Page:Proceedings of the Royal Society of London Vol 1.djvu/309

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The author having some time since observed various instances of super-acid salts, in which he found that the quantity of acid was exactly double of what would be necessary merely to saturate the alkali present, had intended to have pursued the inquiry, but was I prevented by the publication of Mr. Daltou’s theory of chemical combination, as explained by Dr. Thomson.

However, since it appeared that Mr. Dalton's theory was originally founded on the analysis of gases, which is attended with too many difﬁculties to be repeated by every one who may be desirous of veri- fying the law of simple multiples by experiment, the author thought it might be desirable to select from his observations certain experi- ments extremely easy to be repeated, each of which exhibits in itself the most direct and simple proof of the law under consideration.

The subcarbonates of potash and of soda are named as instances of salts containing exactly half the acid necessary to form their fully-saturated carbonates; and the proof is obtained by taking two quantities of either of these alkalies fully carbonated. One quantity being taken exactly double of the other, is exposed to a red heat, and is thereby reduced to a semi-carbonate; for it now yields the same measure of gas that is given out by the unburnt half quan- tity.

Super-sulphate of potash is adduced as an instance of a salt con- taining an exact double share of acid. The proof consists in taking two equal quantities of potash, to one of Which is added large quantity of sulphuric acid, and the mixture is exposed to a red heat, by which a part of the redundant acid is expelled; but such an ex- cess of acid remains as is neutralized by the second equal portion of alkali reserved for that purpose.

Super-oxalate of potash is also proved to be an exact binoxalate. Two equal quantities are taken of salt of sorrel; one is exposed to a red heat, to destroy the whole of its acid, after which the alkali that remains is just sufﬁcient to neutralize the redundant acid of the other portion.

In addition to the preceding compounds selected as distinct exam- ples of semi-acid and bin-acid salts, the author has observed one re- markable instance of a more extended and general prevalence of the same law. I‘ or when the circumstances are such as to admit the union of a further quantity of oxalic acid with potash, the quantity is again doubled; so that the potash present is sufﬁcient to saturate only one part in four of the acid contained in any‘ quantity of the salt; and, consequently, the three redundant parts of acid require for their neutralization the alkali of three equal quantities of this quadroxalate, which may be obtained by burning, as proof that the proportion has been rightly ascertained.

The last experiment is designed to determine Whether potash would