267 



Similar experinienls witli the kuiizite of Rincoii taught ns, that this 

 temperature is situated soiiiewliat liiglier, at about 995° C. ; in all 

 these cases however, only veij long eontimied healing can lead to a 

 complete transformation of the a-, into the /Mbrni. It is therefore 

 quite evident, that at ordinary temperatures, and even at 400° or 

 500° C, the transformation-velocit}' of ((-, into ,i-forni must be 

 practically equal to zero; thus the «- and ji-spodumenes can be in 

 immediate contact with each other, during an undeteruiined long 

 time, without transformation taking place. 



The transition of «-, into /?-form is accompanied by an enormous 

 increase of specitic volume: it is augmented from 0.31 to 0.41, 

 being about 337o of the original value. It often occurred that the 

 heated and transformed powder had risen over the boi'ders of the 

 platinum ci'ucibles. In the described qnenching-experiments, the trans- 

 formation could often be stated already, when the used platinum folium 

 had not yet been opened : it seemed to be inflated by the increase 

 of volume of the enclosed preparation. Microscopically it is observed 

 that the larger crystals of the «-form, in this transformation primarily 

 get innumerable cracks and fissures; afterwards they change into 

 opaque, no longer normally extinguishing aggregations of fine, felty, 

 or even broader needles, whose extinction is ahnost normally orientated 

 on their longer direction; ihey can be recognized by their weak 

 birefringence, as well as by their low mean refractive index: 1,519. 

 The microphotographs fig. 7 and 9 may give some impression of 

 the aspect of the two modifications between crossed nicols. 



§ 18. It may be expected, that the mentioned transformation- 

 velocity will possibly be affected by some catalysers or by some 

 fiuxes in such a way, that it will show a discernible value already 

 at considerably lower temperatures. 



Indeed we succeeded in proving, that on heating spodumene-glass 

 with molten sodiumtungstate^) at temperatures between 850° and 

 920° C, after 32 hours a partial crystallization has begun, which 

 however was complete only after 65 hours of heating. The crystal- 

 mass had a refractive index of 1,523, and appeared to be no other 

 thiiKj than /3-spodumene ; the determined specific weight was at 25° C: 

 dio = 2,579. 



^\ The great difference between the specitic gravities of the silicate and the 

 molten tungstate, makes it necessary to use a platinum stirrer, to bring the silicate 

 from the surface into the molten mass again and again This stirrer was moved 

 by means of a suitable electromotor-driven mechanism. 



