11 



only very slightly soluble in dilute spirit, and scarcely at all in 

 water, ether, turpentine, or chloroform : acetic, dilute sulphuric, or 

 hydrochloric acid have but little action upon them, whilst concen- 

 trated hydrochloric or sulphuric acid decomposes them. Nitric 

 acid rapidly acts upon them, even in the cold, with- violent evolution 

 of nitrous acid and production of heat, iodine being oftentimes libe- 

 rated in the crystalline form. 

 Alkalies also decompose them. 



Sulphuretted hydrogen, soluble sulphides, sulphurous acid and 

 sulphites, together with chlorine-water, instantly decolour their 

 alcoholic solution, with the production of hydriodic acid. 



In dilute alcoholic solutions, starch gives immediate evidence of 

 iodine, and nitrate of silver gives a yellowish- white precipitate of iodide 

 of silver, and some organic basic compound which can only be re- 

 moved by the action of concentrated boiling nitric acid ; this reac- 

 tion, although commencing at the ordinary temperature, with violent 

 disengagement of nitrous acid vapours, must be perfected by boiling. 

 Baryta salts exhibit the existence of sulphuric acid, which in all 

 instances is an essential constituent in their formation. 



The quinidin and cinchonine salts dissolve with more difficulty, in 

 consequence of their greater thickness and less extent of surface. 



Since the author had the honour of communicating his discovery 

 of the optical salt of cinchonidin to the Royal Society (a preliminary 

 notice of which was published in the ' Proceedings/ vol. viii. No. 24), 

 he has ascertained that its primary form is, like that of the quinine 

 salt, that of a right rhombic prism, and usually very thin, but having 

 for its acute angles 43, and 137 for its obtuse, with the rectangular 

 axes M|vj^- ; Ty.- oiro - ; PVoDoT ^e quantity for P a being variable 

 and very minute. In a former communication to the Royal Society, 

 published in the ' Proceedings' (Feb. 16, vol. vi. No. 24, 1854), the 

 quinine salt was shown to have a primary rhombus, having 65 for 

 the acute, and 1 15 for the obtuse angles, with the three rectangular 

 axes, thus related : M^ ; Tf, Tnn7 ; PVoTuTT- 



In both salts the optical characters are usually examined through 

 the shortest axis, P a : in some recent observations on the quinine 

 salt, the author has discovered that it transmits a blood-red beam of 

 plane-polarized light through the axes M and T a , and this is also a 

 beam polarized in a plane parallel to that of the axes M a and T a . 



