At 0 Fahr........................ 1558 pounds.
At -10 Fahr........................ 1522 pounds.

_Chlorate of Potash Method._--In spite of its higher cost and the
inferior gas produced, the chlorate of potash method of producing oxygen is
used to a limited extent when it is impossible to secure the gas in
cylinders.

[Illustration: Figure 8.--Oxygen from Chlorate of Potash]

An iron retort (Figure 8) is arranged to receive about fifteen pounds of
chlorate of potash mixed with three pounds of manganese dioxide, after
which the cylinder is closed with a tight cap, clamped on. This retort is
carried above a burner using fuel gas or other means of generating heat and
this burner is lighted after the chemical charge is mixed and compressed in
the tube.

The generation of gas commences and the oxygen is led through water baths
which wash and cool it before storing in a tank connected with the plant.
From this tank the gas is compressed into portable cylinders at a pressure
of about 300 pounds to the square inch for use as required in welding
operations.

Each pound of chlorate of potash liberates about three cubic feet of
oxygen, and taking everything into consideration, the cost of gas produced
in this way is several times that of the purer product secured by the
liquid air process.

These chemical generators are oftentimes a source of great danger,
especially when used with or near the acetylene gas generator, as is