52 POPULAR SCIENCE REVIEW. 
inches square. A shower of this alone fired from a gun would be 
quite as effective as grape, and it is possible that 300 lbs. of 
this tremendous powder will form the charge of the new 80-ton 
gun. 
For rifle powder the meal is pressed into thin cakes ; these 
are broken up into irregular pieces by hand, and carried to the 
granulating machine. This machine consists of four pairs of 
toothed cylinders, between which the broken cake is passed. As 
it falls from them in grains, it is received upon a series of 
screens of network. There are three of these, the texture of 
each being closer than that above it, so that large-grain powder 
is retained on the first, while fine* grain and dust fall through 
it. The fine-grain remains on the second, and the dust passes 
on to the third. All the screens are placed in an inclined posi- 
tion, so that the powder runs down them into tubs arranged at 
the lower end, one of which receives the large, another the fine- 
grain, and a third the dust. 
The powder is then rolled for some hours in the glazing- 
barrels, to break off all minute irregularities, and give it a 
smooth surface. Then it is dried, and finally freed from dust 
in the slope-reel. This done, it is finished by being passed 
once more through the glazing-barrels, and it is then packed in 
barrels of 100 lbs. each. 
Such is the process of the gunpowder manufacture in the 
Eoyal Factory at Waltham. We have only briefly indicated the 
principles of each process, for to go into detail would occupy 
far greater space than is at our command ; but even this sketch 
will show how at each step science has been called in to aid art 
in bringing the manufacture to its present high state of perfec- 
tion. No expense is spared in procuring the best materials, 
the most efficient machines, and the most accurate tests ; yet 
the cost of manufacture is only about sevenpence per pound. 
What a contrast to the early days of gunpowder making, when 
in France, in 1375, a pound of gunpowder cost a sum equal to 
ten pounds of our money ! 
In every department the greatest care is taken to prevent 
the danger of explosions. The houses are built from two to 
four hundred yards apart. Wood, copper, and gun-metal are 
the only materials used in the structure of the machines, except 
where, and that rarely, a bolt of iron is introduced for the sake 
of strength, and then the metal is encased in leather. The 
floors are covered with hides secured with copper nails, and 
these as well as the wooden platforms round the houses are 
kept constantly wet. All loose powder is swept away from the 
floors, damped, and carried to a magazine, where it is collected 
and the saltpetre "subsequently extracted. No one is allowed to 
enter a room without putting on a pair of leather £C magazine 
