%6 Experiments reffeHing Heat. 



at the end of one minute. The fragments were then fub- 

 jecled to the heat excited by a ftream of oxygen gas thrown 

 upon the charcoal for 2 6". Two of the pieces became co- 

 lourlefs and have fome refemblance to alum ; the third re- 

 tains, in fome meafure, its original colour. Their prefcnt 

 weight is £|ths of a carat. They have all of them loft a 

 confiderable portion of their tranfparcncy, but have a rough 

 polith, and retain their facets. 



VI. Another fapphire, in the form of a parallelopipedon, 

 weighing f^ths of a carat, being expofed to the ftrong heat 

 for 2' 53", had its angles rounded off, fo that it became re- 

 duced to the form of a tamarind-ftone, and loft its tranf- 

 parcncy. It is now a femi-lranfparent whitifti mafs, but 

 ftill retaining fome traces of its original colour. It is in part 

 covered and interfperfed with a kind of brown fcorix very 

 like copper bronze. The weight is the fame as at firft. 



VII. Seven fapphires, weighing together £|-ths of a carat, 

 heated for 9/ 55'', loft no weight, but became agglutinated 

 together} the fufed coat in which they are enveloped having 

 the appearance of a whitifh femi-tranfparent vitreous cement, 

 through which the remainder of the ftones are feen ftill re- 

 taining fomewhat of their colour. One portion or face of 

 the mafs, containing two of them joined as already men- 

 tioned, was afterwards fubjefted to the lapidary's wheel: it 

 took a good polifh, and proved as hard as at firft. The ap- 

 pearance of the different parts of the polifhed face, is the* 

 fame as that of other fimilar parts of the mafs. 



Oriental Topazes. 



VIII. A topaz, weighing |4ths of a carat, was expofed 

 for %' 19 ' to a heat excited by oxygen gas, thrown upon the 

 charcoal on which it lay» in two ftreams, by means of a 

 double blow-pipe of a new conftru&ion, ftiggefted and exe- 

 cuted by Mr. Varley, and which will be defcribed, along 

 with the other parts of the apparatus, in its proper place. 

 The ftone entirely loft its colour, and now refembles a piece 

 of borax. The fuiion, if there was any, was extremely fupcrfi • 

 cial, being only juft fufheient to deftroy the polifti, the form 

 and facets ftill remaining, with the angles a little obtunded. 

 Its weight is the fame as at firft. 



IX, 



