this class is that the holes in the
tube should be 1/8 to 1/10 inch in diameter, from 1/4 to 1/2 inch pitch; and
the area of the tube must be equal to the combined area of the holes. The
gas supply-pipe must not be less than half the area of the burner-tube.
Those of you who wish to study this matter further will, I think, find
sufficient information in my paper on "The Construction of High-Power
Burners for Heating by Gas," printed in the Transactions of the Gas
Institute for 1883, and in the papers on the "Use and Construction of the
Blowpipe" and "The Use of Gas as a Workshop Tool."

[Illustration]

No doubt many of you have been troubled with the twisting of some special
light casting, and will, perhaps, spend hours in the risky operation of
bending an iron pattern so as to get a straight casting. A ladleful of
lead and tin, melted in a small gas-furnace, will, in a few minutes, give
you a pattern which you can bend and adjust to any required shape. It
enables you to make trials to any extent, and get castings with the utmost
precision. There is also this advantage, that a soft metal pattern can be
cut about and experimented with in a way which no other material admits
of. Awkward patterns commence with us with plaster, wax, sheets of wet
blotting paper pasted together on a shape or wood; but they almost
invariably make their appearance in the foundry after being converted into
soft metal by the aid of a gas-furnace. I refer, of course, to thin,
awkward, and generally difficult castings, which, under ordinary
treatment, are either turned out badly or require a great amount of
fitting. As an illustration of the use of this system of pattern-making, I
have here two castings of my own, from patterns which, under the ordinary
engineer's system, would be excessively costly and difficult to make as
well as these are made. The surface is a mass of intricate pattern work
and perforations. To produce the flat original, as you see it, a small
piece of the pattern is first cut, and from this a number of tin castings
are made and soldered together. From this pattern, reproduced in iron for
the sake of permanence, is cast the flat center plate you see. To produce
the curved pattern I show you, nothing more is necessary than to bend the
tin pattern on a block of the right shape, and we now get a pattern which
would puzzle a good many pattern-makers of the old style.

[Illustration]

I will now show you by a practical utilizati