364 CALIFORNIA ACADEMY OF SCIENCES. 



Dr. Bodewig found by analysis = A; and calculated from the 

 formula) Ca 2 B 6 O n + 5H 3 U = B. 



A B 



Boracic acid 49.70 50.91 



Lime 27.42 27.22 



Water 22.26 21.87 



99.38 100.00 



His results confirm consequently those already published by 

 Mr. Evans. 



Vom Rath's optical investigation found the plane of the optical 

 axes to be normal to the plane of symmetry, making an angle of 

 27° 35' with the edge c : m, and an angle of 82° 42', for Na- 

 yellow, with the vertical axis c, lying in the obtuse angle of the 

 morphological axes. [The writer found this angle to be 83° 25', 

 with ordinary light. Mining and Scientific Press, 1. c] 



Through cleavage lamellae parallel to m, one can apparently 

 observe optical axes in oil. The angle is too great, however, to 

 permit its determination in fatty oil. In cassia-oil the value of 

 the obtuse angle of the optical axes was found. 



2 Ho 122 ; 45' for Na-yeliow. 



The acute angle of the axes measured on a plate cut exactly at 

 right angles to the bisectrix, was found — 



21a = 54° 48' Na-yellow in cassia-oil. 

 2 U = 95° 15' " 

 whence 2 Va = 55° 20' " 



The middle index of refraction = 1.5910. Dispersion p ^> ,3. 

 Bisectrix positive. The dispersion of the axes is small, so that 

 nearly the same values are obtained for red as for yellow. 



In Appendix II, p. 33, Bull. Cal. Acad, of Sci., No. 2, I referred 

 to a geode containing crystals that had commenced to undergo 

 change, being converted in spots into a soft, dull, white substance 

 which fully preserved, however, the form of the crystal. This 

 substance was kindly examined for me in the Chemical Labora- 



