558 Neiv Mode of destroying Insects and Vermin. 



and vermin in horticultural houses : a matter of the first im- 

 portance; the expense and difficulty of which has hitherto 

 kept most of our houses in a comparatively filthy state. 



Ammonia is well known to be fatal to animals of all kinds; 

 and I find in fruit-houses infested with rats, that, applied to 

 their holes, it is better than any trap ; for it either ferrets 

 them out, or kills them in the holes. 



1 have found that it produces no injury to the most de- 

 licate stove or conservatory plants, unless the volume of 

 ammoniacal gas exceeds one fifth of the whole volume of 

 atmospheric air in the house. Succulents will bear any quan- 

 tity. The gas need not be applied in diffusion through the 

 house more than fifteen minutes, during which time every 

 mealy bug and aphis will drop dead. Nothing but oil or 

 rubbing off will kill the scaly bug, I believe, except this gas, 

 applied directly to the affected part of the plant for a short 

 time, from the tube of a retort or other fit vessel. 



The mode of applying it to a house is very simple : — A 

 hole is to be made near the bottom of one of the doors, or 

 other fit place, big enough to let the pipe of a watering-pot 

 through, which is to contain a quantity of the ammoniacal 

 liquor. A small quantity of turf or wood is then to be kindled 

 under it, and the vapour will enter and diffuse itself in the 

 house. 



The proper quantity may be easily estimated with sufficient 

 accuracy. First determine the quantity of ammonia the liquor 

 contains, in a given quantity, by the quantity of acid it w^ill 

 neutralise: reference to any chemical system will give the 

 number of cubic feet this will occupy at the atmospheric 

 pressure and at the temperature of the houses ; and the 

 cubical contents of the houses being known, use just so much 

 of the liquor as will produce one fifth of those contents. When 

 this quautity is found, the best way is to use only so much, 

 and evaporate it to dryness.* 



After the gas has been diffused through the house for 

 about fifteen minutes, the ventilators should be opened to 

 allow it to escape, lest it injure the plants. You will per- 

 ceive the advantage of this in saving expense in tobacco, 

 time, labour, and trouble. It may be usefully applied to kill 

 moths in clothes presses, &c., nnd flies when numerous in 

 houses in summer. I am, Sir, yours, &c. 



Robert Mallet. 

 94. Capel Street, Dubliti, July 14=. 1831. 



* We shall be much obliged to our correspondent to furnish such details 

 as will enable a gardener, having no chemical system to refer to, to apply 

 the gas with certainty and safety. — ComL 



