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VIII. Letter from Dr. HERAPATH to Professor STOKES, " On 

 the Compounds of Iodine and Strychnine." Communi- 

 cated by Professor STOKES, Sec. B/.S. Received June 21, 

 1855. 



June 20, 1855. 



MY DEAR SIR, Will you do me the favour to announce to the 

 Royal Society, that I have been engaged, during some months past, 

 in investigating the optical and chemical properties of some crystalline 

 compounds of iodine and strychnine which appear to be strongly 

 indicative and peculiar ? One of these bodies, from the analysis 

 hitherto made, would seem to have a formula not very different from 

 the following, viz. C 42 H 22 N 2 O 4 +P, and crystallizes in hexagonal 

 prisms, passing by the ordinary replacement planes to the acute 

 rhombohedron and other forms, all apparently derived from the 

 rhombohedric system; some of these crystalline forms are very strange 

 and unusual. This substance possesses " double absorption" in a 

 very evident degree, and when examined by vertically plane polar- 

 ized light, the hexahedral prisms are all obstructive of the polarized 

 beam when the length of the prisms lies parallel to the plane of the 

 incident ray ; in this position they appear dark sienna-brown in 

 colour ; when the long axis of the prisms lies perpendicular to the 

 plane of primitive polarization the crystals transmit a lemon-yellow 

 tint, passing through greenish yellow to sherry-brown. 



The other substance appears to be the sulphate of iodo-strychnia, 

 and has a decidedly metallic green reflexion, crystallizes in stellate 

 aggregations of prisms, brilliantly green by reflected light, but 

 having a deep blood-colour by transmission ; these also possess double 

 absorption, and are very peculiar, as a slight increase in thickness 

 renders them wholly impervious to light. 



When these matters have been more carefully worked out, I hope 

 to have the pleasure of communicating the results to the Society: in 

 the mean time the present notice will be sufficient for the object in 



view. 



I remain, my dear Sir, 



Yours very truly, 



W. BIRD HERAPATH. 

 Professor Stokes, F.R,S. 



