No Person shall sell any Arsenic unless the same be before the Sale thereof mixed with Soot or Indigo in the Proportion of One Ounce of Soot or Half an Ounce of Indigo at the least to One Pound of the Arsenic, and so in proportion for any greater or less Quantity: Provided always, that where such Arsenic is stated by the Purchaser to be required, not for Use in Agriculture, but for some other Purpose for which such Admixture would, according to the Representation of the Purchaser, render it unfit, such Arsenic may be sold without such Admixture in a Quantity of not less than Ten Pounds at any One Time.