676 APPENDIX. 



much more it loses when strongly heated with a given weight of 

 oxide of lead. Suppose we have 7*875 of oxalic acid crystals. If 

 we expose these crystals to the highest temperature they can 

 bear, without decomposition, the loss of weight will be 2*25, 

 which is equivalent to two atoms water. If we mix the 5*625 of 

 residue with fourteen yellow oxide of lead, and heat, the loss of 

 weight will be 1*125, which is equivalent to another atom of 

 water, and there will remain a neutral compound of fourteen 

 oxide of lead, and 4*5 oxalic acid. But fourteen is an atom of 

 oxide of lead, consequently 4*5 is an atom of anhydrous oxalic 

 acid. Now, as oxalic acid is a compound of, 



Carbon, . . 33*33 



Oxygen, ;>w . 66*66 

 It is obvious that it must be composed of, 



2 atoms carbon, . . 1*5 



3 atoms oxygen, . . 3* 



4*5 



Because this number of atoms alone gives the ratios and the ato- 

 mic weight of the acid. 



As another example let us take 26*25 of crystals of citric acid, 

 and heat them sufficiently. The water driven off will weigh 

 2*25. If we mix the residual 24 with 42, or any greater quan- 

 tity of oxide of lead, and heat in a crucible, taking care not to 

 decompose the acid, there will remain 62*625. From this, if we 

 subtract 42, the weight of the oxide of lead, there will remain 

 20*625 for the weight of the anhydrous acid. The loss of weight, 

 consequently, is 3*375, which represents 3 atoms of water. These 

 three atoms of water have been replaced by 42, or three atoms 

 of oxide of lead. Hence, citric acid is tribasic, and its atomic 

 weight in the anhydrous state must be 20*625. It is composed of, 



Carbon, fxtf- . 43-636 



Hydrogen, . . 3*030 



Oxygen, #> . 53-334 



100 



Hence the number of atoms in it must be, 

 12 carbon, = 9 

 5 hydrogen, = 0*625 

 11 oxygen, =11* 



20*625 



