SECT, in.] CONDENSATION OF STEAM. 135 



admitted without passing through the channels which are properly regulated, a 

 thin rim on the under edge of the grate runs in a circular trough filled with sand. 

 These parts, however, will be more clearly understood by a reference to the 

 description of Plate n., where its application to two boilers, which had been 

 previously erected by Boulton and Watt, is shown. The saving of fuel by using 

 this apparatus is stated to be about 25 per cent ; and a grate 5 feet in diameter 

 burns 260 pounds (three bushels) of Newcastle coals per hour, and 336 pounds, 

 or three cwt. of Staffordshire coals ; that is, 13 pounds for each foot of surface of 

 grate for the former; and 17 pounds each foot for the latter kind. I suppose it. 

 requires these quantities also to produce equal effects. The quantity of grate is 

 about two-thirds of that required in the ordinary method. 



APPARATUS FOR BOILERS. 



251. Feeding Apparatus. The use of the feeding apparatus is to supply the 

 boiler with water, in the place of that which is converted into steam. The feed 

 pipe is a vertical pipe passing through the top of the boiler. The lower part of 

 this pipe is turned at the end to prevent steam rising through it ; and where it 

 passes through the top of the boiler, it is made steam-tight, and fixed very correctly 

 in a vertical position. The top of the pipe terminates in a small cistern head, 

 which is kept supplied with water by a small pump from the hot water cistern ; 

 and at the bottom of the small cistern head there is a conical valve, opening 

 upwards, connected by a chain to a lever, which turns on a centre, with a wire 

 attached to the opposite end. This wire passes through an air-tight stuffing box 

 to a flat stone or piece of metal in the boiler, which is so balanced by a weight, 

 on the opposite end of the lever, as to float on the surface of the water. The stone 

 should be so large, in proportion to the surface of water, as to act sensibly on a 

 very slight depression of the water. 



Its action is performed in this manner : when part of the water is evaporated 

 from the boiler, the float descends with the water's surface, and consequently raises 

 the conical valve ; now, the small cistern head, being kept constantly full of 

 water by the pipe from the hot water pump, as soon as the valve is raised, water 

 enters the boiler, and when it is filled to the proper level, it raises the float and 

 shuts the valve, till a repetition of the operation becomes necessary. The surplus 

 water raised by the pump runs off by a water pipe from the cistern head. 



252. The principal circumstance to be attended to in the construction of this 

 apparatus is to make the height of the water in the cistern sufficient to balance 

 the strength of the steam ; for if this height be too small, the water in the boiler 



