COMBUSTIBLE ACIDS. 



raic weight of protoxide of lead, it is clear that 

 7'25 is the atomic weight of citric acid. 



2. But the weight of the crystallized citric acid 



tion of the J 



crystals, employed was 9*5 grains. The excess of weight 

 of these crystals above 7*25 must be owing to 

 combined water. This excess is 2*25, which is 

 equivalent to the weight of 2 atoms of water. 

 Hence it follows, that crystallized citric acid is 

 a compound of 



1 atom real acid . 7 '25 

 9 atoms water . 2-25 



3. I find, when 9*5 grains of crystallized citric 

 acid are exposed to a heat rather below 212, 

 they lose very nearly 0*73 grain of their weight, 

 and fall down in the state of a powder. Now, 

 0*73 is id of 2'25 ; so that, by the application of 

 heat, these crystals give out just the third of 

 their water, and no more can be driven off' 

 without, at the same time, decomposing the acid j 

 for its colour is rendered brown, and a peculiar 

 odour becomes sensible. 



constitu- 4. Berzelius decomposed citric acid by mix- 

 trie acid, ing 1 part of citrate of lead with chlorate of pot- 

 ash, burning the mixture in a glass tube, and 

 collecting the products. He deduced from this 

 analysis that the constituents of citric acid per 

 cent, are 



