MODIFIED by COMPRESSION. or 



therefore found neceffary to oppofe fomething more fubftan- 

 tial and compact, to the thin and penetrating quality of pure 

 borax. 



In fearching for fome fuch fubflance, a curious property of 

 bottle-glafs occurred accidentally. Some of this glafs, in 

 powder, having been introduced into a muffle at the tempe- 

 rature of about 20* of Wedgwood > the powder, in the lpace 

 of about a minute, entered into a ftate of vifcid agglutination, 

 like that of honey, and in about a minute more, (the heat ak 

 ways continuing unchanged,) confolidated into a firm and com- 

 pact mafs of Reaumur's porcelain *. It now appeared, that by 

 placing this fubflance immediately behind the borax, the 

 penetrating quality of this laft might be effectually reftrained ; 

 for, Reaumur's porcelain has the double advantage of being 

 refractory, and of not cracking by .change of temperature. I 

 found, however, that in the act of confolidation, the pounded 

 bottle-glafs fhrunk, fb as to leave an opening between its mafs 

 and the tube, through which the borax, and, along with it, the 

 carbonic acid, was found to efcape. But the object in view was 

 obtained by means of a mixture of pounded bottle-glafs, and 

 pounded flint, in equal parts. This compound (till agglutinates, 

 not indeed into a mafs fo hard as Reaumur's porcelain, but fuf- 

 ficiently fo for the purpofe ', and this being done without any 

 fenfible contraction, an effectual barrier was oppofed to the bo- 

 rax -, (this arrangement is fhewn in fig. n.) ; and thus the me- 

 thod of doling the tubes was rendered fo complete, as feldom 

 to fail in practice f. A ftill further refinement upon this me- 



M 2 thod 



* In the fame temperature, a mafs of the glafs of equal hulk would undergo 

 the fame change ; but it would occupy an hour. 



f A fubflance equally efficacious in retraining the penetrating quality of borax, 

 was difcovered by another accident. It corrhfts of a mixture of borax and com- 

 mon fand, by which a fubftance is formed, which, in heat, affumes the ftate of a 

 very tough parte, and becomes hard and compact on cooling. 



