Dr. Thomson on Oxalic Acid . 
5. The residue which remained in the retort, after the dis- 
tillation was over, was a grey powder, not unlike pounded 
clay slate. To ascertain its constituents, it was dissolved in 
diluted nitric acid with the necessary precautions ; the loss of 
weight indicated the quantity of carbonic acid. The charcoal 
remaining undissolved, was allowed to subside, carefully 
washed by repeated affusions of water, and then dried in a 
glass or porcelain capsule. It must not be separated by the 
filter, for it adheres so obstinately that it cannot be taken off 
the paper, nor weighed. The nitric acid solution was preci- 
pitated by carbonate of soda, and the carbonate of lime ob- 
tained was violently heated in a platinum crucible. What 
remained was pure lime. 
6 . I shall now detail one of my experiments more particu- 
larly. Eighty-nine grains of well dried oxalate of lime were 
exposed in a small retort to a heat gradually raised to redness; 
the products were the following : 
Grains. 
4 5T cubic inches of gas* weighing 14.8 
Water 
- 
6.4 
Residue in retort 
- 
62.4 
83.6 
Loss *3 
£*■*> 
3-4 
Total 80.0 
The loss is obviously owing to the gas which filled the retort 
and tube when the experiment was concluded. We are 
* The gas obtained measured 60 cubic inches, but 14.4 inches of these were found 
to be common air which had previously filled the retort and tube; this quantity was 
therefore deducted, 
