The following are all the vegetable acids hitherto known:
1. Acetous acid.
2. Acetic acid.
3. Oxalic acid.
4. Tartarous acid.
5. Pyro-tartarous acid.
6. Citric acid.
7. Malic acid.
8. Pyro-mucous acid.
9. Pyro-lignous acid.
10. Gallic acid.
11. Benzoic acid.
12. Camphoric acid.
13. Succinic acid.
Though all these acids, as has been already said, are chiefly, and almost entirely, composed of hydrogen, charcoal, and oxygen, yet, properly speaking, they contain neither water carbonic acid nor oil, but only the elements necessary for forming these substances. The power of affinity reciprocally exerted by the hydrogen, charcoal, and oxygen, in these acids, is in a state of equilibrium only capable of existing in the ordinary temperature of the atmosphere; for, when they are heated but a very little above the temperature of boiling water, this equilibrium is destroyed, part of the oxygen and hydrogen unite, and form water; part of the charcoal and hydrogen combine into oil; part of the charcoal and oxygen unite to form carbonic acid; and, lastly, there generally remains a small portion of charcoal, which, being in excess with respect to the other ingredients, is left free. I mean to explain this subject somewhat farther in the succeeding chapter.
The oxyds of the animal kingdom are hitherto less known than those from the vegetable kingdom, and their number is as yet not at all determined. The red part of the blood, lymph, and most of the secretions, are true oxyds, under which point of view it is very important to consider them. We are only acquainted with six animal acids, several of which, it is probable, approach very near each other in their nature, or, at least, differ only in a scarcely sensible degree. I do not include the phosphoric acid amongst these, because it is found in all the kingdoms of nature. They are,
1. Lactic acid.
2. Saccholactic acid.
3. Bombic acid.
4. Formic acid.
5. Sebacic acid.
6. Prussic acid.
The connection between the constituent elements of the animal oxyds and acids is not more permanent than in those from the vegetable kingdom, as a small increase of temperature is sufficient to overturn it. I hope to render this subject more distinct than has been done hitherto in the following chapter.