280 PREPARATION OF CHARCOAL BY STEAM. 
apparatus. The steam is admitted at a pressure of about 
fifteen pounds to the square inch above that of the atmos- 
phere. After passing through the heated spiral pipe, it first 
enters the outer cylinder, passes through its whole length, 
gains access to the inner cylinder by its anterior open end, 
penetrates and carbonizes the wood, and finally escapes, 
together with the products of distillation from the latter by 
a tube provided for the purpose. The temperature is regu- 
lated by the aid of certain small vertical iron tubes, having 
their lower ends closed, which penetrate into the inner 
cylinder. These tubes contain portions of tin, lead, and an 
alloy of intermediate fusibility, by the melting of which the 
temperature of the cylinder is indicated with sufficient pre- 
cision. The operation commonly lasts about two hours. 
When completed, the current of steam is stopped for a few 
minutes, the cylinder opened, and the perforated metal enve- 
lope containing the charcoal withdrawn, and immediately 
received into an iron extinguishing vessel, which is instantly 
closed and rendered air-tight. Without this precaution the 
charcoal would probably take fire on contact with the air. 
Another envelope, containing a fresh charge of wood, pre- 
viously prepared, is then introduced into the apparatus, the 
cylinder, closed, the steam admitted, and the operation in 
this manner indefinitely repeated. With moderate care 
and skill the product obtained consists almost wholly of 
charbon roux, absolutely free from tarry matters, and 
amounting to about thirty-six or thirty-eight per cent, of the 
weight of the wood; a quantity vastly exceeding that 
yielded by the old processes, which, as a mean, gave but 
fourteen or fifteen per cent, of the proper kind of charcoal, 
the rest being black from overheating, and unfit for making 
gunpowder. 
M. Violette terminates his memoir by calling attention to 
several other important applications of heated steam. The 
waste steam which escapes from the apparatus just de- 
scribed, bearing with it the various products of destructive 
