66 
Dr. Thomson on Oxalic Acid. 
Now this is equivalent to 
Real acid - - 77 
Water 23 
100 
So that the crystals of oxalic acid contain very nearly the fourth 
part of their weight of water.* 
II. Alkaline and Earthy Oxalates. 
1. The preceding experiment gives us likewise the com- 
position of oxalate of lime. This salt, when merely dried in 
the open air, still retains a portion of water which may be 
driven off by artificial heat. It is necessary to know that it 
parts with this water with considerable difficulty, so that a 
long exposure on the sand or steam bath, is necessary to get 
it thoroughly dry. It afterwards imbibes a little water if it be 
left in a moist place. Well dried oxalate we have seen is a 
compound of 
Acid 45 or per cent, 62.5 acid. 
Base 27 - - 37.5 base. 
72 100 
*VAuquELiN in a late dissertation on cinchona, marked with that profound skill 
which characterizes all the productions of this illustrious chemist, has mentioned 
incidentally, that the crystals of oxalic acid contain about half their weight of water. 
He dissolved too parts of cinchonate of lime iu water, and precipitated by means of 
oxalic acid ; 22 parts of crystallized oxalic acid were necessary; and the oxalate of 
lime formed weighed 27 grains. From this experiment he draws the conclusion which 
lhave stated, (See Ann de Chem. lix. 164.) But this ingenious chemist does not seem 
to have been aware of the real composition of oxalate of lime. 27 grains of that salt 
are composed very nearly of 10 grains of lime and 17 grains of acid. But the weight of 
the crystals used by Vau^uelin was 22 ; the difference, 5, is obviously the water of 
crystallization in 22 grains of the crystals. But if 22 grains contain 5 of water, it is 
obvious, that 100 contain very nearly 25. So that his experiment in reality coincides 
with mine. 
