AN:o24) The melting- and boilingpoints of metalloidsulphides. 7 



from one another, resulted in the above stated meaii value. 

 — In his investigation of the system sulphur-arsenic J o n- 

 k e r ^) has found the meltingpoint of AsS to be 320° and 

 also determined the boilingpoint of AsS containing dissolved 

 As of 534°. 



Aiiripigment, As^S^. Pulverized auripigment is of a light 

 brownish yellow colour. On heating it darkens by degrees 

 and obtains a reddish tint. If the meltingpoint is not passed 

 the powder will very nearly recover its original colour on 

 cooling, a heated auripigment is always a shade browner 

 than the fresh material. If the temperature is raised to 320°, 

 feeble sintering is perceptible and the grains of the sample 

 stick a little together, but even a continued heating at a 

 temperature only a few degrees lower fails to have any 

 effect. At 320° the mineralpowder darkens manifestly and 

 at 325° it is completely fluid, though viscous, and of a red- 

 dish black colour. Af ter cooling from this temperature the 

 colour of the material becomes a clear brownish red, and the 

 mineral stays amorphous, which easily can be stated under 

 the microscope. The boiling sets in at 690° and before this 

 temperature, only an insignificant destillate gathers in the 

 capillary above the surface of the bath. — Auripigment from 

 Felsöbanya gave the meltingpoint between 325° and 330°, 

 a. from Osorzan, Mutsu, Japan 324°. The above mentioned 

 boilingpoint belongs to material from Felsöbanya. — As 

 early as 1889 C u s a c k 2) has investigated the fusibility of 

 the mineral and fixed the meltingpoint at 325°. Låter 

 J o n k e r (1. c.) found 310° by the thermic method. It may 

 be possible that the thermic method gives uncertain results 

 for a mineral which only slowly changes state especially if 

 the heatingcurve has to be used and not the cooling curve, 

 as is the case with this mineral. — Experiments, at which 

 two capillaries, one containing realgar and the other auri- 

 pigment, were heated at the same time side by side, showed 

 that realgar has a decidedly lower meltingpoint than auri- 



'j Zeitschr. anorg. Cli. 62. 89. (1909). 

 ') N. Jb. f. Min. etc. 1889. I. 196. 



