

Different Kinds of Coal for the purpose of Illumination. 81 



very rarely below 80, — on an average, it was a little beyond 80, 

 say 80. The pressure at the burner varied from jVVths to -\\ ths. 

 The sp. gr. was, on an average, about 640. Thus, then, the 

 illuminating power of the gas with which the towns in Scotland 

 r 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 

 I durability is as 1\>8 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 En- 

 glish 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 2-03 to 2*72, say 2 7. From the 

 mixed coal employed in different towns, a ton yielded on an av- 

 erage 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 formed of the comparative value of these coals for that pur- 

 pose, independent of the price paid for the coals, and also of the 

 returns made for coke, and other matters 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 



is, 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 



°t the coals for yielding light, by the consumption of their gases, 



] s as 2-23 for the one quantity, and 2-5 for the other; taking the 



average, we state the value of English cannel coal as 2 35, or say 

 2i to Newcastle caking coal as 1. 



Scottish Parrot. — While the English cannel coal may be con- 

 sidered as of the same value at different places, it is not so with 

 the Scottish parrot. I have said that it varies very much in dif- 

 ferent districts; and hence, though the value of the gases with 

 which the different towns are supplied is very nearly the same in 

 a ", owing to mixtures of coals of superior and inferior quality 

 being used, yet the value of the different coals vanes considera- 

 bly, owing to the quality and quantity of gas winch they afford 

 varying. 



as 



I have taken the average value of the Scottish parrot-coal gas 

 5, compared to that from the English caking coal as 1. The 

 quantity of gas from the latter being 8000, and that from the 



Second Series, Vol. VII, No. 19.— Jan., 1849. 11 



