3872 The Principles of Fruit-growing. 
called for by the formula.—The sulfate of copper may 
be put into solution and kept in this condition in- 
definitely, ready for use. A simple method is to 
dissolve forty or fifty pounds of sulfate in as many 
gallons of water, pulverizing the material and hang- 
ing it in a eoffee-sack in the top of the barrel. 
A gallon of water, therefore, means a pound of 
sulfate. The lime may also be slaked and kept in 
readiness for use. Slake it into the creamy condi- 
tion familiar to masons, cover lightly with water, 
and then close the box or vessel to prevent the 
water from evaporating. When making the Bordeaux 
mixture, pour the requisite quantity of the stock 
solution of sulfate of copper into the barrel, and 
then dilute with four or five times the quantity of 
water. Now add the lime, and then add enough 
water to satisfy the formula. If the ferrocyanide 
test is used, place a spoonful of the mixture in a 
saucer or plate, and add a drop of the test olu- 
tion. If a red color appears, the mixture needs 
more lime. If the test solution is added° directly 
to a tank or barrel of the mixture, the color re- 
action is apt to be lost in the mass. An excess 
of lime ensures the safety of the mixture. 
10. How can one tell if soluble arsenic is present 
in Paris green?—It is the soluble arsenic which 
burns the foliage. This is present in London pur- 
ple, but good Paris green should have little of it. 
Farmers are always asking how they can determine 
if Paris green contains soluble arsenic. This may 
be determined by the use of the sulfur test. This 
