106 



as will more readily inflame, to assist the burning. They are 

 supposed to contain less oxygen with the carbon than other 

 coals, and therefore require the assistance of those which 

 contain more oxygen. It may not be amiss to observe here 

 that diamonds require oxygen to assist their burning, in the 

 proportion of 4 parts to 5 in a Strong heat ; and in burning 

 they pass into the black state of charcoal, continuing to 

 burn like it, and giving out carbonic acid gas (see de- 

 scription, Tab. I.*) in the same way, the carbon being 

 aerated by the caloric or matter of heat. Although dia- 

 mond has always been of high value, and well-known from 

 the earliest ages, yet it was left for Mr. Tennant in the year 

 1 796 to prove it to be a pure carbon. See Phil. Trans. 1 797- 

 p. 123. 



There are other sorts of coals about Swansea, of which 

 we shall speak hereafter. Coals mostly appear to be the 

 combustible remains of vegetation, provided apparently to 

 secure whole forests for the use of after generations. They 

 are mostly formed in the strata of plains, composed of 

 marie, sandstones, and limestones, most of which show 

 the remains of animal and vegetable petrifactions, or im- 

 pressions. See Sandstones, Tab. XL. The blackened parts 

 in those figures are apparently the remains of bituminous 

 carbon, as it were in the last stage of infiltration. 



* It is found native in some caverns, well?, and mines, and is called choke 

 damp of the miners. It is often fatal to them. 



