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Calculating a Percent Solutions with a Liquid Formulation
To prepare a percent solution using liquid formulations, you need to know the volume of the spray tank, the weight of the active ingredient (a.i.) per gallon of formulation and the weight of a gallon of water. The weight of water is a constant, being approximately 8.34 pounds. Assume you have measured the volume of the spray tank and find that it holds 100 gallons of water. You are given a recommendation to apply a 1% solution of glyphosate for control of aquatic weeds, using a high pressure sprayer with a handheld spray nozzle. The formulation of glyphosate that you are to use contains 5.4 pounds of active ingredient per gallon.
- Find the total weight of the liquid in the filled tank by multiplying 100 gallons by 8.34 pounds per gallon:
100 gal x 8.34 lb/gal = 834 lb.s - Multiply this weight by 0.01 (1%) to determine the weight of a.i. required to mix a 1% solution:
834 x 0.01 = 8.34 lb.s - Divide the required weight of a.i. by the weight of a.i. in the formulation. The result is the number of gallons of liquid formulation that should by added to 100 gallons of water to achieve a 1% solution:
8.34 lb a.i. / 5.4 lb a.i. per gal = 1.54 gal formulation
In this example, one tank of liquid should contain 1.54 gallons of glyphosate formulation. The total volume of water combined with the glyphosate formulation should equal 100 gallons, the capacity of tank. You would therefore use 98.46 gallons of water and 1.54 gallons of formulated glyphosate.
Calculating the Percent Active in Dilutions
Sometimes it is necessary to know what percentage of active ingredients is in a dilution. To calculate this you need to know the volume of the spray tank, the weight of active ingredient per gallon of formulation, the weight of a gallon of water, and the number of ounzes in a gallon. The weight of water is a constant, being approximately 8.34 pounds.
Assume your spray tank measures 50 gallons. You are asked to determine the percent active in a dilution containing 30 ounzes of Malathion 57E in 50 gallons of water. Malathion 57E contains 5 pounds of active ingredient per gallon.
- Find how much active ingredient you have by dividing the 30 ounces into 1 gallon and multiplying by 5 lb.s per gallon.
30 oz x 5 lb per gal / 128 oz per gallon = 1.17 pounds active - Find the percentage of your active ingredient by dividing 1.17 lb.s by 50 gallons of water and then dividing further by the weight of water, 8.34 pounds per gallon.
1.17 lb.s / (50 gal x 8.34 lb.s) = 0.0028 = 0.28%
In this example, a dilution of 30 ounces Malthion 57E in 50 gallons of water will contain 0.28% Malathion.
