Experiments refpeSling Heat. 27 



IX. Three more, weighing |~ ths of a carat, heated for 

 4' 26", became agglutinated together, but were found to 

 have loft none of their weight. Being heated a fecond time 

 for 4' 30", they melted into a globule, which broke in cool- 

 ing. The principal portion is roundifh, and the fufion has 

 evidently been complete : it has a browni(h appearance on 

 the fufed furface, but is clearer in the fracture ; the whole 

 being fomewhat like a piece of dirty camphor. The weight 

 is a little increafed. 



X. A topaz, weighing ?-^ths of a carat, after being ex- 

 pofed to the heat for 4' 33", was found to have loft -„ 3 T ths. 

 It had, like the laft, loft its colour, but ftill partly retains its 

 original figure. One fmall furface was afterwards tried on 

 the lapidary's wheel, and found to be as hard as before. 



Brazilian Topaz. 



XI. A Brazilian topaz, weighing J*ths of a carat, after 

 being in the heat for 3' 26', came out *'ths. It was per- 

 fectly fufed, and had become of an opake white, like a fufed 

 fait; fuch, for example, as fal prunelUv. 



Oriental Rubies. 



XII. One weighing £|ths of a carat, heated for 2 '9", 

 feetns flightly and fuperficially fufed : it is cracked, but the 

 pieces have nqt feparated. The weight and colour are the 

 fame as before. It is well known that rubies, when expofed 

 to a common lamp and blow-pipe, become colourlefs, but 

 recover their colour fuddenlv and initantlv on cooling, when 

 a little below a red heat. This ruby, after its expofure to the 

 iutenfe heat excited by the dccompofition of the oxygen gas, 

 returned its colour as it would have done if it had been ex- 

 pofed to a lower heat. 



XIII. Five rubies, weighing together half a carat, were 

 expofed to the heat for 4' without lofing any weight. The 

 whole became agglutinated into a (liapelefs mafs, in which 

 the remains of the original ftones now appear interfperfed in 

 a white vitreous cement. The colour of the fmaller ftones 

 was changed whitifh, but one larger portion wa6 but little 

 altered in this refpeft. 



E z XIV. 



