The flash point of oils is determined in two ways - by the " open test" and by the " close test." By the first method a small porcelain or metal dish is partly filled with the oil and placed on a sand bath heated by a burner; a thermometer suspended with the bulb in the oil registers the temperature. As the temperature rises a, lighted taper is quickly passed over the surface of the oil, and when a faint vanishing flame is noticed, the temperature is rend off; this is the flash point. For the close test method the apparatus devised by Prof. Abel is employed; this is fully described in the Petroleum Act of 18711. The apparatus is really a jacketed copper water-bath heated by a burner; the oil is contained in a small cup fitting into the lid of the bath, and there are thermometers in the bath and oil cup. The oil cup is covered with a lid and a slide, and hinged to it is a small spirit lamp. When the slide is drawn out the spirit lamp istilted over the oil cup so that the flame is right over one of the holes in the lid, and on replacing the slide the lamp a sumes its vertical position again.

The testing is done by drawing the slide, which brings the spirit lamp in contact with the vapour from the oil cup; when flashing occurs the temperature is noted on the thermometer immersed in the oil. Water is used in the bath for oils which flash below 100° C. (212° F.), but for oils which flash above that temperature mercury must be employed.