CHEMISTRY. 197 



is tlieii pressed into solid buttons, and melted in lime crucibles 

 with the oxyhydrogen blow-pipe. If proper precautions are 

 taken in purifjing the ferrous sulphate and the sulphate of 

 sodium, almost absolutely pure iron is obtained ; careful analysis 

 fails to detect piiosphorus or silicon, while the amount of sulphur 

 varies from 0.00025 to 0.0007 per cent. — Chem. News, Aug., 18G9. 



APPLICATION OP CHLORINE GAS TO THE TOUGHENING AND 



REFINING OF GOLD. 



A method of effecting the toughening and refining of gold has 

 been devised by F. B. Miller, F.C.S., of the Sydney Branch of 

 the Royal Mint, which appears to be superior to those now in 

 use, and to answer all the requirements of the case in a single 

 operation. A French clay crucible is saturated with borax by 

 immersing it in a strong and hot solution of the salt and then dry- 

 ing. The gold is melted in this crucible with a little borax, and 

 a stream of chlorine gas is allowed to pass tin-ongh it by means 

 of a clay tube. In a few hours the whole of the silver is con- 

 verted into chloride, which floats on the gold. The borax pre- 

 vents the absorption of the chloride by the crucible, and also its 

 volatilization, except in very minute quantities. As soon as the 

 gold has become solid, the still liquid chloride of silver is poured 

 off, and the gold is now found to have a fineness of say 993 in 

 1,000. The apparent loss of gold is very little greater than is 

 found in ordinary gold melting, — being 2.9 parts in 10,000, 

 whereas in the ordinary process it is two. A small sample of the 

 gold is removed from time to time during the operation, by means 

 of a piece of tobacco-pipe used as a pipette. This is rapidly 

 assayed approximately, and thus the progress of the operation is 

 judged of. The fused chloride of silver, obtained as a slab by 

 this operation, is reduced by placing it between two plates of 

 wrought iron in a bath of dilute sulphuric acid. The spongy 

 silver thus obtained contains gold, which is separated by nitric 

 acid ; the silver is then thrown down as chloride and again, re- 

 duced. — Chem. Soc, reported in Chem. News. 



REDUCTION OF OXIDES BY HYDROGEN. 



M. W. Miiller, as a result of a series of- experiments made to 

 determine the temperature at which various oxides are reduced 

 by hydrogen, finds that oxide of iron, prepared by cautiously 

 heating metallic iron in the air, is reduced at 285° C. ; that oxide 

 of iron prepared from the nitrate is reduced at 286° ; when rather 

 moist hydrogen was employed on oxide of iron pre))ared from 

 ferrous oxalate, the reduction took place at 278°. Precipitated 

 oxide of copper, previously heated to 300°, was reduced at 135° ; 

 strongly ignited oxide of copper at 1'42° ; oxide of cobalt at about 

 132°; oxide of tin at about 174°; oxide of lead at from 310° to 

 315° ; peroxide of mercury at 230° ; oxide of silver at between 



17* 



