150 PRACTICAL LESSONS IN SCIENCE. 



burn rapidly enough. It must be broken up into grains, which 

 are separated by sieves, so that the grains of the same size go 

 together. These grains are polished by friction among them- 

 selves in revolving barrels, sifted from dust, dried and sifted 

 again, when the powder is ready for packing. For cannon powder 

 the grains are sometimes a half inch in diameter, and sometimes 

 they are made in molds, so that the form is definite. 



Good powder should be composed of hard angular grains 

 which do not soil the fingers, and when fired on a sheet of paper 

 should burn without sparks and without scorching the paper or 

 soiling it to any great degree. The products of the combustion 

 of powder are chiefly potassium carbonates and sulphates, with 

 carbon dioxide, carbonic oxide, hydrogen and marsh gas. The 

 solid powder changing into these gases, which are expanded by 

 the great heat of the combustion, accounts for the mechanical 

 effects of the explosion. 



It is estimated that the temperature resulting from the ex- 

 plosion of powder as ordinarily used is over 5,000 F., at which 

 temperature some of the gases might be separated into their 

 elements, which would increase the expansive force. It has been 

 estimated that the explosion of a cubic inch of good gunpowder 

 would exert a pressure of about fifteen tons to the square inch if 

 it could all be burned on the instant. It is at present impossible 

 to fully explain the phenomena of the combustion of powder, as 

 the products and conditions at the time of explosion must be 

 different from what they are afterward when the products may 

 be collected and studied. Gunpowder is of very great value. 

 Some have considered its influence on civilization as next in im- 

 portance to the discovery of the printing press and application 

 of steam to machinery. Besides its use in war it is of immense 

 value in all mining and quarrying industries and in many en- 

 gineering operations, although other explosives are supplanting 

 it in some directions. Gunpowder is superior to most other ex- 

 plosives in the uniformity of its action, in that its manufacture 

 and transportation are less dangerous, in that it is not liable to 

 change when stored, and for use in gunnery its slower action 



