164 Dr. Thomson on Coal Gas, 



cherry coal, splint coal and cannel coal. Of these the cannel 

 coal, or parrot coal as it is called here, yields the best gas; 

 the caking coal, or Newcastle coal, yields the worst, and the 

 cherry and splint, though very different in their appearance, 

 yield an intermediate gas, the quality of which, whether from 

 cherry or splint coal, is nearly the same. 



There are three varieties of cannel coal in the neighbour- 

 hood of Glasgow, named from the localities where they occur, 

 Skaterigg, Lesmahagow and Monkland. 



The specific gravity of these varieties of coal is as follows :— 



Caking coal . . 1*280 Mr. Richardson. 



Cherry coal . . 1-268 



Splint coal. . . 1-307 



Skaterigg . . . 1-229 Dr. R. D. Thomson. 



Lesmahagow . 1-198 



Monkland ... 1-189 

 Besides ashes, these six varieties of coal consist of carbon, 

 hydrogen, azote and oxygen, combined in various proportions 

 according to the coal. I shall here give the composition of 

 each ; that of the first three was determined by Mr. Richardson 

 of Newcastle in the laboratory at Giessen ; that of the last 

 three in the College laboratory by Dr. R. D. Thomson. The 

 azote is small in quantity, so small that Mr. Richardson did 

 not succeed in determining its exact quantity ; but we found 

 no difficulty in coming to very exact conclusions by the pro- 

 cess of Will and Varrentrapp*. As the quantity in all our 

 varieties tried varied from 1*48 to 1-75 per cent., I have sup- 

 posed that the azote in the three varieties determined by Mr. 

 Richardson was the mean of these two quantities, or 1-61 per 

 cent. The following table shows the composition of these coals : 



100- 100- 100- 100- 100- 100- 



It will facilitate our conception of the composition of these 

 different coals if we exhibit their condition by empirical for- 

 mulas representing the atoms of each constituent, the quan- 

 tity of azote being reckoned one atom : we leave out the ashes, 

 because they have nothing to do with the production of the 

 gas, excepting that they materially influence its quantity. 



* This process was first proposed by Dr. Schafhaeutl, in Phil. Mag. 

 [S. 3. vol. xvi. p. 44.] 



