other varieties, as the disc-engine, the arrangements of which present peculiarities different from those which we have already described. In the mean time we hasten to describe the various details of the cylinder engines.

fig. 57.

CHAPTER III.

DETAILS OF BOILERS AND ENGINES.

BEFORE describing the appliances of boilers as now adopted in modern practice, we propose giving a few sketches, illustrative of the varieties of boilers which have been introduced from time to time.

In the sketch given in fig. 19 of Smeaton's Chacewater engine, the form of boiler will be seen. Smeaton paid great attention to the construction of boilers; and a favourite form of his is known as the "hay-stack,” or

66

hay-cock" boiler. A diagram, showing its form, is given in fig. 58; a is the fire-place, cc the upper flues, bb the lower ditto; the steam was taken from the upper-part d through the pipe e. This boiler was formed

of plates of cast-iron, joined together with flanges and bolts. The cylindrical boiler, as in fig. 59, is constructed with two circular or semi-spherical ends, as at aa: the ends of this form of boiler are in America generally made flat. In some instances an internal circular flue, as a, fig. 60, is provided in this form of boiler; the flue extends from end to end, and the heated air and smoke, after passing from the fire-place, goes through this flue in its passage to the chimney. This form of cylindrical boiler, called the "Trevethick," from its introduction being attributed to that engineer, is generally used for high-pressure engines. When properly constructed it is very strong, and capable of resisting a very high degree of pressure.

We have already figured the form of boiler known as the " waggon" adopted by Watt. A boiler very generally used for condensing engines,

and known as the "Cornish," consists of a cylindrical boiler, having a large internal circular flue, in which the fire-place is situated. The introduction of this form of boiler "has effected great improvements in the economy of fuel as well as the strength of the boiler." This form is shown in the sectional diagram in fig. 61, where aa is the boiler, the internal flue, c the fire-bars. In order to obtain a larger fire-place in the Cornish boiler, one-half of the end in some instances has been cut away: this was first done by the Butterley Iron Company, and the boilers in which this arrangement is adopted are known as the "Butterley;" they are much used in Lancashire. The form is shown in the diagram fig. 62.

The form of boiler which is considered by competent authorities as a very effective and economical kind, is that known as the double-flued

and double-furnaced boiler, a sectional diagram of which is given in fig. 63; aa the flues, bb the furnaces, cc the boiler. This is now in general use, and is fast superseding all other constructions. "It consists," says Mr. Fairbairn of Manchester, "of the cylindrical form, varying from five to seven feet in diameter, with two flues, which extend the whole length of the boiler; they are perfectly cylindrical, and of sufficient magnitude to

admit a furnace in each. This boiler is the simplest, and probably the most effective, that has yet been constructed. It presents a large fluesurface as the recipient of heat; and the double flues, when riveted to the flat ends, add greatly to the security and strength of these parts. It moreover admits of the new process of alternate firing, so highly conducive to perfect combustion, and the prevention of the nuisance of smoke."

The boiler known as the "French," as having first been introduced into practice in France, and which is much used in Lancashire, is figured in fig. 64: a is the cylindrical boiler; cc, two tubes, stretch longitudinally

below the boiler, and receive their supply of water by the vertical tubes b b, a brick arch fis thrown over, between the tubes cc; by this arrangement the flame and heated air from the furnace at d, fig. 65, pass along the under-side of arch ƒ and tubes cc; returning to the chimney along the space between the bottom of tubular boiler a a and upper-side of arch ƒ. This form of boiler is highly efficient; and the principle of making the flame and heated air impinge upon the outside of tubes containing water, instead of passing through the inside of tubes surrounded with water, is considered by some to be possessed of such superior advantages, as to be likely soon to supersede all other arrangements. This principle is carried

out in a very effective manner by Messrs. Galloway in their patent boilers, which are taking a high place in the engineering world. Fig. 67 is a