Dr Fyfe on the Evaporative Power of Coal. 273 



would have been a greater amount of evaporation, of course 

 a smaller loss of the heat evolved by the combustion. 



The next set of experiments was made with the view 

 of ascertaining the evaporative power of English caking, com- 

 pared with common Scotch coal. Of course, the strength of 

 these must vary according to circumstances, the results now to 

 be stated must therefore be considered as applying only to 

 those on which the trials were made. The English coal used 

 was imported at Leith and said to be of the best quality ; 

 being got direct from the vessel, it may be considered as free 

 from admixture. The Scotch coal with which it was com- 

 pared was from the neighbourhood of Edinburgh, and is ge- 

 nerally reckoned good. 



I regret that I had not an opportunity of trying these coals 

 in the furnace used for the anthracite. I was obliged to have 

 recourse to one of much smaller dimensions, and in which, 

 though the combustion was as complete as frequently occurs, 

 yet there was a considerable waste of heat. I give these ex- 

 periments, therefore, not with the view of shewing what can 

 be done by these coals ; but as the waste would affect both 

 fuels equally, the results will prove their comparative eva- 

 porative power in practice. 



The boiler employed was made of thin sheet copper. Tt 

 was of the waggon form, with a flue returning through it, 

 and capable of holding 50 gallons of water. The fire surface 

 of the furnace was 16 inches by 14, and the surface of the 

 boiler exposed over the fire and otherwise to the heated pro- 

 ducts of combustion, was in all 18 feet. As the boiler was 

 open, of course the evaporation was conducted under the 

 usual atmospheric pressure. The water supplied was in all 

 the trials at the temperature of 50°. It was measured when 

 thrown into the boiler, and to check the results, a graduated 

 gauge was attached to the boiler, by which the height of the 

 fluid within could be ascertained, and the amount of evapo- 

 ration known. Six trials were made with the Scotch coal, 

 each lasting nearly nine hours. It is unnecessary to give the 

 results of the whole. I select one which was conducted with 

 great care. The following is a tabular view of s the work- 

 ing :— 



