2 AbsU-act of Frof. Hess's Tkermometrical Researches. 



Experiments with nitric acid. — The experiments with nitric 

 acid were carried on in precisely the same manner as those 

 already described. The acid employed had the specific 

 gravity 1-325. By combination with potash the quantity of 

 heat evolved from an atom of this nitric acid was found to be 

 expressed by the numbers 419*5 and 399*4, mean 409*45. 

 "With soda, the numbers 410*9 and 409*2 were obtained 

 (mean 410*05). With ammonia, the experiments being car- 

 ried on in the calorimeter, the results were 398*5, 404*5, and 

 400*8, the mean being 404*3. "When combining with dry 

 lime an atom of nitric acid was found to evolve heat, in pro- 

 portions expressed for five trials, by the numbers 459*3, 459*3, 

 450*6, 435*6, and 451*7, the mean being 451*3. 



The composition of the nitric acid used being expressed by 

 the formula N O5 + 8 HO, the general results obtained by the 

 combination of the bases and acids experimented on by M. 

 Hess may be arranged as in the following table, in which the 

 numbers exhibit the proportional quantities of heat, expressed 

 by each base with an atom of the acid at the head of each 

 column. 



Although the mean numbers are here given without any 

 correction, it is yet evident that the three first in each column 

 are the same, differing only by quantities which fall within 

 the limits of unavoidable experimental error. 



The numbers given for lime are all much higher, but it is 

 to be remarked, that with sulphate of lime this results evidently 

 from the fixation of water (see Phil. Mag.,S. 3., vol.xix. p. 181), 

 and that the other lime salts also fix water. It hence follows 

 that if the numbers in each vertical column are the same for 

 all bases, a constant proportion holds between the numbers 

 in each horizontal line, which are given by any one basis for 

 the different acids, and this in-oportioji is the savie for every 

 base (supposing the salt to be neutral and anhydrous). It is 

 only necessary, therefore, to know the quantity of heat evolved 

 by the union of an acid with any one base, to determine either 

 the quantity of heat evolved by this base with any other acid, 

 or by the same acid with any other base. It may be objected 

 that this result may not be general, but hold only for a cer- 



