210 On certain Products ohtaineil 



Tlic sensible qualities of the bituiriens (their taste and smeU) 

 avc in all states ntteily and entirely different Aoai those of the' 

 vegetable tar. Petroleum is also much less soluble in alcohol^ 

 a ad further differs from the vegetable tar in being perfectly solu- 

 ble in naphtha. In their solubilities in oil of turpentine thev 

 resemble each other, as well as in their habitudes with acetic 

 acid and the alkaline lixivia, althongh the vegetable tar will btV 

 found the more readily soluble of the two. I need not repeat 

 the circumstances in which the essential oil of wood differs fVonv 

 luiphtha. It is a sufficiently characteristic one, that it forms no 

 union with tiiis latter. 



It has been already shown that the difference between tlm 

 pitch and asphaltum is considerable, when the former is in its first 

 state, particularly with regard to its solubility in alcohol. 



But if we compare the most brittle spcciuiens of the pitch 

 with common specimens of asphaltum, the differences, except as 

 far as smell and taste are concerned, are not so apparent, and 

 the reason of this will be oijvious on considering their funda- 

 mental similarity of composition. The chief ingredients of both 

 are carbon and hydrogen. By the application of heat, the propor- 

 tions of these substances are altered in both cases, the hydrogen 

 being abstracted in the greastest ratio, to form the new com- 

 pound (the oil) in which hydrogen predominates. The ultimate 

 result of both is charcoal. Asphaltum will be found to combine 

 pretty nearly in the same way, with all the substances I have 

 above enumerated as combining with the pitch. Its essential 

 difference however consists in its solubility in naphtha, and l>y 

 this test they are readily distinguished. 



The chemical difference to which these different properties of 

 substances so similar are owing, will be evident on considering 

 some of the circumstances before related. The disprojjortion of 

 acetic acid and carbonic oxide produced from the wood pitch, when 

 compared with the produce of the bitumen, proves that it con- 

 tains oxvgen and azote in proportions different from those in 

 which the same substances exist in the bitumens ; and that in 

 particular it contains a considera1>le quantity of the former. Tlic 

 result would not repay the toil required to investigate these pm- 

 portions, which are probably also subject to considerable varia- 

 tion. 



It is obvious that this substance is a new compovmd, formed 

 by the action of fire on vegetable elementary matter ; but all that 

 we can determine of its nature is, that, in conformity to modern 

 chemical nomerclature, it is formed of carbon, hydrogen, oxy- 

 gen, and azote. The carbon and hydrogen constitute its basis, 

 as they do that of the bitumens, and the large proportion of 

 oxygen appears to give it the pecyliar properties by which ii is 



distinguished 



