552 APPENDIX. 



in the centre, the instantaneous escape of the gases. This is 

 shown by Abel's experiments, already referred to, when he 

 observed velocities of 5300 m. to 6000 m. 



The facts set forth in this paper show that the explosive wave 

 only exists with its simple characteristics and definite laws, in the 

 detonation of gases. These laws and characteristics only partially 

 hold in the detonation of liquids and solids while remaining 

 subject to the same general notions of physico-chemical dynamics. 



On the different modes of explosive decomposition of picric acid and 

 nitro compounds. 1 



Considerable diversity of opinion has existed as to whether 

 picric acid can be exploded by simple heating. It is indeed much 

 less explosive than nitric ethers like nitroglycerin and gun-cotton, 

 for if a fairly large mass be heated gradually in a capsule or flask 

 it melts and emits vapours which catch fire and burn with a 

 fuliginous flame, but without giving rise to any explosion. A 

 very small quantity carefully heated in a glass tube may even be 

 volatilised without decomposition. 



But it is a mistake to believe that picric acid is incapable of 

 exploding by simple heating. Now this body, when submitted 

 to a high temperature, decomposes with disengagement of heat, 

 oxidising itself at the expense of the nitrous vapours it contains. 

 The author has experimentally proved that when a reaction 

 liberates heat its rapidity increases, on the one hand, with the 

 condensation of the matter for the same temperature, and, on the 

 other hand, with the temperature for the same condensation. 

 The latter increase takes place very rapidly, according to a law 

 expressed by an exponential function of the temperature. This 

 tends to render the reaction explosive. 



When a closed vessel is used the heat disengaged by the 

 reaction helps further to elevate the temperature, and consequently 

 to accelerate the phenomena. 



In conformity with these principles picric acid may be caused to 

 detonate violently in an open vessel at the ordinary pressure, 

 when it is suddenly heated in a vessel which has been previously 

 raised to a high temperature, and the mass of which is such that 

 the introduction of a small quantity of picric acid does not 

 appreciably modify the general temperature. 



The experiment may be made in the following way : A glass 

 tube is taken, closed at one end, and about 25 mm. or 30 mm. in 

 diameter, placed vertically over the flame of a gas burner, and 

 heated to visible redness, without, however, melting the tube. 

 Two or three crystals of picric acid, not exceeding a few milligrams 

 in weight, are projected into the bottom of the tube, when they 

 immediately explode violently, before having had time to be 

 reduced to vapour, a very bright white light and characteristic 

 noise being also produced. 



An experiment was made in an atmosphere of nitrogen, and 

 only a few flakes of carbon remained. 



1 "Annales de Chimie et de Physique," 6 C serie, torn, xv. pp. 21-25. 



