Dr. J. Stenhouse on Alpha- and Beta-Orcine. 5 



course of a day or two the liquid becomes filled with a mass 

 of brownish-coloured crystals, which must be collected and 

 pressed between folds of blotting-paper to free them from ad- 

 hering resin and colouring matter. 



The crystals must be further purified by digestion with 

 animal charcoal, and by being repeatedly crystallized out of 

 water: they then form hard, slender, brittle prisms, which 

 still retain a faintish yellow shade, and are about half an inch 

 long. In order to obtain beta-orcine perfectly white, it must 

 be crystallized out of weak spirits, assisted, as before, by a 

 little animal charcoal. So soon as the crystals are all deposited, 

 they should be removed from the solution and dried on blotting- 

 paper, as the mother-liquor, on standing for some time, becomes 

 reddish-coloured. Beta-orcine crystallizes out of weak spirits 

 in larger and more regular crystals than those obtained from 

 its aqueous solutions. It forms four-sided prisms, surmounted 

 at either end by well-defined four-sided pyramids. These 

 crystals are hard and brittle, have a brilliant lustre, and are 

 from an inch to three-quarters of an inch long. I am indebted 

 to Professor W. H. Miller of Cambridge for the subjoined 

 measurement of their angles. 



Pyramidal. Symbols, a 100, c 001, m 110, s 101, £ 201, 

 ;• 111. 



Angles between normals to the faces. 



Beta-orcine. 



No cleavage observable. 



Beta-orcine, like ordinary orcine, to which in so many re- 

 spects it bears a very close analogy, may be also obtained by 

 boiling usnic acid with an excess either of caustic potash or 

 of lime or baryta. By none of these methods, however, is it 

 so readily procured as by destructive distillation. By much 

 the larger portion of the usnic acid is converted by the potash 

 into an acid resin, with which the alkali combines; the free 

 alkali is also apt to destroy most of the orcine as it is formed. 



