Taking an ordinary drilled tube, such as is commonly made, and
of the dimensions before given--i. e., 11/4 inch bore--if the holes are
drilled 1/8 inch in diameter the tube will supply 10 x 10 = 100 of these
holes. In practice this rule may be modified.
"The variations from the rule, however, must be a matter of experience
with each form of burner. There is also the fact that with small divided
flames it is not necessary to mix so large a proportion of air, as each
flame will take up air, on its external surface; but in this case the
flames are longer, hollow, and of lower temperature. As a matter of
actual practice, where a burner is used which gives a number of flames
or jets, the diameter of the mixing-tube does not need to exceed eight
times the diameter of the gas jet; the remainder of the air required
being taken up by the surfaces of the flames.
"Wire gauze, made of wire the thickness of 22 iron wire gauge, 20 wires
to the linear inch, and tinned after weaving, has an area in the holes
of 1/4 its surface.
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