If you want to determine the actual salicylate concentration for a sample that gives you a darker color than the highest standard, you would need to make a dilution of it. If you dilute it by mixing .25 mL of sample with .75 mL of water and then find that this mixture has a salicylate concentration of .4 mg/mL, what is the concentration of the unknown substance?

Wouldn't that be 0.4mg/mL x (1.00/0.25) = ?