24 Experiments refpefling Heat. 



ginal weight. It had loft its tranfparency, figure, and pb= 

 liture. 



Bergman obferves, that the diamond, urged by a very in- 

 tenfe heat, contracts a fort of foot upon its furface : no ap- 

 pearance of this kind was dbferved on the prefent occafion. 



The unconfirmed portion of the diamond, which was re- 

 cut after the experiment, now exhibits exa&ly the fame fpe- 

 cies of luftre as before. It originally " drew colour," as 

 jewellers term it ; that is, it had a flight brown tinge 

 throughout, fomewhat like that of a fmoked topaz, but very 

 pale. It has ftill the fame colour. Mr. Frartcillon, whofe 

 experience in matters of this nature is equal to that of moil 

 perfons, made an obfervation on this circumftancc which 

 deferves to be mentioned. It feems that there are fome dia- 

 monds which, although in themfelves colourlefs, contain 

 " fouls" or " fpecks," as they are called, which are cavities 

 filled with red, yellow, or brown earths ; and thefe colours, 

 being reflected through the tranfparent fubftance of the ftone 

 when cut, give it the appearance of being itfelf coloured. 

 When fuch (tones are fubje&ed to heat, the earth in thefe 

 cavities turns black ; the ftone after this '* plays colour- 

 lefs," and the defect is cured. Thofe which "draw colour," 

 that is, which are themfelves tinged, undergo no change by 

 beinor heated. 



o 



II. Another diamond, which weighed 3'ths of a carat; 

 was fubjected to heat excited by oxygen gas in the fame 

 manner as the former. At the end of \' 53" it was with- 

 drawn, and was found to have loft -^hs, or ffths of its orU 

 ginal weight. In a few feconds more, it would have en- 

 tirely difappeaved. It was indeed the intention of the Society 

 to have produced this effect ; but one of thofe fortunate cir- 

 cumstances which fometimes lead to confiderable discoveries, 

 prefented on this occafion a phenomenon even more inter- 

 efting than that of the total diffipation of the gem, though 

 no lets to have been expected. The diamond was at this 

 time accidentally thrown from the charcoal, and was clearly 

 and diJhnElly jeen to flame as a comhujlihle body in its tajfagt 

 through the air. The flame was of a blueifh pearl colour, and 



nearly 



