Prof. J. Joly on the Apopltorometer. 303 



may actually weigh more than the original sample of the 

 substance. 



Certain substances may alloy with the platinum and, o wing- 

 to the extreme thinness of these wdde ribbons, cause it to 

 fuse. These may be dealt with either on heavier platinum 

 ribbon or on carbon. Moulded strips of carbon would, 

 doubtless, be obtainable. In point of temperature-range 

 •carbon has also advantages, but this is of minor importance, 

 for there are few sublimates not obtainable by the use of 

 platinum. It should be remembered that ordinary carbon 

 may contain volatile impurities. If we desire to deal with 

 very high temperatures, the watch-glasses should be ot' 

 transparent vitreous silica. 



I will now quote a few recent results as illustrating the 

 uses of the apophorometer. 



Clausthalite. Pb Se. Pb 72*4; Se 27*6. Weight taken 

 21'5 mgrms. 



(1) The substance fused at a very low red heat, and a 

 brick-red sublimate collected (Se). Weight of sublimate 

 6"2 m or ins. 



(2) The residue on the ribbon presented the appearance of 

 litharge, A reheating at former temperature gave no 

 further sublimate. But when the temperature was brought 

 to a full red a copious white sublimate was formed. Weight 

 12*1 mgrms. 



Some litharge still adhering to the ribbon, this was 

 ■weighed and found to weigh G'6 mgrms. 



Taking the sublimate as PbO and the residue as approx- 

 imating to the same composition, we have Pb = 17*6 and 

 Se = 6*2. On the formula the weights should be Pb = 15*6 ; 

 Se = 5'9. This was the first gravimetric experiment on 

 sublimates which I made. 



Proustite. Ag 3 AsS 3 . Ag 65*4 ; As 15*2 ; S 19*4. Weight 

 taken 11*3 mgrms. 



(1) At a temperature below visible red a rapidly formed 

 white sublimate collected (As 4 O c ). Weight 2*1 mgrms. 



(2) No further sublimate was obtained at temperature 

 of (1). The residue was a blackish slag suggesting Ag 2 S. 

 Eaised to a dull red the residue slowly whitened and took on 

 a metallic lustre (Ag). A very small trace of whitish sub- 

 limate also appeared. On weighing the ribbon the silver 

 ■was found to amount to 8*3 mgrms. 



Taking the white sublimate as As 4 6 we have As = 1'5. 

 Also Ag=8*3. By difference 1'5 mgrms. of S have passed 



