Fill a tumbler full of water at 110° Fahr. Stir in a tablespoonful of the oil to be tested, and leave until the oil reaches about the same temperature. Pass a lighted match over the oil as it floats on the surface. If the oil does not ignite, it can be safely used; if it does, discard it, however cheap the price may be. Improved test proposed by Dr. Van der Weyde: Fill a narrow test-tube with the petroleum to be tested, close it with the finger, invert it, and plunge entirely in water of some 140° Fahr.; wait until the temperature has descended to 110°; if then any gas-bubbles are seen in the closed upper part of the test-tube the oil contains dangerous inflammable vapors. As all vapors of petroleum are inflammable, it is not necessary to ignite them; the demonstration of their presence in this way is sufficient to condemn such oil.