Proceedings of tee Polytechnic Association. 841 



American anthracite, about three per cent of the combustible is 

 hydrogen. The semi-anthracite combustible contains about live per 

 cent ; and the bituminous varieties a larger proportion^ varying with 

 the locality of the mines. It is authoritatively stated, that in some 

 varieties of Ohio and west Pennsylvania coal, the hydrogen element 

 is often twenty-four per cent of the whole combustible. For the 

 consumption of equal weights of hydrogen and carbon, the Urst 

 requires three times as much oxygen as the latter ; the heat resulting 

 should, therefore, bear a somewhat similar proportion. Favre, Sil- 

 berman, Andrews, and others, have, for experiment, estimated the 

 calorific value of one pound of carbon to be the heating of about 

 14,000 pounds of water, one degree Fahrenheit. The correspond- 

 ing value of hydrogen was similarly determined to be about 60,000 

 heat units. Bituminous coal, containing considerable hydrogen, 

 should therefore produce very much more heat in combustion than 

 anthracite ; but in practice the difference is comparatively small. 

 Mere differences in mechanical structure appear to have a greater 

 influence than chemical constitution. The reason is not evident. 



The latent heat of the steam resulting from the combustion of 

 hydrogen, which is lost in the atmosphere, will not nearly account 

 for the discrepancy. WitliDut attempting an explanation, except, 

 perhaps, imperfect combustion, we can, for our purpose, only turn to 

 the records of practical experiments, and find what different kinds of 

 coal have done, and may tlierefore l>e expected to do again. 



Bourne gives the evaporation efficiency of thirty varieties of coal, 

 fi'om different parts of the British Isles, or from T to 10.2 pounds of 

 water from a temperature of 212 degrees. The average was 8.7 

 pounds. The coals are, as is well known, of the soft or bituminous 

 variety. The results of experiments made by the navy department, 

 with thirteen varieties of American anthracite, from different parts of 

 the Pennsylvania coal field, gave a mean evaporative efficiency per 

 ■ pound of coal of 8.9 pounds of water, from a temperature of 212 degi-ees 

 Fahrenheit. Three specimens of American bituminous coal gave a 

 mean result of 9.9 pounds under similar conditions. The figures 

 make it appear that our American coals are superior to those of other 

 nations. Professor Johnson, at an earlier period, made some experi- 

 ments for our government, with smaller quantities, but obtained 

 more marked results in the same direction. On the contrary, the 

 engineers of the English and French steamers, out of this port, speak 

 of our Cumberland and kindred varieties of coal as inferior to those 



