32 Dr Fyfe on the Comparative Evaporative 



provided the wliole of the volatile matter were expelled ; but 

 this is seldom done when it is prepared on the large scale. 

 Accordingly, when subjected to analysis, the coke was found 

 to yield inflammable gas by exposure to heat. It must also 

 be borne in mind that coke always absorbs moistm-e from the 

 atmosphere. The composition of the coke, as found in the 

 market, was — 



Moisture, 3.5 



Inflammable matter evolved by heat, , 6.6 



Fixed Carbon, • . , . , 81. 



Ashes, 9.0 



100.0 



The gaseous inflammable matter was, therefore, in the coal 

 and coke in the ratio of 34.5 to 6.5, while the fixed carbon 

 was 50.1 in the former, and 81 in the latter. The proportion 

 of ashes in the coke was greater than that afforded by the 

 coal which yielded only 2.4 per cent. Accordingly, as 100 of 

 coal gave 52.5 of coke, 100 of coke ought to have given 4.5 

 of ashes, whereas the quantity amounted to 9. 



In conducting the experiments with the view of ascertain- 

 ing the comparative evaporative power of these fuels, I had re- 

 course to the small furnace and boiler, with which some of 

 the trials stated in my former paper were made. The boiler 

 was of the waggon shape, with a returning flue, and capable 

 of holding 50 gallons. The fire surface of the furnace was 

 16 by 14 inches, and the surface of the boiler exposed to the 

 fire was in all about 18 feet. The water supplied to the 

 boiler was at the temperature of 42, and the quantity evapo- 

 rated was, as formerly, ascertained by a glass gauge accurately 

 graduated. The boiler being open, the evaporation was con- 

 ducted under the natural pressure. 



The trials were first made with coke, so as to have the sur- 

 face of the boiler exposed to the fire as clean as possible. It 

 is unnecessary to give the results of all the experiments. I 

 select the following as the most satisfactory 



