402 Mr. Graham on the Heat disengaged in Combinations. 



grains of water, and the containing vessel and stirrer to 49 

 grains, making together 60*5 grains of water ; the capacity of 

 the salt dissolved or formed rarely exceeded that of 12 grains 

 of water. 



I. Neutralization of Hydrate of Potash by Nitric and 

 Hydrochloric Acids. 

 The equivalent proportion of this acid adopted in these ex- 

 periments is 33*85 grains, that is one-twentieth of 677, the 

 usual equivalent of nitric acid on the oxygen scale. Nearly 

 one-half the quantity mentioned was used in an experiment, 

 namely 0'455 equivalent, diluted in the crucible with about 

 four-fifths of the water, while the remaining portion of the 

 1544 grains of water, in a small and thin glass flask, contained 

 hydrate of potash in quantity sufficient to saturate the acid, 

 and leave a slight excess of alkali. The two liquids were af- 

 terwards brought to exactly the same temperature, which was 

 observed by two thermometers, the corresponding points of 

 which were accurately determined, and the potash solution 

 then emptied into the nitric acid. The following are the re- 

 sults of three observations of the temperature of the liquids 

 before mixture, and the temperature after mixture : — 

 Before mixture . . 61°*91 62°*13 62°*13 

 After mixture . . . 66°*70 66°-91 66°*89 

 Rise of temperature . 4°*79 4°*78 4°*76 

 Increasing 4°*78 the mean of the experiments, in the pro- 

 portion of 0*455 to 1, we have 10 o, 50 as the rise of tempera- 

 ture on saturating a whole equivalent of potash by nitric acid. 

 The heat evolved upon combination is sensibly affected by 

 a considerable difference in the temperatures at which the acid 

 and alkali are mixed ; being less at the lower temperature. 

 This appears by the following experiments, in which 0*5 equi- 

 valent of nitric acid was neutralized at a temperature twenty- 

 two degrees lower than in the former experiments. 



Before mixture . . 40°*25 40°*60 

 After mixture . . . 45°*43 45°* 80 

 Rise of temperature . 5°*18 5°*20 Mean 5°*19. 



Hence we have the heat from the neutralization of nitric 

 acid by hydrate of potash — 



10°* 50, at 62° F. 

 10°* 38, at 40° F. 



Half an equivalent of hydrochloric acid, 11*38 grains, was 

 neutralized with hydrate of potash in slight excess, exactly as 

 the nitric acid was treated in the preceding experiment. 



