NICOTINE SULPHATE AS AN OVICIDE AND LARVICIDE. 13 



At the suggestion of Mr. V. I. Safro, Mclndoo washed separately 

 50 sprayed pear-tree leaves in 50 cc. of water. The resulting filtrate 

 was acidified with hydrochloric acid and then tested for the presence 

 of nicotine by adding phosphomolybdic acid and silicotungstic acid. 

 Each test apparently showed the presence of nicotine. Fifty un- 

 sprayed leaves were likewise tested as a control; no precipitate was 

 observed. One hundred unsprayed leaves were also tested, using the 

 same amount of water ; this time a precipitate was observed, and the 

 same result was obtained thereafter on several occasions. Only green 

 and unbroken leaves were used in these tests. At all tunes there is 

 more or less foreign organic matter in the form of dust on the leaves ; 

 this is readily seen in microscopical sections through unsprayed 

 leaves, and alkaloidal reagents precipitate it, as well as the nicotine 

 which may be present. Consequently the preceding method should 

 not be regarded as reliable; nevertheless, Mr. Safro (9) has pub- 

 lished his method and says : 



Generally we are able to obtain a definite indication of the presence of nico- 

 tine in as little as 25 cc. of water by rising five leaves that had been sprayed 

 at the usual strength (about 0.05 of 1 per cent nicotine). 



On the fourth day after the pear tree used in the experiments had 

 been sprayed, about a quart of the sprayed leaves were collected and 

 washed in water containing sodium carbonate, each leaf being washed 

 separately. Next the leaves were washed in running water for 5 

 minutes, and were finally ground and tested as described above. By 

 adding phosphomolybdic acid to the resulting distillate, a faint pre- 

 cipitate was obtained, but none by adding silicotungstic acid. On 

 the eighth day after the leaves had been sprayed, the test was re- 

 located, but .this time the leaves were washed for 10 minutes in running 

 water. Xo precipitate was observed in this test even by adding 

 phosphomolybdic acid. In each of the two foregoing tests the water 

 containing the sodium carbonate and foreign matter removed from 

 the leaves was distilled. Adding either acid to the resulting distillate 

 invariably produced a precipitate, but in none of the tests with 

 sprayed leaves did the distillate ever emit a nicotine odor. The 

 second experiment described above indicates either that the spray 

 solution did not pass into the leaves or that the amount of nicotine 

 still held by them was too small to be detected by the method em- 

 ployed. The following results will substantiate the former view : 



A small quantity of nicotine-sulphate solution (1:800) containing 

 fish-oil soap (2 pounds to 100 gallons of water) was colored with car- 

 mine acid (Griibler's Carminsaur) and an equal quantity with 

 indigo carmine (sodium sulphindigotate). Several leaves on a pear 

 tree were sprayed with each of the colored solutions, and two entire 

 detached leaves were submerged in each solution for 15 minutes ; the 



