October, '17] SAFRO: TESTS FOR NICOTINE ON PLANTS 459 



HOW TO TEST FOR THE PRESENCE OF NICOTINE ON 

 SPRAYED PLANTS 



By V. I. Safro, Louisville, Ky. 



It has been generally believed that as soon as a nicotine spray 

 dries on the plant it disappears and that any results following the 

 application of nicotine must necessarily occur immediately or very 

 shortly after the application. This belief, however, has been rendered 

 uncertain in the light of recent developments, several of which have 

 appeared in print, regarding the effects of nicotine insecticides. 



The writer conducted some tests last fall which showed definitely 

 that nicotine may be present a considerable time after the spray has 

 dried and apparently disappeared from the plant. This new finding 

 tends to assist in explaining some of the hitherto unlocked for effects 

 of the application of nicotine insecticides. Because of the wide- 

 spread interest among entomologists and the many inquiries the 

 writer has received as to the method of indicating the presence of 

 nicotine upon sprayed plants, he believes it will be of interest to 

 describe briefly the procedure, so that entomologists may be in position 

 to conduct tests of this kind in the course of their own investigations. 



The Test 



Take a number of leaves that have been sprayed and which it is 

 desired to test for nicotine, and thoroughly rinse them in a minimum 

 amount of distilled water. Bark, twigs and fruit may be subjected 

 to the same test as the leaves. The number of leaves or amount of 

 material necessary to use in order to obtain a test depends on the 

 amount of nicotine present. In some of our own tests where five 

 leaves gave a doubtful reaction, ten leaves gave a definite one. Gener- 

 ally we were able to obtain a definite indication of the presence of 

 nicotine in as little as 25 cc. of water by using five leaves that had 

 been sprayed at the usual strength (about .05 of 1 per cent nicotine). 



After having rinsed thoroughly, filter and make filtrate slightly acid 

 with a few drops of hydrochloric acid. If a precipitate is formed at 

 this point, filter again. To this filtrate add several drops of 1 per cent 

 silicotungstic acid. A white cloudiness denotes the presence of 

 nicotine. It will be found convenient to conduct this test in a glass 

 beaker over a dark surface. 



We have found that silicotungstic acid obtained from J. T. Baker 

 Chemical Co., Phillipsburg, N. J., or from Merck & Co., New York 

 City, satisfactory for this purpose. 



After making up the 1 per cent aqueous solution, settle and filter. 

 This solution will keep indefinitely. 



