Dr. R. Hare on the Explosiveness of Nitre. 535 



the walls and surrounding earth having given way in a man- 

 ner which created astonishment. 



19. In order to amplify the practical basis upon which the 

 preceding inferences had been founded, I made some experi- 

 ments on the combustion of gunpowder in an exhausted 

 receiver, so as to secure the gaseous products evolved. A 

 cylindrical glass receiver, such as is usually employed as a 

 candle-shade, was ground upon a lap-wheel, so as to fit air- 

 tight between two discs of sheet brass. The disc for closing 

 the upper opening of the receiver was furnished with two 

 cocks severally, for communicating with an air-pump and ba- 

 rometer gauge. The disc for closing the lower opening of 

 the receiver, so as to form the bottom of the space included, 

 was furnished with an arch of platinum wire soldered to two 

 stouter brass wires, of which one was soldered to the disc, the 

 other secured and insulated in passing through it by a collet 

 of leather, compressed about it by an appropriate screw. 

 These preparations being made, a portion of gunpowder, 

 weighing about twenty-five grains, was so supported on a tray, 

 as to include the middle portion of the platinum wire. The 

 receiver being put into its place, so as to be duly supported 

 by the lower disc and covered by the other, the air was with- 

 drawn, as far as practicable, with a good air-pump. In the 

 next place, the wire was ignited to incandescence. To my 

 surprise, the gunpowder only smoked at first, and did not 

 flash until a perceptible interval had elapsed. When this 

 result ensued, it appeared to be owing to the radiant heat, as 

 the early volatilization of a portion of sulphur had driven the 

 granules away from the wire, so that it did not touch any of 

 them. Subsequently, on allowing the air to enter, and re- 

 moving the receiver, it appeared that the gunpowder was only 

 partially burned. Thus it became evident that in this way a 

 complete combustion could not be effected. The feebleness 

 of the flash in vacuo shows how much confinement is essential 

 to give energy to the explosion of this powerful agent; and its 

 not being forthwith ignited by an incandescent wire, demon- 

 strates, that, as in the case of the apparent quiescence of a glo- 

 bule of volatile matter in an intensely heated cavity, a capa- 

 bility of volatilization delays this process, by preventing the 

 contiguity requisite to a communication of heat. 



20. This leads to a discrimination which has not, to the 

 best of my knowledge, been made heretofore. I allude to the 

 difference existing between fulminating combinations and ful- 

 minating mixtures. As an example of the latter, we have 

 gunpowder and other pulverulent mixtures consisting par- 

 tially of nitre, or chlorate of potash, while, as an exemplifica- 



