Oct. 27, 1923 
193 
Arsenical Injury to Plants 
About 1,300 cc. of dew obtained from mature cotton plants was col- 
lected. Duplicate analyses on 500 cc. portions gave the following 
results, expressed as parts per million: 
Total solids. 1, 023 
Silica (Si 0 2 ). 13 
Oxids of iron and aluminum (R 2 0 3 ). 17 
Sulphur trioxid (S 0 3 ). 26 
Chlorin (Cl)... i 9 
Calcium oxid (CaO). 529 
Magnesium oxid (MgO). 100 
Carbon dioxid (C0 2 ) (by titration). 618 
A small proportion of carbon dioxid (equivalent to 40 parts per million 
of calcium carbonate) was present as carbonate, all the rest being in the 
form of bicarbonate. No attempt was made to determine the alkali 
metals, but the agreement between the substances determined and the 
total solids indicates the presence of but little such material. 
Evidently the principal constituents are bicarbonates of calcium and 
magnesium. Whether these have come into the dew by osmosis or by 
actual exudation was not determined, the former being more probable. 
Hardness titrations were run on several other small collections of dew. 
All showed large quantities of bicarbonate and relatively small quantities 
of carbonate. The only other determination of total solids gave 960 
parts per million, which agrees closely with the results of the analysis of 
the first collection. This dew was used for a soluble arsenic determina¬ 
tion on a sample of calcium arsenate, showing with boiled distilled water 
0.08 per cent of soluble arsenic oxid. With the same dilutions and 
conditions, 8.7 per cent of arsenic oxid was dissolved by the dew. 
A properly made calcium arsenate, then, may undergo extensive decom¬ 
position after being applied to a plant. Of course, in interpreting the 
results of the laboratory experiments it must be remembered that the 
relative proportions of dust and liquid, as well as their degree of agita¬ 
tion, may largely influence the result. As the proportion of dust and 
liquid is a prime factor in determining the percentage of arsenic dissolved 
from calcium arsenate, an attempt was made to estimate it under field 
conditions. Freshly dusted plants were analyzed to determine the 
quantity of arsenic held by them, and the quantity of dew present was 
estimated. A normal dusting with a hand gun left about 0.4 gm. of 
calcium arsenate upon each plant used in the tests, and a dripping dew 
left between 100 and 200 cc. of moisture on each plant. This is equiva¬ 
lent to a concentration of from 2 to 4 gm. of arsenate per liter, as compared 
with 2 gm. per liter, used in the water-soluble arsenic determinations. 
As there must be an enormous variation in this concentration, these figures 
are merely approximate. 
The calcium arsenate used for the soluble arsenic determination with 
dew was part of a lot which had caused some damage tq cotton at Rose- 
dale, Miss., earlier in the season. No other sample was taken for com¬ 
parison, but numerous experiments were made, using tap water, which 
was very hard with calcium, magnesium, and ferrous bicarbonates, thus 
somewhat resembling the dew. Nine samples of calcium arsenate 9 
\vhich averaged 0.10 per cent water-soluble arsenic oxid with distilled 
water gave with tap water from 0.8 to 2.2 per cent, with an average of 
1.4 per cent of arsenic oxid. Eight samples from the stock which caused 
the trouble at Rosedale, averaging 0.11 per cent with distilled water, 
9 Representing the products of four manufacturers. 
