Intelligence and Miscellaneous Articles. 33 i 



solved to a clear solution in water. To ascertain the presence of 

 cholesteric acid, the silver salt was prepared by dissolving the acid 

 gummy mass in water, neutralizing with ammonia, and precipitating 

 with nitrate of silver; it was deposited in thick white flakes. Oxalic 

 acid was not present. To obtain the silver salt in a crystalline state, 

 some nitrate of ammonia was added to the mother-ley from which 

 it had been precipitated, in order to increase the solubility of the 

 silver salt in it, then boiled with the precipitate, when the greater 

 portion dissolved ; on cooling, the cholesterate of silver separated 

 from the hot filtered liquid, on the bottom and sides of the glass, in 

 granular crystalline yellowish crusts; more of the salt was obtained 

 by evaporating the mother-ley. The salt, dried at 212°, yielded 

 57*69 oxide of silver, 23*81 carbon, and 2*35 per cent, hydrogen ; 

 leading to the formula AgO, C 8 H 4 O, which is that of the choleste- 

 rate of silver. 



The contemporaneous occurrence of cholesteric acid in the pro- 

 ducts of decomposition of choloidic acid, cholesterine and cholic 

 acid by nitric acid exhibits the close relationship of these three 

 bodies as respecis their constitution. — Liebig's Annalen, lviii. p. 

 375. 



ON A NEW PROPERTY OF LIGHT EXHIBITED IN THE ACTION 

 OF CHRYSAMMATE OF POTASH UPON COMMON AND POLAR- 

 IZED LIGHT. BY SIR D. BREWSTER*. 



The chrysammate of potash, which crystallises in very small, flat 

 rhombic plates, has the metallic lustre of gold, whence it derives its 

 name of golden fluid. "When the sun's light is transmitted through 

 the rhombic plates it has a reddish yellow colour, and is wholly 

 polarized in one plane. When the crystals are pressed with the 

 blade of a knife on a piece of glass, they can be spread out like an 

 amalgam. The light transmitted through the thinnest films thus 

 produced, consists of two oppositely polarized pencils, — the one of 

 a bright carmine red and the other of a pale yellow colour. With 

 thicker films, the two pencils approach to two equally bright car- 

 mine red pencils. It is to the reflected light, however, and its new 

 properties, that I wish to direct attention. Common light, reflected 

 at a perpendicular incidence from the surfaces of the crystals, or of 

 the films, has the colour of virgin gold. It grows less and less 

 yellow as the incidence increases, till it becomes of a pale bluish 

 white colour at very great incidences. The compound pencil, 

 thus reflected and coloured, consists of two oppositely polarized 

 pencils, — one polarized in the plane of reflexion, and of a pale 

 bluish white colour at all incidences, and the other polarized per- 

 pendicular to the plane of reflexion, and of a golden yellow colour at 

 small incidences, passing successively into a deeper yellow, greenish 

 yellow, green, greenish blue, blue, and light pink, as the angle of 

 incidence increases. This very remarkable property, which I have 

 discovered also in some other crystals, is not caused by any film of 

 oxide formed upon the natural surface of the crystal, nor is it the 



* Read at the Southampton Meeting of the British Association. 



Z2 



