i A. T. of the ore will produce 10x5=50 mgrs. of silver, and the assayer reports the ore as car- rying 50 ounces of silver to every ton. If 4 A. T. of the ore were used and a 10 mgr. button obtained, then -^ or 2\ would be the number of ounces per ton of silver that the ore would produce. The simplicity of the arithmetic, rapidity of calculation, and diffi- culty of making mistakes are all apparent here ; there remains only to explain the con- nection of the A. T. with our ounces, pounds, and tons. In this particular case the French or metric system of weights is the one employed as a basis ; but that is immaterial, as will be shown further along. To proceed : i ton avoirdu- pois=2,ooo pounds avoirdupois; i pound avoirdupois=7 > ooo grains Troy ; therefore, i ton avoirdupois=7,ooox 2, 000= 1 4,000,000 grains Troy ; i ounce Tr5z=48o grains Troy; 62 MANUAL OF ASSAYING. hence 14,000,000 divided by 480 equals 29,166 ounces Troy in i ton avoirdupois. Now the assay unit, called the assay ton, is (in this case) a weight of 29.166 grammes (a gramme being equal to 15.4 grains Troy), or, (i gramme being equivalent to 1,000 milli- grammes), 29,166 milligrammes. Hence the relation of milligrammes to ounces is as i to i in other words, a milligramme corresponds to an ounce, so that if by assay of i A. T. of the ore we obtain gold or silver to the amount of 4 mgrs., then, without any calculation, we know the ore will run 4 oz. to the ton. The above calculation starts out with the short or American ton of 2,000 pounds. The long or British ton weighs 2,240 pounds, but we can use it in like manner as a factor, thus : 7,000x2,240=15,680,000; 15,680,000 divided by 480 equals 32,666. Hence the unit of an assay ton system for Great Britain or Canada, based on the ton of 2,240 pounds, would weigh 32.666 grammes, and accordingly as we took fractions or multi- APPARATUS USED IN ASSAYING. 63 pies of it in assaying ores, so would our resultant beads of the precious metals be fractions or multiples of an ounce per the long ton. Those who may object to the metric sys- tem can still use the assay ton system by making the unit a weight of 291.66 grains Troy, or 326.66 grains Troy. In actual work, it has been found that \ A. T. of the gramme system equals 5.83 grammes, equals 90.01 grains Troy, is a good quantity of ore to use in a scorification assay. An equivalent amount, or nearly so, in the grain assay ton system first given, would be \ A. T. equal to 97.22 grains. The adoption of any system of Assay Ton weights avoids long calculations and the use of tables. By employing a whole number for the weight, then dividing the result by the said number and multiplying the quotient by 29.166 or 32.666, we obtain the same figures as by the Assay Ton system, but this necessi- 64 MANUAL OF ASS A YING. tates considerable multiplication or the use of previously prepared tables. Besides the above three sets, it will be found desirable to have a fourth set of grain weights, which may range between 1,000 grains and y^ grain, or 300 grains and -^ grain. They need not be extremely accu- rate. The first set will cost $10 or $11; the second $2. It is sometimes necessary to weigh a bead, button or other object directly in grains, when these weights will be handy. For large weighings in pounds, the proper weights will usually be found to accompany the scales.* (See tables of weights in appendix.) FURNACES. There are three distinct and separate ope- rations to be performed in an assay furnace * If many gold bullion assays are to be made, the assayer will find it extremely convenient to have a set of so-called "gold weights." (See the article " The Assay of Gold Bullion.") APPARATUS USED IN ASSAYING. 65 roasting, crucible fusion, and muffle work (i.e. scorification and cupellation). In an assay laboratory of any extent, where many assays are daily performed, it will be advantageous, if not imperative, to have a special furnace for each of the above classes of work, but ordinarily the assayer can man- age to get along with one. It is requisite, then, that the one selected be adapted to carry on all the aforementioned operations. As to the particular kind he must consult his individual preference and his purse. I can- not here describe all the varieties of furnaces which have from time to time been devised ; all I can do is to speak of a few considered the best. The heat-supplying medium of a furnace may be any one of three kinds of fuel, which fact, therefore, will serve to form a classifica- tion of the furnaces themselves into three divisions: A. Furnaces employing gaseous fuel. B. Furnaces employing liquid fuel. 66 MANUAL OF ASSAYING. C. Furnaces employing solid fuel. Strictly speaking, the heat in any case comes from the combustion of a gas, for whether the fuel be liquid or solid, the burning matter is either the liquid transformed into gas, or it is gas driven off from the solid fuel, But the distinctions drawn will do well enough for my purpose. A. Fitrnaces Employing Gaseous Fuel. These are the so-called gas furnaces, mean- ing thereby that the source of heat is our common illuminating gas. But as this fuel will not be on hand for the majority of those for whom this book is written, they are re- spectfully invited to pass over the following dozen pages. The furnaces I am about to describe are made by the Buffalo Dental Manufacturing Company. This company manufactures fur- naces for either crucible or muffle work, or both, some of which require a blast, others only the natural pressure of the gas. The student is APPARATUS USED IN ASSAYING. 67 referred to their circulars, also to Mitchell, pages 79 to 100. FIG. 24. 68 MANUAL OF ASSAYING. Figure 24 gives a very faithful representa- tion of a group of gas furnaces as it was de- signed by and arranged for myself. Its duty is to do roasting, crucible fusions, scorification and cupellation. The furnace at the left is for roasting sulphurets or other FIG. 25. ores, for experimentation or actual work. It is what is known as a Fletcher No. 163 (shown in section as fig. 25), and consists of a fire- clay body strapped with sheet-iron bands, and a burner (No. 16 Fletcher). The opening at APPARATUS USED IN ASSAYING. 69 the top (protected when not in use by the cover shown) is to allow the heat to have full play upon the roasting-dish placed on it. The heat and flame pass from the burner through the furnace and out and up the chim- ney-pipe. The funnel-shaped pipe over the cover is to catch and draw the fumes up the chimney. When the burner is lighted a most powerful draft 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 bore rubber tub- ing. A east-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 mid- dle furnace, for crucible fusions. It, likewise, consists of a furnace and burner. The latter is a Fletcher No. 15, of same construction, however, as the No. 16. The furnace proper (shown in detail in fig. 26), is made in five parts, the central section (a cylinder of MANUAL OF ASSAYING. fire clay), the bed- plate upon which it rests, and which has an opening for the flame to pass through, the cover (with handle attach- ed), and which also has an opening filled by a plug, all of fire' clay, and finally a plumbago lining, rubber tube, chim- ney connection and damper, as with the other furnace. Finally, at the right, is shown a furnace for scorification and cupellation, and which I have, I think fitly, designated as the " Moni- tor." Fig. 27 shows it enlarged and uncov- ered. In form it is almost that of the re- verberatory furnace, the movable bricks, when in place, being the roof. Looking at it from FIG. 26. APPARATUS USED IN ASSAYING. J\ another point of view, it may be described as a muffle with the flame as well as the heat inside. Its exterior dimensions are as fol- lows: 20 inches long, 7 inches wide and 5^ inches deep. In the interior, upon the bot- FIG. 27. torn, are four little wedge-shaped bridges of fire clay, which are movable, and upon them rests a false bottom or floor, also movable. The latter corresponds to the muffle bottom of an ordinary furnace, and upon it is done 72 MANUAL OF ASSAYING. all the work. It is 3^ inches wide by 7! inches long and \ inch thick, and has a shoul- der or bench running across its entire width on the end nearest the burner. The cover- ing bricks, four in number, are each 7 inches long by 2f inches wide and if inches high, each with a slotted bridge for its convenient handling. The burner is the No. 16, Fletcher. Similar connections to the first-mentioned furnaces. The 3-inch stove pipes of all three furnaces are fitted into one long horizontal pipe, which fits snugly into the chimney. The bench or table upon which rest the furnaces described, is made of pine, well seasoned and firmly jointed, to resist as much as possible the warping influence of heat and to support the weight of the furnaces and table tiles. Its dimensions, not figuring on the top, which overlaps i inch all around, are : 4 feet 6 inches long, i foot 7 inches wide, and 2 feet i inch high plus the thickness of the top, which is if inches. A double coat APPARATUS USED IN ASSAYING. 73 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 2\ inches width and \ inch thickness, and of such lengths as to alternately overlap at the angles, making smooth joints. The top of this sort of wall is f inch above the bed of the table. Upon the latter are 114 fire-clay tiles, or, rather, 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 3^ inches by 3 inches across and if inches high. They are so arranged on the 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 some- what on the fire-clay portions of the furnaces. A f-inch bore gas pipe, with proper taps and nozzles, is screwed to the front of the table. 74 MANUAL OF ASS A YING. I have been somewhat lengthy in the above detailed descriptions, but have done so for the benefit of such as may care to duplicate the outfit. The manner of operating the furnaces is simple. As regards the roasting furnace it is merely to shut off the dampers of the other furnaces, turn on and light the gas, and regu- late the heat to suit the particular ore. (See under Roasting.} The control of the mix- ture of gas and air is made by means of the milled handle at the burner. Next as to the crucible furnace. Remove cover, turn gas on full at tap, light, and regu- late by milled handle. Crucibles that contain charges that are to be heated gradually can be placed in 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, I have made good fusions of refractory ores in 25 minutes from time of lighting. The furnace will take crucibles in size up to the Battersea APPARATUS USED 7 AT ASSAYING. 75 " S," which is 4^ inches across by 5 inches deep. Use no covers. Finally the " Monitor," for which I may claim, not originality (that belonging to Mr. Thomas Fletcher), but merely applicability and decided improvements in the form, the original one being the roasting furnace al- ready described. To manage it, remove the covering bricks, open the clamper and shut those of the other furnaces, turn the milled handle at the gas entrance to the burner back so as to allow a full flow of gas, turn gas on full at tap and light, and put back the bricks into place. In from 12 to 20 minutes the interior will be hot enough for work. The bricks are removed again, the charged scorifiers placed on the false floor, the bricks set. back, and the excess of gas turned off at the burner. When the charges have melted, slide the bricks aside more or less, and principally those nearest the burner, to admit of air for oxidation. In 76 MANUAL OF ASSAYING. cupellation, the gas is turned down more than in scorification. The time of performing either scorification or cupellation (which see) 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 consumption of gas is not far from 30 cubic feet per hour. It is not intended nor claimed that this furnace can take the place of one required to be run from TO to 12 hours per day, for here, of course, a solid fuel will be cheaper, but for small runnings of from i to 4 hours or so it is economical, as are also the others. For small laboratories, then, the advantages of this furnace are many: convenience of op- erating, whereby the assayer sees every step and stage of the operation, and so can tell when and where to change or improve ; com- fort in manipulation, for it does not heat up the vicinity of the furnace and the room itself (quite a desideratum in the summer time); APPARATUS USED IN ASSAYING. 77 perfect control of the source of heat, so that a higher or lower temperature, a reducing or oxidizing effect may be produced in an in- stant ; entire noiselessness, in which charac- teristic it is the superior of all blast assay furnaces; saving of time, which, for furnaces employing coke, charcoal or coal, is spent in " bedding down," feeding, breaking coke, etc. freedom from the annoyances of dust, ashes and smoke ; absence of waste ; and, finally, its remaining qualifications, which need not be dwelt upon, are simplicity of construction, durability and portability. The complete plant, as illustrated, costs very close to $75.00. />. Furnaces Employing Liquid Fuel. There are many varieties of furnaces that come under this heading, their fuel being refined petroleum, gasoline, etc. As with gas furnaces proper, some are intended for cruci- ble fusions, others for muffle work ; still others are for both. The air pressure in some forms MANUAL OF ASSAYING. is derived directly from foot bellows, in others from air compressed by an air pump. (Consult the circulars of the Buffalo com- pany already mentioned for descriptions of their furnaces ; also Mitchell, pp. 72 to 78.) Fig. 28 represents Hoskins' Hydro-carbon Assay Furnace. FIG. 28. The apparatus shown in full above has now been in practical operation for several years in many parts of the country, and is past the experimental stage. There are many inconveniences and annoyances necessarily connected with the use of coke and coal fur- naces whereas this apparatus does away with all dust, ashes, constant replenishing of fuel APPARATUS USED IN ASSAYING. 79 and a large amount of radiated heat; in fact it has all the advantages of a blast gas furnace, with the additional advantage that it may be forced to almost any extent without the- use of a blower, and being at the same time auto- matic. The maximum expense of running is about five cents per hour, and in our large cities will not exceed three cents. Although there has been and is a prejudice against gaso- line as a fuel, this apparatus, as will be seen from its construction, is perfectly safe, and no accident can occur except through gross care- lessness. FIG. 29. Fig. 29, P is an ordinary force pump, at the bottom of which, at A, is* a valve whfch closes automatically upon releasing the pres- 8O MANUAL OF ASSAYING. sure from the pump; C is a check valve, which closes the inlet to the tank T com- pletely; F is the filling screw ; V is the vent screw, for letting off the pressure when through ; H is the pipe leading from the tank to the burner D ; E is the burner regulator, terminating in a fine point, closing the orifice of the burner; S S are packing boxes. Upon opening C and pumping a few strokes a pres- sure is created in the tank and on top of the fluid, which is forced through the tubes of the heated burner, vaporizing the gasoline, which finally issues from the orifice at the end of E as a highly heated gas, and burns as such in a powerful blast. After once starting, the heat of the flame passing through the burner vapor- izes the fluid in the tubes, and hence the ap- paratus is automatic ; requires pumping up only once every quarter of an hour or half hour, according to the power of blast desired. Its action may be controlled from the heat of an ordinary Bunsen burner to that required to melt cast iron, etc. APPARATUS USED IN ASSAYING. 8 1 Fig. 30 represents the muffle furnace which is made in two sizes, one taking a C Battersea (inside measurements, 8 inches long, \\ inches wide, 3 inches high), and the other an F Battersea (inside measurements, 10 inches long, 6 inches wide, 4 inches high) FIG. 30. muffle. The inlet for the blast is opposite and below the mouth of the muffle, and cannot be seen in the cut. In this muffle everything can be done that can be done in the ordinary coal furnace muffle. Fig. 31 represents the crucible furnace made in two sizes, takingfromthelarge 5 Hessian (pinches high, 3 inch- es across top, outside), down. DIRECTIONS FOR USE. Close E, unscrew F, and in- troduce from two quarts to one gallon of gasoline, of 74 Beaume, according to the ca- MANUAL OF ASSA Y1NG. pacity of the tank. Replace F and close V ; open C one or two turns, and give three or four strokes of pump P, and close C. Heat the burner by igniting some of the fluid in a suitable vessel placed under the burner (an old scorifier will do to hold the gasoline) ; when hot enough apply a match and open E gradually until the action is more or less uniform. If no spray or liquid issues from the orifice, the burner is hot enough. If not hot enough, burn slowly until no liquid or spray issues. When sufficiently heated the blast can be made of any intensity desired by the use of the pump as above. To stop its action, shut the regulator E, or open screw V, or both ; when not in use the vent V should invariably be kept open. The mouth of the burner D should be two to three inches from the fire hole of the furnace. For high temperature and muffle work pro- ceed as follows : First, light as above, and heat inside of fur- nace to redness at least. APPARA TUS USED IN ASSA YING. 83 Second, place the burner against the inlet of furnace. Third, turn out the blast with E and im- mediately turn it on again without lighting it (or simply blow the flame out of the burner tube), when, if the furnace is hot enough, the gas will ignite inside of the furnace. The heat can be regulated as in the first method of burning. When- burning inside of furnace there must be no flame in the burner tube. C. Fitrnaces Employing Solid F^leL In this class are found the best known furnaces, using as fuel, wood, charcoal, coke, hard and soft coal, or mixtures of them. The furnaces themselves may be divided into two general classes, portable and permanent, accordingly as they may be intended to be moved about or remain fixed. I. PORTABLE FURNACES. Very many forms have been manufactured. Space compels me to reduce the description to three ; the Battersea, Judson's and Brown's. 8 4 MANUAL OF ASS A YING. The Battersea furnace is of fire clay, made in sections and bound with iron bands. Fig. FIG. 32. 32 is a sectional view of the muffle furnace, of which the following sizes are obtainable in this country : Height, Diameter, Sizes of Muffles, No. inches. inches. in inches. Price. c 27 i 4 y 2 9 long, 3*J high, 5^ wide $25 oo D 28^ i$y 2 10 " 4 * * 6 r 30 00 E 29^ i*U 12 4 * * 6 " 35 00 F 30 iiy 2 14 " 5 * * 8 ' ' 40 OO K 48 23 15 ' 6 " 9 " 80 00 APPARATUS USED IN ASSAYING. Judsori s Sectional Assay Furnace (patent- ed) is represented in fig. 33. Two sizes are specified. Dimensions in inches : , Muffle , .\'o. High. Wide. Deep. Long. Wide. High. 1 36 1 8 13 12 6 4 (Battersea J) 2 42 22 16 15 <) 6 (Battersea L) FIG. 33. No. i is made of part steel and part iron (weight about 300 pounds, price $45.00), or all 86 MANUAL OF ASSAY IXC. steel (weight 250 pounds, price $52.00). No. 2 is manufactured both entirely of cast iron, and part iron and part steel (the latter weighs about 450 pounds, price $60.00). For details concerning the preceding fur- naces consult the various catalogues and cir- culars of the manufacturers. Brown s Portable Assay Furnace. Fig. 34. - This furnace consists of a sheet-iron frame 27 inches high and 14 inches square, lined with fire-brick in sections, the interior being smooth and straight from top to bottom. The cover is cast-iron, and is ridged to lessen the danger o,f cracking. The muffle door is cast-iron, and is fitted with a circular open- ing, filled with mica, that the operations going on within the muffle may be seen when the door is closed. The draft-doors are also of cast-iron, and are provided with wheel open- ings to further regulate the draft. The circu- lar holes at bottom are in all four sides of the furnace, and serve to keep cool the true bot- tom of the furnace upon which the ashes fall. APPARATUS USED IN ASSAYING. 87 The muffle seen in the opening rests equally upon the fire-brick in front and in the rear of FIG. 34. the furnace, leaving a space of \ inch between the end of the muffle and the brick to allow the passage of fumes. The grate is formed of cast-iron bars, 10 88 MANUAL OF ASS A YING. inches long, i inch square, 6 in number, rest- ing upon a cast-iron frame. The space below the true bottom is to be filled with fire-brick or sand or other material convenient. The chimney hole is 5 inches in diameter, thus accommodating a stove-pipe of same dimensions. The bottom of this hole is 1 7 inches from the true bottom of the furnace, and 8 inches from the bottom level of the muffle. There is a handle upon each side of the fur- nace to allow more convenient handling. The furnace can take either H or J muffle of the Battersea pattern, Size H. Length, 10^ in. Width, s l 4 in - Height, 3% in. " J. " 12 " " 6 " "4 " but is better adapted for size J, the most com- monly used muffle. Entire weight of furnace boxed is 125 pounds. The above furnace possesses the following advantages : APPARATUS USED IN ASSAYING. 89 i st. Simplicity. Having no complicated parts to get out of order. 2d. Usefulness. It can be used both for muffle work and for crucible operations. 3d. Capacity. There is no other furnace manufactured of similar dimensions and weight which can accommodate so large muffles, and consequently produce so much work and so rapidly. 4th. Durability. Being made of heavy sheet-iron, it cannot be broken by handling nor injured by heating. 5th. Adaptability. Any fuel may be em- ployed for which the draft of the chimney is sufficient. 6th. Light weight. Boxed, this furnace weighs but 125 pounds, as against 250 to 400 pounds of other furnaces. 7th. Cheapness. This furnace is from one- third to two-thirds cheaper than any other furnace that will do as good work. Boxed for transportation, $20.00. (See advertisements in the appendix.) 90 MANUAL OF ASSAYING. II. PERMANENT FURNACES. Whenever an assayer becomes permanently settled in any locality, it may pay him to erect a brick furnace, which, under such circum- stances, possesses some advantages over the so-called portable furnaces. For descriptions of these, whether to be used for roasting, fusion, scorification and cupellation work, see Mitchell, pp. 57, 63, etc. The various stamp mills, smelting and samp- ling works, and mining corporations scattered throughout the West, have usually perma- nent furnaces burning coke, charcoal, soft or hard coal, which may profitably be imitated. Fi- ^S Sfives a vertical section, and fig- ?6 a o ., carbonates of potash and soda), is somewhat more fusible than either alone, the use of this carbonate is advisable in cru- cible assays, particularly of gold and silver ores. It should be ground to a fine powder and kept from the air, as otherwise it would rapidly absorb moisture. Its action is the same as that of the bi-carbonate of soda. j>. Cyanide of Potash (potassic cyanide). The cyanide which is sold in cakes can be used, after being pulverized, or, what is bet- ter, the so-called granulated cyanide, which is fine enough for all purposes. In case that in form of -cakes is on hand, it must be finely RE-AGENTS USED IN ASSAYING. 131 pulverized, which ought to be done in the open air, using an iron mortar, the top of which is tied over and around with a towel. Also it is well to breathe through a wet cloth wrapped around the head across the nostrils, for the cyanide is so poisonous that inhaling the fine dust even is a dangerous practice. Use the box sieve for sifting. Keep from the air, as this salt absorbs moisture therefrom. Employed in the lead assay. Action de- sulphurizing and reducing (that is, taking away the oxygen from metallic oxides and so reducing them to the condition of metals ; it is the reverse of oxidizing). 4. Borax Glass (sodic bi-borate). - - The most valuable flux the assayer possesses. He employs it both for the crucible and scorifica- tion processes for gold and silver ores, and the crucible process for copper and lead ores. It has a neutral action. The unfused borax, in powder, is often used in the lead assay. The ordinary borax of the shops contains from 30 to 47 per cent of water of crystalliza- 132 MANUAL OF ASSAYING. tion, which must be gotten rid of before the borax is fit for use. Borax, on being strongly heated, swells very considerably while losing this water, and then gradually sinks down into a clear liquid, which, on cooling, becomes the glass. Take a large size sand crucible ("S" of Battersea make) and carefully coat its interior with either dry chalk or chalk wash. Place this in a hot fire, and drop in small pieces of borax, letting the swelling subside some- what after each successive addition. It is well not to allow the. crucible to become more than one-third full of the melted borax, as, in spite of the chalk lining, it is liable to attack the crucible and run through. When thoroughly fused, appearing like wa- ter, pour into a frying pan coated with chalk or ruddle, and let cool. Powder in an iron mortar and sift through a 4O-mesh sieve. That which goes through had best be reserved for crucible mixtures ; the moderately coarse re- maining on the sieve will do for seorifications. RE- AGENTS USED IN ASSAYING. 133 A strong iron coffee-mill with teeth or jaws close together, will crush borax glass very finely, and in much less time than it can be done with mortar and pestle. An iron crucible can be employed in place of the sand one. It will color the borax somewhat, which, however, does no damage. 5. Flour. Wheat flour is serviceable in the lead assay, its action being reducing. But it is more commonly employed together with bi- carbonate of soda, forming what is known as 6. Black Flux Substitute. h. mixture of ten parts bi-carbonate of soda and three of flour. It can be used to great advantage in the crucible assays of all of our four metals. 7. Argol (crude bi-tartrate of potash; when pure called cream of tartar or hydro-potassic tartrate). This is a good reducing agent, and is much used in the lead assay, and in crucible charges for gold, silver and copper ores. The following list of the reducing powers of various reducing agents will be found to be 134 MANUAL OF ASSAYING. very useful. The values are approximate only, as no two samples of any one listed will reduce to exactly the same amount, but for all practical assaying they are sufficiently near. I have included only those substances which are procurable in alfnost any section of the country. TABLE OF REDUCING TOWERS OF REDUCING AGENTS. Ipart of ll'iil Reduce Parts of Metallic Lead Ordinary wood charcoal 22 to 30 Powdered coke 24 " hard coal 25 soft " 22 Wheat flour 15 Corn starch n% to 13 Laundry starch u}4 to 13 Pulverized white sugar 14^2 gum arable n Crude argol S/4 to &/4 Cream of tartar 4/4 to 6*4 See chapter III., iv., pp. 161-2 for methods of determining reducing powers of above substances. RE-AGENTS USED IN ASSAYING. 135 8. Common Salt (sodic chloride). Ordi- nary table salt. Very useful in -every cruci- ble assay. It serves somewhat as a protect- ing cover, and as a wash, bringing down from the sides of the crucible adhering metals or fluxes. If moist, place in frying pan and heat till dry, then crush free from lumps. >. Carbonate of Ammonia (ammonic car- bonate). Of very little importance, save to assist in the roasting of certain ores. It ex- erts a desulphurizing action. To be employed as a fine powder. 10. Nitre or Saltpetre (potassic nitrate). Ordinary saltpetre of commerce. Is a basic flux and oxidizing agent, and is used in the crucible assays of gold, silver and lead ores. Pulverize finely and keep dry. Determine oxidizing power as shown on page 162. n. Wood Charcoal (carbon, more or less impure). Very valuable on account of its reducing and desulphurizing properties. It exercises the latter action when employed in the roasting of antimonial and arsenical gold 136 MANUAL OF ASSAYING. and silver ores. Let it be in a fine condition, keep dry, and determine reducing power in same manner as for argol or cream of tartar. (See page 161.) One part of ordinary wood charcoal will reduce from 22 to nearly 32 parts of metallic lead from litharge, according to the purity of the charcoal. In the scorification assay of certain ores (arsen- ical, antimonial, etc.), charcoal exerts a beneficial action in breaking up the crust which sometimes forms on the surface of the charge. A few pieces of roughly pulverized charcoal introduced into the matrass in part- ing gold bullion, excite local action and so pre- vent the bumping of the nitric acid solution. There are quite a number of substances con- taining carbon in varying proportions, which, for the sake of their reducing action, might be used as substitutes for cream of tartar and charcoal, but not one of them is so effective as either of the two mentioned, and since the latter are so easily obtained, I refrain from extending the list given on page 134. RE-AGENTS USED IN ASSAYING. 137 12. Silica (silicic di-oxide). This is a valu- able acid flux, that is, it is to be used as a* flux for ores which are basic in character (as calc spar, dolomite, barytes, fluor spar, etc.), also for ores containing large quantities of iron oxides and carbonates and with little or no silica. It is required for the assays of cer- tain ores of gold and silver in both the cruci- ble and scorification processes, as will be shown. The best form in which to use it is as precipitated silica (sold very cheaply), since it is then in a very fine state of division suitable for intimate mixture with ores and fluxes. It should be perfectly dry. As substitutes, in emergencies, fine, clean, dry sand can be used, and some kinds of glass (which are silicates of soda or potash, with lime, lead, etc.). Lime glass is to be preferred, but on no account is lead glass, or any containing arsenical compounds or easily reducible metallic oxides, to be employed. Common window glass and ordinary bottle glass, broken finely, will serve, and will be 138 MANUAL OF ASSAYING. found to be free from objectionable metallic ingredients. There is no advantage gained in using these substitutes, since the precipitated silica answers admirably, only it is well to know what to make use of, in case supplies run out. /j>. Lead. In thin sheets, called lead-foil, this metal is occasionally necessary for cupel- lations, as described under the assaying of gold and silver, and in the gold bullion assay. It should be tested for silver. (See page 160). In the granulated form (when it is some- times called test lead) lead is as invaluable as borax glass for the scorification assay. It can be purchased of varying degrees of fine- ness and purity, or it can be made from bar lead by the assayer himself, as here directed. Melt pieces of the bar lead in any conven- ient vessel (odd sizes of sand crucibles, for instance), and when it is of a temperature just hot enough to char a splinter of wood, pour into a compactly-joined cigar box with- out a cover, or a strong starch box. Imme- RE-AGENTS USED IN ASSAYING. 139 diately give a gentle rotary motion to the contents of the box, till the lead begins to thicken, and emits a slight creaking noise, when the motion is to be increased to a final vigorous shaking from side to side. A min- ute or two of this latter, and the thing is done. Sift through a 2O-mesh or an ordinary flour sieve, and remelt that which remains on the sieve. When the entire batch has been thus granulated, assay for silver, following the directions on page 158. /^. Litharge (plumbic mon-oxide, yellow oxide of lead). -^-Employed mainly for the crucible assays of gold and silver ores. It should be dry, and free from any considera- ble amount of red oxide of lead, as this causes oxidation of silver, and consequently loss. Mitchell says: " Ordinary litharge can be easily freed from this oxide by fusing it and pouring it into a cold ingot mould, then pulverizing, and carefully keeping it from contact with air, as it readily absorbs oxygen, and if it be allowed to cool in the atmos- I4O MANUAL OF ASSAYING. phere, it will nearly all be converted into the red oxide." Litharge can quite easily be procured free from large quantity of red oxide, and if it is kept in a tightly-stoppered bottle or tin can with closely fitting cover, there is little dan- ger of conversion to this oxide. It is used to furnish metallic lead that serves as a solvent for the precious metals in the ore. When in the melted state it has the power of giving up its oxygen to almost all the metals (save gold, silver and those of the platinum group), converting them into oxides, and since these are generally ex- tremely fusible, they go into the slag. Thus we are able to separate gold and silver from any baser metals they may be combined or associated with. Litharge is a very powerful desulphurizing agent (see Mitchell, pp. 181 to 187), and also serves as a metallic flux. It may safely be stated that all litharge contains silver to a greater or less degree. RE- AGENTS USED IN ASSAYING. 141 It may be, and generally is, in small quantity, but it is absolutely necessary to determine the amount, and to allow for it in the calcula- tion of silver in any ore tested. For the determination of this, see page 154. White lead (ceruse, plumbic carbonate, or carbonate of lead), and sugar of lead (plumbic acetate), can be made use of as substitutes for litharge, but they do not act quite so well. 75. Iron. A good desulphurizing agent, and as such is much employed in the assay of galena or sulphide of lead. Wire of y 1 ^- inch diameter, and eight-penny nails are the cor- rect sizes. Iron filings can sometimes be used. 16. Silver. Can be bought as very thin foil. It is quite often needed in inquartation (which see). It should be tested for gold by dissolving -J- gramme in pure nitric acid. After the solution is complete, there should be no black specks (gold), no matter how small, in the liquid. There is generally no difficulty in procuring silver perfectly free from gold. 142 MANUAL OF ASSAYING. 77. Sulphur. Ordinary commercial sul- phur. It is the sulphurizing agent. Used in Aaron's crucible method to form mattes. (Oxide of iron and iron pyrites may be wanted for the assay of refractory copper ores they need no especial description.) WET RE-AGENTS FOR ASSAYING. The ivet re-agents necessary in the assaying of our chosen four metals, are but two in number ; distilled water and nitric acid. I. Distilled Water. It is not worth the while to give directions for the preparation of this liquid ; it is simply to boil water and con- dense the steam by those means most con- venient to the assayer. It can be purchased in the large cities, but is quite expensive. Pure rain water is a very fair substitute. The mail? point in any case, is to see that it contains no chlorine (indicating usually, chloride of sodium or common salt). Test the water for this element, by acidulating a clear sample with pure nitric acid, and adding a RE-AGENTS USED IN ASSA YING. 143 drop or two of nitrate of silver solution (made by dissolving one part of the dry nitrate of silver in twenty parts of distilled water). The water should remain perfectly clear, that is, theie should not be in it the slightest cloudi- ness or turbidity. If it does show this, reject, and prepare or secure a fresh supply. 2. Nitric Acid (\\y&ric nitrate). Indispens- able for parting, i.e., the separation of silver and gold by dissolving out the former. It can be procured perfectly pure, but should always be tested for chlorine, in same manner as is distilled water. Should it contain this objec- tionable ingredient, it can be removed by adding one drop of nitrate of silver solution and letting the acid stand in the light till the purple-black precipitate of chloride of silver settles to the bottom of the bottle. Then add a second drop, and let remain undisturbed as before. Continue these successive single drop additions until finally the last drop ceases to form any precipitate or milkiness in the acid. Draw off the clear acid and keep tightly stop- 144 MANUAL OF ASSAYING. pered. There are two reasons why chlorine should not be found in the nitric acid. First, it will tend to throw down, as silver chloride, the silver dissolved ,out of a bead by the nitric acid in the process of parting. Secondly, it indicates the presence of hydrochloric acid, and this acid forms aqzia regia with the nitric acid, which could easily dissolve the very small amounts of gold sometimes left after parting. RE-AGENTS FOR ANALYSIS. The other re-agents, wet and dry, used in the qualitative tests, analyses, and special pro- cesses, are the following : Acetic Acid. Needed in qualitative tests. Should be pure. Dilute with two parts dis- tilled water. Alcohol. Wanted in the copper analysis and perhaps as fuel for a lamp. Use either common alcohol or wood spirits. Ammonia Water (ammonic hydrate, caustic ammonia, aqua ammonia). If very strong, RE- AGE NTS USED IN ASSAYING. 145 dilute one part with two parts of distilled water. Bi-chromate of Potash (potassic di-chro- mate). Used in the volumetric determination of iron. Should be procured pure. Black Oxide of Manganese (manganese di- oxide). Necessary to aid in the preparation of chlorine gas. Does not need to be per- fectly pure. Bromine. Used to remove manganese from its solution, by precipitation, in the volumetric copper analysis. Agitate some of the liquid bromine with distilled water in a glass-stop- pered bottle, and use the resulting aqueous solution for the precipitation. Carbonate of Ammonium (ammonic carbon- ate, carbonate of ammonia). Needed in the volumetric copper analysis. Should be pro- cured chemically pure. Carbonate of Sodium (sodic carbonate, car- bonate of soda). Used in the volumetric cop- per and other analyses, to precipitate iron, manganese, blow-pipe test for manganese, etc. 146 MANUAL OF ASSAYING. Should be pure. Dissolve in ten parts dis- tilled water. Caustic Potash (potassic hydrate). One part of common stick potash, dissolved in ten parts of water. Caustic Soda (sodic hydrate). In stick form. Dissolve in distilled water four parts when wanted. Chloride of Barium (baric chloride, muri- ate of baryta). One part of the pure salt dissolved in ten parts of distilled water. Chloride of Calcium (calcic chloride). The dry, fused lumps, used to keep moisture away from fine scales. Need not be chemically pure. Citrate of Ammoniiim (ammonic citrate). Dissolve one part of the salt in ten parts of distilled water. Citric Acid. Pure, for volumetric copper and other analyses to keep iron in solution. Cyanide of Potassium (potassic cyanide, cyanide or prusside of potash). Pure, for the volumetric copper analysis. Ferrocyanide of Potassium (potassic ferrocy- RE-AGENTS USED IN ASSAYING. 147 anide, yellow prussiate of potash). One part of the pure salt, dissolved in twelve parts of distilled water. Hydrochloric Acid (muriatic acid). To be pure. One bottle may be of the concentrated, a second of a mixture of one part acid with four parts of distilled water. Hyposulphite of Sodium (sodic hyposulphite or thiosulphate). The pure salt is employed for the volumetric determination of mangan- ese, the chlorination test for silver, and as a precipitant for copper in the volumetric analyses of the ores of this metal. Iodide of Potassium (potassic iodide, iodide of potash). Wanted in the volumetric deter- mination of manganese and as a test re-agent for lead. When used for the latter purpose, it may be either in the solid form, or in solution in water one part in ten. Lime Water (calcic hydroxide). Place a very little slaked lime in a bottle ; fill with water and shake. Keep tightly corked, and, when wanted, draw off the clear liquid with- out disturbing the sediment. 148 MANUAL OF ASSAYING. Mercuric Chloride (corrosive sublimate). Needed only for the volumetric determination of iron, which see. Metallic Copper. Wire for battery pur- poses, sheet for amalgamation test in panning, and some pure to form test solutions in the volumetric copper analysis, will be needed. Metallic Iron. Pure, to precipitate copper from its solution, in the volumetric analysis of the latter metal. Metallic Mercury (quicksilver). Some that is impure can be employed to amalgamate the zinc plates of a battery, and some free from gold and silver will be wanted in the various amalgamation tests. Metallic Zinc. In plates, forming a part of a battery. As a re-agent, zinc in pencils, or granulated, will be needed pure. Nitrate of Silver (argentic nitrate, lunar caustic). See testing of distilled water for chlorine. Nitric Acid. A bottle of pure and concen- trated acid, and one of the common commer- RE- AGENTS USED IN ASSAYING. 149 cial (concentrated) for battery, should be on hand. Stannous Chloride (proto-chloride of tin, "tin salts"). For the volumetric determina- tion of iron. Sulphate of Iron (ferrous sulphate, green vitriol, copperas). In solution in water (of no particular strength) it is used to precipi- tate gold from its solution as a chloride, after the chlorination assay. Sulphate of Magnesiiim (magnesic sulphate, sulphate of magnesia, " Epsom salts "). In a pure state, to precipitate arseniates in the volu- metric copper analysis, as a test re-agent for phosphates, etc. Sulphide of Iron (ferrous sulphide, sulphuret of iron). See next paragraph but one. Can be purchased, or made by holding roll sulphur against a bar of red-hot iron. Sulphocyanide of Potassium (potassic sul- phocyanide). One part of the pure salt dis- solved in ten parts of distilled water. Sulphuretted Hydrogen Water (hydrogen I5O MANUAL OF ASSAYING. sulphide gas dissolved in water). Very use- ful in qualitative analysis. To generate it, fit together a simple piece of apparatus similar to fig. 89. The larger bottle, which may be of any capacity above six ounces, is provided with a doubly-perforated cork, through one hole of which passes a straight glass tube to nearly the bottom of the bottle, and terminat- ing in a funnel. Through the other hole a second tube passes a little way into the larger bottle, and bending twice at right angles, goes through the cork of the smaller bottle to nearly its bottom. A third tube leaves this smaller bottle and connects by a bit of rub- ber tubing with a fourth tube dipping into the receiving bottle containing distilled water. Place an ounce or two of sulphide of iron broken in small pieces in the bottom of the large bottle and fill half way up with ordi- nary water. The small bottle is to be half- filled with distilled water to wash the gas. Pour some common sulphuric acid into the funnel-tube, when the gas will at once be RE-AGENTS USED IN ASSAYING, 151 given off. To ascertain when the water in the re-agent bottle is saturated, hold the thumb tightly over its mouth, and shake. On releasing the pressure a little the thumb will be held down if the water is not saturated, but will be forced up, if the contrary is true. A little glycerine put in the re-agent bottle will help to retain the gas in solution. FIG. 89. Sulphuric Acid(v\\ of vitriol). A bottle of pure and another of common, both concen- trated. If dilute acid is wanted, mix, in a beaker, one part of the acid with five of dis- tilled water. Tartaric Acid. Used to retain iron, 152 MANUAL OF ASSAYING. alumina, etc., in solution, in the volumetric copper analysis and in qualitative analyses. The pure salt can easily be procured. MISCELLANEOUS. Bone-ash. For making cupels, which see. It is best to use a good quality. Chalk and Chalk Wash. Ordinary chalk, to be used dry, and the same finely ground and rubbed up with water, for coating cru- cibles, etc. Clay Lute. Fire-clay and sand, with solu- tion of common borax in water to bind them together. Horse and cow-hair may also be mixed with them. Riiddle (ferric sesqui-oxide, red oxide of iron, hematite). A lump for marking cupels and scorifiers, and a paint (prepared by put- ting an ounce or two of the fine powder with water in a bottle, and shaking) for marking crucibles, coating frying-pan, etc., are wanted. CHAPTER III. TESTING OF RE-AGENTS. * BEFORE proceeding to make the regular assays, the student will find it expedient to examine his re-agents, either to ascertain the presence or absence of silver (and in the for- mer case, to determine its quantity), or to learn their various strengths, as shown in their reducing or oxidizing powers. The following five divisions include all the requisite tests of re-agents : I. Testing of Litharge for Silver. II. Testing of Granulated Lead for Sil- ver. III. Testing of Sheet Lead for Silver. IV. Determination of the Reducing Pow- ers of Reducing Agents. V. Determination of the Oxidizing Pow- er of Nitre (Nitrate of Potash). 153 154 MANUAL OF ASSAYING. I. TESTING OF LITHARGE FOR SILVER. As stated in the chapter on re-agents, almost all litharge contains silver, generally as a small amount. However minute this may be, we must know exactly what it is, and allow for it in calculating the value of an ore. This we do by the crucible process, in the same manner as we should run an ore. (See Part II, Chapter I.) Mix very thoroiighly the particular lot of litharge to be examined, and sample as usual. Make the charge * Assay ton [Gramme Grain weights, weights. weights. Bi-carb. soda V z A. T 15 grammes.. 240 grains = y a oz. Carb. potash % " jVz " .- 120 " =54" Litharge i}4 ll 45 7 20 =i/4 " Charcoal, [ Any "] V 2 gramme ^gramme... 7*4 u Flour, -j one of j- i " i ... 15 Argol, ( these, j 2 grammes... 2 grammes.. 30 " Salt cover. Any one of the above charges will produce a lead button of from 1 5 to 20 grammes ( 1 3 1 to 308 grains). Mix everything well, and brush into an " S " * See Chapter I, pp. 60-4, for full explanation of these weights. TESTING OF RE-AGENTS. 155 Battersea crucible or its equivalent (4f inches by 4^ wide). Have the fire quite hot, and heat crucible till contents are in quiet fusion, which will be in from twenty-five to thirty-five minutes. Take out, let cool, break, and hammer button into shape. If the button is too large for any cupel, re- duce by scorifying, then cupel. (See " Scori- fication and Cupellation," Part II, Chapter I.) Weigh the resulting silver button, and de- duct its weight from the gold and silver bead obtained from any crucible assay where the same quantity of litharge has been employed. If more or less than i^ A. T. (or its equiva- lent in grammes or grains) is used, calculate and deduct accordingly. For example, one lot of litharge I have tested carried 0.75 (J) of a milligramme for the \\ A. T., which amount was made the factor for that particular lot. The above amount, equivalent to \ ounce per ton of 2,000 pounds, is of course very 156 MANUAL OF ASSAYING. small, and, in the calculation of the value of an ore running say 100 oz. and upward, need not be deducted from the weight of the silver bead, since the loss of silver by absorption and volatilization from such a bead while cupelling, would more than counterbalance it. But it is very important that it should be deducted in the case of a poor ore, and especially when there is a question as to the presence or absence of silver in any ore. For the sake of practice, it will be well for the student to perform this crucible assay of litharge three or four times. Many assayers, and particularly those newly entered into the profession, continually try to obtain litharge (and for that matter, granu- lated lead) free from silver, meaning that it shall contain absolutely no silver. But, in the first place, they cannot procure it, and, in the second place, if they could, there would be nothing gained, in my opinion, by using such, as I will endeavor to show. First, in assaying ores which might be rich TESTING OF RE-AGENTS. 157 in either gold or silver, it would make no dif- ference whether the litharge employed con- tained absolutely no silver, or the small amount it usually carries, for in the latter case its weight would not be deducted from that of the button for reasons just given. Sec- ondly, in ores very low in gold, it becomes very difficult, and sometimes impossible, to find the minute speck of gold left from the assay (particularly as the result of a scorifica- tion assay), even with the aid of the magnify- ing glass ; but when the litharge does contain a little silver, the latter not only leaves itself and the gold together in a visible and tangible form on the cupel, but it also serves to collect the gold during the process of crucible fusion, and retains it always thereafter. Thirdly, a small but known amount of silver in litharge, tests the assayer, his methods and practice, the litharge itself and some of the ores worked upon, for he ought to get the constant figure of the silver in the litharge when testing the 158 MANUAL OF ASSAYING. many worthless ores he is bound to examine in the course of his work. II. TESTING OF GRANULATED LEAD FOR SILVER. As in the case of litharge, all granulated lead must have its amount of silver deter- mined, which is done by the scorification process. Mix and sample as usual. Rub the interior of the scorifier with a little fine silica before pouring into it any of the lead ; it will serve to protect the scorifier from corrosion by the molten lead. Weigh very carefully 2 A. T., 60 grammes or 960 grains (2 oz.), of the lead, and pour into a 2f inch scorifier, and deposit on the top a piece of borax glass about the size of the head of a pin. Scorify and cupel as shown in the next chapter, and weigh resulting bead. The weight of the silver bead, divided by two, will give the number of milligrammes or fractions, that one assay ton (30 grammes, 480 grains, or i ounce) of the lead contains, which I TESTING OF RE-AGENTS. 159 have found to vary from T 3 milligramme to 1.2 milligrammes. Make a table of the amounts of silver con- tained in fractions and multiples of one assay ton, and post it in some convenient place for reference. I give an example of one particu- lar lot : 0.50 A. T. contains 0.40 milligramme silver. i. oo " " 0.80 1.50 " " 1.20 2.00 " " 1.60 If other weights of lead are used, calculate accordingly. Deduct silver, in proportion due to the amount of lead used, from beads coming from ores ranging less than 100 ounces; above that disregard it, as with litharge. As with litharge, make several runnings of the lot of lead. The reasons given for desiring a litharge with some little amount of silver present are almost equally applicable to granulated lead. l6o MANUAL OF ASSAYING. III. TESTING OF SHEET LEAD FOR SILVER. Sheet lead can generally be purchased re- markably free from silver, and as it is seldom that a piece of more than ten or twelve grammes (120 to 150 grains) in weight is re- quired, the quantity of silver such a piece will contain will be exceedingly small. Moreover, its chief use being to enwrap gold and silver beads for recupellation, this amount of added silver is too minute to counterbalance the loss of silver by volatilization and absorption. Sheet lead is sometimes employed to aid in cupelling gold beads that have been in- quarted, and here a loss or addition of silver is not important. But should the lead-foil be suspected of carrying any quantity of silver, its exact amount can be determined by cutting off from various parts of the foil, and in small shreds, two or four assay tons (60 or 120 grammes, 2 or 4 ounces), which are to be scorified and cupelled as usual. TESTING OF RE-AGENTS. l6l IV. DETERMINATION OF THE REDUCING POWERS OF REDUCING AGENTS. /. Argol (p. 133). Weigh out the follow- ing charge : Bi-carbonate of soda. . 15 grammes, 240 grains ( ^-oz.) Carbonate of potash.. 7^ " 120 " ( \ " ) Litharge 45 720 " (\\ " ) Argol 2 30 " Salt cover. Put into a small crucible (size " V " of Bat- tersea), place in a hot fire, cover, remove when thoroughly fused, cool, detach button from slag, weigh, following the directions given for the crucible assays of gold and silver. The result, divided by two or thirty, will give the number of parts of metallic lead that one part of argol is able to reduce from litharge. It ranges around 8.5 parts. 2. Cream of Tartar, or bi-tartrate of potash (p. 133). Same charge as abo.ve, excepting that the two grammes or thirty grains of argol are to be replaced by three grammes or forty- 1 6 2 MANUAL OF ASSA YING. five grains of the tartar. One part of pure tartaric acid will reduce 6 parts of lead, and the same amount of ordinary cream of tartar will reduce 6.4 parts of lead. j>. Charcoal (p. 135). Make up this charge : Bi-carb. of soda. . 2 A. T., 60 grms., 960 grains or 2 oz. Carb. of potash ..J " 7$ " 120 " "| Litharge 2 " 60 " 960 " " 2 " Charcoal i gramme or 15 grains. Salt cover. Use an " S" crucible. As previously stated, the reducing power of one part of charcoal varies between 22 and 32 parts of lead. The reducing powers of the other sub- stances given on page 134 are determined in a similar manner to the three quoted above, running coals and coke as for charcoal, white sugar as for cream of tartar, flours, starches, etc., as for argol, etc. V. DETERMINATION OF THE OXIDIZING POWER OF NITRE (NITRATE OF POTASH). Determine the oxidizing power of the fine, dry salt (p. 135) by the following charge : TESTING OF RE-AGENTS. 163 Bi-carb. of soda. . 2 A. T., 60 grms., 960 grains or 2 oz. Carb. of potash . .J- " yj- " 120 " " J " Litharge 2 " 60 " 960 " " 2 " Charcoal i gramme or 15 grains. Nitre 5 grammes or 75 grains. Salt cover. Use an "S" crucible, and treat as in the previous crucible operations. The difference between the weight of the lead button ob- tained and that found in the assay of the charcoal, divided by five or seventy-five, will give the oxidizing power of the nitre, per part. It is about four parts. PART II. ASSAYING PART II. AS SA YI N G. CHAPTER I. GOLD AND SILVER ORES. OCCURRENCE. Gold is found in large quan- tities in the native state, designated by the various names of free gold, flour, leaf, wire and nugget gold. The minerals which most frequently carry gold are oxide of iron, pyrites of iron and copper (known as auriferous sul- phurets), arsenopyrite, and tellurium ores ; of these, the most abundant are the first two. Minerals which less frequently are gold- bearing, are galena, blende, gray copper and " carbonate ores." 1 68 MANUAL OF ASSAYING. For a classification of silver ores I quote from Kustel's " Roasting of Gold and Silver Ores": " IMPORTANT SILVER ORES. The most important silver ores are those found in such quantities as to be an object of metallurgical operations. The principal min- erals of this kind are the following : A. Silver ores with 2invariable amount of silver. a. Sulphuret of silver, or silver glance, with 87 per cent of silver. It is of common occurrence. b. Brittle silver ore (stephanite), or sulphuret of silver and anti- mony. This mineral contains 68 per cent of silver, and is quite common, c. Polybasite, sulphuret of silver, antimony and some ar- senic, with 75 per cent of silver, d. Ruby silver. The dark red silver ore, or antimonial variety, with 59 per cent, and the light red silver ore, or arsenical variety, with 65 per cent of silver, are valuable minerals. e. Miargyrite, sulphuret of silver and antimony; 36.5 per cent of silver, f. Horn silver, or GOLD AND SILVER ORES. 169 chloride of silver, with 75 per cent of silver. g. lodic and bromic silver of yellow and green colors. B. Argentiferous ores with variable amount of silver. a. Stromeyerite, or silver copper glance, a sulphuret of silver and copper con- taining up to 53 per cent of silver, b. Stete- feldite, with 25 per cent of silver, is an oxide ore. c. Silver fahlore, argentiferous gray cop- per ore. It contains silver in very variable proportions up to 31 per cent. This ore is quite common, and for this reason is impor- tant. It is also one of the most rebellious ores, containing copper, antimony, arsenic, sulphur, lead, iron, zinc, and sometimes gold and quicksilver, d. Chloride ores (so-called), mostly decomposed ores, generally of an earthy appearance and different colors. They contain more or less finely divided chloride of silver. C. a. Argentiferous lead ores, galena, or sulphuret of lead, lead glance. "Generally, this is not rich in silver, containing from $20 to I7O MANUAL OF ASSAYING. $60 per ton. Specimens assay sometimes as high as $300.* b. Cerussite, carbonate of lead. If pure, without admixture of copper and other carbonates, it is poor in silver in most cases, c. Argentiferous zinc blende, sul- phuret of zinc. Pure zinc blende contains usually only traces of silver ; often, however, it assays well, even up to $400 per ton. d. Argentiferous pyrites. Copper and iron py- rites are poor in silver, but often auriferous. There are, besides, numerous classes of decomposed silver ores, generally of earthy nature ; also, half decomposed ores which have lost their metallic glance, having a black or bluish-black color, and being generally cupriferous." f ASSAY. We can best consider the system- atic fire treatment of gold and silver ores, by dividing it into a series of operations, and taking each in turn and in detail. * I have found them as high as $1,500 per ton. (W. L. B.) f See appendix for extended lists of the minerals of or contain- ing gold and silver. GOLD AND SILVER ORES. The three main divisions are : I. Preparation of the sample. II. Scorification process. III. Crucible process. I. PREPARATION OF THE SAMPLE. The first thing to be done in the treatment of an ore, whether it is to be assayed for gold, silver, copper, lead, or any other metal, is to place it, that is, to label it. This is best ac- complished by giving to it a running number, never to be repeated. By adopting this sys- tem of numbering all samples, any danger of confusing specimens from various mines or parts of the same mine or vein, is entirely gotten rid of. Have a notebook at hand, and, in it, under the number, write such items as may be necessary or useful, as the date when sample was received, name of person sending it, character of the ore, nature of the charge, weights employed, calculations, etc. To pieces of the ore which are to remain whole, affix gummed labels, bearing the same 172 MANUAL OF ASSAYING. number. To preserve the final pulverized samples, bottles of about four ounces capacity, cork-stoppered, and similarly labelled, can be employed, or what is even better, pasteboard boxes in size about 5^ inches long by 3^ inches wide and 2 inches high, will be found to be very serviceable. They can be written on, thus requiring no labels. The next step is to secure an average sample for assay, and its importance cannot be over- rated. An ore is by no means of uniform character, being, in general, made up of the gangue or valueless portion of the ore, through which are scattered the valuable minerals. Therefore, unless the sample finally chosen for assay represents an average of the entire lot, being a mixture in the same proportions, of the richest, the medium and the poorest portions, as in the original ore, the assay itself is worthless, no matter how carefully it may have been performed.* * In this connection, I would refer the student to an article "On the Commercial Sampling of Minerals, "by Mr. L. S. Austin, of Salt Lake City, Utah, which appeared in the "Engineering and Mining Journal" (July 22, Aug. 5, Aug. 26, and Sept. 16, 1882). GOLD AND SILVER ORES. 173 To illustrate the averaging, take a quantity of ore weighing fifty pounds, which may be as a single lump, or, better, the result of the selection of samples across a section of the vein. In order to get a fair average, it is not necessary to operate on a larger quantity than this amount, for above it, should come in, as a more practical test, the mill-run. With a heavy sledge-hammer, break up the entire mass into pieces of about the size of a hickory-nut. Should the rocks be so large or so very hard as to obdurately resist the ham- mer, they may be brought into submission by that process called " astonishing," by Prof. Chapman, in his valuable little work. It con- sists in heating red-hot the resisting pieces, and plunging them while thus into some cold water in a pan. This heroic treatment will either at once reduce the lump to small pieces, or render it so friable that light pound- ing will pulverize it. Pour off the water and dry the contents thoroughly, th'en break into small pieces as directed. Transfer to a large 174 MANUAL OF ASSAYING. sheet of heavy brown or manilla paper, then, with a large iron or steel spatula, thoroughly mix,' by turning over and over and by stirring in together with the dust, the finer and coarser particles, till satisfied that the whole is a homogeneous mixture. (At this stage of the operation it is a good plan to reserve a characteristic lump or a few pieces, from an examination of which the nature of the ore may be determined, and process of treatment decided upon.) Now divide in halves by means of a very large spatula or piece of heavy sheet brass, 18 inches long by 4 inches wide, and -J-inch thick. Break up still finer (to the size of a hazel-nut or less) the half selected. Mix again and halve as before. Continue the crushing, mix- ing and halving until about one pound has finally been sampled down. [57 FIG. 90. GOLD AND SILVER ORES. 175 Instead of halving, the piles may be quar- tered, and two of the diagonally opposite quarters taken as a half. Fig. 90 shows the pile entire, divided, quartered, and two of the quarters removed ; parts i and 4, or 2 and 3, are to be put together. When the ore to be assayed is less than fifty pounds, ranging down to a pound or two, it can be broken still smaller in the successive steps, and when it is but a few ounces in weight, the whole of it should be crushed and pulverized, as directed. Wet or damp ores and pulps should be dried before pulverizing. The student must exercise his judgment in a measure, with regard to the sampling of an ore, simply remembering that the object, as before stated, is to obtain a final product which shall be an exact counterpart, in rela- tive proportions, of the metals and gangue of the original ore. Instead of halving, the broken ore may be taken up on a sampling shovel, and thrown on a tin or copper sampler, making it a rule I 76 MANUAL OF ASSA YING. to reject either all that which goes between the prongs or ribs, or that which remains up- on them. These two articles are convenient, but not necessary. The third step is to pulverize the sample finally obtained, which may be done very sim- ply though somewhat laboriously (depending considerably upon the nature of the ore), by means of an iron mortar and pestle. A towel wrapped loosely around the pestle and across the top of the mortar will prevent loss due to flying particles. Sift through a sieve of eighty or ninety or even of one hundred meshes, since the finer the powder, the more quickly will it be acted upon in the furnace. Ores which contain much clay or lime are very apt to clog the meshes of the sieve so that little will pass through. This may generally be obviated by placing in the sieve an ounce weight or equal- ly heavy piece of smooth iron, the movement of which in shaking keeps the meshes open. Do the sifting over a piece of brown paper, GOLD AND SILVER ORES. 177 and be sure that all the sample passes through the sieve, for the few minute parti- cles or scales, that might remain on the sieve and be hastily thrown away, could be of suffi- cient value to vitiate the assay. I might give here, however, a little suggestion made me by Mr. H. H. Corbin, of Telluride, Colo. Cer- tain ores contain free silver (with a little gold in it, sometimes), to such an extent that while they will not produce many scales, yet there may be a few left on the sieve. In such cases dump the scales on the grinding plate and cover them with the finely-powdered ore which has already gone through the sieve. Grind heavily for quite a little while, then sieve again. It will be found that most of the scales have been ground by the ore (particu- larly when the latter is quartzose), fine enough to go through a loo-mesh sieve. If they will not, repeat the treatment until they will. Three grindings will usually suffice. The sievings are to be very carefully mixed. Even all this trouble is less than that of the 178 MANUAL OF ASSAYING. ordinary scale method of treating ores con- taining the precious metals in the free state. (See in appendix, 4< Assaying of Ores con- taining Free Gold or Free Silver".) Mix again the fine powder, and with a large brush transfer to the properly marked box or bottle, when the sample is ready for assay. Do not shake the box or bottle between the times of grinding and weighing, as this tends to cause the gold, silver, sulphurets, or other heavy minerals to settle, resulting in an un- equal distribution of the various constitu- ents of the ore. If much time elapses be- tween the weighings and the second treat- ment the ore should be remixed. When very many assays have to be per- formed daily, the rubbing-plate and rubbers will be found so very convenient and so time- and-labor-saving, that they will become almost necessities. (See pp. 28-31 for description.) The operation of grinding, or rubbing, or pulverizing, is managed as follows : The ore, previously broken into fine pieces as directed, GOLD AND SILVER ORES. 179 is placed upon the clean surface of the plate, the rocker is now laid upon it, and with one hand firmly pressed upon the body of the rocker, and the other grasping its handle, it is moved backward and forward with an oscil- lating motion. This knack of grinding, al- though not easy to describe, is soon acquired. After grinding, the plate should be thor- oughly cleaned, which can be done by rubbing on it either sand, quartz, broken glass, com- mon salt, old cupels or scorifiers, broken cru- cibles, the slags from scorifications, or some worthless ore, finishing with an old rag. Very great pains should be taken to perfectly clean the plate after grinding much free gold ore or such rich ores as tellurides. In place of the sheets of brown paper al- ready mentioned, and which quickly become soiled and full of holes, the zinc sifting-pans (p. 35, fig. 13) can be used to advantage. To guard against loss of dust, the tin box- sieve (p. 34) is recommended. There is an- other laboratory plan for systematic sampling, ISO MANUAL OF ASSAYING. which is very fair, though slow and best suited for small lots of from 5 to 20 pounds of ore. For this the assayer needs four sieves in addition to the fine one they are 4, 8, 16 and 32-mesh, respectively. Crush the sample so that it will just about go through the 4-mesh sieve, mix thoroughly, divide in halves, reject one-half, and crush the remainder so it will just pass through the 8-mesh sieve. Again mix, divide in halves, reject half, and crush the other half for the i6-mesh sieve. Mix, halve, reject half, and crush for the 32-mesh sieve. The half kept from this is all to be pulverized and put through the loomesh. All this insures thorough mixing and uniform crushing and sampling. Having now finely ground the ore to be assayed, we must next decide how to treat it. There are two methods of assaying gold and silver ores, the scorification and the cru- cible. The process to be chosen depends chiefly GOLD AND SILVER ORES. l8l on the nature of the ore. In general, we may say the scorification process is better adapted for all silver ores, and for rich gold ores (in- cluding telluride ores of any degree of rich- ness). The crucible process serves better for low grade gold ores. The advantage of this pro- cess lies mainly in the fact that it enables us to operate upon a larger quantity of ore; oth- erwise it is no better than the scorification method and indeed in many respects the lat- ter is to be preferred. The scorification process is so much simpler to use, easier to comprehend, and so satis- factory in its working, that I shall give it the first place in this manual. II. SCORIFICATION PROCESS. The object of this process is to so act upon an ore with heat, access of air, and certain re-agents, that the precious metals shall be driven out of their combinations with the impurities of the ore (or if free, separated I 8 2 MA NUAL OF A SSA YING. from them), and be retained alloyed with another metal, lead, and from which they can afterwards be separated. The chief re-agents are lead, in a granu- lated condition, and borax glass. Besides these, silica, iron, and bi-carbonate of soda are occasionally employed. The ore, mixed with the 1'ead, and covered with the borax glass or other flux, is put into a scorifier and subjected to heat in a muffle. Under the action of the heat, the lead melts, and being scattered throughout the ore, seizes upon the gold and silver and set- tles with them to the bottom of the scorifier. The borax o-lass or other flux attacks the o gangue and impurities present, and uniting with them and with litharge resulting from oxidation of some of the lead, forms a slag or glass, which floats upon the surface of the molten lead. So much for the theory of scorification; in practice we follow in regular rotation the steps here given: GOLD AND SILVER ORES. 183 a. Preparation of Charge (including weigh- ing of ore, roasting, weighing of re-agents, mixing, etc). b. Scorification. c. Cupellation. d. Weighing the Gold and Silver Bead. e. Parting. f. Inquartation. g. Weighing the Gold Residue. h. Calculations-. a. Preparation of Charge. Whatever subsequent treatment an ore is to undergo, the quantity required for assay must be weighed first. Certain ores may possibly be subjected to a preliminary opera- tion known as roasting, but the ore must be weighed out before this, not after. If the ore in question is in a bottle, pour all out upon a clean piece of black glazed paper or piece of sheet rubber, or if it is in a box, it can be sampled therein. Weigh the amount de- sired, sampling from various parts of the ore.. 184 MANUAL OF ASSAYING. Have ready cleaned a number of the scori- fiers. Number or letter each scorifier with ruddle (liquid or lump), weigh the requisite amount of granulated lead, divide approxi- mately in halves, and transfer one-half to the scorifier. Upon it brush the ore (roasted or not) and mix by means of a small steel spatula. Pour the remaining half of the lead evenly over the surface of the mixed ore and lead, and over all sprinkle the borax glass. In simi- lar manner prepare all the other charges. A deviation from this method has been fol- lowed by some assayers. Their procedure is to put, say, \ of the lead at the bottom of the scorifier, then the ore and \ of the lead mixed previously, topping all with the remaining \ of the lead. This change is due to the fear of unacted-upon ore remaining at the bottom of the scorifier. I am inclined to consider it an almost unnecessary refinement. In many assaying establishments, notably the larger ones, the practice of marking scori- fiers, cupels, and crucibles does not obtain. GOLD AND SILVER ORES. 185 Instead of this, a systematic order of arrang- ing these articles is kept up, either in or out of the furnace, and this routine of position and order of working is never varied, so that by relative place a sample can always be identi- fied. This plan is indeed a good one, and perhaps imperative where very much work is done, but for the beginner, for a time at least, the custom of marking everything had better be adopted. CHARGES. (For manner of roasting see " III. Crucible Process.") 1. One for "every day" ores, serving well for the common run of ores in which the metals are not in excess of the gauge, is the following: Ore \ A. T. , 5 grammes, 96 grains or \ oz. Granulated lead i^ " 45 720 " i^ " Borax glass 250 mgrms., or 4 grains. Use it for ores that do not contain much copper or lead. 2. Copper glance or copper pyrites : Ore -jJjj- A. T., 2^ grammes, 48 grains or T J 7 oz. Granulated lead . . . 2| "75 " 1,200 " 2^ " Borax glass 200 mgrms., or 3 grains. I 86 MANUAL OF ASSAYING. For the above ores, a preliminary roasting can be made, if considered advisable. If not to be roasted, and when there is not very much of the sulphurets present, heat gently for a time, till the roasting in the scori- fier is done. If rich in sulphurets, a strong heat can be applied at once, melting everything down into a sort of matte, then proceeding as usual. 3. Copper matte: Matte Y 1 ^ A. T., 2^ grammes, 48 grains or r \y oz. Granulated lead .... 3 " 90 1,440 " 3 ' Use no borax glass ; instead : Powdered silica ^V A. T., i| grammes, 24 grains or -rf oz. 4. Gray copper ores : Ore Y 1 ^ A. T., 2| grammes, 48 grains or ^ oz. Granulated lead 2 " 60 960 " 2 " Borax glass 300 mgrms., or 5 grains. 5. Sulphurets of iron : Ore \ A. T., 7 1 grammes, 120 grains or \ oz. Granulated lead i\ " 75 1,200 " o.\ " Borax glass 200 mgrms., or 3 grains. Litharge can be used to advantage in this as in other unroasted sulphurets. GOLD AND SILVER ORES. 187 Always weigh the litharge, so as to allow for its contained silver. 6. Oxide of iron : Ore \ A. T., 5 grammes, 96 grains or \ oz. Granulated lead i^ " 45 " 7 2 o J i " Silica i " 'or 15^ Borax glass 350 mgrms., or 5-| grains. The silica to be mixed with the charge it can be diminished as the percentage of silica in the ore increases. 7. Galena : Ore A. T. , 15 grammes, 240 grains or | oz. Granulated lead i| " 45 " 720 " i " Borax glass 100 mgrms., or i| grains. Gentle heat. A nail in the scorifier aids in the desulphurization. 8. " Carbonate" ores : Ore I A. T., 5 grammes, 96 grains or oz Granulated lead .2 " 60 " 960 " 2 " Borax glass | gramme or 7^ grains. 9 "Chloride" ores : Ore i A. T., 5 grammes, 96 grains or oz. Granulated lead i^ " 33 " 576 " i " Borax glass 300 mgrms., or 5 gfains. Use as low a heat as possible until the 1 88 MANUAL OF ASSAYING. charge has covered over, then heat more strongly to complete fusion. 10. Blende : Ore | A. T., 5 grammes, 96 grains or \ oz. Granulated lead .. 3 " 90 " 1,440 " 3 " Borax glass 400 mgrms., or 6 grains. Needs a good heat and care in its assay. 1 1. Arsenical and antimonial ores : Ore A. T., 5 grammes, 96 grains or oz. Granulated lead 4 " 120 " 1,920 " 4 " Borax glass i| grammes or 23 grains. This charge may have to be divided sometimes requires several re-scorifications. A piece of charcoal laid over the scorifier, or some of it pulverized and dropped therein, often aids the fusion, as has been previously remarked. 12. Tellurides.: Ore $ A. T., 2^ grammes, 48 grains or T ^ oz. Granulated lead 2 " 60 " 960 " 2 " Litharge T V " 2$ " 48 Borax glass 250 mgrms. , or 4 grains. Sprinkle the litharge over the mixed charge. The buttons may need repeated scorifications with plenty of lead (20 to i). GOLD AND SILVER ORES. 189 13. Native gold or silver, or very rich ores of any kind : Ore T V A. T., 2| grammes, 48 grains or T ^ oz. Granulated lead \\ " 45 " 720 " \\ " Borax glass 250 mgrms., or 4 grains. Ores, either those already described or any others, having a great quantity of lime or baryta, will require more borax glass than the quantities given. It may need to be as much as the ore taken in such cases the charge may have to be divided, and several scorifica- tions and re-scorifications made. Such large quantities of borax are best added at inter- vals, not at the beginning. Stirring will often aid. Give a strong heat. Make use of silica also. The weights of borax glass are put down more to serve as indications than for precise- ness' sake. It need not be weighed at all ; after a time the assayer will learn to use it in pinches. Study and experiment are necessary here. Ores will be found made up of several of those given separately above new combina- IQO MANUAL OF ASSAYING. tions of minerals are constantly coming to light. The operator must then work over the par- ticular ores he comes in contact with, until he learns them thoroughly. The colors shown by the interiors of scori- fiers are often characteristic of the ores tested, and in conjunction with the colors of the cupels after cupellation make valuable tests. The following descriptions may per- haps be of some value to the student in this connection : . COPPER. Scarifier (See color plate). A green, more or less deep, according to the percentage of this metal. Where the coating is somewhat thick, as on the edges of the scorifier, the color becomes a dark brown, but the prevail- ing tint is green. Ciipel. Slate green, ranging to blackish green prevailing tint very dark blackish green. There is frequently a rose coat on the SCORIFIER COLORS. COPPER. IRON. LEAD. MANGANESE. CHROMIUM. URANIUM. GOLD AND SILVER ORES. IQI outside of cupels from ores rich in copper, which need not be mistaken for the rose color of oxide of silver. This rose tint meeting the slate green produces a purplish black or purp- lish green. IRON. Scarifier (See color plate). With large amounts of iron the interior is black with a gray metallic lustre (this indicates a poor fusion), from which the color ranges down through a deep rich mahogany and varying shades of red-brown to a light yellow-brown. A red-brown is, however, always present, and is the prevailing color. Cupel. A brown tint, more or less decided. LEAD. Scarifier (See color plate). Various shades of lemon yellow. (Vanadium, cadmium, and bismuth give same shades.) CupeL Bright, rich yellow to lighter shades. 1 92 MANUAL OF ASSAYING. (Small amounts of antimony, arsenic, bis- muth, cadmium or zinc retained in the button also leave yellow markings on the cupel.) MANGANESE. Scarifier (See color plate). From a purple- black to a light violet-brown or amethyst color. Cupel. Blackish green to a lighter green, usually the latter. It is never so deep nor the cupel so thoroughly permeated by the color as is the case with copper ; the color also is different. CHROMIUM. Scarifier (See color plate). Blood-red - thicker portions of the glaze a green, but pre- vailing tint is an orange or blood red. Cupel. Lemon-yellow, with reddish edges, surface also somewhat mottled with reddish- brown blotches characteristic appearance. NICKEL. Scarifier. A dirty, brownish yellow, and not very characteristic. A lead ore with a little iron would imitate it exactly. GOLD AND SILVER ORES. 193 Cupel. Brown, almost identical with iron. URANIUM. Scarifier (See color plate). A peculiar red. Cupel. Brown, as for iron. COBALT. Scarifier. A beautiful blue ; toward the bottom it struggles with a green, which is probably due to the union of the yellow oxide of lead and the cobalt blue. This color will not be obtained from any ore, but it is proba- ble that it has its effect in modifying other colors. Cupel. Brown, as for iron. TELLURIUM. Scarifier. A yellowish color, with some red spots ; not very characteristic. C^lpeL Yellow, with small green stains. It must be borne in mind that combinations of the metals are liable to influence these col- ors and to produce mixed shades. Also both the scorifier and cupel must be examined, not one alone, for the scorifier may 1 94 MANUAL OF ASSAYING. reveal one metal, the cupel another. Thus an ore containing about equal parts of copper and iron gives a red-brown in the scorifier, in- dicating iron, while the green of the copper is almost entirely masked. On the other hand, the cupel is green-black, indicating copper, while no brown of the iron is visible; hence both tests prove both metals to be present in the original ore. b. Scarification. Place the scorifiers, by means of the scori- fier tongs (page 94, fig. 43) in the middle and back of the muffle, which should be decidedly hot, close the door and augment the draft. Then begins the first operation, the melting or fusion of the lead, due to intense heat and absence of oxygen, which takes from three to four minutes. When the lead is liquid, open the door, thus admitting a current of air to supply oxygen, and which will also tend to diminish the heat somewhat. Now, in the case of ores containing or re- GOLD AND SILVER ORES. 195 taining antimony, arsenic, sulphur, or zinc, a second operation, roasting, begins and con- tinues till the greater proportion of the sub- stances named have volatilized, the remainder of them going into the slag. During this time the borax glass has melted and begun uniting with the gangue of the ore and with oxide of lead to form a slag which surrounds as a ring the molten lead. As the scorification goes on, the melted lead grows smaller and smaller by oxidation and the volatilization of the greater part of the oxide formed, while the ring of slag grad- ually closes in and finally covers the lead, which is seen no more. Finally increase the heat for a minute or two to fully liquefy the slag, which will finish the process of scorification. Remove the scorifiers, and pour their con- tents into the cups of the scorification moulds (page 99, figs. 53 and 54), which should not be cold, covering each receptacle with its proper scorifier to retain its identification. (If neces- ig6 MANUAL OF ASS A YING. sary, these scorifiers can be again employed for ores, etc.) After having poured the charge, it will be well to let the slag and button remain in the cavity of the mould until they are stone cold before dumping them out, as otherwise there is danger of the lead adhering firmly to the slag. Instead of pouring, the leads can be allowed to cool in their scorifiers, but no advantage is gained by this, and they take a longer time to cool. In either case, however, when cold, detach the lead buttons from their slags, and hammer each button into a clean cube with flat- tened .corners (fig. 91). Were the FIG. 91. corners to be left sharp, they would injure the cupel when the button came to be dropped into it. The weight of the button will vary accord- ing to the conditions ; the nature of the ore, the size of the charge, the heat of the furnace and the length of time the charge was allowed GOLD AND SILVER ORES. 197 to remain in it, all exert an influence. A good weight is from twelve to sixteen grammes, which will make a cube of about one-half inch. The button of lead is to be marked with some identifying number or letter with the point of a file or knife-blade. The button should be perfectly malleable ; if brittle it has probably retained antimony, arsenic, zinc or litharge, which can be gotten rid of by re-scorification. But with ores very rich in gold proceed with care, for the brittle- ness may be due to the gold itself, as beyond a certain limit gold takes away from the malleability of lead. If the button is large no extra lead need be added; if small an assay ton or two may be melted with it. Again, the button may be very hard on ham- mering or show red in places, and perhaps on taking out of the scorification mould may have mossy copper on the bottom. In such cases the button must be re-scorified until no more copper is seen, or until it is very malle- 198 MANUAL OF ASSAYING. able. Plenty of lead must be used to alloy with the copper. Since there is a greater loss of silver by cupellation than in scorification, very large buttons should be scorified down to a size suited to the cupels. Examine the slag, and if it contains any globules of lead, hammer them flat, then place them on top of the main button, and cupel all together. The slag should be vitreous or glassy, and of uniform character, its color depending upon the nature of the ore. The scorifier should be perfectly smooth in its interior, that is, it should have no semi- fused lumps adhering thereto. Occasionally it may be corroded or eaten away, which does not necessarily injure the assay, unless the corrosion extends through the dish and allows its contents to flow out upon the floor of the muffle. In such a case (when of course the assay must be repeated) at once cover the floor of the muffle with dry sand or bone-ash, GOLD AND SILVER ORES. 199 using the muffle shovel (fig. 51), and scrape out the mass adhering to it by means of the hoe or scraper (fig. 55). If this cleaning out of the muffle after an accident by spilling or leakage is not attended to, it leads to either one or both of two evils : first, the melted lead and borax attack the muffle and rapidly eat a hole through it ; secondly, they stick to any scorifier or cupel placed in the muffle, making it almost impossible to move or remove either without breakage or loss of contents. The corrosion of the scorifier is a good hint to add silica to similar ores, for usually it is the lack of this in the ore that causes the abstraction of silica from the scorifier, though there are times when a mixture of much lead and little ore is being scorified, that the lith- arge formed by the oxidation of the lead itself attacks the scorifier, and again, as in case of compounds rich in copper (a copper matte, for instance), the oxide of cop'per attacks the scorifier. 2OO MANUAL OF ASSAYING. Sometimes in the process of scorification a crust forms over the surface of the charge and refuses to break. Such a crust is gener- ally due to arsenical and antimonial ores pres- ent, and may often be destroyed by dropping in the scorifier some powdered charcoal wrapped in a wad of thin paper. The oxidation can also be commenced by stirring the charge with a bent wire, until the lead is uncovered and begins to act. Withdraw the wire, break off the mixture adhering to the end and return it (the slag, etc.) to the scori- fier, as it will probably carry some of the ore. c. Cupellation. This operation consists in oxidizing the lead of the lead buttons, the litharge formed by the heat being partly absorbed by the cupel and partly driven up the chimney, leav- ing the gold and silver together as a bead upon the surface of the cupel. Other metals that may have remained in small quantity from the previous operations, are also oxi- dized and so gotten rid of. GOLD AND SILVER ORES. 2OI Take a good cupel (pages 107-1 10, fig. 65), in weight about one-third greater than that of the button that is to go in it, blow out any dust or impurities from the interior, mark on its sides in three or four places with ruddle or the point of a file, its appropriate number or letter, and with the aid of the cupel tongs or cupel shovel and hoe, place it in the muffle and there let it remain some four or five minutes that it may acquire the temperature of the furnace. As can be inferred from the preceding paragraph, the size of the cupel depends upon the size of the lead button. And as mentioned under cupel-making, it is a good plan to have on hand cupels of various weights. It is stated that a good cupel will absorb its own weight of litharge, and further- more, it is able to take a button heavier than its own weight, for a large amount of litharge (or oxide of lead) is driven off in fumes and consequently does not enter into the body of the cupel. But it is better to employ a cupel 202 MANUAL OF ASSAYING. the weight of which is from one-fourth to one- third more than that of the button, for when a cupel becomes nearly saturated with litharge, the cupellation proceeds too slowly, when, on the contrary, it ought to be somewhat hastened, and cases occur that the cupellation ceases, though there may be at the bottom of the cupel enough unattacked bone-ash to absorb the remaining lead. At other times an assayer may carelessly put altogether too large a button in a cupel, and therefore all the bone-ash in the cupel be saturated with litharge while there is yet melted lead above; This error may some- times be rectified by putting a second cupel, red hot and inverted, under the soaked cupel, when the cupellation will proceed, though slowly. But it is better to reduce by scorifi- cation, in the first place, the excessively large button. When the cupel or cupels have been in the muffle a few minutes, and consequently have become of the same temperature as the inte- GOLD AND SILVER ORES. 203 rior of the muffle, the lead button or buttons are to be placed in them, each one in its proper cupel, by means of the smaller curved tongs (page 94, fig. 41), and the muffle-door of the furnace closed, having previously, if necessary, placed a couple of pieces of coke or charcoal in the mouth of the muffle. If the muffle has been of the proper tem- perature, in a minute's time or less, all the lead buttons will have quietly fused, and, on opening the muffle-door, each will be seen as a little lake of molten metal, from which arise fumes of oxide of lead. The closing of the door at first is simply in order to melt the lead buttons, by the in- creased heat and absence of air. It is very difficult to give in words direc- tions for the proper conducting of this impor- tant step of cupellation. Experience is the best instructor. In general, do not have the furnace too hot. This is not a matter of so much importance in the cupellation of the lead buttons from 204 MANUAL OF ASSAYING. gold ores, but in those from rich silver ores it is such. " The heat is too great when the cupels are whitish, and the metallic matter they contain can scarcely be seen, and when the fume is scarcely visible and rises rapidly to the arch of the muffle" (Mitchell), and particularly when the melted lead bubbles. " The heat is not strong enough when the smoke is thick and heavy, falling in the muffle, and when the litharge can be seen not liquid enough to be absorbed, forming lumps and scales " (Mitchell), in short, to speak seem- ingly paradoxically, when the muffle and con- tents look cold. An extremely high heat is bad, but a low heat is worse. " When the degree of heat is suitable the cupel is red, and the fused metal very luminous and clear" (Mitchell), and when scales of litharge are found in small quantity around the inner circumference of the cupel; in short, this "feathering" shows that the fire has not been too hot. GOLD AND SILVER ORES. 205 All this time, however, the buttons have been growing smaller and smaller, by oxida- tion and by volatilization and absorption of the oxide, changing from flat liquids to con- vex ones, and this reduction continues until we reach the point when the last of the lead leaves the bead. This is known as the " brightening," "flashing," " blicking," "cor- uscation," or " fuguration." As the button of gold, silver, and lead arrives near this stage it appears to revolve with great velocity, and rainbow colors succeed each other all over its surface. Finally a film passes over the bead, and then no more action is visible. (With poor silver ores and ordinary gold ores the final bead is so small that it is diffi- cult, if not impossible, to. see the "blicking," but on beads from silver ores of any richness the brightening shows well that the operation of cupellation is concluded.) Now move the cupel to the hottest place in the muffle, or increase the heat by closing the muffle door, that the last traces of lead may 2O6 MANUAL OF ASSAYING. be driven off. One source of error in silver assays is due to the assayer not getting rid of all his lead from the beads, but instead he weighs and reports it as silver. Better err by under-reporting rather than over, so take the chances of volatilizing a little silver from the bead than to allow lead to remain with the silver. A minute is generally sufficient to drive off the last lead, but with ores contain- ing more gold than silver, let the cupel remain in the hot part three or four minutes, for there is no danger of losing any gold in that time. Very rich ores betray themselves by a pe- culiar mottled appearance of the molten lead shortly after the cupellation begins. The luminous blotches of litharge as they form string themselves out and cover the lead as with a network. This is very characteristic, and once seen is again easily recognized. This mottling appears also with almost any buttons a little before the blicking ; in short, the richer the button the sooner it is observed. GOLD 'AND SILVER ORES. 207 Silver beads, on being suddenly brought from the hot interior of the muffle to the front where it is cooler, or out into the open air, sometimes " spit " or " blossom " that is, the bead sprouts or vegetates, forming foliated protuberances all over its surface. This may occasion loss, as the spitting throws off parti- cles of the silver; hence, guard against this as much as possible by moving the cupel by de- grees to the front, and when at the mouth of the muffle cover with an inverted hot cupel. With beads weighing less than 30 milligrammes or thereabouts this need not be done, but above that weight proceed carefully. If the assayer is running a number of as- says, let him so arrange the cupels that those intended for buttons from poor silver ores or gold ores shall be in the center or hottest part of the muffle, while those for rich silver ores shall be in the fore part or cooler section. The reason for so doing is this: silver is sensi- bly volatile at a high heat, and the higher the temperature the greater the loss. On the 2O8 MANUAL OF ASSAYING. other hand, the smaller the percentage of sil- ver in a silver-lead, the less loss of this metal. By therefore placing the rich silver-lead in the cooler portions, the tendency is to decrease the loss by volatilization. With any furnace, the heat of which cannot be instantly controlled, the muffle often becomes a little too hot for perfect cupellation. When but few cupels are therein this does not matter much, since they can be slid to the front; but it is of impor- tance when the muffle is so well filled that it becomes difficult or impossible to move any particular cupel or group of cupels to a cooler spot. By now putting in the muffle a small cold scorifier or cupel, letting it rest on the edges of four of the cupels, the interior can be cooled down considerably. Several scori- fiers or cupels thus arranged have quite a low- ering effect on the temperature, at least for a time. When many cupels are being managed at once make a chart of their relative positions in the muffle, that there may be no " cases of GOLD AND SILVER ORES. 2CK) mistaken identity" afterward, for with large buttons in small cupels the litharge often ob- literates the ruddle marks. If the furnace is too cold cupellation ceases, and the lead button is said to " freeze," form- ing a bunchy mass which undergoes no fur- ther action. A piece of charcoal laid upon the cupel, and additional heat applied, will sometimes finish the cupellation, or the but- ton may be dug out of the old cupel, wrapped in a piece of lead-foil, and be re-cupelled in a new cupel. The result either way is none too accurate. The final silver and gold bead from any cupellation should adhere with some tenacity to the cupel, have a bright, rounded surface, and appear frosted below. d. Weighing the Gold and Silver Bead. When cold detach the bead from its cupel, using the point of a knife-blade, and keeping a finger on the bead while s'o doing if the bead be small, for otherwise the exertion put 2 TO MANUAL OF ASSAYING. forth to loosen the bead might easily snap it out of the cupel and past finding. Lift the bead from the cupel by means of delicate pincers (p. 1 18), and cleanse from any adhering cupel dirt by rolling in the palm, by using a small stiff brush, or, if necessary, by flattening a little by means of a small steel hammer and anvil. If the bead be very small, fold it in three or four thicknesses of tissue paper, to prevent its flying away under the strokes of the hammer. Weigh on the bullion scales in milli- grammes and fractions. e. Parting. The separation of gold and silver by dis- solving out the latter is designated by the term "parting." The bead after weighing is flattened a little if it has not been so treated before. Now place in a little clean porcelain capsule or cru- cible (fig. 69), and fill about a quarter full with water (free from chlorine, see p. 142), and add four to six drops of concentrated GOLD AND SIL VER ORES. 2 I I nitric acid. No exact rule as to the amount of acid to add can be given, nor indeed is it necessary. But in general add drop by drop till it begins to "bite" the bead that is, when the latter seems in violent motion and bub- bles are thrown rapidly off. Instead of add- ing concentrated acid to. water containing the bead, until it takes hold of the latter, the assayer may use a diluted acid of known strength. 16 parts of nitric acid of 41 Beaume (specific gravity 1.41) with 30 parts of dis- tilled water will make an acid of 21 Beaume (specific gravity 1.16). This will do for ordi- nary small beads; for large ones, after having treated them with the above 1.16 acid, add some of 32 Beaume (specific gravity 1.26), made by mixing 16 parts of the strong 41 acid with 10 parts of distilled water. Make these up in quantity and preserve in well stoppered bottles. Now place the capsule on a sand-bath or wire triangle, and heat gently, not enough to cause the acid solution to boil. After a time 212 MANUAL OF ASSAYING. no more action goes on. If there is no gold in the bead it will not blacken on adding the acid, and nothing will remain undissolved in the capsule ; it will contain only the clear solu- tion of nitrate of silver, formed by the silver dissolving in the acid. In this case nothing further need be done than to wash out the contents of the capsule into a bottle containing silver residues. But should one or more black specks be seen at the bottom of the capsule or float- ing about in the liquid, gold may or may not be present ; at all events, these specks, how- ever small, must be treated as though they were gold. Pour off the liquid above the black particles, first lightly tapping the cap- sule in order to cause the floating gold to settle to the bottom. If tapping will not either settle the gold or bring the particles together, try "churning" -that is, stir the contents of the capsule vigorously with a glass rod. In many cases, and unless the gold is in too fine a state, this will coagulate the GOLD AND SILVER ORES. 213 gold, as it were that is, bring the particles together into a spongy mass when tapping will quickly settle it. It is best to pour into another clean porcelain dish, so that should the gold, .by some mischance, go over with the outpouring solution, it may be recovered. Fill up the capsule with water, care being taken that no speck of gold is blown out of the cap- sule by the jet of water from the wash-bottle. This is to wash out the nitrate of silver from the gold. Tap the gold to the bottom, pour off the washings, and repeat the washing. If there is much gold, a third washing may be necessary. All this to insure complete re- moval of the silver nitrate. Finally drain off, wipe the capsule dry, remove, by means of filter paper (or clean blotting paper), any drops of water adhering to the interior of the capsule (being careful not to take away any of the gold), and heat very gently at first till all moisture has been driven off, then intensely for a minute or two. The' gold has now changed in color from black to its normal yel- 214 MANUAL OF ASSAYING. low, and is very nearly pure, enough so for all practical purposes. Let the capsule and con- tents cool. f. Inquartation. When a bead of gold and silver contains the gold in a greater proportion than about one-third of the silver, it possesses the power of resisting the solvent action of nitric acid. A certain amount of the silver may dissolve, according to the relative proportions of the two metals, but the larger part of it will remain so enveloped by the gold, that the strongest acid will not attack it. Hence we resort to inquartation, or the operation of producing an alloy of gold and silver in such proportion that the latter metal may be extracted by nitric acid. By the color of the bead the assayer can judge whether it needs to undergo this opera- tion. If it be of a moderately yellow color or a brighter yellow, it will probably need it. But there can be no doubt of it if it refuses to be acted upon by the acid. GOLD AND SILVER ORES. 215 Remove it from the capsule, and dry. Weigh some thin and pure silver foil, in quantity about twice the weight of the bead. Wrap the latter in the foil, and place both in a cupel (or in a small hole bored in the back of the cupel), and fuse them well together in the flame of a blow-pipe. When cool, remove the now largely increased bead from the cupel, flatten and part as directed. Instead of employing the blow-pipe, the bead and silver can be enfolded in some sheet- lead, and be re-cupelled in the usual manner. Indeed, if the original bead weighs more than ten milligrammes, it will be easier to alloy it by cupellation than by blow-piping, and a much better fusion be obtained. g. Weighing the Gold Residue. By means of a pointed slip of wood or sharp knife-blade, transfer the gold (which should be one scale or film) to the scale-pan of the bull- ion balance, and weigh with exceeding care, as usual in milligrammes and fractions. It often happens that the minute black pin-point of 2l6 MANUAL OF ASSAYING. gold becomes too small to be weighed after the heating. It can then be reported only as a "trace" or "color." h. Calculations. By the use of the system of assay ton weights, the calculation of the gold and silver value of an ore becomes very simple. Two examples will show this very clearly : EXAMPLE No. i. Amount of ore taken \ A. T. Amount of test-lead used i \ " MGRMS. Weight of gold and silver bead 8.50 silver in i A. T. lead 25 True weight of gold and silver bead 8.25 Weight of gold in the bead i.io Weight of silver in the bead 7.15 7.15 X 5 = 35-75 = 35i milligrammes = 35! ounces per ton of silver in the ore. 1.10x5 = 5.5 = 5^ milligrammes = 5^ ounces per ton of gold in the ore. VALUE OF THE ORE! Gold 5^ ounces @ $20.67 per oz $113.68 Silver 35f " " 1.29 " 46.11 Total value per ton $159.79 GOLD AND SILVER ORES. 217 EXAMPLE No. 2. Amount of ore taken \ A. T. Amount of test-lead used i " MGRMS. Weight of gold and silver bead 231.90 Weight of silver in test-lead* o.oo True weight of gold and silver bead 231.90 Weight of gold, " faint trace " o.oo Weigh of silver in the bead 231.90 23 1.9x2 =463.8=463^ milligrammes=463 1 %- otmces per ton of silver in the ore. Value : 463-8 x $1*29 =$59 7.^0 per ton. CRUCIBLE PROCESS. This process is much more complicated than the scorification, and, to use it success- fully, we should know pretty thoroughly the nature of the re-agents employed, the kind and degree of their re-actions upon each other and upon the ore while in the crucible sub- jected to heat, and, finally, the characters of the various ores and their modes of behavior * Not deducted. Read remarks on testing of granulated lead for silver, p. 159. 2l8 MANUAL OF ASSAYING. in the crucible. Knowing all these things, we can decide upon such a modification of treatment as is best adapted to the particular ore in question. The crucible process can be applied to any gold and silver ore, of whatever mineralogical nature, and whether rich or poor, but it has been found by experience to be best fitted for certain ores and classes, as is the scorification for certain others. By some assayers the crucible process is reserved almost entirely for low grade ores (whether in gold or silver), and the scorifica- tion for high grade ores, and, for a general rule, this will do very well. Another broad distinction is that of confining the crucible process to gold ores, and the scorification to ores of silver. This latter rule is quite a safe one to follow, since the majority of gold-bear- ing ore is low grade, and hence is best assayed by the crucible process, which operates upon a larger quantity than the scorification. Fur- ther, an ore of silver which is so poor as to GOLD AND SILVER ORES. 2I 9 give no results by the scorification process, is practically worthless, and needs no more test- ing by any method. The following classification covers the ground, both generally and, in a measure, spe- cifically: CRUCIBLE PROCESS. 1. Gold ores. 2. Low grade gold ores.* 3. Low grade silver ores. 4. " Chloride ores " (sil- ver), including: " Chlorides, Bromides, Chloro-bromides, Iodides. SCORIFICATION PROCESS. 1. Silver ores. 2. High grade silver ores, with the exception of the chloride and al- lied ores. 3. High grade gold ores. 4. Telluride ores. 5. Arsenical and antimo- nial ores. 6. Ores containing tin. 7. Ores containing nickel or cobalt. An outline of the crucible process is as follows : The ore is mixed with lead in some form, * For the purposes of assaying, a gold ore which runs over $5 to the ton may be considered high grade ; below that figure, low grade. 22O MANUAL OF ASSAYING. fluxes, with or without some reducing, oxidiz- ing, sulphurizing, or desulphurizing agent, transferred to a crucible and heated. The reduced lead absorbs the gold and silver, and settles with them to the bottom, while all im- purities are fluxed (i.e., slagged), matted, or volatilized. After removal from fire the lead is freed from slag, and the gold and silver separated from it by cupellation, as previously described. To elaborate the above description some- what, we may state, that, in the crucible pro- cess, as in the scorification, lead is added (save for lead ores) to extract the precious metals from the ore ; but, instead of using it in the metallic state and oxidizing the excess, we start with a compound which is almost in- variably the oxide, litharge, and by means of a reducing agent, or by the reducing action of the ore itself (or by both combined), reduce enough lead to retain all the gold and silver, but which amount of lead shall not be too large to be manageable. GOLD AND SILVER ORES. 221 To secure a perfect crucible fusion, which means practically the separation of the gold and silver from everything else that may have been associated or combined with them in the ore (excepting, perhaps, some of the lead), we need to do several things. To get rid of the gangue (or earthy portion of the ore) we use fluxes, which convert the gangue into a slag. All metals present, save the precious ones, may be removed in various ways : By uniting them with sulphur into a matte ; by oxidizing them and fluxing the oxides into the slag ; by oxidizing them and volatilizing the oxides entirely out of the crucible ; or, in the one case of lead, by bringing either the whole, or such a proportion of it as may be wanted, down with that obtained from the litharge. Next, we may or may not need some reducing agent to reduce the requisite amount of lead ; or, on the contrary, a/i oxidizing agent may be necessary to oxidize and so remove sulphur or the excess of lead when an ore of this metal is being treated. Finally, a protecting cover 222 MANUAL OF ASSAYING. of some easily fused inert substance will be wanted, although it is not indispensable. The chief fluxes are litharge, the carbon- ates and bi-carbonates of potash and soda, borax, silica, and nitre. The reducing agents are charcoal, argol, cream of tartar, flour, or some other similarly carbonaceous substance, for it is the carbon of the reducing agent which removes the oxygen of the litharge, leaving metallic lead. The most commonly used oxidizing agent is nitre. Sulphur is the sulphurizing agent, and common salt the pro- tecting cover. (The chemical composition and reactions of all the above are given in detail in the chapter on re-agents, which see.) It will now be well, and in order, to under- take a little study of gold and silver ores, or of ores which are imagined to contain the precious metals, that we may know how to apply to them their proper treatment, which includes a knowledge of the principles of the important art of fluxing. GOLD AND SILVER ORES. 223 Every ore must belong in some one of the following divisions : Metalliferous min- Gangue matter with eral or minerals no perceptible met- with a gangue ; alliferous mineral examples, galena or minerals; ex- or iron pyrites in amples, quartz, quartz. fluor spar or ba- rytes. Metalliferous min- eral or minerals with no gangue; examples, pure galena, iron py- rites, or any "con- centrates." The third division can, of course, include specimens that actually contain no metallifer- ous minerals, perceptible or imperceptible, as, for example, pure white quartz, while in others, as stated, they may be present so mi- nutely disseminated as to be invisible to the naked eye (or even to the eye assisted by a good magnifying glass), as is often true of samples carrying gold in that very fine condi- tion known as " flour gold." There are also instances where that which is' ordinarily a metalliferous mineral may act as a gangue ; for example, galena in spathic iron. Here the latter is a gatngue, whereas at other times it may be found as a mineral 224 MANUAL OF ASSAYING. in a true gangue. No confusion, however, need arise, if we consider only the question of the composition of the particular sample lying before us. The. chief value of the above classification lies in the fact that a knowledge of the class to which an ore belongs aids us in its fluxing. It would be almost impossible to write such descriptions as would enable the student to determine the mineralogical character of an ore or to place it in its proper division above. He must learn by experience, by observation, and by an application of the information im- parted by the standard authorities on miner- alogy and blow-pipe analysis which are listed in the appendix. The few simple qualitative tests given in the latter may aid him some- what. As regards the relative amounts of gancrue o o & and mineral in an ore, I can give but one gen- eral, and rather indefinite, line of advice : The heavier an ore, the greater the percent- age of metalliferous mineral ; the lighter an GOLD AND SILVER ORES. 22$ ore, the greater the percentage of gangue. There are a few exceptions to this rule ; the chief one commonly met with is barytes or heavy spar, a gangue which is three-fifths as heavy as galena, the chief ore of lead. If an ore to be treated belongs to the first division that is, if it possesses no gangue we supply an artificial one, as it were, when we come to prepare the charge, by adding silica. For purposes of assay treatment, we may consider under one heading those ores which appear to be all gangue, or made up of both gangue and mineral. The nature of the gangue is important in determining the nature of the flux necessary to change it all into a slag. The gangue may be acid, basic, or both acid and basic ; conse- quently, the simple rules for fluxing a gangue are almost self-evident. An acid gangue re- qiures a basic flux / a basic gangue requires an acid flux. Now, what do we mean by an acid or a basic gangue ? An acid gangue is 226 MANUAL OF A SSA YING. simply one which acts as an acid, requiring a base to form a salt. A basic gangue, on the contrary, acts as a base, and therefore requires an acid to form a salt. As examples of these chemical facts, take metallic copper, which is a base. To convert it into a salt of copper we need an acid, which may be sulphuric, this making sulphate of copper (common blue vitriol), or silicic acid, forming silicate of cop- per (the mineral chrysocolla is the hydrated silicate of copper), or any other acids, form- i,ng corresponding salts. So in fluxing, an acid gangue, as silica, forms salts with a basic flux, as litharge or soda, producing a slag which is composed of the silicates of lead and soda, and a basic gangue, as lime, unites with acid fluxes, as silica or borax, producing a slag which is composed of the silicate and borate of lime. There results then the fol- lowing classification : GOLD AND SILVER ORES. 227 ACID GANGUES. 1. Quartz, or other forms of uncombined silica ; as quartz crystals, quartz rock, quartz- ite, sandstone, sand, etc. 2. Silicates, or silica com- bined with some base; as clay, clay slates, mica, etc. 3. Rocks in which silica predominates; as gran- ites, feldspars, por- phyry, etc. As a rule, then, an acid gangue is silicious. BASIC GANGUES. 1. Calc spar (carbonate of lime). Also lime- stones. 2. Heavy spar (barytes, or sulphate of baryta). 3. Fluor spar (fluoride of calcium). 4. All so-called earths; as alumina, and various combinations of lime, magnesia, baryta, etc., without silica. 5. Sparry iron, or carbon- ate of iron. 6. Various metallic ox- ides; as those of iron, manganese, etc., when in sufficient quantity to be con- sidered as gangues. We can easily see now that the gangue of an ore may be both acid and basic, by its being made up of representatives o'f both classes. Theoretically, then, such a gangue should 228 MANUAL OF ASS A YING. flux itself. Practically, however, we may find it necessary to help the fusion a little. Try to ascertain the mineralogical character of the gangue. When this is known, con- sider only the element which is in excess of the others, and flux that ; the remaining ones will usually take care of themselves. ACID FLUXES. 1. Borax. 2. Silica. 3. Silicates ; as glass, and silicate of lead or lead-glass formed by the fusion of litharge and silica. Hence these flux the basic gangues enumer- ated. BASIC FLUXES. 1. Litharge. 2. Nitre. 3. Carbonate of soda. Carbonate of potash. Bicarbonate of soda. Bicarbonate of potash. Hence these flux the acid gangues enumer- ated. The metalliferous minerals of an ore play a very important part in its treatment. T^hey may exert either one of two very opposing actions, viz.: reducing, that is, taking away oxygen (from the litharge), or oxidizing, that is, giving up oxygen (to the reducing agent). GOLD AND SILVER ORES. 22Q To explain a little more fully: Sulphur, arsenic, antimony, and zinc are the principal reducing elements of an ore. (If an ore con- tains none of these, it will not be at all reduc- ing.) They all act in a similar manner to the carbon of a reducing agent, removing oxygen from the litharge, and so leaving metallic lead, themselves being converted into oxides. The various methods for eliminating these obnox- ious substances will be considered further along. An effect contrary to that produced by the elements mentioned is that caused by certain oxides and oxidized minerals. They are chiefly the oxides of iron, lead, copper, and manganese, in their highest forms of oxida- tion. Exposed to heat in a crucible, and sur- rounded by the reducing agent, they give up to it a portion of their oxygen, themselves being converted into their lower oxides and going into the slag. The presence, then, of either reducing or oxidizing elements in an ore is made manifest 230 MANUAL OF A SSA YING. by the size of the resulting lead button, the former tending to produce lead, the latter to keep it in the oxidized state by appropriating to themselves the carbon intended for reduc- ing. Thus, some ores will be more or less reducing, bringing down more lead than is wanted, just enough or too little, or they may reduce no lead at all. On the other hand, they may be oxidizing, not only not bringing down any lead, but preventing the reducing elements of the ore (if present) and the re- ducing agent added from exerting their action. Hence it is important to know what an ore's action is. It is advisable to reduce a certain portion of the litharofe in order to obtain a button of 5 a convenient size for cupellation. It should be large enough to extract all the gold and silver from the ore, yet not be so large as to be too long time cupelling, which may cause a loss in silver. A standard weight is 15 grammes for those who use the metric sys- tem, or 240 grains (^ ounce) for those accus- GOLD AND SILVER ORES. tomed to the grain weights. If the buttons obtained should chance to be somewhat larger or smaller, it will make no material difference; but it is well to use either weight given, and calculate ores and oxidizing and reducing agents to such a basis. For the sake of reference, I next give lists of the principal ores and minerals whose direct or indirect action upon the litharge has just been discussed. Metalliferous minerals which have a rediic- ing action : SULPHURETS. 1. Sulphuret of zinc (sphalerite, blende, zinc blende, "jack" or "black jack"). 2. Sulphuret of manganese (manganblende, alabandite). 3. Sulphuret of iron (pyrite, iron pyrites, mundic). 4. Sulphuret of iron (pyrrhotite, magnetic iron pyrites). 5. Sulphuret of iron with arsenic (arsenopy- rite, mispickel, arsenical iron pyrites). 232 MANUAL OF A SSA YING. 6. Sulphuret of copper (chalcocite, copper glance, vitreous copper). 7. Sulphuret of copper and iron (chalcopy- rite, copper pyrites). 8. Sulphuret of copper and iron (bornite, erubescite, variegated copper pyrites, " horse-flesh ore "). 9. Sulphuret of copper and antimony with sulphurets of iron, zinc, silver, mercury, bismuth, arsenic, etc. (tetrahedrite, gray copper, fahlerz). 10. Sulphuret of antimony (stibnite, gray an- timony). 11. Sulphuret of lead (galenite, galena, " py- rites of lead," " mineral ). 12. Sulphuret of silver (argentite, silver glance). The above list enumerates the chief sul- phurets which are likely to be assayed for gold and silver, though there are many other intermediate and mixed sulphurets, for de- scriptions of which consult the mineralogies. It can easily be remembered, however, that GOLD AND SILVER ORES. 233 any sulphuret, or mixture of sulphurets, is reducing. To the above add the various arsenides, antimonides, bismuthides, selenides, etc., of more or less rarity, and more commonly ores containing graphite or plumbago. Metalliferous minerals which have an oxid- izing action : 1. Red oxide of iron (" decomposed iron ore "). 2. Red oxide of lead (minium). 3. Black oxide of copper (tenorite, melaco- nite). 4. Black oxide of manganese (pyrolusite). (More rarely the chromates). Since an oxidized ore commonly results from the decomposition of a sulphuretted one, it may be very possible to find an ore not entirely decomposed or oxidized, and therefore both reducing and oxidizing. As examples, one often meets with a specimen carrying sulphurets and oxides of iron, or 234 MANUAL OF ASS A YING. copper pyrites and black oxide of copper in- termingled, or galena and carbonate of lead. A preliminary examination of an ore may then be necessary to determine its character and subsequent mode of treatment. An ex- pert mineralogist, metallurgist, miner, or as- sayer can tell almost at a single glance the nature of an ore as to its constituents and oxidizing or reducing powers, but the begin- ner will find it somewhat difficult at first. Here then again comes in the opportunity to make blow-pipe and qualitative examinations. To ascertain the presence or absence of sulphurets, try the following very simple test: Powder a little of the sample and heat it in an iron spoon over a strong flame or on top of a good fire, and note its behavior. If, shortly after it is heated, star-like sparks are quickly thrown off (particularly noticeable when the powder is stirred with a wire), then the mass begins to glow around the edges (resembling a charcoal fire), while closely above it hover small blue flames, and finally GOLD AND SILVER ORES. 235 the entire mass becomes red-hot, with fumes and an odor as of a burning match is per- ceived, then sulphurets of iron or copper or both are present, and so the ore will be decid- edly reducing. If, in addition, an onion or garlic-like odor and whitish fumes are noticed, arsenic (probably as arsenical iron pyrites) is also present. Antimony and zinc give white fumes with no odors. Blende and galena are not so liable to glow and to scintillate as are the iron and" copper sulphurets, but the smell of a burning match should be perceptible upon heating them or any other ore which contains a fairly large percentage of sulphurets. It will also be noticed that after the mass has been thoroughly heated and allowed to cool, it will have lost its metallic shimmer, and be- come of a dull, dead color, indicating oxida- tion. A simple chemical test for sulphurets may easily and quickly be tried. Place a small portion of the finely ground Ore in a test- tube, pour in a little water, shake, add a few 236 MA NUAL OF ASS A YING. drops of hydrochloric acid, and warm gently. If the smell peculiar to rotten eggs (sulphu- retted hydrogen) is now recognizable, sulphu- rets are certainly in the ore. Finally, when it is suspected that not a very large quantity of any sulphuret is in the sam- ple, try the following plan, which is much more delicate than either of the preceding : Fuse a little of the ore with bicarbonate of soda and borax on charcoal, by means of the blow-pipe. When the mass has fused remove it, by means of a knife-blade, to the surface of a bright silver coin, add a drop of water, and work the paste thus formed for a short time. The same gas above spoken of (sulphuretted hydrogen) is given off from the sulphide of sodium, which has been made by the union of the sul- phur of the ore and the soda, and blackens or browns the coin, according to the amount of sulphur in the original ore. A very close guess as to the kind of sul- phuret contained in an ore, or of which it is mostly composed, can frequently be made (de- GOLD AND SILVER ORES. 237 pending on the purity of the sulphuret) by noting the color and character of the pulver- ized sample, then heating some quickly in a roasting dish, observing its action under heat, finally examining the heated ore, after it has cooled. Compare it with the following table : 2 3 8 MANUAL OF ASSAYING. KIND OF SULPHUKET. BEFORE HEATING. DURINC- Color of Ore. Character. Fumes. Character. I. 2. 3- 4- 5- 6. 7- 8. 9- 10. ii. 12. Blende Manganblende . . Pyrite... . ( Brown, shading \ < to green, red, > / and yellow. ) ) Green, green- ( 1 ish-gray. f (Greenish or i < brownish > 1 black. j Gray-black Gray-black Shining Dull {Shining, not ( "/ magnetic. f (Shining, is I | magnetic. ) Shining Very slight Slight Slight Slight Pyrrhotite . . Arsenopyrite Chalcocite Chalcopyrite Bornite Tetrahedrite Stibnite Galenite ( White, very > ') thick. f Slight Green-black Dark-green Dark-gray Lead-gray Gray ( Gray - black, J -c pink and> f brown shades, j Shining Shining . . . Some fumes Some fumes Much White fumes. . . ( Fumes con- .' "/ siderably. )" Some Shining . . Shining Very decided shine. Very little shine . . . Argentite ... (Each sulphuret will give a little odor of sulphur, but GOLD AND SILVER ORES. 239 HEATING. AFTER HEATING (WHEN COLD). Fumes. Other Char- acteristics. Color of Ore. Character. Composition. Odor. None fGlows,! i yellow- -j green}- whe n 1 I hot. J j Buff or yel- j 1 lowish. f Dead, dull .... Oxide of zinc. None Glows. ...... Brown . . Dead, dull j Brown oxide | ofmanganese. None Glows ( Red to black ) < m any V ( shades. \ Dead, dull | Red oxide of | iron. None Glows ( Red to black ) < man y V ( shades. \ Dead, dull j Red oxide of / iron. Like garlic ( Glows, | "/ swells. 1 ( Red to black ) -< m any V ( shades. ) Dead, dull.... ( Red oxide of ( iron. None Glows, fuses. Gray 1 Shining, ) < powdefV ( red. \ i Oxide of cop- "/ per. None . . Glows, fuses Gray ( Shining, 1 < powderV ( gray. ) ( Oxides of iron "( and copper. None Glows Gray (Shining, 1 < powderV ( brown. \ j Oxides of iron 1 and copper. ( Garlic odor ) A some- > f times. ) (Glows, ) < swells, V \ fuses. | Gray Shining Mixed oxides. None (Swells, ) < melts, V ( boils, i Gray-green ( A thin film 1 C of shining > ( mass. j j Oxide of anti- j mony. None Fuses Yellow-green . . Shining Oxide of lead. None Fuses Gray J Somewhat > I shining, f ( Oxide of silver -< s o m e w hat f reduced. it is not to be confounded with the odor of arsenic.) 240 MANUAL OF ASSAYING. An approximate determination of the per- centage of " sulphurets " in an ore can be made by mixing 10 grammes or 100 grains of the ore with as much powdered silica and twice as much borax glass, placing the mix- ture in a suitably sized crucible, topping with salt, covering, and heating pretty strongly for fifteen minutes. Remove, cool, break out button as a " matte," weigh, and multiply weight by ten, giving percentage. The blow-pipe tests for antimony and zinc are not satisfactory, especially in the hands of a beginner; hence, I have given the following analytical scheme, which, although it seems complicated, is really simple. It can be ap- plied to the most complex ores; for the more simple ones some of the steps can be omitted, as the student will learn by experimenting with it on the various ores and minerals. To prac- tice it, make a mixture of iron and copper py- rites, blende, galena, arsenopyrite, sulphuret of antimony, and black oxide of manganese. The test can be made in an hour's time. GOLD AND SILVER ORES. 241 Make a mixture, in equal parts, of hydro- chloric, nitric and sulphuric acids. Place this in a beaker, and into it drop some of the powdered ore, and heat ; then add water, and filter. Do not wash. Residue and Precipitates. Sand, silica, clay; mercury, silver, and lead as chlorides; lead, calcium, barium, and strontium as sulphates; antimony as oxychloride. Wash thor- oughly with water while on the filter. Filtrate. Add sulphuretted hydrogen gas, and filter from precipitate formed. Precipitate. Mixture of various sul phu- rets ; r e - ject. Filtrate. Boil off excess of sul- phuretted hydrogen, add caustic soda in ex- cess, boil and filter. Filtrate. Not needed, reject. Res. and Pre. Remove from filter, boil with solution of , and filter. tartaric acid Precipitate. Iron, chro- mium, al- uminium, and man- ganese as hydra ted sesqui o x- ides. Filtrate. Add acetic acid in excess, and treat with sulphuretted hydrogen; a white precipitate in- dicates the presence of zinc. Res. As first given; re- ject. Filtrate. Run sulphuretted hy- drogen gas through it, or add water saturated with this gas; an orange-colored pre- cipitate indicates antimony. It is difficult to give tests for the highly oxidized ores listed. Dull, dead ores in gen- eral are likely to be in an oxidized condition, though not necessarily in the highest state of oxidation. If the ore is red and does not 242 MANUAL OF ASSAYING. answer to any test for copper, it will proba- bly be the red oxide of iron (possibly of lead). If it is black, apply the simple tests for cop- per and manganese given in the appendix. But even without a knowledge of the ore, gained by observation and experience, or by applying tests, its reducing or oxidizing power can be determined by certain preliminary and arbitrary assays. If it is suspected th^t the ore is reducing, prepare the following PRELIMINARY CHARGE TO DETERMINE REDUCING POWER. A. 7\ Weights* Gramme Weights* Grain Weights.* Litharge . . . ij A.T. 45 grammes 720 grains. Ore ^ 14 " 24 Salt cover. (The above weights of ores are each -fa of the respective standard weights taken for the crucible process.) Weigh first the litharge and brush it on to * These weights do not correspond exactly with one another (although sufficiently so), nor is it demanded that they should. They simply represent the most appropriate quantities for the purpose in the several systems of weights. The student can take his choice. GOLD AND SILVER ORES. 243 a clean sheet of black glazed paper, then weigh very carefully the finely pulverized ore, sampling it as usual; brush it on top of the litharge, and mix them thoroughly (indicated by the uniform color and character of the re- sulting compound) with a large steel spatula. Pour the charge into a small sand crucible, which it should not more than two-thirds fill (size " W " of the Battersea make, 3 inches deep by 2\ inches across, will do nicely) ; tap gently till contents are level, sprinkle some dry salt over the glazed paper, stir it around thereon by half turning over the sides of the paper, finally pour it on top of the charge - in this manner any of the charge left adher- ing to the paper is " dry washed " into the cru- cible. There should be about \ inch salt on top. There will then remain an inch or so space between top of crucible and the salt, to allow for the expansion of the charge when fusing. Have the fire quite hot, place in it the cru- cible, covered, bank around it with the hot 244 MANUAL OF ASSAYING. coals, and heat quickly till contents are in quiet fusion, which requires fifteen to twenty minutes. When satisfied that the charge is well fused, remove cover, lift out the glowing crucible by means of the long -handled crucible tongs (figs. 37 to 41), and tap it gently on a brick three or four times (in order to gather into one button any little pellets of molten lead that may be scattered throughout the fused mass), then cover, and let stand till cold. When stone-cold, break the crucible, detach from all adhering slag the lead button (if there is any), hammer into shape as usual, and weigh it. We shall have one of two alternatives : i st. A lead button. 2d. No lead button. ist Case. A lead button is obtained. This result shows that the ore has a reduc- ing action the weight of the button will indicate its power. There will be then one of three results : GOLD AXD SILVER ORES. 245 A. The lead button has a weight less than one-half that of the ore. B. The lead button has a weight about equal to one-half that of the ore. C. The lead button has a weight greater than one-half that of the ore. I take each supposition in turn. A. The lead button has a weight less than one-half that of the ore. Rule. Multiply the weight of the lead button by 20 (to ascertain what the standard weights of i A.T., 30 grammes or 480 grains would produce), and subtract the product from the standard weight of button desired (15 grammes or 240 grains). The result is the weight of lead which must be reduced by some reducing agent. Divide this by the reducing power of the reducing agent to be used, and the quotient will be the weight of the reduc- ing agent necessary to be added in the regular assay. Examples. Suppose the -^V A. T. or i^ grammes of ore produced a lead button weigh- 246 MANUAL OF ASSAYING. ing \ gramme, then i A. T. or 30 grammes would produce Jx2o = 5 grammes, 15 5 = 10, so that the lead button lacked 10 grammes of the standard weight. We have therefore that amount to be reduced by an added reducing agent. Taking charcoal as 25 and dividing that into the 10 gives us f gramme as the weight of charcoal to be employed. In a similar manner would we proceed when gr'ain weights are used. If 24 grains of ore reduced 4 grains of lead, then 4x20 = 80; 240 80=160; i6o-f-25 = 6f- = grains of charcoal to be used. Should the particular sample of charcoal employed possess a greater or lesser reducing power than 25, or should argol (reducing power about 7^), or flour (reducing power about 15), or any other reducing agent be made use of, then simply substitute in the above calculations the appropriate figures. B. The lead button has a weight aboiit eqiial to one-half that of the ore. This case is very simple. The quantity of GOLD AND SILVER ORES. 247 ore taken for the regular assay will, of course, as in the preliminary assay, reduce half its own weight of lead (giving buttons of about the right size), hence there is needed no ad- ditional reducing action. C. The lead button has a weight greater than one-half that of the ore. Here we have an instance of too great a reducing action, hence the excess of lead must be oxidized away, or, to put it more correctly, we must supply enough oxygen to satisfy that proportion of the reducing elements of the ore which would reduce the excess of lead, and then they will leave the oxygen of the litharge alone. The oxygen-supplying medium is nitre. Rule. Multiply the weight of the lead button by 20, and subtract from the product the standard weight of button desired. The result is the excess of lead which is to be re- tained in the form of litharge by use of nitre. Divide this by the oxidizing power of the 248 MANUAL OF ASSAYING. nitre* used, and the quotient will be the weight of the latter to be employed. Examples. Suppose the -fa A. T. or the i grammes of ore produced a lead button weighing 3.15 grammes, then i A. T. or 30 grammes would produce 3. 15x20=63 grammes, 63 1 5 =48= weight of lead to be kept oxidized 48-^4=12 = grammes of nitre to use. If the grain weights are used, and the 24 grains of ore have reduced say 50 grains of lead, then 50 x 20 = 1,000 ; 1,000 240 = 760, 760-^-4=190= grains of nitre to keep oxidized the 760 grains of unnecessary lead. The various sulphurets possess varying re- ducing powers ; hence, by starting with a knowledge of the reducing power of each kind of sulphuret, and estimating, by the eye, the proportion or percentage of whatever kind may be in the ore in question, we may ap- proximate pretty closely to the amount of nitre to add in order to oxidize all the sulphur but that which we want present to bring down * One part of nitre oxidizes four parts (very nearly) of lead. COLD AND SILVER ORES. 249 the proper weight of lead, and so can avoid making a preliminary assay. The adjoining table will be found useful for reference : Percentage of the sulphu- Parts of lith- ret which with charg- Parts of KIND OF SULPHURET. arge re- quired to completely oxidize i part of the sulphuret. Parts of me- tallic lead reduced by i part of the sulphuret. es of i A.T., 30 grms. or 480 grains, will reduce a lead but- ton of about 15 gram- nitre re- quired to complete- ly oxidize i part of the sul- phuret. mes or 240 grains. i. Zinc blende ... 25 6,5 7-7 2. Manganblende . 30 6-7 7-5 3. Iron pyrites ... 50 8.6 5-8 2.5 4. Arsenopyrite . . . 40 7-3 6-5 5. Copper pyrites . 30 7-2 7 6. Copper glance . 25 3-8 13 7. Gray copper . . . 35 6 S 8. Gray antimony . 25 5-7 9 9. Galena 1.8 2.8* 18 ! * All the lead of the galena and litharge. Should the assayer decide to roast the ore, of course it will not be necessary to make a preliminary assay to determine its reducing power, as the roasting will eliminate the re- ducing elements. But it should be remem- 250 MANUAL OF ASSAYING. bered that the roasting converts the sulphu- rets of copper, iron, manganese, and lead, and their lower oxides, into the higher oxides of the same metals. It will, therefore, make their ores highly oxidizing, requiring a greater amount of reducing agent .in the actual assays, and, perhaps, necessitate preliminary assays to determine their oxidizing powers, as shown in the succeeding paragraphs. 2d Case. No lead button is obtained. This result shows conclusively that the ore has no reducing action. It may also have no oxidizing action ; but, on the other hand, it may. In case it has no oxidizing action, then, for the regular assay, take such an amount of whatever reducing agent is used as will pro- duce the proper weight lead button. Thus: Grammes or Grains Of ordinary 2! 38 Cream of tartar ij 28 Argol i 16 Flour J. 8 Charcoal Will reduce a lead button > of about 15 grammes or 240 grains. GOLD AND SILVER ORES. 251 To determine the exact oxidizing power of the ore, prepare and run the following PRELIMINARY CHARGE TO DETERMINE OXIDIZING POWER. A. T. Weights, Gramme Weights, Grain Weights. Litharge . . i A.T. 30 grammes. 480 grains. Ore JF " 4 " 2 4 Charcoal.. .050 grms. .050 " " Salt cover. Use a "W" crucible, treat in the usual manner, and weigh resulting button. As in the tests for reducing powers, there will be either : i st. A lead button. 2d. No lead button. ist Case. A lead button is obtained. The weight of the lead button will, of course, vary, giving rise to one of three re- sults : A. The lead button has a weight less than o one-half that of the ore. B. The lead button has a weight about equal to one-half that of the ore. 252 MANUAL OF A SSA YING. C. The lead button has a weight greater than one-half that of the ore. To proceed in regular order. A. The lead button has a weight less than one-half that of he ore. Rule. Multiply the weight of the lead but- ton by 20 (to bring the calculations up to the standard weights of i A. T., 30 grammes or 480 grains), and subtract the product from 15 or 240. The difference is a part of the amount of lead kept oxidized by the standard weight of ore employed, and this action is to be neu- tralized by an extra amount of charcoal. Di- vide this difference by the reducing power of the charcoal used, and the quotient will be the weight of charcoal needed. Examples. The figures given were derived from assays on an ore which was composed of about one-half silica and one-half red oxide of iron. The charcoal used had a reducing power of 23.4 that is, one part of the char- coal reduced 23.4 parts metallic lead from the litharge. GOLD AND SILVER ORES. 253 The charge given was run twice, and but- tons weighing o. 30 grammes obtained . o. 30 x 20=6.00; 15.00 6.00=9.00= grammes of lead kept as oxide by the action of the ore. 9-=- 23.4=0.384= grammes of charcoal to neutral- ize this action. Hence, Grms. Charcoal. Grms. Lead. .050X20 = i. ooo to reduce 6.00 9^-23.4 = 0.384 9.00 Or a total of .. 1.384 " " 15.00 Had there been no oxidizing ore present, the i gramme charcoal would have reduced a button of 23.4 grammes, as stated. It actu- ally reduced but 6 grammes ; hence, 23.4 6= = 18.4= grammes of lead kept oxidized by the ore, but, as seen, we cared to reclaim only 9 grammes 6f this 18.4 grammes the re- mainder can be left oxidized. About the same calculations in the grain system would be as follows : 4.62 grains = weight of lead button reduced by f grain charcoal; 4.62x20 = 92.4; 24092.4 = 147.6 = deficiency in grains of lead of a 240 grain but- 254 MANUAL OF ASSAYING. ton ; 147.6-^23.4 = 6.3 = grains of charcoal to reduce that deficiency. Hence, Grains Charcoal. Grains Lead for 0.75X20 = 10.5 to reduce 92.4 147.6 -5-23.^= 6.3 147.6 Or a total of 16.8 ." " 240.0 B. The lead button has a weight about equal to one-half that of the ore. In this case simply multiply the charcoal and ore twenty times for the regular charge. For example, an ore with .050 grammes char- coal as usual gave me a lead button of 0.765 grammes ; hence for the regular assay I took i gramme charcoal to i A. T. or 30 grammes ore to obtain a 15 gramme (15.30) button. In other words, the ore oxidizes such a pro- portion of the charcoal that the remainder of the latter is just sufficient to bring down a button of the right size. C. The lead button has a weight greater than one-half that of the ore. Here we have an example of too slight an oxidizing action, which allows of too great a GOLD AND SILVER ORES. 255 reducing action on the part of the charcoal, resulting in too large a button. There is then needed more oxidizing action, which is effected by adding an oxidizing agent, or, which amounts to the same thing, by lessen- ing the quantity of charcoal. Rule. Multiply the weight of the lead but- ton by 20, and divide the product by 15 or 240. The quotient multiplied by the original amount gives the right quantity of charcoal to reduce a 15 gramme or 240 grain button. Examples. Imagine that the charge on a certain ore gave a button of i.io grammes. This multiplied by 20 is 22 grammes, which is too large a button ; hence, better diminish the quantity of charcoal. If i gramme char- coal with this particular ore brings down a 22 gramme button (instead of 23.4, the ore ox- idizing the difference of 1.4 grammes), then 15 -h 22 r=o.68 ; 0.68x1 = 0.68 grammes, the amount which will reduce a 15 gramme button. In grains, let the lead button weigh 17 ; 17 256 MANUAL OF A SSA YING. grains x 20 340 grains (too large a button) ; 240-^-340=0.7; 0.75x0.7=0.525, or say grain. 2ct Case. No lead button is obtained. This would show that the ore is extremely oxidizing, and to learn its precise strength necessitates the repeating of the preliminary with double, treble, etc., the quantity of char- coal, or till a button finally is obtained. But, in general, it will be safe to use twice the weight of charcoal given, or for the regular assay 2 grammes or 31 grains where the pre- liminary produces no lead or a very minute button. We have previously spoken of certain re- ducing elements in ores viz.: sulphur, arsenic, antimony, and zinc. Aside from the reducing action which they exert upon the litharge, tending to produce too much lead, their pres- ence in an ore is apt to affect the accuracy of the crucible assay. Thus the sulphurets may combine with oxygen, forming oxysulphurets, which possess the undesirable property of taking silver with them into the slag, or, if GOLD AND SILVER ORES. 257 they remain undetomposed, they may easily retain some gold. Arseniates and antimoni- ates, whether existing naturally in the ore, or whether formed by oxidation during the fusion, are also liable to keep silver away from the lead button. Blende or other zinc ores car- rying silver may volatilize this metal or retain it in the slag. The objectionable elements mentioned may be gotten rid of in two ways : by oxidation in the crucible during the fusion, or by a prelimi- nary and separate operation known as roasting. If the sulphur, etc., are in small quantities, the fluxes, litharge and soda, will oxidize them into the slag. If in large quantities, nitre must be used. It is yet a disputed ques- tion among assayers whether to roast an ore for crucible assay or not. Much can be said with truth on each side. If roasting is not performed we save the trouble of an extra operation, and the danger of loss which extra steps are always likely to cause, including the possibility of volatilizing silver by too great a 258 MANUAL OF A SSA YING. heat in roasting. On the other hand, if roast- ing is not performed, and nitre is not used, there are the various chances of loss of pre- cious metal already described. If nitre is used, there is danger of mechanical loss by the foaming of the charge, which may overflow the crucible or leave lead sticking to the sides, high up; or if too much nitre be taken, the lith- arge may not be reduced, so care must be ex- ercised when using it. My own experience with beginners is that they are more success- ful when they previously roast refractory ores, than when they omit this step. It certainly brings the ore into a much more workable condition, as the oxides of iron and copper which are usually left are easily treated. With any particular ore the safest way to proceed is to run duplicate or triplicate assays on both the roasted and unroasted sample, and then to adopt or dispense with the roasting accord- ingly as the results are richer with or without it. For the benefit, then, of learners, for whom this book is written, and not for ad- GOLD AND SILVER ORES. 259 vanced assayers, I give herewith a very care- ful description of the manner of performing this important operation. Roasting. Weigh the ore carefully, sam- pling as usual. Next transfer it to a sheet of black glazed paper, and mix with it about its own bulk of fine charcoal. The latter is usu- ally recommended only when arseniates and antimoniates are present or likely to be formed by a plain roasting ; but I consider it advisable to use it every time, for one cannot always tell when small quantities of arsenic and an- timony are in the ore, besides which, the char- coal aids in expelling the sulphur, and in indi- cating the termination of the roasting. At the worst, it can do no possible harm. If the ore should contain much sulphide of lead (galena) or sulphide of antimony (antimony glance), both of which are quite easily fusible, add to the ore and charcoal on the paper some fine sand or precipitated silica, and mix all well together, for without this addition the minerals while roasting would soon fuse, cake 26O MANUAL OF ASSAYING. together, and adhere to the dish or pan, thus ruining the assay. The proportion of silica to use depends upon the percentages of the minerals named, it increasing as they increase roughly speaking, it can be employed bulk for bulk. In case the ore is a sulphide or mixture of sulphides (of whatever metal or metals), with very little or no gangue, it is best to add silica, to the amount of at least three-fourths of the weight of ore. The contents of the glazed paper are now brushed into either a frying-pan (page 123), or a clay roasting dish (page 105), accord- ingly as an open fire or the muffle is to be used. The frying-pan should be protected by a coating of dry chalk or ruddle (or a water paint of either can be used and the pan dried), or plumbago. The roasting dish may be similarly protected, but it is not so neces- sary. If the standard weights of i A. T., 30 grammes, or 480 grains is used, the ore mix- ture can be roasted in the largest roasting GOLD AND SILVER ORES. 261 dish which will go in the muffle ; but above those weights use the frying-pan, or else roast several charges in the dishes, and unite them for fusion. Place the roasting dish, with contents, in the forward part of the muffle, before the latter has reached a dull red heat. The ore is to be continually stirred with a stout wire, hav- ing a loop at the end at right angles to the wire, ~ ~~A. In a little while, minute sparks will be thrown off, and the ore will begin to glow in places like burning charcoal. Stirring should be continued till the glowing ceases (by which time there will be little danger of fusion), and the whole seems of one color, and yielding to the stirrer like dry sand. The dish can now be moved back to the hottest part of the muffle, and left un- stirred for some little time. When, on bring- ing out to the open air and stirring, the ore gives off neither fumes nor odor, the opera- tion is finished, the ore being now " sweet." Let cool, and examine. 262 MANUAL OF ASSAYING. The roasted ore should be of a dull, dead, earthy color (usually some shade of red or black), having no metallic lustre, containing no large, hard lumps, and having no portions adhering to the dish. See that all the char- coal is burnt out. Should the ore contain many lumps, grind in a mortar, mix with charcoal, return to the dish, and repeat the roasting. If the assayer is too busy to spare the time needed for stirring, let him take the dish, and spread its contents out thinly, or ridge the ore from the center to the edges, so as to increase the surface exposed, and place it in the muffle, and warm it gently for a time ; then increase the heat for about the same length of time ; finally heat quite hot. Take out dish, cool, grind finely, return to dish, and roast again. Repeat the roasting two, three, or more times if necessary. All this will occupy time, but not the direct attention of the assayer. The roasting in the pan is done similarly. GOLD AND SILVER ORES. 263 Whether open-air pan roasting, or dish in muffle roasting is performed, guard against too high a heat at first, as that may cause fusion, or too sudden a delivery of the vola- tile metals mentioned, which may carry off silver, or even too great heat at any stage of the roasting, tending to volatilize silver or gold from some of their combinations. The roasting with charcoal is supposed to decompose all sulphates, arseniates, and anti- moniates, and to expel them ; but where the ore was or contained copper pyrites, a certain quantity of sulphate may remain unchanged. Hence, with ores of this nature, mix the roasted ore with from one-fourth to one-half its weight of fine and dry carbonate of ammo- nia. Return to dish, cover with an inverted roasting dish, and place in a moderately warm part of the muffle till no odor of ammonia can be perceived. The sulphate of copper is converted into sulphate of ammonia, which, being very volatile, is quickly driven off. If the laboratory is provided with gas, the 264 MANUAL OF ASSAYING. ore can be roasted in the usual roasting dish over the Fletcher burners or the Fletcher roasting- furnace, illustrated on page 68, which will work very nicely, as the temperature can be regulated to any degree. Methods of the crucible assay. There are two general methods or systems of crucible assays in use in this country. The first, more ancient, better known, and more commonly used one employs an excess of litharge, and we can therefore consistently call it the lith- arge crucible process. Mr. C. H. Aaron, in his very valuable little work on assaying, designates it as the first system, while another method, which he is the first to describe, he calls the second system. In justice to him, I prefer to call it Aaron s crucible process. The distinction between the two systems is this : The first mentioned uses litharge for two purposes, to furnish lead enough for a lead button to retain the gold and silver, and to aid in fluxing the ore, hence an excess of the litharge is employed. The second uses GOLD AND SILVER ORES. 265 just enough litharge to provide lead for the lead button. In the first, the excess of lead not only slags off the gangue, but it oxidizes all the base metals, save lead, and takes them also into the slag. In the second, the gangue is slagged by soda, borax, or silica, while the base metals are either volatilized, united with sulphur into a matte, or combined with iron. Any ore may be assayed by either of these processes, but each is better suited to certain classes. Mr. Aaron argues that while an assay by the litharge process " is quickly made, and generally gives accurate results," yet " it has the disadvantage of requiring considerable modification for the various ores, as to the fluxes proper, and to the reducers or oxidizers by which the production of lead is controlled. Sometimes a preliminary assay is necessary." For his process he claims the following advantages : " The right quantity of lead may nearly always be got at once, for, al- 266 MANUAL OF ASSAYING. though any lead which the ore may contain will inevitably come down together with that from the litharge used, yet this can be allowed for by reducing the quantity of litharge, or omitting it. As litharge yields ninety-three per cent of lead, it is not difficult to make the adjustment nearly enough. Galena con- tains eighty-six per cent of lead ; hence, if the ore is nearly pure galena, but little litharge is needed. The method requires but slight modification for different ores, and may with little disadvantage be made universal. The button is never much contaminated by cop- per, as it often^ is in the other system, unless a very large proportion of litharge is used, which is disadvantageous in some ways. The crucible is but little attacked, and the assay is not liable to boil over. The method is es- pecially useful for ores carrying much galena or other sulphuret, and when copper in any form is present." An additional advantage, resulting from the above, as remarked by Mr. GOLD AND SILVER ORES. 267 Aaron elsewhere, is the saving in litharge and crucibles. My own experience with Mr. Aaron's pro- cess shows that it takes considerably more time than does the litharge process, and that beginners find it more difficult to operate, and to get satisfactory results. The student can take his choice of either process, apply it to any ore, and experiment till he strikes that combination of correct proportion of the ingredients of the charge, degree of heat, and length of time in furnace, which will give him the best results. Let him remember that the principles of fluxing are true for either process. Preparation of the charge. After having obtained a knowledge of the ore by tests o based upon the study of all the preceding, the proper charge is made up. Further on I have given special charges and directions for certain ores, but here I make it only general. The most convenient and commonly used amount of ore is either one of the standard 268 MANUAL OF ASSA YING. weights I have so frequently spoken of, viz.: i A. T., 30 grammes, or 480 grains. If a very low grade gold ore is under examination, the above quantities can be doubled, trebled, or quadrupled, or, if necessary, ten or even twenty times the standard weight may be used. But such large quantities, with the fluxes accompanying, are rather difficult to handle, so that it is best to run several charges of the standard weight (or, perhaps, double it), and to unite the resultant buttons by scorification. If it should happen that there is not enough of the ore to make a fair charge (say not half the standard weight), then do not trouble about the crucible process at all, but treat the sample by scorification. Bi-carbonate of soda, or, as it is commonly called, soda, is used in every crucible assay. Although not absolutely necessary, still a mixture of it with carbonate of potash gives somewhat more fluid slags. About one part of the latter to four parts of the former is a good proportion. Considering the ore as one GOLD AND SILVER ORES. 269 part, the amount of soda (or of soda and car- bonate of potash together) varies from one- half to three parts. A safe quantity to use is two parts. . Litharge is also used in all crucible assays save those of ores very rich in lead. The proportion varies from one part to eight parts one to two parts being the usual range. Silica is usually employed only for ores full of lime, magnesia, baryta, etc. ; in short, for those whose gangues are basic, or when the ore contains no gangue; but I make it a uni- versal rule to use it in all crucible assays. For those ores which have no gangues or are basic, it is certainly needed. For those which contain silica I still add it, to be certain to convert the excess of lead over and above that required for the standard weight of lead button into silicate of lead, a most efficient flux. This for ores worked by the litharge process. In those treated by Aaron's pro- cess, the added silica converts the soda into 2 7O MA NUAL OF A SSA YING. silicate of soda (or soluble glass), a good flux, although not so powerful as the lead glass. For pure carbonate of lime and similar gangues, use the same weight of silica as of ore. For pure quartzose ores, one-half the weight of ore. For less pure quartz, three- fourths the weight of ore. In brief, my final advice is, not to be afraid of using plenty of silica in crucible charges. Borax is best used in the form of borax glass. For quartzose ores, none is absolutely needed, but about 10 per cent the weight of ore does no harm, and seems to help the fusion. Strongly basic ores need 50 per cent of borax glass. As they diminish in lime, etc., clown to quartz ores, diminish the borax glass down to 10 per cent. Charcoal and other reducing agents, and the oxidizing agent, nitre, are to be used according to their several powers and as the ores vary. It should also be remembered that where gas furnaces are constantly used, there will GOLD AND SILVER ORES. not be required so much reducing agent in the crucible charges as in those made up for solid fuel furnaces, the flame and heat of the gas furnaces being more reducing. A cover of salt is to be invariably used. Select the crucibles, which should be free from cracks and flaws. A good size for the charges to go with the standard weights of ore is 4^ inches wide by 4^ inches deep, outside measurement (size "S" of Battersea make). Clean the crucibles inside if they need it, and number or letter each by means of liquid ruddle, in several places and in large characters, that there may be no difficulty in identifying them after fusion. Weigh out next the soda for the charge, and brush on to a clean piece of black glazed paper. Next weigh the litharge very care- fully, and brush on top of the soda. The silica, weighed approximately, is followed by the ore, charcoal, or other reducing agent, or nitre, each weighed carefully. If sulphur is used, it can come next. Finally, weigh the 272 MANUAL OF ASSAYING. carbonate of potash, rapidly and but approx- imately, as it quickly absorbs moisture from the atmosphere; transfer to the paper, and mix everything thoroughly. Brush the charge into the proper crucible, which it will probably fill two-thirds, tap gen- tly till the contents are level, drop the weighed borax glass on top, and cover with about one- half inch common salt. If nails are used, in- sert them in the charge before the salt is added. Another method of charging or "dressing" the crucibles is to pour the soda into the cru- cible, then the ore, following with the other fluxes, and mixing all together in the crucible with any convenient utensil, as a spatula, spoon, or glass rod. The marking of the crucibles may be dis- pensed with if the fusions are made in regular order; but in this case, great care must be exercised, for doubt once entertained as to the identity of any crucible may dispel faith in those following or preceding it. GOLD AND SILVER ORES. 273 Running the Crucibles in the Fire. Have the fire quite hot, and place on the coals the crucible, holding it with the tongs with one hand, and banking it around with the fuel till it sets firmly and uprightly in place. Place the cover on, and surround with coke, charcoal, or coal, as the case may be. Coke works the best when of about the size of an egg, charcoal may be in somewhat smaller pieces. The finer particles of either are often useful when the fire gets too hot, by choking the draft. Arrange the draft and damper so as to permit of a gradually increasing heat. Occasionally examine the crucible to see if all is working smoothly. In from twenty-five to forty-five minutes the contents of the cru- cible should be in quiet fusion. The length of time that a charge requires to be thor- oughly melted in depends so much upon the ever varying conditions of temperature of the furnace, character of ore, size and nature of 274 MANUAL OF ASSAYING. charge, etc., that no exact rule can be given only see that the charge is fused. When satisfied of this, remove cover, lift out the glowing crucible by means of the long- handled crucible tongs, tap gently, cover, and let cool, or pour into the scorification mould, which will hold the button and some of the slag ; the excess of the latter can run to waste. If nails have been used, before tapping or pouring rinse each nail in the slag, tap and remove. No lead should adhere to them. Crucibles that have had their contents poured out can be employed a second time, or even more often. In case of ores that have shown little or no gold or silver this may do, but with ores of any richness it is a danger- ous experiment. Accuracy should never be sacrificed to a spirit of false economy. Never try to cool a crucible by dipping it into, or holding it under, cold water, as the but partially cooled lead is liable to separate into GOLD AND SILVER ORES. globules of various sizes, incurring danger of loss. When stone-cold, break the crucible by striking it a few sharp blows down one side with a hammer. If skilfully done, the cruci- ble will separate in halves the entire length, exposing the lead button. Such a section would appear about as here shown, showing at the bottom the lead button containing the gold and silver, above it the slag, and topping all a layer of fused salt. (The thin body just above the button shows FIG. 92. how a "matte" would appear were any formed by the fusion of a sulphuret.) From the broken crucible or the poured charge in the mould save a piece of the slag for future examination and comparison. It should be uniform in color and composition -the former will vary with the character of the ore and proportions of the ingredients of the charge. If the latter has been poured, 276 MANUAL OF ASSAYING. the crucible should be but little corroded, and smoothly lined with a thin glaze of the slag, and retain no lumps of semi-fused nature or pellicles of lead. Free the button from the slag, which it should easily and cleanly leave, hammer into shape, as usual, and mark. It may be well to weigh it, so that the assayer may know whether he has used the proper quantity of reducing or oxidizing agent, etc., or to modify the treatment on the same or similar ores in the future. If the button is too large, it may be re- duced by scorification ; but this introduces an additional step, and may not give quite so accurate a result. Finally, cupel the button, weigh, part, in- quart, etc., as previously directed. With all ores poor in silver, deduct the silver known to be in the litharge, according to the amount of the latter employed. General Charges. From what has been pre- viously written of the varying characters of GOLD AND SILVER ORES. 2JJ ores the student can see how difficult, if not impossible, it is to give a charge of fluxes, etc., which shall satisfy every ore. Still, there are a few general formulae useful to have and o quite easy to remember, which can be more or less modified to suit any particular ore. MITCHELL'S CHARGE FOR ALL GOLD AND SILVER ORES. Ore i part. Soda i " Litharge 5 parts. Borax glass i part. Nitre or charcoal and always a cover of salt. The above in each of the three systems of weights : A, T. Weights, Gramme IV eights. Grain Weiglits. Ore i A.T. 30 grammes 480 grains= i oz. Soda i " 30 " 480 " =i " Litharge ....5 " 150 " 2,400 " =5 -" Borax glass .. i " 30 " 480 " = i " Salt cover. A similar but more commonly used propor- tion is : 278 MANUAL OF ASSAYING. Ore , i part. Soda i Litharge if " Borax or silica, nitre or charcoal, and salt cover. Or, to put it more conveniently : A. T. Weights. Gramme Weights. Grain Weights. Ore i A.T. 30 grammes 48ograins=i oz. Soda i " 30 " 480 " Litharge . . if* " 50 " 800 " Salt cover. Mr. George L. Stone has published the fol- lowing as a universal flux for basic silver ores (i.e., those in which the gangue is lime, ba- ryta, etc. for instance, the three spars, calc- spar, heavy- spar, and fluor-spar) : Bi-carbonate of soda 9 parts. Borax glass 3 " Argol i part. " Mix thoroughly, and keep on hand ready for use. For one-third assay ton of ore fill *i| A.T. or i.66| A.T. cannot be exactly weighed with the A.T. weights, but the sum of the following weights will approxi- mate it sufficiently : I A.T. +0.50 + 0.10 + 0.05 = 1.65. GOLD AND SILVER ORES. 279 the crucible about two-thirds full of the flux, adding two or three iron nails if the ore con- tains much sulphur." CHAPMAN'S CRUCIBLE FLUX. "A useful flux, employed largely by the writer during the past ten or twelve years, and which has been found, both in his own practice, and in that of others, to yield good results in all general cases, has the composi- tion given below : 3 Ibs. carb. soda, 2 " dried borax, \ Ib. cream of tartar, 2 oz. white sugar. " The re-agents in these proportions must be intimately intermixed. The above quanti- ties will dress from 18 to 20 crucibles, when about 25 grammes of ore are taken for assay." (Chapman's Assay Notes, 1881, p. 31.) 28O MANUAL OF ASSAYING. AARON'S GENERAL FORMULA. (For ores to be worked by his second system. See page 264.) Ore i part. Soda 3 parts. Litharge , i part. Borax part. Sulphur T V " Flour T V " Iron 3 nails. Glass. Salt to cover. " Melt, and leave in strong fire about twenty minutes after fusion." (Aaron's Assaying, 1884, p. 530 The above amplified as usual is as follows : A. T. Weights. Gramme Weights. Grain Weights. Ore i A.T. 30 grammes 480 grains^ i oz. Soda 3 " 90 " 1,440 " Litharge . . i " 30 " 480 " Borax J " 15 " 240 " = \ " Sulphur... T V " 3 48 " = T V" Flour T V " 3 " 48 " = T V Iron 3 nails. Glass. Salt cover. GOLD AND SILVER ORES. 281 The same excellent authority, Mr. Aaron, gives the following charge for " ordinary ores containing little or no sulphuret, some quartz, clay, lime, iron, oxide, etc. " : Ore i part. Soda i " Litharge 2 parts. Dried borax i part. Flour yig- " Salt cover. " Fuse quickly ; keep in furnace five to ten minutes after subsidence." (Aaron, page 49.) Putting the above in the three systems of weights, and reducing the flour one-half, since the quantity given is based on a standard of \ A. T. ore, we have the following : A. T. Weights. Gramme Weights. Grain Weights. Ore i A. T. 30 grammes 480 grains^ i oz. Soda i " 30 " 480 " = i " Litharge ... 2 " 60 " 960 " =2 " Dried borax, i " 30 " 480 " =i " Flour i grm. i grm. 16 " Salt cover. The following and concluding charge of 282 MA N UAL OF A SSA YING. this section is one I have used many times for ores similar to those above spoken of; that is, not containing much sulphuret, or oxidized metal ; " dry ores," in short, or, as Mr. Aaron calls them, " ordinary ores." The nature of the gangue is unimportant, as I have gotten as perfect and as vitreous slags from pure limestones as from pure quartzose rock, by using it. A. T. Weights. Gramme Weights. Grain Weights. Ore i A. T. 30 grammes 480 grains= i oz. Bi-carb. soda i| " 45 " 720 " =ij " Carb. potash \ " 15 " 240 " = i " Litharge . . . i| 45 " 720 " =i| " Silica i " 30 " 48o " =i " Borax glass. \ " 15 " 240 " =i" Charcoal . . . T 6 o grms. ^ " 9i " Salt cover. The charcoal is used on the basis of a reducing power of about 25. Time in fire, about one-half hour. Special charges and directions. I shall here give charges for certain well known ores, as examples of the varying modes of treatment. GOLD AND SILVER ORES. 283 These are iron pyrites and its oxide, the sul- phurets of copper and their oxides, and galena. All other ores and combinations can be worked by some one of the general or special methods, or some slight modification of one of them. I. IRON PYRITES. Pyrite, the true iron pyrites, is one of the most widely distributed of minerals, is found in the rocks of every age, and is a common and abundant source of gold. There are many varieties of it, and of another and simi- lar mineral, pyrrhotite, which have received many names, as pyrites, iron pyrites, pyrite, marcasite, mundic, bi-sulphuret or bi-sulphide of iron, sulphuret or sulphide of iron, and pyrrhotite, magnetic pyrites, magnetic iron pyrites, magnetic sulphuret of iron, magneto- pyrites, etc. But since the assay treatment makes no mineralogical distinctions, I shall include under the one simple and well known heading of " iron pyrites " any combination 284 MANUAL OF ASSAYING. of iron and sulphur, with or without a gangue, and direct accordingly. Iron pyrites has frequently united or asso- ciated with it varying amounts of other met- als, as nickel, cobalt, copper, zinc, manganese, arsenic, antimony, etc. If in small quanti- ty, none of these need influence the charge or manner of treatment. If in large quantity, making either a compound mineral, or a com- bination of various minerals, they may necessi- tate some variation in the mode of treatment. Since, as stated, iron pyrites is found in rocks of every geological epoch, we may ex- pect to have every kind of gangue ; but, by remembering the rules already given, that acid and basic gangues are to have basic and acid fluxes, no trouble need be feared. Sil- ver, if present, will come down with the gold. METHOD A. Desulphurization by a preliminary roasting. For the ore without any gangue, or for GOLD AND SILVER ORES. 285 " concentrates," mix i part (i A. T., 30 grammes, 480 grains) with i part of silica. Mix the above, or the ore alone, if it has a gangue, with its bulk of fine charcoal, and roast according to pages 259-264. After roasting, add the other constituents, so that the total charge will be as follows : CHARGE. A. T. Weights. Gramme Weights. Grain Weights. Ore (roasted) . i A.T. 30 grammes 48ograins=i oz. Bi-carb. soda .ij " 45 " 720 " =ij" Carb. potash . J " 15 " 240 " = i " Litharge i " 45 " 720 " = i" Silica i " 30 " 480 " =i " Borax glass . . \ " 6 " 96 " = % " *Charcoal . . . . J grm. f " n-J- " Salt cover. Use an "S" Battersea crucible (4! inches deep, 4-J- inches across, outside measurement). If it is feared that a little sulphuret may re- main unoxidized during the roasting, one nail may be pushed into the charge, and is to be removed immediately after fusion. * Assumed to have a reducing power of 25. 286 MANUAL OF ASSAYING. Time in fire about thirty minutes, or, at all events, let remain heating for ten minutes after the charge has settled into quiet fusion. It is well to bear in mind that iron pyrites (pyrite) loses exactly one-third of its weight by being roasted into the red oxide, so that one part of the sulphuret becomes but two- thirds of a part of oxide. (The varieties of pyrrhotite lose from one-seventh to one-eighth in weight.) Further, that one part of the red oxide keeps oxidized about \\ parts of litharge, or, more exactly speaking, it oxidizes the charcoal which would reduce \\ parts litharge. The charge given, as stated, is for an ore almost, if not entirely, iron pyrites. From such a large percentage it may run down to a very small amount of the mineral, the gangue, of a necessity, increasing accordingly. If the gangue is silicious, diminish the added silica in the charge as the proportion of gangue increases, but do not altogether omit it for even the most silicious ore retain from \ to GOLD AND SILVER ORES. 287 ^ a part. If the ore is limey or otherwise basic, retain the full part of silica, and increase the borax glass to \ a part. The charcoal (or any other reducing agent) must, of course, be decreased as the iron py- rites decreases, for the less there is of the latter the less oxidizing power there is in the roasted ore. The actual quantity of charcoal to use on any particular ore is determined by either guessing the percentage of sulphuret in the unroasted ore, or by making a prelimi- nary assay to determine the oxidizing power of the roasted ore. Instead of doing the lat- ter additional work, the assayer can come closely enough to the size of the button he wants (15 grammes or 240 grains) by adding charcoal as the redness of the roasted sample increases, and vice versa, as follows (the char- coal considered to be of a reducing power of 25): 288 MANUAL OF ASS A YING. Grammes of Color of Roasted Ore. Charcoal to Use. Very deep red o . 850 Deep red o . 800 Medium deep red o . 750 Red o . 700 Medium light red .... 0-675 Light red . . . 0.650 Very light red 0.625 Very light rose or pink o . 600 The slags from crucible runnings of the ore we are discussing, if the fusions have been properly conducted, will always be homogene- ous and glassy in texture, and will be translu- cent or transparent when not much iron oxide is present, opaque when the oxide prepon- derates ; in color, ranging from very light green to a black, with a greenish or grayish tint accordingly as the iron oxide increases. METHOD B. Desulphurization during the fusion. With ores treated by this method we do not get rid of the sulphur of the iron pyrites by a preliminary operation, but do the desul- GOLD AND SILVER ORES. 289 phurizing during the fusion by the oxidation of all the sulphur (save a sufficient quantity to bring down a 15 gramme or 240 grain but- ton) by means of nitre. CHARGE. For pure pyrites (i.e., free from gangue) and "concentrates."' A. 7\ Weights. Gramme Weights. Grain Weights. Ore i A.T. 30 grammes 480 grains=i oz. Bi-carbsoda .\\ " 45 " 720 " =ij" Garb, potash. " 15 " 240 " = J" Litharge \\ " 45 " 720 " =i|" Silica i " 30 " 480 " = i " Borax glass.. \ " 6 " 96 " = |" Nitre 2 " 56^ " 870 Salt cover. Use Battersea "J" crucible (6f inches deep, 4f inches across, outside measurement). Time, about half an hour. The oxidizing power of nitre varying, the amount used may have to be altered some- what according to its strength, as determined on page 162. The quantity taken was deduced from the following calculation for example, the weight in grammes: i gramme iron pyrites reduces 8.6 grammes lead (according to the 2QO MANUAL OF ASSAYING. table on page 249); hence, 1.74 grammes py- rites will reduce about 15 grammes lead; 30 1.74 = 28.26=1 grammes of iron pyrites to be oxidized, i gramme iron pyrites requires for oxidation' from 2 to 2\ grammes nitre; hence, 28.26x2 = 56.5= grammes nitre to use. Run in good fire, twenty minutes to fusion, ten afterward. Slag brown-black, vitreous, opaque. If the button is at all brittle from presence of sulphur, add lead and scorify. For other ores, as the iron pyrites diminishes (and the gangue increases), lessen the silica and nitre. The quantity of the latter to use is determined by experience and experiment, or by ascertaining the reducing power of the ore, for which latter see page 242. METHOD c. Desulphurization during the fusion. This method of treating the ore is to use an excess of nitre, i.e., more than enough to oxidize all the sulphur, bringing everything into quiet fusion, and then throwing down GOLD AND SILVER ORES. 29! the proper weight of lead by adding a known amount of some reducing agent, as charcoal, or a mixture of charcoal and litharge, or galena and litharge. The reduced lead in its passage down through the molten charge ab- sorbs the gold and silver. CHARGE. For iron pyrites with no gangue, or concentrates. A. 7\ Weights. Gramme Weights. Grain Weights. Ore i A.T. 30 grammes 480 grains=i oz. Bi-carb. soda.i-| " 45 " 720 " =i" Carb. potash. - " 15 " 240 " = " Litharge 6 " 175 " 2,880 " =6 " Silica 2 " 60 " 960 " =2 " Borax glass.. i " 30 " 480 " =i " Nitre 2- " 75 " 1,200 " 2% " Salt cover. Use a "J" crucible. Begin with a very gentle heat, and grad- ually bring up to a full red heat (thirty-five minutes). When in full fusion add the fol- lowing weight of charcoal wrapped in tissue paper (considering the weight, of the paper as charcoal) : i gramme, or 15^ grains. 292 MANUAL OF ASSAYING. When again in quiet fusion (five minutes), remove and tap, or pour. Slags brownish- black, vitreous, opaque. For less pyritic ores use less nitre. METHOD D. Desulphurization with iron. CHARGE. Make up the ore with fluxes as follows: A. T. Weights. Gramme Weights. Grain Weights. Ore i A.T. 30 grammes 480 grains i oz. Bi-carb. soda.i^ " 45 " 720 " =i-J- " Carb. potash. 4 " 15 " 240 " -j- " Litharge 1 " 45 720 " = 1^ " Silica i " ,30 480 " =i " Borax glass.. -J- " 6 96 Iron nails, 6. Salt cover. Use " S " crucible. Time, one-half hour. Tie the nails with wire together, and stick the bunch into the charge, points down. After fusion, should any " matte " be formed, it must be scorified, with the lead button, to a pure and malleable condition. Slags brown-black, vitreous, opaque. GOLD AND SILVER ORES. 293 METHOD E. Converting the iron pyrites into matte. Aaron s process (modified). CHARGE. For concentrated pyrites. A. T. Weights. Gramme Weights. Grain Weights. Ore i A.T. 30 grammes 480 grains = loz. Bi-carb. soda. 3 " 90 1,44 " = 3 " Litharge \ " 15 " 240 " =r 1 " Silica i " 30 " 480 " =i " Borax glass., " 15 " 240 " | "' Nitre f " 12 " 18* " Iron nails, 6. Salt cover. Use " S" crucible. Time forty minutes. The nitre is to oxidize the excess of sul- phur ; i.e., that over and above the amount necessary to reduce all of the litharge, and yet not enough of this re-agent is used to prevent the formation of a matte. Slag coal-black, vitreous, opaque. Mr. A. H. Low, of Argo, Colo., has given me a good hint in the crucible running of sul- phuret ores, which I herewith note. Make 294 MANUAL OF ASSAYING. the fusion in the usual manner, and when it is supposed to be completed, take out, and pour off as much of the slag as possible without losing any of the lead. The button can now be easily seen, and if all the sulphur has not been driven off, replace the crucible in the fire at an angle, and scorify, as it were, till the sulphur has gone ; take out, pour, and the result will be a clean button. For ores which are much richer in gold than silver, and in which it is not desired to determine the latter, the operation of inquar- tation of the resultant bead can be dispensed with by putting in the charge before running a piece of pure silver of the proper weight ; it will help to collect the gold, moreover. Comments on the Jive preceding processes. With these, as with others, each assayer will find some certain one will, with him, work better, and give higher results than the oth- ers. He can then practice until he ascertains which one suits him the best, and always employ that. GOLD AND SILVER ORES. 295 My own experiments, and those of my stu- dents, tend to prove that each of the first three methods is pretty sure to bring down all the gold ; that the fifth method must be worked very carefully to obtain correct results, and that the fourth is the most unsatisfactory of all. Further, that the first method gives higher silver than any of the others, which supports the theory that, with sulphur in an ore during its fusion, oxy-sulphureta are formed, which drag silver with them into the slag. Many ignorant assayers insist that from unroasted sulphuret of iron ores, no gold will be obtained by crucible fusion. This extra- ordinary idea, which, however, seems to spread, is entirely unfounded, or, at best, is based upon botchy experiments. The stu- dent may rest assured that he can, with care- ful working, extract all the gold from an unroasted ore by any one of the nitre meth- ods. 296 MANUAL OF ASSAYING. II. OXIDE OF IRON. One of the results of the decomposition of iron pyrites is oxide of iron, existing either as limonite, which is the oxide with water, or as hematite, the oxide without water. It is even more widely distributed than iron pyrites, and since the latter is one of the most common sources of gold, so likewise is oxide of iron, with the advantage that that precious metal is retained therein in a free-milling condition. It is so universal that any brownish, yellow- ish, or reddish coating on an ore is almost certain to be partially, if not entirely, oxide of iron. The ore can be treated in two ways, by the charge given for the iron pyrites after roast- ing (on page 285), remembering that there is a full part of this ore, against three-fourths of a part of the roasted sulphuret, or by Aaron's process. GOLD AND SILVER ORES. 297 CHARGE. LITHARGE PROCESS. A. T. Weights. Gramme Weights. Grain Weights. Ore i A. T. 30 grammes 48ograins=i oz. Bi-carb. soda i J " 45 720 " =i-J-" Garb, potash | " 15 " 240 " -J- " Litharge ... \\ " 45 720 " = i" Silica i " 30 " 480 " =i " Borax glass. \ " 6 " 96 " \ u Charcoal . . . i grm. i " 15^ " Salt cover. The above charge is, for the oxide ore, quite free from gangue. As has before been stated, diminish the silica and charcoal as the gangue increases. It may be as well to add a cautionary note, to the effect that limonite, the hydrous oxide (yellow or brown in color), contains about 14^ per cent, of water of combination, while hematite, the red oxide, contains none what- ever; hence use more charcoal, or other reduc- ing agent, for the latter than for the former. 298 MANUAL OF ASSA YING. CHARGE. AARON'S PROCESS (MODIFIED). A. T. Weights. Gramme Weights. Grain Weights. Ore i A. T. 30 grammes 48ograins=i oz. Bi-carb. soda 3 " 90 " 1,440 " Litharge . . . " 15 " 240 " Silica i " 30 " 480 " =i " Borax glass. " 15 " 240 " = % " Sulphur -J " 15 " 240 " = i" Flour ^ 12 " i8J Iron nails, 6 Salt cover. Many times the assayer will meet ores which are mixtures of iron pyrites, and its decomposed substitute, iron oxide. Such must be treated by the methods given for the former mineral. If the pyrites is in very small quantity, Process A, without a prelimi- nary roasting, may be used (in this case em- ploy but from one-third to one-half the amount of charcoal), as the fluxes will do all the necessary desulphurizing. III. SULPHURETS OF COPPER. Including sulphuret of copper (chalcocite, copper glance, vitreous copper, copper sul- GOLD AND SILVER ORES. 299 phide), which when pure contains 79.8 per cent of copper and 20.2 per cent sulphur, and which is more liable to carry silver than gold ; copper pyrites (chalcopyrite, sulphuret of cop- per and iron), a valued source of the precious metals, and which is composed of about equal parts of copper, iron, and sulphur ; bornite (purple copper ore, variegated copper ore, va- riegated copper pyrites, erubescite, " horse- flesh " ore, sulphuret of copper and iron), an ore similar to the preceding, but with less iron; gray copper ore ("fahlerz," tetrahe- drite), a sulphide of copper and antimony with smaller and varying amounts of other sulphu- rets ; and finally, all other and rarer sulphu- rets with copper as an important ingredient, such as Barnhardite, Bournonite, Carrollite, Covellite, Harrisite, Stromeyerite, and Ten- nantite. These ores can be treated by any one of the five methods given for the sulphuret of iron, and which I repeat here, with some alterations in the proportions of the ingredients of the 300 MANUAL OF ASSAYING. various charges, and, for the sake of space, in tabular form. Even these charges will have to be modi- fied more or less to suit any particular sam- ple, for it may be a mixture of two or more of the above-named ores, but they will serve as representative methods. Salt cover to all, as usual. METHOD A. METHOD B. METHOD C. METHOD D. METHOD E. Ore. i A.T. 30 grins. 480 grains. Roasted. i A.T. 30 grms. 480 grains. i A.T. 30 grms. 480 grains. i A.T. 30 grms. 480 grains. i A.T. 30 grms. 480 grains. Bi-carb. Soda. 4 A. T. 45 grms. 720 grams. . i^A.T. 45 grms. 720 grains. i| A. T. 45 grms. 720 grains. 4A.T. 45 grms. 720 grains. 3 A. T. 90 grms. i, 440 grains. Carb. Potash. \ A. T. 15 grms. 240 grains. U.T. 15 grms. 240 grains. iA.T. 15 grms. 240 grains. iA.T. 15 grms. 240 grains. Litharge. 2 A.T. 60 grms. 960 grains. 2 A.T. 60 grms. 960 grains. 6 A.T. 175 grms. 2,880 grains. 2 A.T. 60 grms. 960 grains. iA.T. 15 grms. 240 grains. Silica. i A.T. 30 grms. 480 grains. i A.T. 30 grms. 480 grains. 2 A.T. 60 grms. 960 grains. i A.T. 30 grms. 480 grains. i A.T. 30 grms. 480 grains. Borax glass. |A.t. 6 grms. 96 grains. i A. T. 6 grms. 96 grains. i A.T. 30 grms. 480 grains. iA.T. 6 grms. 96 grains. iA.T. 15 grms. 240 grains. Charcoal. T 8 ff grm. 12^ grains. o After fusion i grm. 15^ grains. Nitre. if A. T. 50 grms. 770 grains. 2! A.T 67 grms. i, 080 grains. r =18.95=07. silver per ton of scales. or 208-7-10.97102, J o.i -=-320=0.0284375 ; then 0.0284375X29.166, "I or 9.1X0.09114, > =0.83=02. gold per ton of scales. or 9.1-7-10.97102, 51.75 mgrms. silver, total. Siftings : 319.74 grammes, 30 grammes produced j [52.25 51.75^-30=1.725; i.725X3i9-74=55i.55i5; 551.5515-^320= 1.7236; then 1.7236X29.166, ] = 50.2=07. silver per ton of or 551.5515X0.09114, } siftings. or 551.5515-5-10.97102, J 1.50-5-30=0.05 ; 0.05X319.74 = 15-987, 15.987-5-320=0.04996 ; 332 MANUAL OF ASSAYING. then 0.04996X29.166, "1 or 15.987X0.09114, V =1.45=02. gold per ton of siftings. or 15.987-7-10.97102, J Silver : in scales, 18.95 oz., @ $1.29 per oz., =$24.44 per ton. " siftings, 50.20 " " " " = 64.75 total, 69.15 " " " " $89.19 " Gold: in scales, 0.83 oz., $20.67 per oz.,=$i7.i5 per ton. " siftings, 1.45 " " " " = 29.97 " " total, 2.28 " " " " =$47.12 Total value of scales $24.44-f$i7.i5=$ 41.60 per ton. Total value of siftings . . .$64.75~|-$29.97=$ 94.72 " Total value of ore $89.i9+$47.i2=$i36.3i " Check.* 0.260 : 208: : 29.166 : x, o.26ox 29.166X208=6066.928, x =6066.928-5-0.260=23334.338,23334.338X1.29=30101.29. 0.260: 9.1 :: 29.166 : x; o.26ox=29.i66X9. 1 = 265. 4106, x =265.4106-^-0.260=1020.81, 1020.81X20.67=21100.14. 30101 .29+21 100. 14=51201 .43. 0.260 tons scales, @ $51,201.44 per ton=$i3,3i2.37 319.740 " siftings, " 94. 72 = 30.285.77 320 tons original ore, worth $43,598.14 ; or i ton is worth $136.24. *The idea of the check or verification is taken from C. H. Aaron's excellent little work on assaying, and consists in consid- ering the ore as made up of two kinds of material, assaying each part as though it was the original ore, and from the number of imaginary tons of each kind, calculating the actual value of a ton of the mixed or original ore. APPENDIX. 333 III. ANALYSIS OF COPPER ORES. The wet process or analysis of copper ores is so much more accurate than the dry pro- cess or assay, that it should always be employed when practicable. As in the assay of copper, so in the anal- ysis, there are many methods, here included under three heads ; volumetry, gravimetry and electrolysis. While there are good ways of determination among the first two classes, yet I prefer one in the third, owing to its simplicity, accuracy, freedom from intricate calculation, and the ease with which it can be acquired. The process I now describe is known as the Luckow method, and consists, briefly defined, in dissolving the copper out of its combina- tions by means of acids, and then depositing it as the metal itself upon another metal, platinum, by the action of an electric current. It makes no difference whatever in this method, how the copper is 'originally com- bined, whether as a sulphide or in a mixture 334 MANUAL OF ASSAYING. of sulphides of other metals, an oxide or car- bonate, a matte or an alloy ; the copper comes out as metallic copper in any case. * PROCESS. Prepare the sample in the usual manner, being sure to use a loo-mesh sieve. Sample and weigh out very carefully on the ore scales, one gramme, if the ore be at all rich (say above 20 per cent), or five grammes if it be poor in copper (below 20 per cent). Brush into a casserole, i.e., a porcelain evaporating dish with a handle (fig. 75), and cover with a clock-glass (fig. 68), of slightly larger dimensions, and add 10 cubic centi- metres of pure and concentrated nitric acid, by means of a 10 c.c. pipette (fig. 76). Now place the casserole either on a sand- bath (a common tin plate holding some dry * If accessible, consult a very interesting paper, entitled "Com- parison of Various Methods of Copper Analysis," by Mr. W. E. C. Eustis of Boston, which was read at the August, 1882, meeting in Colorado of the American Institute of Mining Engineers, and is to be found among the published transactions of that society. APPENDIX. 335 sand), or on a piece of wire gauze, supporting either on a ring-stand (fig. 81), and heat with a Bunsen burner (fig. 83), or alcohol lamp. Continue this heating some little time, then let cool. When cold, add, from another pipette, 5 c.c. of pure and concentrated sul- phuric acid, and heat to boiling till no more red fumes are given off, but in their stead dense ivhite vapors are delivered. The red fumes are from the nitric acid, the excess of which we wish to get rid of, which is done by means of the sulphuric acid, and the white fumes show that the former acid is about gone. Let the casserole stand till cold. Now add about 50 c.c. of distilled water, stir with a glass stirring rod, heat, and let stand till any undissolved matters have set- tled to the bottom of the casserole. While this is doing, prepare for filtering, that is the separating of the dissolved copper (and other metals) from the undissolved silica, etc. Place in proper position a filter- stand (fig, 87), glass funnel (fig. 74), and 336 MANUAL OF ASSAYING. glass beaker (fig. 73). The filter-paper is fitted by cutting a piece in a square, then folding in half, diagonally, and then into quar- ters ; it will form a triangular figure, and if the corners are cut off in a curved line, a circle will be formed on spreading out. Upon open- ing the folded paper so that three thicknesses come on one side and one on the other, a filter is obtained, which is placed in the funnel and wetted by means of the wash-bottle (fig. 67). This useful piece of apparatus is oper- ated by simply blowing in at a ; a fine stream of water at once issues from b, which can be directed against any part of the funnel. Filter the liquid in the casserole by holding the glass-rod outside the lip of the vessel, allowing the solution to run down the rod into the funnel, till the latter is nearly full. Repeat the operation until nearly all the solu- tion has passed through the funnel, and only the sediment, nearly dry, is left in the casserole. Examine the residue, and if it is dark-colored, it is best to repeat the treatment with acids. APPENDIX. 337 Generally, however, once is enough. Finally wash the contents of the casserole into the funnel, which fill three or four times with water, which will be sufficient to wash out all the copper solution. The residue on the filter-paper consists of silica and other substances insoluble in the acids used. It should contain no copper. The filtrate, that is the filtered liquid, con- tains the copper as sulphate (with perhaps some nitrate), also it may be, iron, lead, etc., but these do no harm. The next thing is to deposit the copper upon platinum. We may use a vessel entirely of platinum, or a copper dish lined with plati- num, or a horseshoe shaped strip of platinum suspended in a glass beaker. In case the operator possesses the platinum or platinum- lined dish, clean it thoroughly by washing. If it is a new vessel, best rinse it first with some solution of caustic soda or potash to remove grease, then rub it gently with a little fine sand, thus giving the interior a surface favor- MANUAL OF ASSAYING. able for deposition. Be sure to wash off all the soda or potash solution and sand, then warm till it is perfectly dry. When cool, weigh carefully on the ore scales and note the weight. Pour the copper solution into the platinum dish, using the glass-rod, which rinse off with water into the dish; finally rinse out the beaker with a little water into the dish. We now have a weighed dish containing copper in solution from a known weight of ore. It remains to connect it with a battery, which latter is now described. FIG. 93. Fig. 93 represents two cells of what is com- monly known as the " Bunsen Carbon," which APPENDIX. 339 form a battery powerful enough for our pur- pose. A quart size will be about right. It consists of a glass cell or jar to contain the dilute sulphuric acid, a cylinder of cast-zinc, of which the ends do not quite meet ; a po- rous earthenware cup, to hold nitric acid, and a rod of compressed carbon. Prepare a mixture of strong sulphuric acid (ordinary commercial) and water in the pro- portion of one part of the former to ten of the latter, observing the precaution of pouring the acid into the water, never the reverse. Let the zincs stand in this acid solution for two or three minutes, then pour over them a little mercury, and rub with a piece of soft rag tied around a stick, till the entire surface, inner and outer, of the zincs, is coated with amal- gam. Put each cell properly together and fill the glass jars with the sulphuric acid mixture, just covering the tops of the zincs. Next, nearly fill the porous cells with concentrated (com- 34O MANUAL OF ASSAYING. mercial) nitric acid. * See that the binding screws are filed bright, also the connecting wires, to make good contact. Arrange appa- ratus as follows : The zinc of the first cell is to be united with the platinum dish by means of a coil of copper wire underneath the latter. A strip of platinum foil (cleaned with potash solution and sand) just dips into the solution of cop- per, and is connected to the carbon of the second cell by a copper wire. Another wire between the zinc of this latter cell and the carbon of the first, completes the circuit. Cover the dish with two pieces of window- glass, to prevent loss by spattering. The copper at once begins to line the inte- rior of the dish, and in from four to six hours the deposition will generally be complete. Time is often gained by starting the action at evening, and letting it run a!4 night. Prove the complete deposition of the cop- * A bench of from two to six so-called "gravity" cells will do instead of the pair of Bunsen Carbons, and are more constant. APPENDIX. 341 per by taking one drop of the solution and adding to it one drop of sulphuretted hydro- gen water, mixing the two on a white surface (cover of a porcelain capsule). If no colora- tion ensues, the copper has all been thrown down ; if a black discoloration follows, then there is still copper in solution. In this latter case, continue the current till the test is negative. In the former case, pour the contents of the dish into a clean beaker, rinse the dish, the under surfaces of the glass plates and the platinum strip, into the same beaker. On adding to the contents of this beaker an excess of aqua ammonia, no blue coloration should be seen. Add a few drops of alcohol to the dish, rinse around and drain off. Set fire to the little remaining in the dish, and when the lat- ter is cool, weigh. The difference between this latter weight and the original weight of the dish is metallic copper.* I give an example : 34 2 MANUAL OF ASSAYING. Weight of ore taken =i gramme. GRAMMES. Weight of platinum dish and copper=56.4o8 copper from i gramme^ 0.749 0.749 multiplied by 100, gives 74.9 per cent of metallic copper in the ore. As before mentioned, instead of the platinum dish, which is quite expensive, a glass beaker can be used to contain the copper solution. A second platinum strip, on which is to be deposited the copper, must be used here. Dip this in the beaker and connect with a zinc element. The platinum strip in straight form connects with the other carbon as usual. If the copper should form dark colored on the platinum, it is because the solution is too acid. Nearly neutralize with a little ammo- nia water, to counteract its bad effect. Too strong a current should also be avoided. I have given this process well in detail, but it will be found to be much easier learned than described. It is a very pretty and satisfactory method. APPENDIX. 343 Volumetric analysis of copper ores. If very many tests of copper ores, slags, mattes, etc., are to be made daily, it will be better to use the volumetric process, for while it is not quite so accurate as the battery pro- cess just described, it is much more rapid. My thanks are hereby tendered to Mr. F. E. Fielding, of Virginia City, Nev., for many of the details embodied in the following de- scription. Preparation of standard solutions. Solution of cyanide of potassium. Dissolve 130.2 grammes of the pure salt in i litre (1,000 c.c.) of distilled water, and preserve from the light in a glass-stoppered bottle. Solution of metallic copper. -- Dissolve i gramme of pure copper in 25 c.c. nitric acid of 32 Beaume (specific gravity 1.26, see page 211) in a covered beaker; then add 7 c.c. of dilute sulphuric acid. When dissolved and cool add caustic ammonia, or, better still, am- monium carbonate, in slight excess, or until the blue color is perceptible throughout. Di- 344 MANUAL OF ASS A YING. lute, when cool, with distilled water to exactly i litre. Standardizing the cyanide solution. Divide the copper solution in two beakers, so that exactly 500 c.c. shall be in each one, repre- senting \ gramme of pure copper. Run in the cyanide solution from a burette until a faint violet color is produced. Treat the sec- ond portion in the same manner, and take the mean of the two results as the standard. Multiply each result by two to bring it up to the basis of i gramme of pure copper, repre- senting 100 per cent. The cyanide solution should be re-standardized every day or so. Preparation of the ore solution. Weigh 2 grammes of the ore, or 5 grammes if very poor in copper, place in a flask, beaker, or casserole, moisten with about 7 c.c. sul- phuric acid, then add 25 c.c. of nitric acid. Digest at a gentle heat, or until the silicates look white, showing that all the metals have been extracted. Boil until fumes of nitrous acid are no longer evolved, cool, and add am- APPENDIX. 345 monia or carbonate of ammonia in slight ex- cess ; allow the solution to become cool and the separated flakes of brown-red hydrated sesquioxide of iron (if present) to settle to the bottom of the vessel. If necessary, filter, and wash the filter paper thoroughly. The analysis. The standard solution of cyanide is now gradually added from the burette (constantly stirring the copper solution), until the blue color has entirely disappeared, and has been replaced by a faint violet tint, corresponding as nearly as possible to the shade produced in titrating the solution of pure copper in stand- ardizing the cyanide solution. The number of c.c. used to produce this is now read off, and from it the percentage of copper in the ore is calculated. A single example will illustrate the simplicity of the calculations. We will imagine it required 125 c.c. of the cyanide solution to neutralize the i gramme of pure copper representing ioo per cent, 346 MANUAL OF ASS A YING. while it took but 75 c.c. for, say, 2 grammes of ore. 125x2=250; 75-5-250=0.30; 0.30x100=30, or 30 per cent. Hence the rule : Multiply the number of c.c. of cyanide solution used for the pure cop- per test by the number of grammes of ore taken. Divide the product into the number of c.c. employed on the ore test, and the quo- tient multiplied by 100 will give the percentage of copper in the ore. When a sulphuretted ore is to be operated upon, it will, in a majority of cases, be com- pletely oxidized by a mixture of sulphuric and nitric acids, but should any globules of sulphur remain, they may be taken out after the dilution of the solution, ignited, and the residue dissolved by nitric acid, and added to the original solution. (Or such ores may pre- viously be roasted in the manner described in the section on gold and silver ores.) Some ores are best attacked by aqua regia (i part nitric acid to three parts hydrochloric acid). Owing to the influence of varying quanti- APPENDIX. 347 ties of ammonia and of ammonium salts upon the decolorization of copper solutions by po- tassium cyanide, it is necessary that both the test solution originally prepared and the vari- ous copper solutions subsequently titrated should contain, as nearly as possible, equal amounts of ammonia. Interferences, and their removal. Zinc, nickel, and cobalt. These, if present, render the analyses unreliable, so that, in such cases, the copper must be removed by precipi- tation from its solution. This may be done by placing a piece of iron or zinc in the solu- tion care being taken that nitric acid is not present. The precipitated metallic copper thus obtained is, after removal from the re- maining solution of interfering metals, dis- solved in the usual manner.* The copper may also be precipitated as sulphide by means of sulphuretted hydrogen (see page 150) in * Instead of re-dissolving, it can be drie'd and weighed as me- tallic copper, giving approximately the percentage of this metal in the ore. 348 MANUAL OF ASS A YING. acid solution, or by solution of sodium thio- sulphate (hyposulphite of soda), and the sul- phide re-dissolved and estimated as described. Manganese is not often found in copper ores in sufficient quantity to interfere. If present, it may be removed by adding to the ammoniacal solution sodium carbonate, and a few c.c. of bromine water, and boiling. When cool add the standard solution in the usual manner. Arsenic does not interfere, excepting in the presence of iron, when it forms an arseniate soluble in ammonia, and gives rise to a brown- ish color in the liquid. It may be removed by adding magnesium sulphate (epsom salt) in excess. As soon as a precipitate is no longer formed, and the solution has recovered its characteristic blue color, run in the stand- ard solution. Silver. If this be present to any great ex- tent, it may be removed by adding a few drops of hydrochloric acid to the solution, and filtering before the addition of ammonia. (Or APPENDIX. 349 the hydrochloric acid may be added at same time as the nitric and sulphuric acids.) Iron. This, in the state of ferric hydrate, does not interfere chemically, but obscures changes of color by its being disseminated throughout the solution ; hence, it must be allowed to settle after each addition of the standard solution. It may be kept in solu- tion by means of tartaric or citric acid. If it is allowed to be thrown down by the ammonia, whether to be removed by filtration or not, it should be borne in mind that in the case of ores very rich in iron, the iron precipitate will retain copper, which cannot be dissolved out of it by either boiling water or ammoniacal water. Up to about five per cent of iron, no special pains need be taken, but above that amount, the copper ought to be first removed from the solution by sul- phuretted hydrogen, then dissolved as usual. Lead, bismuth, antimony, and magnesia do not interfere. Lime in large quantity tends to confuse the 3 5 O MANUAL OF A SSA YING. results ; it may be removed by addition of oxalate of ammonia. The preceding statements regarding inter- ferences are well borne out by a series of ex- periments carried on by Messrs. Torrey and Eaton, New York, and described in the En- gineering and Mining Journal, New York, May 9, June 9 and 27, 1885. The results, in brief, were as follows : Zinc: 3 per cent caused an (apparent) in- crease of \ per cent copper. Arsenic: From 5 to 15 per cent did no harm. Silver : 25 per cent caused an error of only T a per cent copper. Iron: 30 per cent caused a loss of 3.71 per cent copper. Lead : From 5 to 40 per cent had no in- jurious effect. Bismuth : 20 per cent allowed the same approximation as the silver. Consult the above article, also " On the Volumetric Determination of Copper by Means of Potassic Cyanide," by J. J. and C. APPENDIX. 351 Beringer, Chemical News, Vol. XLVIII, No. 1,241, Sept. 7, 1883, pp. 111-113, an d Sutton and Hart on volumetric analysis. IV. AMALGAMATION ASSAY OR LABORATORY MILL RUN. By M. G. NIXON, M.E. The wet copper assay bears somewhat the relation to the fire copper assay that the fire gold assay does to the amalgamation gold assay. In a certain sense, no one cares to know the ultimate amount of metal that an ore contains. What is desired in practice, is the yield under the most skilful treatment, and this informa- tion is approximately obtained by fire for copper, and the amalgamation process for gold. There are those so practised in "panning," that from a "panful" of "pulp" they can very closely guess the yield by the number of "colors" and their size. Of course this method is not very popular, nor can it ever be. 352 MANUAL OF ASSAYING. Something more a matter of weighing, and less a matter of judgment and practice is required. The amalgamation assay in its simplest form consists in "panning" a weighed amount of " pulp " with few or many drops of mercury, accordingly as the ore is poor. or rich. The tailings are washed out as clean as may be, the pan is then placed over a fire to dry and then what remains of dirt and dust is blown out with the breath ; the pan is again placed over the fire and the mercury volatilized, leav- ing the gold ("retort") ready for weighing. This process is quite largely followed by pros- pectors in some of our free-gold districts. An improvement on the method just de- scribed consists in grinding the pulverized ore in a large iron mortar with which water and mercury are introduced, with the pestle. When the grinding is complete, the whole is washed into a pan to be collected and finished as before. These methods are not recommended, but APPENDIX. 353 may be resorted to when other apparatus can not be obtained. The third method consists in grinding say ten or twenty pounds of ore in a laboratory "arrastre" by hand two hours or more, or, where possible, by power half as long. It is well to pass the ore through a 4O-mesh sieve before placing it in the " arrastre." From two to four ounces of mercury are then squeezed through a piece of chamois skin, or blown through a tube the end of which is drawn out so as to make a pin-hole exit. Having put the pulp and mercury into the " arrastre " mortar, a piece of potassium cya- nide as large as the end of one's little ringer is dropped in, the grinder adjusted, enough water added to cover the ore, and the grind- ing performed. After it is finished, the grinder is first washed off into a collecting pan, then the mortar with its contents is treated in the same manner. The best way to collect the amalgam is to 'hold the pan under a running stream or water faucet, and 354 MANUAL OF ASSAYING. very gently to stir it with the hand. The amalgam is then placed in chamois skin and squeezed so as to get rid of as much mercury as possible. The residue is next placed in a small iron retort, and what remains, of the mercury is driven off by heat gradually increased. Of course, for reasons of economy, it is well to condense the mercury.; it may then be sold to mills or others, but neither that portion con- densed nor that squeezed through the chamois should be used over again, since it is almost impossible to get rid of the last traces of gold. The " retort " is then to be scorified, cupelled, inquarted, etc., etc.* The writer has saved 93 per cent of the fire *An amalgam obtained as a result from either the preceding method, from panning with mercury, or from any other process, can be treated in the following manner, provided it is not in too great quantity. Into a new scorifier (say 2^ inches in diameter) introduce the amalgam after it has been separated from the free mercury by squeezing in a piece of chamois skin. On top of the scorifier place another of same size, inverted, having first bored through it a hole about l /fa inch in diameter. By rubbing down a little the tops of the scorifiers, and painting their edges with a thick wash APPENDIX. 355 assay on the same ore that a mill at the time under his superintendence returned 89 per cent. V. PAN TEST FOR GOLD. ("PANNING.") The estimation of gold in ores in which the metal is in the free state is unreliable by of ground chalk and water, all danger of loss of amalgam by its spirting through at the sides, is avoided. Heat in muffle or furnace till the mercury has been driven off in vapor through the fine opening above, take out, let cool and remove the upper scorifier. Now put the chamois skin on top of the residue in the scorifier and burn to ashes in muffle or furnace, remove a second time and cool. Finally mix the residue and ashes with granulated lead and scorify. Re-scorify with more lead if the resulting button is brit- tle. Cupel in the usual manner and treat the bead obtained as gold bullion. If it is not thought worth while to save the mercury, the fluid amalgam can be treated directly as described without first squeez- ing through a chamois skin, in which case the accompanying step of burning the latter, etc., is dispensed with. Heat very gradually. Even with this apparatus the mercury can be saved by attaching to the upper scorifier a small iron tube which bends over and dips into water. The advantages of the above method are that it is simple, easy to operate, and that all the work (up to the cupellation) is done in one vessel, and so any liability to loss of gold in transferring from a retort, etc., is done away with. Furthermore, working with small quantities of amalgam, in even the smallest retort obtainable, is unsatisfactory. W. L. B. 356 MANUAL OF ASSAYING. either the crucible or scorification process, owing to the impossibility of securing an average sample. The ore, for supposition, may be of such value that even when put through a loo-mesh sieve one flake that would go through such a mesh could represent the amount of gold in two assay tons. If then of two assay tons of ore of the above character, one is taken, it must run either nothing or double the true value of the ore. Again, on low grade ores and with the charge most convenient to employ, the result or weighable button is so small that its esti- mation is liable to error. Many ores containing small quantities of gold are frequently profitable to work, as in the case of placers and of large quartz ledges where the rock is soft and gold free. In such cases the assay report based upon the small quantity of ore used in the scorification, or even in the crucible assay, is unsatisfactory for this and the previous reasons. APPENDIX. 357 Here, then, we resort to the pan test, for by it we can treat large amounts of ore, and the greater the quantity operated upon the more reliable the result. The pan test is a process of concentration (doing on a small scale that which concentra- tors effect on the large), the product being either gold particles, or gold sulphurets, iron, sand, etc., depending on how far the process is carried. The pan itself is a Russia sheet iron vessel of a shallow truncated conical shape (diameter about i6J inches). That form sold by min- ing outfit establishments has been found most useful in practical operations. A round shallow wooden dish with its bottom sloping to a point, and technically known as a " Batea," is a useful modification (fig. 48 of Atwood ; size of batea : diameter, 1 7 inches ; depth, i finches; thickness, f inch; angle of sides, 12; material, Honduras mahogany). Each person will exercise his own choice after learning the operation. After the requisite MANUAL OF ASSAYING. skill has been acquired, a pan can be extem- porized from almost any kind of dish, or a section of bullock's horn or an iron spoon may serve as substitutes. The requisite amount of ore from 100 to 500 assay tons (5 to 25 pounds, or in French weights 3 to 15 kilos), depending upon its richness, is sampled, crushed and pulverized as directed in the chapter on gold and silver ore. The pulverization, however, need be carried no finer than to cause the ore to pass through a 40, 50 or 60 mesh sieve (the latter preferred). Weigh now the ore and put in the pan, which latter must be free from grease. Moisten and let it stand for a few moments in order that particles may not float off when the pan is put in water. When wet, the whole pan and ore is gently sunk below the surface of a tank of water (a common wash tub will do nicely in the labora- tory). A peculiar oscillatory motion or side vibration is commenced, though not enough to throw any particles of ore over the edges APPENDIX. 359 of the pan. The object of this is to settle the heavier particles (the free gold, heavy miner- als, black sand, etc.), and have nothing on the surface but rock or quartz ; a little experience will teach the point. Then slightly incline the pan, and so wash it around as to carry the surface rock over the edge ; only a little at a time, however. Level the pan and resettle as at first ; again incline and wash more over the edge. Keep up this operation, gradually getting more and more rock over the edge, and becoming more careful and washing more delicately as the process continues. Toward the end of the operation, that is, when the rock is nearly gone, be careful to keep the ore under the surface of the water, as the gold might otherwise become dry and float off. Also make no sudden or unusual lurch, or the whole result may go off the pan. The above manipulation is far more difficult to describe than to perform after having once been acquired. Dry the residue. 360 MA NUAL OF A SSA YING. If gold alone is obtained, that is, gold (or gold and silver) free from sulphurets, etc., it must be treated as an alloy, weighed, parted and weighed again, or cupelled with lead, weighed, parted and weighed ; in both cases giving gold and silver. If the panning is not carried to such a point as to get rid of all the rock, the concentration is all scorified with test lead (or run down in a crucible), cupelled, parted and weighed. In the case of an ore supposed to carry aurif- erous sulphurets it should be panned so far as can safely be done without losing metallif- erous particles and the concentration treated as above described. If the ore is quite poor, or a large quantity is desired to be worked, the panning can be carried on roughly and the successive con- centrations finally panned together. The results are based upon the amount of ore taken in the pan. If much of this work was to be done, a set of weights from 500 A. T. down (approximately accurate) would APPENDIX. be very convenient and save calculation. The result would be as many times the number of ounces contained in the ore as the quantity of ore was more than one assay ton. For example, the ore was supposed to be very poor and therefore : 500 A. T. were taken. Bead weighed 50 mgrms. /. 500 A. T. : i A. T. : : 50 mgrms. : y 1 ^ mgrm., or the ore ran y 1 ^ oz. Troy per ton. If 100 A. T. had been taken and the same weight bead obtained, we would have : 100 A. T. : i A. T. :: 50 mgrms. : - mgrm., or the ore would run -J oz. Troy per ton. As an example of the calculation required ^v^thout the large assay ton weights, I give the following : Weight of panful of ore, 2^ kilogrammes = 2, 250,000 milligrammes. Weight of bead obtained, gold 20 mgrs., silver 50 mgrs., then 2,2 5 o,ooomgrms 29166 20 mgrms. x , 2,250,000 mgrms. 20166 and - - : : X = ATT oz. 50 mgrms. x The free gold can be separated from the 362 MANUAL OF ASS A YING. sulphurets (if it be desired to determine how much of the gold is " free " and how much in the "sulphurets") by washing in an amal- gamated pan. Such a vessel may be simply made by bending a piece of thin silver-plated copper (about 6 inches by 12 inches) so as to form curved edges on three sides, the silvered sides in. The side not turned up is one of the narrow ends. A little mercury (free from gold and silver) will quickly amalgamate the interior, and if the ore is washed carefully over this, most of the free gold will become amalgamated and stick to the pan. A piece of chamois skin made into a rubber will push the gold, which can be seen as little specks of amalgam, to the open edge of the pan and into a crucible. The mercury can be driven from the gold by heat. No investigation has been made to deter- mine if any silver is carried by the mercury to the assay from the pan, but if such be the fact, the result is still accurate for gold. If carefully performed the results ought to be APPENDIX. 36, above the yield from a stamp-mill with amal- gamated plates. A more common test than with the above silver-plated amalgamated copper pan, is, after having panned down, to drop a few globules of clean "quicksilver" (i.e., mercury) into the pan and a little cyanide of potassium (to keep the mercury clean). Work up with a spatula till the mercury has taken up the free gold, then collect, and run off the mercury. Clean it and dissolve in nitric acid (for the gold only) or drive off the mercury in the muffle, weigh the residue of gold and silver, part and weigh gold. The residue in the pan should then be assayed and the gold and silver (actual weight) determined. Suppose Original weight of ore. 2^ kilos. Gold and silver after retorting 35 mgrms. Gold after parting 15 " Hence silver , 20 mgrms. Gold in sulphurets 50 mgrms. Silver " 90 " 364 MANUAL OF ASSAYING. Then we have : Free gold -j^^ oz. per ton of original ore. Silver in free gold j 2 /^ oz. per ton of original ore. Gold in sulphurets -ffa oz. per ton of original ore. Silver in sulphurets i T V 6 o oz - P er ton f origi- nal ore. Total gold y 8 ^ oz. per ton of original ore. Total silver lyW oz - P er ton f original ore. There is a certain loss in panning, hence the results are not analytically accurate, but are close indications of the practical result of the working of gold ores in a mill with copper plates.* VI. CHLORINATION ASSAY OF GOLD ORES. If gold exists free in the gangue, that is, not combined with sulphur, arsenic or tellu- rium, it can be chlorinated directly without roasting. * For the information comprised in the above article I am largely indebted to Mr. S. A. Reed of Irvvin, Col., and Mr. Ray G. Coates of Chicago, APPENDIX. 365 But sulphurets, arseniurets or tellurides must be first roasted and thoroughly at that. The chlorination can be done in the labora- tory on either a large or moderately large scale. For the former, operating say on 20 pounds (yihr f a ton )> consult the section in Kustel, entitled " Extraction of Gold from Sulphurets, Arseniurets or Quartz, by Chlor- ination," pp. 136-139. For the latter grind up 5 to 8 ounces (or 5 to 10 A. T.), and, if necessary, roast in the usual manner. Use a frying pan for this purpose, and see that the sulphur is entirely driven out so that no smell (as of a burning match) is perceptible at the finish. Cool, grind in an iron mortar, and re-roast at a red heat. When cold, reserve i A. T. of the ore for regular assay; the remainder is to be chlori- nated in the apparatus herewith described. It consists of a flask, provided with a funnel tube for acid supply and delivery tube for the chlor- ine gas generated. The latter tube dips into 366 MANUAL OF ASSAYING. a wash bottle containing water to wash the gas. From the latter the gas passes up into a separatory funnel containing the ore. The exit tube from the funnel may pass into a flue or the open air, or into a cylinder holding shavings moistened with alcohol. Place in the flask a mixture of 3 parts of black oxide of manganese, 4 parts of common salt, and 4^ parts of water, all well mixed. Place the ore, which has been dampened with water, in the separatory funnel, having put in at the bottom a very little cotton to prevent the fine ore from stopping the pas- sage of the gas. Having now made all ready, pour down through the funnel tube 7^ parts of sulphuric acid at intervals. After a time the flask is to be gently heated, that all the chlorine may be driven off. Run the operation for about two hours, then disconnect the flask and let the funnel stand over night. Finally take out the upper APPENDIX. 367 cork and wash out the chloride of gold with distilled water. To the solution in a beaker or tumbler add a few drops of hydrochloric (muriatic) acid, then some solution in water of sulphate of iron (green vitriol or copperas), stir with a glass rod, warm and let stand undisturbed until all the gold has been thrown down to the bottom and the liquid above is perfectly clear. Half of this liquid is drawn off with a syphon, the remainder containing the gold is filtered as usual, washing with warm water. Dry the filter, burn, scorify ashes and cupel, or cupel directly with sheet lead, weigh, etc. Compare result with unchlorinated sample. Consult Kustel as above, and Aaron's " Leach- ing Gold and Silver Ores," p. 90, on the ''Work- ing Test." VII. CHLORINATION TEST FOR SILVER. In smelting-works it is often necessary to test ores that have been subjected to chlorid- izing roasting, to ascertain the amounts of chloride of silver contained in them. Two assays are made of each ore. 368 MANUAL OF ASSAYING. Several pounds of the ore are taken from various portions of the entire lot, well mixed and sifted. From this, weigh out two charges of _i_ A. T. Scorify and cupel one charge in the usual manner. The other charge is brushed into a filter paper held in a glass funnel, and over it pour a warm solution of hyposulphite of soda (six or eight ounces in a quart of water), which rapidly dissolves the chloride of silver from the ore. Continue this treatment until a small portion of the filtered liquid contained in a test-tube, darkens but slightly and does not lose its transparency upon the addition of a few drops of a solution in water of sulphide of sodium. Wash the mass in the filter with warm water, remove filter and all, dry and burn in scorifier in muffle, at a low heat, mix ashes with lead, scorify and cupel as usual. (The hyposulphite solution dissolves out sulphate of silver as well as the chloride. If, as is sometimes the case, it is desired to know APPENDIX. 369 the amount of sulphate present, leach a third charge with warm water, which will take out the sulphate, but will not touch the chloride or any unacted-upon ore. Scorify and cupel the residue as directed.) The difference between the two cupellations shows the amount of silver which has been changed into the state of a chloride. Thus : ist charge ran 180 oz. per ton. 2d charge ran 10 oz. per ton. Hence, 18010^170 oz. of chloridized pulp. To obtain percentage : 180 : 170 :: 100 : x = 94.4 per cent. " If there should be gold in the ore, this must be subtracted from both assays, because, although the amount of gold would be equal, the chlorination result, as it should be, must come out higher after the gold is subtracted." (Kustel.) VIII. THE ASSAY OF GOLD AND SILVER BULLION. The larger portion of this article is taken from the Fourth Annual Report of the State 370 MANUAL OF ASSAYING. Mineralogist of California for the year ending May 15, 1884, by the kind permission of Mr. Henry G. Hanks, State Mineralogist. His very able and complete paper could hardly be improved, hence the extracts are given almost verbatim, as many will not succeed in obtain- ing copies of the report, the edition of which is already exhausted. The remainder of the description is made up partially from information given me per- sonally by Mr. F. E. Fielding, assayer of the Consolidated Virginian and Consolidated Cal- ifornia Mines, of the Comstock Lode, Virginia City, Nevada, and partially from other sources, together with a little as the results of personal experience. Bullion, or the precious metals in bars more or less impure, is of very varying composition, running down from that which is mostly gold, through mixtures where the gold and silver are more equally divided, and where the silver predominates (all containing various impuri- ties or base metals, as lead, copper, etc.), to A PPENDIX. 371 base bullion, or that in which the lead is in excess of all the others. The latter kind is treated of in another portion of the appendix. Here I consider only those bullions in which the gold and silver form the greater amount. Absolutely accurate assays of gold and sil- ver bullion require care, skill, and first-class apparatus. The skill may soon be acquired by practice, but the apparatus must not only be of the very best quality, but must be kept in the most perfect state of adjustment. It is not enough to purchase chemicals which are marked " pure," or a balance supposed to be accurate. The chemicals must be tested, and the accuracy and adjustment of the bal- ance and weights verified, before correct re- sults can be certain. The process of assaying gold and silver bullion is divided into several operations, as follows : Melting and refining the crude bull- ion, and casting the bar, cutting the assay chips, or otherwise preparing the assay sam- ples, the preliminary assay, the assay proper, 372 MANUAL OF ASSAYING. calculating the results, weighing the bar, and stamping the fineness and value upon it. Melting, refining, and casting the crude biill- ion. For melting, a wind furnace is best, but a good coal stove, such as used in offices, will answer the purpose if the amount operated upon is small. The wind furnace is a square box of fire- bricks, built in the form of a cube of three- foot face, with an opening in the centre of the upper face. The fire-box is about a foot square, and fourteen inches deep, provided with an ash pit, movable grate, bars, and slid- ing cast-iron cover. The flue should be a horizontal opening, about three by six inches, near the top of the fire-box, and connected with a chimney at least thirty feet high, to insure a good draft. The furnace can be built by any bricklayer of ordinary skill and judgment. No mortar should be used in lay- ing the fire-brick, but good clay, mixed with a portion of coarse sand, substituted. The bullion is generally melted in a black APPENDIX. 373 lead crucible. Before such a crucible can be safely used, it must be annealed. Were this neglected, and it should be placed in the fire without this precaution, it would soon fly to pieces. This is caused by the water it con- tains being converted into steam ; and the structure of the material being such that the steam cannot make its escape, destruction of the crucible follows. It is best to commence annealing the crucible some time before it is wanted. It should be set near the hot fur- nace for several days, and turned occasionally. When the fire is nearly spent, it may be placed, rim downward, upon the hot sand, generally placed on top of the furnace. A day or two of such treatment will make it safe to hold it over the open furnace by the aid of the crucible tongs or poker. After it has been frequently turned, and is hotter than boiling water, it is safe to place it, rim down- ward, upon the burning coals. After the rim is red hot, all danger is passedj and it may be 374 MANUAL OF ASSAYING. turned, and placed in position for the recep- tion of the gold. If the fuel is charcoal, it will be best not to use small pieces, or, at least, not coal dust. Pieces the size of an egg, or larger, will make the best fire. When the crucible becomes red hot, a long piece of quarter-inch gas pipe is used to blow out any dust or ashes that may have fallen into it. A cover is then placed on the crucible, and lumps of coal built up around it with a long pair of cupel tongs. When the crucible has attained a full, red heat, one or two spoonfuls of borax, wrapped in paper, are placed in it, using the cupel tongs. When the borax has melted, a small quantity of the bullion, also wrapped in paper, is placed in the crucible in the same manner. Several portions may be thus added, accord- ing to the size of the crucible. A fresh sup- ply of charcoal must be built up around the crucible when required, the cover having been previously replaced. When the bullion has melted down, more is added in the same man- APPENDIX. 375 ner, until the crucible has received all that is to constitute the bar. In the meantime, the ingot mould, in which it is intended to cast the gold, must be made smooth and clean inside. This is best done by rubbing with sandpaper and oil, or with a dry piece of pumice stone. It is then wiped dry and clean with a rag, oiled slightly, and placed on the edge of the furnace in such a position that it may become quite hot ; not so hot, how- ever, as to approach redness, nor to cause the oil to burn. When the bullion is in a fluid state in the crucible, the mould must be placed on a level surface, and oil poured into it. To make a clean bar, it will be found best to use consid- erable oil sufficient to cover the bottom of the mould to the depth of at least one-fourth of an inch. The mould should be turned in such a manner as to allow the oil to flow to all parts of its interior, and then placed again level, and in the position it is to occupy while casting the bullion. If the latter is clean, 376 MANUAL OF ASSAYING. and the quantity less than fifty ounces, it is best not to attempt to skim it. Two spoon- fuls of nitrate of potash may be added, and one of carbonate of soda, and the whole allowed to melt and flow over the surface of the melted metal. When very hot, and the slag perfectly fluid, the crucible is lifted from the furnace, and with a bold and steady hand, its contents are poured into the mould, the crucible being held for a little time in an inverted position, to allow the last portion of metal to flow from it. The oil inflames, and remains burning on the slag, which flows evenly on the surface of the bullion. If the mould is clean, and of the right temperature, and if sufficient oil is used, a clean bar will result. A little practice will enable the ope- rator to hit the exact conditions. The oil used should be a cheap animal oil ; common whale oil answers every purpose ; lard oil is also well suited ; coal oil is too inflammable, as well as dangerous, and should never be used. When cold, the bar falls easily from APPENDIX. 377 the mould. A slight tap with a hammer sepa- rates the slag, and the bar may be cleaned with water and nitric acid, or, if necessary, with sand and a suitable brush. A good plan is to place the bar in the furnace until it becomes nearly red hot, and then to quench it suddenly in water. This will be unneces- sary if proper precautions have been observed in preparing the mould. When the bullion is very impure which is the case when in the form of retorted amal- gam which has not been properly cleaned a different method of treatment should be adopted. - A large-sized crucible will be re- quired. Three or four times the amount of flux must be put in, with the addition of a spoonful of carbonate of potash. A skimmer - must be prepared by forming the end of a large wire, about the size of a common lead pencil, into a spiral about an inch and a half in diameter, and bending it so that when the skimmer is let down vertically* into the cruci- ble the spiral will lie flat upon the surface of 378 MANUAL OF ASSAYING. its contents. A bucket of water is set near the furnace, and when the slag has become fluid, and it is beyond question that the bull- ion has become perfectly melted, the skimmer is touched to the slag and gently moved from side to side ; a portion of the slag adheres to the iron, the skimmer is removed and plunged into the water, and immediately replaced in the crucible ; an additional portion attaches itself to the skimmer, which is again quenched in water. This is repeated until a large por- tion of the slag is removed, and a new charge of flux, consisting, this time, of borax and nitrate of potash, is allowed to fuse upon the surface of the bullion. The first flux is re- moved from the skimmer by a slight blow with a hammer, and the crucible is skimmed with it as before. This must be repeated until all iron and other impurities have been removed, and the surface of the molten metal appears, when exposed, clean and reflective as a mirror. It may then be poured into the mould, as described before. Care should be APPENDIX, 379 taken not to clip the wet skimmer beneath the surface of the bullion, or an explosion will take place. In large meltings it is customary always to skim the bullion before pouring, and so far to remove the slag that any remaining portion may be left on the sides of the crucible, and the metal only allowed to flow into the mould. This requires some skill and considerable practice. As it is imperative that the bar should be homogeneous to insure a correct assay, it is usual to mix the melted metals thoroughly before pouring. This is done in the large way by stirring just before lifting from the furnace. It may be done with an iron rod, with a piece of black lead held with the tongs, or with a clay stirrer made specially for that purpose, in which case it will be nec- essary to allow it to remain in the crucible until it has acquired the temperature of the fused metal ; otherwise, a portion of the bull- ion may attach itself to the stirrer, and be re- moved with it. In small meltings it will be 380 MANUAL OF ASS A YING. found sufficient to mix the bullion by giving the crucible a rotary motion while holding it with the tongs just previous to pouring. This must be done so quickly that the crucible has no time to cool. For very small fusions it is best to use a small Hessian crucible, and, when the bullion is melted with plenty of flux, to set it aside to cool, and then break the cru- cible, and separate the pieces of crucible and portions of slag by slight blows of a hammer on the edges of the button. It is very diffi- cult to pour small quantities of gold without loss from portions remaining on the sides of the crucible. Preparation of samples for assay. When the bar is clean, a small portion must be taken from different parts for assay. This is done in several ways, very frequently by cutting pieces from opposite corners or edges with a cold-chisel or hollow punch, but this is extremely clumsy, and in every way inconven- ient. If the bar is brittle, a much larger piece may break off with the chip than is re- APPENDIX. 381 quired. If the proper-sized chip is cut off successfully, it is likely to fly away and be lost. A second way of sampling is to bore into the bar, top and bottom, with a small drill. This maybe done v in a lathe or by means of a ratchet drill. The bar should be placed in a clean, copper pan, so that no loss may occur ; the surface borings, resulting from the first revolutions of the drill, should be rejected. Those that follow, to the extent of a little more than one gramme, are to be placed in a suitable vessel, and carefully pre- served for assay, each lot separate. Before cutting or boring the bar the number of the assay should be stamped upon it, and the same number placed with the clippings or borings. This number should represent the bar through every stage of the assay by which its value is ascertained. Some assayers stamp the initial of their name on the cut faces, so that no portion can be removed after it leaves their hands. A third manner of sampling is that by " granulation." While the bullion is 382 MANUAL OF ASSAYING. still in the melted state in the crucible, but is already refined, it is well stirred, and two samples are scooped up with a small ladle, one from the bottom of the crucible, and the other from the top. Each ladleful is poured, slowly and carefully, and .in a narrow stream, into a clean copper basin containing warm water, which is rotated quietly by means of a broom or paddle. Keep the resulting granu- lated metal from top and bottom of the cruci- ble apart, drying each lot. The selected pieces of the granulations, or the chips cut from the bars, are flattened on the anvil and passed through the rolls until thin enough to be readily cut by the snip- shears. (Fig- 85.) They, or the borings, if borings are taken, are now ready for weigh- ing. Weights and weighing. For the bullion assay a special set of weights known as "gold weights" is used. As the basis of the bullion assay is 1,000 parts, so the unit of the "gold weight" system is a 1,000 APPENDIX. 383 piece, from which the weights range down to a YOTOT pi ece - The actual weight of each piece in this system is one-half of its corresponding piece in the French or metric system; thus the 1,000 piece weighs actually 500 milligrammes, and so on. Gold and silver in bullion are always reported in thousandths; that is, in parts of one thousand, taken, as before stated, as the standard of the assay ; hence the use of the weights described. By difference between the fineness and the 1,000, we learn the number of parts of the base metal contained in the bullion. Thus, if 1,000 parts of a bullion, after treatment, weighs 900 parts, it has a ''fineness" of 900, or it is 900 "fine," and the base metal is 100. In weighing, always remember that the rider, or index needle, when marking tenths for gold, is to be multiplied by two, as each mark on the beam or index plate only represents T L- in the metric system, while it should be T 2 Q- for the "gold weight" system. Half-tenths 384 MANUAL OF ASS A YING. are always reported in the tables for gold, but not in those for silver. As shown from the preceding, the metric weights can be employed if. the ''gold weights" are not obtainable. The method of weighing is conducted as follows: The assayer seats himself before the balance, having the clippings or borings in a convenient position inside the case. A 1,000 piece (or half a gramme weight) is placed in the right-hand pan of the balance, and por- tions of the clippings or borings in the other until nearly correct, but the bullion should be in excess. The largest piece is then removed by the aid of a pair of pincers, and a small corner cut off with the shears. This done once or twice will nearly balance the pans; but by touching the piece of bullion selected against a clean file, still more minute portions can be removed. By careful manipulation nearly 'the exact point will soon be obtained; but with the greatest care, if the balance is delicate, it will be found nearly impossible to APPENDIX. 385 adjust the weight so perfectly that the index needle will not point either one side or the other of the zero. In such a case, it will be necessary to make a memorandum of the error, and mark it with the number of the assay, and in weighing the cornet, to take the same reading of the index needle. Preliminary Assay. It has been found that silver cannot be dissolved out of an alloy of that metal with gold, unless the proportion of silver is at least two and one-half times that of the gold. If a larger proportion is pres- ent, the gold is left after the extraction of the silver in the form of a powder, and can- not be dried and weighed without danger of mechanical loss. If less, the gold protects the silver, and the action of the acid ceases, while some of the silver remains undissolved. An alloy of three parts of silver to one of gold was formerly taken, from which the terms quartation and inquartation come; but of late years the above proportions have been found to be best. 386 MANUAL OF ASSAYING. In order, then, to form such an alloy, the assayer should know the amount of silver in the bullion, that he may consider it in adding silver to a bullion mostly gold, or gold to a bullion nearly all silver. The following imag- inary and reversed bullions will illustrate this point plainly: BULLION NO. I. 200 parts gold need 80 parts more to make 280 parts. 700 " silver = 2^ times the 280 parts gold. loo " base metal. i , ooo ' ' BULLION NO. 2. 700 parts gold 200 " silver need 1,550 parts more to make 1,750 parts = 2$ times the 700 parts gold. 100 " base metal. 1,000 The proportions of silver and gold in the bullion in question are ascertained in several ways. First, by merely looking at the bullion, having had previously such experience with similar alloys that the knowledge becomes almost instinctive. Secondly, by direct com- parison with slips of known "fineness.* 1 Third- ly, by use of the touchstone and needles. APPENDIX. 387 (For the methods of making and using the latter, see the article in Mr. Hanks' Report.) Fourthly, by a preliminary fire assay. This is by far the best way, and should always be done where great accuracy is required. Take the 1,000 parts of the bullion already weighed out, wrap in a piece of pure sheet lead of about 2 grammes (30 grains or so) in weight, cupel and weigh the resulting bead. If it seems mostly silver, roll it out, boil in nitric acid of 32 Beaume (1.26 sp. gr.), decant, wash, dry, ignite, and weigh the gold. If the bead appears very yellow, add three or four times as much pure silver, wrap up to- gether in sheet lead, recupel, part as above, and weigh the gold. The latter may come down as a fine powder, and a slight loss occur in washing, but the results will be sufficiently accurate for the purpose. From the data obtained above, it will be easy to make up the proper alloy for the regular assay and the proof centre, as shown by the following simple examples: 388 MANUAL OF ASSA YING. Example No. i. Suppose the 1,000 parts of bullion taken weigh, after cupellation, 520.5 parts, then 479.5 parts (1,000 520.5) are base metal. The gold, after parting, weighs 15 parts. These figures enable us to prepare the assay proper and the proof centre, as hereby shown: Gold and silver bullion taken 1,000.0 parts. " " " after cupellation 5 20 -5 " Leaving base metal 479.5 " Gold and silver after cupellation 5 20 -5 parts. " after parting 15.0 " Silver in the bullion 55-5 " 55-5 X 2.5 = 202.2 parts. Deduct gold already in the bullion 15.0 " Leaving gold to add 187.2 " Hence: Bullion { composed of Proof centre. take J 505.5 parts silver = 505.5 parts silver. 1,000.0 parts I 479.5 " base = 479.5 " copper. I 15.0 " gold) 187.2 " gold to add ) = 202.2 " gold. 1,187.2 " total. 1,187.2 " total. APPENDIX. 389 Example No. 2. Gold and silver bullion taken 1,000.0 parts. " after cupellation 764.4 " Leaving base metal 235.6 " Gold and silver after cupellation 764.4 parts. " after parting 602. i " Silver in the bullion 162.3 " 602.1 X 2.5 = 1,505.2 parts. Deduct silver already in the bullion .... 162.3 " Leaving silver to add 1,342.9 " Hence: Bullion f composed of Proof centre. take ; 602.1 parts gold == 602.1 parts gold. 1,000.0 pts. | 235.6 " base = 235.6 " copper. I 162.3 " silver ( 1,342.9 " silver to add )==i>5o5.2 " silver. 2,342.9 " total. 2,342.9 " total. The silver, gold, and copper added are, of course, pure. The Assay Proper. Two assays of a large bar are always made, the samples being taken from the top and bottom. A proof 3QO MANUAL OF ASSAYING. centre or "check" is always run through with each set of assays, and consists of pure gold, pure silver, and pure copper in such propor- tions as shall correspond as nearly as possi- ble to those of the bullion under trial, as shown in the above examples. The proof cupel is always placed in the centre of the muffle, those for the bullions at each side, the object being to correct the loss by volatilization. The loss in weight of the proof centre bead is to be added to each weight of the bullion bead. Make the weighings of the duplicate bul- lions, and the gold or silver that is to go with each, and also the three metals or so for the proof centre. Wrap each lot in a piece of pure sheet lead, and squeeze all into a bullet. According to the difference in fineness of the bullions are the amounts of pure sheet lead varied, and the latter must contain no gold whatever. Its purity being established, it is easily prepared by rolling out to a uniform APPENDIX. 391 thickness (about -^ inch or so), ancl about if inches wide. The weight of so many inches of the lead is determined, and the rest of the samples are cut from measurement of the one weighed. These pieces are known as "lead cornucopias," and should always be prepared by the assayer himself, and kept on hand in sufficient quantity. If too much lead is used in the cupellation of the buttons, the loss in precious metals is increased by the greater length of time re- quired for the cupellation. On the other hand, if there is a deficiency in lead, the beads are ill-shaped, and are liable to contain some of the base metals. If a large amount of cop- per is in the bullion, the lead must be in- creased. "Long experience has proved that silver opposes the oxidation of copper by its affinity, so that it is necessary to add a larger amount of lead in proportion to the quantity of silver present." (Mitchell.) In cupelling bullion say from 980 to 1,000 fine, 30 grains (about 2 grammes) of lead are 3Q2 MA NUAL OF A SSA YING. best used, and for very base bullion, and where the base is mostly copper, 100 to 130 grains (6.5 to 8.5 grammes, nearly) are gener- ally used. Mark appropriately with ruddle three good cupels, place them in the muffle, the proof cupel between the other two, as directed before, and when hot, a piece of pure lead, weighing 3 grammes (about 45 grains), is placed in each. The leads will soon melt and begin to "drive"; that is, begin to be absorbed by the cupel ; the assays are then to be added, using the cupel tongs. When perfectly melted, the cupels are drawn forward to that point in the muffle which experience has shown to the assayer that cupellation progresses most successfully. When the cupellation is finished, and the buttons have assumed a brilliant metallic lustre, they are removed, hammered slightly on their edges on a clean anvil, the last blow being given near one edge, to make that part thinner, in order to facilitate the rolling process which follows, and examined with a magnifying glass APPENDIX. 393 to see that all bone ash has been removed. Weigh and note results. The two bullion beads should weigh exactly alike; if this should not be the case, the heavier one must be examined carefully, to see if any particle of bone ash may have been overlooked. If this should fail, there is no recourse but to make another assay, which should agree with one of the first. Generally, if care is used, the first pair will agree. Then add to the weight of the assay beads proper the loss sus- tained by the bead of the proof centre. Next the beads should be annealed; which can be done in the muffle, if still hot, or upon char- coal, with the flame of a spirit lamp urged with a blowpipe. After cooling, they are passed through the rolls, being drawn into ribbons about 2\ inches in length. The proper letter or number is stamped on the end of each slip, somewhat deeply, and all are then re-annealed. Each slip is then rolled up into a spiral form upon a glass rod or lead pencil, commencing at that end of the slip which is 394 MANUAL OF ASSAYING. not stamped. A slight pinch, or reverse bend, after the rod is removed, will prevent their unrolling. The "cornets," so prepared, are then ready for treatment with acid, after which step the letters or numbers stamped upon them will be as distinctly seen as they were before. Introduce each cornet into a separate part- ing flask or matrass, and add i fluid ounce (29^ c.c.) of pure nitric acid of 21 Beaume (sp. gr. 1.16), place on the sand bath which acts as cover of the furnace, or on a small sand bath supported on the ring of a retort stand over a spirit lamp or gas burner, and boil until no more red fumes are evolved (say ten minutes). Just at the point of coming to a boil add one or two "pepper carbons" (made by heating whole or unground pepper beans to carbonization on an iron shovel or pan). They prevent spirting or bumping. A folded piece of paper, or a pair of wood- en tongs, is used to lift the flasks, and the acid, decanted carefully into some convenient APPENDIX. 395 vessel kept to receive it, as the silver is valu- able, and may be recovered when a sufficient quantity has accumulated. The same quan- tity of 32 Beaume acid (1.26 sp. gr.) is then poured into each flask, and, being placed on the sand bath, again boiled for ten minutes, with the " pepper carbons "-as usual. After this, the acid is poured off, and each flask is filled up with distilled water, gently rotated, and the water decanted and thrown away. Repeat the washing, and finally fill, for the third time, the flasks with distilled water, this time quite to the brim. Over the mouth of each flask an annealing cup is placed, mouth downward, like a cap, and the flask and cup inverted together. By these means the cornet is deposited gently, and without loss or injury in the cup. The flask is then gently raised until on a level with the edge of the cup, when with a quick side motion the flask is removed, the water from it, of course, running to waste. The water in the cup is poured out carefully, and the cup and its cornet are heated, at first 396 MANUAL OF ASSAYING. gently on the sand bath till all the moisture has been driven off, then in the muffle to red- ness, making the third time of annealing. Take out and let cool. The gold has recov- ered its natural color, and is firm enough to be handled with pincers. It must next be weighed accurately, using the "gold weights" (or the gramme weights and multiplying by two), and noting any memorandum regarding the position of the index in weighing out the bullion in the first operation. The weight of the cornet in parts of the 1,000 piece (or in half milligrammes) will represent the fineness of gold in the bar, expressed, as before, in thousandths. A small amount of silver will always remain in the cornet, no matter how carefully the manipulations may have been conducted. This surcharge, so called, must be deducted from the weight of the gold by subtracting from it one-half, one, or two thousandths (or "points") accordingly as the fineness ranges from 500 to 900, or as experience indicates. APPENDIX. 397 Weighing the Bar. The next step is to ascertain the weight of the bar in troy ounces and decimals. This must be done with the greatest accuracy. A good bullion balance is much to be desired; but a bar can be weighed on a defective balance if it is sufficiently deli- cate to turn distinctly with the hundredth part of a troy ounce. This method of weigh- ing is called counterpoising, and is conducted as follows: The beam must first be brought to a level by putting sand, small shot, or other conven- ient weights into the lighter pan. When in perfect equilibrium, a small weight is placed in one of the pans to test the delicacy of the movement, and if satisfactory, the bar is laid in one pan, and the equilibrium restored by putting any convenient substance, as sand, into the other. The bar is then removed, and ounce weights put in its place, which will be the exact weight of the bar, all errors of the apparatus being corrected by counter- poising, which will be evident to the reader 398 MANUAL OF ASSAYING. without further explanation. Of course the ounce weights must be proved by experiment to be correct among themselves. It is sometimes impossible to obtain troy ounce weights, in which case avoirdupois may be used. The same rule as to accuracy applies equally to them. Each pound equals 14.5833 troy ounces. An excess of even pounds must be made with ounces and decimals, which can be prepared by any person of moderate me- chanical skill. The value of an avoirdupois ounce is 0.91 1458 ounce troy, or one-sixteenth of a pound. To make the calculation, it is only necessary to multiply pounds by the former and ounces by the latter factor, and add the two together. The following table may be used to facilitate the calculation : APPENDIX. 399 Avoirdupois, Troy Ounces. Avoirdupois. Troy Ounces. i ounce = 0.911458 13 ounces = 11.848958 2 ounces 1.822916 14 = 12.760416 3 " = 2.734374 i5 " = 13-671874 4 = 3-645 8 33 i pound = 14.583333 5 = 4-55729I 2 pounds = 29.166666 6 = 5-468749 3 " = 43-749999 7 " = 6.380208 4 = 58.333333 8 = 7.291666 5 " = 72.916666 9 " = 8.203124 6 = 87.499999 10 = 9-H4583 7 = 102 083333 ii = 10.026041 8 = 116.666666 12 " = IO -937499 9 " 131.249999 Suppose the bar to weigh twelve pounds and nine ounces; set the figures down thus: 10. pounds. 2. pounds. .9 ounces. 12.9 Look for 10 pounds in the table, which will be the same as i pound with the decimal point moved one place to the right, 145.833; opposite 2 pounds will be found 29.166; 9 ounces will be found to be 8.203, which are to be added as follows: 4 J Window r Block Working Table i .Assay Furnace LABOKATOBY Window Coke or Charcoal Bin Closet Window Door Desk for Chemical Work Water Water Cabinet Book Case Window Door OFFICE Desk Window Scale Shelf Window Window 438 MANUAL OF ASSAYING. FORM FOR CERTIFICATE OF ASSAY. Almost every assayer has his own particular blank, but so long as the certificate states plainly the results of his work, any little differences of detail are un- important. The form given below is about as satis- factory as any. i . P 3 CL ^ o' o D P c/i a; t/i i 03 w 3 a o o _g20 i "8 a ? 2. " i a- - po ; H 1 -*i ; < I5f*j 1 n> ! s | -*** Elfl <-! > 3* < m : ^ o Rlf*} ' f8 P If ^ ^ P o (ft v> i Remarks. C/l - s- M ? % S Of 1 APPENDIX. 439 OUTFIT. With the following outfit, it is believed the assayer can perform the ordinary crucible and scorification assays of gold, silver, copper and lead ores : Hammers, sledge, medium and small $2 oo Iron mortar (8 inch diam., i gal. capacity) and pestle, wt. 1 9 Ibs i 25 Steel spatulas, one large and one small 75 Sieves, 20, 40 and 100 mesh 2 50 Hand-scales for fluxes 3 oo Ore or pulp scales 22 oo Assay balance, with weights (i grm down to fa mgrm) 65 oo Set gramme weights, 100 grms down 6 oo Set assay ton weights 6 50 Furnace, Brown's portable 20 oo 6 muffles, Battersea J 8 25 i pair crucible tongs * . . . i 25 i pair scorifier tongs i oo i pair cupel tongs i oo Shovel, scraper and hoe 75 Scorification mould i oo Crucibles, S. T. U. V., i doz each, .with covers 4 50 Crucibles, Colorado, 2 doz i 10 440 MANUAL OF ASSAYING. Scorifiers, 200 2| inch, 200 2% inch, 9 50 Cupels, 4 doz. i inch 3 oo Cupel mould 2 25 Piece rubber cloth i oo Alcohol lamp 50 Ring stand i oo Wire triangle 10 i doz. i inch porcelain capsules 2 oo i doz. i inch porcelain capsules 250 i quart wash-bottle 75 i pair 3 inch watch-glasses 50 Blow-pipe 20 Magnifying glass, pocket size 75 Magnet 20 Small steel hammer and anvil i 75 Pair brass pincers 25 Small cold chisel 50 Horn spoon 25 1 Ib. bottle pure nitric acid '50 2 Ibs. bi-carbonate soda .... 20 i Ib. carbonate of potash 20 \ Ib. cyanide of potash 25 1 Ib. borax glass 50 2 Ibs. flour 20 1 Ib. argol 1 8 2 Ibs. nitre (nitrate potash) 30 2 Ibs. litharge - . 2*5 APPENDIX. 441 i lb. charcoal, pulverized $ 25 i lb. silica 20 \ lb. sheet lead 25 1 lb. granulated lead 40 2 Ibs. bone-ash 36 i oz. pure silver foil 75 $179 64 Note-books, gummed labels, tin boxes for dry re- agents, bottles, bags or boxes for samples, etc., accord- ing to fancy of purchaser. BLOW-PIPE OUTFIT. Apparatus for Blow-piping, according to Prof. Platt- ner, the whole in elegant velvet-lined, polished ma- hogany case, with handle and lock, for travelling, complete, with case, $38. The set includes: i set of three porcelain i charcoal borer, 4 cor- dishes. i diamond steel mortar. i pair platinum pointed forceps. i pair heavy tip steel for- ceps. i pair steel forceps. i steel chisel. nered, with spatula. i charcoal borer, club shape. i pair fine scissors. i wire holder, with 3 plat- inum wires in the han- dle. i Planner's blow - pipe 442 MANUAL OF ASS A YING. lamp, with patent swivel, nickel-plated. i charcoal saw. i holder for the mat- rasses. i nickel-plated Plattner's blow-pipe. i heavy platinum tip for same. i steel hammer with wire handle. i set mould and stamps. i pair of steel nippers, Plattner's. i dquble lens. i knife, ivory handle. i dropping pipette. i camel's hair brush. 6 matrasses. i alcohol lamp, with nick- el-plated air-tight top. i chamois skin. 6 glass tubes. 6 pieces square-cut char- coal. Metal trays for coal, ashes, and filters. 1 8 flat-top, stoppered and labelled re-agent bot- tles, containing the fol- lowing re-agents: Test lead. Tin. Phosphorus salt. Borax powder. Borax glass. | Boracic acid, fused. Boracic acid, cryst. Plattner's flux. Bismuth flux. Carbonate soda. Potash oxalate. Salt. Soda nitrate, i Charcoal. Boneash, sieved. Boneash, washed. Copper oxide. Bi-sulphate potash. Test papers. SECTION III. TABLES. MULTIPLICATION TABLE FOR GOLD AND SILVER. - SILVER. GOLD. OUNCES. VALUE. OUNCES. VALUE. I $1 2 9 2 58 3 87 5 16 6 45 7 74 9 03 10 32 1 1 61 $20 67 4i 34 62 01 82 68 103 35 124 02 144 69 105 36 186 03 2 2 -? . A . . B 6 J ' 6 7 7 8. 8 NOTE The above table is more relative than actual. $20.00 is commonly used as a factor for gold, and for silver the value per ounce fluctuates with the market. 443 444 MANUAL OF ASSA YING. TABLE OF VALUES OF GOLD AND SILVER. WEIGHT. Of Gold is worth Of Silver is worth i grain Troy $O 0430 $O 0026 i pennyweight Troy 24 grains Troy i.o'?'?q o 0646 i ounce Troy = 20 penny- weights Troy = 480 grains Troy 20 67 18 I 2O2Q i ounce Avoirdupois = 43 y-J- grains Troy 1 8 841 q i.^yy I I 78/1 i pound Troy = 1 2 ounces Troy = 240 pennyweights Troy = ^,760 grains Trov. . 248.0620 1.1 J UZJ. 1C C i e i i pound Avoirdupois = 16 ounces Avoirdupois = 7,000 grains Troy -7QI d.6A2 1 8 8551 i ton Avoir. = 2,000 pounds Avoir _ ( 29,166 ounces Troy ( _ ~ 1 32,000 ounces Avoir, j 14,000,000 grains Troy .... 6O2 O28 4660 27 710 ^84.6 NOTE. The above values are figured on the basis of $20.67 P er Troy oz. for gold, and $1.29 for silver. Were the factors made $20 for gold, and the fluctuation prices of $i.ioand $1.15 for silver, the values given would be varied considerably. APPENDIX. 445 TABLES OF WEIGHTS. AVOIRDUPOIS WEIGHT. 16 Drams=:i Ounce. 1 6 Ounces = i Pound. 28 Pounds^ i Quarter.* 4Quarters=i Hundredweight. 20 Hundred weight=i Ton of 2240 pounds. AVOIRDUPOIS WEIGHT. i dram. i ounces 16 drams, i pound= 16 ounces= 256 drams, i quarter=28 pounds=448 ounces = 7i68 drams, i h'dwt = 4 quarters=ii2 pounds=iy92 ounces= 28672 v drams. i ton=2o h'dwt 80 quarters 2240 pounds = 35840 ounces =5 7 3440 drams. AVOIRDUPOIS WEIGHT. 25 Pounds=i Quarter. 4 Quarters^ i Hundred weight. 20 Hundred weight^i Ton of 2000 pounds. AVOIRDUPOIS WEIGHT. i quarter= 25 pounds = 4oo ounces=64oo drams. * In some parts of the United States. 446 MANUAL OF ASSAYING. i h'dwt 4 quarters ~ioo pounds =1600 ounces = 25600 drams. i ton = 2o hdwt=8o quarters = 2000 pounds = 32000 ounces:=5i2ooo drams. TROY WEIGHT. 24 Grains=i Pennyweight. 20 Pennyweights i Ounce. 12 Ounces=n Pound. TROY WEIGHT. i grain. i pennyweight = 24 grains. i ounces 20 penny weights^ 480 grains. i pound =12 ounces=24o pennyweights=576o grains. APOTHECARIES' WEIGHT. 20 Grains=i Scruple. 3 Scruples^: Dram. 8 Drams^i Ounce. 12 Ounces=i Pound. APOTHECARIES' WEIGHT. i grain. i scruple=2o grains, i dram = 3 scruples=6o grains, i ounce= 8 drams=24 scruples=48o grains, i pounds 1 2 ounces = 96 drams=288 scruples = 576o grains. APPENDIX. 447 i pound, Troy, =5760 grains. i pound, Apothecaries', =5760 grains, i pound, Avoirdupois, =7000 Troy grains. FRENCH OR METRIC SYSTEM OF WEIGHTS. i Milligramme .001 of a Gramme. i Centigramme =.oi " " i Decigramme =.i " " i Gramme = i Gramme. i Decagramme 10 Grammes. i Hectogramme^ 100 i Kilogramme = 1000 i Myriagramme = 10000 or 10 Milligrammes (mgrs) = i Centigramme (cgr). 10 Centigrammes = i Decigramme (dgr). 10 Decigrammes =i Gramme (grm). 10 Grammes ==i Decagramme (dkgr). 10 Decagrammes = i Hectogramme (hgr). 10 Hectogrammes =i Kilogramme (kgr). 10 Kilogrammes = i Myriagramme(myrgr). i mgr. i cgr. = 10 rrigrs. i dgr. = io cgrs. = ioo mgrs. i grm. = 10 dgrs. = ioo cgrs.= i,ooo mgrs. i dkgr.= 10 grins. = 100 dgrs.= 1,000 cgrs.= 10,000 mgrs. 44-8 MANUAL OF ASSA YING. i hgr.= io dkgrs.= ioo grms.= 1,000 dgrs.= 10,000 cgrs. 100,000 mgrs. i kgr.=rio hgrs.= ioo dkgrs.= 1,000 grms.= 10,000 dgrs. = 100,000 cgrs. = 1,000,000 mgrs. i myrgr. = io kgrs.z=ioo hgrs.= i,ooo dkgrs.=: 10,000 grms. = ioo,ooo dgrs. = i,ooo,ooo cgrs. = 10,000,000 mgrs. i gramme= 15.43235 Troy grains. APPENDIX. 449 EQUIVALENTS OF SOME OF THE ENGLISH AND FRENCH WEIGHTS.* Troy Grains. Grammes. i .064798 2 := 129697 3 = .194396 4 2 59!95 r 323994 6 388793 *j 45359 2 8 = 518391 9 = 583190 Grammes. Troy Grains. i I5-43235 2 =^ 30.86470 3 46.29705 4 61.72940 r 77.16175 6 = 92.59410 7 108.02645 8 = 123.45880 9 138.89115 T. Egleston's Tables of Weights, Measures, Coins, etc., p. 24. 450 MANUAL OF ASSAYING, ASSAY TON EQUIVALENTS IN GRAMMES, TROY GRAINS, AND TROY OUNCES. Based on i gramme = i5. 43235 Troy grains; hence i assay ton or 29.166 grammes = i5. 43235 x 29.166=450.09992 Troy grains. Assay Tons. Value in Grammes. Value in Troy Grains. Value in Troy Ounces. 0.05 1.458 22.504 0.10 0.15 2.916 4.374 45.009 67.514 0.20 5.833 90.019 0.25 7.291 112.524 0.30 8.749 135.029 0.35 10.208 157.534 0.40 11.666 180.039 0.45 13.124 202.544 0.50 14.583 225.049 0.55 16.041 247.554 0.60 17.499 270.059 0.65 18.958 292.564 0.70 20.416 315.069 75 21 874 337 574 0.80 23 333 360.079 0.85 24 791 382 584 0.90 26 249 405.089 0.95 27.708 427.594 1.00 29.166 450.099 APPENDIX. 451 ASSAY TON EQUIVALENTS CONTINUED. Assay Tons. Value in Grammes. Value in Troy Grains. Value in TroyOunces. 1.05 30.624 472.604 1.10 32.083 495.109 1 . 032 1.15 33.541 517.614 1.078 1.20 34.999 540.119 1.125 1.25 36.458 562.624 1.173 1.30 37.916 585.129 1.219 1.35 39.374 607.634 1.266 1.40 40.833 630.139 1.313 1.45 42.291 652.644 1.360 1.50 43.749 675.149 1.407 1 .55 45.208 697.654 1.453 1.60 46.666 720.159 1.500 1.65 48.124 742.664 1.547 1.70 49.583 765.169 1.594 1.75 51.041 787.674 1.641 1.80 52.499 810.179 1.667 1.85 53.958 832.684 1.735 1.90 55.416 855.189 1.782 1.95 56.874 877.694 1.829 2.00 58.333 900.199 1.875 452 MANUAL OF ASSAYING. ASSAY TON EQUIVALENTS CONTINUED. Assay Tons. Value in Grammes. Value in Troy Grains. Value in Troy Ounces. 2.05 59.791 922.704 1.922 2.10 61.249 945.209 1.969 2.15 62.708 967.714 2.016 2.20 64.166 990.219 2 . 063 2.25 65.624 1012.724 2.110 2.30 67.083 1035.229 2.157 2.35 68.541 1057.734 2.204 2.40 69.999 1080.239 2.250 2.45 71.458 1102.744 2.297' 2.50 72.916 1125.249 2.344 2.55 74.374 1147.754 2.391 2.60 75.833 1170.259 2.438 2.65 77.291 1192.764 2.485 2.70 78.749 1215.269 2.531 2.75 80.208 1237.774 2.579 2.80 81.666 1260.279 2.626 2.85 83.124 1282.784 2.672 2.90 84.583 1305.289 2.719 2.95 86.041 1327.794 2.766 3.00 87.499 1350.299 2.813 APPENDIX. 453 ASSAY TON EQUIVALENTS CONTINUED. Assay Tons". Value in Grammes. Value in Troy Grains. Value in Troy Ounces. 3.05 88.958 1372.804 2.860 3 . 10 90.416 1395.309 2 . 905 3.15 91.874 1417.814 2.954 3 . 20 93.333 1440.319 3.001 3.25 94.791 1462.824 3.048 3.30 96.249 1485.329 3.094 3.35 97 . 708 1507.834 3.141 3 . 40 99.166 1530.339 3.188 3.45 100.624 1552.844 3.235 3.50 102.083 1575.349 3.282 3. 55 103 . 541 1597.854 3.329 3.60 104.999 1620.359 3.376 3.65 106.458 1642.864 3 . 423 3.70 107.916 1665.369 3.470 3.75 109.374 1687.874 3.516 3.80 110.833 1710.379 3.563 3.85 112.291 1732.884 3.610 3.90 113.749 1755.389 3.657 3.95 115.208 1777.894 3.704 4.00 116.666 1800.399 3.751 454 MA N UA L OF A SSA YING. ASSAY TON EQUIVALENTS CONTINUED. Assay Tons. Value in Grammes. Value in Troy Grains. Value in Troy Ounces. 4.05 118.124 1822.904 3.798 4.10 119.583 1845.409 ! 3.845 4.15 121.041 1867.914 3.891 4.20 122.499 1890.419 3 . 938 4.25 123.958 1912.924 3 . 985 4.30 125.416 1935.429 4.032 4.35 126.874 1957.934 4.079 4.40 128.333 1980.439 4.126 4.45 129.791 2002 . 944 4.173 4.50 131.249 2025 . 449 4.220 4.55 132 . 708 2047.954 4.267 4.60 134.166 2070.459 4.313 4.65 135.624 2092 . 964 4.360 4.70 137 . 083 2115.469 4.407 4.75 138.541 2137.974 4.454 4.80 139.999 2160.479 4 . 500 4.85 141 . 458 2182.984 4.548 4.90 142.916 2205.489 4.595 4.95 144.374 2227 . 994 4.642 5.00 145 . 833 2250.499 4.689 APPENDIX. 455 ASSAY TON EQUIVALENTS CONTINUED. Assay Tons. Value in Grammes. Value in Troy Grains. Value in Troy Ounces. 5.05 5.10 147.291 148 . 749 2273.004 2295.509. 4.735 4.782 5.15 150.208 2318.014 4.829 5.20 151.666 2340.519 4.876 5.25 153.124 2363 . 024 4.923 5.30 154.583 2385.529 4 . 970 5.35 156.041 2408 . 034 5.017 5.40 157.499 2430.539 5 . 0(54 :> . 45 158.958 2453 . 044 5.111 5.50 160.416 2475 . 549 5.157 5.55 161.874 2498 . 054 5 . 204 5 . 60 163.333 2520.559 5 . 251 5.65 164.791 2543.064 5 . 298 5.70 166.249 2565 . 569 5.345 5.75 167.708 2588 . 074 5.392 5.80 169.166 2610.579 5 . 439 5.85 170.624 2633.084 5.486 5.90 172.083 2655.589 5 . 532 5.95 173.541 2678.094 5.579 6.00 174.999 2700.579 5.626 45 6 MANUAL OF ASS A YING. ASSAY TON EQUIVALENTS CONTINUED. Assay Tons. Value in Grammes. Value in Troy Grains. Value in TroyOunces. 6.05 176.458 2723.084 5.673 6.10 177.916 2745.589 5.720 6.15 179.374 2768.094 5.767 6.20 180.833 2790.599 5.814 6.25 182.291 2813.104 5.861 6.30 183.749 2835.609 5.908 6.35 185.208 2858.114 5.954 6.40 186.666 2880.619 6.001 6.45 188.124 2903.124 6.048 6.50 189.583 2925.629 6.095 6.55 191.041 2948.134 6.142 6.60 192.499 2970.639 6.189 6.65 193.958 2993.144 6.236 6.70 195.416 3015.649 6.283 6.75 196.874 3038.154 6.329 6.80 198.333 3060.659 6.376 6.85 199.791 3083.164 6.423 6.90 201.249 3105.669 6.470 6.95 202.708 3128.174 6.517 7.00 204.166 3150.679 6.564 APPENDIX. 457 ASSAY TON EQUIVALENTS CONTINUED. Assay Tons. Value in Grammes. Value in Troy Grains. Value in Troy Ounces. 7.05 205.624 3173.184 6.611 7.10 207.083 3195.689 6.658 7.15 208.541 3218.194 6.705 7 . 20 209.999 3240.699 6.751 7.25 211.458 3263.204 6.798 7.30 212.916 3285.709 6.845 7.35 v 214.374 3308.214 6.892 7.40 215.833 3330.719 6.939 7.45 217.291 3353.224 6.986 7.50 218.749 3375.729 7.033 7.55 220.208 3398.234 7.080 7.60 221.666 3420.739 7.127 7.65 223.124 3443 . 244 7.173 7.70 224.583 3465.749 7.220 7.75 226.041 3488.254 7.267 7.80 227.499 3510.759 7.314 7.85 228.958 3533.264 7.361 7.90 230.416 3555.769 7.408 7.95 231.874 3578.274 7.455 8.00 233.333 3600.779 7.502 458 MA NUAL OF A SSA YING. ASSAY TON EQUIVALENTS CONTINUED. Assay Tons. Value in Grammes. Value in Troy Grains. Value in TroyOunces. 8.05 234.791 3623.284 7.54',) 8.10 236.249 3645 . 789 7 . 595 8. 15 237.708 3668.294 7.642 8.20 239.166 3690.799 7.689 8.25 240 . 624 3713.304 7.736 8.30 242.083 3735 . 809 7.783 8.35 243.541 3758.314 7.830 8.40 244.999 3780.819 7.877 8.45 246.458 3803 . 324 7.924 8 . 50 247.916 3825.829 7.970 8.55 249.374 3848 . 334 8.017 8.60 250.833 3870 . 839 8.064 8.65 252.291 3893 . 344 8.111 8.70 253.749 3915.849 8.158 8.75 255 . 208 3938.354 8 . 205 8.80 256.666 3960 . 859 8.252 8.85 258.124 3983 . 364 8 .'299 8.90 259.583 4005 . 869 8.346 8.95 261 . 041 4028 . 374 8.392 9.00 262 . 449 4050.879 8.439 APPENDIX. 459 ASSAY TON EQUIVALENTS CONTINUED. Assay Tons. Value in Grammes. Value in Troy Grains. Value in Troy Ounces. 9.05 263 . 958 4073.384 8.486 9.10 265.416 4095.889 8.533 9.15 266.874 4118.394 8.580 9.20 268.333 4140.899 8.627 9.25 269. 79L 4163.404 8.674 9 . 30 271.249 4185.909 8.721 9.85 272.708 4208.414 8.768 9 . 40 274.166 4230.919 8.814 9.45 275.624 4253.4-24 8.861 9.50 277.083 4275.929 8.908 9 . 55 278.541 4298 . 434 8.955 9.60 279.999 4320.939 9.002 9.65 281.458 4343.444 9.049 9.70 282.916 4365 . 949 9.096 9.75 284.374 4388.454 9 . 143 9.80 285.833 4410.959 9.189 9.85 287.291 4433 . 464 9.236 9.90 288.749 4455 . 969 9.283 9.95 290.208 4478.474 9.330 10.00 291.666 4500.979 9.377 INDEX. AARON, references to, 142, 264, 265, 267, 280, 281, 282, 293, 296, 298, 301, 302, 332, 367, 434. AARON'S ASSAYING, 434. ACETATE OF LEAD, re-agent, 141. ACETIC ACID, re-agent, 144. ACICULAR BISMUTH, mineral, 422. ACID, ACETIC, re-agent, 144. ACID, CITRIC, re-agent, 146. ACID FLUXES, 225, 227; silica, 129, 137- ACID GANGUES, 225, 227. ACID, HYDROCHLORIC (muriatic), 147. ACID, NITRIC, re-agent. 143, 148; preparation of various strengths, 211; to free from chlorine, 143. ACID, SULPHURIC, re-agent, 151. ACID, TARTARIC, re-agent, 151. ACTINIUM, element, 14. AIKINITE, mineral, 418, 422. AINSWORTH balance, 51. ALABANDITE, 231. ALASKAITE, mineral, 418, 425. ALCOHOL, re-agent, 144. ALDEN CRUSHER, 24. ALGODONITE, mineral, 421, 422. ALPHABETS AND FIGURES, steel, 126. ALTAITE, mineral, 418, 421, 425. ALUMINA, and lead phosphate, mineral, 427; crucibles, 103. ALUMINIUM, element, 13. AMALGAMATION, assay, 351; mor- tar, 33. AMALGAM, gold, mineral, 417. AM. INST. MIN. ENG., reference to, 334- AMMONIA, aqua (caustic, hydrate, water), 144; carbonate, 129,135, 145; citrate, 146. ANALYSIS, books on, 429; blow- pipe, books on, 431; copper ores, 333; definition, 15; re- agents for, 144; volumetric, books on, 430 ANGLESITE, mineral, 425. ANNEALING CUPS, no; plate, no. ANTIMONIAL ores, 188, 219; red silver ore, 168, 420; silver, 419; sulphide of silver and lead, 419, 426. ANTIMONY, and lead sulphide, 425; and silver sulphide, 168, 420; arsenic and silver sulphide, 168, 419 ; bismuth and lead sul- 461 462 INDEX. phide, 426; copper and lead sulphide, 422, 425 ; cupel color, 192; element, 13; gray, 232, 249; in copper ores, 349; met- al, 16; native, 421; oxide, 420; qualitative scheme for, 240; sulphuret, 232; vapors, 235. ANVILS, and methods of mount- ing, 119. APOTHECARIES' weights, tables of, 446. APPARATUS, for analysis and as- saying, 19; glass and porcelain, in; graduated, 114; miscella- neous, 116; sulphuretted hy- drogen, 150; used in furnace, IO2. APPENDIX, 325. AQUA AMMONIA., re-agent, 144. ARGENTIFEROUS, gold, 417, 419; gray copper, 169; lead ores, 169; ores, 168; pyrites, 170; zinc blende, 170. ARGENTIC NiTRATE,re-agent,i48. ARGENTITE, mineral, 232, 238, 418. ARGOL, re-agent, 128, 133, 222; reducing power, 161. " ARRASTRE," 33. ARSENATE, LEAD, mineral, 426. ARSENIC, antimony and silver sulphide, 168, 419; cupel color, 192; element, 13; in copper ores, 348, 350; native, 418, 421; sulphuret, 232; vapors. 235. ARSENICAL, copper, 423; ores, 188, 219; silver ore, 168, 419. ARSENIDE, COPPER, mineral, 422, 423, 425- ARSENOPYRITE, or arsenical iron pyrites, mineral, 167, 231, 235, 238, 249, 418, 421. ASH, BONE, 152. ASSAY, amalgamation, 351; base bullion, 404; certificate, 438; chlorination, 364; copper, 305; crucible, methods of, 264; ga- lena, 312; gold and silver, 170; gold and silver bullion, 369; laboratory, plan of, 437; lead, 312; ton equivalents, 450; ton weights, and explanation, 60. ASSAYING, apparatus, 19; books on, 434; definition, 15; dry re- agents for, 128; free gold and silver ores, 329; methods of, 180; of various minerals in an ore, 327; outfit, 439; re-agents used in, 128, wet re-agents used in, 142. " ASTONISHING," 173. ATACAMITE, mineral, 422. ATTWOOD, blow-pipe assaying, 431; reference to, 13, 357. AURICHALCITE, mineral, 422. AURIFEROUS SULPHURETS, 167. AUSTIN, L. S., references to, 172, 406. AVERAGE SAMPLES, obtaining of, 172. AVOIRDUPOIS to troy weights, tables of, 399. AVOIRDUPOIS WEIGHTS, tables of, 445- INDEX. 463 AZURE COPPER ORE (azurite), mineral, 301, 305, 422. B BALANCES, Ainsworth, 51, 52; Becker, 44, 45, 48; bullion, 44; for weighing gold and silver beads, 44; Oertling,48; special directions for, 54; Troemner, 44, 45, 46, 47, 48. BALLING'S Works on Assaying, 434- BARIUM, chloride (muriate), re- agent, 146; element, 13. BARKER'S ELEMENTARY CHEMIS- TRY, 428. BARNARD'S METRIC SYSTEM, 435. BARNHARDITE, mineral, 299, 421, 422. BASE BULLION, assay, 404; sam- pling, 406. BASIC FLUXES, 129 135, 225, 227. BASIC GANGUES, 225, 227. BATEA, 357. BATHS, sand, 122. BATTERSEA, crucibles, 104-5; fur- naces, 84; muffles, 102; roast- ing dishes, 105; scorifiers, 106. BATTERY, Bunsen carbon, 338; "gravity," 340. BEADS, gold and silver, balance for weighing, 44; inquarting, 183; parting, 183; weighing, 183, 209. BEAKERS, glass, 114. BEAUFAY CRUCIBLES, 103-4. BECKER'S BULLION BALANCES, 44, 45, 48; pulp scales, 38. BERINGER, C. and J. J ., refer- ence to, 351. BI-CARBONATE OF SODA, re-agent, 128, 129, 222; properties, 129. BI-CHROMATE OF POTASH, re- agent, 14*5, 222. BISMUTH, acicular (cupreous), 422; cupel color, 192; element, 13; in copper ores, 349, 350; lead and antimony sulphide, 426; metal, 16; native, 418, 421; scorifier color, 191; silver, 420, 427; silver and lead sul- phide, 418. 420, 425, 427; sul- phuret, 232. BISMUTHINITE, mineral, 418. BI-SULPHURET, or bi-sulphide of iron, 283. BI-TARTRATE OF POTASH, re- agent, 128, 133, 161. BLACK, flux substitute, 128, 133; copper or oxide of copper, 233, 301, 304, 424; glazed paper, 117; oxide of manganese, re- agent, 145 ; oxide of manga- nese, mineral, 233; silver, 420; tellurium, 417, 427. " BLACK JACK," 231. BLACK LEAD CRUCIBLES, 103. BLAKE CRUSHER, 24. BLENDE, 167, 188, 231, 238, 249; argentiferous, 170. " BLICKING," 205. " BLOSSO'MING," 207. BLOTTING PAPER, 117. 464 INDEX. BLOW PIPE, 123; analysis, books on, 431 ; outfit, 441. BLUE carbonate of copper (blue malachite, mountain blue), 301, 305, 422, 423. BLUE COPPER, mineral, 423. BLUE VITRIOL, mineral, 423. BODEMANN & KERL'SJ works on assaying, 434; reference to, 310. BOILING FLASKS, 113. BONE-ASH, 152. BOOKS, note, 116; list of useful, 428. BORAX, 128, 131; glass, prepara- tion of, 132; re-agent, 128, 131, 222. BORNITE, mineral, 232, 238, 299, 421, 422. BORON, element, 13. BOSWORTH CRUSHER, 27. BOTTLE WASH, 112. BOTTLES, re-agent, in; sample, in. BOULANGERITE, mineral, 421, 425- BOURNONITE, mineral, 299, 422, 425- BOWIE, A. J., Treatise on Hy- draulic Mining, 433. BOXES, SAMPLE, 117, 172. BOYER, C., reference to, 6. BRIEF SCHEME FOR SILICA, iron, and manganese, 413. "BRIGHTENING," 205. BRITTLE SILVER ORE, mineral, 168, 420. BROCHANTITE, mineral, 422. BROMIC SILVER (bromide of sil- ver, bromyrite), 169, 418. BROMINE, element, 13; re-agent, 145- BROWN'S ASSAY FURNACE, 86. BRUSHES, 118. BRUSH'S MINERALOGY, 431. BUCKING HAMMER, 29. BUFFALO DENTAL MFG. Co., 66, 78. BULLION, balances, 44; base, as- say of, 404; gold and silver, assay of, 369; punch, 126. BUNSEN, battery, 338; burners, 122. BURETTE, 114; stands, 127. CADMIUM, element, 13; cupel color, 192; scorifier color, 191. CESIUM, element, 14. CAIRNS' QUANTITATIVE ANALY- SIS, 429. CALAVERITE, mineral, 417, 421. CALCIUM, chloride, 146; element, 13; hydroxide, 147. CALC-SPAR, mineral, 278. CALCULATIONS in scorification process, 183, 216. CALEDONITE, mineral, 423, 425. GALLON'S LECTURES ON MINING, 431- CAPSULES, porcelain, 112. CARBON, element, 13. CARBONATE, of ammonia, re- agent, 129, 135, 145; of copper, INDEX. 465 blue and green, minerals, 301, 305, 422, 424; of lead, mineral, 170, 312, 425 ; of lead, re-agent, 141 ; of potash, re-agent, 128, 130, 222; of sodium, re-agent, 145, 222; of zinc and copper, mineral, 422. "CARBONATE ORES," 167, 187. CARBONATES, tests for, 408. "CARBONS, PEPPER," 394. CARPENTER'S MINING CODE, 436. CARROLLITE, mineral, 299, 423. CASE, GLASS, for pulp scale, 38. CASSEROLE, 115. CAUSTIC ammonia, 144; lunar, 148; potash, 146; soda, 146. CERARGYRITE, mineral, 419. CERIUM, element, 14. CERTIFICATE OF ASSAY, form for, 438. CERUSE, re-agent, 141. CERUSSITE, mineral, 170, 312, 421, 425. CHALCANTHITE, mineral, 423. CHALCOCITE, mineral, 232, 238, 298, 305, 423. CHALCOPYRITE, mineral, 232, 238, 299, 305, 418, 421, 423. CHALK, dry, 152; wash, 152. CHAMOIS SKIN, 127. CHAPMAN'S crucible flux, 279. CHAPMAN, references to, 173, 279. CHAPMAN'S FURNACE ASSAY, 434. CHARCOAL, WOOD, charge for testing, 162; properties of, 135, re-agent, 135, 222; reducing power, 134, 162. CHARGES, Aaron's general, 280, 281; Chapman's, 279; crucible for galena, 303; crucible for quartz, sand, or "dry ores," 281, 282; for argol, 161 ; for charcoal, 162; for chlorides, 187; for copper mattes, 186; for copper oxides and carbon- ates, 307; for copper oxides, 302; for cream of tartar, 161; for "dry ores," 282; for gran- ulated lead, 158; for iron oxide, 297, 298; for iron pyrites, 285, 289, 291, 292, 293; for lead carbonates, 321; for lead in galena, 312, 315, 316, 317, 319; for lead oxides, 321; for lith- arge, 154; for native copper, 306; for nitre, 163; for ordin- ary scorifications, 185; for ox- ides of iron, 187; for sulphur- ets of copper, 300, 308 ; for tellurides, 188; Mitchell's, for all gold and silver ores, 277; for testing ores, 242, 251; gen- eral, for crucible, 276; in scor- ification process, 185; prelim- inary, to determine oxidizing power, 251; preliminary, to determine reducing power, 242; preparation of, in scorification process, 183; scorification for arsenical and antimonial ores, 188; for blende, 188; for " car- bonate " ores, 187; for "chlor- ide" ores, 187; for copper glance or pyrites, 185; for cop- 466 INDEX. per matte, 186; for "every- day " ores, 185 ; for galena, 187; for gray copper ore, 186; for native gold or silver, 189, for oxide of iron, 187; for sul- phurets of iron, 186; for tellu- rides, 188; special, 282; Stone's, 278. "CHECKING," 109. " CHECKS," 390. CHEMICAL TECHNOLOGY," Wag- ner's, 428. CHEMISTRY, Barker's, 428; gen- eral books on, 428; Miller's, 428; reference books on, 428; Roscoe and Schlorlemmer, 428; Roscoe's Elementary, 429; the- oretical text-books on, 428; Watts' Dictionary, 428. CHEM. NEWS, reference to, 351. CHISEL, cold, 126. CHLORIDE, and phosphate of lead, 427; basic, 146; calcic, 146; mercuric, 148; of silver, 169, 419; sodic, 135; stannous, 149. "CHLORIDE ORES," 169, 187, 219. CHLORINATION assay of gold ores, 364; test for silver, 367. CHLORINE, element, 13; in dis- tilled water, 142; to free nitric acid from, 143. CHLORO-BROMIDE OF SILVER, mineral, 219, 419. CHROMATE OF COPPER AND LEAD, mineral, 425, 427. CHROMIUM, element, 13; colors in cupel and scorifier, 192, CHRYSOCOLLA, mineral, 226, 302, 423- "CHURNING," 212. CITRATE OF AMMONIUM, re-agent, 146. CITRIC ACID, re-agent, 146. CLASSEN'S QUANTITATIVE ANAL- YSIS, 429. CLASSIFICATION of ores in assay- ing, 219; of silver ores, 168. CLAY, crucibles, 104; crucibles, French, 103, 104; lute, 152. CLOCK-GLASSES, 112. CLOTH, oil and rubber, 117. COAL, reducing power of, 134, 162. COATES, R. G., reference to, 6, 364- COBALT, colors in cupel and scor- ifier, 193; element, 13; in cop- per ores, 347; metal, 16; nickel and copper sulphide, 423. COFFEE-MILL, 133. COKE, reducing power of, 134, 162. COLD CHISEL, 126. COLLINS' MINING AND QUARRY- ING, 433. COLORADO crucibles, 105; min- erals, 427. COLORADOITE, mineral, 418, 421. COLOR TESTS, cupel, 190; scori- fier, 190. " COLORS," 351. COLUMBIUM, element, 14. COMMON SALT, re-agent, 129. 135- INDEX. 467 "CONCENTRATES," 285. COPP'S MINING CODE, 435. COPPER, analysis, methods, 333 ; and antimony, 232; and iron sulphide, sulphuret or py- rites, 232, 299, 305, 422, 423; and lead chromate, 425, 427, and silver sulphide or sulphur- et, 169, 420, 424; and uranium phosphate, 424; and zinc car- bonate, 422 ; argentiferous gray, 169; arsenical, 423; ar- senide, 422, 423, 425 ; assay, 305; azure, 422; black oxide, 233, 3oi. 304. 424; blue, 423; blue carbonate, 301, 305, 422; blue malachite, 422; carbon- ates, 301, 305 ; cobalt and nickel sulphide, 423; colors in cupel and scorifier, 190; element, 13; glance, 185, 232, 249, 298, 423; gray, 167, 186, 232, 249, 299, 305, 420, 424; green, 424; green carbonate, 301, 305, 424; indi- go, 423; lead and antimony sulphide, 422, 425; matte, 186; metal, 16; metallic, 148; metal- lurgy, 432 ; minerals in the United States, 422; muriate, 422; native, 304, 421,424; na- tive, assay, 306; occurrence, 304; oxides, 301, 304; oxides, assay, 301, 307; oxy-chloride, 422; phosphate, 424; purple, 422; pyrites, 185, 232, 249, 299, 423; pyritous, 423; red oxide, \ 304, 423; silicate, 423; spatu- , las, 36; sulph-arsenite, 423, 424; sulphate, 422, 423; sul- phides or sulphurets, 232, 298, 305, 423; sulphides, assay, 307; tests for, 410; uranite, 424; variegated, 232, 422 ; vitreous, 232, 298, 423; vitriol, 423; volumetric analysis, 343. COPPERAS, re-agent, 149. COPP'S AMERICAN MINING CODE, 435- CORBIN, H. H., reference to, 177. " CORNETS," 394. CORN STARCH, reducing power of, 134- "CORNUCOPIAS," lead, 391. CORNWALL'S BLOW-PIPE ANALY- SIS, 431. CORROSIVE SUBLIMATE, re-agent, 148. "CORUSCATION," 205. COTTA'S TREATISE ON ORE DE- POSITS, 430. COUNTERPOISING, 397. COVELLITE, mineral, 299, 423. CREAM OF TARTAR, re-agent, 128, 133, 222; reducing power, 134, 161. CRUCIBLE, process, 171, 180, 181, 217. CRUCIBLE TONGS, 92. CRUCIBLES, alumina, 103; Batter- sea, 104-5; black lead (graphite or plumbago), charcoal-lined, 103; clay, 104; "Colorado," 105; French clay or "Beau- fay," 103, 104; gold, 103; 468 INDEX. "Gramme," 105; Hessian, iron, magnesia, platinum, 103; porcelain, 103, 112; quicklime, 103; round, 104; sand, 104; silver, 104; triangular, 104. CRUSHERS, Alden, Blake, Fors- ter. Lipsey, 24; Bosworth, 27; Krom, 25. CUPEL, color tests, 190; moulds, 123; rake, 98; shovel, 98; tongs, 96. CUPELLATION, 183, 2OO. CUPELS, directions for making, 107. CUPREOUS, bismuth, 422; oxide, 423; sulphato-carbonate of lead, 423, 425. CUPRIC OXIDE, mineral, 424. CUPRITE (or cuprous oxide), min- eral, 301, 304, 423. CUPS, annealing, no. CYANIDE OF POTASH, properties, 131; re-agent, 128, 130, 146. CYCLOPEDIA, Johnson's New Universal, 428. CYLINDERS, measuring, 114. D DANA, Manual of Geology, 430; Manual of Mineralogy, 431; reference to, 427; System of Mineralogy, 427, 430; Text Book of Geology, 430. DARK RED SILVER ORE, 168, 420. DAVIES, D. C., Treatises on Min- erals, 433. DAVYUM, element, 14. DECHENITE, mineral, 425. DECIPIUM, element, 14. " DECOMPOSED iron ore," 233. DEFINITIONS, of analysis, 15; of assaying, 15. DENDRITIC SILVER, 419. DENVER FIRE-CLAY CRUCIBLES, 105. DESCLOIZITE, mineral, 425. DESULPHURIZING ACTION, of bi- carbonate of soda, 129; of car- bonate of ammonia, 135; of cyanide of potash, 131 ; of iron, 141; of litharge, 140. DETERMINATION OF, moisture in an ore, 415; oxidizing power of nitre, 153, 162; of ores, 251; reducing powers of argol, 161; charcoal, 162; cream of tartar, 161; ores, 242; reducing agents, 153, 161; sulphurets in an ore, 240; sulphur in pyrites, 416. DI-CHROMATE, p o T A s s I c , re- agent, 145. DICTIONARY OF CHEMISTRY, Watts', 428. DIDYMIUM, element, 14. DIRECTIONS FOR, cupellation, 200; filtering, 336; operating Hos- kins' furnace, 81; sampling ores, 172; setting up and test- ing pulp scales, 39; special, for bullion balances, 54. DISHES, ROASTING, 105. DISTILLED WATER, chlorine in, 142; re-agent, 142. INDEX. 469 DIVIDERS, 31. DOMEYKITE, mineral, 423. DOUGLAS & PRESCOTT'S QUALI- TATIVE ANALYSIS, 429. " DRESSING" charges, 272. " DRIVING," 392. DRY RE-AGENTS, list of, 128. DYSCRASITE, mineral, 419. EGLESTON'S WEIGHTS, MEASURES, AND COINS, 435, 449. EGLESTON'S METALLURGY, 433. ELDERHORST'S BLOW-PIPE ANAL- YSIS, 431. ELECTRUM, mineral, 417, 419. ELEMENTS, lists of, 13, 14. ELEMENTS OF CHEMISTRY. MIL- LER'S, 428. ELIOT AND STORER'S QUALITA- TIVE ANALYSIS, 429. EMBOLITE, mineral. 419. ENAKGITE, mineral, 421, 423. ENGINEERING AND MINING JOUR- NAL, references to,-i72, 350,405. ENGLISH AND FRENCH WEIGHTS, equivalents of, 449. EPSOM SALTS, re-agent, 149. ERBIUM, element, 14. ERUBESCITE, mineral, 232, 299, 422. EUSTIS, W. E. C., reference to, 334- " EVERY-DAY" ores, 185. EXPLANATION of assay ton weights, 60. FAHLERZ, 232, 299. FAHLORE, silver, mineral, 169. " FEATHERING," 204, 407. FERRIC SESQUIOXIDE, 152. FERROCYANIDE, POTASSIC, re- agent, 146. FERRO-TELLURITE, mineral, 418, 421. FERROUS sulphate, re-agent, 149; sulphide, re-agent, 149. FIELDING, F. E., references to, 343, 370. FIGURES, steel, 126. FILINGS, IRON, re-agent, 141. FILTERING, directions for, 336. FILTER paper, 117; stands, 126. " FINENESS," 383. FIRE CLAY, in clay lute, 152. " FLASHING," 205. FLASKS, litre, 114, 115; parting or boiling, 113. FLETCHER'S gas furnaces, 68, 264, 317. FLOORS, MUFFLE, 103. FLOUR, re-agent, 128, 133, 162, 222. FLOUR GOLD, 167, 223, 417. FLUORINE, element, 13. FLUOR SPAR, mineral, 278. FLUXES, acid, 225, 227; basic, 225, 227; bi-carbonate of soda, 128, 129; black flux substitute, 128. 133; borax, 128, 131; carbonate of potash, 128, 130; Chapman's crucible, 279; cyanide of pot- INDEX. ash, 128, 130; flour, 128, 133; glass, 137; litharge, 129, 139; metallic, 138, 140, neutral, 131; nitre, 129, 135; sand, 137; scales for, 37; silica, 129, 137; Stone's universal, 278. FLUXING POTS, 104. FOIL, lead, re-agent, 138; lead, silver in, 138, 153, 160; silver, re-agent, 141. FOLIATED TELLURIUM, mineral, 417, 427. FORM FOR CERTIFICATE OF AS- SAY, 438. FORSTER CRUSHER, 24. FOYE'S MINERAL TABLES, 431. FRAZER'S MINERAL TABLES, 431. FREE GOLD, 167, 417; assay of in ores, 329; in ores, to grind, 177. FREE SILVER, 419; assay of in ores, 329. "FREEZING," 209. FREIESLEBENITE, mineral, 419, 426. FRENCH CLAY CRUCIBLES, 103, 104. FRENCH OR METRIC WEIGHTS, 59; equivalents in English weights, 449; tables of, 447. FRESENIUS' QUALITATIVE AND QUANTITATIVE ANALYSIS, 429; reference to, 414. FRYING PAN, 123. FUEL, metallurgy, Percy, 432. " FUGURATION," 205. FUNNELS, glass, 115; separatory, FURNACES, 64; apparatus used in, 102; Battersea, 84; Brown's, 86; Fletcher's, 68; gas, group of, 67; Hoskins', 78; Judson's, 85; " Monitor," 70; permanent, 90; portable, 83; tools for, 92; using gaseous fuel, 66; using liquid fuel, 77; using solid fuel, S3- GADOLINIUM, element, 14. GALENA or galenite, 167, 169, 187, 232, 238. 249, 311, 418, 421, 426; crucible charge for, 303; iron in assay of, 141, 313, 315, 317; methods for, 312; scorifi- cation charge for, 187. GALLIUM, element, 14. GANGUES, acid and basic, 225, 227. GAS FURNACES, Fletcher's, 68; " Monitor," 70. GAS, hydrogen sulphide, re-agent, 149. GAUZE, wire, 122. "GEM PLATE," 100. GENERAL chemistry, books on, 428; charges for crucible proc- ess, 276 ; qualitative and quan- titative analysis, books on, 429; science, books on, 428. GEOCRONITE, mineral, 421, 426. GEOLOGY, books on, 430. GERMANIUM, element, 14. GLANCE, copper, 185, 232, 249, 298,423; lead, 169; silver, 168, INDEX. 471 232, 418; silver-copper, 169, 420, 424. GLASS, and porcelain apparatus, in; beakers, 114; borax, 128, 131; borax, preparation, 132; case for pulp scales, 38; flasks, 114, 115; funnels, 115; magnify- ing, 125; mortars, 116; pi- pettes, 115; re agent, 137; stir- ring rods, 115; spatulas, 36. GLASSES, watch or clock, 112. GLUCINUM, element, 14. GLYCERINE, for sulphuretted hy- drogen water, 151. GOLD, amalgam, 417, 421; and lead telluride, 417; argentifer- ous, 417, 419; assaying of, 170; assaying of free, 329; bullion assay, 369; chlorination assay, 364; crucible, 103; crucible process, 217; element, 13; flour, free, leaf, native, nugget, wire, 167, 417; in silver foil, 141; Lock's work on, 432; metal, 16; minerals in United States, 417; minerals likely to carry, 418; multiplication table, 443; na- tive, 417, 421; native, assay, 189; occurrence, 167; pan test or "panning," 355; residues, weighing of, 183, 215; tellu- ride, 417, 427; tables of values of, 403, 444 ; testing of silver foil for, 141; washing pans, 126. " GOLD WEIGHTS," 64, 382. GOLD AND SILVER, and lead tellu- ride, 417, 426; assaying, 167, 170; beads, balances for weigh- ing, 44; beads, weighing of, 183, 209; bullion, assay of, 369; calculations, 216 ; crucible process, 217; cupellation, 183, 200; inquartation, 183, 214; metallurgy, books on, 431; multiplication table, 443; oc- currence, 167; ores, charges for, 277-282 ; parting, 210 ; preparation of charge, 183 ; preparation of sample, 171 ; residue, weighing, 215; roast- ing, 183, 185, 257, 259; scorifi- cation charges, 185; scorifica- tion process, 181; table of val- ues. 403, 444; tellurides, 417, 419, 420. GRADUATED APPARATUS, 114. GRAIN WEIGHTS, 64. "GRAMME" CRUCIBLES, 105. GRAMME WEIGHTS, 59. GRANULATED LEAD, preparation, 138; re-agent, 129, 138; test- ing for silver, 138, 153, 158. "GRANULATION," 381. GRAPHIC TELLURIUM, mineral, 417, 420. GRAPHITE CRUCIBLES, 103. GRAY, antimony, 232, 249; cop- per, 167, 186, 232, 249, 299, 420, 424 ; copper, argentiferous, 169. GREEN, carbonate of copper, 301, 305, 424; copper ore, 424; lead ore, 426; malachite, 305, 424; mountain, 423, 424; vitriol, 149- 472 INDEX. GRINDER, 29. GRINDING PLATE, 28; Mr. S. A. Reed's, 30. GUM ARABIC, 134. GUMMED LABELS, 116. H HAMMERS, 118. HAND SCALES, 43. HANKS, H. G., reference to, 370, 387- HANKS, H. G., Report of State Mineralogist of CaL, 431. HARD COAL, reducing power of, 134- HARRISITE, mineral, 299, 423. HART, references to, 351, 414. HART'S VOLUMETRIC ANALYSIS, 430- HEAVY SPAR, mineral, 278. HELIUM, element, 14. HEMATITE, re-agent, 152; min- eral, 296. HENRYITE, mineral, 418, 421, 426. HESSIAN CRUCIBLES, 103. HESSITE, mineral, 418, 419, 421. HOLMIUM, element, 14. HORN, silver, mineral, 168, 419; spatulas, 36; spoons, 36. " HORSE-FLESH" ORE, 232, 299, 422. HOSKINS* ASSAY FURNACE, 78. HYDRATE, ammonic, re-agent, 144; potassic, re-agent, 146; sodic, re-agent, 146. HYDRIC NITRATE, re-agent, 143. HYDROCHLORIC ACID, re-agent, 147. HYDROGEN, element, 13; sulphide, 149; sulphide, preparation of as re-agent, 150. HYDRO-POTASSIC-TARTRATE, re- agent, 133. HYDRO -SODIC -CARBONATE, re- agent, 129. HYDROXIDE, CALCIC, re-agent, 147. HYPOSULPHITE OF SODIUM, re- agent, 147. IDUNIUM, element, 14. ILMENIUM, element, 14. IMPLEMENTS FOR PULVERIZING, SAMPLING, etc., 20. IMPORTANCE OF AVERAGE SAM- PLES, 172. IMPORTANT SILVER ORES, 168. INDIGO COPPER, mineral, 423. INDIUM, element, 14. INGOT MOULDS, 125. INQUARTATION, 183, 214. INTRODUCTION, 13. IODIC SILVER (iodide of silver, io- dyrite), i6q, 419. IODIDE OF POTASH, re-agent, 147. IODINE, element, 13. IRIDIUM, element, 13. IRON, and copper sulphide, sul- phuret, or pyrites, 167, 185, 232, 299, 305, 422, 423; and silver sulphide, 420; brief scheme for, INDEX. 473 413; colors in cupel and scori- fier, 191; crucibles, 103; desul- phurizing action, 141 ; element, 13; filings, 141; in copper ores, 349, 350; metal, 16; metallic, 148; mortars, 20, 22; nails, 141; oxide, 167, 187; oxide, crucible charges for, 297, 298; oxide, re-agent, 142; pyrites, crucible charges for, 285, 289, 291, 292, 293; pyrites, mineral, 231, 249, 283; pyrites, re-agent, 142; re- agent, 129, 141; red oxide, 152, 233; retorts, 127; spatula, 36; sulphate, 149; sulphide or sul- phuret, re-agent, 149; sulphu- rets, ores, 186, 231, 232, 283; tests for, 410; wire, 141. IVORY SPATULAS, 36. "JACK, BLACK," 231. JACKSON, J. C., reference to, 92. JAMESONITE, mineral, 426. JOHNSON'S NEW UNIVERSAL CY- CLOPAEDIA, 428. JOSEITE, mineral, 418, 421. JUDSON'S cupel tongs, 97; fur- naces, 85; scorification tongs, 95- K KERL'S METALLURGY, 432; Works on Assaying; 434. KOBELLITE, mineral, 426. KROM'S LABORATORY CRUSHER, 25- KUNHARDT'S PRACTICE OF ORE DRESSING, 433. KUSTEL, references to, 168, 365, 367, 369; Roasting of Gold and Silver Ores, 168, 432. LABELS, gummed, 116. LABORATORY, arrastre, 33; ma- nipulation, books on, 430; mill- run, 351; plan of assay, 437. LAMBORN'S METALLURGY, 432. LAMPS, 122. LANARKITE, mineral, 426. LANTHANUM, element, 14. LAUNDRY STARCH, 134. LEAD, acetate, 141; and alumina phosphate, 427; and antimony sulphide, 425; and copper chro- mate, 425, 427; and gold tellu- ride, 417, 427; and silver, anti- monial sulphide of, 419, 426; and silver, metallurgy, 432; and zinc vanadate, 425; argentifer- ous ores, 169; arsenate, 426; assay, 312; bismuth and anti- mony sulphide, 426; bismuth and silver sulphide, 418, 425 ; carbonate, mineral, 170, 312, 425; carbonate, re-agent, 141; carbonates, assay, 320; colors in cupel and scorifier, 191; cop- per and antimony sulphide, 422, 425; "cornucopias," 391; cu- 474 INDEX. preous-sulphato-carbonate, 425 ; element, 13; foil, re-agent, 138; foil, silver in, 138, 153, 160; glance, 169; granulated, prepa- ration, 138; granulated, re- agent, 129, 138; granulated, silver in, 139, 153, 158; in cop- per ores, 349, 350; metal, 16; metallurgy, 432; minerals, 425; molybdate, 427; native, 427; ore, green, 426; ore, white, 312, 425; ore, yellow, 427; ores, 311; ores, argentiferous, 169; ores, assay, 312; ores, occur- rence, 311; oxides, assay, 320; phosphate of alumina and, 427; phosphate and chloride of, 427; pyrites, 232, 302; red oxide, mineral, 233, 312; red oxide, 426; removal from litharge, 139; sheet, silver in, 138, 153, 160; silver and bismuth sul- phide, 418, 420, 425, 427; sil- ver and gold telluride, 417, 426; spar, 427; sugar of , 141; sulph- antimonite, 426; sulph-arseno- antimonite, 426; sulphate, min- eral, 425; sulphate-carbonate, 423, 426; sulphates, assay, 312; sulphide or sulphuret, assay , 312 ; sulphide, or sulphuret, mineral, 169, 232, 302, 311, 426; sul- phide, iron in assay of, 313, 3 I 5 3 1 7> telluride, 425, 426; test for, 411; tungstate, 427; vanadate, 425; vitriol, 425; white, re-agent, 141; yellow oxide, mineral, 426; yellow ox- ide, re-agent, 139. LEADHILLITE, mineral, 426. LEAF gold, 167, 417; silver, 419. i LE CONTE'S ELEMENTS OF GE- OLOGY, 430. LEUCOPYRITES, mineral, 421. LIBBER'S ASSAYER'S GUIDE, 434. LIGHT RED SILVER ORE, 168, 419. LIME, in copper ores, 349; sul- phate of, 424. LIME water, re-agent, 147. LIMONITE, mineral, 296. LIGNITE, mineral, 418, 421. LlPSEY CRUSHER, 24. LISTS AND REFERENCES, 417. LISTS, copper minerals, 422; dry re-agents for assaying, 128; ele- ments, 13, 14; gold minerals, 417; lead minerals, 425; min- erals carrying gold, 418; min- erals carrying silver, 421; re- agents' for analysis, 144; silver minerals, 418; useful books, 428; wet re-agents for assaying, 142. LITHARGE, properties, 140; re- agent, 129, 139, 222; to free from red oxide, 139; silver in, 140, 153, 154. LITHIUM, element, 13. LITRE FLASKS, 114. LOCK'S WORK ON GOLD, 432. Low, A. H., reference to, 293. LUCKOW method of copper anal ysis, 333. LUNAR CAUSTIC, re-agent, 148. LUTE, CLAY, 152. INDEX. 475 M MAGNESIA, crucibles, 103; in cop- per ores, 349. MAGNESIUM, element, 13; sul- phate, re-agent, 149. MAGNET, 125. MAGNETIC IRON PYRITES, etc., 231, 283. MAGNIFYING GLASS, 125. MAGNOLITE, mineral, 418, 421. MAKIN'S MANUAL OF METAL- LURGY, 433. MALACHITE, 301, 424; blue, 422; green, 305, 424. MANGANBLENDE, 231, 238, 249. MANGANESE, black or di-oxide, 145, 233; brief scheme for, 413; colors in cupel and scorifier, 192; element, 13; in copper ores, 348; sulphuret,23i; test for, 411. MANIPULATION, LABORATORY. books on, 430. MARCASITE, 283. MASSICOT, mineral, 426. MATRASSES, 113. MATTE, COPPER, 186. MATTES, 275. MEASURING CYLINDERS, 114. MELACONITE, mineral, 233, 301, 304, 418, 421,. 424. MERCURY, chloride, 148; ele- ment, 13; metallic, 148; nat- ive, 421; re-agent, 148; sul- phuret, 232; with gold, 417. METALLIC copper, iron, mercury, zinc, 148; scales, 177, 329. METALLURGY AND MINING, books on, 432. METHODS, assay for copper ox- ides and carbonates, 307; assay for copper sulphides, 307; as- say for galena, 312; assay for iron pyrites, 284; assay for lead oxides and carbonates, 320; assay for native copper, 306; of assaying, 180; of cop- per analysis, 333 ; of crucible assays, 264; special, 327. METRIC SYSTEM, books on, 435. MEO-RIC WEIGHTS, 59; equivalents in English, 449; tables of, 447. MIARGYRITE, mineral, 168, 419. MILL, coffee, 133; run, labora- tory, 351. MILLER'S ELEMENTS OF CHEMIS- TRY, 428. MIMETITE, mineral, 426. " MINERAL," 232. MINERALOGY, books on, 430. MINERALS, assaying of, in an ore, 327; copper, 422; gold, 417; lead, 425; likely to carry gold, 418; likely to carry silver, 421; silver, 418. MINERS' gold washing pans, 126. MINING LAW, books on, 435. MINIUM, mineral, 233 312, 426. MISCELLANEOUS, apparatus, 116; materials, 152. MISPICKEL, mineral, 231. MITCHELL, references to, 78, 90, 108, 139, 140, 204, 277, 310, 323, 3Qi. 476 INDEX. MITCHELL'S MANUAL OF PRAC- TICAL ASSAYING, 435. MOISTURE in ores, determination of, 415- MOLYBDATE OF LEAD, mineral, 427. MOLYBDENUM, element, 13. " MONITOR " gas furnace, 70. MORFIT'S CHEMICAL MANIPULA- TION, 430. MORTAR, amalgamation, 33. MORTARS AND PESTLES, glass, 116; iron, 20, 22; porcelain, 116; spring attachment for, 21. MOSANDRIUM, element, 15. MOULDS, cupel, 123; ingot, 125; scorifier, scorification, or slag, 99. MOUNTAIN blue, 422, 423; green, 423, 424- MUFFLE, floors, 103; hoe or rake, 98, 101; scraper, 101; shovel, 98, 101. MUFFLES, 102. MULLER, 29. MULLERITE, mineral, 417, 421, 426. MULTIPLICATION TABLE FOR GOLD AND SILVER, 443. MUNDIC, 231, 283. MURIATE OF BARYTA, 146; of cop- per, 422; of silver, 419. MURIATIC ACID, 147. N NAGYAGITE, mineral, 417, 421, 427. NAILS, iron, re-agent, 141. NATIVE, antimony, 421 ; arsenic, 418, 421; bismuth, 418, 421; copper, 304, 421, 424; copper, assay, 306; gold, 417, 421; gold, assay 189; lead, 427; mercury, 421; silver, 418, 419; silver as- say, 189; tellurium, 418, 421. NEEDLE ORE, mineral, 422. NEPTUNIUM, element, 15. NICKEL cobalt and copper, sul- phide, 423; cupel color, 193; element, 13; in copper ores, 347; metal, 16; scorifier color, 192. NITRATE OF SILVER (or argentic), re-agent, 143, 148. NITRE, oxidizing power, 135, 153, 162; re-agent, 129, 135, 222. NITRIC, acid, preparation of vari- ous strengths, 211; re-agent, 143, 148; to free from chlorine, 143- NITROGEN, element, 13. NIXON, M. G., Amalgamation Assay, 351. NORTH'S PRACTICAL ASSAYING, 435- NORWEGIUM, element, 14. NOTE-BOOKS, 116. NOTES ON SETTING UP the Oert- ling Balance, 48. NUGGET GOLD, 167, 417. OCHRE, PLUMBIC, 426. OCCURRENCE OF ORES, copper, INDEX. 477 304; gold, 167; gold and silver, 167; lead, 311; silver, 167. OERTLING'S BULLION BALANCE, 48 ; notes on setting up, 48. OIL CLOTH for sampling, 117. OIL OF VITRIOL, re-agent, 151. OLDBERG, O., Weights, Measures, and Specific Gravity, 435. ORDER OF WORK, in assaying, 171; in scorification process, 183. "ORDINARY ORES," 281, 282. ORE, antimonial silver, 168; ar- gentiferous gray copper, 169; arsenical silver, 168, 419; as- saying of minerals in, 327; azure copper, 422; brittle sil- ver, 168; dark red silver, 168, 420; gray copper, 299, 420, 424; green copper, 424; green lead, 426; "horse flesh," 422; light red silver, 168, 419; nee- dle, 422; purple copper, 422; " tile," 423; variegated copper, 422; white lead, 312, 425; yel- low lead, 427. ORES, analysis of copper, 333; argentiferous lead, 169; arsen- ical and antimonial, 185 ; blende, 188; "carbonate." 167, 187; "chloride," 169, 187; chlorina- tion assay of gold, 364; con- taining free gold or silver, as- saying of, 329; copper, 304, 422; copper, assay, 305; copper glance or pyrites, 185, 298; copper matte, 186; copper, oc- currence, 304; determination of moisture in, 415; directions for sampling, 174; "every-day," 186; galena, 187; gold, 167; gold, assay, 170; gold, occur- rence, 167; gold and silver, 167; gold and silver, assay, 170; gold and silver, charges for, 277, 282; gold and silver, oc- currence, 167; gray copper ore, 187; important silver, 168; lead, 311; lead, assay, 312; lead, occurrence, 311; native gold and silver, 189; oxide of iron, 187; oxidizing powers, 228; pulverizing, 176; reducing powers of, 228; silver, 418; sil- ver, assay, 170; silver, occur- rence, 167; sulphurets of iron, 186; tellurides, 188; volumetric analysis of copper, 343. OSMIUM, element, 14. OUTFIT, assaying, 439 ; blow-pipe, 441. OVERMAN'S ASSAYING, 435. OXIDE, antimony, 420; copper, 304; copper, black, 232, 301, 304, 424; copper, red, 301, 304, 423; cupric, 424; cuprous, 423 ; iron, 167, 187; iron, crucible charges for, 297, 298; iron, re- agent, 142; iron, red, 152, 233; lead, red, mineral, 233, 312, 426; lead, red, to remove from litharge, 139; lead, yellow, mineral, 426; lead, yellow, re- agent, 139; manganese, black, 478 INDEX. re-agent, 145; manganese, black, mineral, 233; uranium, 424. OXIDES, copper, assay, 307; lead, assay, 320. OXIDIZING, action of bi-carbonate of soda, 129; action of nitre, 135; action of ores, 228; power of nitre, 153, 162. OXY-CHLORIDE OF COPPER, min- eral, 422. OXYGEN, element, 13. PALLADIUM, element, 13. PAN TEST on "panning" for gold, 355- PANS, frying, 123; miners' gold- washing, 126; zinc sifting, 35. PAPERS, black glazed, blotting, brown or manilla, filter, tissue, 117. " PARTING," 183, 210. PARTING-FLASKS, 113. " PEPPER CARBONS," 394. PERCY'S METALLURGY, 432. PERMANENT FURNACES, 90. PETZITE, mineral, 417, 419, 421. PHILIPPIUM, element, 15. PHILLIPS' ASSAYERS' COMPANION, 435- PHILLIPS' METALLURGY, etc., 433. PHOSPHATE, and chloride of lead, 427; of alumina and lead, 427; of copper, 424; of uranium and copper, 424. PHOSPHORUS, element, 14. PINCERS, 118. PIPETTES, 115. PLAN OF ASSAY LABORATORY, 437. PLATE, annealing, no; gem, 100; pouring, 99; pulverizing or rub- bing, 28. PLATINUM, crucibles, 103; dish, 337; element, 14; metal, 16; spatulas, 36; vessels, 127. PLATTNER, reference to, 91, 44. PLATTNER'S BLOW-PIPE ANALY- SIS, 431. PLUMBAGO crucibles, 103. PLUMBIC, acetate, re-agent, 141; carbonate, re-agent, 141; mon- oxide, re-agent, 139; ochre, 426. PLUMBOGUMMITE, mineral, 427. PLYMPTON'S BLOW-PIPE DETER- MINATION, 431. " POINTS," 396. POKERS, 101. POLYBASITE, mineral, 168, 419. POMEROY'S MINING MANUAL, 433- PORCELAIN, and glass apparatus, in; casserole, 115; crucibles or capsules, 103, 112; mortars, 116; spatulas, 36. PORTABLE FURNACES, 83. POTASH, bi-carbonate, 222; car- bonate, 128, 130, 222; caustic, or hydrate, 146; cyanide, 130, 146; bi- or di-chromate, 145 ; bi-tartrate, 128, 133, 161; fer- rocyanide, 146; iodide, 147; INDEX. 479 nitrate, 135, 153, 162; sulpho- cyanide, 149; yellow prussiate, 147. POTASSIUM, element. 14. POTS, FLUXING, 104. POURING PLATES, 99. PRECIPITATED SILICA, re-agent, 137- PREFACES, 5, 7. PRELIMINARY CHARGES, to deter- mine oxidizing power, 251; re- ducing power, 242. PREPARATION OF, borax glass, 132; charge in crucible process, 267; charge in scorification process, 183; granulated lead, 138; sam- ples, 171; various strengths of nitric acid, 211. PROCESS, crucible, 171, 180, 181, 217; scorification, 171, 180, 181. PROOF CENTRES, 388. PROTO-CHLORIDE OF TIN, re- agent, 149. PROUSTITE, mineral, 419. PRUSSIATE OF POTASH, yellow, 147- PSEUDOMALACHITE, mineral, 424. PULPS, scales for, 37; setting up and testing, directions for, 39. PULVERIZER, 29; Richards, 33. PULVERIZING OF ORES, 176; sam- pling, etc., implements for, 20; plate and rubbers, 28; manner of using, 178. PUNCH, bullion, 126. PURPLE COPPER ORE, 299, 422. PYRARGYRITE, mineral, 420. PYRITE, mineral, 231, 283, 418, 421. PYRITES, 231, 238, 249, 283; ar- gentiferous, 170; arsenical iron, 231, 235; copper, 185, 249, 299, 423; crucible charges for, 285, 289, 291, 292, 293; determina- tion of sulphur in, 416; iron and copper, 167, 299; iron, re- agent, 142; magnetic iron, 231; of lead, 232, 302. PYROLUSITE, mineral, 233. PYROMORPHITE, mineral, 427. PYRRHOTITE, mineral, 231, 238, 283. QUALITATIVE ANALYSIS, Douglas and Prescott's, 429; Eliot and Storer's, 429; Fresenius', 429; general, books on, 429. QUALITATIVE TESTS, 408; car- bonates, 408; copper, 410; iron, 410; lead, 411; manga- nese, 411; silver, 411; sul- phates, 409; sulphides, 409; tellurides, 409. QUANTITATIVE ANALYSIS, Cairns', 429; Classen's, 429; Fresenius', 429; general, books on, 429; Rammelsberg's, 429; special, books on, 429; Wohler's, 429. QUICKLIME CRUCIBLES, 103. QUICKSILVER, 148. 480 INDEX. R RAKE, cupel, 98. RAMMELSBERG'S QUANTITATIVE ANALYSIS, 429. RANDALL'S QUARTZ OPERATOR'S HAND BOOK, 433. RE-AGENTS, dry, for assaying, 128; for analysis, 144; bottles for, in; in scorification pro- cess, 182; testing of, 153; wet, for assaying, 142. REALGAR, mineral, 421, RED OXIDE OF COPPER, 301, 304, 423; iron, 152, 233, 297; lead, mineral, 233, 312, 426; lead, removal of, from litharge, 139. REDUCING POWER OF, argol, char- coal, coke, corn starch, cream of tartar, gum arabic, hard coal, laundr^tstarch, 134; ores, 228, 242, 251; reducing agents, 134, 153, 161; soft coal, wheat flour, white sugar, 134. REED, S. A., reference to, 30, 364. REFERENCE BOOKS ON CHEMIS- TRY, 428. REFERENCES AND LISTS, 417. REPORT ON COLORADO MINERALS, 427. REPORT, Fourth Annual, for Cal- ifornia, 370. RESIDUES, gold, weighing of, 183, 215- RETORTING in scorifiers, 354. RETORTS, iron, 127. RHODIUM, element, 14. RICHARDS' PULVERIZER or labor- atory arrastre, 33. RICKETTS' NOTES ON ASSAYING, 435- RING STAND, 121. ROASTING, carbonate of ammonia used in, 135, 263; charcoal used in, 259; dishes, 105; of ores in crucible process, 257, 259; of ores in scorification process, 183, 185; silica used in, 259. ROCKER, 29. RODS, glass stirring, 115. ROLLS, 125. ROSCOE and Shorlemmer's Chem- istry, 428 ; Elementary Chem- istry, 429. Ross, W. A., books on blow-pipe analysis, 432. ROUND CRUCIBLES, 104. RUBBER, iron, 29; sheet or cloth, 117. RUBBING PLATE, 28. RUBIDIUM, element, 14. RUBY SILVER, mineral, 168, 419, 420. RUDDLE, 152. RUNNING crucibles in fire, 273. RUTHENIUM, element, 14. RUTLEY'S STUDY OF ROCKS, 430. SALT, COMMON, re-agent, 129, 135. SALTPETRE, re-agent, 135. SALTS, Epsom, re-agent, 149; tin, re-agent, 149. INDEX. 481 SAMARIUM, element, 14. SAMPLE, bottles, in; boxes, 117, 172; preparation of, 171; shov- els, 31, SAMPLERS, 31. SAMPLES, to obtain average, 172. SAMPLING, of base bullion, 406; implements for, 20; systematic, 179- SAND, baths, 122; crucibles, 103, 104; in accidents to muffles, 198; re-agent, 137. SCALES, and balances, 36; hand, 43; pulps and fluxes, 37; set- ting up and testing pulp, direc- tions for, 39. SCALES, metallic, 177, 329. SCANDIUM, element, 14. SCHAPBACHITE, mineral, 420, 427. SCHEME FOR SILICA, IRON, AND MANGANESE, 413. SCHIRMERITE, mineral, 420, 427. SCIENCE, GENERAL, books on, 428. SCISSORS, 125. SCORIFICATION PROCESS, 171, l8o, 181; borax glass in, 182; but- tons from, 196; calculations, 183, 216; charges, 185; cupel- lation, 183, 200; granulated lead in, 182; inquartation, 183, 214; order of work, 183; part- ing, 183, 210; preparation of charge, 183; re-agents used for, 182; roasting of ores in, 183, 185; scorification, 183, 194; scorifiers from, 198; silica in, 182, 199; slag from, 198; theory of, 182; weighing gold and silver bead, 209; weighing gold residues, 216. SCORIFIER, color tests, 190; moulds, 99; tongs, 94. SCORIFIERS, 106; " retorting" in, 354- SCRAPER, MUFFLE, 101. SELENIUM, element, 14. SEPARATORY FUNNEL, 115. SESQUIOXIDE, FERRIC, re-agent, 152- SETTING UP and testing pulp scales, directions for, 39. SETTING UP the Oertling balance, notes on, 48. SHEARS, 125. SHEET lead, re-agent, 129, 138; testing for silver, 138, 153, 160; rubber, for sampling, 117. SHOVELS, cupel, 98; sample, 31. SIEVES, 34. SIFTING OF ORES, 176; pans, 35. SILICA, acid flux, 137, 228; brief scheme for, 413; in scorifica- tion process, 186, 187, 199; precipitated, 137; re-agent, 129, 137, 222. SILICATE OF COPPER, mineral, 302, 423. SILICIC DI-OXIDE, re-agent, 137. SILICON, element, 14. SILVER, and antimony sulphide, 168, 419, 420; and copper sul- phide, 169, 420, 424; and gold, beads, weighing of, 183, 209; and gold, metallurgy, 432; and 482 INDEX. gold, multiplication table, 443; and gold ores, assaying, 170; and gold ores, charges, 277, 282; and gold telluride, 417, 419; and gold values, table of, 403, 444; and iron sulphide, 420, and lead, antimonial sulphide of, 419, 426; and lead, metal- lurgy, 432 ; antimonial, 419, 420; antimony and arsenic sulphide, 168, 419, 420; arsenical, 419; assay, 170; assaying of ores containing free, 329; bismuth, 420; bismuth and lead sulphide, 418, 420, 425, 427; black, 420; brittle, 168, 420; bromic or bromide of, 169, 418; bullion, assay of, 369; chloride, 169, 419; chlorination, test for, 367; chloro-bromide, 419; copper glance, 169, 420 424; crucible, 104; dark red, 168, 42.0; den- dritic, 419; element, 14; fah- lore, 169; foil, gold in, 141; foil, re-agent, 141; free, 419; glance, 168, 232, 418; gold and lead telluride, 417, 426; horn, 168, 419; in copper ores, 348, 350; in granulated lead, 139, 153, 158; in lead foil, 138, 153, 160; in litharge, 140, 153, 154; iodic or iodide of, 169, 419; leaf, 419; lead and bismuth sulphide, 418, 420; light red, 168, 419; metal, 16; metallur- gy, 432; minerals carrying, 421; minerals in United States, 418 ; muriate, 419; native, 418, 419; native, assay, 189; nitrate, re- agent, 143, 148 ; ores, 168 ; ores, assaying, 170; ores, im- portant, 168; ores, occurrence, 167; ruby, 168, 419, 420; spat- ulas, 36 ; sulphide or sulphu- ret, 168, 232, 418; telluric or telluride, 419; tests for, 411; testing of granulated lead for, 158; testing of litharge for, 154; testing of sheet lead for, 160; vitreous, 418; wire, 419. SILVERSMITH'S HAND-BOOK FOR ASSAYERS, 435. SLAG from scorification process, 198; moulds, 99. SMALTITE, mineral, 421. SMITH, J. A., Report on Colorado Minerals, 427. SODA, bi-carbonate of, 128, 129, 222; carbonate of, re-agent, 145; caustic or hydrate, 146. SODIC, bi-borate, re-agent, 131; carbonate, 145, 222; chloride, 135; hyposulphite or thiosul- phate, 147. SODIUM, element, 14. SOFT COAL, reducing power of, 134- SPAR, calc, fluor, heavy, 278; yel- low lead, 427. SPATULAS, 35. SPECIAL, charges for crucible proc- ess, 282; directions for bullion balances, 54; methods, 327; INDEX. 483 quantitative analysis, books on, 429. SPHALERITE, mineral, 231, 418, 421. "SPITTING," 207. SPOONS, HORN, 36. SPRING attachment for mortars and pestles, 21. "SPROUTING," 207. STAND, burette, 127; filter, 126; ring, 121. STANNOUS CHLORIDE, re-agent, 149. STARCHES, reducing powers of, 134, 162. STEEL, alphabets and figures, 126; spatulas, 36. STEPHANITE, mineral, 168, 420. STERNBERGITE, mineral, 420. STETEFELDITE, mineral, 169, 420. STIBNITE, 232, 238. STIRRING RODS, glass, 115; wire, 261. STOLTZITE, mineral, 427. STONE'S universal flux, 278. STOVES, 122. STROMEYERITE, mineral, 169, 299, 420, 424. STRONTIUM, element, 14. SUBLIMATE, corrosive, re-agent, 148. SUBSTITUTE, black flux, 128, 133. SUGAR, of lead, re-agent, 141; white, 134, 162. SULPH-ANTIMONITE OF LEAD, mineral, 426. SULPH-ARSENITE OF COPPER, min- eral, 423, 424. SULPH-ARSENO-ANTIMONITE OF LEAD, mineral, 426. SULPHATES, copper, 422, 423; iron, 149; lead, 425; lime, 424; magnesium, 149; test for, 409. SULPHATO-CARBONATE, of lead, 423, 426. SULPHIDES or SULPHURETS, ac- tions of and upon, 249; anti- mony, 232; auriferous-, 167; bismuth, silver, and lead, 418, 420, 425, 427; cobalt, nickel, and copper, 423; copper, 232, 298, 305, 423; copper and iron, 167, 232, 299, 305, 422, 423; copper and antimony, 232; copper, lead, and antimony, 422, 425; determination of in an ore, 240; ferrous or iron re- agent, 149; iron, 186, 231, 283; iron and arsenic, 231 ; iron and copper, 167, 185, 232, 299, 305; lead, 169, 232, 302, 311, 426; lead and antimony, 425; lead, bismuth, and antimony, 426; manganese, 231 ; roasting of, 238; silver, 168, 232, 418; silver and antimony, 168, 419, 420; silver and copper, 169 420, 424; silver and iron, 420; silver and lead, antimonial, 419, 426; sil- ver, antimony, and arsenic, 168, 419, 420; tests for, 234, 235. 236,409: zinc, 170, 231. 484 SULPHOCYANIDE OF POTASSIUM, re-agent, 149. SULPHUR, element, 14; determin- ation of, in pyrites, 416; re- agent, 129, 142, 222; vapors, colors of, SULPHURETTED HYDROGEN, prep- aration, 150. SULPHURIC ACID, re-agent, 151. " SURCHARGE," 396. SUTTON, references to. 351, 414, 415. SUTTON'S VOLUMETRIC ANALYSIS, 430. "SWEET" ORES, 261. SYLVANITE, mineral, 417, 420, 421. SYSTEMATIC SAMPLING of ores, 179. TABLES, apothecaries' weights, 446; assay ton weights in grammes, grains, etc., 450; avoirdupois to troy weights, 399; avoirdupois weights, 445; equivalents of English and French weights, 449; French or metric weights, 447; multi- plication for gold and silver, 443; reducing powers of reduc- ing agents, 134; sulphurets, 238, 249; troy, 401, 446; troy to avoirdupois weights, 401; values of gold and silver, 403, 444; weights, 443. TANTALUM, element, 14. TARTAR, cream of, re-agent, 128, 133; reducing power, 161. TARTARIC ACID, re-agent, 151. TECHNOLOGY, CHEMICAL, WAG- NER'S, 428. TELLURIC SILVER, mineral, 419. TELLURIDES, 417; by scorification process, 188; gold, 417; gold and lead, 417, 427; gold and ' silver, 417, 419, 420; gold, sil- ver, and lead, 417, 426; lead, 425, 426; silver, 417, 419; test for, 409. TELLURITE, mineral, 418, 421. TELLURIUM, black, 417, 427; col- ors in cupel and scorifier, 193 ; element, 14; foliated, 417, 427; graphic, 417, 420; native, 418, 421; ores, 167; with gold, 417; yellow, 417, 420. TELLURPYRITE, mineral, 418,421. I TENNANTITE, mineral, 299, 424. TENORITE, mineral,. 233, 301. TERBIUM, element, 15. TESTING OF, distilled water for chlorine, 142; granulated lead for silver, 158; litharge for sil- ver, 154; pulp scales, directions for, 39; re-agents, 153; sheet lead for silver, 160; silver foil for gold, 141. TESTS, chlorination for silver, 367 ; cupel and scorifier color, 190, 194; qualitative for car- bonates, copper, iron, lead, manganese, silver, sulphates, sulphides, tellurides, 408- IfiDEX. 485 413; for sulphurets, 234, 235, 236. TEST TUBES, 113. TETRAUYMITE, mineral, 418, 421. TETRAHEDRITE, mineral, 232, 238, 299, 305, 418, 420, 424. TEXT-BOOKS on theoretical chem- istry, 428. THALLIUM, element, 14. THEORY OF, crucible process, 219; scorification process, 182. THIOSULPHATE, sodic, re-agent, 147. THORIUM, element, 14. THULIUM, element, 15. " TILE-ORE," 423. TIN, element, 14; metal, 16; pro- to-chloride, or "tin salts," re- agent, 149. TISSUE PAPER, 117. TITANIUM, element, 14. TONGS, crucible, 92; cupel, 96; scorifier, 94. TOOLS, FURNACE, 92. TORBERNITE, mineral, 424. TORREY AND EATON, reference to, 350. TREATISE ON, Chemistry, Roscoe and Schorlemmer's, 428 ; ore deposits, Cotta's, 430. TRIANGLE, WIRE, 121. TRIANGULAR CRUCIBLES, 104. TRIPLE SULPHURET OF COPPER, LEAD, AND ANTIMONY, 422, 425. TRIPLETT'S How TO ASSAY, 435. TROEMNER'S bullion balances, 44, 45, 46, 47, 48; pulp scales, 38. TROY WEIGHTS, tables of, 401, 446; to avoirdupois, 401. TUBES, TEST, 113. TUNGSTATE OF LEAD, mineral, 427. TUNGSTEN, element, 14. u UNITED STATES, minerals found in; copper, 422; gold, 417; lead, 425; silver, 418. UNIVERSAL FLUX, Stone's, 278. URANIUM, and copper, phosphate, 424; colors in cupel and scor- ifier, 193; element, 14; oxide, 424. URANOCHALCITE, mineral, 424. USEFUL BOOKS, list of, 428. V VALUES OF GOLD AND SILVER, table of, 444. VANADATE, OF LEAD, 425 ; and zinc, 425. VANADIUM, element, 14; color in scorifier, 191. VAN WAGENEN'S HYDRAULIC MINING, 433. VARIEGATED COPPER ORE or py- rites, 232, 299, 422. VAUQUELINITE, mineral, 425, 427. "VEGETATING," 2O7- VESSELS, platinum, 127. VITREOUS COPPER, 232, 298, 423; silver, 418. 4 86 INDEX. VITRIOL, blue, 423; copper, 423; green, 149; lead, 425; oil of, 151- VOLUMETRIC ANALYSIS, of copper ore, 343; Hart's, 430; Button's, 430. W WADE'S MINING LAW, 436. WAGNER'S CHEMICAL TECHNOLO- GY, 428. WASH-BOTTLE, 112. WASH, CHALK, 152. WATCH-GLASSES, 112. WATER, ammonia, 144; distilled, chlorine in, 142; lime, 147; re- agent, 142; sulphuretted hydro- gen, 149. WATTS' DICTIONARY OF CHEMIS- TRY, 428. WEHRLITE, mineral, 418, 421 WEIGHING gold and silver beads, 183,209; gold and silver beads, balances for, 44; gold residues, 183, 215. WEIGHTS, 59; and measures, Egleston's and Oldberg's, 435 ; apothecaries' tables, 446; assay ton, 60; assay ton, explana- tion of. 60; assay ton, in grammes, grains, etc., 450; avoirdupois, tables. 445; avoir- dupois to troy, 399; equivalents of French and English, 449; French, metric or gramme, 59; French or metric tables, 447 ; "gold," 64; grain, 64; tables of, 446 ; troy tables, 401 ; troy to avoirdupois, 401. WET RE-AGENTS FOR ASSAYING, 142. WHEAT FLOUR, 133, 134. WHITE LEAD ORE, 312, 425; re- agent, 141. WHITE SUGAR, 134, 162. WHITNEYITE, mineral, 425. WILLIAMS' CHEMICAL MANIPULA- TIONS, 430. WILSON'S MINING LAWS OF THE U. S., 436. WINDOW GLASS, as re-agent, 137. WIRE, gauze, 122; gold, 167, 417; iron, re-agent, 141 ; silver, 419; stirring, 261; triangle, 121. WOHLER'S MINERAL ANALYSIS, 429. WOOD CHARCOAL, properties, 135; re-agent, 135; reducing power, 134- WORK, order of, in scorificatfon process, 183. WULFINITE, mineral, 427. YELLOW, lead ore or spar, 427, oxide of lead, mineral, 426; oxide of lead, re-agent, 139; prussiate of potash, re-agent, 147; tellurium, 417, 420. YTTERBIUM, element, 14. YTTRIUM, element, 14. INDEX. 487 ZINC, and copper carbonate, 422; and lead vanadate, 425; blende, argentiferous, 170, 231, 249; color on cupel, 192, color of vapors, 235; element, 14; in battery, 148; in copper ores, 347, 350; metal, 16; metallic, re-agent, 148; qualitative scheme for, 240; sifting-pans, 35; sulphide or sulphuret, 170, 231, 232. ZIRCONIUM, element, 14. ESTABLISHED 1852. E. H. SARGENT & Co. 125 State St., CHICAGO. IMPORTERS AND DEALERS IN Assayers' Materials, FURNACES, ACCURATE BALANCES AND WEIGHTS, BLOW PIPE APPARATUS, GLASSWARE, PURE CHEMICALS AND LABORATORY SUPPLIES. WE ARE AGENTS FOR THE BATTERSEA CRUCIBLE COMPANY, LONDON. FREIBERG, SAXONY, SMELTING WORKS Dr. Schuchardt's Absolutely Pure Chemicals. BECK'S MICROSCOPES. BF.CKER'S, OKRTLING'S, TROEMNER'S, AND SCHICKERT'S FINE BALANCES. HOSKINS' HYDROCARBON FURNACE. ASSAYER'S OUTFITS FURNISHED PROMPTLY, Brown's Portable Assay Furnace. ADVANTAGES OVER OTHER FURNACES. ist. Simplicity. Having no complicated parts to get out of order. 2 d. Usefulness. It can be used both for muffle work and for crucible operations. 3d. Capacity. There is no other furnace manufactured, of similar dimen- sions, which can accommodate so large muffles. 4th. Durability. Being made of heavy sheet-iron, it cannot be broken by handling nor injured by heating. 5th. Light weight. Boxed, this furnace weighs but 125 pounds, as against 250 to 400 pounds of other furnaces. 6th. Cheapness. This furnace is from one-third to two- thirds cheaper than any other furnace that will do as good work. This furnace will be properly boxed for transportation, complete for $20. E. H. SARGENT & CO., Dealers in Assayers' Material, 125 State Street, CHICAGO. Established 185B. G. A. MARINER & Co ASSAYS AND ANALYSES OF ALL KINDS, --SUCH AS ORES. BULLION, COMMERCIAL PKODUCTS, FOODS, WATERS, ETC. Send samples by mail or express. WRITE FOR TERMS. 81 S. Clark St, (Top Floor), CHICAGO, ILL. HYDRO-CARBON BLOW PIPE AND RURNACES. PORTABLE, AUTOMATIC, ECONOMICAL, AS DESCRIBED IN THIS BOOK. Send for Descriptive Price List to WILLIAM HOSKINS, 81 S. Clark Street. Chicago. IE5 O ILi Hi S FOR Crushing and Pulverizing Ores, ALSO ORE BREAKERS, SCREENS, DRY KILNS, PLANS FOR MILLS, ETC., ETC., ETC. SEND FOR CATALOGUE TO S- K. IKZESOM, 93 Washington Street, - NEW YORK, N. Y. HENRY TROEMNER, 71O MARKET STREET, PHILADELPHIA, ^^^^ / ^^ssftyj OUR NEW (No. 5) ASSAY BALANCE. MAKER OF ACCURATE Analytical and AseayBalancEB = WEIOHTS. = In use at all the Uuited States Mints and Assay Offices. A full description sent on application. BUFFALO DENTAL MANUFACTURING COMPANY would inform CHEMISTS, ASSAYERS and others inter- ested, that they are the exclusive manufacturers and owners of patents in the United States of FLETCHER'S CELEBRATED Gas Laboratory Apparatus, and are prepared to construct special gas or gasoline heating or melting apparatus for laboratories or factories, from original drawings, in addition to their already extensive apparatus. Parties desiring special apparatus will find it of advantage to correspond. Catalogues of LABORATORY APPARATUS sent on application. Biffalo Dental Manufacturing Co., Pearl Street, corner of Court. BUFFALO, N. Y- Denver 1 Ffre-GlaiJ GompaniJ, OFFICE : P. O. Box : FACTORY : 411 LARIMER ST. 1931. 3isT AND BLAKE STS. DKNVKR, COLORADO. 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