The boiler figured in the annexed cut, is of a cylindrical figure in the lower part, but combines some peculiarities that are deserving of notice. It is a patented arrangement by Messrs. Horton and Fisher, who are large boiler manufacturers, near Birmingham. The object of it is to form a reservoir of steam within the boiler, surrounded by the hot water, in order that the pressure of the steam may not be reduced by radiation, which the inventors presume to be the case in a greater degree in boilers of the ordinary construction. Fig. 1 represents a longitudinal section of the boiler, and Fig. 2 a transverse section of the same : the letters of reference apply to similar parts in each view. a a a shows the external form around which the furnace and flues are to be con structed; b b b is the internal vessel or reservoir, for containing the steam generated, surrounded by %the water which is supplied by the tube o o from another reservoir placed above, but not introduced into the drawing. The heat having caused the steam to fill the upper part of the boiler d, it passes thence through the bent tube c into the steam reservoir b below, from whence it is con ducted to the engine by the steam pipe e, the top of which a is designed for the situation of the safety valve. At f is a cock for drawing off whatever water may be condensed in the steam chamber, and at k may be placed another for discharging the boiler. At II are man-holes for gaining access into the interior. We do not ourselves perceive bow the intention of the patentees to make the internal vessel b b a store of high steam for the supply of the engine, can be effected by this arrangement, for the hottest steam will be rather disposed to obey the laws of nature, and ascend into the upper vessel through the bent tube, than descend through the same to the lower vessel, according to the desire of the contrivers. It must, however, be admitted that there is a considerable degree of originality in this boiler, and it may prove a useful and effective generator of steam.
In 1803, Mr. Woolf patented his boiler, which has obtained much deserved celebrity. It has been for many years very extensively and successfully employed in Cornwall, for the production of steam for the large mining engines there. We have already observed that the long cylindrical boilers possess great advan tages over those of a tubiform or rotund figure. To increase their safety, and their capability of producing steam at very high pressures, Mr. Woolf greatly extended the principle of the cylindrical form. One of the most simple of this gentleman's construction consists of eight tubes of cast iron (of six or more inches in diameter), connected to each other by a bent tube at their extremities, with communications to a larger cylinder above them, employed as a reservoir for the steam. The furnace is divided by a wall longitudinally into two parts, and the eight tubes are fixed horizontally across both these. The fuel chamber is at one extremity of one of the divisions, and arched above the two first so as to reverberate the flames and heated vapours, which then pass under the third tube, over the fourth, under the fifth, over the sixth, under the seventh, and partly over and partly under the eighth tube, when the flue turns into the second division of the furnace, on the other side of the wall, built under, and in the direction of, the large steam cylinder before mentioned. Passing now under the seventh cylinder, the course of the flue is over the sixth, under the fifth, over the fourth, under the third, over the second, and partly over and partly under the first, when it enters the chimney. To produce this long ser
pentine reverberation, the upper and under side of the brick-work is formed in arches, alternately reversed, their extremities abutting against the tubes, covering about a sixth part of their circumferences, but exposing the rest to the action of the current of heated matters from the fire. Each of the tubes is provided with a flanged disk at one end, fastened on by screw bolts, that they may be easily removed, and the tubes cleaned out at pleasure from sediment and in crustations. The water carried off by evaporation is replaced by the usual means of a force pump, and the steam generated is conducted to the engine or other object, by a tube connected to the steam reservoir. " It may not be im proper," says Mr. Woolf, "to call the attention of those who may hereafter wish to construct such apparatus, to one circumstance : namely, that in every case, the tubes composing the boiler should be so combined and arranged, and the furnace so constructed, as to make the fire, the flame, and the heated air, to act around, over, and among, the tubes, embracing the largest possible quantity of their surface. It must be obvious to any one that the tubes may be made of any kind of metal ; but I prefer cast iron as the most convenient. The size of the tubes may be varied; but in every case care should be taken not to make their diameter too great ; and it must be remembered, that the larger the diameter of any single tube in such a boiler, the stronger it must be made in proportion, to enable it to bear the same expansive force as the smaller cylinders." Mr. Woolf also directs that the lower tubes should be always kept filled, and the upper, or steam cylinders, half filled with water, that is, as high as the fire is allowed to reach, and that in no case the water ought to be allowed to get so low as not to keep full the branches which join the lower tubes to the upper cylinder.
The annexed engraving exhibits an arrangement of parts combining the leading features of several previous inventions, and was patented by Mr. Thomas Tippet, of Gwennap, in Cornwall, in 1828. Fig. 1 represents an end view, and Fig.2 a side view of the boiler; the same letters of reference in each indicating similar parts. a is a large cylindrical boiler, containing an internal cylinder, which constitutes the fire place and principal flue. From the external cylinder, which contains water, proceed three rows of open vertical pipes b b b, which support a semi-cylindrical steam vessel c. At the farthest extremity of the cylinder a there proceeds horizontally a short open pipe d, communicating with a small supplementary boiler, which is a cylinder of the same area as a, but very short. This boiler is built in a furnace, in which the flues are so arranged that the heated air, in passing out at the end f of the furnace flue, shall impinge against the flat side of the supplementary boiler ; the flue thence proceeds upwards, and along the underneath flat side of the semi-eylindrical vessel, between the vertical tubes to the front of the boiler, where it descends, passing under the bottom of the latter, then round the back of the supplementary boiler, and over the top of the semi-cylinder to the chimney, which is in front, nearly over the furnace doors.