Dr. Thomson on Oxalic Acid. 
and lose a part of their weight, which they afterwards recover 
when left exposed in a moist place. When cautiously heated 
on a sand bath they fall to powder, and lose about a third of 
their weight. But as the acid is itself volatile, it is not probable 
that the whole of this loss is water. To ascertain the quantity 
of water contained in these crystals I had recourse to the fol- 
lowing method. 
l. Seventy grains of crystallized oxalic acid were dissolved 
in 600 grains of water, constituting a solution which weighed 
670 grains. 
Fifty grains of pure carbonate of lime, in the state of cal- 
careous spar, were dissolved in muriatic acid ; this solution 
was evaporated to dryness to get rid of the excess of acid, and 
the residue redissolved in water. 
Into this muriate of lime the solution of oxalic acid was 
dropt by little and little as long as any precipitate fell, and the 
oxalate of lime thus formed was separated by the filter. Pure 
oxalic acid is not capable of precipitating the whole lime from 
solution of muriate of lime, the muriatic acid evolved being 
always sufficient to retain the last portions in solution. 
It was necessary to get rid of this excess of acid ; the method 
which appeared the least exceptionable was to saturate the 
muriatic acid with ammonia ; accordingly when the oxalic acid 
ceased to occasion any farther precipitate, I cautiously added 
pure ammonia, till the liquid ceased to produce any effect 
upon vegetable blues. A copious additional precipitate of ox- 
alate of lime was thus obtained. Oxalic acid was now added 
again as long as it rendered the liquid muddy. By thus alter- 
nately having recourse to the acid solution, and to ammonia, 
and by adding both with great caution to avoid any excess, I 
