4G Dr Andrew Fyfe on the Comparative Value of 



yields an article of much higher value for the purposes of 

 illumination ; but then, were this coal used in England, it 

 would, most probably, owing to carriage, &c., become so ex- 

 pensive, as to cause the charge for the same light to be more 

 expensive than it is at present. 



In considering the results of the trials now recorded, the 

 most superficial observer must be struck with the remark- 

 able fact, that gases, having the same illuminating power, 

 require, with the same burners, very dift'erent times for 

 the consumpt of equal volumes; and hence, as I have al- 

 ready said, it is necessary, in ascertaining the value of a 

 gas, for the purposes of illumination, to take into account, 

 not only the illuminating powers, but also the durability. 

 Though I alluded to this in a former paper, published in 

 the Transactions of the Society for 1842, my attention has 

 been more particularly drawn to it during the investigations 

 in which I have been lately engaged, by observing the strik- 

 ing difference between the durabilities of gases obtained from 

 Scottish cannel coals, procured from different districts ; and 

 hence, the remarkable circumstance, that two coals may both 

 yield the same quantity of gas, and which gases, when burned 

 under similar circumstances, are of the same illuminating 

 power, yet these coals may be of different value for the manu- 

 facture of gas, in so far, that the gas from the one will burn 

 a longer time than that fi'om the other will do, when con- 

 sumed in the same way. This is well illustrated with the 

 coals of the Lothians, and of the west of Scotland. Thus, 

 the average condensation by chlorine, of the gas from the 

 Marquis of Lothian coal, was, in my trials, 13125, the average 

 durability 59' 30" ; while, with the Lesmahago coal gas, the 

 former was 15-77, but the latter was only 62' 24". Had the 

 one been in proportion to the other, the durability ought 

 to have been 71' 30", or nearly so. The same remark is ap- 

 plicable to the varieties of coal from the west of Scotland, 

 when compared with one another. Thus, the average indi- 

 cation by chlorine, with the Skaterig and Knightswood coal 

 gas, was 9, the durability 46' 45". With the Lesmahago, as 

 above, they were resi>ectively 1577 and 62' 24". The latter, to 

 keep pace with that of the former, ought to have been 81''54". 



