Öfversigl af Finska Vctcnskaps-Societetens Förliandliimar. 

 Bd. F.VII. 1914—191.'). Afd. A. N:o 24. 



The melting- and boilingpoints of metalloidsul- 

 phide-, selenide-and- tellurideminerals. 



By 



L. H. Borgström. 



The mcltingpoints of the silicates have in recent years 

 been zealously studied and not a few meltingpoints of mi- 

 nerals belonging to other groups are known. Tlie majority 

 of the determinations are performed according to the thermic 

 method viz. the coolingcurves or the heatingcurves of the 

 substances are construeted and tlie meltingpoints or inver- 

 sionpoints found as more or less pronounced bends in these 

 curves. The method gives very accurate and reliable results, 

 but requires a large quantity of pure and homogeneous 

 material; preferably 10 to 20 g and at least 2 to 3 g. The 

 method is on that account applicable only in the case of 

 a comparatively large quantity of the mineral being available. 

 Beside the thermic method certain optic methods have been 

 used. According to the latter methods the sample is exposed 

 to a slowly increasing temperature and carefully scrutinized 

 the while with a microscope or with the eye alone. The 

 optic method, especially if a microscope is used, renders 

 possible the determination of the meltingpoint of a single 

 little mineralsplinter weighing only a few milligrams, While 

 on the other hand against the method it is said, that it 

 usually does not warrant an exact estimation of the temper- 



