42 T>v Andrew Fyfe on the Comparative Value of 



ton. In the north, however, it becomes higher and higher, 

 according to the distance, and, consequently, to the carriage 

 from the pits. 



In the larger towns that I have visited, I have found very 

 little variation in the quality of the gas obtained from the dif- 

 ferent mixtures used. The chlorine indicated from 13 to 15 ; 

 the average may be taken as 14. The durability was from 70' 

 to 90' very rarely below 80, — on an average, it was a little be- 

 yond 80, — say 80. The pressure at the burner varied from 

 iVoths to iVoths. The sp. gr. was, on an average, about 640. 

 Thus, then, the illuminating power of the gas with which the 

 towns in Scotland are supplied, is, on an average, as 3-23 to 

 the Newcastle coal gas, and 1-85 to the average of English 

 cannel, both taken as 1. The durability is as 1-58 to English 

 caking, and 1-45 to the other, both as 1. Accordingly, taking 

 both into account, the value of these gases, bulk for bulk, 

 for the purpose of illumination, is English caking 1, English 

 cannel 1-85, the average of the gas in the towns of Scotland 

 5-1, say 5. Taking the English cannel-coal gas 1, then the 

 Scottish is from 263 to 2-72, say 2-7. From the mixed coal 

 employed in different towns, a ton yielded on an average 

 9500 feet of gas. 



2. Value of Coals for the purpose of Illumination. 



Keeping in view what has now been said regarding the 

 quality of gas which the different kinds of coal afford, an 

 estimate may be foi-med of the comparative value of these 

 coals for that purpose, independent of the price paid for the 

 coals, and also of the returns made for coke, and other mat- 

 ters disposed of, such as ammonia, &c. ; and in doing so, I still 

 take the English caking coal as unity. 



A ton of English caking coal yields, on an average, at 

 gas-works, 8000 feet of gas, and though a larger quantity 

 was given with my apparatus, yet we must take 8000 as the 

 quantity on a large scale. The value of the coal is taken as 1. 



The Wigan cannel yielded 9500 and 11,500 ; the value of 

 the gas, bulk for bulk, being the same, viz., 1-85 to the former 

 as 1. Now, taking into account the quantity of gas afforded, 

 the value of the coals for yielding light, by the consumpt of 



