SOME EFFECTS OF SODIUM ARSENITE 3 
ber and sugar-cane plantations. One large sugar plantation alone 
has saved $100,000 on weeding through the introduction of the spray. 
Sal soda (2 pounds) and white arsenic (1 pound) were boiled to- 
gether and subsequently diluted with 1 gallon of water, 100 gallons 
of this solution being used per acre. Killing effects were manifest 
two to three hours after spraying. 
Gray (13, 14) tried a sodium- arsenite spray on wild morning- 
glories in California. He made a stock solution of 10 pounds of 
caustic soda (98 per cent) and 10 pounds of white arsenic (99 per 
cent) with water to make 5 gallons. A gallon of this was used to 
100 gallons of water, and 300 gallons were applied to the acre. From 
85 to 90 per cent of the morning-glory roots were killed to the depth 
of 4 feet or more when the spray was applied to mature vines at 
the proper time (October). The second paper by Gray (1919) 
reports a failure of the spray for root killing at reasonable expense. 
Hutcheson and Wolfe (31) in Virginia used one-half pound of 
sodium arsenite to 1 gallon of water for the control of hawkweed 
without injury to Kentucky blue-grass. The latter recovered much 
more quickly from the effects of arsenic than from salt. Burrows 
(10) found sodium arsenite useful in killing timber. He suggests 
the use of 1 pound of arsenic and 1 pound of washing soda or one- 
half pound of caustic soda to 4 gallons of water, and one-half pound 
of whiting for color. This he applied to the tree when dormant into 
frills cut entirely around the trunk. 
TOXIC AND STIMULATING EFFECTS ON PLANTS 
The extreme toxicity of arsenic to so many plants has indicated 
a possible danger from the too free use of sprays or weed killers 
which contain it, and considerable experimentation has been done 
to determine the effects of arsenic on the soil and on the germina- 
tion of seeds and growth of plants. Greaves has investigated the 
influence of arsenic upon the biological transformation of nitrogen 
in soils (15, 16), nitrogen-fixing power (17, 18), and bacterial activi- 
ties in the soil (19) . He found that water-soluble arsenic may exist 
in soils to the extent of 82 parts per million without stopping am- 
monification and nitrification processes. Lower concentrations 
stimulated these processes and higher concentrations were toxic. 
Na 3 As0 4 became toxic at concentrations of 40 parts per million, and 
at 250 parts per million nitrification was stopped entirely. PbAsO,. 
was not toxic at 400 parts per million. AsS ? . and ZnAs0 4 were only 
slightly toxic at the latter concentration. The greatest stimulation 
was noticed when the concentration of water-soluble arsenic in the 
soil was 10 parts per million. The bacterial activities of the soil 
were checked only with enormous quantities of arsenic. Small 
amounts stimulated soil bacteria and caused the liberation of insolu- 
ble plant-food materials, especially phosphorus. 
Headden (£7, 28) found that orchard trees were sometimes killed 
by arsenic used in sprays. He demonstrated that orchard soil where 
arsenic sprays had been used contained as much as 138 parts of 
arsenic per million. The contention that insoluble arsenic as used 
in sprays was the cause of killing orchard trees was questioned by 
Ball (3, 4)- He stated that collar-rot and alkali were the principal 
