Fig. 18

This type consists of a thick walled tube 9 inches long and 2 inches in diameter, made of an alloy of magnesium with a small proportion of aluminum. One end of the tube is fitted with a tail 5 inches long. The tube is filled with a priming composition of the thermit type. The bomb is fitted with an igniter which may be either in the nose or tail end of the tube.

The bomb weights about 2 lbs. 2 ozs. and, with the exception of a few ounces in the tail and igniter, there is no dead weight, the whole being incendiary material. The bomb functions on impact, a needle in the igniter being driven into a small percussion cap which ignites the priming composition. The bomb does not explode.

Fig. 18

Is should be noted that, althrough this bomb is often called a thermit bomb or a thermit electron bomb, the main incendiary agent is not the thermit composition but the mag-nesium tube, which is not in itselfs readily inflammable. The priming composition burns for 40 – 50 seconds at a temperature of about 2,500° C., and its great heat serves to melt and ignite the magnesium tube. The molten magnesium burns for 10 to 15 minutes at a tempera- ture of about 1,300° C. It may remain active for as long as 20 minutes and will set fire to anything inflammable within a few feet.

During the first 50 seconds or so, while the priming composition is still burning, the bomb looks very violent. Jets of flame are emitted from the vent holes and pieces of molten magnesium may be thrown as far even as 50 feet. After the first minute the bomb be-comes less active because the magnesium tube melts and the pressure within is relea-sed.

The thermit composition contains its own oxygen and so cannot be extinguished by smo-thering, but the magnesium must get its oxygen from the air or sourrounding materials in order to burn.