32 THE HOP APHIS IX THE PACIFIC REGION. 
should supply at least two lines of hose at 120 to 150 pounds pressure 
and should be in such order that there will be few breakdowns or 
delays. Good work can be done with the hand pumps (see PI. VII, 
fig. 1), the gasoline power outfits (PL VIII, figs. 1, 2), the compressed- 
air sprayers, etc., provided they meet these requirements and are 
supplemented by an efficient mixing and supply system. 
The knapsack spraying machine (PL VII, fig. 2) may, under some 
circumstances, be of value for work on a very small scale, but is not 
at all practical in a commercial hopyarcl. 
BOILING AND MIXING PLANT. 
In designing a boiling and mixing plant for work on a large scale it 
is very desirable to arrange the tanks so that their filling and empty- 
ing is accomplished by gravity. 
The uppermost tanks should be used for steeping the materials and 
should be supplied with water from a hydrant; the lower ones 
should be filled by drawing from the upper ones, or, when diluting is 
necessary, from a hydrant. The lower tanks, however, should be 
high enough to drain into a supply wagon. 
DESCRIPTION OF TANKS. 
The boiling and mixing tanks at Independence, Oreg., were made 
of No. 18 galvanized iron, riveted and soldered together, a f-inch 
iron pipe forming a brace for the tops. Three braces of ,^-inch angle 
iron, placed 3 feet 4 inches apart and riveted to the sides of the tanks, 
together with a framework of 2 by 4 planks, prevented the tanks 
from bulging. 
ARRANGEMENT OF TANKS. 
The arrangement of tanks shown in Plate VI, figure 2, was found 
very satisfactory. Two boiling tanks 10 by 3 by 3 feet 9 inches, 
heated by steam, were placed upon a 10 by 12 platform, elevated 10 
feet from the ground. Passageways were left between and around 
the tanks. On a near-by but lower platform were three 375-gallon 
tanks for mixing and storage. A swinging outlet pipe drained the 
boiling tanks and directed the materials into any one of the three 
tanks. From the lower tanks the material was run through a long 
hose into the supply wagons. In order thoroughly to strain the 
materials the entrances of all the outlet pipes were screened with 
wire gauze and the ends of the hose were covered with cheesecloth. 
FIELD OPERATIONS. 
SUPPLY WAGONS. 
When extensive spraying operations are being carried on it is 
essential to have an adequate supply system. In an emergency a 
farm wagon containing barrels of spray (PL VIII, fig. 2) can be used, 
