increases with the pressure until at forty atmospheres it is very
explosive. Mixed with acetone, the gas loses this dangerous property and is
safe for handling and transportation. As acetylene is dissolved in the
liquid the acetone increases its volume slightly so that when the gas has
been drawn out of a closed tank a space is left full of free acetylene.

This last difficulty is removed by first filling the cylinder or tank with
some porous material, such as asbestos, wood charcoal, infusorial earth,
etc. Asbestos is used in practice and by a system of packing and supporting
the absorbent material no space is left for the free gas, even when the
acetylene has been completely withdrawn.

The acetylene is generated in the usual way and is washed, purified and
dried. Great care is used to make the gas as free as possible from all
impurities and from air. The gas is forced into containers filled with
acetone as described and is compressed to one hundred and fifty pounds to
the square inch. From these tanks it is transferred to the smaller portable
cylinders for consumers' use.

The exact volume of gas remaining in a cylinder at atmospheric temperature
may be calculated if the weight of the cylinder empty is known. One pound
of the gas occupies 13.6 cubic feet, so that if the difference in weight
between the empty cylinder and the one considered be multiplied by 13.6.
the result will be the number of cubic feet of gas contained.

The cylinders contain from 100 to 500 cubic feet of acetylene under
pressure. They cannot be filled with the ordinary type of generator as they
require special purifying and compressing apparatus, which should never be
installed in any building where other work is being carried on, or near
other buildings which are occupied, because of the danger of explosion.