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8. Explain the method of making gunpowder by the pounding mill.
The charcoal in small pieces is first placed in the mortars, with a quantity of water, and pounded for half an hour; after which the saltpetre and then the sulphur, previously pulverized and sifted, are put in, and the whole well mixed with the hand; it is then pounded in the mortars, and at the end of each hour, the composition is passed from each mortar into the next. At the sixth or eighth change, add half a pint of water; it is then pounded two hours without changing the mortars, in order that it may form into cake. It is then partially dried, and grained in a graining sieve, or passed between wooden rollers. The grains are then sifted to separate those which are too coarse and too fine, and also to separate from each other the different kinds of grains for cannon, musket, and rifle powder. It is then glazed in large glazing barrels, which make 15 or 20 revolutions in a minute. A charge of 500 lbs. is thus treated for about twenty-four hours. It is then dried either in the open air, or in a drying house. If in the open air, when the sun is too hot, the powder should be covered to prevent the loss of sulphur. It is then dusted, by being sifted in fine sieves, or through bolting cloths.
9. What other machines besides the pounding mill are used in pulverizing and incorporating the ingredients of gunpowder?
Rolling barrels, and the cylinder or rolling mill.
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10. What advantage is gained by the use of the rolling barrels?
It lessens the duration and danger of pounding in the mortars. After the ingredients are pulverized and mixed in the rolling barrels, the mixture is placed under the pestles of the pounding mill, 10 per cent. of water is added, and it is beaten for three hours only.
11. Which mill is now generally used?
The CYLINDER MILL, which forms 50 lbs. of composition into cake in from one to three hours.