462 PICRIC ACID AND PICRATES. 



flask to show its explosion, the latter having been propagated 

 backwards along the trail of dust up to the principal mass. 



2. The formula for picric acid is C 6 H 3 (N0 2 ) 3 0, its equivalent 

 229. 



3. Its heat of formation from the elements (p. 277) 



C 6 (diamond) + H 3 + N 3 + 7 = C 6 H 3 N 3 7 + 491. 



This body hardly contains more than half the oxygen necessary 

 for its complete combustion. 



4. Its heat of total combustion by free oxygen 



2[C 6 H 3 (N0 2 ) 3 0] + 13 = 12C0 2 + 3H 20 + 3N 2 , 



is equal to -f 61 8 '4 Cal. (water liquid), according to the results 

 of the experiments of Sarrau and Vieille. 



5. The equation representing its explosive decomposition has 

 not been studied. Admitting provisionally the following 



2[C 6 H 3 (N0 2 ) 3 0] = 3C0 2 -f SCO + C -f 6H + 6N, 



the heat liberated would be + 13O6 Cal., or 570 CaL per 

 kilogramme. 



6. The reduced volume of the gases would be 190 litres per 

 equivalent, or 829 litres per kilogramme. 



7. This figure divided by n, or -, practically represents 



the permanent pressure, owing to the small volume occupied by 

 the carbon, with the usual exception of the liquefaction of the 

 carbonic acid. 



10942 atm. 



8. Lastly, the theoretical pressure = . These 



values are only given with all due reserve. 



9. To obtain a total combustion of picric acid, recourse must 

 be had to a complementary oxidising agent nitrate, chlorate, 

 etc. It has been proposed, for instance, to mix picric acid 

 (10 parts) with sodium nitrate (10 parts) and potassium 

 bichromate (8 '3 parts). These proportions would furnish a 

 third of oxygen in excess of the necessary proportion. 



But it is doubtful whether this powder has ever been pre- 

 pared on a large scale or kept. In fact, the mechanical mixture 

 of bodies of this nature can only be executed without danger 

 on the condition of wetting the pulverised substances before 

 incorporating them under the millstone or otherwise. Now, 

 as soon as water intervenes, the picric acid displaces the nitric 

 acid of the nitrates, even in the cold, and this volatile acid dis- 

 appears wholly or partly during the drying in the stove. This 

 circumstance hardly permits of employing free picric acid in 

 the manufacture of powders. 



An analogous reaction renders its mixture with potassium 

 chlorate particularly dangerous. 



