( 32S ) 



thefe fluids. I refolved, in confequence, to 

 fufe within mairafles various volcanic pro- 

 dudls ; fucii, efpecially, as, by the fupera- 

 bundance of their gafeous bubbles, rife from 

 the bottom of the crucibles, and expand 

 over them. I fitted the necks of the ma- 

 trafles to a chemical pneumatic apparatus 

 v>^ith mercury, in order to colled: and exa- 

 mine the gafes which fhouid be difengaged, 

 by the adion of the fire, from the liquefied 

 fubftances. The matrailes were of clay, of 

 the fame kind with that ufed for the re- 

 ceivers in which melted glafs is kept for the 

 making of different veUels in a glafs-houfe. 

 They had a fpherical bottom with a long 

 neck, and were of the thicknefs of lix full 

 lines. I tried them by plunging them into 

 water and blowing ftrongly into them, 

 when I did not find the fmallefc bubble of 

 air efcape. For the greater fecurity I coated 

 them externally, and tried them with the 

 air-pump ; but I did not perceive the leafl 

 hiffing found that might indicate the efcape 

 of air. I repeated thefe proofs, likewife, 

 after I had made my experiments, and thus 



■ ' was 



