AN:o24) The niellin^- and boilingpoints of metalloidsulphides. 3 



material lor some Lime at a temperature just below the 

 approximately kiiown meltiiigpoint and another sample at a 

 temperature above this point. The heated substauces have 

 beeu rapidly cooled and afterwards examined, usually in 

 thin sectious under the microscope. The new variant of the 

 methcd has in such respects advantage över the older one, 

 in that a verv long time is necessary for a larger quantity to 

 reach a uniform temperature (especially if the material is 

 a bad conductor of heat) while only a few seconds are 

 needed for the tiny quantity in the capillary to assume the 

 temperature of the bath, which can be regulated at will. 



The heating of a mineralsample in a capillary is practi- 

 eable even if the mineral may not be exposed to the air 

 during the heating, as for instance at the determination of 

 the meltingpoints of oxidizable metals, sulphides and ferro- 

 compounds. The circulation of the gases in a capillary are 

 so slow that no great quantity of oxygen will reach the sample 

 from without or from the upper part of the capillary during 

 the trial (of at most 5 minutes). The amount of oxygen pre- 

 sent in the lower part of the tube can again easily be calcula- 

 ted. The air in a tube 2 cm in length and 1 mm in diameter 

 contains only 0,oo5 mg oxygen. If the diameter is 2 or 3 

 millimeter, the corresponding values are 0, 02 and 0,o4 mg 

 oxygen. The quantity of oxygen, which is contained in the 

 capillary is thus evidently negligeable at room temperature, 

 at higher temperatures (500^ — 1,000°) it is several times 

 smaller still. 



As receptacles for the baths, only platinum and porcelain- 

 vessels have been tried. The latter crack usually if the 

 bath is allowed to solidif}" in them. The nitrate mixture is 

 an exception in this respect and can without danger be 

 repeatedly fused and solidified in a porcelain crucible. 



The gaslamp, Bunsenlamp, Mékerburner or blastlamp are 

 the most convenient for heating up to 1,000° as they allowof 

 a more rapid regulation than the electric heating. The 

 electric platinum wire furnace or the Friedrich-furnace with 

 cryptolfilling seems to render comparatively good services 

 at higher temperatures. 



