8 BULLETIN 866, U. S. DEPARTMENT OF AGRICULTURE. 
To prepare Pickering (C) sprays containing in the finished spray 
the equivalent of — 
0.36 per cent copper sulphate: Mix enough of the stock solution of copper sulphate 
to obtain 1 pound. 8 ounces of crystallized copper sulphate ^rith 38.98 U. S. gallons 
of the stock Iimewater.. and make up the total volume to 50 U. S. gallons. 
0.23 per cent copper sulphate: Mix enough of the stock solution of copper sulphate 
to obtain 15.3 ounces of crystallized copper sulphate with 18.52 U. S. gallons of the 
stock Iimewater, and make up the total volume to 50 U. S. gallons. 
0.115 per cent copper sulphate: Mix enough of the stock solution of copper sulphate 
to obtain 7.7 ounces of crystallized copper sulphate with 9.26 U. S. gallons of the stock 
Iimewater, and make up the total volume to 50 U. S. gallons. 
Samples of water used in the various localities for the preparation 
of Pickering and Bordeaux sprays, analyzed by the Water Laboratory 
of the Bureau of Chemistry, contained very little lime or any other 
constituent that might interfere with the preparation of sprays, 
such as the Pickering sprays, which are made according to definite 
formulas and are said to depend for their activity on the presence of 
definite compounds, the basic sulphates of copper. According to 
the tests of Bedford and Pickering (3, 4), slight variations in the 
amounts of iimewater employed result in the formation of different 
basic sulphates of copper, each of which functions as a fungicide in 
a characteristic way. 
In slaking lime it is important to add just enough water to make 
it heat, after which water is added slowly to keep the lime from 
burning. When the reaction nears completion more water is added 
to make a paste. Finally, when the total amount of water required 
has been added, the solution is stirred to form saturated Iimewater. 
RESULTS OF INVESTIGATION. 
POTATOES. 
Blight Control and Yield, 
pickering axd standard bordeaux sprays in 1916. 
Six acres of Green Mountain potatoes in northern Maine (near the 
Aroostook Farm at Presque Isle) were selected for these experiments. 
As the sprayer was made to spray four rows at a time, the field was 
divided into four-row plats which, in turn, were subdivided into 
200-foot lengths. Since the field was 800 feet long, four subdivisions 
were made in each group of four rows. A certain spray was applied 
to the first and third 200-foot plats, another one to the second and 
fourth 200-foot plats, etc. Thus each spray was applied to one plat 
in the front and to one in the rear of the field. The plats were so 
arranged that each four-row plat where any particular spray was 
being tested had a four-row plat of Bordeaux-sprayed potatoes on 
one side and a four-row check plat on the other. 
Seven Pickering sprays were tested. Four (those used on plats 
1, 2, 3, and 4) were made according to Formula A. while three (those 
