13 



In the foregoing comparative Chart of the physical properties of 

 the two salts, the axis has been assumed to coincide with a line 

 drawn through the short diagonal of the primary rhombic crystal, 

 which will coincide with the long diameter of the a-prism, and the 

 plane of the breadth of the ft -prism, and is therefore the T fl of the 

 three rectangular crystallographic ares. 



It has been compiled from the observations of Professors Stokes 

 and Haidinger and the author. It appears to form a complete 

 optical description of the two salts, as far as they are at present known. 



Whilst in both salts the indicative body-colours, or those due to 

 the more absorbed pencils (3), are only to be seen in the thinnest 

 crystals, it is evident that the reflected rays may be seen indifferently 

 in crystals of all thicknesses ; and the author is inclined to believe 

 that the cinchonidin salt possesses even greater tourmaline absorbent 

 powers upon ordinary light, inasmuch as much thinner plates are 

 required in order to obtain the indicative body-colours, perfect 

 absorption, and therefore total obstruction, being more early arrived 

 at than in the case of the quinine salt. 



The author's more recent analyses of the cinchonidin salts have 

 produced the following results : 



Sulphate of lodo- Cinchonidin. 



I. II. III. IV. 



Iodine 39'727 39'462 39'246 38-488 



Sulph. acid. . 8'390 8*673 8*882 8*593 



Carbon 34'936 3573 35'792 



Hydrogen .. 4-321 4'30l 



Nitrogen 2'976 



Oxygen 9'650 



100-000 

 which lead to the following composition : 



