INSECTS AND INSECTICIDES 375 



Carbolic acid emulsion is sometimes used against root- 

 maggots. 



Soap 1 pound 



Water 1 gallon 



Crude carbolic acid . 1 pint 



The soap is dissolved in hot water, the crude carbolic acid is 

 added and the mixture is agitated into an emulsion. For use 

 against root-maggots, this stock solution should be diluted with 

 30 parts of water. 



Tobacco. 



Tobacco is one of the most useful insecticides. The poisonous 

 principle in tobacco is an alkaloid, nicotine, which in the pure 

 state is a colorless oily fluid, slightly heavier than water, of 

 little smell when cold and with an exceedingly acrid burning 

 taste even when largely diluted. It is soluble in water and 

 entirely volatile. It is one of the most virulent poisons known ; 

 a single drop is sufficient to kill a dog. 



Commercial tobacco preparations have been on the market 

 for many years. The most important of these are "Black 

 Leaf 40" and Nicofume. 



''Black Leaf 40" is a concentrated tobacco extract contain- 

 ing 40 per cent nicotine in the form of nicotine sulfate. Its 

 specific gravity is about L25. In this preparation the nicotine 

 is in a non-volatile form, it having been treated with sulfuric 

 acid to form the sulfate. "Black Leaf 40" is used at strengths 

 varying from 1 part in 500 parts of water to 1 part in 1600 

 parts. It can be satisfactorily combined with other sprays, 

 as, for instance, bordeaux mixture, arsenate of lead and the 

 various soap solutions. When used with water, 4 to 8 pounds 

 of soap should be added to each 100 gallons to make the mixture 

 spread and stick better. 



Nicofume is a tobacco extract containing 40 per cent of 



