WATER OF CRYSTALLIZATION. 



21 



Curve c shows the metallic reflection band found by Aschkinass, 1 

 and it will be noticed that the position of the maximum as found by 

 him at 8.69 /t is shifted from that indicated by the present transmission 

 curves. The same lack of coincidence of the maximum of the reflection 

 band with the minimum in the transmission curve will be found in 

 calcite and in mica. This is the first attempt to explore the region of 

 transmission near a reflection band and the explanation to be offered 

 later on for the discrepancy may not hold when more data have been 

 accumulated. 



QUARTZ (SiO 2 ) ; OPAL (SiO a +xH 2 O). 



(Quartz: Cut perpendicular to axis; / = 1.30 mm. Opal: Massive, transparent; 



t = 0.12 mm. Fig. 5.) 



'00% 



3456 



FIG. 5. Opal (b) ; Quartz. 



The specimen of quartz examined was made for polariscopic work 

 and was perfectly clear. Its transmission curve (a, fig. 5) shows small 

 bands at 2.9 /x and 4.35 p. Curve c, which shows a series of bands at 



1 Aschkinass : Ann. der Phys. (4) , i, p. 42, 1900. 



