HEAT OF FORMATION OF NITROGLYCERIN. 423 



not permit of allowing nitroglycerin, either free or associated 

 with a pulverulent substance, to remain long in a current of 

 water. 



It is poisonous. 1 



5. Nitroglycerin is very sensitive to shock, and explodes 

 easily by the shock of iron on iron or silicious stone. The fall 

 of a flask or of a stone jar has occasionally sufficed to cause 

 explosion. The shock of copper on copper, and especially of 

 wood on wood, is considered less dangerous ; however, there are 

 instances of explosion provoked by a shock of this kind. 



6. Pure nitroglycerin keeps for an indefinite time. The 

 author has kept a bottle of it in his collections for ten years 

 without it showing any signs of alteration. But a little 

 moisture, or a trace of free acid, is sufficient to excite a 

 decomposition, which, when once commenced, is sometimes 

 accelerated up to the point of inflammation, and even of ex- 

 plosion of the substance. 



The action of s)lar light also causes the decomposition of 

 nitroglycerin, as well as that of the nitric compounds in general. 



Electric sparks inflame it, though with difficulty. They may 

 even cause it to explode under certain conditions ; for instance, 

 under the influence of a series of strong sparks, nitroglycerin 

 changes, turns brown, then explodes. 



Submitted to the action of heat, it is volatilised to an ap- 

 preciable extent, especially towards 100; it may even be 

 completely distilled, if this temperature be long maintained. 

 But if the temperature be suddenly raised to about 200, nitro- 

 glycerin ignites; and a little above it, explodes with terrible 

 violence. 



Its inflammation, caused by contact with an ignited body, 

 gives rise to nitrous vapour and a complex reaction, with the 

 production of a yellow flame, without explosion, properly so 

 called, at least as long as small quantities of matter are operated 

 upon. But if the mass be too great it ends by exploding. 



The explosion of nitroglycerin corresponds to a very simple 

 decomposition 



2C 3 H 2 (N0 3 H) 3 = 6C0 2 + 5H 2 + 6T + 0. 

 It will be seen that nitroglycerin possesses the exceptional ^ 

 property of containing more oxygen than is necessary for com- 

 pletely burning its elements. 



7. Heat of formation from the elements (p. 282) 



C 3 (diamond) + H 3 + N 3 + O 9 = C 3 H 2 (N0 3 H) 3 liberates 

 + 98 Cal. 



8. The heat of total combustion and the heat of decomposi- 



1 For the preparation with the aid of two binary mixtures made beforehand, 

 see Boutmy et Faucher, "Comptes rendus des stances de 1'Acade'rme des 

 Sciences," torn. Ixxxiii. p. 786. 



