Asbestos fibre and also ordinary fireclay are often used to make a backing
or mould into a form that may be placed behind aluminum and some other
metals that flow at a low heat and which are accordingly difficult to
handle under ordinary methods. This forms a solid mould into which the
metal is practically cast as melted by the torch so that the desired shape
is secured without danger of the walls of metal breaking through and
flowing away.

Carbon blocks and rods are made in various shapes and sizes so that they
may be used to fill threaded holes and other places that it is desired to
protect during welding. These may be secured in rods of various diameters
up to one inch and in blocks of several different dimensions.




CHAPTER III

ACETYLENE GENERATORS


Acetylene generators used for producing the gas from the action of water on
calcium carbide are divided into three principal classes according to the
pressure under which they operate.

Low pressure generators are designed to operate at one pound or less per
square inch. Medium pressure systems deliver the gas at not to exceed
fifteen pounds to the square inch while high pressure types furnish gas
above fifteen pounds per square inch. High pressure systems are almost
unknown in this country, the medium pressure type being often referred to