August, '19] SAFRO: STRENGTH NICOTINE SOLUTIONS 349 



THE STRENGTH OF NICOTINE SOLUTIONS 



By V. I. Safro, Louisville, Ky. 



The terms designating the strength of nicotine solutions are very 

 often used quite loosely and in some cases erroneously. Too often, 

 for instance, we see mentioned "40 per cent nicotine sulphate" when 

 the intent is to specify ''40 per cent nicotine as sulphate" — far from 

 being an equivalent statement. It is highly desirable, then, that the 

 factors that constitute the strength of nicotine solutions be well known 

 and that certain old erroneous ideas be definitely disposed of. In 

 order to bring this matter to the attention of entomologists, these 

 nontechnical remarks are submitted. 



When properly used as a spray, nicotine solutions are practically 

 independent of sunlight, humidity, or any other atmospheric conditions 

 for their effectiveness as contact insecticides, the problem in the 

 field being concerned solely with wetting the insects thoroughly 

 with a solution of the required nicotine strength. (The practice of 

 using a greater nicotine strength is sometimes followed in order to 

 make up for carelessness and lack of thoroughness on the part of the 

 grower, or for the lack of spreading properties of the spray caused by 

 using hard water without the addition of a sufficient softener and 

 spreader.) 



Odor No Indication of Comparative Strength. — Many growers 

 make a practice of endeavoring to ascertain the comparative nicotine 

 strength by the odor of the preparation. This has been a common 

 practice among greenhouse men. As a matter of fact, the charac- 

 teristic odor of tobacco is not due to nicotine. It is due to a great 

 extent to the essential oils of the tobacco plant and to other extractive 

 material with which we are at the present time not very well acquainted. 



The writer has before him the following preparations : 



100% Nicotine ( ) 



43% Nicotine < Uncombined; i. e. "free"> 

 3% Nicotine ( ) 



40% Nicotine as sulphate 



Tobacco oil (no nicotine) 



An attempt to obtain the comparative nicotine value of these prepa- 

 rations by odor is impossible. The preparation that contains the 

 strongest tobacco odor is the preparation of tobacco oil which contains 

 no nicotine whatever. On the other hand, the preparation containing 

 100 per cent " free " nicotine possesses very little odor and that differing 

 quite materially from the tobacco oil. In fact, the odor present in 

 the sample of 100 per cent "free" nicotine has no similarity to the 

 characteristic tobacco odor. The preparation containing 3 per cent 



