ON THE DECOMPOSING POWER OF HOT STEAM. 191 
phuric acid admixed. The acid vapours pass offby the escape 
tube at the top of the cylinder, and are conveyed by stone- 
ware tubes into a leaden chamber, in order to combine them 
into sulphuric acid, by the usual means. The heat should 
not be so high at first, to melt the sulphate of lime in the 
cylinders, but is increased towards the end of the operation, 
as the charge becomes more infusible when partly decom- 
posed. The condition of the escaping vapours is examined 
by an opening in the tube above, placed for that purpose, 
from time to time, and by the relative acidity of these, as 
ascertained by the usual test, the progress of the operation 
is judged of. The current of steam is regulated by a stop- 
cock, and is kept at that volume, which is found to generate 
the most acid vapours. When the evolution of acid vapours 
nearly ceases, the steam is shut off, the charge withdrawn 
from below, and its place re-occupied by a fresh one, to be 
treated as before. The withdrawn charge consists chiefly 
of caustic lime. 
When the object is to obtain the acid and base of the sul- 
phate of magnesia: the salt deprived of its water is placed 
in the cylinder in small pieces as before described for sul- 
phate of lirne, observing to keep the heat at low redness at 
first, to prevent the fusion of the charge, which would choke 
up the cylinder and prevent the passage of the steam. A 
low red heat is sufficient for the decomposition of the raag- 
nesian sulphate, and owing to this, a considerable portion 
of the acid escapes decomposition. The residue is chiefly 
caustic magnesia. 
When sulphates of strontia or baryta are to be treated, 
the patentee prefers to use areverberatory furnace, owing to 
the high heat necessary, which, though less advantageous in 
reference to collecting the acid vapours, is more eligible in 
relation to the fixed bases, which he esteems as the more 
important products of their decomposition. 
A common reverberatory furnace heated by a coke fire 
is used, with the hearth covered with a compact bed of 
