Over-heated Steam applied to the Carbonizing of Wood. 271 
comes black charcoal, and at a lower, the carbonization is incomplete. 
By the old process of heating in closed cylinders, 10,000 kilogrammes 
of wood furnished 2000 kil. of black charcoal, and 1300 of red. The 
eam 
M. Violette communicates now to the Academy some new results. 
He shows that the change to charcoal takes place differently with dif- 
gas retorts, and serves perfectly for electric illumination. The density 
increases in the same proportion. When lighted, charcoals remain 
ture much below that required when alone; the mixture of the two 
prepared between 150° and 400° C., is wholly consumed at 250° C. 
On the contrary, when the charcoal employed has been prepared at 
or 1500°-C., only the sulphur burns. 
To decompose saltpeter, the charcoals require a higher temperature ; 
a heat of 400° C. is needed for charcoals prepared between 150° and 
432°, and a red héat for those made between 1000° and 1500°. 
Sulphur decomposes saltpeter at a higher temperature than charcoal 
requires, viz., at 482°. The sulphur in in common air at 
250° C., and not at 150° as stated in treatises on chemistry. 
