The Spraying op Trees. 579 



constituents. If soluble arsenic is placed on the soil it probably 

 almost immediately goes into insoluble combinations, and remains 

 where it was placed unless slightly washed down by mere mechani- 

 cal means. ]S"ow some plants appear to have the power to take up 

 every minute quantities of arsenic and still thrive — probably so 

 minute that the nicest chemical test can scarcely discover it*— but 

 any appreciable quantity of soluble arsenic in the soil quickly de- 

 stroys the roots. If, therefore, the grass and other plants under 

 sprayed trees continue to live, there need be no fear that the arsenic 

 will injure the soil. 



We have made some study of the movement of arsenic in the soil 

 during the past summer, and the results are here given. The 

 chemical work was done by G. W. Cavanaugh, assistant chemist to 

 the Experiment Station, the determination of arsenic being made 

 bv Marsh's test, which is known to chemists as one of the most 

 delicate means of detecting the poison. 



Experiment I. 



May 26th, 1895. Two ounces Paris green and four ounces lime 

 were mixed in one quart of water, and the liquid was poured into 

 a little hollow as large as a saucer in the bottom of a shallow furrow 

 in firm but rather sterile moist, sandy land. A sample of the same 

 Paris green was taken to the chemist and found to be of normal 

 strength, and to contain a little arsenic soluble in cold creek water. 

 On the night of the 26th nearly an inch (.87 in.) of rain fell, and 

 on the night of the 28th I poured a quart of creek water on the 

 area, covering it three inches deep. Samples of the underlying 

 soil were taken for analysis as follows : 



A. May 30th. Sample taken two inches below the surface of the 

 soil (that is, two inches underneath the stratum of poison). Three 

 most careful analyses were made and not a trace of arsenic was 

 found. 



B. June 6th. Sample taken two inches down, as before. In the 

 meantime a slight rain had fallen (.09 in.) and the weather was very 

 hot. Not a trace of arsenic was found. 



On October 7th, 1895, the soil was examined again. It had now 

 received a total rainfall of about twelve and a half inches (12.35 in.). 



* The student should consult Jiiger's ^' Uher die Wirkungen des Arseniks auf 

 Pflanzen." 



