6 L. H. Borgström. (LVII 



To test the degree of accuracy of the determinations of 

 the temperatures and meltiiigpoints attained by theoutlined 

 method some determinations of known substances were made 

 in the same way as the experiments proper. Three deter- 

 minations of the boilingpoint of mercury gave 356°, 358° 

 and 360° (356,9). The boilingpoint of sulphur was found 

 to be 442° and 444° (444,5°), the meltingpoint of NaCl 

 to 802° and 804° (801°) and the meltingpoint of Na^CO^ to 

 841° and 844°. A determination on 15 g of this last substance 

 by the thermic method resulted in an agreeing value, of 846°. 

 These numbers show that the used method can give satis- 

 factory results. 



Different minerals may on heating in a capillary exhibit 

 other remarkable characteristics than the fusibility. Not a 

 few let off water, sulphur, arsenic or other more or less 

 volatile matter. Sometimes there appear sudden changes 

 in colour or it happens that the mineral shows decrepitation, 

 phosphorescence or some other phenomenon. In general there 

 may occur any of the multitude of possibilities, which are 

 mentioned in the mineralogical textbooks under the head, 

 »behaviour by heating in closed tube». A decided progress 

 compared with the older procedure is, that the temperatures, 

 at which the different manifestations set in, are recorded. 



The method here described is especially suitable for the 

 investigation of the sulphides etc. of the metalloids. The 

 meltingpoints of these are mostly so low, that no dazzling 

 light is evolved and the meltingprocess accordingly can be 

 seen and followed. These materials do not corrode the glass 

 of the capillary, not even at high temperatures. 



Realgar AsS. If heated in a capillary or in the closed 

 tube the realgar darkens and fuses at 310° without any 

 preceding stage of sintering to a rather fluid, dark cherry-red 

 liquid. At about 500° a feeble destillate appears and grows 

 slowly stronger until the boilingpoint is reached at 589°. — 

 The meltingpoint of realgar from Felsöbanya was determined 

 at 307°. A sample from Kapnik gave 312° and r. from Mol- 

 dova 314°. Several determinations of the boilingpoint of 

 material from Felsöbanya, which differed only by 4° — 8° 



