

the Sulphate of Iodo-quinine or Herapathite. 369 



The various formulae necessary to produce different crystalline 

 forms are given in detail. 



The author enters into a re-discussion of the double refractive 

 powers, and attempts to show that Herapathite possesses a prin- 

 cipal axis having " positive " characters. He also endeavoured to 

 measure the thickness of certain very thin plates, by the differen- 

 tial tints produced by the exercise of their doubly refracting 

 powers upon the colours of the selenite stages, and found that 

 these thin plates raised the blue of the second order to the yellow 

 and violet ; the red of the second to the violet and blue-gray ; 

 and the green of the same to orange and violet of the second 

 order. Assuming, therefore, this substance to have similar 

 doubly refracting powers to selenite, and of equal intensity, and 

 also the same index of refraction, their thickness may be estimated 

 as equal to that of a plate of selenite necessary to give the same 

 difference in tint, viz. - 000517 of an inch. 



These very thin plates no longer possessed the Cantharides- 

 like or brilliant metallic green colour when examined by reflected 

 light. They appeared more like portions of the elytra of the 

 Blatta germanica ; still reflecting a polarized beam, but of a 

 brown colour, and also retaining their doubly absorbent powers 

 when examined by transmitted light. 



The author considers that his recent investigations indicate 

 that whatever properties Professor Stokes may have assigned to 

 the ray reflected from the a-prisms (which alone were experi- 

 mented on by him) in the principal plane of the breadth, must 

 be equally true in that reflected from the primary rhombic prism 

 in the principal plane of its length, i. e. its long diameter; and 

 whatever properties he may have assigned to the reflected ray 

 from the principal plane of the length of the a-prism, will be 

 equally true of that reflected from the primary rhombus in the 

 principal plane of the breadth, i. e. its short diameter. 



The paper concludes with some recently determined facts 

 relating to the chemical characters of this peculiar substance. 



Its sp. gr. at 60° Fahr. was found to be 1*895. 



It is very sparingly soluble in pether, turpentine or water at 

 the ordinary temperatures, scarcely more than % Jg^dth part ; 

 boiling water does not dissolve TT j' n (jdth part. It does not appear 

 more soluble in aether or turpentine by boiling. Chloroform 

 does not dissolve it, but has a great attraction of surface for it. 



Alcohol of -837 dissolves ^th part at 57° Fahr., and by 

 boiling, it takes up j^th part, which readily crystallizes on 

 cooling in /3-hexagons. 



Acetic acid, sp. gr. 1 -042, dissolves 7 ^th part at 60° Fahr., 

 and »' th part at boiling temperature — iodine volatilizing if the 

 heat is prolonged. 



Phil. Mag, S. 4. Vol. 9. No. 60. May 1855. 2 B 



