If the mixing-tube is upright, new sources of interference comes in;
notably the varying specific gravity of the mixture. Except with one
definite gas supply, the result is always more or less imperfect, and
regular proportions cannot be obtained. This is now so well known that
the upright form has been practically discarded for many years, and
is now only used where the peculiar necessities of the case give some
special advantage.
[Illustration: Fig. 1. SPECIAL HIGH POWER BURNER. SHEWING ATTACHMENT B
WHEN USED WITH A BLAST OF AIR]
"The diameter of the mixing tube is a matter of importance, as it
rules the quantity of gas which can be satisfactorily burnt in any
arrangement. With large flames, given a certain size of gas-jet, the
diameter of the mixing-tube should be not less than ten times as great.
For instance, at 1 inch pressure, a jet having a bore of 1/8 inch will
pass about 20 cubic feet of gas per hour. To burn this quantity of gas,
a mixing tube is necessary 10/8 or 11/4 inch in diameter.
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