MANUFACTURE, ETC., OF GUNPOWDER. 727 



state of the atmosphere, the different degrees of moisture in the pow- 

 der-meal, its varying bulk and elasticity, and other minor causes. The 

 only practicable method of securing an approximately uniform density 

 is to test the product of various pressings and then mix them, so as to 

 reduce the whole to the average density required, and this is the con- 

 stant practice at Waltham. 



We have alluded incidentally to the decrease of pressure in the 

 gun as the density of the powder increases. With the immense guns 

 constructed in recent years, it is important to reduce the strain on the 

 metal as far as possible, as this is the only way in which the gun can 

 be safely fired. But it must be remembered that, by seeking to ac- 

 complish this by indefinitely increasing the density of the powder, we 

 would at the same time decrease the velocity of the shot, or, in other 

 words, its useful effect. Artillerists have, therefore, had recourse to 

 the expedient of using a powder, each grain of which is a lump of 

 press-cake. The effect of this is to make it burn slower than grain- 

 powder ; for these lumps, when ignited at the surface, burn, as it were, 

 in concentric layers, until the whole is consumed ; and by this means 

 the explosion, though to all appearance instantaneous, is in reality 

 much more gradual than that which follows the ignition of smaller 

 grains. In other words, the explosion of the charge in a heavy gun 

 is made to be less of the character of a violent blow on the sides of the 

 bore and the base of the shot, and more like a gradual shove given to 

 the shot with a corresponding pressure on the gun. 



The first form proposed for cannon-powder for heavy guns was 

 that invented in America by Dr. Doreraus, in which the whole charge 

 was made into a solid disk, the size of the bore of the gun. This, how- 

 ever, was found to give very unsatisfactory results. Then the Rus- 

 sian Government adopted a powder compressed into large hexagonal 

 prisms, and in Belgium another powder was made in the form of cy- 

 lindrical pellets. This was adopted by our Government, and an im- 

 mense sum was spent on erecting machinery at Waltham for its manu- 

 facture, but the pellet-powder has since been superseded by a simpler 

 form, much easier to make, and giving better results ; and the pellet 

 machinery has been altered, and, we believe, is now used in the manu- 

 facture of gun-cotton. 



The pebble-powder now in use consists of cubes of compressed gun- 

 powder, with sides about four-fifths of an inch square. These pebbles 

 are made by passing press-cake of that thickness between two pairs 

 of rollers, armed with sharp-cutting edges. The first pair of rollers, 

 by means of these edges, cuts the cake into several small bars, about 

 four-fifths of an inch square at the ends, and these bars, on passing be- 

 tween the second pair of rollers, are divided into cubes or pebbles. 

 After having been rolled in a hollow cylinder, or reel, to round off the 

 sharp edges and get rid of the dust, the pebbles are carried to the 

 drying-house to be freed from the moisture they contain. 



