48 



REPORT — 1851. 



ance in tlieir heating powers, and must not be neglected in comparing the analyfical 

 with the economic vesiilts." How this conclusion is to be justified from the data 

 afforded, either by the comparison of Newcastle coals among themselves, or by a com- 

 parison of them with the coals of Wales with which those of Newcastle are supposed 

 to compare the more favourably, in consideration of their containing a higher per- 

 centage of hydrogen, it seems not easy to conceive. In fact, whether wc compare the 

 eighteen Newcastle coals among themselves, or the thirty-six Welsh coals among them- 

 selves, or whether we compare the whole of the Welsh with the whole of the New- 

 castle series, we find that the higher evaporative efficiency is in neither case indicated 

 by a higher per-centage of the hydrogen element. 



The first nine of the Newcastle coals (Table 3, p. 5, 3rd Report) have an average 

 evaporative power of 8-G3 ; the last nine have 7'S8 ; while the average hydrogen of 

 the two sets of nine is in each case precisely the same, namely, 5'3l percent. 



It therefore appears that the hydrogen element could have exercised no influence 

 on the i-elative heating powers of the two halves of the Newcastle series. But the 

 carbon element in the first h.alf of the series is greater than in the last half, in the 

 proportion of S2'69 to 81"o5. 



The first eighteen of the Welsh series gave an average evaporative power of 9*74, 

 and the second eighteen an average of 8"50; the average per-centage of hydrogen in 

 the first eighteen being 4-64, and in the second eighteen 4-97 ; in other words, the 

 lower heating power belongs in this case to those coals which have the greater pro- 

 portion of hydrogen. If " the hydrogen has exercised a very essential importance," 

 it has certainlj' done it by diminishing, not by augmenting, the evaporative power. 

 How stands the case when we compare the carbon element with the evaporative power ? 

 The first eighteen give carbon 87'14 and the second 80'71 . Arranging the sets in the 

 order of evaporative powers, we have — 



If, instead of the mode of comparison just given, we take the three entire series of 

 British experiments as presented in the three reports respectively, and select from each 

 the six highest results in evaporative power, and also the six lowest, and then com- 

 pare those results with the respective per-centages of carbon and of hydrogen, we have 

 the following averages : — 



In the American series it had been shown, by comparing the results of ultimate ana- 

 lysis on six varieties of coal with the calorific power expended both on the water of 

 the boiler, and on the gaseous and vaporous products of combustion, that, in those 

 cases at least, there was a perfect correspondence of the total heating power with the 

 total carbon constituent of the coal. 



Some comparison may nov/ be made to show how far the steam-generating power 

 of the coals may be inferred from their lead-reducing power, when burned in contact 

 •with litharge according to the method of Berthier. As all the American coals tried 

 in 1843, as well as all the British coals since tried, were tested in this way, we have 

 for the purpose of this comparison fourfold series of results embracing about 147 sam- 

 ples of coals. Taking the six highest and the six lowest evaporative results of each 



