Other objections that have been made to the principle, that oxygen is exclusively the source of acidity, are of less force. The substances to which the names of Prus sic acid, and Uric acid, have been given, have been sup posed to contain no oxygen ; but from the complicated products of their analysis, this has scarcely been deter mined with accuracy, and indeed rather appears to be a mistake. And it deserves to be remarked, as even fa vourable to the conclusion, that acidity depends on oxy gen ; that of these two substances, into the composition of which oxygen has been supposed not to enter, the acid powers are so weak, that some chemists have sup posed, that they ought not to be received into the class of acids.
Muriatic acid, by an addition of oxygen, it has been stated, has its acid powers riot augmented, but much diminished. It loses its sour taste ; becomes less solu ble in water ; and does not redden the vegetable colours. But it still retains the most characteristic acid proper ty—that of neutralizing the alkaline properties ; and, as Berthollet has justly remarked, the reciprocal satura tion of the muriatic acid and the oxygen in this combi nation, must weaken their tendency to other combina tions, hence diminish some of the acid properties; while the excess of oxygen not retained by a strong affinity, must give rise to other properties not usually observed in acids, such as that of destroying, instead of reddening, the vegetable colours.
It thus appears, that there is still sufficient reason to conclude, that oxygen is exclusioely the principle of acidity. It is no doubt possible. a that the pro
perty which we name acidity, characterizi d chiefly by the power of combining with the alkaline bases, and neutralizing their properties, may acise from other binations, or be even displayed by a simple substance ; but the facts, that in general oxygen is cor;',,,ined toose substances ttliicli are possessed of this propero, and that this element communicates acid powers to (hi substances with it hid) it «,mbita 5, appear to establish the conclusion that it is the principle of acidity. Nor does it follow from this, that all the compounds which it. limns should be acid ; for if present in small p-oportion, and particularly w he n combioed ith an clement, the chemical action of which is energetic, the powers may not appear which it would communicate were it predo minant in the composition, And accordingly in many combinations, the presence or a small proportion of oxy gen dues not communicate acidity, while this property appears when the oxygen becomes noire predominant.
In C011Se \illenCe of the researches or modern chemis try the number of known acids is now considerablo. They amount to about twenty-eight. Of these, eighteen exist in the mineral kingdom, or are formed from mini rap substances ; Mite are products of the vegetable sy tens; and five arc of animal origin.
The plan of our being in general to place the account of each branch of science, those detail, which are more particularly connected with it, we ref, to the article CnENIISTRY for the history of the individual acids, and any farther obsery ations on the chemical pr.. perty of acidity. (1)