50 



REPORT — 1851. 



form of volatile matter, from 2 to 4 or 5 per cent, more of the weight of coal than a 

 moderate or slow application of heat would do. 



The four series of experiments afford the following comparison between the higliest 

 and the lowest six results in heating power, as related to the fixed carbon in the 

 sevei-al coals : — 



It is here evident that calculation gives in every case a lower result than experi- 

 ment; indicating that coals of a highly bituminous nature will be under-estimated in 

 comparison with coals of low bituminousness, and that the amount of this undervalu- 

 ing is 4-1 per cent, for the first, 7-2 for the second, 6-5 for the third, and 4-5 for the 

 fourth series, and, on an average of the whole, 5-5 per cent, of the entire power of 

 those weaker coals. 



As coals of high bituminousness yield up, together with their hydrogen, a con- 

 siderable quantity of their carbon while undergoing the coking process, it is apparent 

 from the experiments that the steam-generating power of such coals is dependent, in 

 a small degree at least, upon the volatile product of their distillation ; but, as it has 

 already been shown that the hydrogen element is not that on which coals depend for 

 this power, we are led to infer that it is the volatilizable part of the carbon which in 

 such coals makes up for the calculated deficiency of the fixed carbon. 



Reference has already been made to some experiments which seem to demonstrate 

 that the total calorific or evaporative eflSciency of coals, as proved by direct evapora- 

 tion and by reducing the heat expended on the products of combustion to its equivalent 

 evaporative power, is proportional to the total amount of carbon. . 



It must be evident that either in a sensible or in a latent state a very large amount 

 of caloric must pass from a furnace to its chimney. By an examination of the tem- 

 perature and composition of the gaseous and vaporous mixtures sent into the chimney 

 during the combustion of different varieties of coals, our experiments in America 

 proved that, while the anthracites seldom expended more than 12i per cent, of their 

 whole heating power on the products of their combustion, the highly bituminous class 

 expended 18, 20, and sometimes as high as 24 per cent, in the same way. It may 

 consequently happen that when, as in the British experiments, we compare the carbon 

 element with the evaporative power expended on the boiler alone, the calculated will 

 exceed the experimental result in the highly bituminous coals. The highest and low- 

 est sets already compared give the following average per-centage of carbon, viz.— 



Carbon, Carbon, Steam, Steam calculated Steam by experl- 



highest six. lowest six. highest six. for lowest six. ment, lowest six. 



First series 34-89 : 77-72 : : 10-59 : 9-65 7-72 



Second series... 88-65 : 78-44 : : 10-51 : 9-30 7-14 



Third series ... 84-92 : 77-11 :: 9-90 : 8-98 7-09 



Compared with the fixed carbon these figures show that the coals of highest eva- 

 porative power lost by coking 11-13 per cent, of their carbon, and those of lowest 

 evaporative power 34-6 per cent. They also show that the calculated exceeds the ex- 

 perimental result in every one of the three cases; and that the average excess is 27-3 

 pel cent, of the experimental evaporative power, reckoned from the quantity of steam 

 expelled from the boiler. 



From this statement it follows that computations founded on the per-centage of 

 fixed carbon will give nearer approximations to the practical action of coal in evapo- 

 rating water from a steam-boiler than either of the other methods ; and that the error 

 will seldom exceed 5 or 6 per cent. It does not, however, follow that the direct man- 

 ner of ascertaining the economic values of coals can be dispensed with. So many 

 questions besides that of the bare evaporative power merit attention in selecting coals 



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