Q.Are all land boilers of the same construction as that which you have just described? A.No; many land boilers are now made of a cylindrical form, with one or two internal flues in which the furnace is placed.

An unwholesome smell of wet earth, a damp, subterranean coolness, enveloped Rudolph as he slid down a flue of greasy clay, and stooping, crawled into the horizontal bore of the tunnel.

I wish you would build me, among your buildings, some small Prophet Chamber, fifteen feet square, with a flue for smoking, sacred from all noises of dogs, cocks, and piano-fortes, engaging some dumb old woman to light a fire for me daily, and boil some kind of a kettle.

Adjacent to the chimney a slit must be left in the top of the flue with a groove in the brickwork to enable the sliding door or damper to be fixed in that situation, which by being lowered into the flue will obstruct the passage of the smoke and moderate the draught, whereby the chimney will be prevented from drawing the flame into it before the heat has acted sufficiently upon the boiler.

In Boulton and Watt's modern flue boilers they allow for the evaporation of a cubic foot of water 8 square feet of heating surface, 70 square inches of fire grate, 13 square inches sectional area of flues, 6 square inches sectional area of chimney, 14 square inches area over furnace bridges, ratio of area of flue to area of fire grate 1 to 5.4.

The smoke and flame, when they reach the end of the boiler, pass in this case through an iron flue or tube, reaching from end to end of the boiler; and on arriving at the front of the boiler, the smoke splits or separatesone half passing through a flue on the one side of the boiler, and the other half passing through a flue on the other side of the boilerboth of these flues having their debouch in the chimney.

The practice of introducing a hanging bridge is a beneficial one in the case of some boilers, but is not applicable universally, as boilers with a small calorimeter cannot be further contracted in the flue without a diminution in their evaporating power.

A. It is a crushing in of a flue by external pressure.

Taking the amount of heating surface in the 45 horse boiler at 9 square feet per horse power, we obtain 18 square inches of sectional area of flue per horse power, which is also Boulton and Watt's proportion of sectional area for marine boilers with internal flues.

This effect is prevented by heating, in any convenient way, the tube or flue through which the foul air escapes.

A.It is Boulton and Watt's method; but some very satisfactory boilers have been made by allowing a proportion of 0.6 of a square foot of fire grate per nominal horse power, and making the sectional area of the flue at the largest part 1/7th of the area of fire grate, and at the smallest part, where it enters the chimney, 1/11th of the area of the fire grate.