IrltE CYANIDE REACTION WITH YELLOW LEPIDOPTERA. 107 



reaction. So marked a parallelism points clearly to a common 

 cause ; and it is, I tliink, a very legitimate assumption that the 

 same yellow pigment combines in the one case with potassium 

 cyanide or hydrocyanic acid to form the brilliant cyanide-red ; 

 and, in the other, reacts with lithium sulphate, barium chloride, 

 or one of several other compounds, to produce the purple-pink 

 colour. As to the nature of this latter reaction, it seemed 

 doubtful whether to attribute the colour to the formation of a 

 definite compound between the pigment and the reagent, seeing 

 that any one of some seven or eight reagents may produce it ; 

 while the fact that among them must be reckoned at least two 

 organic acids bars the suggestion that had previously occurred to 

 me, viz., that the lithium, barium, and other salts, were efficacious 

 as salts, and not as containing any given element or radicle. How- 

 ever, the nature of this purple-pink reaction is a subject for future 

 investigation. 



Here, then, the matter stands for the present. In addition to 

 the foregoing results sundry other experiments have been made, 

 which were discussed in my paper presented to the Linnean 

 Society, but which I pass over here ; and I also omit a discussion 

 which closed my paper (for I do not wish to trespass unduly on 

 the space which the Editor has kindly invited me to occupy by 

 this account) ; but it would be ungrateful to conclude without 

 acknowledging my great indebtedness to Mr. Warburg for his 

 kindness in supplying me with specimens for experiment. The 

 greater part of the work recorded in this paper has been carried 

 on with materials sent me by Mr. Warburg. To sum up : — 



I. Various yellow and orange species of the Pieridse rapidly 

 become of a brilliant red when exposed to the action of " sloppy- 

 solid " potassium cyanide. 



II. Faint indications of a similar nature are obtained by the 

 use of sodium cyanide. 



III. No such reaction can be obtained with ferrocyanides, 

 sulphocyanides, ammonium salts, nitrates, or with any other of 

 many reagents examined. 



IV. When exposed under similar conditions to the action of 

 lithium sulphate, a fine purple-pink colour is produced, staining 

 the salt. Similar, more or less faint, results are obtainable 

 with several other reagents. 



V. All of these reactions are confined to the Pieridse, and are 

 obtainable from no other yellow or chestnut Rhopalocera or 

 Heterocera yet examined. 



VI. The cyanide-red is probably produced by the union of 

 the yellow pigment with potassium cyanide or hydrocyanic acid. 

 The nature of the reaction by which the purple-pink colour is 

 produced is at present uncertain. 



