THE CYANIDE -REACTION WITH YELLOW LEPIDOPTKRA. 3 



III. — Experiments with other Cyanides. 



Having established the occurrence of this reaction, the next 

 step was to endeavour some explanation of it. It seemed to me 

 almost certain, originally, that the effect was due to the cyanogen 

 radicle in the compound KCN ; and it therefore was important 

 to determine whether or no other cyanides would have a like 

 effect. A series of experiments was therefore instituted to clear 

 up this problem.* Of course the nearest analogue to KCN is 

 sodium cyanide, and the action of this reagentf was therefore 

 tested by exposing to it several yellow species that were known 

 to react readily with KCN. These included Catopsilia crocale, 

 rhamni, echisa, hyale. Altbough no bright red was produced as 

 in the potassium cyanide experiments, yet there is a clear, though 

 weak, tendency in the same direction, for a distinct patch of dull 

 claret-red appeared on the cleopatra wing ; and it appears to me 

 especially interesting that in Catopsilia, although no red was 

 found, yet the dull yellow or lemon-yellow of the natural insect 

 was transformed into orange, since my former experiments led 

 me to conclude that orange was a stage usually passed through 

 in the evolution of red from yellow. Another noticeable point 

 was the very rapid solvent action of the damp sodium cyanide on 

 the yellow pigment of cleopatra. 



Having thus detected a faint action of this kind in sodium 

 cyanide, I thought it of interest to experiment with a few other 

 cyanides, and accordingly the effect of mercury, zinc, and copper 

 cyanides was tested upon O . cleopatra and C. crocale. These 

 reagents, however, proved to be unworkable, as indeed might be 

 anticipated in view of their physical characters. It was, however, 

 observed that in the wings of G. cleopatra placed upon mercury 

 cyanide and copper cyanide the veins had become of a bright 

 holly-green. It is clear that the reddening reaction can only be 

 expected in the case of a cyanide that can be kept in the sloppy- 

 solid condition already referred to ; and consequently when the 

 physical character of any cyanide is such that it cannot well be 

 kept in this condition, i. e., when it is comparatively insoluble, 

 it is useless to attempt any experiments with it. 



Besides testing these simple cyanides, I also tried what could 

 be done with the sulphocyanide (thiocyanate) of ammonium, and 

 the ferri and ferrocyanides of potassium. In no case was any 

 sign of reddening observed, although the experiments were made 

 upon species that had been proved to be verj^ susceptible to the 



* These experiments are not detailed in the chronological order in which 

 they were made. 



f This is by no means so easy a reagent as KCN to >work with, on 

 account of physical differences between the two salts. It will be understood 

 that in the whole of the experiments detailed in this paper the reagents used 

 were in a sloppy-soHd or stiff-mud condition. 



B 2 



