MODIFIED by COMPRESSION. OI 
therefore found neceflary to oppofe fomething more fubftan- 
tial and compact, to the thin and penetrating quality of pure 
borax. 
In fearching for fome fuch fubftance, 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 Wepcwoop ; the powder, in the {pace 
of about a minute, entered into a ftate of vifcid agglutination, 
like that of honey, and in about a minute more, (the heat al-’ 
ways continuing unchanged,) confolidated into a firm and com- 
pact mafs of Reaumur’s porcelain*. It now appeared, that by 
placing this fubftance 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, fo 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 ftill 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 
{enfible contraétion, an effectual barrier was oppofed to the bo- 
rax; (this arrangement is fhewn in fig. 11.) ; and thus the me- 
thod of clofing the tubes was rendered fo complete, as feldom 
to fail in practice t. A ftill further refinement upon this me- 
M2 : thod 
* In the fame temperature, a mafs of the glafs of equal bulk would undergo 
the fame change; but it would occupy an hour. 
+ A fubftance equally efficacious in reftraining the penetrating quality of borax, 
» was difcovered by another accident. It confifts.of a mixture of borax and com- 
mon fand, by which a fubftance is formed, which, in heat, aflumes the ftate of a 
very tough pafte, and becomes hard and compact on cooling. 
; 
