450 
Iron . 
possessing a bad effect upon the quality of the metal. The effect 
of the roasting ought nb'w to be, not only to render the ore easily 
broken as before, but also to expel the greater part of the sulphur, 
in some measure by sublimation and chiefly by acidification. Ill 
this process the sulphur combines with oxygen sufficient to con- 
vert it into sulphureous acid, which is extremely volatile and which 
does not act upon iron, and this flies off in vapour producing the 
peculiar smell that proceeds from sulphur when undergoing com- 
bination. In this way the sulphur may in most cases be burnt 
off, but cannot be got rid of by sublimation alone ; because for this 
purpose it would be necessary that the air should be totally ex- 
cluded and at the same time that a free passage should be afforded 
to the sulphureous vapour-— a combination absolutely impossible 
without a radical change in the whole of the present system of 
torrefaction. 
Upon this subject, which is indeed as Mr. Mushet considers 
it, fully entitled to the utmost attention of the manufacturer, I shall 
bring to my support the experiments of M. Guineveau upon de- 
sulphuration, by which it is plainly shewn that a free concourse of 
air is necessary to the process ; and that it can neither be per- 
formed in close vessels by the most carefully conducted distilla- 
tion, nor in a covered crucible by the strongest fire. The Swe- 
dish iron masters’ mode of torrefaction as detailed by Swedenborg 
is decidedly in favour of the same opinion. Their ores are al- 
ways roasted with dry wood, and he mentions some instances in 
which he has heard of the process being repeated three times in 
order to expel the sulphur. Their success must be good, since 
they make the best iron in Europe, yet they never exclude the 
atmosphere ; on the contrary their mode of operation jfensures a 
steady and great supply of this important agent, and the author I 
quote from, particularly states that the suffocating odour of burn- 
ing sulphur (that is to say of sulphureous acid gas) is always very 
perceptible and that for several days together from the same pile. 
Nay even the British mode with which Mr. Mushet finds so much 
fault, is in that respect tolerably advantageous, since I should 
think the swelled and spongy form which the coal assumes in 
coaking, must be very favourable to keeping up a supply of air 
for a considerable time and thus tend greatly to remove the real 
enemy of the smelting process — not oxygen, but sulphur. 
' If these principles be correct, and they have received the 
stamp of practice as well as the seal of scientific investigation, it 
