4504 Insects. 



almost immediate suffocation. A head of sealing-wax should be 

 fixed to the needle, to prevent the insect fluttering off the cork sup- 

 port into the water. 



This plan answers well for all specimens bred in confinement 

 or otherwise well placed for operation, but it is nearly useless in col- 

 lecting Tortrices, Tineidae, or other minute insects which require 

 delicacy in handling. 



From the fact, proved by experiment, that the vapour of hydro- 

 cyanic acid diffused through a bell jar is very deleterious to insects, 

 and the consideration that there are many obvious objections to 

 the common use of so volatile and deadly a poison, I have been led 

 to search for a solid compound of cyanogen sufficiently powerful in 

 its properties for such a purpose, yet more portable and less dan- 

 gerous than the acid itself. These desiderata are to be found in 

 cyanide of potassium, which has the peculiar advantage of being 

 slowly decomposed by moisture (that of the atmosphere is sufficient) 

 into hydrocyanic acid, ammonia, and other products. 



The apparatus necessary is very simple, and consists of a wide- 

 mouthed glass jar or bottle, fitted with a brass cup, having an aperture 

 capable of being pretty accurately closed by a slide. The jar is fur- 

 nished with a false bottom of cloth or blotting-paper, under which 

 from twenty to thirty grains of the cyanide are placed in coarse 

 powder. The blotting-paper serves to absorb any moisture which 

 may arise from the deliquescent nature of the salt. After the lapse of 

 a short time a poisonous atmosphere is produced, which may be re- 

 tained with all its efficacy for several weeks, without the necessity of 

 renewing the charge of cyanide. A small glass bell and card com- 

 plete the instrument, which may be taken into the fields, and made to 

 take the place of a collecting-box. A transfer of an insect from the 

 net is easily effected, by capturing it first in the bell glass with assist- 

 ance of the card. After placing the whole on the cap of the instru- 

 ment, the card and slide are removed, when the insect drops through 

 the aperture and is suffocated in a space of time varying from forty 

 seconds to two minutes. The apparatus is then free for another 

 operation. 



I am aware that many of the advantages here described are 

 to be found equally in the use of crushed laurel-leaves, the vapour of 

 which contains pure hydrocyanic acid. The convenience of the new 

 over the old plan may be thus stated. The fresh leaves are not 

 always to be procured, and the bruised mass after a short time loses 

 its poisonous property : the leaves cannot, therefore, be stored 



