Dr. Thomson on Oxalic Acid. 
8 5 
oxalate of lime, contains considerably more carbon than the 
whole quantity which they assign to the oxalic acid decom- 
posed. M. Fourcroy informs us, that oxalic acid is converted 
into carbonic acid and water, when acted upon by hot nitric 
acid ; and this decomposition seems to have been the method 
employed, to ascertain the proportion of the constituents of 
oxalic acid ; but the numbers assigned by him do not corre- 
spond with this statement. For 10 parts of hydrogen require 
6 o of oxygen to convert them into water, and 1 3 of carbon 
require at least 33 of oxygen. So that instead of 77 parts of 
oxygen, there would have been required no less than 98 to 
convert the hydrogen and carbon into water and carbonic 
acid. It is true, that the surplus of oxygen may be conceived 
to be furnished by the nitric acid ; but if this be admitted (and 
I have no doubt from experience, that the nitric acid actually 
does communicate oxygen ) , it is difficult to see how the con- 
stituents of oxalic acid could be determined by any such de- 
composition, unless the quantity of oxygen furnished by the 
nitric acid were accurately ascertained. 
IV. Composition of Oxalic Acid. 
The knowledge of the relative weights of the elements 
which compose oxalic acid, though of importance, is not suffi- 
cient to convey a clear idea of this compound, and in what 
respect it differs from tartaric acid, alcohol, sugar, and various 
other bodies possessing very different properties, though com- 
posed of the very same elements in different proportions. 
It has been ascertained, by numerous and decisive experi- 
ments, that elementary bodies always enter into combinations 
in determinate proportions, which may be represented by 
