A Volatile Alkali, then, has the same property as a Fixed Alkali with regard to acids: yet they differ in this, that the affinity of the former with acids is weaker than that of the latter: and hence it follows, that any Sal Ammoniac may be decompounded by a Fixed Alkali, which will lay hold of the acid, and discharge the Volatile Alkali. A Volatile Alkali will decompound any neutral salt which has not a Fixed Alkali for its basis; that is, all such as consist of an acid combined with an absorbent earth or a metallic substance. By joining with the acids in which they are dissolved, it disengages the earths or metallic substances, takes their place, and, in conjunction with their acids, forms Ammoniac Salts. Hence it might be concluded, that, of all substances, next to the Phlogiston and the Fixed Alkalis, Volatile Alkalis have the greatest affinity with acids in general. Yet there is some difficulty in this matter: for absorbent earths, and several metallic substances, are also capable of decompounding Ammoniacal Salts, discharging their volatile Alkali, and forming new compounds by uniting with their acids. This might induce us to think, that these substances have nearly the same affinity with acids. But it is proper to observe, that a Volatile Alkali decompounds such neutral salts as have for their basis either an absorbent earth or a metallic substance, without the aid of fire; whereas absorbent earths or metallic substances will not decompound an Ammoniacal Salt, unless they be assisted by a certain degree of heat. Now, as all these matters are extremely fixed, at least in comparison with a Volatile Alkali, they have the advantage of being able to resist the force of fire, and so of acting in conjunction therewith; and fire greatly promotes the natural action of substances upon one another: whereas the Volatile Alkali in the Ammoniacal Salt, being unable to abide the force of fire, is compelled to desert its acid; and that so much the more quickly, as its affinity therewith is considerably weakened by the presence of an earthy or metallic substance, both of which have a great affinity with acids. These considerations oblige us to conclude, that Volatile Alkalis have a somewhat greater affinity, than absorbent earths and metallic substances, with acids. Ammoniacal Salts projected upon nitre in fusion make it detonate; and the Nitrous Sal Ammoniac detonates by itself, without the addition of any inflammable matter. This singular effect evidently demonstrates the existence of an oily matter in Volatile Alkalis; for it is certain that nitre will never deflagrate without the concurrence, and even the immediate contact, of some combustible matter.