The smoke torch is a pyrotechnic device which produces a dense cloud, used primarily to form a smoke screen for the purpose of concealment.
Fig. 199. - Sectional drawing of smoke torch.
Fig. 198. - Smoke torch.
4. First-fire composition.
5. Match (imbedded).
7. Paper disk.
9. Match (through cardboard).
10. Strike-blob composition.
11. Blob guard.
15. Striker composition.
16. Striker protector.
22. Box lining.
23. Box strap and nails.
Figure 200 shows the concealing effect produced by the functioning of half-a-dozen smoke torches. Climatic conditions and the velocity of the wind materially influence the effectiveness of the smoke torch. Following is given a series of pictures showing the development of a smoke screen under a very unfavorable condition of high winds, as indicated by the way the smoke is blown almost horizontally from the stacks in the background. Despite this unfavorable condition the smoke screen produced from the 16 smoke torches has almost concealed the plant in the background which covers an area of approximately six acres.
Fig. 200. - Smoke screen.
Fig. 205. Successive stages half-minute intervals of smoke screen under high wind.
The smoke is a dense white cloud with a slight tinge of yellow and apparently does not injure the membrane of either eye or throat. The smoke torch consists of a 20-gauge tinned-iron cylinder, 3 3/8 inches in diameter by 6 1/4 inches high, which is filled with a smoke-producing composition. The cylinder has a cover of tinned iron through the center of which is an orifice 1 inch in diameter, that allows for the ignition of the charge and the emission of the smoke. In firing the smoke torch a striker, which is a small cardboard strip coated on one side with a striking composition, is rubbed across a blob of quick-firing mixture. The blob envelopes a fuse or match, which carries the fire to a prime of first fire placed on top of the smoke-producing composition within the can.
Figure 206 is a photograph of the case to which the cover has been attached. This case is made in the form of a cylinder from No. 20-gauge tinned iron with a double side seam and a double-seamed bottom of the same material. The seam along the side of the cylinder is double-lapped as is also the bottom, so that soldering is unnecessary. This case measures 3 3/8 inches in diameter by 6 1/4 inches high. At a distance of 3/8 of an inch from the top of the cylinder a groove is expanded, which serves as a snap lock to hold firmly in place the cover when forced on the cylinder.
The cover is made of the same material as the case, being stamped with the sides drawn to a depth of 3/4 inch, and is made to fit snugly over the case. A groove is rolled in the cover to correspond with the groove in the case, thus providing a simple means of assembling or locking the cover in position. A secure lock between the case and the cover is found to be necessary in order that when the torch is in operation a sufficient gas pressure shall be generated in the container to cause the emission of the gases from the orifice in the cover to a height of approximately 2 feet. Unless the cover is held firmly in place it is likely to be blown off.
Fig. 206. - Case and cover showing orifice and locking groove.
The formula for the smoke-producing torch composition is as follows -
Powdered calcium carbonate...................
This formula remains fairly constant The variable factor, however, is the saltpeter. It is the saltpeter that causes the rapid burning and high heat-producing effect necessary in order to produce the combustion. If the composition burns too freely, producing too high a heat of combustion to function properly, the saltpeter is decreased slightly, and the reverse in the event that the composition is too slow in burning.