as a rule, a downward vertical or nearly vertical position is usually the best for any blowpipe.  As an example of this class of work, I may instance the shrinking on of collars and tires, which, with suitable ring-burner and a Root’s blower, could be equally heated in five minutes for shrinking on; in fact, the work could be done in less time than it would usually take to find a laborer to light a fire.  When the rings vary much in size, the burners can easily be made in segments of circles.  But then they are not nearly so handy, as each needs to be connected up to the gas and air supply; and it is, in practice, usually cheaper to have separate ring burners of different sizes.  Of course, you will understand that a 1/2-inch gas-pipe will not supply heat enough to make a locomotive tire red hot, and that for large work a large gas supply is necessary.  Our own rule for burners of 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.