called stomach poisons. Sprays which
kill indirectly are used for insects which suck the sap or juice from
the tree or fruit and are called contact sprays. Arsenical compounds
have supplanted practically all other substances used to combat
external biting insects. Two stomach poisons are commonly used,
namely, arsenate of lead and paris green, but the former is rapidly
replacing the latter.

ARSENATE OF LEAD is prepared by mixing three parts of crystallized
arsenate of soda with seven parts of crystallized white sugar
(acetate) of lead in water, but it will not as a rule pay the grower
to mix his own material, as arsenate of lead can be purchased in
convenient commercial form at a reasonable price. The preparation on
the market is a finely pulverized precipitate in two forms, one a
powder and the other a paste. These are probably about equally good
and are readily kept suspended in water. Less free arsenic is
contained in this form than in any other compound of arsenic, making
it safer to use, especially in heavy applications. Arsenate of lead
may be used without danger of burning the foliage as strong as five or
six pounds to fifty gallons of water, but three pounds is the usual
and a sufficient amount for the control of any apple insect for which
it is efficacious.

PARIS GREEN is being rapidly displaced by arsenate of lead for several
reasons. It is a compound of white arsenic, copper oxide, and acetic
acid. The commercial form is a crystal which in suspension settles
rapidly, a serious fault. It is more soluble than arsenate of lead and
hence there is greater danger of burning the foliage with it.
Moreover, it costs from twenty to twenty-five cents a pound, and the
arsenate of lead can be purchased for from eight to ten cents a pound.

The amount which it is safe to use in fifty gallons of water is from
one-half to three-quarters of a pound. When paris green is used alone
as a poison lime should be added. Both these arsenicals should be
thoroughly wet up by stirring in a smaller receptacle before they are
put into the spray tank, in order to get them in as complete
suspension as possible. They may be used in the same mixture with
Bordeaux or lime sulphur.

CONTACT SPRAYS.--Four compounds are used as contact sprays in
combating sucking insects, namely, lime sulphur, soaps such as whale
oil soap, kerosene emulsion, and tobacco extract. Of these lime
sulphur is the most used and for winter spraying is probably th