ON BITUMENS, &C. 197 



§ VI. 



The powerful action which alcohol exerts on moft of the Experiments on 

 refins, may juftly be regarded as forming a narked diftinaion ^J™^^* 116 

 between thofe fubftances and the bitumens. But, as fome of hoi. 

 the bitumens are acted upon by alcohol, ill a flight degree, I 

 was defirous to afcertain whether a fmall portion of refin was 

 contained in any of thefe ; or, if that was not the cafe, I wifh- 

 ed to determine the nature of the fubftances which could be 

 feparated, although very fparingly, by this menftruum. I 

 therefore made the following comparative experiments, o?i 

 the foft brown elaftic bitumen from Derby (hire ; on the genu- 

 ine afphaltum ; on very pure cannel coal ; and on the com- 

 mon pit coal. 



JOO grains of each were digefled with three ounces of 

 alcohol, in matrafles placed in warm fand, during five days, 

 fome alcohol being occafionally added, to fupply the lofs 

 cauled by evaporation. After the above-mentioned period 

 had elapfed, the liquid contained in each matrafs was poured 

 into feparate velfels. 



I. The alcohol which had been digefled on the elaftic bitu- Refulu; 

 men was not tinged, nor, when fpontaneoufly evaporated, did 



it leave any film or flain on the glafs. 



II. From afphaltum, the alcohol had extracted a yellow 

 tincture, which, in fome iituations, appeared of a pale olive 

 colour, and. being fpontaneoufly evaporated, a thick brown 

 liquid was depofited, in fmall drops, on the glafs; thefe drops 

 did not become hard after two months, and poflefled the 

 odour, and every other property, of petroleum. The afphal- 

 tum had loft in weight about one grain and a half. 



III. The cannel coal had communicated a pale yellow tint 

 to the alcohol, which, in the manner above defcribed, was 

 ascertained to be caufed by petroleum ; but, from the fmall- 

 nefs of the quantity, the weight could not be determined. 



IV. The alcohol which had been digefled on pit coal, had 

 not aflumed any colour; but, by fpontaneous evaporation*, 

 it left a film on the glafs, which, by its odour, was alfo found 

 to be petroleum. 



By thefe experiments we find, that the action of alcohol on Alcohol i&s 

 the bitumens is very flight ; and that the fmall portion which jj^* on bltu " 



* Spontaneous evaporation, by expofure to the air, was em- 

 ployed in thefe experiments, for reafons which muft be fufficiently 



obvious. 



may 



