210 



Allen, Crenshaw, Johnston, and Larsen- 



E 



To 



Fig. 14. 



furnace. 



Vacuum 



cementing in a small 

 glass plug, because 

 the former invariably 

 leaked through the 

 closed end. A small 

 hole is drilled through 

 this tube at 0, so that 

 all the air in the appa- 

 ratus may be removed by the pump. The 

 crucible of unglazed porcelain has a capacity 

 of 15 g. of pyrrhotite. It rests on a ring of 

 refractory clay, and is heated as usual by a 

 resistance furnace after the apparatus has 

 been exhausted by the oil pump. 



Repeated determinations of the melting 

 temperature of ferrous sulphide under these 

 conditions, showed in general that each suc- 

 cessive determination was a few degrees 

 lower than the one which preceded it, and 

 analyses of the products as well as determi- 

 nations of their density showed that they 

 contained less sulphur than ferrous sulphide. 

 The following data make it evident that 

 ferrous sulphide slowly dissociates into 

 sulphur and iron, in the vicinity of its melt- 

 ing point, and that the successively lower 

 melting temperatures obtained are caused 

 by the gradual accumulation of free iron in 

 the melt. About 15 g. of a sulphide previ- 

 ously melted in the vacuum furnace, and 

 shown to contain less sulphur than ferrous 

 sulphide, was introduced again into the vac- 

 uum apparatus, which was then completely 

 exhausted by the pump. The pump was 

 then stopped and the heating was begun. 

 At about the melting temperature the pres- 

 sure had increased to 9*5 mm . The product 

 was now melted and frozen several times, 

 and then the apparatus was cooled to room 

 temperature. Next morning the manometer 

 read 8 mm , showing that the pressure was not 

 due to a leakage but doubtless to the evolu- 

 tion of gases occluded by the crucible and 

 by the glaze of the porcelain.* When the 

 crucible was removed from the vacuum tube 



* For data on this point, see Holborn and Day, On 

 the Gas Thermometer at High Temperatures, this 

 Journal (4), viii, 178, 185, 1899 ; Guichard, The Gases 

 Disengaged from the Walls of Tubes of Glass, Porce- 

 lain, and Silica, C. R., clii, 876, 1911. 



