PROGRESS IN ELECTRO-METALLURGY—KERSHAW. 229 
already been reduced from 4s. to 1s. 8d. per kilogram by the improve- 
ments in the Castner electrolytic process, will be still further reduced. 
The sodium produced by the electrolytic method is largely em- 
ployed for the manufacture of sodium cyanide, and of sodium perox- 
ide. ‘ Oxone” is the trade name given to fused sodium peroxide, 
and this product is being advertised and sold in America for the 
generation of pure oxygen. 
Tin.—Electrolytic or electro-thermal methods have not been ap- 
plied with any success to the extraction or refining of tin, but in a 
branch industry—namely, “ tin stripping ”—they have become of con- 
siderable value and importance. 
In the manufacture of cans, boxes, and vessels of all kinds from 
tin plate an immense amount of waste occurs with the cuttings, and 
the recovery of the tin from these has been carried out for some years 
by electrolysis. The process usually employed was first applied indus- 
trially by Goldschmidt at Essen in Germany, and consists in the use~ 
of the scrap and cuttings as anode material in a bath of sodium hy- 
drate. Stannic-chloride solution has also been used as electrolyte in 
the Bergsoe process at Copenhagen. In the former case, only the 
tin is dissolved at the anode; in the latter case the iron is also attacked, 
and care is therefore required to prevent the solution of tin-chloride 
from becoming supersaturated with the iron salt. The chief develop- . 
ment of the electrolytic tin-stripping industry has occurred in Ger- 
many, but similar factories have also been erected and carried on in 
Denmark, Austria, England, and America. The chief difficulty in 
working the process has been to maintain an adequate supply of tin 
scrap and cuttings, and some of the works have had to close down 
from this cause. Purely chemical methods of stripping by means of 
chlorine gas are also now coming into favor. 
This will still further accentuate the difficulty of supplies, since 
the electrolytic alkali and bleach works will enter the market as pur- 
chasers of the tin scrap and cuttings. By this method of stripping, 
stannic chloride is produced, and not metallic tin. The manufacture 
of “ tin salts” has already been taken up by some of the electrolytic 
alkali works in Europe and America. 
Zine—The attempts to apply electrolytic and _ electro-thermal 
methods in the zine industry have met with only partial success, and 
the greater proportion of the zinc found in commerce is still produced 
by the old metallurgical method of distillation. 
The coating of iron articles with a protective deposit of zinc is, 
however, carried on in a large number of works by the electrolytic or. 
wet method, a solution of zine sulphate being generally employed as 
electrolyte, with lead anodes. “ Electro-galvanizing,” as it is called, 
is then an important branch industry. 
