Size of Chimneys.

above the foundation $1,850. One 81⁄2 feet diameter and 150 feet high cost $2,800, and one 13 feet internal diameter and 200 feet high cost $8,750. The latter had 16-inch walls for 70 feet.

The formula for area of chimneys:

Area =

120 X square feet of grate

V height

A table has been prepared by Mr. Wm. Kent and is published in most hand books. Mr. Kent based his table on the consumption of five pounds of coal per horsepower, so as to have it ample during bad weather.

Mr. George H. Babcock's rule of thumb was: “The area of chimney should be % the area of grate. It should never be less than 1-10."

In a high chimney, the velocity being greater, the area can be smaller than with a low chimney. There is an idea that the chimney should have an area equal to that of all the tubes. This would make the chimney too large. If we have a boiler with 70 tubes 4 inches in diameter we have an area of 500 square inches and a friction surface of 375 inches. A stack 28 inches in diameter would carry that all right, and this would have a friction of only 90 inches. Besides we have seen that a boiler flue is never full of gas at the full velocity of chimney. The flues between the boiler and the chimney should be slightly larger than the chimney, as, like the boiler flues, they are generally horizontal and have bends.

Of late years many owners of steam plants have put in induced draft.

One of the drawbacks to chimney draft is that, when strong, it draws air through all cracks and interstices, as

Dia. in

inches.

Induced and Forced Draft.

well as through the brickwork itself, thus diluting the gases and cooling them.

Induced draft has the same drawback. The induceddraft apparatus is made up of steel plates, which must be acted on the same as a steel stack. It is, or a portion of it at least, subject to repairs and breakdowns and a continuous expense for fuel. The products of combustion are discharged into the air that is breathed by the operatives and nearby residents.

If high chimneys are not desired, would it not be better to build a chimney, say, 100 feet high, and put in the air by fan under the grate? It would not draw air through boiler setting to cool off the boiler, and the surrounding air would be purer. The apparatus would be more durable and could be smaller, as the volume of cold air is not so great as the hot air.

Objections have been made to the steam jet for aiding or increasing combustion, on account of the large amount of steam used.

One engineer tried to learn the amount of steam used with steam jets, and the result of his investigation was that the steam jet, as he used it, required 8 per cent. of the fuel burned to operate it. He then took the difference between the amount of fuel used when running with natural draft and with the steam jet, and found the net result was that the jet took per cent. more coal.

Whatever system of draft is used there should be a draft regulator. There are damper regulators made now that are very powerful and will regulate the steam pressure within 2 pounds.

For burning small anthracite and use a steam jet to help out. Put a valve in the steam pipe that leads to the jets and arrange the damper regulator so that when steam

Dampers.

rises it will close this valve first and then the damper in the flue. Of course, when steam lowers, the damper opens first and then the jets.

The Engine Room.

When James Watt took hold of the steam engine it. consisted of a cylinder in which steam was admitted under the piston and raised it to the top of the stroke when cold water was admitted and the vacuum, or rather, the pressure of air on top of the piston forced it down, thus doing mechanical work.

Watt built a separate condenser and used steam on both sides of the piston. He also invented and used the indiHis researches led him to foretell the advantage of using steam expansively and of compounding the same, but he did not live to see it carried out.

Later mathematicians took hold of the matter, and, by figures, showed the saving by expanding steam.

A professor in Providence was looking over these figures, and, becoming interested, took them to a young man who had shown inventive ability while working at the harness maker's trade by inventing the sewing machine for stitching leather. This young man was George H. Corliss. Elias Howe afterwards invented the placing of the eye at the point of the needle, thus making the sewing machine practical for all purposes.

Young Corliss set about making an expansion engine,