C 167 3 



III. Compound bituminous Substances. 



Mr. Hatchett, whofe divifion of bituminous 

 fubftances I have chiefly followed, is of opinion 

 that the progreffive changes of naptha into pe- 

 troleum, mineral tar, mineral pitch, and afphal- 

 tum, is caufed by the gradual diffipation of part 

 of the hydrogen of the bitumen, and the confe- 

 quent difengigement of carbon; and although the 

 divific^ of the fimple bituminous fubftances ter- 

 minates in afphaltum, nature appears to have 

 glided on by an uninterrupted chain, which con- 

 nects the fimple bitumens with the compounds. 



a. Jet) is a compact black body ; harder and 

 lefs brittle than afphaltum; may be formed into 

 trinkets ; it breaks with a conchoidal fracture, 

 and the internal luftre is glofly. It has no odour, 

 unlefs when heated, and it then refembles afphal- 

 tum. * 



b. Coal, of which carbon is a condiment prin- 

 ciple, is found in various parts of Europe in 

 ftrata beneath the furface of the earth ; it is foli- 

 ated, brittle, black, and glittering. Befides carbon, 

 it's conftituent parts are, petroleum, maltha, and 

 afphaltum, combined more or lefs with other ear- 

 thy particles, and, frequently with fulphur, and 

 the remains of vegetable matter. 



c» Miiier al Elastic Gum ; difcovered in 1786, 



near 



