jujy2 191 7 Neglected Factor in Use of Nicotine Sulphate 49 



These tests show that nicotine sulphate is relatively, if not absolutely, 

 nonvolatile. The death of the flies in the experiment with commercial . 

 40 per cent nicotine sulphate was due to the vapor from the small amount 

 of free nicotine contained in these extracts. This quantity of free nico- 

 tine is apparently not sufficient to kill the croton bug. 



Mclndoo ^ apparently was working with commercial nicotine sulphate, 

 and the odor and vapor of nicotine sulphate that he speaks of is really 

 the odor and vapor of the free nicotine contained in these commercial 

 extracts. If the death of the insects when sprayed with tobacco extracts 

 is due entirely to the penetration of the vapor of the nicotine into the 

 body of the insect, as claimed by Mclndoo, then commercial tobacco 

 extracts containing nicotine sulphate are really ineffective unless the 

 nicotine is freed by rendering the solution alkaline. A small quantity of 

 commercial tobacco extract was heated for a short time to evaporate the 

 free nicotine. This extract was- then made into a spray, using i part 

 to 100 parts of distilled water. Chrysanthemums were thoroughly 

 sprayed with this solution, killing about 40 to 50 per cent of the chrysan- 

 themum aphids {Macrosiphum sanhorni) infesting the plants. A portion 

 of this solution was then rendered alkaline with sodium carbonate and 

 used to spray other chrysanthemums. The alkaline solution killed 100 

 per cent of the aphids. This experiment was repeated, using pure nico- 

 tine sulphate and snapdragons {Antirrhinum spp.) infested with aphids 

 {Myzus persicae). The solution of nicotine sulphate in distilled water 

 killed less than i per cent of the aphids, probably only those knocked off 

 the plant in spraying. Later, after the plants had been watered with 

 tap water, a number (probably between 20 and 40 per cent) of the aphids 

 on these plants died. This water was alkaline and apparently set free 

 some of the nicotine, as a distinct odor of nicotine was noticed. The 

 same solution of pure nicotine sulphate was rendered alkaline with 

 sodium carbonate, to free the nicotine, and used on the snapdragons^ 

 when 100 per cent of the aphids were destroyed. 



By titrating spray solutions containing commercial 40 per cent nicotine 

 sulphate at the rate ©f i part to i ,000 parts of water it was found that 

 the tap water at this Station would decompose about one-half of the 

 nicotine sulphate contained in the solution. The addition of soap at 

 the rate of i pound to 100 gallons of water broke down the rest of the 

 nicotine sulphate. These results, however, will vary according to the 

 alkalinity of the water, the amount of alkali in the soap, and the brand 

 of commercial nicotine sulphate used. 



The above facts probably explain the different results obtained in the 

 use of tobacco extracts, and also why soap greatly increases the efficiency 

 of sprays containing nicotine sulphate. Inasmuch as the vapor of nico- 

 tine is the principal cause of the death of insects in spraying with tobacco 



1 McIndoo, N. E. Op. cit. 



