368 Morgan and Talhnon — Occurrence of Bitumen. 



cavity and the action began again. Since the oxidation would 

 take place over the whole surface of the minute drop exuding 

 from the pore in the shell, the cavity formed would naturally 

 assume the spherical shape which these pits possess. 



The Bituminous Material. 



The tar is a semifluid substance of very dark brown color, 

 resembling natural asphalts in appearance and physical prop- 

 erties. At 10° C. it is brittle, showing a conchoidal fracture 

 with brilliant surfaces, the edges of the fracture becoming 

 rounded on standing. As the temperature rises it grows 

 softer, until at 100° C. it becomes a fluid with considerable 

 viscosity. Its specific gravity is a trifle less than that of boil- 

 ing water. It is readily and completely soluble in petroleum 

 ether, turpentine, carbon disulphide and chloroform ; much less 

 in acetone and ether, and only very slightly soluble in alcohol 

 even when boiling. ~No residue of an organic or inorganic 

 nature is left by any of these solvents. In all of these points 

 it resembles the " petroleum-ether-soluble " fraction of all 

 natural asphalts, long known as " petrolene." 



In cold fuming nitric acid it is soluble, separating partially 

 a jelly-like mass which resembles silicic acid. If the solution 

 be now poured into water a flocculent precipitate separates, 

 resembling aluminum hydroxide colored slightly with ferric 

 hydroxide. This precipitate is soluble in fuming nitric acid. 



If the solution of tar in nitric acid be heated, the jelly-like 

 substance dissolves, and is not completely oxidized by evapo- 

 rating to dryness. ■ On boiling the residue with dilute nitric 

 acid everything dissolves as the acid concentrates, and when 

 poured into water now gives a flocculent red precipitate like 

 ferric hydroxide, to which reference is made by Day,* in his 

 investigation of gilsonite. This ferric-hydrate-like precipitate, 

 on being heated with water, collects as a thick reddish oil, very 

 slightly soluble in petroleum ether, but readily soluble in 

 alcohol, especially when warmed, thus showing it to be a dif- 

 ferent body from the original tar. 



Concentrated sulphuric acid dissolves the tarry material also, 

 giving a dark red-brown solution which, on treatment with 

 water, gives a precipitate similar to that from fuming nitric 

 acid just described. 



By the sodium nitroprusside reaction the tar gives qualitative 

 tests for the presence of sulphur. A comparison of the inten- 

 sity of color given by tests made on the tar with similar solutions 

 containing known amounts of sodium sulphide would indicate 

 about 0*2 per cent of sulphur in the tar. How much of the 

 total amount present in the tar would escape conversion into 

 * Jour. Franklin Institute, cxl, p. 239 (1895). 





