48 On definite Proportions. 
the oxygen of the acids and that which has been more directly 
determined. But I have endeavoured to distribute this error as 
equally as possible through all the results, so that the first per- 
fectly correct and well-established analysis of an acid or an oxide 
may correct the whole at once. 
2. Citric Acid. 
Some crystallized citrie acid was finely powdered, and dried 
for some hours in the sun, 
a.) Five grammes of this acid were dissolved in water, and 
mixed with 15 gr, of levigated protoxide of lead, which had 
been ignited the instant before ; the mixture was slowly evapo- 
rated to dr yness, and the salt of lead, mixed with the protoxide, 
was then dried, in as strong a heat as it would bear, on a sand 
bath, until it “lost_no more_of its weight. The mixture now 
weighed 18°95 gr. Consequently the acid had contained 21 per 
cent. of water. 
b.) Ten grammes of the same citrie acid, treated in the same 
way as the tartaric, afforded 23°756 gr.of the citrate of the prot- 
oxide of lead. 
c.) Five grammes of the same citric acid, kept melted in a 
gentle heat, as long as they lost any part of their weight, were 
found to be deficient, when they were congealed into a solid 
mass, ‘304 gr. or 7°08 per cent. 
d.) Ten grammes of citrate of the protoxide of lead, treated 
with diluted sulphuric acid, gave 9-056 gr. of sulphate of the 
protoxide, in which are contained 6-666 gr, of the protoxide. 
Consequently this salt contains one third of its weight of acid, 
and consists of 
Citric acid 4 83°35 100 
Protoxide of lead 66°667 200 
Hence 100 parts of citric acid must saturate a quantity of the 
base which contains 14:3 of oxygen. If we compute from ex- 
periment /.), according to this analysis, we find again that the 
citric acid contains 20°85 per cent. of water. Now this acid had 
lost, in a temperature not high enough to decompose it, 7:08 
per cent. of water; and this makes about a third of the whole 
that it contains. The remaining 13-77 parts of water were at- 
tached to the acid by a stronger attraction. But if 79-15 parts 
of dry citric acid contain 13°77 of water strongly attached to 
them, 100 parts of dry acid must combine with 17:14 of water, 
_ which contain 15 of oxygen, or a little more than is contained 
in the protoxide of lead which saturates 100 parts of the dry 
acid. This small difference depends on the impossibility of ob- 
taining perfectly correct results from substances, W hich, like the 
citric acid, are easily decomposed in a temperature somewhat 
elevated. 
