POTASSIUM PERMANGANATE PROCESS. 177 



word, the nitrite and the bromine are not entirely changed into 

 nitrate and hydrobromic acid under these conditions, but there 

 exists in the solution a bromonitric compound analogous to 

 aqua regia, and the continued presence of which interferes with 

 the application of the calorimetric calculation by means of the 

 equation given above. 



As a matter of fact the calculation applied to the results of 

 these experiments has given results falling below the theoretical 

 reaction Ba(N0 2 ) 2 dissolved -f O 2 = Ba(N0 3 ) 2 dissolved ; the 

 value obtained fluctuating about 4- 18 Cal. instead of -J- 22 Gal. 

 These results are, therefore, not included in the averages on 

 account of the incomplete nature of the transformation. But it 

 has been thought proper to point out, from the purely chemical 

 point of view, the true character of the reaction of bromine on 

 the nitrites. 



Fourth process. Potassium permanganate. It is well known 

 with what accuracy this reagent may be employed to convert 

 nitrites into nitrates. 



The experiments were performed with a solution of absolutely 

 pure potassium permanganate of known strength, 1 mixed with 

 a large excess of dilute sulphuric acid ; 2 for instance, 192 cms. of 

 the permanganate solution (20 grms. = 1 litre) and 1800 cms. of 

 a solution of dilute sulphuric acid, mixed in a large platinum 

 calorimeter and 2*470 grms. of crystallised barium nitrite, 

 Ba(N0 2 ) 2 H 2 0, added. The reaction is instantaneous. The heat 

 liberated is measured as soon as the reaction is accomplished, 

 the excess of the permanganate is reduced by a standard solution 

 of oxalic acid (160 cms. for instance), the whole of the carbonic 

 acid formed remains dissolved. The quantities of heat liberated 

 in this second reaction are also measured. 



The sum of the quantities of heat which result from the fore- 

 going experiments represents the heat liberated. 



As a check, the excess of oxalic acid remaining in the liquid 

 is ascertained. These measurements, combined with the data 

 contained in the author's Memoir e sur la chaleur de combustion 

 de I'acide oxalique? and with the figures obtained in the reduction 

 of potassium permanganate by oxalic acid, 4 enable us to calculate 

 the heat liberated in the transformation of barium nitrite into 

 nitrate. 



Finally, by this method it was found that the reaction 

 Ba(N0 2 ) 2 dissolved -f 2 gas = Ba(N0 3 ) 2 dissolved liberates 



First trial + 21-7 Cal. 



Second trial +20-5 



Mean + 2M 



These results are rather less reliable than those of the two 



1 " Annales de Chimie et de Physique," 5 e sdrie, torn. v. p. 306. 



2 Ibid., p. 308. 3 Ibid., p. 305. * Ibid., p. 309. 



N 



