SECT. m.J CONDENSATION OF STEAM. 129 



always be preferable to employ several of these boilers of a middling size, placed 

 beside each other, and heated each by a separate fire, instead of using one large 

 boiler heated by one fire. For Count Rumford has shown by experiment, in his 

 Sixth Essay ' On the Management of Fire and Economy of Fuel,' that beyond a 

 certain limit, there is no advantage derived from augmenting the capacity of a 

 boiler. 



The additional surface obtained by using tubes is unquestionable ; and the 

 construction proposed by the Count might be applied with much benefit where 

 much surface is to be gained in a small space. The tubes should, however, have 

 that proportion of capacity necessary for an engine boiler, and not be too small to 

 contain an ascending and descending current. 



233. Woolf s Boilers. The idea of cylindrical tubes and a magazine for water 

 and steam was further expanded by Mr. Woolf into a variety of forms, which were 

 successively adopted and abandoned. His first project was to have a horizontal 

 cylinder for containing steam and water, with a series of horizontal tubes below it, 

 crossing it at right angles, and connected to the cylinder by short necks ; the 

 lower tubes and half the cylinder to be filled with water, and the flame and smoke 

 to pass alternately over and under the tubes in a waving course. And where very 

 strong steam was required, he had two other smaller cylinders, one on each side, 

 in lines parallel to the large one and above the cross tubes, which are connected 

 alternately to these by short necks ; the larger cylinder communicating only with 

 the side cylinders. 1 The immediate object of this arrangement is to introduce the 

 cold water so as not to interrupt the rising of the steam, which is the fault of both 

 the first arrangement and also of Count Rumford's. 



Another mode of application adopted by Mr. Woolf consists in placing the tubes 

 longitudinally, as the larger cylinder, parallel to each other, but in a gently sloping 

 direction : the upper ends of the tubes all open into the large cylinder near to its 

 end. The tubes are about ten inches in diameter, and extend the whole length of 

 the fire-place, which is formed below them ; and the fire acts directly on the lower 

 surfaces of the tubes, and the flame and smoke on the lower side of the principal 

 cylinder. This plan seems to be the latest he has contrived, and a wonderful stock 

 of ingenuity has been exhausted to very little purpose. 



234. But there is another form given by Woolf to the boiler, which is too 

 ingenious to be passed without notice : it consists in forming an upper and a lower 

 boiler, and connecting them by short tubes. For a low pressure boiler the arrange- 

 ment gives much surface, but would be more troublesome to execute than the 



* Philosophical Magazine, vol. xvii. p. 40. 



R 



