Florida Agricultural Experiment Station


 Since mixtures containing free copper sulphate are liable to
cause burning, it is advisable to test them to determine whether
or not this copper salt has been completely neutralized by the
lime. One method of testing in the field is to place a new nail,
bright knife blade (not a stainless steel one), or other bright
piece of steel in the bordeaux mixture for a few minutes. If no
copper is deposited and the metal remains bright the test in-
dicates that the mixture is either neutral or alkaline and, there-
fore, safe to use.
 Another, and more reliable, test can be performed with a so-
lution of yellow prussiate of potash (potassium ferrocyanide).
A small bottle of a 10 percent solution of this poisonous salt can
be secured from a druggist. After stirring the bordeaux mixture
thoroughly, take out a sample in a clean glass or white cup and
add a drop of the testing solution. If the copper sulphate has
been neutralized, the test solution will remain a clear yellow
until it blends with the mixture. If free copper be present, how-
ever, the drop of the test solution will immediately turn to a
reddish-brown color when it strikes the mixture. The latter
reaction indicates that more milk of lime should be added to the
bordeaux mixture until the test solution fails to produce the
reddish-brown color.
 Bordeaux mixture should be used shortly after it is prepared,
since it deteriorates rapidly during warm weather. If delays
are unavoidable, the good qualities of the spray mixture may be
preserved temporarily by adding 1/ pound of sugar to each 100
gallons of the bordeaux mixture and agitating thoroughly.
 PRACTICAL FIELD METHODS OF PREPARING BORDEAUX
 MIXTURE FOR LARGE SPRAYING OPERATIONS
 For commercial spraying with modern power spraying outfits,
the following method of preparing the bordeaux mixture has been
found the simplest in field practice, since it eliminates the need
of dilution barrels. Start filling the tank with water and pour
in the required amount of stock bluestone solution and start the
agitator. When the tank is about three-fourths full, stir up
the stock milk of lime and pour the required amount slowly
through the tank screen. Shortly before the tank becomes full,
pour in the required amount of oil emulsion and, when the tank
is filled, the operator is ready to start spraying.
 A new method of preparing bordeaux mixture instantaneously