Object of dusting.
The keeping qualities of powder are very much improved by removing the dust, which quickly absorbs moisture from the atmosphere. How performed for large-grain.This operation, for large-grain, is performed by cylindrical reels, about 8ft. 6in. long, and 3ft. 8in. in diameter, clothed with 28-mesh canvas, which revolve at the rate of thirty-eight times per minute. Those for large-grain are called horizontal reels, in contradistinction to those for fine-grain, that are called slope reels. Each is enclosed by a wooden case, to prevent the dust flying about the house. When the powder has run its time, one end of the reel is lowered. It then runs out into barrels placed to receive it. Glazed at same time.This entirely separates the dust, and imparts a fine black gloss, which is sufficient glazing for the large-grained powder.
DUSTING FINE-GRAIN POWDER.
Dusting fine-grain.
The fine-grain powder has a much greater proportion of dust when it leaves the granulating house than the large-grain, and it is found necessary, on this account, to use a different kind of reel. They resemble those for the former powder, except that they are covered with 44-mesh canvas instead of 28, and are placed at an incline which prevents their being choked up with the quantity of dust; each end is also open, and a continuous stream of powder, fed by a hopper, passes through while they revolve, and pours out at the lower end into barrels. This process is repeated a second time, which sufficiently frees it from dust.
GLAZING FINE-GRAIN POWDER.
Glazing fine-grain.
The fine-grain powder thus dusted, is then glazed for three hours in barrels capable of holding 300lbs. which are 3ft. 6-in. in length, and 2ft. 8-in. in diameter, revolving at the rate of thirty two times in a minute. By the mere friction of the grains against each other and the inside of the barrel, a glaze is imparted, presenting a fine polished surface to the grain.