General Notices. 4^1 



Destruction of Insects hy Ammoniacal Gas, — Sir, Among the various 

 plans hitherto proposed for the destruction of insects injurious to vegetation, 

 particularly under glass, there is scarcely one, if anj^, that is not liable to 

 some great objection : one of the best, tobacco smoke, leaves a disagreeable 

 smell, very difficult to be got rid of, and is chiefly useful against the aphides. 

 Sulphur, if exposed to a temperature very little above that required for slow 

 evaporation, forms sulphuric acid gas, which is highly destructive to vegeta- 

 tion. Lime renders the plants unsightly, and lime-water is liable to the same 

 objection ; while soap is difficult to apply, and more difficult still to wash 

 off, if allowed to dry on. It was with some pleasure, therefore, I saw that 

 Mr. Major, in his work on insects, proposes for the destruction of the red 

 spider a trial of ammoniacal gas, it having been found by Sir H. Davy to 

 be instantly fatal to insect life. In order to ascertain how far this might 

 be applied to plants with safety, in October last I submitted a plant of 

 slender fuchsia (Fuchsza gracilis) infested with the red spider, another of 

 common myrtle (ilfjrtus communis) affected with the turtle, or scaly 

 insect (Coccus hesperidum), and a third of nutmeg-scented storksbill 

 (Pelargonium fragrans), covered with the common green aphis, to the 

 action of this gas, decomposing the muriate (sal ammoniac) by quicklime in 

 a saucer, and placing the whole under a large hand-light. The result was, 

 that the Fiichsza lost, with the insects, all its leaves; the other plants did 

 not seem injured, the turtle insect appeared destroyed, but the aphides 

 seemed to have sustained little or no injury. I beHeved at the time I had 

 used too great an excess of lime, which, from the heat evolved, I then 

 thought had destroyed the leaves of the fuchsia. I next procured some 

 leaves with cocci (turtle insects) upon them, and others with aphides, and 

 placed them in solutions of ammoniacal gas in water (diluted hartshorn) 

 of various degrees of strength, but found it had little effect upon the latter 

 insects, unless placed in hartshorn of the medium strength ; but the turtle 

 insects were soon destroyed, even in the weaker solutions. 



It then occurred to me that it would be very easy to saturate an atmo- 

 sphere of a given extent with the gas itself j but as it is very fugitive, 

 though at the same time rapidly absorbable by water, I thought the best 

 way would be first to saturate the air with moisture, by throwing water 

 upon the heated flues, and, as soon as the plants contained in the house 

 were sufficiently damp, to liberate the ammonia. In a green-house 16 ft. by 

 8 ft., and about 10 ft. deep, I placed four saucers containing sufficient quick- 

 lime to decompose 2 oz. of sal ammoniac dissolved in water, the vapour of 

 which seemed to have had no effect upon either insects or plants the next 

 morning. Considering the vapour not strong enough, I next placed 3 oz. 

 of the salt, and decomposed it in the same way ; and by the next day the 

 turtle insect appeared destroyed ; but the aphides, though weakened, were 

 left in sufficient numbers to replenish the house, although the gas had been 

 so powerful as to change the more delicate blue and red flowers to green, 

 and, as I in a day or two found, to destroy the leaves of many of the 

 plants, and a few of the plants altogether. The succulent plants suffered 

 most, with a few exceptions : the (Senecio elegans, Lobelk caerulea, Leuco- 

 dendron argenteum, Indigofera filifolia, and ^yoscjamus aureus, were 

 entirely killed ; the cinerarias, fuchsias, lobelias, Lachenalk tricolor, He- 

 liotropium peruvianum, Maurandya Barclay««a or ontirrhiniflora, Phoe^nix 

 dactylifera. Primula prae'nitens (or sinensis), Strelitzi« reginae, Bocconza 

 serrulata, Calla (now Richardi«) aethiopica, Coh(s'a scandens, ^ulbine 

 alooides, cassias, and some of the mesembryanthemums, were much injured; 

 while the hoyas, oleanders, citrons, acacias, cameUias, aloes, crassulas, 

 most of the mesembryanthemums, and heaths, escaped altogether, though all 

 were equally exposed to the vapour. Its effect upon the red spider I 

 could not ascertain, as none were at the time in active existence. 



As it is still probable this gas may be serviceable in the destruction of 



