264 Dr Fyfe on the Evaporative Paver of Coal. 



and supplied with plugs, the temperature of the air passing 

 into the ash-pit was ascertained. 



The apparatus just described is that patented by Mr Bell, 

 with the view of increasing the heating surface exposed to 

 the water in the boiler, and thus increasing the amount of 

 evaporation. I do not, however, bring the experiments for- 

 ward with the intention of proving the efficacy of this patent. 

 It is not at all my intention to enter into its merits. I had re- 

 course to this apparatus, merely as a means of enabling me 

 to burn the anthracite, so as to make it subservient for the 

 purpose of raising steam, and of keeping up the supply ; and 

 thus also to enable me to compare its practical evaporative 

 power with that of bituminous coal. 



The mode of conducting the experiments was as follows : — 

 One person was intrusted with the weighing of the coals, the 

 weighing being at the same time checked by another. To 

 another was intrusted the measuring of the water supplied to 

 the boiler. This was done by measuring it by a four-gallon 

 measure into a vessel, in which was the mouth of the pipe con- 

 nected with the force-pump by which the water was forced 

 into the boiler. The water was in all of the experiments at 

 the temperature of 45°. The height of the water in the boiler 

 was known by a float connected with a wheel and index, 

 which moved easily as the fluid rose and fell. This index was 

 always brought to the same point at the commencement and 

 termination of the trial ; and, accordingly, the water in the 

 boiler was always at the same height at these periods. Before 

 beginning, the fire was examined a considerable time after 

 the stoking, and adjusted to the proper height, and it was 

 brought as nearly as possible to the same state at the termina- 

 tion. Jn this way there was a constant quantity in the fur- 

 nace at the commencement and termination, and accordingly 

 it was only that which was supplied during the continuance of 

 the trial that was considered as the fuel consumed. 



I am aware that objections may be made to this mode of 

 ascertaining the quantity of fuel used, as it is difficult to bring 

 the fire exactly to the same state at the different periods men- 

 tioned. This objection, I allow, would apply, were the trials 

 of short duration ; but in a six or eight hours' trial, any slight 



