192 ON THE DECOMPOSING POWER OF HOT STEAM. 
native carbonate of magnesia three or four inches thick. 
The steam is introduced by several clay pipes passing 
through the roof of the furnace, so as to throw a current of 
heated steam over the whole width of the hearth. The 
sulphate, broken in pieces about half an inch in diameter, 
is spread over the hearth of the furnace, and brought to a 
high red or low white heat, when the steam is admitted. 
The charge requires to be stirred occasionally, the oxidiz- 
ing state of the atmosphere kept up, and the intensity of 
the heat attended to; requiring to be higher for these two 
bases than for the sulphate of lime. When, on testing the 
charge, it is nearly or entirely soluble in dilute nitric acid, 
it may be withdrawn, and consists chiefly of the hydrate of 
strontia or of baryta. 
The patentee obtains muriatic acid and strontia or baryta 
by treatii]g the muriates of those bases by the same process 
as has been described for their sulphates. 
The sulphates of potash and soda, though decomposable 
by the same means as directed for the sulphate of baryta, 
owing to the volatility of their bases, are not eligibly thus 
treated. The patentee employs a substance to aid their 
decomposition by fixing the bases in combination, and yet 
capable of giving up the alkali to water or carbonic acid 
water with readiness, which agent he calls a combining 
substance. Of the many substances thus endowed, he pre- 
fers alumina, or its sub-phospliate. Equal quantities of the 
sulphate of soda or potash and pure alumina are mixed in 
fine powder, spread on the hearth of areverberatory furnace, 
and treated precisely like the sulphate of baryta, and when 
no notable quantity of sulphate remains undecomposed, the 
charge is vv^ithdrawn, lixiviated with hot water, and when 
the clear solution of aluminate of potash or soda has become 
cold, carbonic acid is passed through it till all the alumina 
is precipitated, when the solution of carbonate of potash or 
soda is drawn off and evaporated. The alumina thus pre- 
cipitated is again used as the combining substance. 
