287 



proportion which he had before observed to take place in the super- 

 oxalate 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, car- 

 buretted 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 carbu- 

 retted 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 in- 

 flammable 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 

 Vauquelin and himself, the quantity of carbonic acid appears much 

 too small ; and Dr. Thomson is convinced their method must be erro- 

 neous, 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 hy- 

 drogen 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 ex- 

 pressed by these numbers, or by small multiples of them ; for instance, 



Oxyg. Hydr. Carb. Azote. 



Water consists of .... 6 1 



Carbonic oxide 6 4*5 



Carbonic acid 2x6 4*5 



Carburetted hydrogen. . 2x1 4*5 



Olefiant gas 1 4'5 



Nitrous oxide ., 6 2x5 



Nitrous gas 6 5 



Nitrous acid 2x6 5 



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 



