94 Dr. Thomson on the Composition of [Aug. 



34 atoms carbon 



34 atoms hydrogen 



2 atoms azote 



1 atom oxygen 



34-25 100-00 



Thus we see that in cherry coal (abstracting the earthy part) 

 the absolute weight of carbon is almost as great as in splint coal, 

 or caking coal ; yet it yields less coke than either of these 

 species, and burns away also much more rapidly than either of 

 them. The reason is obvious when we know that cherry coal 

 contains twice as much hydrogen as splint coal. In splint coal, 

 the atoms of carbon are to those of hydrogen as two to one ; in 

 cherry coal as two to two. Hence the reason why cherry coal 

 burns so rapidly, why it yields so much gas, and why it furnishes 

 so little coke. 



4. Cannel Coal. 



The experiments on this species of coal were conducted pre- 

 cisely in the same way as the others. The gaseous products 

 from one grain of the coal reduced to the mean temperature and 

 pressure were as follows : 



Carbonic acid gas 4-585 cubic inches^ 



Azotic gas 0-450 



The weight of the water extricated amounted to 1*8 gr. equi- 

 valent to 0-20 gr. of hydrogen. Hence the constituents of this 

 coal are as follows : 



Carbon 0-626 



Hydrogen 0-200 



Azote 0-142 



Ashes 0-100 



1-068 



Here there is a slight excess in the weight of the products 

 above that of the original coal ; so that we have no reason to 

 infer that cannel coal contains oxygen as a constituent. In this 

 respect it differs materially from the other three species of coal, 

 all of which contain less or more of that principle. 



When we convert these weights into atoms, we have the 

 composition of cannel coal as follows : 



1 1 atoms carbon = 8-25 64-72 



22 atoms hydrogen = 2-75 21-56 



1 atom azote = 1-75 13-72 



12-75 100-00 



Thus cannel coal contains twice as many atoms of hydrogen 



