FLASH POINT When oils are heated to a sufficiently high temperature, vapors are driven off which are inflammable and which create the danger of explosion. The temperature at which the oil gives off suffi cient vapor to form a momentary flash when a small flame is brought near the surface of the oil is called the "flash point." The flash point is determined by heating the oil in a suitable device and testing with a lighted taper or with a spark. There are two types of flash testers, the open-cup and the closed-cup. There are many makes of both types on the market. The most common closed-cup testers are the New York State, the Pensky-Martens and the Abel, and the most common open-cup testers are the Tagliabue and the Cleveland. Figure 8 shows the Tagliabue closed-cup testers which may be operated with either gas or oil to supply the ignition flame. The method of testing with the standard "Tag". closed-cup tester as outlined by the American Society for Testing Materials, Tentative Standards 1917, pages 445-6 are as follows: The test must be performed in a dim light so as to see the flash plainly. Surround the tester on three sides with an in closure to keep away drafts. A shield about 18 inches square and 2 feet high, open in front, is satisfactory. See that tester firmly and level. For accuracy: the flash point thermometers which are especially designed for the instrument should be used as the position of the bulb of the thermometer in the oil cup is essential. Put the water-bath thermometer in place.' Place a receptacle under the overflow spout to catch the overflow. Fill the water bath with wafer at such a temperature that when test ing is started, the temperature of the water bath will be at least 10° C. below the probable flash point of the oil to be tested. Put the .oil cup in place in the water bath. Measure 50 c.c. of the oil to be tested in a pipet or a graduate and place in oil cup. The temperature of the oil must be at least 10° C. below its probable flash point when testing is started. Destroy any bubbles on the surface of the oil. Put on cover with flash point thermometers
in place and gas tube attached. Light pilot light on cover and adjust flame to size of the small white bead on cover. Light and place the heating lamp, filled with alcohol, in base of tester and see that it is centrally located. Adjust flame of alcohol lamp so that temperature Of oil in cup rises at the rate of about 1° C. (1.8° F.) per minute or not faster than 1° C. (1.8° F.) nor slower than 0.9° C. (1.6° F.) per minute. Record the "time of applying the heating lamp," record the "temperature of the water bath at start," record the "temperature of the oil sample at start." When the temperature of the oil reaches about 5° C. below the probable flash point of the oil, turn the knob on the cover so as to introduce the test flame into the cup and turn it promptly back again. Do not let it snap back. The time consumed in turning the knob down and back should be about one full second, or the time re quired to pronounce distinctly the words "one thousand and one." Record the "time of making the first introduction of the test flame" and record the "temperature of the oil sample at time of first test." Repeat the application of the test flame at every 0.5° C. rise in temperature of the oil until there is a flash of the oil within the cup. Do not be misled by an enlargement of the test flame or halo around it when entered into the cup or by slight flickering of the flame; the true flash consumes the gas in the top of the cup and causes a very slight pqff. Record the "time at which the flash point is reached," and the "flash point." If the rise in temperature of the oil from the "time of making the first introduction of the test flame" to the "time at which the flash point- is reached" was faster than 1.1° C. or slower than 0.9° C. per minute, the test should be questioned and alcohol heating lamp adjusted so as to correct the rate of heating. It will be found that the wick of this lamp can be so accurately adjusted as to give a uniform rate of rise in temperature of 1° C per min ute and remain so.