Mr. Graham on the Heat disengaged in Combinations. 403 



Before mixture . . 60°-20 60°'00 59°'95 

 After mixture . . . 65°'3Q 65 0, 15 65 0, 10 

 Rise of temperature . 5 o, 10 5°' 15 5°' 15 

 Mean rise 5°'13 for 0*5 equivalent of hydrochloric acid, or 

 10 o, 26 for 1 equivalent of that acid. The neutralization of 

 hydrate of potash, therefore, in very dilute solutions with 

 these two different acids produces nearly the same disengage- 

 ment of heat, the result with nitric acid being 10 o, 50. 



The heat of combination appears also to be sensibly affected 

 in amount by the temperature of the experiment: — 

 Before mixture . . 40°-00 40°-25 

 After mixture . . . 45°-02 45°'30 

 Rise of temperature . 5 o, 02 5°'05 Mean 5°'03 

 From which it follows that the heat from the neutralization 

 of hydrochloric acid by hydrate of potash is — 

 10°- 26, at 60° F. 

 10°-06, at 40° F. 

 It is remarkable how large a proportion the cold produced 

 on dissolving in water crystallized nitrate of potash and 

 chloride of potassium, the salts produced in these experiments, 

 bears to the heat observed in the formation of the same salts. 

 One equivalent of crystallized nitrate of potash (63*25 grs.) 

 well dried, pounded and sifted, was dissolved in the usual 

 quantity of water : — 

 Before solution . 61°'80 62°-20 61°'88 

 After solution . . 56°' 10 56°'45 56°' 18 

 Fall of temperature 5°'70 5°'75 5 U> 70 Mean 5°«72. 

 Before solution . 56 *45 57°'70 55°-45 

 After solution . . 50°-80 52°-00 49°*75 



Fall of temperature 5°-65 5°'70 5°'70 Mean 5°-68. 

 The cold on dissolving this salt is not quite constant, but 

 increases sensibly at low temperatures, a law which appears 

 to prevail in a class of salts : — 



Before solution . 47 o, 00 46°-40 45°*95 



After solution . . 41°-Q5 40°-47 40°-Q0 



Fall of temperature 5°*95 5°-93 5°*95 Mean 5 0, 94. 

 It appears, on comparing the last set of experiments with 

 that immediately preceding it, that a difference of ten degrees 

 at this part of the scale makes a difference of o, 26, or 

 l-22nd part, in the fall of temperature consequent upon 

 the solution of an equivalent of nitrate of potash. It is 

 this increased absorption of heat at the low temperature pro- 

 bably which occasions the observed heat of combination of 

 the salt to diminish at the same part of the scale. 



2 D2 



