Gaylussite and Hanksite from California. 129 



With a prism of 56° 41^, whose faces were approximately 

 parallel to 110 and 110, the vahies of /3 and 7 for red, Li; 

 yellow, Na ; and green, Tl, were also obtained. 



Red 1-5056 1-5710 



Yellow 1-5084 1-5747 



Green 1-5115 1*5789 



The value of ^ for yellow is probably not as accurate as that 

 obtained by means of total reflection. 



The divergence of the optical axes, 2E, was measured on a 

 plate parallel to 010. The values that were obtained are as 

 follows : 



Red, Li. Yellow, Na. Green. Tl. 



2E at 25°C. = 47°45' 48°14' 48°22' 



Hence 2V = 31°llV 31°26' 31°27' 



The value of Y^.y is 16° 43' and agrees favorably with the 

 value 16° 24^ obtained by calculation from the three indices of 

 refraction. 



It was observed that the angle 2 E varied somewhat, and to 

 determine to what extent this was dependent upon the tem- 

 perature the following measurements were made : 

 Temperature 20°O. 30° 40° 50° 60'' 70° 90° 



2Ej. = 48°16' 48^10' 48°4' 47°55' 47°50 47*'45 47°38' 



Chemical comjposition. — Suitable material for analysis was 

 readily obtained and the results are as follows : 



Found. Average. Ratio. 



. I II 



CO, .... 36-23 35-91 36-07 -819 = 2-00 



CaO 23-28 23-48 23-38 -417 = 1-02 



Na^O 25-69 25-71 25-70 -414) .,^ _ . ^„ 



K.O -17 -13 -15 -002 [^^^ - -^'^^ 



H^O -_ 14-74 14-73 14-78 -818 = 2-00 



Al^OgCtc. .. -13 -13 



SiO, -36 -22 -29 



100-45 

 The ratio for CO, : CaO : Na,0 : H,0 is very close to 

 2:1:1:2, which gives the formula CaC03.^XC03.2H,0. 

 The theoretical composition is given below, together with the 

 analysis, after deducting impurities, substituting for K2O its 

 equivalent of J^a^O and recalculating to 100 per cent. 



Calculated for. 

 Found. CaCO3.Na2CO3.2H2O. 



CO, 36-08 36-36 



CaO 23-39 23-14 



Na,0 25-80 25-62 



H,0 . ]4-73 14-88 



100-00 100-00 



