On the intimate mixture and proper proportions and purity of the ingredients. 7. In what does the manufacture of gunpowder consist? In pulverizing the ingredients, incorporation, compression, granulation, drying, glazing and dusting. [Sidenote: 84]] 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. [Sidenote: 85]] 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. 12. Does powder inflame instantaneously? No; its inflammation is gradual, and progressive, and in a gun the projectile commences to move before the whole charge is ignited. 13. Why should gunpowder be grained? In order to facilitate the transmission of the flame. When the powder is very fine, and in large and compact charges, the flame cannot penetrate it, and it burns slowly and in successive layers. 14. Which burns quickest, the small or large grained powder? Before coming to the limit of dust, the smaller the grain, the more rapid the combustion, and the greater the bursting force of the powder. 15. What is the difference between the ignition and combustion of large and small grained powder?