1820.] Accum on Coal Gas. 289 



One chaldron of coal produces Cubic feet of gas. 



Welch coal, 



First variety, from Trarasaren, near Kidwelly 2,116 



Second variety, from the yard vein at the same place . . 1 ,656 



Third variety from Blenew, near.Llandillo 1,416 



Fourth variety from Rhos, near Ponty Barren 1,272 



Fifth variety from the Vale of Gwendrath 1,292 



Sixth variety from ditto 1,486 



In Part IV. the author gives us an account of the retorts 

 employed for manufacturing coal gas. They are made of cast- 

 iron, and a cylindrical shape has been ultimately preferred. 

 They are 6i feet long, and 1 foot in diameter. Five of these are 

 now arranged in a kind of oven, which are raised to the requisite 

 temperature by means of three fires below, and so contrived that 

 the flame plays equally round the retorts. For the contrivances 

 for conveying away the gas and separating the tar and the 

 aramoniacal liquor, I must refer to the work itself. The quantity 

 of coal necessary to be burned as fuel in order to decompose 

 100 lbs. of coal, varies from 20 lbs. to 25 lbs. 



The gi'eatest quantity of gas is disengaged at first, and the 

 quantity of product diminishes continually during the process. 

 But the author proves in Part V. by satisfactory experiments 

 made on a large scale, and repeated for a sufficient length of 

 time, that it is more economical to continue the application of 

 the heat to the retorts for eight hours than to stop after an 

 interval of six hours. 



In Part VII. the author shows that in London it is more 

 economical to decompose the coal by a strong red heat, though 

 the retorts are sooner destroyed, than to employ a low heat, which 

 yields less gas, but allows the retorts to last longer. The 

 retorts ought to be made of hght-grey cast-iron, not of the soft- 

 est kind, which is unable to resist a continued heat. They must 

 be always kept red-hot as long as they last. If they be allowed 

 to cool, they waste much sooner. In London, 1000 cubic feet of 

 gas can be made for seven shilHngs. Cannel coal it appears 

 yields its gas at a lower temperature than any other, and is, 

 therefore, best adapted for making coal gas. 



One of the most curious parts of the coal-gas machinery is 

 •what is called the horizontal rotary retort invented l^y Mr. Clegg, 

 and gradually brought to perfection. Our author employs the 

 seventh part of his work in explaining this curious apparatus. 

 We cannot do better than quote this article (abridging it a little) 

 as a specimen of the work, which is likely to interest the reader. 



Jtorizontal Jiotary Retorts, lately brought into Uicfur manufacturing Coal Cits. 

 The many disadvanlages attendant on the plan of decomposing coal in masses 

 from live to (en inches in thiekne»s, as already siiflicicntly exposed in the preced- 

 ing parts, had naturally the eflect of developing a principle of manufacturing co.il 

 gas, which practice has now fully established, namely, that to decompose coal, in 



Vol. XV. N° IV. T 



