V 
186 ON THE DECOMPOSING POWER OF HOT STEAM. 
drous, or as hydrates, whilsy heir acid is driven off partly as 
sulphurous acid and oxygen, and partly as sulphuric acid. 
The degree of heat necessary varies with the salt. Sul- . 
phate of magnesia gives off its acid at a low red heat, and 
a large proportion of it escapes decomposition. The sul- 
phate of lime, strontiaand baryta require much higher tem- 
peratures, especially the last, which is best acted on at a 
low, white heat, and nearly the whole of the acid is re- 
solved into the sulphurous acid and oxygen, in which state 
Ave will see that Mr. Tighlman proposes to apply it directly 
to the manufacture of oil of vitrol. 
Successful in the preceding cases our author was not 
slow in extending the application of his experiments to 
other compounds; he found that even sub-phosphate of 
lime slowly gave up its acid, when subjected to the same 
conditions. Parallel with this, certain silicates, borates, 
florides and chromates were tried with equal success, thus 
proving the extensive applicability of the principle or law. 
These happy results naturally lead to the inference that 
the sulphates and chlorides of the alkalies proper, would 
readily submit to the same decomposition, but on trial it 
proved that although at first the decomposition was effected 
to a small extent, yet it soon apparently ceased, and no in- 
crease of heat or sieam would vary the small per centage of 
alkali in the residual salt. Referring this peculiarity to the 
vaporization of the alkaline hydrates as soon as liberated, 
substances, capable of forming fixed compounds with the 
alkalies were mixed with their salts before acting on Ihem, 
when it was found that the acids were disengaged with 
facility. The first trials were with lime and magnesia, 
which have but a feeble affinity for the alkalies; but the 
most favourable results occurred when pure alumina was 
used. The acid character of alumina^ in reference to the 
alkalies renders it'peculiarly proper for the function- in ques- 
tion, and it has accordingly been Jadopled as the agent in 
the patented process for obtaining soda from salt. 
