during the Combination of Acids and Bases. 245 



the second atom of carbonic acid is attended with no evolution or abstraction of 

 heat. 



51. The tribasic, phosphoric, and arsenic acids, in their combinations with 

 the fixed alcalis, present a slight divergence from this law, and at the same time, 

 give results closely coincident with each other. In the following table, the 

 increments of temperature are exhibited which were observed, when solutions, 

 containing the compounds denoted by the first and second members of the ex- 

 pression, were mixed together. The symbol NaO corresponds, as before, to 

 .234 gr. soda, and the entire weight of the solution was 30 grammes. 



52. In other words, the combination of the common phosphate of soda with 

 half as much acid as it already contains produces an increment of temperature of 

 0°.46 ; and its complete conversion into the biphosphate, a farther increase of 

 0°.35. Similar numbers were obtained with the arsenic acid. 



(NaO+^-AsA) + iAsA • 

 (NaO + 1 As,0,) + iAs,0, . 



54. The same acid gave with potash, 



55. From these experiments it follows, that during the conversion of the 

 common alcaline phosphates and arseniates into supersalts, a quantity of heat is 

 evolved, which is about one-seventh part of that produced during the formation 

 of those salts themselves. As, however, the alcaline phosphates and arseniates 

 are not strictly neutral in composition, and their solutions have an alcaline re- 

 action, it is, perhaps, scarcely correct to adduce them as exceptions to Law 2. 

 The pyrophosphoric acid, in similar circumstances, scarcely produces any beat ; 



