1816.] respecting the Nature of Oxymuriatic Acid. 437 
p. 31), whether the appearance of fire be owing to the shock which 
the gases, instantaneously set at liberty, give to the surrounding air, 
as we know that the compression of air produces heat, which may 
very well amount to redness. But this does not explain the prin- 
cipal phenomenon of the explosion, namely, the extraordinary 
energy with which the gaseous bodies are set at liberty: and there” 
is another appearance which puts the insufficiency of that explana- 
tion beyond doubt. If a portion of the compound be exploded in a 
vessel containing air, the air is distinctly expended during the ex- 
plosion, and again condenses, which could not take place if the 
fire of the explosion were the consequence of the compression of 
the air ; for in that case the air, during the explosion, must occupy’ 
a smaller space than afterwards, when it has time to expand, and to 
absorb the heat which it has lost.* From what has here been said, 
it follows that the explanation of Gay-Lussac is not accurate, and 
that the elevation of temperature must be owing to the chemiéal 
process which precedes the explosion, and must proceed from the 
same cause as that of fulminating silver, fulminating gold, &c. 
We have now to explain what takes place in the explosion of 
euchlorine. ~According to the old opinion, this gas is the second 
super-oxide of the basis of muriatic acid in which that basis is com- 
* Gay-Lussac inquires whether in this situation we may not have recourse to 
electricity, as we know so many decompositions produced by that agent. From 
this question, as wellas from what he says in the Appendix to his Treatise on the 
Neutrality of Compounds, we may conclude that hitherto he has not paid much 
attention to electro-chemical studies, As this, on the one side, is rather surprising, 
so on the other side it is very encouraging, that even his chemical studies obliged 
him to have recourse to this universally distributed agent, as the new science has 
reason (o expect much from the uncommon talents of this distinguished man, Gay- 
Lussac, among other things, mentions as a fact still unexplained, that when a 
saturated solution of nitrate of ammonia is mixed with its own bulk of water, the 
bulk is diminished, and at the same time cold produced. I shall makea few 
observations on this subject. In my Treatise on the Water of Crystallization I 
have already endeavoured to draw the attention of chemists to the difference 
between solution in water and combining chemically with water, Carbonate of 
magnesia combines chemically with 3 of its weight of water, but is insoluble in 
that liquid. Nitrate of potash contains no chemically combined water, yet it is 
soluble in that liquid. When a body unites chemically with water, heat is pro~ 
duced ; when it dissolves in water, cold is evolved. If muriate of lime previously 
heated to redness be moistened with water, heat is first produced, because the 
water of crystallization combines; but when more water is added, cold takes 
place, The principal cause of the heat is not so much the condensation of water 
as its chemical combination, that is, the opposite electro-chemical neutralization 
of the water and the salt. The cause of the cold by the solution, on the contrary, 
is the increase of the yolume, and the easy solubility of thesalt, which must now 
spread itself through the whole mass of the water. The sum of the bulk of both 
is diminished, because the water, while it receives the salt into its pores, and is 
diluted, contracts itself through the action of the salt. Now as the salt requires 
more heat, in consequence of the proportionally much greater separation of its 
molecules, than the water gives out in consequence of the approach of its par- 
ticles, cold ensues, (1n the opposite case heat would be produced.) The greater 
the proportion of water compared to that of the salt, the more heat is absorbed, 
though the mixture does not lose as much temperature as when the quantity of 
liquid and the mass to be cooled is small. Gay-Lussac’s difliculty is explained by 
this, thatthe molecules of salt double their distance, while those of the water are 
enly condensed a very little, 
4 
