278 COMPOUNDS DERIVED FROM NITRIC ACID. 



of experimental errors ; as the difference does not amount to 

 half per cent, of the heat of combustion. In fact, the heat 

 of total combustion of this salt is, according to calculation 4- 

 688 Gal., according to experiment + 691, for 246 grms., or, 

 for 1 grm., 2797 cal. 



3. We now come to potassium picrate 



C 6 H 2 (N0 2 ) 3 KO = 267 grms. 

 According to table iv., p. 127, the reaction of the acid and base 



C 6 H 3 (lSr0 2 ) 3 (crystal.)^ KHO (solid) 

 = C 6 H 2 K(N0 2 ) 3 (solid) + H 2 (solid), gives off + 30-5 Cal. 



Admitting that K + H + = KHO gives off + 104'3, we get 

 for the heat of formation of potassium picrate from its elements, 

 for 267 grms. 



C 6 + H 2 + K + N 3 + 7 ; + 58 + 104-3 + 30'5 - 704 = 

 + 1224 cal. 



Sarrau and Vieille gave, for combustion in oxygen, 4- 117*5 

 Cal. The difference in these values amounts to less than 

 one-hundredth of the total heat of combustion, thus being 

 within the limits of error ; more so when we take into account 

 that the action of the water, formed in the combustion, on the 

 the potassium bicarbonate has been disregarded by these writers 

 in their calculation, as well as the partial dissociation of the 

 last-named salt. 



4. The heat of total combustion of potassium picrate, with 

 formation of potassium bicarbonate, amounts to 619 4 7 Cal., or, 

 for 1 grm., 2321 cal. 



5. The explosive decomposition of potassium picrate gives rise 

 to complex products : carbonic acid, carbonic oxide, hydrocyanic 

 acid, free hydrogen, nitrogen, marsh gas. The relative propor- 

 tion of these bodies varies with the conditions. 



Thus carbonic acid and marsh gas increase with the pressure, 

 at the expense of the carbonic oxide and hydrogen. 



As to the solid residue, it is composed of potassium carbonate 

 and cyanide containing, according to Sarrau and Vieille, the 

 third of the alkaline metal, with a small quantity of carbon. 

 With a density of charge of '5, the results observed by these 

 writers are represented approximately by the following empiric 

 equation : 



16C 6 H 2 K(N0 2 ) 3 = 4KCN + 6K 2 C0 3 + 21C0 2 + 52CO + 

 6CH 4 + 22N 2 + 4H 2 + 70. 



According to this equation, an equivalent of potassium picrate 

 (267 grms.) would disengage, in decomposing, + 2084 Cal., or, 

 for 1 grm., 780 cal. 



