1813.] Resinous Substance found at High gate. 



Article III. 



Description of a Resinous Substance lately dug out of the Earth 

 at High gate. By Thomas Thomson, M.D. F.R.S. 



During the late attempt to make a tunnel through High- 

 gate-hill, in the neighbourhood of London, a very considerable 

 number of curious fossils were discovered. The beds dug 

 through consisted partly of gravel and partly of clay. The 

 number of shells thrown out, and the round masses of lime- 

 stone, could not escape the must careless observer ; but one of 

 the most remarkable substances detected was a resinous body, in 

 shapeless masses of various sizes. Mr. Sowerby had the good- 

 ness to send me some specimens of this curious substance * and 

 as I am not aware that any account of it has hitherto been pub- 

 lished, I conceive that the following observations whic h 1 made 

 upon the specimen that I received will prove acceptable to my 

 chemical and mineralogical readers. 



I. The colour of Highgate resin is of a dirty yellowish light 

 brown. It is semitransparent. Its lustre is resinous, and its 

 surface smooth; though not perfectly so; but having the appear- 

 ance of having been rubbed, as would have happened had it been 

 mixed with gravel upon the margin of the sea-shore, or a lake. — 

 Brittle; not so easily broken as common resin ; hut much more 

 so than copal : softer than copal; has a resinous and aromatic 

 smell, especially when heated; this smell is peculiar, though it 

 has some faint resemblance to the smell of camphor. 



II. Its specific gravity at the temperature of 6"0° is I "0-16. 

 This agrees almost exactly with the specific - gravity of copal as 

 determined by Brisson ; but on trying the specific gravity of 

 copal, I found it 1*069. Hence either copal differs consider., lily 

 in its specific gravity, or the re>in called copal by Brisson was 

 not the same to which we give that name in Britain. 



III. When heated it melts, and may be rendered as liquid as 

 water without alteration in its colour. It catches fire at the flame 

 of a candle, and burns with a clear yellow flame, and emitting 

 abundance of smoke, as is the case with other resins. At the 

 same time it emits a strong aromatic odour 



IV. When in lumps it is insoluble in all the re-agents I tried, 

 namely, water, alcohol, potash ley, acetic acid; except ether, 

 nitric acid, and sulphuric acid, which act upon it more or less. 



Ether renders it opake, and white, and quite tender ; so that 

 it has lost its cohesion, and crumbles into powder upon tin least 

 pressure between tin' Angers. The ether at the same time dis- 

 solves a portion of it which it deposites, and becomes milky 

 when agitated with water. 



