244 Dr. Andrews on the Heat developed 



result. It is for this reason that the formation of the bitartrate of potash is 

 accompanied by heat, although none is evolved when the neutral tartrate of 

 soda combines with a second atom of acid. 



49. As a farther illustration of the same principle, I am unwilling to omit 

 the description of an interesting experiment, although its complete explanation 

 involves the consideration of a class of phenomena which I have carefully ex- 

 cluded from the present communication. Three solutions were prepared, each 

 containing 25 gr. of liquid ; the first, holding in solution .353 gr. of pure 

 potash ; the second, .520 gr. of carbonate of potash ; and the third, .683 gr. of 

 bicarbonate of potash ; consequently the amount of real alcali the same in all. 

 They were then separately neutralized by 5 gr. of a solution of nitric acid, 

 containing a considerable excess of acid, and the two latter solutions were well 

 stirred, to expel, as far as possible, the carbonic acid gas before the final tempe- 

 rature was observed. The elevations of temperature were, for 



DIF. 



50. Thus we see that the effect of separating the first atom of carbonic acid, 

 in the gaseous state, from its combinations with the alcali, was to cause the 

 disappearance of 4°.l of heat ; while the separation of the second atom, and its 

 complete expulsion in the gaseous state, produced a further diminution of 

 temperature of only 1°.3. In these observations, two distinct sources of an 

 absorption of caloric exists ; one, the separation of the chemical compound into 

 its constituents ; the other, the change of one of those constituents from the 

 liquid to the gaseous state. Had both causes acted equally on the second as on 

 the first atom of carbonic acid, we should have obtained with the bicarbonate, as 

 great a diminution of temperature as had occurred with the carbonate, or the 

 thermometer would have sunk 2°.4 instead of rising .4°. But the conversion of 

 the second atom of carbonic acid into the gaseous state is completely effected, 

 while a considerable portion of the first atom remains dissolved in the liquid ; 

 and consequently, the striking difference in the result can only be accounted for, 

 on the principle stated in the second law, that the combination, or separation of 



