442 Mr, F, A. Abel on the Causes, Effects, [March 21, 



shown by Dr. Frankland's researches). The principle of regulated 

 compression, and of combustion in one direction, is applied to the pre- 

 paration of rockets, signals, and numerous pyrotechnic arrangements, 

 other explosive mixtures being, in some instances, substituted for the 

 gunpowder. 



The advantages offered by materials of a much more powerfully or 

 rapidly explosive character than gunpowder, when employed simply as 

 destructive agents (for instance, in many classes of mining operations), 

 have led to repeated attempts at the application, as substitutes for gun- 

 powder, of highly explosive mixtures, readily obtainable in large 

 quantities, in which chlorate of potassa is employed, in the place of 

 a nitrate, in conjunction with very oxidisable materials, such as the 

 sulphides of arsenic and antimony, and compounds containing carbon 

 and hydrogen (Callow's mining powder and white or German gun- 

 powder are examples of such compounds). All attempts to manu- 

 facture and employ such mixtures have, however, invariably terminated 

 in more or less disastrous results, in consequence of the comparatively 

 low temperature at which chlorate of potassa exerts its oxidizing power. 

 Very slight friction or percussion suffices to inflame many of these 

 mixtures, and the violence of their explosive action is, in many in- 

 stances, as difficult to control as that of explosive chemical compounds. 

 Even in the manufacture and employment of comparatively so safe an 

 agent as gunpowder, which may be subjected, without ignition, to 

 tolerably powerful friction or percussion, and to the direct application 

 of any temperature below that which suffices to ignite sulphur (about 

 550^ Fah.), the neglect of strict precautions, for excluding the pos- 

 sibility of a particle of the powder being subjected to sudden and 

 powerful friction, may, and frequently does, lead to accidental explo- 

 sions. The occasional accidents in gunpowder manufoctories are 

 generally enveloped in mystery, in consequence of their fearfully 

 destructive effects ; in all cases, however, where it has been possible to 

 trace the causes of such explosions, they have been found in the wilful 

 or accidental neglect of simple precautionary measures, indispensable 

 to the positive safety of the works and operators. 



The more highly explosive mixtures, and some few explosive 

 compounds, though inapplicable as substitutes for gunpowder, on ac- 

 count of their great sensitiveness to the effects of heat, have, in con- 

 sequence of this very quality, received important applications in 

 numerous ingenious contrivances for effecting the ignition of gun- 

 powder. Well-known instances of such applications are : — The em- 

 ployment of fulminate of mercury in percussion-caps ; of a mixture 

 of chlorate of potassa and sulphide of antimony, in arrangements for 

 firing cannon by percussion and by friction, and for exploding shells 

 by percussion or concussion ; and of the same mixture, exploded at 

 will, by being brought into contact with a drop of strong sulphuric 

 acid, for the ignition of submarine mines or of signals. 



Other mixtures, combining a high degree of explosiveness with 

 power of conducting electricity, have been successfully applied to 



