Page:Proceedings of the Royal Society of London Vol 1.djvu/307

Rh proportion which he had before observed to take place in the superoxalate and neutral oxalate of potash.

In the decomposition of these salts by heat, Dr. Thomson found the acid to be resolved into water, carbonic acid, carbonic oxide, carburetted hydrogen, and charcoal.

With the view of determining with precision the composition of oxalic acid, Dr. Thomson made choice of the oxalate of lime, of which 100 grains by distillation yielded 60 cubic inches of gas, consisting of carbonic acid gas and inflammable gas, in the proportion of 2 of the former to 7 of the latter. The inﬂammable gas also consisted of 2 parts, seven tenths being carbonic oxide, and three tenths carburetted hydrogen.

Hence if 160 grains of oxalate of lime, which contain 100 oxalic acid, be distilled, the products are, 59.53 carbonic acid, 24.28 inﬂammable air, 11.51 water, 4.68 charcoal: and as the constituents of these products are known, the ultimate elements are, 64.69 oxygen, 31.78 carbon, 3.53 hydrogen; which Dr. Thomson considers to be, 64 oxygen, 32 carbon, and 4 hydrogen.

In the analysis given of this acid by Fourcroy, as performed by Vanquelin and himself, the quantity of carbonic acid appears much too small; and Dr. Thomson is convinced their method must be erroneous, as the quantity of carbonic acid alone that is formed during distillation contains considerably more carbon than they assign to oxalic acid.

From the weights of the elements obtained from oxalic acid by chemical analysis, Dr. Thomson turns to views of a different nature, and hopes to arrive at a more intimate and accurate knowledge of the difference between this acid and other vegetable products consisting of the same ingredients, by attending to certain numerical relations of their elements to each other: and this relation is such, that if hydrogen be expressed by 1, the number which corresponds to carbon is 4.5, and oxygen 6. Azote, expressed according to the same scale, will be 5. The law observable in their union is this, that in all their compounds the proportions of these constituents may be always expressed by these numbers, or by small multiples of them; for instance,

From the knowledge of this law, which was ﬁrst observed by Mr. Dalton, it is difﬁcult (says Dr. Thomson) to avoid concluding, with him, that the numbers above given represent the relative weights of a single atom of each of these elements; that they ﬁrst unite atom