278 Dr Fyfe on the Evaporative Power of Coal. 



state ; and. if so, then in using fuel in furnaces as now con- 

 structed, supposing the combustion to be as perfect as we can 

 expect to make it in these furnaces, we shall find the practical 

 evaporative power to be according to the per-centage of fixed 

 carbon. If this should be found to be the case, then we have 

 an easy method of knowing the practical evaporative power 

 of a fuel — which is merely to ascertain the quantity of fixed 

 carbon. This may be done by exposing a certain weight of 

 it in a covered crucible for some time to a red heat, the time 

 depending in a great measure on the quantity used ; then 

 when cold to weigh the residue, and afterwards to expose it to 

 a red heat in an open crucible, or on a platinum foil, till it 

 ceases to contain any admixture of carbon, which is easily 

 known by the appearance of the residue ; the loss of weight 

 thus sustained, deducted from what was left by exposure to heat 

 excluded from air, will give the weight of fixed carbon. Thus 

 100 gr. of the Scotch coal, used in my trials, exposed to heat 

 in a covered crucible, lost 42 of moisture and volatile inflam- 

 mable matter — the 58 gr. of residue, consisting of fixed carbon 

 and incombustible substance, when heated in air, left 7.5 — the 

 loss, amounting to 50.5, was of course fixed carbon, which was 

 consumed by its union with oxygen. 



From the few experiments I have made, I do not feel that I 

 am warranted in drawing it as a general conclusion, that the 

 practical evaporative power will be found to be as the fixed 

 carbon, but from what I have seen, I have every reason to 

 think that is either so, or very nearly it ; of course it will re- 

 quire a more extended series of experiments, made on a larger 

 scale, before such a conclusion can be proved to be correct. 

 The subject is important, and well worthy of farther prosecu- 

 tion, and I trust that those who have opportunities for testing 

 the practical evaporative power in furnaces properly con- 

 structed, will, from what I have advanced, have their atten- 

 tion drawn to it. Till this is properly tried, it is useless to 

 enter into speculation regarding the heat evolved by combus- 

 tible matter ; at the same time, however, there is one point to 

 which I cannot refrain from alluding. Whether or not it is 

 found that the practical evaporative power is as the fixed car- 

 bon, it must be allowed that in the trials, the results of which 



