tinge

Though a ſingle grain of copper diſſolved in upwards of twenty gallons of clear water may be detected by a viſible blue tinge appearing on the addition of a few drops of volatile alcali, yet this is by no means the caſe in turbid high-coloured liquors, … Hence the neceſſity of diluting ſuch liquors in varying the experiments. In no inſtance did the blue tinge appear with the alcalis, even after the wine was diluted, and yet its abſence does not prove the liquor to be abſolutely free from an impregnation of copper.

https://books.google.com/books?id=9rpMo4As8z8C&pg=PA51 page 51 The following are the results of experiments made with rhubarb, to ascertain the best modes of detecting it in the urine and blood, and the time it takes to pass from the stomach to the urinary bladder. … https://books.google.com/books?id=9rpMo4As8z8C&pg=PA52 page 52 In 17 minutes, half an ounce of urine was voided, which when tested had a light tinge. In 30 minutes another half ounce was made, in which the tinge was stronger; and in 41 minutes a third half ounce was made, in which it was very deep. In an hour and ten minutes 7 ounces were voided, in which the tinge of rhubarb was very weak, and in two hours twelve ounces were voided, in which it was hardly perceptible.