QUANTITY OF ELASTIC FLUID FROM GUNPOWDER. 179 



powder is fired under the ordinary pressure of the air, as 

 for instance in a glass tube, the mouth of which is im- 

 mersed in water, leaving only space enough for the powder 

 at the top. If in this state the powder is fired either by 

 a burning-glass or by galvanism, it will be found to displace 

 water to the extent of nearly two hundred and fifty times 

 its bulk, and as soon as the gas produced by the explosion 

 cools to the temperature of the surrounding air it ceases to 

 contract, and remains a permanently elastic fluid. 



Modes of determining the Quantity of this Elastic Fluid 

 produced from tJie Explosion of a given Quantity of Gun- 

 powder. Different qualities of powder produce different 

 quantities of gas, and therefore in any calculations which 

 are made public, it is necessary to specify the powder which 

 has been used. Most of that sold now is probably far 

 superior to the powder with which Robins made his experi- 

 ments ; but, nevertheless, they approximate to the truth suf- 

 ficiently for our purpose. He used the Government powder 

 of his day, which was, I have reason to believe, not within 

 thirty per cent, of the strength of the Government powder 

 of 1859. He says that " 1 drachm of powder avoirdupois, 

 on explosion, sinks the mercurial gauge 2 inches ; and the 

 mercury in the barometer standing at near 30 inches, 15 

 drachms avoirdupois, or 410 grains troy, would have filled the 

 receiver with a fluid whose elasticity would have been equal 

 to the whole pressure of the atmosphere, or the same with the 

 elasticity of the air we breathe; and the contents of the receiver 

 being about 520 cubic inches, it follows that 15 drachms of 

 powder will produce 520 cubic inches of a fluid possessing the 

 same degree of elasticity with common air ; whence an ounce 

 of powder will produce near 555 cubic inches of such a fluid." " 



But in order to ascertain the density of this fluid, we must . 

 consider what part of its elasticity at the time of this experi- 

 ment was owing to the heat it received from the included hot , 

 iron and the warm receiver, and this is estimated by Robins 

 at about one-fifth of the whole, which brings 555 clown to 

 444. And this last number represents the cubic inches of 

 elastic fluid, equal in density and elasticity with common air, 

 which are produced from the explosion of 1 ounce of 

 powder; the weight of which quantity of fluid, according to 



N2 



