[ 560 ] 



LXXXIII. On the Composition of certain Mineral Substances 

 of Organic Origin, By James F. W. Johnston, y^.M., 

 F.R,SS. Lond. and Ed., F.G.S., Professor of Chemistry and 

 Mineralogy, Durham* 



IV. Retin Asphalt. 



T^HE substance described under this name by Mr. Hatchett 

 -*- is well known to mineral collectors as occurring in the 

 wood coal deposit of Boveyf. It is met with in lumps of 

 various sizes, generally of an earthy aspect and fracture, rarely 

 compact and glistening, and of a colour more or less brown. 

 Throughout its substance are frequently observed small por- 

 tions of carbonaceous matter, long, small, apparently pointed, 

 and when broken across exhibiting under the microscope a 

 hollow quadrangular cavity as if they were the remains of 

 slender spines, or of leaves allied to those of the Coniferae. 

 In the air it melts when heated, burns with a bright white 

 light, much smoke, a slightly aromatic odour, and leaves a 

 pure white ash consisting of alumina with a little silica. 

 Alcohol dissolves a large portion of it, giving a dark brown 

 solution, and leaving a light brown residue. This residue 

 still contains a large quantity of organic matter, which appears, 

 however, to possess in common with asphaltum, which Mr. 

 Hatchett supposed it to contain, no other property but that 

 of being insoluble in alcohol. A portion of the retin asphalt 

 carefully burned left 13*23 per cent, of residuum, after ex- 

 haustion by boiling alcohol 32*52 per cent. It consisted, 

 therefore, of 



Resin soluble in alcohol 59*32') 



Insoluble organic matter 27*4^5 > 100. 



White ash 13*23 ) 



This proportion of the constituents is probably variable. The 

 insoluble matter heated in a tube, blackens and gives off' 

 empyreumatic products. At a red heat in the open air it 

 burns. 



Resin of Retin Asphalt. Retinic Acid. 



Evaporated and the residue dried at 212°, the dark brown 

 alcoholic solution leaves a light brown resin largely soluble 

 in ajther, (from which alcohol throws down the greater part,) 

 and less so in alcohol, from which it is wholly precipitated by 

 water. At 212° it emits a peculiar resinous odour, which be- 

 comes more perceptible as the temperature is raised. At 

 250° Fahr. it begins to melt, and at the same time to lose in 



* Communicated by the Author. 



[t Mr. Hatchett's account of this substance will be found in Phil. Mag., 

 First Series, vol. xxi. p. 147.— Edit.] 



