TARTARIC ACID. 113 



weighed (dried at 100) 12-3 grains. In this ex- 

 periment there was a small excess of tartaric 

 acid, amounting only to 0*125 grain, and it ap- 

 pears from the result, that this small quantity 

 did not form a sensible precipitate when evapo- 

 rated to dryness with muriate of lime. The me- 

 thod, therefore, was not delicate enough to decide 

 the atomic weight of tartaric acid; but it is ob- 

 vious, that the tartrate of lime would consist of 

 3-5 grains of lime united to S-25 grains of tarta- 

 ric acid, and that the excess of the weight above 

 11 '75 must have been water. But this excess is 

 almost exactly half an atom of water ; for half 

 an atom of water is 0-5625, and 1175 + 0-5625 

 = 12-3125. Now, this differs from 12-3 grains 

 by so small a fraction of a grain, that the whole 

 difference may be safely ascribed to an error in 

 weighing. It appears from this, that* when tar- 

 trate of lime is dried in a temperature of 100 it 

 retains just half an atom of water. 



4. From the preceding experiments, which 

 were several times repeated, it is obvious, that the 

 true atomic weight of tartaric acid is S'25, and 

 not 8-375, as I formerly stated, misled by some 

 water mechanically lodged between the plates of 

 the crystals. Hence, the crystals mustiri reality C 



T /- tion of the 



be composed or crystals. 



1 atom tartaric acid 8*25 



1 atom water 1'125 



H2 



