r No. .... Division ... Range Shelf.... Received...... C/^f:^ .. 1 87 r , A MANUAL OF METALLUEGY. A MANUAL OF METALLURGY, MOKE PARTICULAKLY OF THE PEECIOUS METALS, INCLUDING THE METHODS OF ASSAYING THEM. ILLUSTRATED BY UPWARDS OF FIFTY ENGRAVINGS. BY GEORGE HOGARTH MAKLNS, M.R.C.S. F.C.S. ONE OF THE ASSAYERS TO THE BANK. OF ENGLAND ; ASSAYEK TO THE ANGLO-MEXICAN MINTS ; AND LECTURER UPON METALLURGY AT THE DENTAL HOSPITAL, LONDON. LONDON: F. S. ELLIS, KING STREET, COVENT GARDEN. 1862. LONDON: STRANGEWAYS AND WALDEN, Printers, 28 Castle St. Leicester Sq. PREFACE. THE Manual here offered to the student has been published in consequence of the request made by the author's pupils, that he would print the course of Lectures upon Metallurgy annually delivered by him. In carrying out this he has found it neces- sary, in order to render the work complete as far as it goes, to add somewhat to the short series given, by doing which he has caused the book to grow beyond the limit originally contemplated, although it will be seen that such additions are not more than would be absolutely required in order to make it an efficient text-book for the student's use. Thus, although the reader is supposed to have some little acquaintance with the funda- mental truths of chemistry, an endeavour has vi PKEFACE. been made, in some of the early chapters, to elucidate such as are concerned in operations detailed in the special portion of the book. In addition to the strictly original matter contained, facts running throughout the pages of many other writers upon the subjects treated of, have been brought together in small space ; and hence it is believed that good service has been rendered to those whose avocations leave them little time for extended reading upon matters not directly professional. And for the same object a considerable amount of chemical information, in the shape of special analyses, &c., has been incorporated with all parts of the work, wherever such has appeared needful. The author is not without hope that the prominent place he has given to the precious metals may render the work useful to all persons engaged, commercially and otherwise, with them. London, November, 1861. CONTENTS. CHAPTER PAGE i. General Properties of the Metals . . 1 ii. General View of the combining Properties of the Metals 20 in . Combinations of the Metals with the Non-metallic Elements . . . . ... 34 iv. Of Metallic Salts and Alloys , ^ ''&''' 51 v. Of Heating Apparatus, Furnaces, &c. ... 68 vi. Of the Fuels applicable to Metallurgic Opera- tions . . ... . . 94 Metals of the First Class : vii. Mercury' . . . . . . 109 vm. Silver . . . . . 132 ix. Gold . . . 188 x. Platinum ... . 240 xi. Palladium . . . . . 255 Metals of the Second Class : xii. Lead .... 260 xni. Copper . 273 xiv. Bismuth > 291 xv. Antimony ... . 299 xvi. Uranium, Titanium, and Chromium . 308 xvn. Arsenic . . . 318 Vlll CONTENTS. CHAPTER PAGE Metals of the Second Class, Order II. : xvni. Iron 324 xix. Nickel .... 366 xx. Manganese and Cobalt . .371 xxi. Tin 378 xxn. Zinc and Cadmium .... 397 Metals of the Second Class, Order III. : xxin. Aluminium . . . . . 413 Metals of the Second Class, Order IV. : xxiv. Potassium and Sodium . . . 421 xxv. The Principles of Electro-Metallurgy . . 431 Index 455 METALLURGY. CHAPTER I. GENERAL PROPERTIES OF THE METALS. THE operations of the chemist have for their object either, on the one hand, the combination of diverse forms of matter, whereby new compound bodies are produced, or else, on the other, the separation of compounds already existing, so as to reduce them to simpler states ; thus, by the latter method of proceeding, he will arrive at points where the process of separation is no longer practicable, although possibly this stop is put to the decomposing process by our want of means to carry it on in our present state of knowledge. The ultimate forms into which all compound bodies are resolvable are called " elements/' The elements at present known are sixty in number, while of these no less than forty-seven are called " metals/' Their study constitutes the science of Metallurgy, which, although by strict definition means the production of metals, will, throughout the following pages, be extended 2 GENERAL PROPERTIES OF THE METALS. to as much of their chemistry also as relates to their less complex compounds. As chemical changes, or " reactions," as they are termed, are frequently somewhat complex, it is found convenient to be able to express the names of elements in short, and thus, by means of abbreviations, to construct formulae of such changes, whereby the whole operation may at once be brought under the eye. These abbreviations (called "symbols") are commonly formed by employing the first letter of the Latin name of the element, or, where such initial letter is common to more than one, then using the two first letters for the less important one. Again, as each element is supposed to have a definite " atomic weight," as it is expressed, or, in other words, a proportion as compared with the rest, in which it will enter into combination to form a compound body, such number would be called its te equivalent;" a term express- ing the fact that a certain weight of one body is just equiva- lent to, and will replace, a certain fixed weight of another in forming new combinations, the combining equivalent of the gas Hydrogen forming the unit of the system of numbers. The following table contains the names of the elementary bodies, and placed against each is its symbol and combining equivalent. The Non-metallic elements may be divided according to their physical states in the following way : Gaseous Elements. Symbol. Equivalent. 1. Oxygen . . O . . 8 2. Hydrogen . H . . i 3. Nitrogen . . N . . 14 4. Chlorine . . Cl . . 35-5 5. Fluorine . . F . . 19 i. Carbon . C 2. Boron . B 3. Silicon . Si 4. Sulphur . . s 5. Selenium . Se 6. Phosphorus . P 7. Iodine . I Liquid. i. Bromine . . Br GENERAL PROPERTIES OF THE METALS. 6 Solids. Symbol. Equivalent. 6 1 1 H . 16 40 3i . 127 . 78 The Metallic elements may first be divided into two classes : Noble, and Base Metals. 1st, The Noble metals are those whose compounds with oxygen are decomposed by heat alone, and the metal thus set free. They are nine in number : 1. Mercury . . Hg . .100 2. Silver . . Ag . .108 3. Gold . . An . . 196-6 4. Platinum . Pt . . 98-56 5. Palladium . Pd . . 53*24 6. Rhodium . R . . 52-16 7. Iridium v . . Ir . . 98*56 8. Ruthenium . Ru . 'V 52-11 9. Osmium A- . Os . .? 99'4* 2d, The Base metals are those which retain oxygen at high temperatures. This second class may be sub- divided into four orders. Order I. Fourteen metals, which do not decompose water at any temperature : 1. Lead . . Pb . . 103-6 2. Copper . . Cu . . 31-7 3. Titanium . Ti . . 25-0 GENERAL PROPERTIES OF THE METALS. Metals. Symbol. Equivalent. 4. Bismuth . . Bi . .210 5. Uranium . . U . .60 6. Tellurium . Te . . 64-5 7. Antimony . . Sb . .122 8. Tantalum . Ta . * . 68-8 9. Columbium, or ) ^ Q . 8 -vj-. r . > 1> Q . A.O O .Niobium 3 10. Tungsten . W . . 92 1 1 . Molybdenum . Mo . . 48 12. Chromium . Cr . . 26-27 13. Vanadium . V . . 68-46 14. Arsenic . . As . . 75 red heat : f __ i. Iron . . Fe . 28-0 2. Manganese . Mn . . 27-5 3. Nickel . Ni . . 29-5 4. Cobalt . Co . 29-5 5. Tin . . Sn . 59 6. Zinc . . Zn . . 32-7 7. Cadmium . . Cd . . 56 Order 3. Eleven metals which decompose water at ordinary temperatures; although, in the case of some few of these, a slight rise of temperature, or else the addition of some weak acid, becomes necessary. 1. Magnesium . Mg . . 12 2. Cerium . . C . .46 3. Lanthanum . Ln . .48 4. Didymium . . D . . ? 5. Yttrium . . Y . 32 6. Erbium . ? . . ? 7. Terbium . , ? . . ? 8. Glucinium . Gl . . 4-7 GENERAL PRORERTIES OF THE METALS. 5 Metals. Symbol. Equivalent. 9. Aluminium . . Al . . 13-7 10. Thorinum . . Th . . 39-5 n. Zirconium . . Zr . . 33*6 Order 4. Six metals which decompose water with energy, even at low temperatures : 1. Potassium . . K . . 39 2. Sodium . . Na . . 23 3. Lithium . . Li . . 7 4. Barium . . Ba . . 68-5 5. Strontium . . Sr . . 43-8 6. Calcium . . Ca . .20 A metal may be defined as a solid elementary body, which conducts heat and electricity through its substance perfectly, and has a peculiar condition of surface, whereby light is strongly reflected from it ; and hence its surface is more or less lustrous. The latter character is gene- rally so strongly marked that, in speaking in common language of any lustrous body, we say it has " a metallic lustre." It seems to be the result of perfect opacity, by which all rays are reflected from the surface ; for, if we take finely divided gold or silver, we observe it to be a dull, sandy-looking body, yellow in the former, and grey in the latter case ; but the least condensation by rubbing with the smooth face of a hammer or a burnisher, will produce the necessary state of surface for this reflexion of light. The metals are nearly all perfectly opaque, even in thin leaves, although the small number possessing trans- parency may depend on our inability to bring them into a sufficiently attenuated state; for gold, which readily admits of this, is easily shown to transmit green light. This may be very elegantly demonstrated by taking 6 GENERAL PROPERTIES OF THE METALS. some twenty grains of fine gold, and fusing it in a convenient shallow vessel. This is to be removed from the furnace in a completely fluid state ; when, if watched, it will be observed that, just upon cooling, a crust of solid metal will first suddenly form, through which the light of the internal red-hot mass appears of a beautiful brilliant green colour. The non-metallic elements admit of ready division, as we have seen, dependent upon physical differences. The solid bodies of this division have been called "metalloids ; " and between these and the true metals the line of separa- tion is not very definite. For example : Iodine, and also selenium, possess very strong metallic lustre, so that selenium has actually been classed with the metals by some chemists, while silicon, as also tellurium, is now commonly associated with the metalloids. The former commonly being produced as a dull brown powder; and the latter, although possessing lustre, being deficient in conducting power of heat and electricity. The colour most prevailing in metals passes through all shades of white, of which the pure white of silver may be taken as the starting-point, and the blue white of lead the farthest remove from it ; all others, with three exceptions, being rangeable between these two shades. The excep- tions are, gold, which is of a rich yellow, and the two red metals, copper and titanium. But the latter, when finely divided, is steel-grey. The metals are nearly all destitute of odour or taste, but there are some exceptions to this. Thus peculiar odours will be evolved when we heat iron or copper ; and one of our means of discriminating arsenic consists in the characteristic smell of garlic which is emitted when GENERAL PROPERTIES OF THE METALS. 7 it is heated. The taste which is perceived in some is, no doubt, due to some peculiar character, although, in some cases, it may depend upon voltaic action set up by the chemical agency of the saliva ; the metal not being per- fectly pure. This may be illustrated on a large scale by the well-known experiment of placing a piece of zinc on the tongue and a piece of silver under it, and then, joining their edges, when a metallic taste will be per- ceived, dependent on slow solution of the zinc under electric action. The three related qualities of malleability, ductility, and tenacity, differ much among them. Gold may be said to be the type of perfect malleability. Thus, we may take a small button of gold and pass it over and over again between the rollers of a flatting mill. Its malleability and ductility will allow of its extension in an unbroken state, until we are arrested by the imper- fection of the rollers. After this it might be further extended by hammering until each grain would cover a circular space of nearly nine inches in diameter. Then, on the other hand, arsenic or antimony may be powdered in a mortar : in fact, the former is a thoroughly brittle body, in which these two qualities are quite wanting. It may be imagined that the properties of malleability and ductility are so nearly allied, that they are possessed in corresponding degree by metals ; but this is not so. Ductility is evidenced by a metal being readily drawn into wire, the means employed for this being a severe test ; for, after forming a small bar or roll, one end is slightly decreased in diameter, so as to admit of its being passed through a hole made in a hard steel plate ; the end is then seized by a vice, and the whole bar 8 GENERAL PROPERTIES OF THE METALS. forcibly drawn through the hole; the operation is then repeated over and over again, a smaller hole being used in each successive drawing. Thus a metal whose texture is very little fibrous, has its particles elongated step by step, until the texture of the resulting wire is perfectly so. Malleability is shown in the capability of extension in all directions, and a purely malleable metal will admit of this by hammering, and that without any evidence of brittleness, which would be manifested by splitting out at the edges. <, Tenacity has, then, some relation to both the above properties. It means the power of resisting the tendencies of tension to break up a metal. Thus a tenacious metal, alone, will admit of extension into wire. And the dif- ferences of metals, in this property, have been measured upon wires of equal size, by noting the amount of weight a wire will sustain without breaking. The tenacity, or, on the other hand, the brittleness, of metals is much influenced by temperature. Thus, some which at ordinary temperatures will be brittle may be drawn into wire if heated ; while, on the contrary, some are actually rendered brittle by raising their tem- perature. Brass, for example, when heated to dull red- ness, will be rendered quite brittle thereby; and Wertheim, an experimenter upon this point, states that, as a rule, the tenacity of metals is diminished by heating, the only exceptions to this being gold, iron, and steel. Crystalline metals never possess the properties of ductility or tenacity, the crystalline structure being quite incompatible with these qualities. Thus, brass which has been drawn into wire will frequently, after a year or so, become crystalline in structure, by change of molecular arrangement, when it also is found to have become GENERAL PROPERTIES OF THE METALS. 9 thoroughly brittle by the change. Again, by frequently annealing a bar of silver it will be rendered crystalline, and, consequently, brittle. The following table will show the relative order of the more common metals in their possession of these three qualities, by taking them in the order of the numbers placed against each : Metals. Malleability. Ductility. Tenacity. Gold . . I . . I . .7 Silver . . 2 . . 2 . .5 Copper . . 3 . . 6r . .2^ Tin . . . 4" . . 8 . .8 Cadmium . . 5 . .11. .9 Platinum . 6 . 3 .4 Lead . > 5> 6, 8, and 10 grains per sheet. In order to obtain a solid plug of fine gold, not only must the surface be free from extraneous matters, but it must also be in good condition for welding ; hence after the beating operation, comes the important one of annealing, whereby its whole structure, internal as well as GOLD. 239 surface, is rendered fit for its use. Thus there must be perfect freedom of motion in the metallic particles as evidenced by absence of elasticity, whilst the molecular state of the surface produced by this treatment assists the welding; thus the annealing operation will be seen to require much care and experience. After this the metal should be handled very sparingly, and packed carefully in clean paper books ; but even then it may at times again require annealing by the operator. This may be effected by heating in the flame of a spirit-lamp, by which no injurious products of combustion are given off, to attack the surface of the metal. It may be placed for this purpose on a clean plate of metal, a piece of platinum for example. Again it is perhaps needless to remark that the cavity into which the metal is to be introduced should be well cleansed and dried as perfectly as possible; the absorbent material introduced for this being withdrawn at the moment the metal is ready for introduction. In regard to the use of spongy gold for plugging operations, it is sure to fail if too much pressure with an obtuse instrument be employed at first, but from the nature of the material it must be a very useful one. Moderate pressure should at first be made, and the metal pierced to some extent so as to condense the lower portions, and the cavity so formed is to be again filled in. If this be not done the outer part may be solidified and burnished over a perfectly spongy centre. When properly managed its cohesion is most perfect, and is ensured by the crystallo-granular structure which the best-worked forms of sponge gold should possess, and which causes it to dovetail (as it may be said) together, and so to form correspondingly solid and sound plugs. 240 METALS OF THE FIRST CLASS. CHAPTER X. PLATINUM. PLATINUM has probably been very long known in South America, but, owing to the refractory (and in the ordinary way unworkable) nature of this metal, it was cast away, indeed., got rid of as an incumbrance in regard to mining products, with which it is found ; and it is only since the year 1750 that any account of its nature has been made known; and, although many investigators were, from that time down to Dr. Wollaston's, employed upon it, it is to the latter able philosopher that we owe the peculiar chemical and mechanical operations which have mainly brought it into such an important position in the labora- tory both of the experimental chemist, and the manu- facturer. Berzelius and Vanquelain have also added much to the chemistry of platinum, and as late as the number of the Annales de Chimie for August, 1859, publication was made of a valuable improvement in methods of refining, as also of its fusion in considerable quantity. These were effected by Messrs. Deville and Debray in France. It is found largely in Russia in the Ural district; hence in that country it has been employed for coining, PLATINUM. 241 also in Peru, Brazil, California, Australia, and in some parts of North America, in all of which it exists as crude platinum ore, and platiniferous sand, the former being in irregular masses, or nuggets, weighing from several pounds, down to small sand-like grains, of a troy grain or so in weight. This crude ore is a compound of several metals, which, from this association, are known as " pla- tinum metals." These are palladium, rhodium, iridium, osmium, and ruthenium. Then, in addition to these, it very commonly contains iron, and copper, occasionally manganese, lead, and even silver. Again, it has been asserted by Pettenkofer, that there is scarcely any silver free from it, and frequently specimens of gold which come before the assayer for parting are found to contain platinum ; but, in explanation of this, it may be stated that in almost all places where gold is obtained by wash- ing the sand, platinum is found with it, and often in such grains that they can be separated by picking out the latter ; and, if they be too much mixed for this, it only remains to amalgamate the mixture, which treatment will dissolve out the gold without touching the platinum. The analysis of platinum ore has been perfected by Wollaston, and by Berzelius, and of all chemical opera- tions it is one where the most perfect skill has been exercised. But when it is stated that Wollaston's method embraces some twenty-six, and that of Berzelius twenty- eight, distinct complex operations, it will be seen, when we presently examine them, how much the recent French discoveries already alluded to have simplified the manu- facture of this metal. The following is a short summary of the chemical and metallurgic operation of Dr. Wol- laston. It may first be premised that the average pro- portion of platinum in the ore is about 70 per cent, but R 242 METALS OF THE FIRST CLASS. the quantity ranges from 50 to 80 per cent. The pal- ladium seldom exceeds one to two per cent. The crude ore is first treated with aqua regia, made from pure nitric, and hydrochloric acids, but, in order to prevent the solution of one of the metals, viz. iridium, it is diluted for use with an equal bulk of water. The pro- portions he advises are, to 100 parts of ore, as much hydrochloric acid as contains 150 parts of actual (dry) acid, mixed with nitric equal to 40 parts. Solution will be complete after three or four days' digestion, but, towards the end, it is always necessary to assist this by a gentle heat. The vessel is then set aside, in order that suspended matter, which is almost entirely iridium, may be deposited. The clear solution is then syphoned off, and to it chloride of ammonium, amounting to 41 parts, is added. This throws down a yellow crystalline pre- cipitate, which is a chloro-platinate of ammonia, which, on heating, will be decomposed, and yield platinum. By this first precipitation about 65 parts of platinum are at once separated from the ore, the weight of the compound salt being, in this case, about 165 parts. About ii parts of platinum are left in the mother liquor of the crystals, associated with nearly the whole of the other metals. A clean plate of zinc is then put into it, which will precipitate them all. This deposit is first washed clean, and then redissolved in aqua regia, and to the solution ^nd of its bulk of strong hydrochloric acid is added, after which more chloride of ammonium, so as to throw down the remainder of the platinum. This addition of hydrochloric acid last made is for the pre- vention of the precipitation of any palladium, or lead with it. But the palladium may be separated at the first, by first neutralizing the solution with carbonate of soda, and PLATINUM. 243 then adding cyanide of mercury ; this throws down the palladium, after removing which, the addition of chloride of ammonium will precipitate the platinum. The precipitates of chloro-platinate of ammonia are, however, contaminated with iridium, a portion of which has formed a soluble double salt with chloride of ammo- nium ; therefore they are carefully washed with cold water, to remove this, and afterwards pressed slightly between layers of filter-cloth, and then dried. It now only remains to ignite in order to separate the ammonia salt; but this requires much care, so as not to use heat enough to agglutinate the reduced metal, the after working of which mainly depends upon its fine division. For this reduction it is put into a black-lead crucible and heated, until only the platinum, in fine' powder, is left. This is removed, any lumps broken up by the hand, and then rubbed to powder with a wooden mortar and pestle, the rubbing being light, so as not to burnish or condense the powder in the least. It is now sifted through a fine lawn sieve, and mixed with water into a kind of mud. A brass mould is provided, having a cylindrical cavity of 6| inches long, by i'i2 inch wide at the top, and 1*23 at bottom. Thus it is slightly taper. A steel stopper or plug enters this, to the depth of a J of an inch, being made to fit very loosely indeed. This mould is well greased, and the plug wrapped in blotting paper, and set up in a jug of water, with which also it is filled. Then the platinum mud is introduced, which, displacing the water, fills every cavity of the mould ; the water is then allowed partly to drain out, which it does readily by the blotting paper round the loose steel plug. After a time the upper surface of the mud is covered, first, with 244 METALS OF THE FIRST CLASS. paper, and then a plate of copper, and over these it is slightly squeezed, by means of a wooden pestle. The water being thus pressed out, the mass becomes suffi- ciently solid to allow of the mould being laid horizontally in a very powerful press. This press (devised by Wollas- ton) is worked by a lever, by which the steel plug can be forced with an enormous amount of power upon the pla- tinum ; and this compression is carried to its utmost limit, after which the plug, and then the cake of platinum, are removed, an operation rendered easy by the taper form of the mould. The mass is then laid upon a charcoal fire, so as to burn off any grease, and free the porous cylinder from remaining water. Next it is heated in a wind furnace, to a greater heat than the manufactured platinum is ex- pected to bear. It is then removed, and dexterously hammered on the ends, being for this purpose set upright upon the anvil ; and the Doctor says, that if it becomes bent, it is by no means to be corrected by blows upon the side, which, if applied, would cause it to crack irreme- diably, but by careful blows on the extremities, judiciously directed, so as to reduce to a straight line the parts which project. After forging, it is to be cleaned from any ferruginous scales it may have contracted in the fire, by smearing with a mixture of crystallized borax, and carbonate of potass, which, when in fusion, are a ready solvent for such impurities. It is, lastly, put on a platina tray, and covered with a pot, and then exposed to the heat of a wind furnace, and, on removal from the fire, it is plunged into dilute sulphuric acid for a few hours, to dissolve any adherent flux, when it is ready for manufacture. The latter, or mechanical, part of the operation is PLATINUM. 245 described almost in the words of Dr. Wollaston, and his explanations of the process may be given also. He says, " Those who would view this subject scientifically should here consider that, as platinum cannot be fused by the utmost heat of our furnaces, and consequently cannot be freed like other metals from its impurities during igneous fusion by fluxes, nor be rendered homogeneous by lique- faction, the mechanical diffusion through water should here be made to answer, as far as may be, the purposes of melting, in allowing earthy matters to come to the surface by their superior lightness, and in making the solvent powers of water effect, as far as possible, the purifying powers of borax and other fluxes in removing soluble oxides. " By repeated washing, shaking, and decantation the finer parts of the grey powder of platinum may be obtained, as pure as other metals are rendered by the various processes of ordinary metallurgy, and, if now poured over, and allowed to subside in a clean basin, a uniform mud, or pulp, will be obtained, ready for the further process of casting." Notwithstanding the apparent perfection of the process just detailed (and which was the usual manufacturing one up to a very recent date), the manufactured articles from this are very apt to blister considerably upon the surface, and at times to so great an extent, as even after a very few heatings to become seriously injured by it. This is, no doubt, caused by minute enclosures of air, which by the compression and forging operations are firmly encased in the substance of the ingot ; then, when the mass has passed the rollers for manufacture, these air-bubbles are brought sufficiently near the surface to raise blisters in the metal, when somewhat softened by heat. A large manufacturer of platinum told the author 246 METALS OF THE FIRST CLASS. that it was his custom to replace vessels supplied if this state of things occurred when they were newly made, although, of course, at much loss to himself. Then again, the platinum so prepared has always a notable quantity of iridium in its composition, owing to the difficulty of washing it out of the precipitated double salts : thus remaining portions are reduced by heat with the platinum. In the uses of the metal in the experi- mental laboratory for vessels, this alloy is rather bene- ficial, for if a due proportion of iridium be employed to alloy platinum, the metal is not only more resistent of high temperatures, but also less easily acted upon by chemicals. Thus, excellent small vessels may be formed of the crude platinum by fusion, by the method pre- sently to be described, in which way osmium and pal- ladium are driven off (being volatile), and a natural alloy of platinum, iridium, and rhodium left. A process very analogous to Dr. Wollaston's is em- ployed in Russia, in order to render platinum malleable for coinage purposes. It is triturated in a brass mortar, sifted, and then pressed together under a steel die by means of a powerful screw press. Deville and Debray, after working upon the subject for nearly five years, have, to a great extent, superseded the wet processes previously in use, by means of a dry metallurgic operation, whereby the refining is effected in an analogous manner to the operation already described for silver refining, having first taken advantage of the fusibility of certain alloys of platinum to carry it out. They take the ore, and in quantity up to 2 cwts., and with it about its own weight of sulphide of lead. These are then heated in a reverberatory of just sufficient di- mensions, the sole being basin-shaped, and constructed PLATINUM. 247 of very refractory clay, upon a basis of fire-bricks. The ore being heated to bright redness, the galena is thrown in by portions at a time, and constant stirring is kept up so as to thoroughly mix the ore and galena. This done, 2 cwts. of litharge is next added, in similar manner. This supplies oxygen to the sulphur of the galena, and the whole of the lead, thus being reduced, combines with the platinum metals, but at the same time introduces into the mixture any small portions of silver originally contained in the galena. A little glass is used as a flux during this part of the operation. After standing in the state of fusion for a time an upper bath will be formed, containing an alloy of lead with platinum, palladium, and silver : the other metals, being unacted upon by the treatment, will by their superior density subside to the bottom, after which the platinum alloy is carefully ladled off for future refining operations. The first of these consists in cupelling upon a test the platina lead, whereby the lead is disposed of by oxidation. The metal left is then ready for actual refining. The effecting of this depends upon means whereby they have been able to melt platinum, and thus bring the operation into the class of ordinary metallurgic operations. The essential part of the apparatus consists of a kind of furnace, shaped out of well-burned lime, and which may be somewhat compared to a cupel in its use in this process, for it not only absorbs impurities, but assists in getting rid of them. Then, as an exceedingly high temperature is employed, the bad conducting, and good radiating power of lime are most useful. For, not- withstanding the metal being, in the interior, at a full white heat, the exterior will not be, by any means, 248 METALS OP THE FIRST CLASS. extraordinarily hot ; while, by radiation, the interior crown of the furnace will much assist the fusion. Devilled smaller furnace consists of two pieces of lime joined for use in such way as to form a kind of basin with a hollow cover. The lower piece is hollowed out into the basin, for the reception of the metal : it is solid (or may be formed of blocks closely fitted), in either case being like the top piece, also firmly bound round with stout iron wire or bands. The upper cylindrical cover piece has a corresponding cavity hollowed out, and in the centre a round taper hole, tapered slightly from above downwards, for the introduction of a blowpipe jet ; a joint opening is also formed at one side for the introduction of the portions of platinum ; and the lower half forms a spout for pouring the fused metal. The heating apparatus is an oxyhydrogen blowpipe of large dimensions, and of the form already described as an air blowpipe (p. 78). The outer and lower tube carries hydrogen (or coal gas), and the inner and upper one, in place of air, throws a jet of oxygen into the middle of the flame, both supplies being capable of close regu- lation by means of stop-cocks. The tubes themselves are formed of copper, each tipped with platinum. Suppose the object be simply to fuse some scrap plati- num, and cast it into an ingot. The lime furnace is first PLATINUM. 249 put together, and then the hydrogen jet lighted, and turned into the upper opening formed for the blowpipe ; oxygen is then supplied, and the whole apparatus heated as strongly as can be effected. The platinum is then introduced in pieces by the hole at the side : the furnace is at this time cooled down slightly, but the authors say that the metal runs down immediately it enters the furnace. The heat is maintained for a time, after which the metal is ready for casting. When the object is to refine the metal, it is heated upon this bed of lime, until no more vitreous matters are seen to rise to the surface ; the gases are then gradually turned off, beginning with the hydrogen^ and in such a manner as always to leave the oxygen somewhat in excess : thus the mass solidifies, and at length the flame may be quite extinguished. The metal may be cast in an ingot mould, formed of coke or of plates of lime ; and the authors say that thick cast-iron moulds may be used, if they are well coated over with plumbago; the platinum being kept fluid by the jet until poured, for which purpose the jet and upper section of the mould are removed, and the lower one tilted by tongs, so as to pour its contents steadily into the mould. The great difficulty, however, seems to consist in being able at the same moment to discern between the mouth of the mould, and the dazzling white surface of the molten metal. From 7 to 8 Ibs. avoirdupois may be operated on in this manner without danger from the apparatus giving way, and the authors describe a larger and modified apparatus for large quantities. They also employ a melting furnace somewhat analogous to Mr. Griffin's gas furnace, formed very solidly in lime, in which, by the blowpipe above 250 METALS OF THE FIRST CLASS. described, they can melt portions in a crucible formed of coke. Small platinum vessels are readily made by pressing the pulverulent platinum of Wollaston's process, either dry or moist, into a fit mould, the stamp for the interior being driven either by a press or a hammer. They are next heated in an air, and afterwards more strongly in a blast furnace, and lastly, finished by beating red-hot upon an anvil. The properties of platinum are as follows : It is of a white colour, but not so pure a white as silver. In hard- ness it is about the same as copper. It is exceedingly ductile, and niay be drawn into very fine wire ; and Dr. Wollaston, by forming a coating of silver upon a fine platinum wire, and then drawing this through the draw- plate, obtained a fine compound wire, from the outside of which he dissolved the silver, and so left a platinum wire finer than any wire hitherto made. In fact, his object was to endeavour to substitute wire for the spider's web usually employed in micrometers. Platinum exceeds all metals, excepting iron and copper, in tenacity. Its specific gravity ranges from 2O'8 to 217. It welds very readily at a full red heat, so that injured platinum vessels may readily be repaired by heating, and then welding on a piece of foil, also heated, the operation being performed upon an anvil, as in ordinary welds of iron. Indeed, Wollaston's process for manufacturing platinum is based entirely upon this welding capability. It is nearly the most infusible metal, those which excel it in this respect being some associate metal, as rhodium, for example. It is quite unoxidized in the air and untouched by simple acids, the proper solvent being chlorine (as evolved by aqua regia), although the gas itself PLATINUM. 251 is inactive upon it. When platinum is alloyed with silver, however, it will be largely dissolved in nitric acid ; hence, where gold contains a small proportion of platinum, the latter may be separated by quartation of the gold with silver, and a subsequent free boiling in nitric acid. The acid, by this, will acquire a deep straw-yellow colour. The resistent qualities of this metal give it its great value for chemical vessels, but these require care in using. Thus we cannot heat a metal in them to near its fusing point, or they are very liable to alloy with the contained metal. Then, some oxides are very destructive to them, especially if associated with any body (as carbon) which is capable of taking their oxygen. The alkalis and alkaline earths destroy it at a red heat, as also does nitre. Symbol, Pt. Equivalent, 98-56. There are two oxides, 1st, a protoxide, which is black in its hydrated state ; it forms the base of salts of plati- num. These salts, however, are very unstable. The 2nd, or binoxide, has a great tendency also to combine with acids, while, on the other hand, it will combine with bases to form salts: it is a brown powder. The 1st is a com- pound of i equivalent of the metal with I of oxgyen, and the 2nd, I of metal with 2 of oxygen. There is a protochloride of platinum, which is obtained in a precisely analogous way to the corresponding chloride of gold ; but the bichloride, as formed in the ordinary solu- tion of platinum, is the important one. It is obtained by heating the metal in aqua regia, and subsequently evapo- rating the solution carefully at a low temperature. Thus a deliquescent cake of a reddish-yellow colour is obtained, deeper in colour as the water is expelled. It is from this that all the platinum compounds are obtained, either directly or indirectly. It is soluble also in alcohol; and this 252 METALS OF THE FIRST CLASS. solution forms our best test for the presence of potash or ammonia. And (as has already been shown) if the am- moniacal precipitate be heated, spongy platinum alone remains. This is a dull grey, porous form of platinum, easily condensed by ignition, and having the same specific gravity as ordinary platinum. The composition of bi- chloride of platinum is Pt. C1 2 , and its equivalent 169*5. There are two sulphides of platinum; the first, or pro- tosulphide, may be formed by acting upon moist proto- chloride by hydro sulphuric acid. The second cannot be prepared by the usual method in such cases, viz. by passing the acid into bichloride of platinum, for we do not thus get a true bisulphide thrown down, but a compound of chloride and sulphide of platinum. When, however, the acid gas is added to the chloride of platinum and sodium, a bisulphide is precipitated. This must be filtered out and washed with hot water, and then dried in vacuo. When first thrown down, it is a brown powder, which be- comes black upon drying. At a dull red heat the sulphur is driven off and platinum left. Alloys. Worked platinum cannot be amalgamated with mercury, and the only method of forming platinum amalgam consists in rubbing finely-divided platinum and mercury together in a warm mortar : the combination of the two will be accelerated by moistening the two metals with water, acidulated with acetic acid. It forms an unctuous amalgam, increasing in solidity in proportion to the amount of platinum it contains. The more unctuous amalgam may be employed, just as the gold amalgam is, in water-gilding ; and metals may be platinized in an analo- gous way to that by which they may be water-gilt, for the mercury is driven off at a strong heat, and platinum left. Platinum alloys with silver in all proportions: the PLATINUM. 253 latter metal loses somewhat of its whiteness, becoming harder by the association. Hot sulphuric acid will dis- solve the silver from such an alloy, but if nitric acid be used for this purpose, it is a remarkable fact that it will dissolve more or less of the platinum also. With gold, an excess of platinum renders the alloy infusible in a wind furnace 2*5 of platinum to 1*0 of gold, for example. Equal weights will give a very malleable alloy, having very much of the colour of gold. One part of platinum to 9*5 of gold does not diminish the least of the rich yellow of gold, while it affords an alloy of the same density as platinum. A soluble salt of platinum may be discriminated by the following set of reagents : 1st. Hydrosulphuric acid will throw down a blackish brown precipitate, insoluble in nitric or hydrochloric acid alone, but soluble in them when mixed. 2nd. Sulphide of ammonium produces the same pre- cipitate ; but this will be dissolved by excess, and repreci- pitated upon the addition of acids. 3rd. Potash, or ammonia, each throw down a very characteristic yellow crystalline precipitate, soluble when aided by heat, but readily precipitated in a cold solution, especially if it contain any hydrochloric acid. 4th. Soda precipitates a brown hydrated binoxide from persalts of platinum : this is soluble however, if any excess of soda be added. 5th. Protochloride of tin, added to solutions of plati- num salts, gives an intense brown-red colour to them, but does not throw down any precipitate. 6th. Sulphate of iron does not precipitate platinum. Por the quantitative estimation of platinum, we may separate it from almost all metals by the addition of 254 METALS OF THE FIRST CLASS. chloride of ammonium to a platinum solution, and subse- quently a little alcohol ; if this precipitate be collected, and then washed with dilute alcohol, in which it is insoluble, it will be ready for weighing, and every 100 parts will contain 44.28 of platinum. Supposing platinum to be contained in an alloy of gold and silver, it may then be estimated after the latter are separated in the way already described ; and as the oxalic acid by which the gold is thrown down does not precipitate platinum, it will be left in the solution for subsequent precipitation. For this Miller advises neu- tralizing the solution by carbonate of soda, and then precipitating the platinum in the metallic state, by boiling the liquid with a soluble formiate. When assays are made of gold containing platinum, much care is requisite, or the report will be given too high, from its retention. If the quantity associated with the gold does not amount to more than ^th, it will be separated during the acid parting work ; but if above that quantity, extra care must be taken in each stage; and when the platinum reaches 12 per cent, or more, it is scarcely possible to separate it in the ordinary way. Its presence is indicated by the dull working of the button in the cupel, by want of brilliancy in the play of colours and final clearing of the button ; and this will be dull and crystalline upon its upper surface. Then, on parting, the acid will become more or less of a straw colour. It is well, upon these signs, to commence a fresh assay, giving it rather an extra quantity of silver, a stronger furnace heat, and after laminating very thinly, employing a brisk boiling in the acid apparatus. Thus any quantity short of 12 per cent will be thoroughly dissolved out. PALLADIUM. 255 CHAPTER XL PALLADIUM. PALLADIUM is obtained from platinum ore, after the separation of that metal, and it is also associated with some of the gold obtained from Brazil as an alloy of gold and palladium. It is separated, in the former case, after the platinum has been thrown down from the ore solution (page 242), by treating the residuary acid liquor with cyanide of mercury. A white nocculent precipitate is thus thrown down, which is cyanide of palladium. Heating this with sulphur separates the cyanogen, and sulphide of palladium remains, which may be decomposed and its sulphur driven off by heat; or the cyanide is decomposed by heat alone, the cyanogen being driven off. The process usually adopted for the separation of palladium, from Brazilian gold, has been devised by Coek. The gold dust is fused with an equal quantity of silver, and some nitre. The latter oxidizes certain base metals, and, combining with earthy matters, forms altogether a slag, from which the alloy is poured away. This is again fused with a second portion of silver, so as to quartate the gold, and the mixture is poured from the black-lead crucible into water, for granulation. The alloy is then 256 METALS OF THE FIRST CLASS. parted with twice its weight of nitric acid, of 1-30 specific gravity; and, when action has ceased, this is replaced by a second quantity, and the parting operation carried on for two hours longer. The gold removed, the acid liquors contain the palladium and silver, with any copper present. To this liquid common salt is then added, to throw down the silver as chloride. And when this is removed, by decanting the supernatant liquid from the subsided precipitate, a quantity of zinc is placed in the latter : by this the palladium and copper are thrown down as a black powder. This is next removed, and dissolved in nitric acid; after which the solution is supersaturated by ammonia. Thus palladium and copper are held in solution, their oxides being soluble in ammonia, while small portions of platinum, lead, and iron, will be thrown down. Lastly, the nitrate is heated with hydrochloric acid, which separates the palladium as ainmonia-proto- chloride: this, washed, and ignited, will afford pure spongy palladium, as a grey mass. This, however, is not malleable, and for the acquisition of this quality it needs further treatment. It is, therefore, generally fused with sulphur, and the sulphide so formed treated at a second fusion with a little nitre and borax, the crucible having free access of atmospheric air allowed to it. This cleanses it, and it is then taken out and roasted on a porous tile, and the pasty mass resulting pressed into a cake, roasting being kept up so as to expel the sulphur as sulphurous acid, and leave the palladium again as a spongy mass. When nearly cool, it is gently condensed under the hammer, then heated again, and again hammered, so as to solidiiy the mass gradually, without which care it would still exhibit brittleness. Gmelin says, that in this last state, the brittleness results from retention of some of the sulphur. PALLADIUM. 257 Properties. A white metal, much resembling plati- num, but having a specific gravity of 11*8. It is less ductile than platinum, and apt to crack at the edges when rolled. Although the most fusible of the platinum metals, it is not easy of fusion ; but when liquid it evaporates in a green vapour, which, on condensing, forms a dark-brown dust, composed of a mixture of metallic palladium and its oxide. If heated and fused in an oxidising atmosphere, it vegetates on cooling, just as silver does. It does not oxidise in the air, unless the temperature be considerably raised, and then the surface may be again restored by a stronger heat, which drives off the newly formed oxide. It is at times found native in company with platinum, but the grains may be distin- guished from the latter by the fibrous structure which they exhibit. Symbol, Pd. Equivalent, 53*24. Palladium unites with oxygen in three proportions, forming a suboxide, Pd 2 ; a protoxide, Pd 0, which is the base of the salts of palladium; and a biuoxide, Pd0 2 . Palladium also combines with chlorine, and two chlorides exist, a protochloride and a perchloride; the first may be crystallised, but the second, or Pd C1 2 , exists only in solution. A sulphide of palladium is formed when hydro- sulphuric acid is added to a palladium salt : it falls as a black precipitate. Alloys. With mercury palladium forms a grey plastic amalgam, but not easily, and when union does take place it is attended with evolution of heat, hardening quickly as it cools. Wollaston advises the formation of it by decomposing a palladium salt by excess of mercury, when, by agitating the two together for a considerable 258 METALS OF THE FIRST CLASS. time, a soft amalgam is obtained. If the palladium salt is in excess it will form a grey powder, consisting of two equivalents of palladium with one of mercury, and so permanent as to require a white heat for getting rid of the whole of the mercury. Silver and palladium may be combined in any pro- portion, and when in the proportion of one part of palladium to two of silver, the metal retains the exceed- ingly brilliant polish which may be given to it. Gold and palladium form a hard grey alloy when combined in equal proportions. One part to four of gold forms a white alloy. One part to six of gold is but slightly coloured by the latter. They are all brittle. Platinum and palladium in equal parts form a grey alloy, about as hard as bar iron, and which fuses below the fusing point of palladium. Salts of palladium may be discriminated by the follow- ing tests. Hydrosulphuric acid, or sulphide of ammo- nium, gives a black precipitate of sulphide of palladium, insoluble in alkaline sulphides, but soluble in hydrochloric acid. Potash, or soda, throws down a red subsalt from solu- tions of palladium salts, and on the application of heat ; this subsalt will be dissolved in any excess of alkali present. Ammonia and its carbonate throw down a copious flesh-coloured precipitate, an ammonio-chloride soluble in excess, but from the nitrate of palladium ammonia gives no precipitate. Protosulphate of iron reduces palladium salts after a time, and, as with gold, heating the solution facilitates the reduction, but if the solution is very acid, action is pro- portionally slow; the precipitated metal covers the sides PALLADIUM. 259 of the vessel in a film. Protochloride of tin gives a brown precipitate, which is soluble in hydrochloric acid, giving a bluish green solution. Lastly, cyanide of mercury is the characteristic test. This precipitates a yellowish-white cyanide, which becomes white on standing, and is soluble in hydrochloric acid. The estimation of palladium quantitatively is generally made from this precipitate, for, by cyanide of mercury, we have the means of separating it from all the noble metals, and, indeed, from all others, if we except lead and copper. If, then, a solution of the alloy be made in aqua regia, silver will be separated during the solution. The acid of the filtered solution is next saturated with car- bonate of soda, and cyanide of mercury added; lastly, the separated cyanide is heated, and the palladium obtained by its decomposition is weighed directly as metal. 260 METALS OF THE SECOND CLASS. CHAPTER XII. METALS OF THE SECOND CLASS. ORDER I. LEAD. LEAD has been known from very remote times, although the term in some of the very early writings (the Bible, for instance) did not signify the metal now bearing the name. Its chief ore is galena, wherein an average of 80 parts of lead are associated with about 13 of sulphur. Consequently, it is a protosulphide ; but it is also invari- ably associated with silver, and the proportion of the latter is subject to great variation. Thus some Silesian ores contain as much as 20 per cent of silver ore ; but ^rd per cent constitutes a very rich ore, while the average of ordinary galenas is j -fa ^th per cent. Sulphides of anti- mony, copper, zinc, arsenic, and iron, are also found in it. As also quartz, fluor spar, and sulphate of baryta. Galena is classed as blue lead, specular galena, and argentiferous galena ; but the latter is not easily distin- guished as such by any great external difference. Galena is a crystalline ore, its primary form being the cube; but, as would be expected, it is frequently found in octohedra. It is the principal source of English lead, and is found in Cumberland, Wales, Cornwall, and LEAD. 261 Scotland. The united annual produce of these countries ranges from 31 to 6500 tons of lead annually, while, from British lead only, as much as 800,000 oz. of silver have been separated in one year. Lead is also found in Germany, France, Spain, and the United States. The rarer minerals of lead are almost invariably found in association with galena. They are, native oxide or massicot, chloride, sulphate, carbonate, phosphate, and chromate of lead. The lead ore is first sorted, and freed as much as possible from siliceous matters, then ground to powder and washed, when it is ready for the smelting operation. The principle of this consists in heating the ore in such a manner, with free access of air, as shall convert a portion of the sulphide of lead into sulphate, by the oxidation of lead and sulphur. This roasted ore is then mixed with such a quantity of the crude, as that the lead will flow off, leaving the foreign matters of the ore with some unreduced material. A reverberatory furnace is exclusively employed for 262 METALS OF THE SECOND CLASS. this, having a bed of about 10 feet by 8, and formed generally of old slags of former operations. It is well depressed in the centre at D, and at the lowest part a tap-hole, A, is formed for the running off of the metal. A series of openings, B, are also formed in the side for air admission, as also for working through. There is a bridge, c, of at least a foot between the furnace and bed ; and at the back the flue-opening is placed as low as 9 inches above the bed. This is provided with a damper to check draught, and as the lead fumes are very liable to partially choke the horizontal part, its top is always pro- vided with moveable tiles for the clearing this oxide out. From 12 to 30 cwt. of ore are mixed with a flux, which is usually about -^th of lime; and these, after charging in, are spread evenly upon the bed. The openings being closed, heat is got up, and the mixture stirred from time to time. After two hours, any rich slags of former workings are thrown in, and as these will at once yield their lead, the tap-hole is opened for its running off. A little fuel is then supplied, and as the lead from the ore begins to collect in the depressed part of the bed, a little more flux is sprinkled over it, the future produce being sup- posed to be improved by the attendant slight lowering of the temperature. The slags are kept pushed back con- tinually. The lime sets free oxide of lead by decom- posing the silicate, and is itself converted into silicate of lime. The oxide of lead reacts upon the sulphide of lead not already decomposed ; and it is said that the stirring and raking also tend to set free metallic lead, the iron tools somewhat assisting, as shown by their being attacked and destroyed during the operation. The scoriae are also treated with a small quantity of carbon- LEAD. 263 aceous flux, in order to decompose any oxide or sulphate of lead, which is retained by them. At the end of about four hours the lead is allowed to flow out at the tap-hole into iron receptacles. The lead so obtained in most cases requires refining, or, as it is called, "improving." For not only does it contain the silver originally present in the ore, but also antimony, tin, copper, and other impurities ; and this is especially the case in leads obtained from Spanish ores. This is performed in a reverberatory built with a very low dome, and whose bed is a large cast-iron pan, set quite level behind a very broad bridge. At one end, and a little in front, is built up a second furnace, provided with an iron melting-pot. In operating, both fires are lighted, and the pot filled with the coarse metal, six or seven tons being generally worked in one operation. When the metal is fused, it is ladled into the rever- beratory and kept there in fusion. It soon becomes covered with a thick scum or pellicle, which is kept raked out by a door at the side of the furnace, so as constantly to expose a fresh surface. This contains the oxides of tin and antimony, which metals are more readily oxidised than the lead. Thus, after a period varying from 12 hours to several days, the lead will be found to assume a peculiar crystalline texture on cooling, indicative of its purity ; and to learn when this state has been arrived at, a portion is from time to time taken out and examined ; and it is then run into an iron pot for casting into pigs. As the lead still retains the silver, this has now to be removed, which is done by first concentrating the silver into a reduced quantity of lead, and afterwards cupelling this. Formerly, for want of a good and effective process, the lead of commerce always retained a considerable 264; METALS OF THE SECOND CLASS. amount of silver, so much as to render its separation a very profitable operation since Mr. Pattiuson's process has been in use. That gentleman discovered that if we fuse lead containing any notable amount of silver, and then cool slowly, carefully stirring at the same time, crystals will form in the bath and subside to the bottom ; and, moreover, these will be much less rich in silver than the original metal was. Upon this discovery he founded the following operation for removing the poorer lead and concentrating the silver : A series of ten or more iron pots are set adjacent to each other, but with separate fire-places to each ; they are of a size to contain about 5 tons of lead. In the centre one lead is put, of about 20 oz. of silver to the ton : this is fused and skimmed, and then the fire lowered, the metal being kept well stirred meanwhile. As the tem- perature falls the crystals begin to form. A set of per- forated ladles having been kept heated in a small extra pot of fused lead, one of these is now taken, and with it the crystals are removed from the large centre pot, being drained from the uncrystallised metal by means of the perforations. The crystals, as fast as they are removed, are passed into a pot next on the right, and when all are worked out the richer metal left is ladled into the pot next on the left; and now a fresh charge of metal is put into the centre one. The working is then again started, as also at the same time in the pots on each side, the enriched metal being passed on from pot to pot on the left, while the poorer is carried in like manner to the right, till at the end of the series of workings the pot on the extreme left is found to contain metal of about 300 oz. of silver per ton, or just about twenty-five times as rich as the LEAD. 265 original metal ; while the lead in the extreme right-hand one will not contain more than half an ounce of silver per ton. It is not found advantageous to concentrate more than above mentioned, and now the silver lead is ready for cupellation, by which the lead is entirely separated as litharge or oxide,, and the silver left. See page 143. There is another process for desilverising lead, which has been patented by Mr. Parkes. He adds a quantity of zinc to the lead, and fuses them together. This alloy is then subjected to a liquation process, by which the lead is sweated out, and an alloy of zinc with silver left, from which the silver is recovered by distilling off the zinc. Although the lead of commerce is very nearly pure, it is never entirely so; consequently, if it be required che- mically pure, the best quality of commercial lead must be taken and dissolved in nitric acid, and the resulting nitrate crystallised repeatedly to purify it. This is then heated to redness in a crucible, whereby the nitric acid being decomposed and driven off, a pure oxide of lead remains, which may be reduced to metal by heating with black flux. But it may thus retain traces of silver. Properties. When lead is pure it may be cut even with the finger-nail, its clean surface being of a bluish white, which rapidly tarnishes from oxidation. Its spe- cific gravity is 11*35. It is readily rolled even into thin sheets, but it is not very ductile or tenacious, although it may be drawn into wire. It melts at 612, and may be crystallised with care in octohedrons or the primitive form of cubes. If repeatedly heated and fused, it gra- dually becomes harder, probably from absorption of portions of oxide which become diffused through the 266 METALS OF THE SECOND CLASS. mass, but a layer of charcoal put over the metal during fusion will prevent this. Lead, when exposed to the action of pure water containing air, will deposit an oxy- carbonate of lead ; and the scale of this substance falling will leave a fresh surface for renewed action, and thus rapid corrosion is the result. Dr. Miller, who, with Mr. Daniell, experimented upon this matter, observed that certain salts, as phosphates, sulphates, and carbonates, diminish the corrosion, while bicarbonate of lime quite hinders it ; hence spring waters, which generally contain this substance largely, are inactive upon lead ; but chlo- rides, nitrates, and nitrites, are especially injurious. The quantity in either case influencing solution being not more than 3 or 4 grains per gallon. Symbol, Pb. Equivalent, 103 '6. Compounds with Oxygen. There are four of these, a dinoxide, Pb 2 ; a protoxide, Pb ; a binoxide, Pb 2 ; and a compound oxide formed of two equivalents of protoxide with one of binoxide, hence having the composition Pb 3 4 . The second, or protoxide, is the base of the ordinary lead salts ; it is the litharge of commerce, formed on the large scale, by heating lead on an open flat hearth to redness, and removing the oxide as it forms. This is then ground and levigated, whereby the adherent grains of lead are separated and removed. If it is made at a very low temperature, the oxide forms as " massicot/' a yellow powder; the texture and colour of this depend upon the oxide not having been fused. It is this protoxide which is formed in ordinary cupelling opera- tions, and which, by fusion, is rendered sufficiently liquid as to be capable of absorption by the substance of the cupel. It is volatile at a strong red heat, and may be LEAD. 267 dispersed in fumes. Protoxide of lead may be formed on the small scale, by heating pure nitrate of lead, as described in the preparation of pure lead. When pure, it is a lemon -yellow powder ; where it inclines to orange or red, it is an evidence of slight admixture of the com- pound or red oxide with it ; but, by heating litharge, this red colour is assumed, which disappears again on cooling. A crystalline hydrated protoxide may be formed by drop- ping solution of acetate of lead into ammonia, until the precipitate at first formed becomes permanent. The white powder so obtained may be dried at a gentle heat, and on examination by the microscope will be found to consist of minute transparent four-sided prisms. Prot- oxide of lead is the base of ordinary lead salts ; the oxide itself is slightly soluble in water, giving it an alkaline reaction. This reaction is also shown with the subsalts of lead, which this oxide readily forms. The specific gravity of protoxide of lead is 9*3. Composition, Pb 0. Equivalent, nr6. Red oxide of lead or minium is prepared commercially by heating metallic lead in a reverberatory furnace, so as first to form massicot or protoxide; this is removed and finely pounded. The powder is then again heated and kept at a dull red heat for about 24 hours; the mass being frequently stirred, and the heat not allowed to rise above 600. Thus the whole is converted into a brilliant scarlet crystallo-granular powder. The beauty of colour is, however, often much diminished in commercial spe- cimens by adulteration with brick- dust and other red materials. Adulterations of this character are most hurtful in many of the applications of the adulterated body. Thus in red lead, which is much used in the manufacture of 268 METALS OF THE SECOND CLASS. glass, the brilliancy and whiteness of the flint-glass mainly depends upon the lead oxide, and not only will these fraudulent additions spoil the transparency, but they will often (if they consist of other metallic oxides) colour the glass, although its transparency is kept up. Thus, in green bottle glass, the deep colour is entirely due to a proportion of oxide of iron. Minium appears to be, as already stated, a mixture of two equivalents of protoxide with one of binoxide of lead ; (hence it does not combine with acids) ; therefore, upon treating it with dilute nitric acid, we are able to separate the protoxide, which will be dissolved out, and combining with the acid, will form nitrate of lead ; the binoxide of lead remaining untouched as a brown powder, which may be washed from the lead nitrate, and dried. Binoxide of lead is insoluble in acids, excepting dilute hydrochloric, from which it may be again separated by neutralising with potash. Composition, Pb 2 . Equi- valent, 119-6. Chloride of lead is formed when hydrochloric acid, or a soluble chloride, is added to a soluble salt of lead. It falls as a crystalline precipitate, from its sparing solu- bility in water, one part requiring thirty parts of cold water for its solution. This compound is important in connexion with silver assaying. Thus, if a silver under examination by humid assay contain lead, as some of the brittle silvers do, a portion of the salt solution will go to precipitate this chloride, and so a small error of over- estimation of the silver will result. Composition, Pb Cl. Equivalent, 139*1. Sulphide of lead is found native as galena ; but an artificial sulphide is precipitated as a hydrate, when we add hydrosulphuric acid to a solution of a lead salt, or LEAD. 269 even to an insoluble lead compound suspended in water. It is in this case a black powder. Composition, Pb S. Equivalent, ng-6. Many of our valuable pigments are formed of lead compounds. Thus, ordinary white lead of the painter is a carbonate of lead, and the peculiar body and durability which this gives to oil paint has caused it to be an article of large manufacture. Patent yellow, or Turner's yellow, is a compound of chloride with oxide of lead. Again, chrome yellow is a neutral chromate; and again, when this last is fused with five parts of nitre, a dichromate of lead and a chromate of potassa are formed. The latter, washed away, leaves the dichromate as a brilliant scarlet powder. The alloys of lead with the class of metals hitherto considered are not important, as they form in the general brittle unworkable compounds; but they may be enu- merated here. With mercury lead readily amalgamates, either by mixing lead filings with mercury, or by dropping warm mercury into lead in fusion. The resulting amalgam will have a specific gravity above the mean of its constituents, showing that condensation has accompanied the union. Two parts of lead and three of mercury form a solid crystalline amalgam, very white and brittle; with a larger proportion of mercury it will be pasty, or even nearly fluid. In all these amalgams the lead may be partially oxidised by moist air, the oxide formed being a suboxide of lead, which will be mixed with some amalgam as a black powder. The peculiarities of alloys of lead and silver are taken advantage of in their separation : thus, as has been stated, an alloy rich in silver will remain fluid at a lower tern- 270 METALS OF THE SECOND CLASS. perature than a poor one, the poorer crystallising out ; in fact, the homogeneous alloy of silver thus separating itself under mere management of temperature. Silver thus diffused through a very large quantity of lead will render the latter less malleable. Lastly, if a bar of metallic lead be immersed in a solution of nitrate of silver, the precipitated metal will not be pure silver, but an alloy of silver and lead. Alloys of gold and lead are brittle in the extreme. Thus Mr. Hatchett found that -rsVo^ f ^ ea( ^ * n S^ w ^ destroy its coining qualities to some extent, by rendering it less ductile. If the amount of alloy in standard gold be formed of lead, and even added to perfectly pure and ductile gold, the colour will be straw-yellow, and the alloy thoroughly brittle. In all cases, however, where gold or silver is alloyed with lead, the latter may be entirely removed by cupellation. Platinum, with its own weight of lead, forms a pur- plish white alloy, brittle and granular in structure, and acted upon by the air. The metals have so great an affinity for each other, that a platinum crucible will be perforated by fusing lead in it, or even by oxide of lead, when a reducing flux is used with it ; the lead alloying with the metal of the crucible. Lead cannot be separated from platinum by cupella- tion without much care, for although, when the lead is in excess, the alloy is very fusible, as the lead oxidises and the metal becomes richer in platinum, so the fusing point rises, until, at length, the heat of the muffle is apt to be insufficient, and the alloy sets again, retaining portions of lead. Palladium and lead form a grey alloy, which is granular in texture, and very hard and brittle. LEAD. 271 The more important alloys of lead are those which it forms with tin, antimony, bismuth, and some other metals, constituting the classes of solder, type metal, pewter, &c. : these will be considered in their places. Analysis of Compounds of Lead. The presence of this metal is indicated by the following tests : ist. Hydrosulphuric acid or sulphide of ammonium will throw down a black sulphide from its solutions, insoluble in any excess of the precipitant. 2d. Potash or ammonia throw down hydrated oxide : this is soluble in excess of potassa, but not in ammonia. 3d. Alkaline carbonates precipitate a white carbonate of lead, which is quickly blackened by hydrosulphuric acid. 4th. Sulphuric acid is a characteristic test, precipi- tating a white sulphate : this is also thrown down by any soluble sulphate. 5th. Chromate of potash is also a very delicate and characteristic test, precipitating a fine yellow chromate of lead, and acting upon exceedingly dilute solutions. 6th. Hydrochloric acid or a chloride gives a white precipitate, soluble in excess of potassa. yth. A lead salt is readily reduced on a piece of char- coal before the blowpipe, a bead of lead ultimately resulting in the centre of the point of fusion; round which the charcoal will be seen to have absorbed a portion of yellow oxide of lead. When lead has to be estimated quantitatively it is usually precipitated as sulphate of lead, and the preci- pitate washed, dried, and ignited in a porcelain crucible before weighing, the crucible being covered, as sulphate of lead is slightly volatile. 272 METALS OP THE SECOND CLASS. It may also be precipitated as sulphide of lead by hydrosulphuric acid, or, lastly, as protoxide by potash. The analysis of a silver lead would be performed by solution of the specimen in nitric acid. Then largely dilute, and add a large excess of hydrochloric acid to throw down the silver. Chloride of lead is prevented from going down by this dilution and excess of acid. Then the lead is precipitated as sulphide, and the latter washed, dried, and weighed. The analysis of a galena for the amount of lead may be made by digesting a weighed quantity of the powdered ore in strong nitric acid, adding a few drops of sulphuric; thus it will be converted into sulphate. It is next eva- porated to dryness, and the mass then exhausted by treating it with a strong solution of caustic potassa. This will dissolve out the lead salt, leaving the earthy residue. The solution is then filtered, and precipitated by hydrosulphuric acid, which throws down all the lead as a sulphide. This is filtered, washed, and again oxidised by nitric and sulphuric acids. Lastly, the excess of the latter is driven off by evaporation, and the sulphate of lead ignited in a porcelain crucible and weighed. COPPER. 27S CHAPTER XIII. COPPER. ALTHOUGH ores of copper were probably earlier known than those of any other metal, it is likely that the pro- duction of the metal itself is an operation of comparatively recent date, and that in the smelting of early times, zinc or its ores were associated with the copper ore, and so the product was actually brass. Thus, in the Bible, we read of "a land out of whose hills thou rnayest dig brass." Cornwall and Swansea are now the great producing localities of this metal, but much is also sent from Australia, in the state of ore, the latter being rich car- bonates, containing, on an average, about 30 per cent of copper. North America, Siberia, and the Ural district furnish copper ; the two former largely as native copper, the latter as a subsulphide. Ores from Chili and Cuba are also brought to Swansea for smelting; and, lastly, Saxony and Spain furnish copper ore. These ores are as follows : ist. Native copper, found at times in immense masses, so that we have authentic accounts of large flattened masses being found in the neighbourhood of Lake Supe- T 274 METALS OF THE SECOND CLASS. rior (N. America), of 14 to 1 8 cvvt. in weight. A broad, thin, and compact piece of 14 cwt. is described as 42 inches long by 30 broad and 8 thick, and having its surface covered with specks of silver. Mr. Phillips states that masses of no less than 150 tons weight have been found here ; and it is now a received opinion, arguing from analogous laboratory operations, that these masses, which, like gold nuggets, have all the appearance of having been at some time in fusion, may have been formed by electro-chemical agency, the sulphide of copper, on exposure to moist air, becoming sulphate, which by the above means is reduced to the reguline state. 2d. The most common of all copper ores is perhaps the ordinary copper pyrites, from which five-sixths of the copper in Great Britain is obtained. This is a natural combination of sulphide of copper with sulphide of iron, sometimes combined in true chemical proportions, as in the mineral known as purple copper ore. In the majority of cases, however, the copper does not amount to more than 12, or even 6 or 8 per cent. 3d. The blue and green carbonates are the ores of Australia, and the beautiful Russian mineral known as malachite is a green carbonate. 4th. The rarer ores are the red and black oxides and grey copper ore, the latter being valuable from the silver it contains, with occasionally also gold and platinum. About 35 per cent of all British copper is supplied by the mines of Cornwall, but the great smelting-works are at Swansea. Indeed, out of nineteen in operation in this country, seventeen are situated at Swansea; and so extensive are these, that the atmosphere for some miles round is thoroughly impregnated with the noxious fumes evolved. COPPER. 275 Previous to smelting an ore, it is most important to have a correct assay of its value ; and for this purpose, although many excellent wet methods have been devised in order to do away with the dry, which, although most simple, is an arduous and tedious operation, yet the manufacturers far prefer the latter, as more assimilating the after actual operation upon the ore. The dry assay is thus made : About 50 grains of ore may be taken and powdered, then carefully adjusted to the weight, and next roasted at a dull red heat to get rid of sulphur, arsenic, and volatile matters. It is then mixed with a quantity of glass of borax, and some argol, and exposed for from one to two hours to the strong heat of a Sefstrom's or Griffin's gas furnace. On cooling and breaking the pot, if the operation has been successfully performed, a button of copper will be found under a layer of slag, which button only remains to be weighed. Many wet methods of volumetric assay have been devised. . Thus Parkes makes a solution of cyanide of potassium, which has the property of decolorising any solution of copper rendered more intensely blue by am- monia. Then, by experiment upon a known quantity of pure copper, he gets the value of his cyanide solution, and can then apply it to the examination of an ore. For this the latter is digested in nitric acid, so as to oxidise and dissolve its copper ; ammonia in excess is added, then a quantity of water, and next it is filtered ; then from a graduated burette the tested cyanide solution is dropped until it is decolorised, when the volume of solution used will indicate the quantity of copper present. But this process is difficult of execution, from the difficulty of bringing the eye to appreciate the faint tints of blue towards the end of the operation ; then, again, the cyanide 276 METALS OF THE SECOND CLASS. solution is by no means permanent : hence we cannot, as in the salt solution for wet silver assaying, make and store a quantity, but must be constantly preparing and verifying anew. Pelouze uses a similar means, which is probably pre- ferable, because for his decolorising solution he employs a more permanent one, viz. sulphide of sodium ; but here, again, the first objection as to faint colour operates as much as before. Therefore, on the whole (although still dependent upon the appreciation of colour), the plan advised by Brown (Quarterly Journal Chem. Soc., vol. for 1857, p. 65) is probably the best. He digests the ore as before, and when cessation of nitrous fumes indicates the com- plete solution of the metal, adds carbonate of soda till a precipitate formed becomes just permanent; then acetic acid is added, and an excess of iodide of potassium. In this way the copper is converted into a subiodide, and some iodine is set free ; when a few drops of starch added will colour this deep blue. The estimation is then made by ascertaining the quantity of iodine so set free, by means of a standard solution of hyposulphite of soda, which, by oxidising the iodine, destroys the blue tinge it has derived from the starch. This standard solution is made and verified by a known weight of some pure copper, treated in the same way as in the ore operations subsequently to be carried out. Reduction of Copper. This is effected from the sulphide, on the large scale, by means of a series of no less than ten operations, six of which are essential, the remaining four being collateral ones upon certain slags, &c. COPPER. 277 These may thus briefly be reviewed in detail : First, a calcining operation is employed in a large reverberatory furnace, whose bed is large enough to contain at least three tons of ore. This is wheeled on to the top of the crown or arch in barrows, and then thrown in by the hoppers, A A, after which it is raked evenly over the bed. The fire is next raised to a moderate temperature, and maintained at this for some eight hours, care being used that it is not sufficiently high to fuse the surface, and so, by caking the mass, stop the evolution of volatile matters. At the end of two hours, during which much watery vapour and sulphurous acid are given off, the surface is furrowed afresh ; and this is done every two hours, and fresh fuel added, until as much of the volatile matters as possible has been dissipated. For this object twelve hours will generally be requisite, when the fire is urged, and afterwards the doors in the bed opened, and the charge raked into the vault, B a most unwholesome operation, the workmen being exposed to sulphurous and often arsenical vapours. The furnace is not allowed to cool down, but a fresh charge introduced at once. The second operation is performed in a somewhat similar furnace, called the ore furnace. The object is to separate the iron as a silicate, and convert the copper into 278 METALS OF THE SECOND CLASS. a disulphide, containing some oxide of copper. If the ore has contained a sufficient quantity of silica, it is used alone, otherwise some slag of other operations is added to furnish what is required. The bed of this furnace, A, is formed into a deep depression at one side, from which a channel, B, flows to a water-tank, c. This latter is provided with a cage and windlass for raising the matters sunk in it. At the back is an opening, D, for working the charge, and allowing the slag to flow out into the moulds, E E E E. The charge for this furnace is 1 1 tons of calcined ore ; it is about -^rd the size of the calcining furnace. The ore being in, it is gradually heated to fusion, and maintained thus for half-an-hour, so that the matt, as it is called, may subside through the slag ; then, at the end of about five hours altogether, the tap-hole is opened, and the fused coarse metal allowed to flow into the tank, by which COPPER. 279 it is granulated. Next, the slag is drawn out into the moulds placed at the back, and any copper contained in this slag subsides and collects at the bottom ; hence the cakes, on being removed from the moulds, are broken so as to separate the actual slag, the metal so recovered being added to that raised from the tank. The slag is chiefly silicate of iron, and the chemical changes of this operation consist mainly in the formation of this, with accompanying evolution of sulphurous and sulphuric acids. A third operation is now commenced, in a furnace very much resembling the calcining one. It consists in roasting the granulated coarse metal for a period of 24 to 30 hours, at a high temperature. More sulphur is thus got rid of, and some of the sulphide of iron oxidised : the product is a compact, blackish, friable mass, called (t cal- cined coarse metal." The fourth operation is for the conversion of this into " white or fine metal." For this the last product is mixed with rich ore, containing oxide of copper and silica, with but little sulphide of iron. The silica unites with any remaining iron to form a fresh slag of silicate, and any iron not so combined becomes oxidised at the expense of the oxide of copper added. By this operation the whole of the copper becomes disulphide, and the matt so obtained is cast into pigs. These (if the four operations have been well carried out) will contain, in 100 parts, Cu 73, Fe 6-5, S 20-5. The richer portion of them is contained on the upper part of the pig, and is sometimes sold as " best selected copper " at the market sales. The next four operations have been mentioned as collateral ones, for they are not practised upon the 280 METALS OF THE SECOND CLASS. product we have before us, but upon the slags collected, to which rich foreign ores are frequently added; the details of these may therefore be passed over, but their product is added to that of the fourth operation. The ninth, or, if we do not enumerate the above four, the fifth operation, is for the purpose of getting rid of the sulphur, and producing " blistered copper." Some 3 j- tons of pigs are piled upon the floor of a reverbera- tory furnace, the orifices closed, and a quick fire got up. At first both the surface copper and sulphur of the metallic mass are oxidised ; but after a time the pigs fuse, and then a most violent reaction of oxide of copper upon the sulphide takes place, and the molten mass quite boils from the evolution of sulphurous acid ; the heat is therefore lowered, and the metal left to itself for a time, when a crust will form upon the surface, and this swelling and bursting, to allow of the escape of gases, which goes on for some 10 or 12 hours, stirs and breaks up the charge spontaneously, and much better than it could be effected by any mechanical means. Evolution of gas ceasing, the fire is again urged to a brisk red heat, when it will be again set up, and at the expiration of a further 6 hours or so the chief part of it will have been driven off; the heat is then raised to the highest, and the fusion of the whole mass, effected by this, brings about the union of the remaining metallic oxides with silica. The tap-hole of the furnace is then opened, and the reduced copper run off from the silicates, which are left as slag. The copper, running into moulds, constitutes blistered copper; but this is still wanting in tenacity, and so requires a refining operation : this being the tenth (or sixth) and last. In refining or toughening copper, a charge of about COPPER. 281 8 tons is operated upon at once, the process being carried out in a reverb atory having a large grate, so as to allow of the use of a very large body of fuel. By means of a tool resembling a baker's " peel," the ingots of blistered copper are introduced into the body of the furnace, and they are arranged in such a manner as to expose as much as possible of their surface to the action of the flame. After about 6 hours the metal begins to melt, and, when melted, a quantity of oxide of copper is generally formed ; this will be partly diffused through the melted mass, and part will go to oxidise any iron which may chance to be still remaining in it. The evidence of the presence of oxide still in the metal is afforded by taking out a portion, and, when cool, breaking it, when it will be found to be of a very coarse brittle texture, and its bright red colour very much darkened by the oxide. After about 18 hours, any oxides remaining will have united with the silica furnished by the sand adherent to the ingots. The heat is then kept up for some 2 or 3 hours longer; after which the scoria3 are raked off the bath, and the metal is said to be ready for refining; and this, having for its object the reduction of the diffused oxide of copper above mentioned, is effected as follows : The surface of the bath is first covered with powdered charcoal or anthracite, so as to protect it as much as possible from the action of the air, and at the same time to furnish material for the withdrawal of oxygen. Next, in order to bring all the metal under the influence of the carbon, it is vigorously stirred with poles of green birch wood, the fire at the same time being shut off from it. This is a very old practice, but one which has not hitherto been superseded : it is called " polling the copper." The evolution of carbonaceous gases, upon stirring the 282 METALS OF THE SECOND CLASS. melted mass with these, reduces any oxide of copper in their passage through the melted bath ; indeed the first effect of the introduction of the poles into the bath is to produce a violent commotion in the molten matter, and this is kept up some 25 minutes, the charcoal powder being at the same time supplied as it burns away. But the duration of this work is determined by constant trials of the metal during its progress being made by the assayer. When he finds that the product is satisfactory as to colour, fracture, &c., he directly stops the polling, or the product would be deteriorated by it : the metal would become what is called "over-polled." The examination is made by taking out a small bead of metal, and plunging it suddenly in water; a cut surface is then made, in which a fibrous grain should be percep- tible, and the colour should be brilliant, with a silky lustre; at the same time its brittleness is tested by bending. The effect of over will be the same as under-polling, as far as regards the application and use of the metal, for in both cases it will be harsh and brittle. In the latter this depends, as has been already stated, upon the presence of oxide ; but in the former it is probably from a carbide of copper being formed. If this state has been arrived at, the remedy consists in skimming off all the charcoal, and exposing the melted metal to a current of air passed through the furnace, again stopping this when the proper state of texture has been arrived at. The polling properly performed, the fire is again renewed, the scoria? removed, and a few shovelsful of charcoal thrown afresh over the surface. Lastly, the copper is dipped out by means of clay-coated ladles, and cast into ingots. COPPER. 283 The process of copper-smelting thus described is the one usual in England ; and although many patents have been taken out for improvements, the principles of the majority are the same, their merit, if any, consisting in shortening the series of operations. One operation, how- ever, may be mentioned here as an example of a different class : by it the copper ore or sulphides are powdered, mixed with nitrate of soda, and then roasted with exposure to the air ; thus the sulphides are converted into sulphates, and these, with the sulphate of soda also, are dissolved out of the resulting mass in a tank of water, and the gangue allowed to subside j lastly, from the clear metallic solution the copper is precipitated by means of metallic iron. By this means of precipitation the water of copper-mines may have the copper reduced out of it. Although commercial copper is often very nearly pure, yet it frequently contains traces of tin, iron, lead, silver, and also arsenic and antimony. When either of the latter are present, they materially injure the working qualities of the copper. Dr. Miller states that 10 ounces of anti- mony in a ton of copper will render it quite unfit to make brass which is required for rolling. A small proportion of tin will increase the tenacity of copper ; if the quantity be large, it hardens it too much in fact, produces bronze. Of all varieties of copper the Japanese is the purest, but the following methods will produce chemically pure copper : 1st. Electrical precipitation by means of the battery. If the poles of a voltaic arrangement be immersed in a solution of sulphate of copper, the latter metal will be deposited in a solid state upon the negative pole, and, when washed and dried, is quite pure. 28-1 METALS OF THE SECOND CLASS. ad. It may be obtained comparatively pure by igniting copper for half an hour in a covered Hessian crucible, having added one-third its weight of nitre. This addition oxidises the traces of those metals with which it is con- taminated. Copper may be obtained in a pulverulent state by boiling a concentrated solution of sulphate of copper with distilled zinc. The copper solution must not contain any free acid. As soon as the blue colour of the salt dis- appears the zinc is taken out, the solution poured off the subsidised copper, and the latter washed with some very dilute sulphuric acid. This is then poured off and the powder washed with hot distilled water. It is then pressed between folds of bibulous paper and carefully dried, and it is even better to dry it in a flask into which a current of hydrogen gas is passed. If required for amalgamating with mercury it may be used moist, just as washed. Thus obtained it is a reddish brown powder when dry, which when heated and rubbed with a bur- nisher will weld into a solid mass of metallic copper. Properties. Copper is perfectly red in colour. It is sometimes found crystalline, either in cubes or octohedra, and it may be deposited in these forms by voltaic action if this be carried on very slowly. It is very ductile and tenacious, as well as malleable. Copper fuses at 1996, and is very little volatile ; in those volatilised deposits where copper has been supposed to have been carried off, the sub- oxide will be mixed with it. It expands on solidifying, and absorbs oxygen : by some this is stated to be similar to the absorption of that gas by silver^ but I believe it is a surface oxidation only. Copper is unacted upon by the air at ordinary temperatures, notwithstanding the moisture which may be present in it. It is readily soluble in nitric COPPER. 285 acid with evolution of nitrous fumes. By sulphuric acid it is only acted upon by the assistance of heat. Hydro- chloric acid acts slowly upon it, but if air be excluded it is inactive. Ammonia in like manner dissolves it if air assists, but potassa or soda is inactive upon it. The specific gravity is about 8-93, varying slightly according to its state. It has a peculiar and disagreeable odour when heated, and a corresponding taste. Symbol, Cu. Equivalent, 317. Compounds. There are two compounds of copper with oxygen, viz. a suboxide and- a protoxide, and there are precisely corresponding chlorides and sulphides. The suboxide of copper may be formed by heating the protoxide with finely- divided copper (as filings) in the pro- portion of five parts of the former with four of the latter ; in this way, when decomposition has taken place, by raising the heat to redness we get a fused mass. But in the laboratory it is commonly obtained in a red crystalline powder, consisting of octohedral crystals, and by boiling equal parts of the diacetate of copper with sugar, and in four parts of water for about two hours. Suboxide of copper forms subsalts, but these are not very stable, being readily converted into salts of the protoxide by absorption of oxygen. The chief use of this oxide is as a stain in glass- working. From it are produced, when pure, a most beautiful carmine red, as also several other tints, ranging from orange to deep red, by mixing with it a proper proportion of sesquioxide of iron. The brilliant reds of some early specimens of stained glass were due to this oxide, but in employing it much care and judgment are required, because from its unstable nature it is very liable to become protoxidised in the fire. 286 METALS OF THE SECOND CLASS. And, again, its power is so intense, that unless the quantity employed be very small it will render the glass almost opaque. Composition, Cu 2 0. Equivalent, 71*4. Protoxide. This is obtained in a state of purity by dissolving pure electrotype copper in nitric acid, and eva- porating to dryness. The resulting salt is then slowly heated to redness in a clay crucible, the acid is thus separated and decomposed, and the oxide left. It may also be obtained as a hydrate, by decomposing a pure copper salt, by means of potash, a bulky blue precipitate falls; this may be rendered anhydrous by boiling in water after it has been well washed. This oxide is soluble in acids, producing blue (and occasionally green) salts. It is soluble in ammonia, and hence this alkali in place of permanently precipitating it from its solutions colours them an intense blue ; from this solution hydrated crystals will deposit, composed of oxide of copper combined with ammonia and water. If the protoxide of copper be em- ployed in enamelling or glass-staining, a green glass will be produced. Composition, Cu 0. Equivalent, 39*7. A subsulphide of copper may be formed by heating together the proper proportions of sulphur and copper. It is the produce also of the fourth operation in ordinary copper-smelting known as " fine metal." Composition, Cu 2 S. Equivalent, 79-4. Protosulphide of copper is the precipitate obtained in ordinary solutions of copper, by the addition of hydro- sulphuric acid. Thus formed, it is a dark brown hydrate, soluble in nitric acid, and converted even by exposure to air into sulphate of copper. It may likewise be formed by heating together sulphur and copper filings in proper proportion. It is also precipitated by sulphide of am- monium or sulphide of potassium, but in the former salt COPPER. 287 it is slightly soluble. Composition, Cu S. Equivalent, 477- Alloys. With mercury copper amalgamates, but the amalgam must be formed with a little management, for the metals do not readily combine. The best method of obtaining an amalgam is by adding to a quantity of the pulverulent copper described at page 284, a little nitrate of mercury. Thus the copper becomes well coated with mercury; this done, the mercury is poured upon it, and it may be to the extent of two or three times the weight of the copper, then by rubbing the metals in a mortar union of the two will be effected; and, lastly, perfect mixture is completed by gently warming in a crucible. Copper may be mixed with silver in all proportions, and the chief use of this alloy is for the formation of coin and plate. Silver is much hardened by mixture with copper, and in small amount copper does not much colour silver; where, however, the quantity is considerable, the colour of the alloy becomes perceptibly yellow, while it is also rendered very hard. In England the proportions used for coin and plate are u oz. 2 dwts. of fine silver to 18 dwts. of copper, or decimally Ag 925 + Cu 75. This is a well-wearing alloy, but finer even than this is used for the striking of medals. Again, the Indian rupees are composed of 947 silver to 53 of copper. Of continental coins the bulk are decimally alloyed. Thus, French five-franc pieces, and French silver coin generally, are composed of silver 900 to copper 100; but some of the silver coin of Germany and Prussia is very coarse. Thus, Prussian thalers are 811 Ag + 189 Cu. The German 24-kreutzer pieces, 586Ag-h4i4Cu; and the Prussian pieces of 5 silver groschen contain only 283 288 METALS OF THE SECOND CLASS. Ag to 717 Cu. Hence the latter after a little wear have all the appearance of copper. Alloys of gold with copper have already been alluded to (page 219). Copper hardens gold very much, and when the copper is in any considerable quantity the gold is apt to be rendered more or less brittle by it, especially if the former metal be not thoroughly pure; hence great care is requisite in selecting copper for this purpose. At our Mint the kind known as "shot copper" is employed, as being a pure kind ; it is made by fusing the metal and pouring it through perforated ladles into a cistern of cold water. In our own coin 916 '6 parts of fine gold are alloyed with 83-3 of alloy, which may even be all copper. In France, Holland,, and America, the same decimal system is pursued as with the silver coin, viz. 900 parts of gold are combined with 100 alloy; and in coin in which this alloy is all copper the metal is rendered very hard, but when carefully alloyed it is nevertheless not at all brittle. Copper and platinum in equal proportions form an alloy much resembling gold in colour. The specific gravity is also the same, but the metals require the strongest white heat for their combination. Copper alloys with palladium, but the heat required for their union is also very great. Equal parts of the two metals form a light brass-coloured alloy, rather brittle, but Mr. Cock formed a ductile white alloy of four parts of copper to one of palladium. Copper and lead form a brittle alloy ; indeed, when the proportion of lead is only a thousandth that of the quantity of copper, the latter is rendered very unworkable. If the quantity of lead be a hundredth of that of the copper, Karsten states that the copper will be quite useless. Copper alloyed with zinc COPPER. 289 in various proportions forms the different kinds of brass. With tin it yields a variety of compounds, of which bronze is the chief. Lastly, with zinc and nickel, it forms German silver. These alloys will be examined in their appropriate places. Discrimination of Copper. Hydrosulphuric acid or sulphide of ammonium, both throw down a brownish black precipitate. This is at first a hydrated sulphide. Ammonia, or its carbonate, gives a blue precipitate, which is immediately dissolved in excess, producing a deep blue solution. Potash or soda precipitates a light blue hydrated oxide, which on boiling becomes brown and anhydrous ; and the effect of fixed alkaline carbonates is ultimately the same, although at the first precipitation of the copper, it falls as a hydrated carbonate, the water and carbonic acid being driven off by boiling. Ferrocyanide of potassium gives a very characteristic brown precipitate, soluble in ammonia. If the latter be evaporated from such a solution, the ferrocyanide of copper is left unchanged. This precipitate is insoluble in hydrochloric acid. If a bar of iron be placed in a solution containing copper, the latter will be precipitated upon the bar in a metallic state; and tin employed in the same way throws the metal down as a black powder. When a copper salt is heated in the blowpipe-oxidizing flame it will communicate a green tint to it ; and if it be heated in the reducing flame, upon a piece of charcoal, and with a little carbonate of soda as a flux, we get a bead of metallic copper. Estimation of Copper. This may be done by throwing it down as a sulphide, or as an oxide; but the latter method is the best. If the solution under examination contain only copper, or at any rate no other metal whose TJ 290 METALS OF THE SECOND CLASS. oxide is thrown down by potassa, we have only to add an excess of caustic potassa, and well boil the precipitate, and then wash, dry, and weigh. In analysing a mixture of mercury and copper the amalgam is dissolved in nitro- hydrochloric acid, and having nearly neutralised the excess of acid by potassa, we add a quantity of formiate of potassa, and digest at about 130 F. Thus the mercury will be precipitated as subchlodde ; this may be collected on a filter, washed, dried, and weighed. Then the copper is to be separated and estimated as above. The analysis of a mixture of gold, silver, and copper, has been already given at page 221. In cases where copper is associated with metals which are not precipitable by hydrosulphuric acid, the former may be separated from them by throwing it down as a sulphide, by means of that reagent. But the sulphide of copper after being filtered away must be well washed with water, to which a little hydrosulphuric acid should be added to prevent oxidation. This done, the precipitate is to be digested in nitric acid, and when dissolved and the solution diluted, the copper may be precipitated by potash, as above directed. BISMUTH. 291 CHAPTER XIV. BISMUTH. THIS metal has been known for about three centuries, although it is not plentiful, nor are its applications very extensive. It is found principally native, in a matrix of quartz, but it also occurs as bismuth blende (a sulphide) ; bismuth glance; and also in association with lead and copper, in needle ore j sometimes with copper alone, and frequently with silver. Bismuth is obtained largely at Schneeberg in Saxony, also in Bohemia and Transylvania. It is also found at Stirling in Scotland, and in England in parts of Cornwall and Cumberland. The metallurgy of bismuth is very simple. The native metal is operated upon in tubular iron retorts, A, these are arranged in a horizontal row of three or four, and 292 METALS OF THE SECOND CLASS. inclined from the upper to the lower end, as shown in the section here given. From the upper end the brickwork is gradually bevelled down, towards a trough containing water, D; while below the lower end is placed an iron basin, c. Lastly, above each retort is a couple of holes made through the brickwork of the roof, E E, whereby the draught to each can be increased or diminished at plea- sure, by opening or stopping them as required. In operating, the tubes are charged at their upper ends with about 56 Ibs. of native ore. Heat is then applied, and in an already hot furnace, the metal will begin to flow in about ten minutes. A small rake is then introduced by the doors at the upper ends, B, and the ore so opened below, as to allow of a free passage of the fluid metal down to the lower end; thence it flows into the iron dishes, where it is protected from the oxidizing action of the air, by a covering of powdered charcoal. When the whole of the metal is thus fused out, which will generally be in some 40 minutes, the silicious residue is raked out, by the upper door, and allowed to slide down the incline into the water below. These furnaces are heated at Schneeberg by wood, and a brisk but well-regulated draught kept up during distillation; the holes in the roof serving to direct the current of heat to each retort. The metal so obtained is not however pure, it gene- rally contains a variable proportion of silver. This may be separated economically by cupellation, just as in the case of silver lead ; and the oxide of bismuth decomposed again by a reduction operation. Indeed bismuth cupels so well, that it may be used to substitute lead for that operation upon the small scale. But the chief impurities of commercial bismuth are BISMUTH. 293 sulphur, traces of arsenic, and also of lead, and iron. If lead, iron, and silver, are not present, the two former impurities are easily got rid of by simply fusing the bismuth with a little nitre, when they will be oxidised and separated. But, perhaps, in all cases the best method of purification is the following : Dissolve the crude metal in nitric acid, and then con- centrate the solution by evaporation. Next pour the clear solution into a large bulk of distilled water. It will be thus decomposed, and a white sparingly soluble powder falls, which is a subnitrate. This is to be removed, and digested for a time in a little caustic potash, whereby any arsenious or arsenic acids present will be dissolved. Next the subnitrate is to be well washed, dried, and heated with about one-tenth its weight of charcoal in an earthen crucible, thus the salt is reduced, and the bismuth sub- sides in the pot in a state of purity. Properties. Bismuth is of a reddish white colour, hard, and readily broken up from its crystalline structure. It crystallises in rhombohedra, nearly approaching the cube, as their angles vary very little from right angles. These may be formed artificially in beautiful masses, by melting a quantity of the metal in a pot, and after removing it into some glowing coals, or heated sand, allowing the bulk to cool slowly ; and in order to prevent the cooling action commencing at the upper surface, the heat of this is kept up by covering the pot itself with a shallow iron basin, into which a quantity of hot fuel is placed. As soon as a crust of metal is presumed to have formed round the sides, this top is pierced at one side by a redhot iron, and the remaining fluid metal poured out. If then when cold the upper covering be sawn off, the whole interior 294 METALS OF THE SECOND CLASS. surface will be found to have crystallised in most regular forms of hollow cubes and tetrahedra. Bismuth fuses at about 510, and when added to other metals it lowers their melting points in an extra- ordinary manner. It volatilises at a high temperature, and may even be distilled, although with some difficulty. If the metal be exposed at a very high temperature, it burns somewhat like zinc, with a blueish flame, giving off fumes of yellow oxide. At ordinary temperatures exposure to air does not affect it; but at a red heat it is rapidly oxidised, and hence the crystals formed as described above always exhibit a beautiful play of colours, dependent upon the formation of a thin film of oxide, by the agency of the air upon them while still hot. Nitric acid dissolves the metal readily ; sulphuric acid only upon boiling ; and hydrochloric acid has but little influence on it. Its specific gravity varies from 9*550 to 9799 according to its condensation, which state may be increased by powerful pressure. Its symbol is Bi. Equivalent, 210. There are three oxides of bismuth. The first, or teroxide, is the base of the salts of this metal. From this an acid oxide may be prepared, sometimes called bismuthic acid ; and, lastly, these two oxides unite to form a third, but this latter may perhaps be properly regarded as a salt, wherein an equivalent of teroxide is united as base, with an equivalent of bismuthic acid, as the acid of the com- bination. The ordinary oxide of bismuth of commerce, or ter- oxide, may be prepared in the dry way, by heating the subnitrate (as formed for the preparation of pure bismuth) in a porcelain crucible to a low red heat ; thus the nitric BISMUTH. 295 acid is driven off, and a yellow powder remains, which is anhydrous teroxide. In the hydrated state this oxide is a white powder, and may be obtained by the addition of ammonia in excess to a soluble salt of bismuth. The composition of the anhydrous oxide is Ei 3 , and its equivalent 234. In the hydrous oxide this is in combination with one equi- valent of water. There is a corresponding sulphide thrown down when we treat a solution of bismuth with hydro -sulphuric acid or sulphide of ammonium : this precipitate when washed and dried is a black powder. But the sulphide may be formed by fusing the proportions of sulphur and bismuth together in a covered crucible; thus prepared it is a metallic-looking solid of a dark grey colour. Composition, Bi S 3 . Equivalent, 258. Alloys. Bismuth readily amalgamates with mercury. Thus, if bismuth is fused, and then twice its weight of hot mercury be added, a pasty amalgam is obtained, which after a time becomes granular, harder, aud partly crys- talline. Gmelin states that as a small quantity of bismuth diminishes the fluidity of mercury very slightly, it is used to adulterate the latter; but the adulteration may be detected by shaking the mercury with air, when a black powder will speedily separate. Bismuth and silver when fused together in equal parts form an alloy tending to the red colour of bismuth. It is very brittle and scaly in texture, and may be cupelled, whereby the whole of the bismuth will be separated by oxidation, and a mass of pure silver left. Bismuth may in like manner be separated from its alloy with gold. Bismuth may be alloyed with platinum, and also with 296 METALS OF THE SECOND CLASS. palladium. The metals being readily fused together. In the former case I part of platinum may be combined with 2 of bismuth, and for this it is better to use finely divided or sponge platinum. Palladium may be combined with its own weight of bismuth. In both the alloy is grey, brittle, and easily fusible. Bismuth and copper may be alloyed, but the mixture renders the copper harder, and brittle in working. Kars- ten states that even O'6 per cent of bismuth will cause the alloy to crack at the edges when hammered. One part of copper with four of bismuth has a thorough red colour, and the scaly texture of bismuth. Bismuth when alloyed with lead produces an alloy of greater density than the mean ; and if the former be added in small quantity only, the lead is rendered more tough, but without becoming brittle; but if the two are combined in equal proportions, the alloy has the properties of bismuth, viz., it is reddish in colour, and brittle and laminar in texture. The alloys of bismuth, formed with lead and tin, constituting fusible metal and some kinds of solders, &c., are the more important ones, and will be described under the article trn. Detection of Bismuth. The salts of this metal are for the most part devoid of colour, some are soluble, others insoluble j the soluble salts redden litmus paper; and when the water is in considerable quantity, and contains but little free acid, they are decomposed and deposit more or less soluble subsalts. In the case of the subnitrate so formed, it is slightly soluble, but the subchloride, on the other hand, is quite insoluble. The above property of forming subsalts is very characteristic. Hydrosulphuric acid, or sulphide of ammonium, throws BISMUTH. 297 down a black sulphide, insoluble in excess of these pre- cipitants. This sulphide is decomposed, and dissolved by strong boiling nitric acid. The alkalis, potash, soda, or ammonia, throw down white hydrated oxide. Upon boiling this precipitate, it becomes yellow. Chromate of potash throws down a yellow chromate of bismuth, which may be distinguished from the corresponding lead precipitate in being soluble in dilute nitric acid, and insoluble in caustic potash. The metals, tin, copper, iron, or zinc, throw down bismuth in the metallic state. And, lastly, if we heat a salt of bismuth with carbonate of soda in the blowpipe- reducing flame, we get a bead of the metal, surrounded by a crust of yellow oxide. This may again be dis- tinguished from lead, by the brittleness of the bead under the hammer. Estimation of Bismuth. This is invariably done as oxide, the precipitation being first effected by an alkaline carbonate, as that of ammonia, the bismuth compound having been previously in solution in nitric acid ; for this precipitant must not be employed to a hydrochloric solution of the metal. The carbonate of bismuth so obtained must be dried and ignited, and is then ready for weighing, 8974 per cent of the whole will be metal. In precipitating a bismuth solution by hydrosulphuric acid the salt is diluted with water containing a little free acetic acid; this prevents a subsalt falling, which would be the case if pure water were used. The sulphide is then thrown down by the addition of H S. Or in place of this treatment, we may take the bismuth solution, and just neutralise any free acid by ammonia, and then precipitate by sulphide of ammonium. In either case 298 METALS OF THE SECOND CLASS. the sulphide cannot be weighed to obtain a correct result, as it is apt to contain free sulphur, consequently the filter and its contained sulphide are treated in a beaker with strong nitric acid and heating. The salt so obtained is diluted with acidulated water, and again filtered, after which the bismuth is precipitated by carbonate of am- monia, as before described. To ensure its complete precipitation by carbonate of ammonia the beaker containing the solution must stand exposed to the air for 3 or 4 hours, because on the first addition of the ammonia salt, some of the carbonate of bismuth formed is redissolved, but by this exposure it will again completely separate. The analysis of a mixture of bismuth and lead is made by dissolving the alloy in nitric acid. Then on adding to this an excess of caustic potassa, the oxides of lead and bismuth will be precipitated, but the lead oxide is at once redissolved by the alkali. The oxide of bismuth is to be filtered out, washed, ignited, and weighed. The filtrate, containing the lead, may next be treated with excess of hydrosulphuric acid, and the sulphide of lead converted into sulphate, as described at page 272. ANTIMONY. 299 CHAPTER XV. ANTIMONY. THE chief ore of antimony is the tersulphide, and this is the source of very nearly the whole of the antimony of commerce, although the metal does occur native; and, besides this, its sulphide is found in combination with that of silver, also with lead and copper, and in various other associations with lead, iron, copper, bismuth, or arsenic. As the sulphide is contained in a matrix consisting of quartz, limestone, and heavy spar (or sulphate of baryta), the first operation preparatory to obtaining the metal consists in separating the sulphide from this gangue, which requires some care, as the antimonial sulphide is very volatile, and consequently much loss will arise if the heat employed be not carefully regulated. In Germany and some of the French works (and these countries supply the bulk of the antimony), the operation is effected in simple reverberatory furnaces, wherein the bed is made concave, and from its lowest point a channel is formed to convey the fused sulphide into proper recep- tacles ; but as in these the above loss may be large 300 METALS OF THE SECOND CLASS. without much care, the plan used at the French mines at Malbose may be given as by far the best method. At these mines the operation is performed in a rever- beratory furnace, but constructed with a dome -shaped arch, that is, arched each way ; under- neath this is placed a set of four fire-clay cylinders or retorts, A, which rise per- pendicularly through rather larger open- ings in the arch ; these openings being covered by fire-clay covers. The cylin- ders stand perpen- dicularly upon the strong cover of an oblong chamber formed below on each side, wherein a crucible, B, is placed immediately below each cylinder for the purpose of receiving the liquid sulphide; which passes from the clay cylinder down into the crucible by a hole in the chamber cover. The grates run from back to front, and are placed on each side of the crucible chambers at about the level of the pots, the heat being allowed to pass into them by flues. In working, the crude ore is put into the clay cylin- ders, and wood fires are kindled upon the grates, the draught of which is kept up by a chimney which rises over each pair of cylinders. As the sulphide fuses out of the ore it passes down, and is received in the crucible ANTIMONY. 301 below ; the latter, being of cast-iron,, is lined with clay, in order to get the cake of sulphide out more easily when cold. The operation upon a charge of ore occupies about 3 hours. The product so obtained is commercial crude anti- mony, which is really a sulphide. From this the metal is obtained by first powdering it, and then heating upon a reverberatory bed, a roasting or dull red heat being employed. By this much of the sulphur is driven off, together with any arsenic which may have been present ; some oxide of antimony is generally lost, also during this roasting. The two former escape as sulphurous and arsenious acids. The residue, which consists of a mixture of teroxide and tersulphide of antimony, is now worked up with one-fifth its weight of charcoal, which has been previously saturated with a strong solution of carbonate of soda. This mixture, placed in crucibles, is heated in a wind furnace to bright redness : thus the metal is reduced and sinks to the bottom of the pots, under a slag composed of sulphide of sodium with sulphide of antimony. This latter is separated from the pure metal and sold as "crocus of antimony." The yield of metal, owing to this and other loss during its extraction, always falls short of the equivalent contained in the ore. The metal itself is known as " regulus of antimony." Chemically pure antimony is best obtained by Woh- ler's method, which is as follows : Four parts of metallic antimony are powdered with two of dried carbonate of soda and five of nitrate of soda. This mixture is heated to redness, when oxidation of the antimony and arsenic (if the latter be present) takes place at the expense of the oxygen of the nitrate of soda, and antimoniate and arseniate of soda are formed. When deflagration ceases, 302 METALS OF THE SECOND CLASS. the pasty mass is kept over the heat for about half an hour, the operator now and then squeezing it with an iron spatula; after which it is removed, and when cold, powdered and thrown into boiling water; this dissolves away the arseniate, while the insoluble antimoniate is left; this is well washed with hot water. It is then removed, dried, and fused with half its weight of crude tartar. The product of this fusion is next broken up and thrown into water : a copious evolution of hydrogen is at once set up from the oxidation of the potassium, for the mass so treated is an alloy of antimony and potassium. The residue of this action is a powder com- posed of antimony, with any iron and lead which may have been contained in the original metal. To remove these, about one-third of the powder is treated with nitric acid, so as to oxidise it ; this portion, when washed and dried, is mixed with the residue of the metallic powder, and the two fused together in a covered crucible, by which the pure antimony is separated and subsides under a slag composed of the foreign oxides. Properties. Antimony is a blueish-white metal, which, from its crystalline nature, readily breaks up, showing beautiful clean facets. The surface of a fused mass of the metal is commonly, when cooled, covered with stellate crystals. It fuses at 840, and volatilises at a white heat. By slow cooling it may be obtained in distinct rhombic crystals. If exposed to air during fusion, it is speedily oxidised; but at ordinary temperatures it is not acted upon by the air. It is soluble in hydrochloric acid aided by heat, hydrogen being evolved ; but by nitric or sul- phuric acid it is oxidised. In the former case a white insoluble oxide results, and in the latter a sulphate also insoluble, sulphurous acid being evolved. Aqua regia, ANTIMONY. 303 like hydrochloric acid, will convert the metal into a chloride of antimony. The specific gravity of antimony is 6-714; its symbol, Sb; Equivalent, 122. Combinations. With oxygen, antimony forms three compounds : the first, or teroxide, has basic properties, and is, indeed, the base of all salts of antimony; the other two have, on the contrary, acid properties. The teroxide is readily formed by oxidising the metal by means of strong sulphuric acid and heat : thus, as has been before stated, on evaporating all the residual acid away, a white powder is left the sulphate of the oxide in question ; but to free this entirely from sulphuric acid, it is digested in a solution of an alkaline carbonate, washed and dried. It may be formed in the dry way by burning antimony in a crucible wherein the air is free to enter : thus white fumes of oxide (or flowers of antimony) may be condensed in convenient vessels. There is also a scarce ore of anti- mony found native, called white antimony ore : this is composed of the teroxide. All salts of this oxide are violently emetic, and the ordinary tartar emetic is formed by combining it with bitartrate of potash, whereby a compound is produced of neutral tartrate of potash with tartrate of antimony. Composition, Sb 3 . Equivalent, 146. Antimonious acid may be obtained as a white inso- luble powder by heating antimonic acid, or nitrate of oxide of antimony to redness. This compound, as also the teroxide, become yellow by heating, but recover their white colour as they cool. This is a combination of one equivalent of antimony with four of oxygen, but regarded by some as a compound of antimonic acid with ter- oxide of antimony, and hence a salt wherein one oxide 304 METALS OF THE SECOND CLASS. plays the part of acid, and the other of base. Thus its composition must be doubled, and taken as Sb 2 8 ; that is, Sb 3 + Sb 5 . Antimonic acid is prepared by heating the metal in aqua regia until dissolved, then evaporating to dryness, and subsequently heating the mass with a fresh portion of nitric acid. Or by boiling antimony in nitric acid to dryness, and then heating to incipient redness. Thus a lemon- coloured powder is left, composed of Sb 5 , which is antimonic acid. It is quite tasteless and insoluble, but reddens moist litmus paper. The compound known as (( butter of antimony" is a terchloride. It may be obtained by digesting sulphide of antimony in strong hydrochloric acid, with the addition of about a fourth its weight of nitric. This is heated until the solution from a deep yellow becomes colourless. If it be evaporated, and the residue then removed and distilled, a white, semi-transparent crystalline solid is obtained, of about the consistence of butter. The retort used must be wide-necked, or the product will con- dense in it and so stop it up. This solid body is very deliquescent, and fuses to a colourless oily liquid, which fumes in the air, and which, when thrown into water, is decomposed, an oxychloride being precipitated. Com- position, Sb C1 3 . Equivalent, 228-5. A perchloride of antimony may be formed by passing dry chlorine over a quantity of powdered antimony, the latter being slightly heated. In this way the metal may be said to be -dissolved by the gas, and a dense liquid is the result. When pure it is white; if it has a yellow tint, it contains chlorine in solution. This is very vola- tile, and evolves white dense fumes on exposure to the ANTIMONY. 305 air. It is a pentachloride, having the composition Sb C1 5 . There are two sulphides of antimony a tersulphide, Sb S 3 , and a pentasulphide, Sb S 5 . The first, or tersulphide, is the one contained in the ordinary ore of antimony. It may also be prepared in the wet way, by digesting Kermes' mineral with tartaric acid. This is a compound of tersulphide and teroxide of antimony, with a portion of potassa. On heating this in tartaric acid, the oxide of antimony and the potassa are both dissolved out, and pure tersulphide is left. Again, when we pass hydrosulphuric acid into an antimonial solution, we get the same substance precipi- tated as a peculiar orange-coloured precipitate. Both this and the pentasulphide combine with sul- phides of the alkalis, and form (by acting as sulphur acids) sulphur salts. What is known as " Kermes' mineral" is a preparation formed by boiling tersulphide of antimony with an alkaline carbonate. In this way a powder is deposited, of variable colour, according to its method of preparation, but being commonly of a brown or reddish brown. The treatment of the sulphide with carbonate of potash is said to afford the largest product, but it is of a finer red colour where carbonate of soda has been employed. Golden sulphide of antimony may be obtained by adding hydrochloric acid to the liquid whence the Kermes has been deposited. Thus the sulphide of antimony retained in solution falls as a fine bright red powder. Both these compounds have been employed medicinally. The pentasulphide is a sulphur compound of the metal, in composition corresponding to antimonic acid, and to the pentachloride. 306 METALS Of 1 THE SECOND CLASS. ' Alloys. The useful alloys of antimony are chiefly those it forms with lead and with tin, constituting the various forms of type-metal, pewter, &c., and these will be considered in the chapter upon Tin. It is, when associated with the noble metals, peculiarly injurious to them as regards their malleability, ductility, &c. Hence such alloys are never made: indeed it may be said to form brittle alloys with all the malleable metals. In regard to gold, its admixture is particularly to be guarded against, for a single grain added to 200 of perfectly fine and malleable gold, will render it completely brittle in texture. Tests for the Detection of Antimony. I. Hydrosul- phuric acid added to an acidulated solution of antimony occasions an immediate precipitate of very characteristic orange-red colour; but if the solution be alkaline no precipitate will be produced, and but a partial one in a neutral solution : hence the sulphide so thrown down is soluble in excess of potassa. 2. Sulphide of ammonium throws down the same, but the precipitate is soluble in excess of the precipitant. It may, when so re-dissolved, be thrown down again by an acid; but its colour is always lighter under these circum- stances, from sulphur being precipitated with it. 3. Potash, or ammonia, or the carbonates of these, throw down a bulky white hydrate, but not if the solution contain tartaric acid. The precipitate, when formed, is soluble in excess of alkali. 4. If the solution be treated with sulphuric acid, and into this metallic zinc be put, the mixture evolves a gaseous compound of hydrogen and antimony (antimo- niuretted hydrogen) ; and if the gas escaping from the jet of a gas-bottle be inflamed, and a plate of cool ANTIMONY. 307 porcelain be momentarily held over this flame, a deposit of metal is formed as a dark leaden-looking spot, just at the point of contact of the flame. Lastly. If a hydrochloric solution of antimony be treated with a quantity of water, an immediate preci- pitate of an oxichloride falls. This may be dissolved in tartaric acid, the addition of which latter to the water employed will prevent its precipitation. This solubility in tartaric acid distinguishes it from the analogous bismuth precipitation. Estimation of Antimony. This can only be done by its precipitation as sulphide, and subsequently separating the sulphur of the latter, after having previously got its weight. Then, by estimating the sulphur, the difference between its weight and that of the whole precipitate gives that of the antimony. We may operate thus: To the hydrochloric solution add a little tartaric acid, and then pass in H S. Thus the sulphide is thrown down. Wash, dry, and weigh this. Next dissolve it in aqua regia; then mix this with a solution of tartaric acid, and precipitate the sulphuric acid (formed by the oxidation of the sulphur of the sulphide) by means of chloride of barium. From the weight of this when washed, dried, and ignited, that of the sulphur is got at; and the loss represents the antimony. 308 METALS OF THE SECOND CLASS. CHAPTER XVI. URANIUM, TITANIUM, AND CHROMIUM. THREE metals of this class may next be examined, but very briefly, as the metals themselves are not employed in the arts ; but some one or more of their compounds used ; and in each case principally as colouring agents in glass and porcelain-working. For this purpose ura- nium affords an orange yellow and also a black ; tita- nium, a light yellow ; and chromium, a green ; and, by modification of treatment, a pink enamel may be obtained from the latter also. URANIUM. The metal itself is a white metal, resembling polished iron, somewhat malleable, and of very high specific gravity. The source of this, as of all preparations of uranium, is principally from a Bohemian mineral called pitchblende, a natural compound of two oxides of ura- nium, the protoxide and sesquioxide. The minerals uranite and chalcolite (containing this metal) are com- paratively rare. From pitchblende a nitrate of the ses- quioxide is first obtained, and from this salt all other compounds are prepared. URANIUM. 309 The mineral is first powdered very finely, and treated at once with nitric acid. The solution so obtained eva- porated to dryness, and the residue subsequently dis- solved in water ; part will remain undissolved, consisting of arsenious acid and sesquioxide of iron, with some sulphate of lead, the whole forming a red insoluble powder. The solution is filtered, in order to separate this ; and then, upon evaporation, will furnish crystals of nitrate of uranium. Hydrosulphuric acid is passed through the mother liquor after removal of the crystals. This will throw down a further portion of arsenic, as sulphide, together with sulphides of copper and lead. The liquor is then filtered, and again evaporated, and set aside for crys- tallisation. Lastly, the whole produce is purified by recrystallisation. If it be desired to obtain the metal, it is done as follows: A portion of nitrate is heated to decomposition. In this way the nitric acid is driven off, and an oxide left. This is mixed with some charcoal, and placed in a combustion tube, with an arrangement for evolution of dry chlorine attached. The tube is then heated and the gas passed into it. Thus it combines with the uranium, and the chloride produced rises in red fumes, which con- dense into deliquescent crystals in a cool part of the tube. This is protochloride of uranium. The next step consists in speedily making a mixture of this with half its weight of potassium ; and the quan- tity operated upon should be somewhat less than 200 grains of mixture, as the reaction of the two is very violent. For this reason also the platinum crucible, in which the reduction is made, should have its lid fastened on, and be quite enclosed in a second and larger pot. A 310 METALS OF THE SECOND CLASS. gentle heat is at first applied, and when the violence of the action is over, this is raised so as to volatilise the remaining potassium and also to fuse the chloride of potassium formed, as well as to allow of the subsidence of the uranium in it. When cold, the excess of potassium and chloride is removed by solution in water, the metal being left. Its equivalent is 60. Symbol, U. There are two simple oxides of uranium, and by their combination with each other two other compound oxides are formed. The first is a protoxide, a very unstable compound, which is readily peroxidised by ex- posure to air ; its composition is expressed by the sym- bols U O. The second oxide is the sesquioxide. This is the one employed for producing the orange-yellow porcelain colour. It is prepared commercially by precipitating the pernitrate by means of ammonia : but it is not then true ; for this oxide has a tendency to act as an acid in the presence of alkalis, and to combine with them and form salts : therefore, in this case it so combines with the ammonia, and a hydrated uranate of ammonia is pro- duced. Moreover, the ammonia and water cannot be driven off by heat, so as to leave the oxide sought, for either the green or black oxide will be left, according to the degree of heat used. The only way to obtain a true sesquioxide consists in precipitating the purified nitrate by oxalic acid; thus a peroxalate is obtained. This is then exposed to the sun's rays, when carbonic acid will be eliminated by the decomposition of the oxalic acid, and a purplish powder is left, which is the green oxide of uranium in a hydrated state. By exposing this to air, enough oxygen will be absorbed to convert the whole into sesquioxide, and from this last the water may be TITANIUM. 311 driven off by heating carefully to 570 Fahr. The anhy- drous sesquioxide thus produced is a dull red powder, of the composition U 2 3 . The operation, however, requires extreme care in all its stages. The black oxide, which is employed for the black enamel, is obtained by heating intensely the pernitrate. Thus a black powder results, which has the composition 2 U + U 2 3 . The green oxide is obtained from the last by oxidising it in the air, by means of gentle heating; but if, when prepared, the heat be raised strongly, it will be reconverted into the black oxide. Its composition is UO + U 2 3 . Discrimination of Uranium. 1st. Hydrosulphuric acid gives no precipitate. 2d. Sulphide of ammonium gives a brownish-yellow sulphide ; but if the uranium exist as protoxide, this will be black. 3d. Ferrocyanide of potassium gives a brown, just like the precipitate formed by that reagent in a copper solution ; but it may be distinguished from the latter by a portion of the solution not being rendered blue on adding ammonia. TITANIUM. The mineral rutile, a nearly pure oxide, is the chief source of the various preparations of this metal. It is a compound of an equivalent of titanium with two of oxygen. In titaniferous iron, and in iserine, this same oxide is associated with that of iron. The metal itself is commonly described as a purplish-red powder ; but it has been shown by Deville, Wohler, and others, that titanium 312 METALS OF THE SECOND CLASS. has an extraordinary affinity for nitrogen, and that the red product of some of the methods employed for its preparation is really a nitride of titanium; as also are the hard, cubic, copper-coloured crystals, frequently found in iron furnaces, and which have hitherto been regarded as the metal itself. These latter contain, moreover, a certain quantity of cyanide of titanium (cyanogen being itself a compound of carbon and nitrogen). Deville obtains the metal in square prismatic crystals, by first forming a bichloride of titanium; for which purpose he heats a mixture of titanic acid and charcoal in a tube, and passes over this a stream of dry chlorine gas. Having thus obtained a volatile liquid (a bichlo- ride) he passes its vapour over fused sodium, and thus gets the metal itself. It is also obtained by decomposing the double fluoride of titanium and potassium, by means of hydrogen : thus formed, it is a pulverulent metal of a greyish tint. It is, however, very quickly oxidised, and converted into titanic acid by a slight rise of temperature, while exposed to air. Symbol, Ti. Equivalent, 25. Titanium forms three oxides, but it is only the highest (viz. titanic acid) which is of importance, this being the one employed to obtain a pale yellow porcelain colour. Rutile, being nearly pure titanic acid, is employed for its preparation ; for which purpose it is powdered, and mixed with three or four times its weight of bicarbonate of potassa. These are put into a crucible and fused, and the mass so obtained subsequently digested in water. Every two equivalents of titanic acid will in this way have combined with one of potassa, and formed an insoluble salt, which is to be separated and treated with hydro- TITANIUM. 313 chloric acid, and when dissolved, an excess of caustic ammonia is to be added to the solution. Thus a mix- ture of titanic acid with oxide of iron, and perhaps tin, and manganese is thrown down, in which the three latter may be converted into sulphides on adding sulphide of ammonium, and that without action upon the titanium oxide, which remains as such. Next, a quantity of sulphurous acid in solution is poured upon the mixture, whereby the sulphides will be dissolved, and the titanic acid left. It only remains to wash thoroughly and dry it, and thus it is a pure white hydrate of titanic acid. This compound is soluble in sulphuric and hydro- chloric acids, but if heated strongly it assumes a yellow tint, and becomes anhydrous. On cooling it resumes its white colour, but will then be insoluble, except it be boiled in strong sulphuric, or digested with hydrofluoric acid. Composition, Ti 2 . Equivalent, 41. Discrimination of Titanium. The acid, from its ap- pearance and chemical bearings, may be confounded with that of tin, or with silica. From the former it may be distinguished by heating it before the blowpipe. Tin, when heated in the reducing flame, would, on the addi- tion of a little carbonate of soda, be at once reduced to a metallic bead. But titanic acid, if mixed with borax or microcosmic salt, and exposed to the same flame, would give a blue glass. If heated in the oxidising flame, the glass formed is colourless. It may be distinguished from silica by fusion with bisulphate of potassa, by which it will be rendered soluble, so as to form a clear solution on boiling in water; silica being untouched by such treat- ment. 2d. If a solution of a titanate be tested by ferro- cyanide of potassium, an orange-yellow precipitate is formed, which is very characteristic. 314 METALS OF THE SECOND CLASS. CHROMIUM. This metal exists in an ore known as chrome iron ore, which is a mixture of sesquioxide of chromium with oxide of iron. From this, the first preparation obtained is always chromate or bichromate of potassa, and all other compounds are separated or converted from the latter. This is the result of the large application of bichromate of potassa to calico-printing and dyeing, which causes its manufacture to be an important one : it is largely carried on at Glasgow, and the product sold under the name of chrome. The metal is obtained by first forming a sesqui chloride of chromium, and then decomposing it by potassium ; thus it is obtained pure, as a dark grey powder, readily oxidisable by heating in the air. It may, however, be obtained nearly pure by heating a mixture of oxide of chromium with one-fifth its weight of carbon. This is to be made into a paste with oil, and then heated for about two hours in a wind furnace ; thus a porous mass of the metal is left, containing, however, a small quantity of combined carbon. Symbol, Cr. Equivalent, 26*27. It has been stated that the compounds of chromium are obtained from chrome iron ore, by first forming a bichromate of potassa. Now, as the ore is not attacked by acids at all easily, the first step in this preparation is powdering it ; after which it is mixed with sufficient nitre to oxidise the chromium; a quantity of carbonate of potassa being also used : these are exposed to a red heat in a reverberatory furnace, and during the heating constant raking is kept up, in order to expose the whole well to air, and so facilitate the changes to be produced. Thus the sesquioxide of chromium, by the oxygen of the CHROMIUM. 315 nitre, becomes converted into chromic acid ; this decom- poses the carbonate of potassa by combining with its alkali. The roasted materials are next digested in water ; thus the new-formed salt is dissolved, and an insoluble residue left : but as the latter is not yet exhausted of the " chrome," it is set aside for a second treatment. The yellow solution is filtered or syphoned off, and just neutralised with nitric or sulphuric, or better, with acetic acid. Thus the salt, which originally was a neutral chromate, is converted into a bichromate, which being a far less soluble salt than the former, much contributes to its purification from adherent nitrate of potassa. Hence also the preference to be given to acetic acid in its preparation, for with potassa this acid forms an exceedingly soluble salt, much more so than nitrate of potassa, which results from using nitric acid; while sulphate of potassa, which is formed where sulphuric is employed, is yet more insoluble, and, therefore, economy in the price of acid is the only reason for employing the latter. The bichromate of potassa so obtained forms beautiful red four- sided tabular crystals, from which neutral chromate is best formed by dissolving them, adding an equivalent of carbonate of potassa, and re- crystallising. Chromium forms four oxides. The two first, viz. the protoxide and sesquioxide, have basic properties. The other two are acids, viz. chromic and perchromic acids. Of these, the one employed as a porcelain colour is the sesquioxide in its anhydrous state, wherein it is but little acted upon by acids, and may be employed with most fluxes, and so heated strongly without change. It may be prepared by several methods, but of these the three following may be taken as most practical. 316 METALS OF THE SECOND CLASS. 1st. Bichromate of potassa is put into a crucible, and heated to a white heat. Thus it is converted into neutral chromate, and the equivalent of chromic acid taken away, loses as much of its oxygen as leaves it in the state of sesquioxide of chromium. The fused mass is treated with water; by this the chromate is dissolved, and the oxide remains as a green powder. 2d. Chromate of potassa is added to a solution of subnitrate of mercury; thus a precipitate is formed of chromate of suboxide of mercury. This is washed, dried, and heated to redness. The whole of the mercury is thus volatilised, and with it a portion of the oxygen ; the sesquioxide of chromium being left. 3d. Bichromate of potassa may be heated in a char- coal-lined crucible, or in an ordinary pot, if previously mixed with one-fourth its weight of starch, both being powdered together. This, by oxidation, produces car- bonic acid, which converts the chromate of potassa into carbonate; the sesquioxide of chromium, resulting from the decomposed chromic acid, will be separable by washing away the alkaline carbonate. Sesquioxide of chromium is a deep green powder. In its anhydrous state it is little soluble in acids; but when hydrated, as when precipitated by the action of alcohol on bichromate of potassa, it dissolves readily in acids, forming uncrystallisable salts. The anhydrous variety produces a deep green enamel upon porcelain when used alone, but a beautiful rose-pink may be obtained also. In the pink colour, however, it is probable that the oxide is one of higher degree of oxidation. The material for its production is thus prepared: Four parts of chromate of potassa are mixed with 34 parts of chalk and 100 of peroxide of tin. These are CHROMIUM. 317 heated to redness in a crucible, and the resulting mixture powdered, and then treated with weak hydrochloric acid until it assumes its proper tint, viz. a fine rose-pink. This is much used in earthenware painting. Composition of sesquioxide of chromium, Cr 2 3 . Equivalent, 76*5. In the discrimination of chromium the reactions vary according to the degree of oxidation of the metal; but the following tests are indicative of the sesquioxide in solution : ist. Hydrosulphuric acid gives no precipitate. 2d. Sulphide of potassium throws down the green sesquioxide, and not a sulphide. 3d. Potash or ammonia precipitates a hydrated sesqui- oxide. The precipitate is soluble in excess of the former, but it will be reprecipitated again on boiling. In the case of ammonia, although it is partially redissolved, boiling will completely precipitate the oxide again. 4th. If sesquioxide of chromium be fused with nitrate of potassa, chromate of potass is formed ; which latter, as all salts of chromic acid, may be distinguished by the yellow precipitate they give in salts of lead, and the red one in a solution of nitrate of silver. 5th. Before the blowpipe, if heated with microcosmic salt in either flame, a glass is produced, which is yel- lowish-green while hot, and emerald-green upon becoming cold. 318 METALS OF THE SECOND CLASS. CHAPTER XVII. ARSENIC. THE metal arsenic is not commonly employed in its reguline state, but it may be obtained from its most common compound, viz. arsenious acid (the white arsenic of the shops), by simply heating the latter with black flux, or with powdered charcoal. For this purpose an intimate mixture is made of the two, and placed in a crucible ; upon this a second one is luted, and just down to the lute -junction a perforated plate of iron is slipped over the upper one : this protects the latter from heat during the reduction of the metal. The lower pot is then well heated up, and the reduced arsenic, being volatile, sublimes, and is condensed in the upper, cooler pot. Thus it forms a steel-grey brittle cake ; but it soon loses its brilliancy, and, if exposed to damp air, it crumbles, and partly decomposes. It is regarded by Regnault as a metalloid, and not a true metal ; and this is the general opinion of French chemists. The arsenic of commerce is frequently obtained as a secondary product; but when directly procured, it is ARSENIC. 319 generally from a mineral called mispickel, which is an arsenide of iron, combined with an equivalent of bisul- phide of the same metal ; and the treatment of this ore is directed so as not to obtain the metal itself, but arsenious acid. For this purpose, at the Silesian works the ore is first roasted in a furnace constructed with a large muffle- like chamber, so placed, as that the flame and heat of a separate fire shall well circulate round it. About half a ton of the powdered ore is placed in the muffle at a time, being spread evenly over the floor. A dull red heat being got up, it is steadily maintained for about 12 hours, towards the latter part of which time it is allowed to fall somewhat. From the back of the muffle an opening passes into a large condensing room a large chamber placed behind the furnace; from this any uncondensed matters pass to a second and third, and again from these into the first of a series, called at the Silesian works " the poison-tower," and composed of some three floors of double chambers. From the last and upper one a flue passes out into the air, and by this much sulphurous acid (which is uncondensable) passes away. The con- tinual current passing through the apparatus serves to waft the arsenical vapours into the chambers ; and they will be all condensed, the products in the first chambers being the purest, those condensed farthest from the muffle being generally contaminated with sulphide of arsenic, from combination with sulphur. This first product is therefore submitted to sublima- tion. For this purpose a series of deep iron or earthen pots are set in ordinary stove-holes, the latter working into a common shaft or flue. Upon the flange formed to each pot is built up a series of ring-connecting pieces, 320 METALS OF THE SECOND CLASS. and on the top of these a funnel-shaped connector rises up and terminates in a large condensing chamber, formed well up above all. The pots are charged with the crude acid, and then all joints well luted up. A gentle fire is then got up to each, and, after about half an hour, raised and main- tained at a proper heat for subliming the acid. After about 12 hours a charge of about 3 cwt. will all have worked up into the cylinders above the pots, where it is found as a vitreous mass, if the heat has been well managed. The upper portions, again, being less pure, are reserved for re-sublimation with a fresh charge of rough acid. The condensing chamber above serves to retain any which may rise if too great heat has been used, as also the sulphur products separated from the rough acid. Arsenious acid, as thus prepared, is a clear, semi- transparent solid, lamellated, as might be expected, from its gradual deposit by sublimation. By exposure to air it soon loses its transparency and whiteness. In commerce it is usually sold as a white powder, which, when examined by a lens, is found to consist of minute crystals. It combines with bases as an acid, and in this way forms many valuable salts. Thus arsenite of potass, the essen- tial ingredient of " Fowler's solution," forms a medicine much used internally. The arsenite of copper, known as ' ( Scheele's green," constitutes a valuable pigment ; and there is a somewhat similar one, composed of three equivalents of arsenite of copper combined with one of acetate of copper. Arsenious acid is powerfully antiseptic, preventing decomposition in organic substances. Arsenious acid dissolves in hot hydrochloric, but by ARSENIC. 321 treating it with nitric it is converted into an acid of higher grade, viz. the arsenic acid. This forms a white mass, which is capable of crystallisation; but both in this, as in its amorphous state, it is very deliquescent. It is a compound of As 5 . The composition of arsenious acid is As 3 . Equi- valent, 99. The bodies known as orpiment are sulphides of arsenic. The red variety, or realgar, is found native, and at times in a crystalline state ; at others it forms a scarlet amor- phous substance, which, when powdered, gives an orange- yellow powder. It is a bisulphide, consequently composed of As S 2 ; and, when formed artificially, it is effected by heating together the equivalent proportions of arsenious acid and sulphur. Yellow orpiment is a tersulphide, also found, at times, native, but prepared artificially by passing hydrosulphuric acid gas through a solution containing arsenious acid. Thus it falls as a brilliant yellow powder, consisting of As S 3 . If this same plan be followed with a solution containing arsenic acid, a similar precipitate will be obtained, but composed of As S 5 , and known as sulph- arsenic acid, or pentasulphide of arsenic. Arsenic forms alloys with other metals, and, in so doing, it lowers their fusing point; but in all cases it renders them very brittle, even when combined in very small proportion. It is most destructive to the malle- ability of gold. Discrimination of Arsenic. ist. An acid solution will, if arsenic be present, give a yellow precipitate on the addition of hydrosulphuric acid. This precipitate is nearly insoluble in hydrochloric acid, but soluble in alkalis or their carbonates. 3.22 METALS OF THE SECOND CLASS. 2. Spongy gold for plugs, 239. Stannic acid, 385. Stearine for electro-moulds, 453. Steel, 344.. Analyses by Mushet, 344. Berthier, 345. Bessemer's process for, 350. Blistered, 347. Cast, 348. Discrimination of, from iron, 360. forging for hardening, 356. Formation of, 345. hammer hardening, 349. hardening, 352. Cooling down for, 354. Precautions in, 355. Shear, 348. Taranaki, 350. Tempering, 357. Tilted, 348. Stourbridge bricks, 87. clay, 88. Strontia reactions, 428. Sublimation, 65. Subsalts, 53. Sulpharsenic acid, 321. Sulphides, 44. Sulphur salts, 55. Temperatures, Measurement of high, 106. Tempering steel, 358. Tin alloys, 387. Eichloride, 386. Bisulphide, 387. Discrimination, 393. Estimation, 394. History, 378. Impurities in, 381. Liquation of, 381. Metallurgy, 378. ores, 378 Peroxide, 385. plate, 393. Preparation of pure, 382. Properties, 383. Protochloride, 386 Protoxide, 384. Protosulphide, 387. Sesquisulphide, 387. smelting, German method, 381. Titanic acid, 312. Titanium, 310. Discrimination of, 313. Metallic, 312. Nitride, 312. Touchstone, Assay by, 223. Turner's yellow, 269. Type metal, 391. Uranium, 308. Black oxide, 311. Chloride, 309. Discrimination of, 311. Green oxide, 311. Nitrate, 309. Oxides, 310. Sesquioxide, 310. 462 INDEX. Vermilion, 126. Voltaic battery, 437. Cause of loss of power in, 439. Daniell's, 440. Grove's, 439. " Intensity," 437. Smee's, 439. Circuit of one metal, 435. Deposition of copper, 446. gold and silver, 447. Volta plating, 450. Temperature for working, Wad, 372. Water gilding, 218. Watt, Composition for electro-moulds, 452. Wedgwood's pyrometer, 106. White lead, 269. Wind furnace, 80. Wood as fuel, 98. ash after combustion, 98. Wollaston's method of working platinum, 242. Zinc, its alloys, 403. Amalgamation of, for electro-pur- poses, 435. Chloride, 403. Discrimination, 406. Estimation, 406. History, 397. Metallurgy, 398. ores, 397. Oxide, 403. Preparation of pure, 401. Properties, 402. Redistillation, 401. Sulphide, 403. 463 ERRATA. Page 4, line 7 from bottom, for C. read Ce. 10, ,, 2 from bottom, for 1773 reaa> n 13, ,, 2, and 14, line 3, /or 1000 read I'ooo. 15, ,, 9 from bottom, transpose " till correct " to next line, after " cooling down." ,, 19, ,, 14 from bottom, insert after "copper are," " somewhere about." 24, 3 from bottom,/or" electricate" read" electric." ,, 46, ,, 8, /or " photosulphide " read " protosulphide." t> 49 f > 8, ,, 9, at the end, insert " the." 357> , 13 from bottom, iwser/ a comma after " mentioned." LONDON- THIS BOOK IS DUE' ON THE LAST DATE STAMPED BELOW AN INITIAL FINE OF 25 CENTS WILL BE ASSESSED FOR FAILURE TO RETURN THIS BOOK ON THE DATE DUE. THE PENALTY WILL INCREASE TO SO CENTS ON THE FOURTH DAY AND TO $1.OO ON THE SEVENTH DAY OVERDUE. * OCr ** IS39 LD 21-20m-6,'32 YB 1561