the direction it is desired to extend the cut, the rate of advance being
from three inches to two feet per minute through metal from nine inches
down to one-quarter of an inch in thickness.

The following data on cutting is given by the Davis-Bournonville Company:

Cubic
Feet Cost of
Thickness of Gas Inches Gases
of Cutting Heating per Foot Oxygen Cut per per Foot
Steel Oxygen Oxygen of Cut Acetylene Min. of Cut
1/4 10 lbs. 4 lbs. .40 .086 24 $ .013
1/2 20 4 .91 .150 15 .029
3/4 30 4 1.16 .150 15 .036
1 30 4 1.45 .172 12 .045
1 1/2 30 5 2.40 .380 12 .076
2 40 5 2.96 .380 12 .093
4 50 5 9.70 .800 7 .299
6 70 6 21.09 1.50 4 .648
9 100 6 43.20 2.00 3 1.311

_Acetylene-Air Torch._--A form of torch which burns the acetylene after
mixing it with atmospheric air at normal pressure rather than with the
oxygen under higher pressures has been found useful in certain pre-heating,
brazing and similar operations. This torch (Figure 24) is attached by a
rubber gas hose to any compressed acetylene tank and is regulated as to
flame size and temperature by opening or closing the tank valve more or
less.

After attaching the torch to the tank, the gas is turned on very slowly and