486 WRIGHT: CHANGE IN ANGLES OF QUARTZ 



physical systems has led to results of the greatest interest. In 

 crystallography the relations between the differential changes in 

 the crystallographic properties and the attendant differential 

 changes in the optical and other constants should lead to differ- 

 ential equations which on integration would state the relations 

 between the two systems of forces (crystallographic and physical) 

 and thus give us information on the character and order of mag- 

 nitude of the crystallographic forces themselves. It is essential in 

 this connection to measure not only the changes in the crystal- 

 lographical and optical constants with temperature and pressure 

 but also the specific heats at the different temperatures (energy 

 changes) . The measurement of these properties on a few selected 

 minerals is now being carried out at this Laboratory. In the 

 present preliminary paper the results of the measurements of 

 the changes in the crystal angles of quartz with temperature are 

 presented briefly. 



Method and apparatus. The quartz crystals were measured on 

 the thermal two-circled goniometer described recently in this 

 journal.^ With this goniometer "the position of the normal to 

 each crystal face in space was fixed by two angles (angular polar 

 distance and azimuth angle) for each measured temperature. The 

 crystal was mounted in platinum jaws and securely fastened. No 

 effort was made to adjust the crystal accurately because it was 

 evident that any mechanical device consisting of different mate- 

 rials would not remain fixed in position over a temperature range 

 of 1200°. The entire crystal was first measured at room temper- 

 ature and then the furnace heated to a definite temperature, and 

 held there 5 or 10 minutes; at this temperature the entire crystal 

 was remeasured, the temperature being held constant during the 

 measurement and the angular values on several of the faces re- 

 peated to insure constancy of position of the crystal during the 

 readings. This procedure was repeated at each temperature of 

 measurement up to 1250°. By this method adjustment troubles 

 are eliminated and the measurement of the entii-e crystal is com- 

 plete for each temperature and independent of previous adjust- 

 ment and of any slight shifts in position which may have occurred. 



1 Journ. Wash. Acad. Sci., 3: 396-401. 1913. 



