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VII. Account of fome interejling Experiments, performed at 

 the London Philofophical Society, refpecling the Effetls of 

 Heat, excited by a Stream of Oxygen Gas thrown* upon 

 ignited Charcoal, on a Number of Gems and other refrac- 

 tory Subjlajices fubmitted to its Action ; with a Dtfcription 

 of the Apparatus employed. 



[Continued from Page 29*] 

 Wcdgexvood's Pyrometer Pieces. 



XVII.xxFTER the experiments already deferibed, it was 

 propofed by feveraJ of the members that fome attempt fhould 

 be made to determine the degree of heat which had been 

 excited ; and, with a view to this end, a fragment of one of 

 Mr. W edgewood's pyrometer pieces was fubjecled to the 

 blait : in a few feconds, however, it became perfectly fufed. 

 It does not appear, therefore, that we are at prefent in pof- 

 feffion of any better inftrument for appreciating the intenfitv 

 of heat thus produced than the gems themfelves, which, as 

 fome of them are more refractory than others, and many of 

 them more fo than moft other fubftances, may, from the 

 changes which thev undergo, ferve to afford a rough method 

 of eftimating the comparative degree of temperature. 



Spinel. 



XVIII. A ruby-fpinel, which weighed ||ths of a carat, 

 was, like the preceding ltor.es, expofed iu an excavation made 

 in a piece of charcoal ignited by means of a common blow- 

 pipe, to a ftream of oxygen gas from the gaibmeter. At the 

 end of 2' 3'' it had loft neither weight nor colour, but had 

 aflumed the appearance of a rough garnet, having apparently 

 undergone a very flight and fnperficial fufion, juft fufficient to 

 injure its polilh. 



Jargoons. 



XIX. Thefe ftones are colourlefs, and harder than rock- 

 cryftal, but lefs fo than the. ruby. They are ufually found 

 in diamond-mines, and, when well cut and fet, play nearly 

 as well as rofe diamonds. That they are however efTentially 



9 di fie rent 





