12 
Colorado Experiment Station 
anticipate, i. e., that the soils of orchards which have been sprayed for 
some years are already rich in arsenic. 
Some of This Arsenic is Soluble in Water. 
In the application of the sprays it was soon found that the ar¬ 
senic must be insoluble or it would burn the foliage of the trees and 
in order to avoid this an endeavor was made to obtain a compound 
so insoluble that this effect would be avoided. To this end lime was 
added to the Paris green, and the lime, sal soda and arsenic prepara¬ 
tion recommended. I do not know whether any consideration of the 
final effect of the arsenic on the tree was considered or not. The 
insolubility of the spray material is the only protection that our trees 
have had. The term insolubility as here used means nothing more 
than difficultly soluble and that in a somewhat popular conception of 
the term. The spray materials used are somewhat soluble in pure 
water and much more readily so in solutions of sulfate and chlorid 
of soda. The Kedzie formula was supposed to remove the whole of the 
arsenic from the solution because of great excess of caustic lime, 
but this is readily changed into a neutral salt, the carbonate, when its 
protective action is practically destroyed, besides there remains a 
considerable amount of arsenic in solution owing to the solubility of 
the lime salt. Paris green to which the proper amount of lime 
has been added yields arsenic rapidly to water, and arsenate of lead, 
Pb 3 (As 04 ) 2 , will yield 0.3% of its dry weight of arsenic acid. Soil, 
therefore, which contains these spray materials ought to yield arsenic 
to pure water and it does. I at first assumed that the presence of so 
much carbonate of lime, as is present in our soils, would wholly pre¬ 
vent any arsenic from going into solution, but this is not the case. 
Another agent which I thought would also tend to prevent the solution 
of arsenic is the iron which is fairly abundant in our soils, especially 
our red soils. A very large number of our soils are marly, namely, 
contain more than 5% of calcic carbonate, but neither the lime 
nor the iron nor both together prevent the solution of arsenic in our 
soils. This is an easily established fact. Sixteen samples of orchard 
soils from various parts of the state have been tested and found to 
carry very decided quantities of arsenic which is soluble in water. 
[ have weighed the arsenic in a few instances and obtained the follow¬ 
ing figures: 0.68, 0.68, 0.84, 1.04, 1.166, 1.265, an d 1.345 parts of 
arsenic acid per million of soil. These quantities corroborated by 
those obtained with nine other samples are conclusive in regard 
to the presence of water soluble arsenic in the soil in very decided 
quantities and that, too, in quantities which competent experimenters 
have found to be injurious to vegetation when present in nutrient solu¬ 
tions. 
When I wrote Bulletin 131 I feared that the presence of water 
soluble arsenic in our soils might be largely due to the presence of 
sodic sulfate and sodic chlorid. That these salts are present in our soils 
in larger quantities than in eastern soils is a well known fact. It has 
