50 Journal of Agricultural Research voi. x, no. i 



extracts, the maximum efficiency of those containing nicotine sulphate 

 can only be obtained by insuring that the spray gives at the time it is 

 used an alkaline reaction. This may be obtained by the use of hard 

 water, the addition of soap, or in some cases by the addition of a suffi- 

 cient amount of sodium carbonate or lime water to produce an alkaline 

 reaction. 



The fact that nicotine sulphate is nonvolatile explains the cases of 

 poisoning from eating lettuce sprayed with tobacco extracts containing 

 this material. The only chance of removing nicotine sulphate from the 

 lettuce leaves would be by dissolving it ofif in the water used in sprinkling. 

 After sprinkling, the lettuce leaves are covered with drops of water in 

 which the nicotine sulphate is held in solution. When these drops 

 evaporate, there is a possibility of the nicotine being absorbed into the 

 tissues of the leaf. This possibility is shown by the fact that, after 

 several thorough sprinklings of the lettuce in the greenhouse, the plants 

 will still show by chemical analysis slight traces of nicotine. In the 

 experiments cited in this paper a slight burning of the foliage resulted 

 from the use of nicotine sulphate, but not with free nicotine. 



SUMMARY • 



(i) Nicotine sulphate is nonvolatile. 



(2) Alkalies contained in hard water and soap set free the nicotine 

 contained in nicotine-sulphate sprays. 



(3) In order to obtain the maximum efficiency of tobacco extracts 

 containing nicotine sulphates, they should be rendered alkaline before 

 using. 



(4) Commercial tobacco extracts containing nicotine sulphate should 

 not be used in the greenhouse, at least not on plants which are later to 

 be used for food. 



(5) Tobacco extracts or tobacco papers containing free nicotine may 

 safely be used in the greenhouse on plants such as lettuce, without 

 endangering the lives of the consumers. 



(6) Food plants such as lettuce sprayed with tobacco extracts con- 

 taining free nicotine should not be cut for the market until the day after 

 spraying. If the temperature of the house is low, a longer period should 

 be given the nicotine to evaporate from the leaves. 



