On definite Proportions. 49 
elevated. Hence we see that the citric acid contains a quantity 
of water of crystallization, which may be separated from it 
without altering the composition of the acid, and that this water 
of crystallization is half as much as that which is more intimately 
combined with the acid. E 
8. Oxalic Acid. 
It is a fact generally known, that the oxalic acid effloresces or 
falls into powder in dry air. I thought at first that it lost the 
whole of its water during this change ; but upon exposure toa 
temperature somewhat above the boiling point of water, several 
portions of it wereychanged into coherent masses, but never lost 
exactly equal parts of their weight. The variations however 
were only from 28 to 29 and 29-3 per cent. ; and in the last case 
it was obvious that a sujlimation had commenced, for the sur- 
face of the salt was covered by smail crystalline needles. 
I now mixed in a small glass dish four grammes of powdered 
oxalic acid, which had been dried for an hour in the air, with 20 
gr. of finely powdered protoxide of lead, which had just been 
ignited ; I poured water on the mixture, and dried it rapidly, 
stirring it frequently in the mean time. The acid and the prot- 
oxide had now lost 1°68 gr. of their weight. I repeated the 
experiment’ with a result precisely similar. Hence 100 parts of 
oxalic acid contain 42 parts of water. 
Ten grammes of well dried oxalate of the protoxide of lead 
were burnt in an open glass dish exposed to a red heat. The 
dish lost, in different experiments, from 2°52 to 2°53 gr. of its 
weight. The remaining protoxide had a shining yellow colour. 
Consequently the oxalate of the protoxide of lead consists of 
Oxalic acid........ 29°2 100-0 
Protoxide of lead... 74:8 296-6 
Hence 100 parts of oxalic acid saturate a quantity of a base of 
which the oxygen amounts to 21-2 parts. Now we have seen 
that 100 parts of crystallized oxalic acid contain 42 of water, of 
which they lose from 28 to 29 by exposure to the air. But 28 
is exactly 2 of 42; so that the oxalic acid retains 1 part of wa- 
ter for every two that it loses. Hence we find that 100 parts of 
dry oxalic acid unite with 72-414 of water, and lose 48276 of 
these in drying. The remaining 24:138, which can only be 
driven off by the assistance of other substances possessed of 
stronger [positively] electrical powers with relation to it, con- 
tain 21°3 parts of oxygen. 
4, Rawnits, 
We are therefore acquainted with none of the three vegetable 
acids, here analysed, in a separate state ; and it may be presumed 
Vol. 43. No. 189, Jan. 1814. D that, 
