Dec. 13.19 is 
Effect of Arsenic Applied as a Spray for Weeds 
461 
The columns headed “Not irrigated" show the percentage of arsenic 
in the soil at the given depth in the lysimeters which were protected 
from rain and which received no irrigation. The columns headed 
“Irrigated" show the percentage of arsenic in the soil at the given 
depth in the lysimeters which were subjected to irrigation. A com¬ 
parison of the two columns for each soil will show the strong fixing 
power of these soils for arsenic, the influence of different soil types upon 
the fixation, and the danger of its accumulation. Samples of soil No. 3 
were taken at depths different from those of soils Nos. 1 and 2, as shown 
in Table I, because of the concentration of arsenic at the surface in the 
former. 
In order to determine how nearly these results represent actual field 
conditions, samples of soil were obtained from a plantation at Nahiku, 
Maui, which was the first to adopt the use of sodium arsenite as a means 
of weed control. Weeds on this land have been sprayed for five years, 
at the rate of three applications per year, using 5 pounds of arsenic 
(As^g) per acre for one application. During this time the soil has 
received no cultivation whatever and the rainfall averages about 200 
inches per year. The soil is very porous and there is very little run-off 
water. Samples were taken at three depths: Every 4 inches of the 
first foot. The surface 4 inches contained 0.00924 per cent of arsenic 
(As 2 0 3 ), and none was present below this depth. A determination made 
by boiling the soil with water showed an arsenic content of 0.00006 per 
cent, or 0.6 p. p. m., soluble in water. That the arsenic fixed by soils in 
the lysimeters was partly soluble in water indicates that the fixation is 
due in part to physical influences. 
CHEMICAL REACTIONS INVOLVED IN THE FIXATION 
The composition of the spray as prepared by recommended methods 
may be either a solution of the acid salt (Na3O.2AS2O3.2H2O) or the 
neutral salt (Na^O.ASjOg), depending on the proportions of soda (either 
hydrate or bicarbonate) and arsenious acid used. 
H 2 0 +2NaOH+2 As 2 0 3 =Na 2 0 .2 As 2 0 3 .2H 2 0. 
H 2 0 +2 NaOH+As20 3 == Na 2 0 . As 2 0 3 .2 H 2 0 . 
For the following experiments in studying the replacement phenomena, 
a solution of the neutral salt was used. 
One liter of a 1 per cent solution of sodium arsenite was allowed to 
act upon 200 gm. of soil, with occasional shaking, for two weeks. Checks 
were also maintained with 200 gm. of soil and 1 liter of water. The 
arsenic extract was then separated from the soil and a partial analysis 
made to determine the elements with wjiich the sodium arsenite is most 
active. The results are given in Table II, which shows the composition 
of a 1 per cent sodium-arsenite solution after contact with the soil, as 
compared with the solvent action of water. The percentage of humus 
