Effects of Heat modified by Compression. IQh 



sary to oppose something more substantial and compact, to 

 the thin and penetrating quahty of pure borax. 



In searching for some such substance, a curious property 

 of bottle-glass occurred accidentally. Some of this glass, 

 in jiowder, having been introduced into a muffle at the tem- 

 perature of about 20° of Wedgewood ; the powder, in the 

 space of about a minute, entered into a state of viscid agglu- 

 tination, like that of honey, and in about a minute more 

 (the heat always continuing unchanged) consolidated into a 

 firm and compact mass of Reaumur's porcelain*. It now 

 appeared, that by placing this substance immediately behind 

 the borax, the penetrating quality of this last might be ef- 

 fectually restrained; for Reaunuu's porcelain has the double 

 advantage of being refractory, and of not cracking bv change 

 of temperature. I found, however, that in the act of con- 

 solidation, the pounded bottle-glass shrunk, so as to leave 

 an opening between its mass and the tube, through which 

 the borax, and along with it the carbonic acid, was found 

 to escape. But the object in view was obtained by means 

 of a mixture of pounded bottle-glass and pounded flint, in 

 equal parts. This compound still agglutinates, not indeed 

 into a mass so hard as Reaumur's porcelain, but sufficiently 

 so for the purpose ; and this being done without any sen- 

 •sible contraction, an effectual barrier was opposed to the 

 borax; (this arrangement is shown in fig. 1].;) and thus 

 the method of closing the tubes was rendered so complete, 

 as seldom to fail in practice f. A still further refinement 

 upon this method was found to be of advantage. A second 

 series of powders, like that already described, was introduced 

 towards the muzzle, as shown in fig. 12. During the first 

 period of the experin)ent, this last-mentioned series was ex- 

 posed to heat, with all the outward half of the tube {ah); 



• lu the same temperature a mass of the glass of equal bulk would undergo 

 the same change; but it would occupy an hour. 



f A substance equally isflicacious in restraining- the penetrating quality of 

 borax, was discovered by another accident. It consists of a mixture of borax 

 and common sand, by which a substance is formed, which, in heat, assumes 

 thf state of a very tough paste, and becomes hard aud compact en cooling. 



N 2 by 



