22 Dr. M AC CuLLOCH on certain products 



There is a wide interval between the external characters of the 

 lignites and of coal, and though we cannot presume to state the 

 period which Nature has used in her operations, nor during how 

 long a space the causes have continued to act, before the vegetable 

 matter has undergone its ultimate change into coal, nor therefore 

 whether the long continued agency of water and pressure may 

 not have produced the required changes, yet, since Philosophers of 

 high reputation have supposed that fire has been a probable cause 

 of this conversion, and that this theory is supported by considerable 

 evidence in some analogous cases, it is our duty to examine by ex- 

 periment, what effects conducing to this end may result from our 

 limited trials. The foregoing experiments show that the fire of our 

 furnaces does not convert wood into bitumen, and the processes of 

 Nature seem to prove that water can produce this effect, and that 

 jet, the bituminous lignite which approaches nearest to coal in its 

 chemical characters, is the result of this action. Yet there is an 

 interval between jet and coal as I have already observed, requiring 

 explanation. The chemical characters may be identical, but ths 

 mineralogical resemblance is still wanting. It is possible that the 

 agency of fire may account for this ultimate change, and that its 

 action on beds of lignite and peat has converted not wood but vege- 

 table matter already bituminized by water into coal. Pursuing this 

 train of investigations I was induced to try if jet, the most perfectly 

 bituminized lignite, could by the application of heat under pressure 

 be converted into coal. For this purpose I introduced powdered 

 jet into gun ban-els, placing it between two portions of rammed 

 Stourbridge clay, with the view of absorbing a part of the distilled 

 petroleum when it might be formed in greater quantity than was 

 requisite for the success of the experiment, and where by its con- 

 version into hydrogen, it might endanger the bursting of the appa- 



