234 Dr. Andrews on the Heat developed 



30 gr. of water, in a glass vessel, by the combination of .353 gr. potash with 

 nitric acid : 



This number differs by 0.93° from the absolute quantity of heat before found, 

 which is the loss of heat by this method of performing the experiment. It also 

 appears from the coincidence of the results obtained with different proportions of 

 alcali, that the loss of heat is proportional to the rise of temperature, and 

 hence the necessary correction for this error is, in all cases, easily made. 



22. When the base is insoluble in water, and slowly soluble in the acid, a 

 new element enters into the observation, and requires to be estimated, viz., the 

 cooling of the liquid during the prolonged duration of the experiment. In the 

 observations last described, the thermometer attained its maximum in about 45" 

 from the time the liquids were mixed, but in the solution of such substances, as 

 magnesia or the oxide of zinc, not less than 2', or 2|-' will elapse before the 

 liquid becomes transparent, and the thermometer stationary. Even to complete 

 the solution within this period, the liquid requires to be constantly stirred with a 

 glass rod. This circumstance renders these results less precise than those in 

 which the combination occurs instantaneously ; but the amount of error thus 

 produced may be estimated, by repeating the same experiment in precisely the 

 same manner, with a solution of caustic potash, containing exactly the quan- 

 tity of alcali (as deduced by calculation from the foregoing experiments) which 

 should produce the same elevation of temperature as had been obtained with the 

 slowly soluble base. The difference between the increase of heat actually found, 

 and that deduced from calculation, will be equal to the loss of caloric occasioned 

 by the stirring, and length of the experiment ; and consequently the required 

 correction for the number obtained by observation. The precise value of this 

 correction will be given hereafter. 



23. The general conclusions which I shall endeavour to establish in the 

 subsequent part of this communication, may be enunciated in the form of the 

 three following laws : 



Law 1. — Tlie heat developed during the union of acids and bases is de- 

 termined hxj the base and not hy the acid; the same base producing, when 



