| about 3 feet in height. The roof was arch- The pipe discharged into a square tower in ed, with an opening through it for the pipe masonry, and in this the particles were which conveyed away the vapor and products washed and cooled by a continual falling of combustion. The sole was formed of cast- sheet of water. The light flocculent oxide iron plates, which were perforated full of small of zinc was not carried down by this to any holes for admitting the blast to penetrate great extent, but was drawn on by the exevery portion of the charge, as the wind was haust through 3 large pipes to a second tower driven by two large fan-blowers into the re- with three divisions, in which the fans were ceptacle under the furnace corresponding to placed that created the draught. From this the ash-pit. The ores were prepared by first the current, still propelled by the fans, moved crushing them to powder, which was done by on through other pipes that connected with passing them through two pairs of Cornish the system of flannel bags, which in great rolls, and then mixing them thoroughly with numbers, and of extraordinary sizes, were susabout half their weight of the dust of anthra- pended throughout the portion of the buildcite. A fire was kindled upon the grate-bars ing devoted to the final cooling of the oxide, of 250 lbs. of pea coal, and when ignited to and filtering it from the gaseous matters interfull whiteness the charge of 600 lbs. of ore, mixed. Some of the bags extended the whole mixed with 300 of coal dust, was added, and length of the rooms, which were 120 feet when exhausted the charge was withdrawn, long by 64 wide, and the diameter of the largleaving only sufficient coal to ignite the next est of them was over 4 feet. They were archarge, thus working off 4 charges in every ranged near together, and some were carried 24 hours. The proportion of oxide obtained vertically from the horizontal ones up to the from the ore was variable, as the charge was roof. Through the pores of the flannel the not of uniform quality; but it was usually gases escaped, and the oxide of zinc remained between 30 and 40 per cent. As the coal thoroughly purified. Nearly 200,000 square rapidly consumed from the effect of the blast, feet of flannel were worked into these bags; the ores were decomposed, and metallic zinc and one person was almost constantly emsublimed. The vapor rose with the gaseous ployed with a sewing machine, and two others products of combustion, and all were carried working by hand, in making and repairing up the pipe, which just above the roof of them. Along the under side of the horizontal the stack terminate under an inverted fun- bags pipes of cotton cloth, ten or twelve inches nel, the base of which covered the lower pipe in diameter, reached down nearly to the floor, like a hood, and the upper portion was a and were kept tied around their lower ends. pipe like that below. A strong current of These were called the teats; and the oxide of air was created by two exhausting fan- zinc was collected by lifting up the portions blowers, at the other extremity of the ap- of the bags where it had settled, and shaking paratus, and the vapors were drawn up to- the e so as to make it fall into the teats. The gether with much air which flowed in around ends of these were then opened, and the the open base of the funnel, and caused at white zinc was received in strong bags, this point a vivid combustion of the zinc which being tied up were laid upon a truck, vapors, which burned with a pale blue flame, and this was run by steam power back and and were thus converted into oxide. The forth under a compressing roller. The air appearance presented by this combustion dispersed through it, rendering it so-light actively going on in full view under each and bulky, was thus expelled, and the oxide hood was very striking, and was far from was converted into a dense, heavy powder. suggesting to an observer unacquainted with The last process was to grind this with the process, the possibility that from the bleached linseed oil, which was done in the pale flames rushing up the pipes any valua- ordinary paint mills. The paint was then ble product could be recovered. The pipes transferred into small kegs for the market. connected above with a cylindrical sheet-iron receiver that extended over the three stacks, so as to secu e the products of all the furnaces. It was a huge pipe, 6 feet in diameter, and 130 feet long, and passed along under the roof, against a line of windows on each side, through which air was admitted for hastening the cooling of the products. The residuum of the furnace charge, when of red oxide, consisted of some unsublimed zinc ore mixed with franklinite and more or less unconsumed coal. It was raked out in the form of slags, and accumulated in immense piles about the works. In 1853, Mr. Detmold succeeded in using this as an iron ore, and produced excellent iron which proved to be also well adapted for the manufacture of steel. The iron manufacture has been continued, and has become a profitable branch of the operations of the United States Zinc Company, producing about 2000 tons of zinc per annum. The franklinite itself had been used a year earlier for the same purposes by Mr. Edwin Post, at Stanhope, and from this he obtained both iron and steel; but when the manufacture was undertaken upon a large scale by the New Jersey Franklinite Company, at Franklin, New Jersey, it proved unsuccessful in practice. The product of the zinc works of the Passaic Company for the year 1856, was 2,327,90 lbs. of oxide of zinc; and the monthly production for the year 1860 was about 400,000 lbs. from 16 furnaces. With the 24 in blast their monthly capacity was from 280 to 300 tons of 2000 lbs. to the ton. The total annual product of the three establishments was from 6000 to 7000 tons of oxide. For a few years the zinc paints were popular, and made considerable inroads upon the market for white lead; but the general verdict of intelligent and skilful painters is that they are inferior to the lead both in body and permanency, and their sale has fallen off 1849, over 6000 public and private buildings had been painted with his preparations, and the testimony was very strong in their favor. Not one of his workinen had been attacked by the painter's colic, though previously a dozen or more suffered every year from it. The colors were pronounced more solid and durable than the old, were made brighter by washing, and were not tarnished by sulphuretted hydrogen, as occurs to white lead. The best white paint was moreover so pure and brilliant a white, that it made the best white lead paint by its side look disagreeably yellow and gray. No dif ficulty was experienced in making the new colors, mixed with the prepared oil, dry rapidly without the use of the ordinary dryers of lead compound; and used in equal weight with lead, the zinc was found to cover better, and was, consequently, more economical at equal prices per lb. The English, however, found many objectionable qualities in the new paint. Its transparency, which is the cause of its brilliancy, by reflecting instead of absorbing the light, was regarded as a defect, and the painters complained that it had not the body or covering properties of the carbonate of lead. It would not dry rapidly for the second coat without the use of the patent dryers, which contain lead, and therefore it was no better than the lead. Messrs. Coates & Co., who now import into Great Britain about 1000 tons of oxide of Re-exported. zinc per annum, wrote to the editor of the $14,912 Lancet in March, 1860, that the consumption 26,383 of white lead is still nearly 100 to 1 of white 19,100 zinc, and that in 1856 the importation of the latter amounted to only 235 tons. They as3,973 cribe the real cause of the larger consumption 47,790 of white lead, to the almost entire exclusion of 38,108 zinc, to the fact, that white lead can be adul18,028 terated with barytes and other cheap ingre4,022 dients without the adulteration being detected 833 by the eye, thus securing large profits to the The importance of the application of white manufacturer and contractor, which cannot zinc to painting in the place of white lead be realized in the use of zinc paint, for the appears to have been much more fully appre- reason that it has little affinity for foreign subciated in France and the United States than in stances. The experience of the manufacturers Great Britain. Soon after the discoveries of of the United States does not substantiate Leclaire that white oxide of zinc could be this statement as to the difficulty of using the thus used, and produce, with the colored oxide of zinc in mixture with other substances. bases he prepared of this and other innocu- It is employed not only alone, but mixed ous oxides, all the tints required, the French with either barytes or white lead, or with government, recognizing the importance of both of them; and large quantities are thus his inventions, conferred upon him the cross sold and give satisfaction to consumers, who of the Legion of Honor, and adopted the would reject the paint, if they supposed it to paints for the public buildings. By the year be any thing else than white lead. As to its at least nine-tenths since 1865. The rate of the importations of zinc, spelter and manufactures of zinc, with the re-exports of the same from 1859 to 1870, both inclusive, were: 1859 1860.. 1861. 1862.... 1863... 1864.. 1865 1866.... 1887. 1868.. 1-69 1870... Imported. $1,333,112 801,358 590,280 254,033 518,149 675,931 351,876 1,149,895 562,902 561,638 1,197,682 1,003,482 563 4,681 3,174 covering quality, it is found that the oxide of zinc varies according to the manner in which it has been prepared. The light flocculent oxide mixes readily with oil without grinding; but though pressed, it covers much less surface than the same oxide moulded when moistened with water, and dried by artificial heat. This preparation also causes any yellowish or greenish tints to disappear, and the article may be supplied to the consumer in cakes, which when ground with oil will cover more surface than the same weight of white lead. The body of the white zinc may be still further improved by calcination before grinding. The inferior colored sorts of oxide of zinc, such as are collected in the iron receivers near the furnaces, and that made from the pulverized ores of zinc, have been largely employed for painting iron surfaces, especially on board of ships, the paint being found to possess a peculiar quality of protecting the iron it covers from rusting.. Besides its use as a paint, oxide of zinc is applied to the preparation of the mastic for rendering metallic joints tight; and to that of glazed papers and cards, for which white lead and carbonate of barytes have heretofore been used. The French use it in preparing the paste for artificial crystals instead of oxide of lead or other metallic oxides; and they have also made with it some of the finest sorts of cut glass and especially lenses. In the Great Exhibition of 1851, an award was made to specimens of zinc glass which presented a very pleasing and white appearance, and were regarded as especially suited to achromatic purposes. It was remarkable for its being purer and more pellucid than lead glass, and also of greater specific gravity. A patent has been granted in the United States for the manufacture of flint glass with oxide of zinc, and specimens of glass were produced with it in 1860, which were remarkable for their brilliancy and beautiful surface, or "skin," as it is called. The glass is more infusible than that made with oxide of lead, and there seems to be no good reason to prevent it coming rapidly into use. CHAPTER VI. PLATINUM. ALTHOUGH this metal is not obtained in large quantity in the United States, it is found associated with the gold in many lo calities in California and Oregon, and has been detected in Rutherford county, North Carolina, and in traces in the lead and copper ores of Lancaster county, Pennsylvania. From the states on the Pacific it has been supposed that it would yet be afforded as a commercial article. It is a metal of considerable interest from the extent to which it is used in the United States, and the success that has attended the attempts to work it in Philadelphia and New York. The metal is supplied to commerce from no certain source, and finds its way into the United States in a great variety of forms, as in native grains found in washing the gold deposits of Cauca on the western coast of South America, of Brazil, and Oregon, and in manufactured articles imported from Europe and chiefly from France. Russia produced between the years 1824 and 1845 many times as much platinum as all the rest of the world, and introduced the metal into her coinage; but after 1845 it was no longer coined, and the yield of the deposits in the Ural has dwindled away to almost nothing. The supply from Borneo has been very large for some years, the whole product of the island sometimes amounting to 600 lbs. a year. It is found in small grains and lumps in the sands that are washed for gold; and pieces of several pounds have been met with in Siberia, the largest weighing over 22 lbs. troy. The properties which give to the metal its great value, as its power of resisting the ef fects of heat and many of the most powerful chemical agents, also render it exceedingly difficult to work and to convert into useful shapes. The crude grains are generally alloyed to the amount of about 20 per cent. of their weight with the very refractory metal iridium, with osmium, rhodium, iron, and sometimes other metals also. It is separated from the chief part of these and purified by dissolving the grains in aqua regia, a mixture of nitric and hydrochloric acid, and causing the metal to be precipitated by sal-ammoniac. It falls in a yellowish powder, which is a compound of platinum, ammonia, and chlorine. To decompose this the compound is separated from the liquid, and being well washed and dried, is heated red hot in a castiron crucible. This drives off the ammonia and chlorine, and the platinum remains in the crucible in a spongy condition. This is condensed into solid metal by repeated heatings and hammerings. It has always been a matter of great difficulty to raise sufficient heat to soften the platinum, even in quantities less than an ounce, so that it could be worked under the hammer. It used for merly to be brought into a metallic cake by making a fusible alloy of it with arsenic, and then burning out the latter as much as possible, and hammering or rolling the cake into sheets, but the arsenic remaining in the platinum always injures its quality. Dr. Robert Hare, of Philadelphia, was the first to fuse the metal for any practical purpose, and in May, 1838, he exhibited a cake of about 23 ounces, which was run together from grains and scraps by means of the intense heat produced by his oxy-hydrogen blowpipe. From a reservoir of oxygen, and from another of hydrogen, a gas-pipe conveyed the gases into one tube, in which they were mixed just back of the igniting jets; and in this the explosive mixture was kept cool by ice around the tube. Explosion was moreover guarded against by the extreme fineness of the apertures through which the gases were made to pass. This means of working platinum has been applied very successfully by Dr. E. A. L. Roberts, of Bond street, New York, in the preparation of platinum plate and various articles in this metal employed by dentists, such as the plates and fastenings for sets of artificial teeth, and the little pins which secure each tooth in its setting. The annual consumption of these last, it is estimated, amounts throughout the United States to about $60,000 in value, which is nearly of the annual supply of the metal. The apparatus consists of two cylindrical copper gas-holders, one for hydrogen, holding 220 gallons, and one for oxygen, holding 80 gallons. The Croton water, with a pressure of about 60 lbs. upon the square inch, is admitted into the bottom of these gas-receivers, for propelling the gases as they are required. The discharge pipes have each at their extremity a short brass tube, which is full of pieces of wire of nearly the same length as the tube, jammed in very tightly. These unite in another brass tube which is packed in a similar way, and connects by a metallic pipe of only inch bore, with the burner. This is a little platinum box, one end of which terminates in a disk of platinum or copper by 4 inch in size, perforated with Vay 21 very minute holes in 3 rows. This box is buried in plaster of Paris mixed up with fibres of asbestus, forming a lump sufficiently large to contain around the box a receptacle into which, by means of flexible pipes, a current of water is admitted and discharged on the same principle that the water-tuyeres of iron forges and furnaces are constructed and kept cool while in use. The burner points downward, so that the jet is directed immediately upon the face of the metal held up beneath it. The method of using the apparatus is as follows: the platinum scraps being first consolidated by pressure in moulds into compact cakes of 10 to 20 ounces each, these are placed upon a plate of fire-brick, and brought to a full white heat in a powerful wind furnace. The plate with the platinum is then removed from the furnace and set in a large tin pan thickly lined with asbestus and plaster of Paris, and is brought directly under the jet, which at the same time is ignited. The platinum immediately begins to melt upon the surface, and the pieces gradually run together into one mass as the different parts of the cakes are brought successively under the jet. Though the metal melts and flows upon itself, it cools too rapidly to be cast in a mould; nor is this necessary or desirable for the uses to which it is applied. These require a soft and tough material, while the fused metal is hard and sonorous, and of crystalline texture, breaking like spelter. It is made malleable and tough by repeated heatings and hammerings. It is introduced into the muffle of the assay furnace constructed by Dr. Roberts especially for producing the high heat required in these and similar operations, and is heated so intensely that when the door of the furnace is opened the cake of metal is too dazzlingly hot to be visible. It is then taken out with tongs plated with platinum, and hammered with a perfectly clean hammer upon a clean anvil, both of which should be as hot as possible without drawing the temper of the steel. If the process is one of welding, when the platinum has cooled so as to be distinctly visible, it should be heated again, for in this condition every blow tends to shatter and shake it to pieces. The lump is forged by hammering it to a thickness of about 4 of an inch, and then being again heated very hot, is passed instantly through the rolls. It is thus obtained in sheets, which are easily converted into the various uses to which the metal is applied. Upon the opposite page, the apparatus employed and manner of conducting the operations are exhibited in the wood-cut; |