I 



Aqueous Solutions of Acids and Alkalies. 453 



case no heat is disengaged, the whole effects of the cold are 

 thermometric. 



Gay-Lussac's idea, that the production of cold on solution 

 is evidence that the substance dissolved cannot form a hy- 

 drate, or'becdme any further hydrated, appears to me to be 

 erroneous. How is it possible to account for the expansion 

 which occurs on dissolving sal-ammoniac in a minimum of 

 water, except by admitting the exercise of chemical action ? 

 or how account for the condensation it effects with a maximum 

 of water, except by admitting the same agency ? It seems to 

 me, that hydration is evident in both cases, notwithstanding 

 the production of cold. What other explanation also shall 

 we give of the phaenomena attending the solution of crystal- 

 lized carbonate of soda ? While in the very act of dissolving, 

 under production of considerable cold, this salt simultane- 

 ously combines with an additional quantity of water, and 

 causes a large amount of condensation. The heat disen- 

 gaged by this condensation, being spent in liquefying the 

 crystallized hydrate, is not sensible to the thermometer, which 

 only detects the cold that remains in excess. But since the 

 condensation certainly takes place and can be measured, it 

 proves the thermometer to be a very fallible and incompetent 

 guide in this field of research. . 



Table XV. — Ammonia. 

 N 2 H 6 = 214-47 grs. Temperature 62° F. 



