46 EXPERIMENTS ON THE PRODUCTS FROM COAL. 



equal volumes, an illuminating power about one-third greater than that from 

 coal of medium quality. The quantity also from the former substance ex- 

 ceeded by about one-seventh that obtained from common coal. 



In comparing the value of gases produced from different kinds of coal, or 

 from the same kind of coal differently treated, it is not enough to determine 

 the quantity of aeriform products ; and no satisfactory conclusion can be drawn 

 respecting the relative fitness of any variety of coal for affording gas, or the 

 advantages of different modes of distillation, unless the degrees of combustibility 

 of the gases compared be determined by finding experimentally the proportion 

 of oxygen gas required for their saturation. But, as I have before stated, the 

 specific gravities of the various gases form as correct a method of judging of 

 their illuminating qualities as any other, the lighter gas being the poorest. A 

 gas having the specific gravity of O400 I have found, by a great number of 

 experiments on a large practical scale, to be an average standard for compari- 

 son. The gas produced from cannel-coal will average much higher. I have not 

 had an opportunity of making such experiments on this gas as I should wish, 

 to be relied on, as those of practical utility require to be made on a working 

 scale. I think, however, the sp. gr. 0'539 is about the standard. Mr. Clegg 

 obtained once, and once only, gas from a specimen of Wigan cannel, having 

 the specific gravity of 0'640. I have not added this in with the rest for the 

 average, because it is not a general result. 



Table of the Specific Gravity of Coal-Gas, obtained from different Experiments. 



Dr. Henry obtained -600 



- - -431 



340 



Dr. Dalton - - -534 



443 

 410 



-390 



Dr. Faraday - - -430 

 Mr. Lowe - - -425 



- - -408 



Professor Leslie -600 



410 

 Mr. Phillips - - -406 



Mr. Cooper obtained '415 



- - -410 



Mr. Anderson -650 



Mr. Clegg -640 



584 

 470 

 410 

 406 

 400 

 390 

 380 

 380 



- - -370 



The kinds, or rather the different names, of coal used at the London Gas- 

 Works are, South Pelaw, Ellison's Main, Felling Main, or East Garesfield 



