78 Dr. Andrew Fyfc on the Comparative Value of 



arrive at the true value of the gases, and, consequently; cannot 

 compare one with another for the purpose of illumination. Thus, 

 if two gases afford, by their combustion, from the same or similar 

 burners, with the same height of flame, the same light ; but if a 

 foot of the one lasts an hour, and a foot of the other an hour and 

 a-half, then the latter is one-half more in value than the former 

 for yielding light, because it is giving the same light for one-half 

 more time ; or, which is the same thing, one-half more of the 

 former must be used so as to complete the time which the latter 

 will burn. This, I regret to say, has been too often overlooked 

 by many in estimating the value of coal-gas. 



As the chief object I had in view was, not the comparison of 

 the light afforded by coal-gas, or its expense, as compared with 

 other sources of light ; but merely the value of the gases as com- 

 pared with one another, when obtained from different coals, I 

 shall commence with that from English caking coal, and take 

 it as the unit for comparison. 



English Caking-- Coal Gas. — The gas from this kind of coal, 

 on which my experiments were made, was that from Newcastle ; 

 others were also procured by means of an experimental appara- 

 tus, fitted up expressly for the purpose. The condensation by 

 chlorine in the former, was, on an average of several trials, 4*33 

 per cent. 



The specific gravity, at Th. 60, B. 30, was 420. 



The durability, with a four-inch flame, from a platinum jet, 

 ^ ! 3 of an inch in diameter, was 1 cubic foot in 50 minutes 30 

 seconds. The pressure by water-gauge at the burner was } * of 

 an inch. 



From 1 ton of coal, about 8000 cubic feet of gas are obtained. 



The gases obtained with my experimental apparatus, from a 

 variety of samples of the same kind of coal, both lately and sev- 

 eral years ago, were very nearly of the same composition. Dif- 

 ferent heats were used in driving off the gas, with the view of 

 finding the best heat. The condensation by chlorine varied from 

 3*5 to 5 5; the average of the trials, amounting to eight, was 

 nearly 5. The durability varied from 47' 20" to 53' 30" ; the 

 average being 50 / 25". 



The average specific gravity of eight different gases was 464, 

 the highest being 512, the lowest 414. 



As above mentioned, I take the gas from this kind of coal for 

 illuminating power and durability, and, consequently, for value, 

 as my standard of comparison. 



English Cannel-Coal Gas. — The gas obtained from this kind 

 of coal, such as that from Wigan in Lancashire, with which Liv- 

 erpool, Salford, and other places are supplied, and that from coals 

 found in different parts of Yorkshire, which are occasionally used 

 at Manchester, are very nearly of the same quality. 





