ON THE VOLATILITY OP FIXED SALTS. 
257 
The work we are now about treating of not only confirms 
most of the facts previously stated, but greatly adds to the 
number of fixed substances volatile in the vapors of the 
liquids holding them in solution, and, indeed, generalizes 
this fact, for nearly all the bodies on which the author has 
experimented possess this property. It is but right to state 
that M. Larocque has always operated on large masses of 
products, and that the evaporation of the liquid has always 
taken place in the open air, and in vessels of large sur- 
face. 
The substances on which M. Larocque has experimented 
were, in the first place, potash and soda. These two alka- 
lies, the non-volatile character of which has caused them to 
be called the fixed alkalies, are volatilized in sufficient quan- 
tity to produce a violent itching of those parts of the skin 
exposed to the air, as also a marked irritation of the throat 
produced by the vapors escaping from the copper in which 
the evaporation takes place. After potash and soda, M. 
Larocque mentions phosphate of soda, the nitrates of potash 
and soda, and the arseniates of these two bases, and observes 
that the volatility under the influence of aqueous vapors of 
these three kinds of salts, with reference to which so close 
an analogy had previously been traced, unites them still 
more closely. Following these substances come the sul- 
phates of zinc, of mercury, of copper, and of iron, nitrate 
of mercury, nitrate of silver, cyanide of potassium, the red 
and yellow ferruginous cyanides, the neutral tartrate of 
potash, and the double tartrate of potash and soda. The 
volatility of these salts explains, in reference to one of them, 
the occurrence of an ochreous incrustation of subsulphate 
of iron, on the walls of the manufactories in which sulphate 
of iron is prepared on the large scale. 
M. Larocque has also studied the action of heat on the 
solution of metallic chlorides, and he has observed that these 
products also possess the property of being volatilized in the 
vapour of water, but in various degrees. Thus, those of 
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