84 Dr. Andrew Fijfe on the Comparative Value of 



expensive than the English coal ; yet is superior to it for the manu- 

 facture of gas ; in so far that it 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 expensive, as to cause the charge for the same light to * 



be greater than at present. 



In considering the results of the trials now recorded, the most 

 superficial observer must be struck with the remarkable fact, that 

 gases, having the same illuminating power, require, with the 

 same burners, very different times for the consumption of equal 

 volumes; and hence, as I have already said, it is necessary, in 

 ascertaining the value of a gas, for the purpose of illumination, 

 to take into account, not only the illuminating powers, but also 

 the durability. Though I alluded to this in a former paper, pub- 

 lished in the Transactions of the Society for 1842, my attention 

 has been more particularly drawn to it during the investigations 

 in which 1 have been lately engaged, by observing the striking 

 difference between the durabilities of gases obtained from Scot- 

 tish 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 sim- 

 ilar circumstances, are of the same illuminating power, yet these 

 coals may be of different value for the manufacture of gas, in so 

 far, that the gas from the one will burn a longer time than that 

 from the other will do, when consumed 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, or 

 the gas from the Marquis of Lothian coal, was, in rny trials, 

 13-125, the average durability 59' 30" ; while, with the Lesma- 

 hago coal aas, the former was 15*77, but the latter was only 

 62' 24". Had the one been in proportion to the other, the dura- 

 bility ought to have been 71' 30", or nearly so. The same re- 

 mark is applicable to the varieties of coal from the west oi Scot- 

 land, when compared with one another. Thus, the average in- 

 dication by chlorine, with Skaterig and Knightswood coal gas, 

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

 they were respectively 1577 and 62' 24". The latter, to keep 

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



I have observed similar results in trials which I have lately 

 made. Thus three coals, submitted to experiment, yielded gases, 

 the indication of which, by chlorine, w;is 14; the durability in 

 the one being 57', in the other two 66*; and again, with other 

 gases, in which the condensable matter was as high as 19 and 22, 

 the durability did not exceed 77' and 8K In numerous trials I 

 found that the gas from English caking coal gave condensation 

 by chlorine 4-33, and durability 50' 30", or nearly so. That 



