502 
Journal of Agricultural Research 
VoL XXIV, No. 6 
ARSENICAL COMPOUNDS USED AS INSECTICIDES 
As some of the confusion on the subject of arsenical injury can be 
explained by a study of the processes of manufacture resulting in some¬ 
what different compounds being sold under the same name, a brief 
review of these processes will be in order. It will also be necessary to 
discuss briefly the use of the more important arsenical insecticides that 
the significance of the work that follows may be evident. 
ARSENIC TRIOXID 
PREPARATION 
Arsenic trioxid is obtained in large quantities as a by-product in roast¬ 
ing arsenical ores. This is not pure, but contains some metallic arsenic, 
arsenic sulphid, dirt, etc., from which it is purified by resublimation. 
There are two forms of the trioxid known, the amorphous and the crys¬ 
talline. ; The amorphous changes slowly into the crystalline form under 
some conditions. At 25° C. the amorphous form is soluble in about 30 
parts of cold water, while the crystalline requires about 100 parts. Both 
are slowly but completely soluble in about 15 parts of boiling water. 
The above proportions are approximate, as there seems to be a lack of 
agreement in the statements of various writers in regard to the solu¬ 
bility of the oxid. The name “arsenious acid,*' by which it is often 
referred, is a misnomer, since the oxid is an acid anhydride and has no 
acid properties until it unites with water, when arsenious acid is formed. 
In all probability the caustic effect of arsenic trioxid on vegetation is 
due to its combining with water and forming arsenious acid. Therefore 
the injury is proportional to the amount of arsenious acid formed and 
not to the amount of arsenic oxid in suspension. 
USE AS AN INSECTICIDE 
According to Bourcart ( j , p. 95)^ the first trials of using arsenic trioxid 
for spraying were conducted in America in 1867, when Markham used it 
to combat 3 ie Colorado potato beetle. On account of the serious injury 
occurring when it was used, other less soluble arsenical compounds were 
substituted until at the present time the oxid is used almost exclusively 
in the preparation of poison baits, and as a constituent in the prepara¬ 
tion of some of the more usable arsenical compounds. 
CALCIUM ARSENITE 
Arsenite of lime was probably first recommended as an insecticide by 
Kilgore (14). He recommended that it be made by boiling together for 
one-half hour, in 2 to 5 gallons of water, white arsenic i pound, lime 2 
pounds, and diluting the required volume to, say, 100 gallons. It is 
desirable that the lime should be present in the boiling solution of white 
arsenic, since it renders the latter insoluble as fast as it goes into solution, 
thus reducing the volume of water and shortening the time for obtaining 
the arsenite. Calcium arsenite is not manufactured for an insecticide, 
but many cases of foliage injury have been reported from its use, showing 
that it is more or less dangerous to use, and for this reason is not gen¬ 
erally recommended. 
* Reference is made by number (italic) to “ Literature cited,” pp . 53S“S37* 
