530 



METALLUEGY. 



led to immense industries in electro-metallurgy 

 and electro-plating. The extent of them may 

 be gathered from the fact that there are 172 

 electro-platers in Sheffield and 99 in Birming- 

 ham. The term electro-metallurgy was orig- 

 inally applied to the electro-deposition of a 

 thin layer of one metal on another; but this is 

 now known as electro-plating. In 1839, Ja- 

 cobi in St. Petersburg and Spencer in Liver- 

 pool laid the foundation of all we know of 

 these interesting arts. Copper was deposited 

 by them so as to obtain exact reproductions of 

 coins, metals, and engraved plates. The fine 

 metals, gold and silver, are deposited in thin 

 layers on coarser metals, such as German sil- 

 ver, in immense quantities. Christofle, in 

 Paris, deposits annually six tons of silver upon 

 articles of use and of art. The whole of the 

 copper - plates used in Southampton for the 

 production of the Ordnance Survey maps are 

 deposited by current on matrices taken from 

 the original engraved plates, which are thus 

 never injured or worn and are always ready 

 for addition or correction, while the copies 

 may be multiplied at pleasure and renewed at 

 will. Nickel-plating, by which the readily 

 oxidizable metals like iron are coated with a 

 thin layer of the more durable material, nickel, 

 is becoming a great industry. The electro- 

 deposition of iron, as devised by Jacobi and 

 Klein, in the hands of Prof. Roberts- Austen, 

 is giving very interesting results. The designs 

 for the coins which were struck at the mint 

 on the occasion of the Jubilee of the Queen, 

 were modeled in plaster, reproduced in in- 

 taglio by the electro- deposition of copper, 

 and on these copper molds hard, excellent iron 

 in layers of nearly one tenth of an inch was 

 deposited. 



Attention has been given by Prof. "W. Chand- 

 ler Roberts- Austen to the allotropic states of 

 metals. Joule and Lyon Playfair showed, in 

 1846, that metals in different allotropic condi- 

 tions possessed different atomic volumes. Mat- 

 thiessen came to the view in 1860 that in cer- 

 tain cases when metals were alloyed they 

 underwent allotropic changes. Instances of 

 allotropy are observed in Bolley's lead, which 

 oxidizes readily in air ; Schutzenberg's copper ; 

 Fritsche's tin, which falls to powder when ex- 

 posed to an exceptionally cold winter ; Gore's 

 antimony ; Graham's palladium ; and allotrop- 

 ic nickel. Joule proved that when iron is re- 

 leased from its amalgam by distilling away the 

 mercury, the metallic iron takes fire on expos- 

 ure to the air, and is therefore clearly different 

 from ordinary iron or an allotropic form of the 

 metal. Moissan has shown that similar effects 

 are produced in the case of chromium and 

 manganese, cobalt, and nickel, when released 

 from their amalgams. Allotropy also appears 

 in metals released from solid alloys. Certain 

 alloys may be viewed as solidified solutions, 

 and when they are treated with a suitable 

 solvent it often happens that one constituent 

 metal is dissolved and the other is released in 



an insoluble form. If a certain alloy of potas- 

 sium and 10 per cent, of gold is thrown upon 

 water, the potassium takes fire, decomposing the 

 water, and the gold is released as a dark pow- 

 der. One form of this black or dark-brown 

 gold appears to be an allotropic modification 

 of the metal as it combines with water to 

 form auric hydride. If this dark gold be 

 heated to dull redness it readily assumes the 

 ordinary golden color. The Japanese produce 

 with this gold, by the aid of certain pickling 

 solutions, a beautiful patina on copper which 

 contains only 2 per cent, of gold, while even a 

 trace of the latter metal is sufficient to alter 

 the tint of the patina. An alloy of zinc and 

 rhodium is described by Debray in which a 

 simple elevation of temperature induces allo- 

 tropic change in the constituent metals. This 

 property of metals and alloys of passing into 

 allotropic states and the possibility of chang- 

 ing the mechanical properties of metals by ap- 

 parently slight influences may have consider- 

 able industrial importance. 



A new mineral, an arsenide of platinum, 

 PtAsj), discovered by Mr. Sperry at Sudbury, 

 Ontario, and named Sperrylite by Prof. Wells, 

 is of interest as being the first mineral other 

 than natural alloys with metals of the platinum 

 group of which platinum is an important con- 

 stituent. It occurs in the form of a heavy, 

 brilliant sand composed of minute well-defined 

 crystals. After removing impurities, the Sper- 

 rylite sand appears of a remarkably increased 

 brilliancy, with every grain showing extremely 

 bright crystal faces of a tin-white color, re- 

 sembling that of metallic platinum itself. It is 

 very heavy, possessing a specific gravity of 

 10'6. Yet, although it is so heavy, the sand 

 shows a marked tendency to float on water 

 owing to its not being easily wet, and even 

 when the grains do sink they almost invaria- 

 bly carry down bubbles of air with them. A 

 certain similarity in behavior when treated 

 with aqua regia with that of pyrites is rendered 

 all the more important in view of the fact that 

 the platinum and iron groups both occur in the 

 same vertical row (the eighth) in Mendelejeff's 

 periodic classification. 



A process by which wood is made to take on 

 some of the special characteristics of metal has 

 been turned to practical account in Germany. 

 By this process the surface becomes so hard 

 and smooth as to be susceptible of a high de- 

 gree of polish, and it may be treated with a 

 burnisher of either glass or porcelain. The 

 wood then presents the appearance of polished 

 metal and has the semblance of a metallic mir- 

 ror, with the advantage that it is not affected 

 by moisture. To produce this property the 

 wood is steeped in a bath of caustic alkali for 

 two or three days, according to its degree of 

 permeability, at a temperature of between 164 

 and 197 Fahr. It is then placed in a bath of 

 hyposulphite of calcium, to which, after some 

 twenty-four or thirty-six hours, a concentrated 

 solution of sulphur is added. It is then treated 



