PHORUS INTO HAND GRENADES
FILLED WITH WATER--EDGEWOOD ARSENAL]

[Illustration: FILLING SHELL WITH "MUSTARD GAS"

Empty shells are being placed on small trucks to be run into the filling
chamber. The large truck in the foreground contains loaded shell]

For smaller work thermit has two rivals, the oxy-acetylene torch and
electric welding. The former has been described and the latter is rather
out of the range of this volume, although I may mention that in the
latter part of 1918 there was launched from a British shipyard the first
rivotless steel vessel. In this the steel plates forming the shell,
bulkheads and floors are welded instead of being fastened together by
rivets. There are three methods of doing this depending upon the
thickness of the plates and the sort of strain they are subject to. The
plates may be overlapped and tacked together at intervals by pressing
the two electrodes on opposite sides of the same point until the spot is
sufficiently heated to fuse together the plates here. Or roller
electrodes may be drawn slowly along the line of the desired weld,
fusing the plates together continuously as they go. Or, thirdly, the
plates may be butt-welded by being pushed together edge to edge without
overlapping and the electric current being passed from one plate to the
other heats up the joint where the conductivity is interrupted.

It will be observed that the thermit process is essentially like the
ordinary blast furnace process of smelting iron and other metals except
that aluminum is used instead of carbon to take the oxygen away from the
metal in the ore. This has an advantage in case carbon-free metals are
desired and the process is used for producing manganese, tungsten,
titanium, molybdenum, vanadium and their allows with iron and copper.

During the war thermit found a new and terrible employment, as it was
used by the airmen for setting buildings on fire and exploding
ammunition dumps. The German incendiary bombs consisted of a perforated
steel nose-piece, a tail to keep it falling straight and a cylindrical
body which contained a tube of thermit packed around with mineral wax
containing potassium perchlorate. The fuse was ignited as the missile
was released and the thermit, as it heated up, melted the wax and
allowed it to flow out together with the liquid iron through the holes
in the nose-piece. The American incendiary bombs were of a still more
malignant type. They weighed about forty pounds ap