The incorporation, or grinding together, of the three ingredients that form gunpowder is by far the most important process in the whole manufacture, for unless the minute particles of the ingredients be thoroughly blended and brought into the closest contact with each other, all subsequent operations— however well performed—will not compensate for the error. The incorporating mill consists of two large and heavy "hard chill" cast-iron edge runners, revolving on a circular cast-iron bed; the peculiar action of these runners or rollers is well adapted for thoroughly grinding and incorporating the several ingredients; their great weight is for crushing the ingredients; which are also ground together by the twisting action produced by the rollers traveling round in a small circle. Each roller travels over the bed in a separate track, and is assisted by the plough, which mixes the material, so that it is subjected to crushing, grinding, and mixing by the one operation.
The composition attains a body in about one hour after the runners are set in motion, and the action of the ploughs in moving the whole of the material on and across the bed thoroughly mixes it, and subjects every particle to the same amount of pressure. Each pair of runners is provided with a telltale dial, which shows the attendant the time that the mill has to run, and enables him to judge the condition of the cake from time to time. From three to four hours is the period a charge should be on the mill, providing the engine or water-wheel is maintained at its proper speed. The cake should be of a blackish-gray color, and, when broken, of a uniform appearance, without any white or yellow specks in it; the presence of these would indicate insufficient incorporation or grinding. Furthermore, it should not be more than half an inch in thickness, in order to be thoroughly incorporated, nor should it be less than a quarter of an inch thick to insure safety, because if the runners are allowed to come in contact with the bed, the friction caused by their twisting action is so great that an explosion would almost certainly be the result. For fine sporting gunpowder the operation of incorporating is continued in some cases for as long as eight hours, and with heavier rollers, but it is doubtful whether the powder is much, if at all, improved thereby.
Farrow, Edward S. American Small Arms; a Veritable Encyclopedia of Knowledge for Sportsmen and Military Men. New York: Bradford, 1904. Print.
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