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IV. On Oxalic Acid. By Thomas Thomson, M. D. F. R. S. Ed . 
Communicated by Charles Hatchett, Esq. F. R. S. 
Read January 14th, 1808. 
Oxalic acid, from the united testimony of Ehrhart, Hermb- 
stadt, and Westrumb, appears to have been discovered by 
Scheele ; but it is to Bergman that we are indebted for the 
first account of its properties. He published his dissertation on 
it in 17 76, and since that time very little has been added to 
the facts contained in his valuable treatise. Chemists have 
chiefly directed their attention to the formation of that acid, 
and much curious and important information has resulted 
from the experiments of Hermbstadt, Westrumb, Berthol- 
let, Fourcroy, and Vauquelin, &c. but the properties of the 
acid itself, have been rather neglected. My object in the fol- 
lowing pages is not to give a complete history of the proper- 
ties of oxalic acid, but merely to state the result of a set of 
experiments, undertaken with the view of ascertaining dif- 
ferent particulars respecting it, which I conceived to be of 
importance. 
I. Water of Crystallization. 
Oxalic acid is usually obtained in transparent prismatic 
crystals more or less regular ; these crystals contain a por- 
tion of water, for when moderately heated they effloresce 
