261 



enoi-monsly viscous, enclosed air-bubbles are liardly squeezed out, 

 but will rather expand in the mass itself', while the surface of" the 

 liquid can change its height only with extreme slowness. In repeating 

 successively ihe melling and solidifying of the substance a number of 

 times, the deformation-effect will be gradually increased to such an extent 

 that, as fig. 10, N". 2 shows clearly, at last the crucible bursts. The 

 gradual lowering of the liquid surface in successive experiments 

 can be seen in (hose crucibles ; in such a manner it often happens, 

 that with a strong deformation of the platinum vessels, when Ihey 

 finally look like inflated balloons, the junction of the thermoelement 

 e4nerges at last out of the surface of the liquid mass, so that the heat- 

 effects on the heating-curves get gradually worse and will finally 

 disappear totally. 



§ 14. To control the found meltingpoints, we have made a series 

 of experiments to determine it once more (with the kunzite of 

 Madagascar) by means of the quenching-method, which is to be de- 

 scribed afterwards in connection with our experiments for fixing the 

 temperature of beginning transformation. The quenching-system was 

 first calibrated by means of meltingpoint-determinations, made by 

 this statical method with lithiummetasilicate (1201°) and diopside 

 (1391°); the corrections to be applied to the measured temperatures 

 appeared however to be practically zero. 



We found in successive experiments : 



Kunzite, heated during half an hour all 4(500 M.V.and quenched in mercury 



n , , , 14720 M.V. „ , „ , 



, . . . . . „14700M.V. „ , „ , 



, . n „ 14750 M.V. „ „ „ „ 



n , , ,14680M.V. „ „ „ , 



AllcryslaJlizeil- 



All glass. 



All glass. 



All glass. 



Glass and 



crystals. 

 , „ n „ 14660 M.V.„ „ , , : All crystallized 



, . n , 14690 M.V. ,, , „ , :A11 glass. 



Thus, the meltingpoint was found to be 1428'' C. (G. Th.), ipiite 

 in accordance with the direct meltingpointdeterminations after the 

 dynamical method. In these experiments we once obtained a product 

 after longer heating on 14600 M.V., — just somewhat below the melting- 

 point, — consisting of somewhat larger individuals. They appeared to 

 be large, homogeneously exliuguishiug plates, whose bii-efringencc 

 was about 0,007, and with refractive indices of 1,513 and 1,519, 

 like those of the ^-spodumene, obtained from artificial spodumene after 

 melting and cooling. In convergent polarized light the same inter- 

 ference-image as in the former case, was observed : there can thus 



18 

 Proceedings Royal Acad. Amsterdam. Vol. XVII, 



