52 H. L. Wells and S. L. Penfield — Gerhardtite, etc. 



forms x and v with improbable indices would have been re- 

 garded as accidental had they not occurred repeatedly giving 

 very distinct reflections. Tabular fragments, parallel to the 

 basal cleavage, show under the polarizing microscope an ex- 

 tinction parallel to the macro-diagonal cleavage lines and in 

 convergent light a bisectrix normal to c, 001. The optic axes lie 

 in the brachypinacoid, the axial angle is large and could not be 

 measured in air. Measured in the heavy solution of Hgl a in 

 KI (?i=l-703 for yellow, 1-722 for green). 



2H = 76° 20' for yellow. 

 2H = 80° 4' for green. 

 Dispersion p<^v. 



A very thin section had to be used to obtain the character of 

 the dispersion as moderately thick sections were practically 

 opaque to yellow light. The indices of refraction could not be 

 determined owing to the want of suitable material, the Kohl- 

 rausch total-reflectometer giving no total reflection. 



Double-refraction is strong, negative. 



Pleochroism is distinct: 



For vibrations parallel to c, & blue. 

 " « " " 6,- ft green. 



" " " " a, c green. 



Chemical composition. — Qualitative examination showed only 

 the presence of CuO, N 2 5 and H 2 0. 



I. -3975|gram yielded -0457 H a O and -2634 CuO. 

 II. -3986 gram yielded -0449 H 2 0, -2646 CuO, and 19-7 cc. dry N 

 at 12-8° and 759 mm. (cor.). 



Found. Calculated for 



I. II. 4CuO . N 2 6 . 3H 2 0. 



H 2 11-49 11-26 11-56 



CuO 66-26 66-38 66'22 



NO. 22-25* 22-76 22-52 



100-00 100-40 100-00 



Pyrognostics, &c. B.B. fuses at 2, coloring the flame green. 

 With soda on coal easily reduced to metallic coprJer with de- 

 flagration. In closed tube gives nitrous fumes and water which 

 reacts strongly acid. Soluble in dilute acids, insoluble in 

 water. 



It is somewhat surprising that a mineral of this composition 

 has not been found before, owing to the occurrence of nitrates in 

 natural waters, the stability and insolubility of the compound 

 and the ease with which it is made artificially. 



* By difference. 



