If spirits of wine and water are mixed together, a considerable degree of heat is given out, and by mixing sulphuric acid and water, an infinitely larger quantity. If sulphuric acid (oil of vitriol) and spirit of wine, or nitric acid (aquafortis) and spirits of turpentine, at common temperatures, be suddenly mixed, so much heat is set free as to ignite the spirit. In each of these instances there is a condensation of the fluid. In nearly all cases of solution, cold is produced by the absorption of the heat necessary to sustain the salt in a liquid form; but when potash dissolves in water, heat is given out, which is a fact we cannot yet explain. If potassium is placed on water, it seizes the oxygen of the water and sets fire to the hydrogen gas liberated by the heat produced in the change of form. Antimony and many other metals thrown into chlorine gas ignite and burn with brilliancy: the same phenomenon takes place in the vapours of iodine or bromine. Many chemical combinations, as the chloride of potassium and sulphur explode with a blow; whilst the slightest friction occasions the detonation of the fulminating salts of silver, mercury, and gold. Compounds of nitrogen and chlorine, or iodine, are still more delicately combined--the former exploding with fearful violence on the contact of any oleaginous body, and the latter by the smallest elevation of temperature: both of them destroying the vessels in which they may be contained. Gun cotton presents some peculiar phenomena which may merit brief attention. This peculiar compound is prepared by the action of nitric acid on cotton fibre. The general appearance of the cotton is not altered, but a remarkable physical change has taken place. It is now soluble in ether, and forms a gelatinous compound:--it explodes violently at a temperature which is insufficient for the combustion of gunpowder. Indeed, from, as it would appear, slight electrical disturbances taking place in the gun cotton itself, it not unfrequently explodes spontaneously. These fearful disturbances of the forces which hold bodies in combination are explained with difficulty. May it not be, that an enormous quantity of the calorific and chemical principles is held in a state of extreme tension around the particles of the compound, and that the equilibrium being destroyed, the whole is developed in destructive rapidity? The fact of great heat being evolved during the conversion of a body from a solid to a gaseous state, as in the explosion of gunpowder or gun cotton, which is a striking exception to the law of latent heat, as it prevails in most cases, admits of no more satisfactory explanation.