344 Mr. W. J. Sell and Prof. W. J. Lewis. [Feb. 14, 



The angles of the prism varied considerably, the range being 

 between 60 28' and 59 19'. 



Calculated. Observed. 



ao 90 6 90 6 



ar 90 90 6 



ro 42 47 42 47 



oe 25 3 



ar 53 58 53 53 



rr! 72 4 72 7J 



The crystals seem to have no cleavage. 



Nitrate of Chromium Urea. 



The crystals are of a dark-green colour, and are only translucent in 

 moderately thin plates. They belong to the oblique system, and have 

 a very perfect and facile cleavage, perpendicular to the plane of 

 symmetry. This cleavage plane, though absent, or at any rate very 

 infrequent, as a natural plane, has been selected as the base. The 

 planes 0(491) are much striated, parallel to their intersection with 

 one another, and give very bad reflections. The general habit 

 of the crystals simulates that of a crystal of the rhombohedral 

 system with two rhombohedral forms. The faces _p(212) give the 

 best reflections ; the faces g(212) are not well developed, and the 

 reflections are indifferent. The accompanying diagrams show the 

 forms present. Fig. 1 is an orthogonal projection on the plane of 

 symmetry. 



FIG. 1. 



