Question

You are asked to make up 50 gallons of 0.5% toxaphene solution. How many pounds of a 25% wettable powder would you add to 50 gallons of water?

Answer 1

For dry formulations, active ingredient is measured in percentage active ingredient by weight of product. Wettable powders are finely divided (dust-like) solids that are easily suspended in water. ( Wettable powders (WP) are dry forms of insecticides in which the toxicant is absorbed or adsorbed on inert materials that can be mixed readily with water because a wetting agent has been added. )

25 % wettable powder : 25% of every pound of that product, or 0.25 pounds, is active ingredient:  

0.25 pounds A.I. /1 pound product

asked to make up 50 gallons of 0.5% toxaphene solution :

0.5 % = lb of formulation used × % of active ingredient / gallons of spray mixture x 8 (lb per gal water)

lb of formulation used × 25 /50 × 8= 0.5%

Thus, lb (pound) of formulation used = 8 pound ( toxaphene ).