On certain Mineral Substances of Organic Origin. 87 



tine upon the bichloride of platinum. I also intend to exa- 

 mine some other metallic chlorides and haloid bodies under 

 the same circumstances. 



XVIII. On the Composition of certain Mitieral Substances of 

 Orgajiic Origin. Nos. VI. VII. VIII. Mineral Resins. 

 By James F. W. Johnston, M.A., F.E.SS. L. S,- E., F.G.S., 

 <$•€. 4'c., Prof. Chem. and Min., University^ Durham.* 

 No. VI. Highgate Resin or Fossil Cojml. 

 nPHIS substance derives its names from the locality in 

 -*- which it was first found in any quantity, the blue clay 

 of Highgate Hill near London, and from its similarity to co- 

 pal resin in hardness, colour, lustre, transparency, and diffi- 

 cult solubility in alcoholf. For the two fragments which 

 have afforded me the following results I am indebted to the 

 liberality of my friend Mr. Brooke. 



1. The first fragment analysed was translucent, of a dirty 

 gray colour, and when broken emitting a resinous odour. 

 In the air it volatilized by a gentle heat, leaving a small resi- 

 due of charcoal and earthy matter. The former being burned 

 away, the latter weighed 0'136 per cent. 



9*905 grs. burned with oxide of copper gave 1 0*508 grs. 

 of water and 30*795 of carbonic acid. This is equal to 



Carbon = 85*408 



Hydrogen = 11*787 



Oxygen = 2*669 



Ashes = 0*136—100*000. 



2. The second fragment was clear, pale yellow, and semi- 

 transparent. It was covered with a thin coating of a browner 

 apparently altered variety, of which, from the smallness of the 

 quantity at my disposal, I was not able wholly to divest it. 



5*509 grs. gave 5*69 grs. of water and 17*07 of carbonic 

 acid. This is equal to 



Carbon = 85*677 



Hydrogen = 11*4'76 



Oxygen = 2-847— 100*000. 



Assuming the latter specimen to be the purer, this sub- 

 stance is represented by the formula C40 H32 Oj , since 



Calculated. Found. 



40 Carbon = 3057*480 85*968 85*677 



32 Hydrogen = 399*347 11*228 11*476 



1 Oxygen = 100*000 2*804 2*847 



3556*827 100*000 100*000 



• Communicated by the Author. 



t For a description of this substance sec Phillips's Mineralogy. 



