Explosives . ng thepowdei through slope reels. The next operation is the important one of hardening the grain by treatingit with solvent. This is frequently done by spraying it with the solventinside a drum, which can be closed hermetically and rotated about its a few minutes rotation the grains are thoroughly moist. The powderis then allowed to sleep for some time either in the same vessel or anotherone. and then it is dried. The preliminary drying may be carried out in asolvent recovery plant consisting of a rotating drum provided with a steamjacket and a hollow axle, which is con
Explosives . ng thepowdei through slope reels. The next operation is the important one of hardening the grain by treatingit with solvent. This is frequently done by spraying it with the solventinside a drum, which can be closed hermetically and rotated about its a few minutes rotation the grains are thoroughly moist. The powderis then allowed to sleep for some time either in the same vessel or anotherone. and then it is dried. The preliminary drying may be carried out in asolvent recovery plant consisting of a rotating drum provided with a steamjacket and a hollow axle, which is connected through a condensing coil witha vacuum pump. The coil, pump, etc., are placed in a separate compartmentfrom the drying drum, which is isolated by means of a wall having noopenings, in order to minimize the danger of fire. A considerable proportionof the solvent is recovered in ilns way, and after redistillation may be usedagain, but in order to obtain a satisfactory recovery it is necessary to cool the. FAST-BURNING SMOKELESS POWDERS 325 coil by means of refrigerated brine to a temperature considerably below thefreezing-point of water. The drum is fitted with ribs inside to prevent thepowder simply sliding round in a cake. The exit is covered with wire gauze andcotton wool to prevent dust being drawn into the condenser. The man-holelid tits air-tight, and can be held on by means of thum-screws, but duringthe drying these screws are removed so that the lid is held on by the vacuumonly. If pressure arises at any time during the drying the lid will at oncefall off and relieve the pressure. The temperature of the powder shouldnever exceed about 50° C. (122° F.). The powder as it comes from the drumscontains 3 or 4 per cent, of water and solvent. The drying is completed ontrays in a drying stove. When dry it is sifted so as to remove the grains thatare too large or too small : these are added in small proportion to a furthercharge in the milling operation. Finally, the powd
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