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That afphalt burns with flame and foot, but melts and fwells, 

 and requires for its intire confumption an increafe of heat, leaving 

 fcarce any coal, and but little aflies. 



It is moreover well known that liquid bitumens contain in- 

 flammable air and carbon. That they abforb atmofpheric air 

 when long expofed to it and light. That in confequence of this 

 abforbtion they are thickened, blackened and condenfed, firfl: into 

 mineral tar, then into mineral pitch or maltha, and laftly into 

 afphalt. That almoft all fpecies of mineral coal yield more or 

 lefs of both fpecies of bitumen on diftillation, leaving a fliining 

 coaly refiduum, but that the proportion is variable in every fpe- 

 cies, according to the degree of heat applied ; that the refiduum 

 always obftinately retains a proportion of bitumen, and that con- 

 fequently diftillation, in addition to its other imperfedions, is an 

 infufficient medium whereby to difcern the proportion of carbon 

 and bitumen, and confequently to difcriminate the various forts 

 of mineral coal from each other. 



2°. Decompojition of nitre. It has long ago been remarked by 

 the juftly celebrated Macquer| that nitre detonnates with no 

 oily inflammable matter until fuch matter is reduced to a coal, 

 and then only in proportion to the carbonaceous matter it con- 

 tains ; an obfervation the truth of which will fully appear in the 

 fubfequent experiments. Hence it occurred to me that fince in 



the 



t I Didlion. Chym. 2d Edition, p. 481. 



