I have been trying to recreate the derivation of the formula mg/L (or ppm) = lbs/gal x 120,000.
I know that the constant 120,000 comes from 1,000,000/8.33 (the weight of a gallon of water) but I can't make the constant come out in the numerator of the equation. I'm starting by saying one ppm = one pound in one million pounds or one gallon in a million gallons.
I'd like to see the proper derivation.