492 



Wright: change in angles of quartz 



It is of interest to note the similarity in shape between the curves 

 representing the changes in other properties of quartz.^ These 

 are Hsted in Table 4 and are represented graphically in figure 2 

 after reduction to a common unit. From these curves it is evi- 

 dent that whatever it is that produces the changes in quartz 'as the 

 inversion point is approached, the relative changes produced bear 

 practically linear relations to one another. This applies to crystal 

 angles, total expansion, specific volume, birefringence and circular 

 polarization. The curves representing refractive indices as de- 

 termined by Rinne and Kolb^ are, however, somewhat different in 

 shape. No satisfactory explanation of this divergence has yet 

 been found. A redetermination of the refractive indices of quartz 

 at various temperatures is being undertaken in this Laboratory. 



TABLE 4 



In order to form an idea of the energy relations involved I ob- 

 tained from Dr. White of this Laboratory the values of his deter- 



*The equations which represent the changes in the different properties of 

 quartz with temperature are: 



Birefringence, y = 0.00910 - |o.ll5735i - 0.171195 (ei^o _ i) I lO'^ 



Specific volume y = 0.3772 + |o.l54944i + 0.202369 (eToo _ i) j lO"* 



Total expansion, in cal- \ ^ ^ ^ + /o.090812i + 0.0961713 (.tItt _ {)\ io-4 



^ . t ./ • 



y= 0.0061302( + 0.0200392 (e'""-l). 



/ 



ones per gram, 



Excess spec, heat, per de- 

 gree 



The constants in these equations were obtained by the least square method 



from the data of observation. 



6 Neues Jahrbuch fur Mineralogie, 2 : 138-158. 1910. 



