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A NEW TYPE OF ENTOMOLOGICAL KILLING-BOTTLE. 



By Malcolm E. MacGregor, 



Wellcome Field Laboratory, Surrey, Wellcome Bureau of Scientific Research. 



The " cyanide bottle " is never a very attractive part of the entomologist's 

 equipment. When made up in the old way, i.e., plaster of Paris poured over lumps 

 of solid potassium cyanide and the plaster then allowed to set, the contrivance 

 has an attractive appearance, but is an abomination to use, especially if small 

 insects are being dealt with. The large amount of water utilised in making up the 

 plaster of Paris can never be dried out properly, and the potassium cyanide being 

 deliquescent to some extent the presence of moisture is unavoidable. Moreover 

 the cyanide soon decomposes and turns brown, imparting its colour to the plaster 

 and forming an ugly-looking mass on which small insects are not contrasted and 

 may be easily overlooked and lost. 



The newer method of making up the killing-bottle by powdering the cyanide 

 and mixing this with about an equal weight of powdered borax, compressing the 

 mass at the bottom of the bottle, and afterwards pouring over it a small amount 

 of plaster just sufficient to secure the powders, is a distinct improvement in so far 

 as the approach to anhydrous conditions is concerned and the more rapid liberation 

 of HON gas. However, the mass decomposes more rapidly with the addition 

 of the borax, and the unfortunate brown coloration is accentuated. 



There are too the methods that depend on fixing the potassium cyanide in the 

 cork instead of in the bottle, which are certainly improvements in that the insects 

 are left lying on the glass, against which they can be easily seen ; but with this 

 method the cyanide is not in a very safe situation, and furthermore cannot so 

 rapidly evolve as much HON gas as cyanide that is distributed over the bottom 

 of the bottle. 



In addition to the faults peculiar to whatever method is employed in making 

 up the cyanide killing-bottle there are the following disadvantages in the use of 

 cyanide : — (1) the bottle is a potential danger to the ignorant if not properly looked 

 after, owing to the highly poisonous nature of potassium cyanide ; (2) if the bottle 

 is accidentally broken, cases of poisoning may result unless every scrap of the 

 cyanide and plaster is collected and destroyed ; (3) the kiUing power of the 

 preparation speedily weakens if the bottle is constantly used ; (4) insects recover 

 more often from HON gas in weak concentration than they do from concentrated 

 chloroform vapour ; (5) when the cyanide bottle is exhausted it is preferable to 

 throw the whole thing away (unless the bottle is of the type where the cyanide is 

 secured in the cork) rather than to attempt to chip out the hard plaster to renew 

 the apparatus, and a new kiUing bottle has therefore to be obtained. 



On the strength of these objections I have for several years preferred to use 

 chloroform as an insect poison, utihsing chloroform-saturated rubber in place of 

 cyanide. The method is ideal as far as its action is concerned, but the one great 

 drawback has been the rapid evaporation of the chloroform and the constant 

 addition of the fluid that has been necessary. 



