Properties of the Feldspars. 101 



as indicated in fig. 1, the heating current properly regulated 

 and observations of the temperature made at intervals of one 

 minute, while the glass softened and passed gradually over into 

 a thin liquid (800°). Then the current was reduced and the 

 cooling curve observed in the same way. These observations 

 gave an unbroken curve both for the heating and cooling, as 

 in the case of all the glasses,* without a definite melting or 



Fig. 2. 



solidifying point, although the arrangements for detecting an 

 absorption or release of heat were very sensitive. Prodding 

 at intervals with a platinum rod showed the change to be per- 

 fectly gradual from a clear, hard cake through all degrees of 

 viscosity to a fairly thin liquid and back again. This observa- 

 tion is of considerable interest as showing that the absence of 

 bounding phenomena between the cold glass which fulfils the 

 mechanical conditions for a solid very perfectly, and the liquid, 

 is not confined to mixtures of complicated chemical composi- 

 tion, but is exhibited also by true chemical compounds of 

 undoubted purity. It is therefore not conditioned by compo- 

 sition but by the physical nature of the substance. Having 

 verified this behavior of anhydrous borax by several repetitions 

 of the experiment, various disturbing influences were applied 

 to the slowly cooling liquid in the hope that some temperature 



* See Tammann, loc. cit., also Roozeboom "Die heterogenen Gleich- 

 gewichte, etc." Braunschweig, 1901. 



