Mr. Graham on the Heat disengaged in Combinations. 419 



Before mixture . . 63°'41 63°-50 63°'50 



After mixture . . . 67 0, 40 67°'52 67°'49 

 Rise of temperature . 4°'09 4 o, 02 3°'99 



Doubling 4 o, 03, the mean result, we have 8 o, 06 F. as the 

 heat disengaged in the formation of one-third of an equivalent 

 of subarseniate of potash, or in the neutralization of each of 

 3 equivalents of potash by a single equivalent of arsenic acid. 

 Hence the successive addition of 3 equivalents of potash to 

 1 of arsenic occasions the following disengagements of heat :— 

 By first KO 10 o, 20; formation of binarseniate of potash. 

 ... second KO 8 o, 10; formation of arseniate of potash. 

 ... third KO 5°*88; formation of subarseniate of potash. 

 24°'18 = 8*06 X 3. 

 Of hydrated phosphoric acid, which had been boiled in 

 water for a considerable time to render it fully tribasic, half 

 an equivalent was mixed with half an equivalent of potash, to 

 form biphosphate of potash (2HO, KO, P0 5 ) :— 



Before mixture . . 64°'00 64°'00 64°'03 

 After mixture . . . 69°'01 68°-99 69°'02 

 Rise of temperature . 5°-01 4°-99 4°«99 



Taking 5 o, 00 as the mean, we have 10 o, 00 F. as the heat 

 disengaged on saturating 1 equivalent of potash with 1 equi- 

 valent of phosphoric acid in the formation of biphosphate of 

 potash, containing KO + 2HO as bases. 



By mixing one-fourth of an equivalent of phosphoric acid 

 with half an equivalent of potash, phosphate of potash (HO, 

 2KO, P0 5 ) was formed :— 



Before mixture . . 64°'00 63°-61 63°-63 



After mixture . . . 68°-49 68°-08 68°-18 



Rise of temperature . 4°'49 4°*47 4°-55 



Doubling the mean result, 4°*50, we have 9°'00 F. as the 



heat disengaged in forming half an equivalent of neutral 



phosphate of potash, or in saturating each of 2 equivalents of 



potash by 1 equivalent of phosphoric acid, in the formation of 



phosphate of potash. 



The same phosphate of potash was formed by mixing solu- 

 tions of half an equivalent of biphosphate of potash with half 

 an equivalent of potash : — 



Before mixture . . 64°-06 64°- 14 64°- 15 



After mixture . . . 68°-09 68°- 15 68°' 16 



Rise of temperature . 4°-03 4°-01 4°-01 



Doubling 4°*02, the mean result, we have 8°-04 F. as the 



heat disengaged on saturating an equivalent of potash with 



the acid of biphosphate of potash. 



2 E 2 



