212 Dr. John Davy on the Effects of certain Agents, fyc. 



tained any appreciable loss, — a circumstance which perhaps might 

 have been anticipated, considering that the prussic acid used was 

 the dilute hydrocyanic acid of the London Pharmacopoeia, which 

 contains 2 per cent, only of real acid. 



These few experiments may perhaps suffice to show the great 

 efficacy of the acid, the intensity of its action, and the very minute 

 quantity requisite to occasion death, and that in a few seconds (at 

 least a motionless state terminating in death, exposure to the 

 acid vapour being prolonged), of such powerful and comparatively 

 large insects as the Bombus hortorum and Geotrupes stercorarius ; 

 and, further, in conjunction with the qualities of the acid, espe- 

 cially its great volatility, the boiling point of the pure acid being 

 only 79° Fahrenheit, the manner in which it should be used when 

 employed for the purposes of the Entomologist. 



As to precautions, the poison being so volatile, it need hardly 

 be remarked, that a close tube (one made air tight, by a good cork, 

 will be best) ought to be used for confining the insects to be 

 acted on ; and, on the same account, that the receiving tube 

 should not be very capacious, nor the small tube or bottle to be 

 included in it, charged with the acid, one of narrow or contracted 

 aperture. The dimensions of the two duly proportioned, the 

 effects, deprivation of life, even from a few grains of the acid, 

 should be almost instantaneous and quite certain, and this at the 

 ordinary temperatures of our rooms, supposing them to range 

 throughout the year between 50° and 70°. As to bad effect from 

 moisture, there appears to be no ground for apprehension, inso- 

 much as in the short time the effect is being produced, even 

 should the insect be allowed to remain in the tube more than an 

 hour, there will be no appreciable loss from the ascent of aqueous 

 vapour ; and, even if there were, it would be most easy to coun- 

 teract its influence by the introduction in another small tube of 

 a few drops of strong sulphuric acid, or grains of chloride of 

 calcium. As, in the instance of the Bombus, the prussic acid 

 proved destructive to the parasitic insects infesting it, it is not 

 improbable that it may be equally fatal to parasitic animals gene- 

 rally, and their ova and larvae. If so, would not this be an 

 additional inducement to employ it, and no small advantage ? 



J. D. 



April 19, 1851. 



