HEAT OF FORMATION OF SILVER HYPON1TRITE. 187 



by operating in presence of a very great excess of sulphuric 

 acid more concordant results may be obtained, such as 8'3 ; 

 7-5; 8-4; 8;9. 



These figures correspond sensibly to three equivalents of 

 oxygen absorbed. 



The solutions do not contain ammonia, but liberate by 

 ebullition a considerable quantity of nitrogen monoxide. In 

 another experiment, the oxygen absorbed and the nitrogen 

 monoxide were ascertained by analysis. The following results 

 were obtained : 



fixed : 8-3 : : N 2 liberated : 8'0 per 100 parts of salt. 



These figures correspond very sensibly to the following 

 transformation : 



Ag 4 N 4 5 + 3 + H 2 = ]ST 2 + 2HN03- 2 Ag 2 combined with 



the acid. 



This is therefore a fresh confirmation of the formula. The 

 analysis by the permanganate must be made by introducing 

 the salt of silver in a body into the mixture of perman- 

 ganate and sulphuric acid made beforehand and in excess, 

 as the hyponitrous acid set free slowly absorbs the oxygen 

 of the air. 



These facts being established, we have proceeded to the 

 calorimetric measurements, and successively determined the 

 heat of formation of the salt of silver, that of the acid itself, as 

 well as the heat liberated by its union with silver and potassium 

 oxides. 



5. Heat of formation of silver hyponitrite. We determined 

 the heat of formation of silver hyponitrite by oxidising it with 

 bromine water in accordance with one of the foregoing 

 experiments. 



The figures obtained are sufficiently close. The following is 

 a list of them : 



First Series. Action effected by a single operation for Ag= 108 grms. 



First ' ... 29-83 Cal.\ m . ftn o . fi o 



Second ... 31-54 / 



Second Series. Successive actions of HC1 and Br. 



Third ... 28-00 Cal.) 



Fourth 29-85 V mean 28'62. 



Fifth ... 28-00 ) 



The general mean of both series is equal to 29'65 Cal. 



The experimental ratio between the silver and the bromine 

 absorbed in equivalents was found to have a mean value of 

 3'71 ; a figure which is rather too high, owing, as before stated, 

 to the loss of bromine by evaporation. The theoretical ratio is 

 3-50. Let therefore the initial system be Ag 4 N 4 5 + 7H 2 + 



