132 OF THE GENERATION AND [SECT. in. 



from the fuel which is in combustion, whereas nothing can be more injurious to the 

 perfectness of that process than a rapid abstraction of heat. The sides of the fire 

 ought to be lined with fire bricks as far as the burning fuel extends ; and the saving 

 arising from the more perfect combustion of the fuel, and in the duration of the 

 boiler, would more than balance the inconvenience of the construction. 



A boiler for a steam boat constructed in this manner is shown in Plate xvn. 

 Fig. 1, 2, and 3. It differs in some respects from the usual forms, but not in any 

 essential points : the great object is to obtain a sufficient quantity of fire surface, 

 and facility of clearing the flues is of considerable importance. 



244. Portable high pressure Boilers. Boilers for steam carriages, and other 

 purposes where a permanent seat of brickwork cannot be applied, should be 

 arranged in the same manner as those for steam boats, with the exception of the 

 forms being adapted to resist the effect of the steam. 



Both the boiler and the flues within it should be cylindrical. The difficulty of 

 the case consists in obtaining even the due proportion of fire surface, without 

 rendering the boiler too large in diameter. Hence, the only thing that seems 

 capable of being done to improve the present construction, is to make the boilers 

 much longer with less diameter ; to have the boiler filled with water, and the fire 

 tube larger, with the spaces for steam formed by short vertical cylinders round the 

 steam cylinders. 



OF FIRE-PLACES. 



245. Various methods have been tried for improving the construction and the 

 mode of supplying the fuel to the fire-places of steam boilers. Smeaton improved 

 them so far that there has been little more useful effect obtained since, than 

 was done by some of his boilers. The later researches on combustion induced 

 Mr. Watt to add a few further improvements, but experience taught him that what 

 might be done by scrupulous attention and just principles was not to be expected 

 in ordinary practice. 



246. Watt's Fire-place. In improving the furnace, Mr. Watt proceeded nearly 

 on the principles of Argand's lamp. The grate and dead plates were laid in a 

 sloping direction downwards from the fire door, at an angle of about 25 to the 

 horizon ; the fire being lighted in the usual manner, and a small quantity of air 

 admitted through one or two openings in the fire door, so as to blow directly on 

 the blazing part of the fire. The fire at first was kept near the dead plate, and the 

 fresh coals with which it was supplied were laid upon that plate close to the 

 burning fuel, but not upon it. When it needed mending, the burning coals and 

 those upon the dead plate were pushed further down without being mixed, and 

 more coals were laid upon the dead plate, but never thrown on the top of those 



