ON I III: PERSISTENCE OF ARSENITE OF SODA IN 



THE SOIL. 



By Charles William Mally, M.Sc, F.L.S., F.E.S. 



{Read July 9, 191 8. J 



The possibility of arsenic accumulating to an injurious extent 

 in soil under fruit trees, through their being sprayed annually with 

 arsenical compounds has received considerable attention, espe- 

 cially in the United States of America; but in South Africa a new 

 phase of the question arose when it was proposed to use poisoned 

 bait containing arsenite of soda for the destruction of house flies 

 in stables and around manure heaps. Based on experience in 

 the use of arsenite of soda for the destruction of weeds and of 

 dodder in lucerne lands, certain farmers feared that the arsenic 

 in the bait might have an injurious effect in the soil. Even though 

 it might not be noticeable the first season, would it accumulate 

 sufficiently to become a serious factor in the future ? 



Amount of Arsenite in Baited Manure. 



To get direct evidence on this point it was decided to take 

 samples from baited manure heaps that had been accumulating 

 for about six months — the usual length of time before the mamn^e 

 is carted away and spread on the land — and determine the 

 amount of arsenic therein. 



The following sami)les were taken at the School of Agricul- 

 ture. Elsenburg, Mulders Vlei, Cape Province, and submitted to 

 Mr. D. C'. Crawford, chemist at the school, for analysis. The 

 manure had accumulated from the stable, where baiting was 

 carried on systematically, and hence there was a certain amount of 

 bait in the manure from that source. In addition to this, the 

 manure hea]) had been covered with eucalyptus branches and 

 sprinkled regularly with the following solution : — Arsenite of 

 soda. 1 II)., sugar 10 lbs., water 10 gallons. The leaves of the 

 branches would therefore carry an excessive amount of the 

 bait, and sample A was taken because of the accumulation of 

 leaves at that s]iot. so as to get some idea of the relative 

 importance of the leaves. This .should not be overlooked in 

 connection with the analysis of this sample. The following are 

 Mr. Crawford's results and his interpretation of them :— 



Sampi.ks of ,Maxi;re Tksteu for Arsenite. 



Sample A. — From depression on top of manure lieap. Surface dry, 

 strawy : certain amount of leaves included in the sample. 

 Sample 2A. — Taken from depth of 2 ft. 

 Sample .^A. — Taken from depth of t, ft. 6 in. 



Sample B. — Taken from top at edge of manure heap, dry and strawy. 

 Sample 2B. — Taken from depth of 2 ft. 

 Sample 3B. — Taken from dejith of 3 ft. 6 in. 



