£16 
is unable to prove the date. Dr. C.V. Riley,* in Missouri, and Mr. George 
Liddel,t of Fairplay, Wis., both used Paris green for the destruction of 
the potato-beetle in 1868. 
White arsenic seems first to have been used mostly in soluble form. 
In the report of the Entomologist (Report of the U.S. Department of 
Agriculture for 1884, p. 327) Dr. Riley speaks of arsenic being used as 
an insecticide in 1871, and we find no account of its use prior to that 
date. 
London purple, so far as we can learn, was first put to practical use 
by Dr. Riley for the destruction of the Cotton Worm in 1878. 
COMPOSITIONS AND PROPERTIES OF THE ARSENITES. 
Arsenious acid (or arsenious oxide), As,O3, is the active principle in 
the arsenical combinations used as insecticides. Commercial white 
arsenic is practically pure arsenious acid. It is entirely soluble in ten 
parts of boiling or one hundred parts of cold water and has a specifi¢ 
eravity of 3.7. It is cheaper than either London purple or Paris 
ereen, and as it contains the active principle (As,O3;) in larger propor- 
tion than either of these substances, it would, at first, seem reasonable 
that it should be most used as an insecticide, but it is not, and for 
several reasons probably never will be. Its white color is objectionable, 
rendering it liable to be mistaken for materials used in cookery, The 
powder mixes with much difficulty with water, and when mixed settles 
quickly on account of its high specific gravity. When in solution it 
is so extremely injurious to foliage that it is not safe to use for the 
destruction of insects. 
It is readily mixed, however, in a small amount of soapy or lime water 
and, on account of being least§ injurious of the arsenites when freshly 
mixed in water and applied, it is specially adapted for use upon tender 
plants. As it is only the dissolved arsenic in water that does injury to 
foliage, and as white arsenic is waclly,and London purple and Paris 
green but partially soluble in water, it seems strange at first thought 
that the pure arsenic should be least injurious. The reason evidently 
lies in the fact that white arsenic passes into solution much more 
slowly than the soluble arsenic in either London purple or Paris green. 
From the experiments of B. W. Kilgore (published in Bull. 77), North 
Carolina Experiment Station, p. 6,) we find that one pound each of arse- 
nic, Paris green, and London purple in a gallon of water had arsenic 
in solution at the end of one hour as follows: the arsenic mixture .053 
erams, Paris green mixture .057 grams, and the London purple mixture 
17 grams. At the end of ten days the arsenic mixture had seven — 
times as much arsenic in solution as the London purple and fifty times — 
* INSECT LIFE, vol. v, p. 44. 
tRept. of Ent. U. S. Dept. of Agr., 1884, p. 327. 
t Bull. 10, Iowa Exp. Sta., p.404; Bull. 14, Ark. Exp. Sta., p.5. 
§ Bull. 2, lowa Exp. Sta., p.30; Bull. 10, lowa Exp. Sta., p. 413. 
