3 2 ^ Experiments ref petting Heat: 



fays that the breaking of the jars may be prevented if paper 

 coating he applied under that of the metal. Dr. Van Marum 

 found this to be true, hut ohferved at the fame time that the 

 coating was thereby weakened. 



VI. Account of fame interfiling Experiments^ performed at 

 the London Pbilojbphical Society, rejp'e&ing the Effects of 

 Heat, excited by a Stream of Oxygen Gas thrown upon 

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

 tory Subjlances fubmittsd to its Action ; with a Defcription 

 of the Apparatus employed. 



[Concluded from Page ;66.] 



L 



N the experiments that have been defcribed, no account 

 was taken of the quantity of oxygen gas expended on each, 

 as the objects the Society had chiefly in view were : 



j. To fufe, if poffiblc, fome of tbofc refractory bodies 

 which had before refitted every effort hitherto made to bring 

 them into a ftate of fufionj 



2. To afcertain whether any or which of the gems would 

 retain their original colour, tranfparency and hardnefs, after 

 fiilion, with the view of determining whether it would be 

 pofiiblc by fuch a procefs to unite fmall ftones or fragments 

 into one mafs pofi'effing the properties of the native unfufed 

 gems ; 



3. To determine whether any other gems befides the dia- 

 mond could be diflipa'ted by a ilrong heat ; and, 



4. To obferve what other effects might be produced by the 

 powerful agents employed in the experiments. 



The oxygen gas employed Was obtained from oxyd of man- 

 ganefe by expofing it to a Ilrong heat in an iron retort, and 

 was received over water in a pneumatic apparatus. The ori- 

 fices of the blow-pipes were about a fixtcenth of an inch in 

 diameter, and the gas was difcharged under a prefiure of 

 about three pounds weight on the bell of the jrafometer. 



The view of the. apparatus (Plate IX. fig. 1.) will convey 

 a very i.a of the gafometer, and of the arrangement* 



made for the laftexpejimentj viz. the one upon plaiina. 



8 The 



