PART II.

OF PRIMARY COMPOUNDS.

By the term primary compound, is meant a combination of two or more simple bodies with each other. Thus potash is a primary compound, being composed of potassium and oxygen united together. Cyanogen is another of these compounds, being composed of carbon and azote united in definite proportions; as is also arsenic acid, which is a definite compound of arsenic and oxygen. Almost every one of these primary compounds have been noticed at least in the first part of this work, in which almost all the known direct combinations of the simple bodies with each other have been noticed. But it will be requisite in this second part to treat of the most important of them in greater detail than could be done with propriety while treating of the simple bodies. Now all the primary compounds naturally divide themselves into three classes, namely, acids, alkalies or bases, and neutrals. These three classes will be described in succession in the three following chapters.

Part II.

CHAP. I.

OF ACIDS.

acid.

By acid at present is understood a substance, which has the Definition of property of combining with and neutralizing alkalies or bases. Formerly it was considered as requisite that bodies, in order to belong to the class of acids, should have a sour taste, should be soluble in water, and should have the property of reddening vegetable blue colours-and these properties do indeed belong to some of the most common and powerful acids; but there are various acids which have no taste, and which are not sensibly soluble in water, and some which are incapable of altering the colour of the most delicate vegetable blues. All the acids with which we are at present acquainted are compounds.

Chap. I.

Consist of nine classes.

Lavoisier endeavoured to prove that oxygen constitutes an essential constituent in them all. And this opinion holds good with the greater number of acids which chemists were acquainted with in his time, though not with the whole of them.

It is now known that not merely oxygen, but all the other simple supporters, namely, chlorine, bromine, iodine, and fluorine, are capable of forming acids, by uniting with several of the acidifiable bases, and indeed also when they unite with several of the alkalifiable bases; especially those belonging to the last family, and described under the name of noble metals. In fact the greater number of the metals belonging to this family, are scarcely entitled to the name of alkalifiable bases; though they hardly possess sufficiently energetic characters to entitle their compounds, if we except their chlorides, to be considered as acids.

Besides the five supporters, cyanogen, sulphur, selenium, and tellurium, have also the property of forming acids when they unite with the acidifiable bases. Indeed it is not improbable that this property may belong to most if not to the whole of the acidifiable bases, though at present it has only been ascertained to hold with respect to those which have been just named. Thus it appears that the acids at present known may be divided into 9 classes, namely,

1. Oxygen acids,
2. Chlorine acids,
3. Bromine acids,

4. Iodine acids,

5. Fluorine acids,

6. Cyanogen acids,
7. Sulphur acids,
8. Selenium acids,
9. Tellurium acids.

These 9 classes of acids will be described in succession, so far as the present imperfect state of the science will enable us to go.

CLASS I.

OXYGEN ACIDS.

The acids which contain oxygen as an essential constituent, have been longer known and more carefully examined by chemists than those which constitute the other eight classes. This is probably the reason why they are at present so much more numerous than all the other acids put together. There can be no doubt that the chlorine acids, and those belonging

to each of the other classes, will increase very much in number as the science extends.

The oxygen acids are of two kinds. Some consist of oxygen united to a single acidifiable base or a single supporter. Thus sulphuric acid is a compound of sulphur and oxygen; carbonic acid of carbon and oxygen; and bromic acid of bromine and oxygen. But there are a considerable number of oxygen acids in which the oxygen is united at once with two and sometimes with three bases. Thus acetic acid is a compound of oxygen, carbon, and hydrogen; while uric acid is a compound of oxygen, carbon, hydrogen, and azote. This second set of acids is very numerous. They either exist ready formed in the vegetable and animal kingdoms, or they are formed from vegetable and animal bodies by certain chemical processes. We must, therefore, subdivide the oxygen acids into

1. Acids with a single base.

2. Acids with a compound base.

The first of these divisions includes the most important of those acids that are employed as instruments of chemical investigation. But there are also several of the acids with compound bases that are nearly indispensable in a chemical laboratory, for some of the most frequent and useful processes which the practical chemist has occasion to perform. These reasons make it indispensable for us to take a view of these acids in this part of the work.

DIVISION I.-ACIDS WITH A SIMPLE BASE.

The oxygen acids with a simple base, so far as we present acquainted with them, amount to about 36. names are as follows:

Class I.

Div. I.

Chap. I.

25. Arsenic,

26. Arsenious,

31. Molybdic,

32. Tungstic,

Chlorous

acid.

27. Antimonic,
28. Antimonious,

29. Chromic,

30. Uranic,

33. Columbic,

34. Titanic,

35. Manganesious,
36. Manganesic.

I shall take a view of each of these acids in succession.

SECTION 1.-OF THE ACIDS OF CHLORINE.

Chlorine and oxygen unite in three different proportions so as to form acids. These are

These three acids have been described in Vol. I. p. 66; the first under the name of quadroxide of chlorine. It has been generally considered as an oxide, because when we attempt to unite it with a base, it undergoes decomposition. However, if it be placed in contact with an alkaline base in its nascent state, a combination takes place, and a chlorite is formed having a peculiar and acrid taste similar to that of the acid. These salts have the property of destroying vegetable colours. There can be little doubt that Von Stadion's analysis is accurate, so that it is a compound of

1 atom chlorine

3 atoms oxygen

4.5

3

7.5

and its atomic weight is 7.5.

The facts respecting chloric and perchloric acids stated in the first volume of this work, constitute every thing hitherto ascertained respecting them.

The circumstance of two substances, both of which are so strongly negative, as oxygen and chlorine, uniting together, seems at first sight rather incompatible with the electric theory of chemical affinity. I have endeavoured to obviate this difficulty in the Introduction to this work (Vol. I. p. 39). The affinity between the oxygen and chlorine is obviously weak. Hence heat which seems to increase the intensity of the negative electricity of chlorine, easily occasions a decomposition of these acids.

SECTION II.-OF THE ACIDS OF BROMINE AND IODINE.

The oxygen acids of bromine and iodine hitherto observed are only 1 acid for each of these bodies, constituting bromic and iodic acid, analogous as their names imply to chloric acid. Their properties have been already described in p. 74 and p. 82 of the first volume of this work. I do not notice here the iodous acid of Sementini, nor the hypiodous acid of Mitcherlich, because I have already stated all the facts respecting these supposed acids with which I am acquainted. Bromic acid is a compound of

Class I.

Div. I.

Iodous acid (if it exist) ought, from analogy, to be a compound of

SECTION III.—OF THE ACIDS Of azote.

Azote and oxygen combine in three proportions, forming the three acids which have been called nitric, nitrous, and hyponitrous acids.*

When the French chemists contrived their new chemical nomenclature in 1787, a base was supposed to be capable of uniting only with two doses of oxygen, and of forming two acids. They distinguished these acids by making the acid containing most oxygen terminate in ic, and the one containing least in ous. Thus nitric acid contains most oxygen, and nitrous acid least. It was afterwards discovered that in some cases acids exist con

taining less oxygen than those in ous. These are distinguished by prefixing the syllables hypo, as hyponitrous. The mode is still imperfect. For some bases unite with four or even five doses of oxygen, and form four or even five acids.