Mr. Graham on the Heat disengaged in Combinations. 415 



V. Neutralization of Oxalic Acid by Hydrate of Potash. 

 Half an equivalent of oxalic acid was neutralized by potash 

 under the usual circumstances: — 



Before mixture . . 64°*60 64°*66 64°*69 



After mixture . . . 69°*84 69°*89 69°*95 



Rise of temperature . 5°*24 5°*23 5°*26 



Doubling 5°*24, the mean result, we have 10°*48 F. as the 



heat evolved on the saturation of a whole equivalent of oxalic 



acid by hydrate of potash. 



One equivalent of crystallized oxalic acid, 39 '50 grains, 

 containing 12*5 grains of water of crystallization, was dissolved 

 in 1533 grains of water at 67° F., with a fall of 3°*04, 3°*06, 

 3°*04 ; of which the mean is 3°*05. 



One equivalent of oxalate of water deprived of its water of 

 crystallization, 28*25 grains, was dissolved in 154-4 grains of 

 water at 67° F., with a fall of 0°*99, 0°*99, l°*0l ; of which 

 1°*00 is the mean. The difference between the falls on solu- 

 tion of the hydrated and anhydrous oxalate, is occasioned by 

 the hydration of the latter on solution. The heat disengaged 

 when oxalate of water combines with its two atoms of consti- 

 tutional water is therefore 3°*05 — l c *00 = 2°*05 F. 



Neutral oxalate of potash crystallizes with a single atom 

 of water, which requires a heat of 212° to expel it. 1 equi- 

 valent of the crystallized salt, 57*76 grains, containing 6*25 

 grains of water, was dissolved in 1538 grains of water at 67° F., 

 with a fall of 2°*65, 2°*66 and 2°*67 ; of which the mean is 

 2°*66 F. 



Of the same salt made anhydrous by heat, one-half of an 

 equivalent, 25*75 grains, was dissolved in 1544 grains of water, 

 with a fall of 0°*76, 0°*71, 0°*74; of which the mean is 0°*74. 

 A whole equivalent of the salt would therefore have dissolved 

 with a fall of 1°*58, which is 1°*08 less than the fall from the 

 hydrated salt. The last quantity represents the heat of com- 

 bination of oxalate of potash with one atom of water of cry- 

 stallization. It approaches nearly to one-half of the heat 

 disengaged by oxalate of water, in combining with two atoms 

 of water, one-half of 2°*05 being 1°*025 ; the difference is 

 within the errors of observation. 



When hydrated oxalate of potash is dissolved in water 

 containing oxalic acid, the change of temperature is very 

 much the same as in pure water, although in the former case 

 a superoxalate will be formed. One-fourth of an equivalent 

 of oxalate of potash, 14°*44 grains, was dissolved in 1544 

 grains of water containing in solution one-fourth of an equi- 

 valent of hydrated oxalic acid, at 67° F., with a fall of 0, 70, 



