go ■ [SepteuiVier, 



NOTE ON THE ACTION OF POTASSIUM CYANIDE ON OUaANIC 

 COLOURING- MATTER. 



BY G. B. BUCKTON, F.E.S. 



The action of potassium cyanide, both as to discharging or alter- 

 ing the colours of insects, is worthy of the entomologist's attention. 

 The phenomena may, however, be in the greater part explained, when 

 we remember that water, or aqueous vapour, decomposes this salt into 

 either caustic or carbonated alkali, with the simultaneous formation 

 of ammonium cyanide, to the efficacy of which, in the state of vapour, 

 the substance acts as an insecticide. 



Mr. C. G. Barrett has lately described* the change of the yellow 

 colour of Gonopteryx rhamni to a crimson under the influence of 

 potassium cyanide. Alkalies are well known to convert many organic 

 dyes into rich browns (as in turmeric), and into tints approaching to 

 red, and advantage is taken of such action by way of chemical 

 testing. Alkalies will destroy some colours altogether, and Mr. G. T. 

 Bakerf notes the bleaching of insect colours by cyanide in the last 

 number of this Magazine. 



In all cases where potassium cyanide is used as an insecticide by 

 the entomologist, the specimen should be exposed only to the vapour dis- 

 engaged slowly but surely from the damped salt placed between sheets 

 of filtering paper. The vapour acts through the spiracles of the in-ii 

 sects, in the Hymenoptera very rapidly, in the more sluggish nocturnal)' 

 Lepidoptera much more slowly. I believe that I was the first to re-t 

 commend this use of the alkaline cyanides, when I exhibited to iM. 

 Biological section of the British Association at Liverpool, in 1854,}, 

 the identity of action in the vapour given of£ by crushed laurel leaver 

 and that of decomposing potassium cyanide. 



Care of course is necessary in using potassium cyanide in quan>i 

 tity ; but it may be noted that bird and other natural history casei 

 may be cleared from moth by a temporary but prolonged exposure t( 

 cyanide vapour, under which treatment Tinea pellionella^ &c., surel 

 succumbs. 



Weycombe, Haslemere : 



July %\st, 1884. 



* Ent. Mo. Mag., vol. xxi, p. 23. t id., p. 66, 



\ Report of the British Association at Liverpool, 1854, p. 106. 



