2S2 PREPARATION OF CHARCOAL BY STEAM. 
stove. In chemical manufactories the distillation of sub- 
stances of difficult volatility, and upon which water has no 
action, might be advantageously conducted in a stream of 
heated vapor. 
On considering the application of heated steam, described 
or suggested by M. Violette, it will be apparent that one 
of the principal difficulties to be encountered lies in the 
construction of the heating-spiral, and that this difficulty 
will increase with the temperature which may be required. 
At the Esquerdes powder-works, the wrought iron tube 
described answered very well, the steam being heated by 
its means to about 600° Fahr. For temperatures much 
above this, however, there can be no doubt that the iron 
would be very speedily acted upon by the vapor of water, 
some portion of which would suffer decomposition, giving 
rise to hydrogen and oxide of iron. Cast-iron would pro- 
bably be still more objectionable. Copper resists the vapor 
of water at a red-heat, but is rapidly destroyed by oxidation 
when exposed at that temperature to the air. Perhaps 
a compound pipe, copper within and iron without, might 
be found useful. This could easily be prepared by insert- 
ing'a copper tube of the proper size into along straight piece 
of stout wrought-iron barrel pipe, the whole being afterwards 
bent cold into a spiraL in the manner practised with this 
kind of tubing. In this manner the iron would be shielded 
from the action of the water, and the copper from that of * 
the air, and the advantages of both combined. It is need- 
less to say that the steam must not be allowed to penetrate 
between the two tubes. 
In connexion with this subject of the action of heated 
steam upon organic bodies, may be mentioned some curious 
observations by Mr. W. Ferguson, on the effect of steam at 
a temperature not exceeding 212° in apparently charring 
felt, which had been used for five or six months as a cover- 
ing to a high-pressure boiler in which a temperature of 
232° Fahr. was maintained. The charring took place at 
