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rency of bitumens, should be essayed. It has been sug-gested the colouring of naphtha depends upon the increaseof its relative proportion of carbon and oxygen, manifestedby the deposition of the oxyde of carbon, the inspissationof charcoal may take place in various degrees, according tocircumstances. Thus on one hand, whilst the naphtha retainsits primitive subterraneous situation, it may come in contactwith the sulphuric acid, which readily yielding its oxygen tothe carbon, and at once gives it darkness of colour; but, onthe other hand, where no excess of oxygen is present, themore fluid parts of the bitumen may gradually exhale, with-out its undergoing any decomposition or alteration in theoriginal proportion of its principles; and thus may thelighter coloured and harder bitumens be produced. To Mr.Hatchett’s discoveries in the chymical nature of bitumens,and their various changes, this ingenious author confesseshis obligations; who appears to have ascertained that theprogressive change of naphtha to petroleum, mineral tar,mineral pitch, and asphaltum, proceeds from the disengage-ment of carbon. Thence he believes originates the changeof colour, the degrees of inspissation, the increased pro-portion of carbon found in these substances by chymicalanalysis. By this observation, Mr. Hatchett, however, meansonly relatively to be increased, in respect to other ingredi-ents, in a given quantity of these bitumens, and that itpredominates in proportion to the dissipation of a certainportion of hydrogen, which was originally necessary to theforming of the bitumen conjointly with the carbon ." 5
To account for the origin of amber, first a postulate isassumed, that it is bituminous; its analysis manifests itsproperties: exposed to the fire it liquifies, if heat be strong,softening and bubbling, without running into drops; whichcircumstance distinguishes it from resins: inflamed, it dif-fuses a thick smoke with a pungent odour. Its flame isyellow, variegated with blue and green: after combustion,it leaves a black shining coal, yielding by incineration avery small quantity of earth, mixed with a slight proportionof iron. Thence he, Mr. Parkinson , would be led withouthesitation to seek for its formation in the subterranean labo-ratories of nature; both for its bearing accidental but equi-vocal marks of having existed during some of the stages ofits process, either actually on or very near to the surface ofthe earth. He next examines the opinions of various natu-ralists respecting its origin. Theophrastus speaks of amber
20 Philosophical Journal, v. ii. p. 206.