Repeat Tests—It is not necessary to turn off the test flame with the small regulating valve on the cover, but leave it adjusted to give the proper size of flame. Having completed the prelim inary test, remove the heating lamp, lift up the oil cup cover and wipe off the thermometer bulb. Lift out the oil cup and empty and carefully wipe it. Throw away all oil samples atter once using in making test. Pour cold water into the water bath, allow ing it to overflow into the receptacle until the temperature of the water in the bath is lowered to 8° C. below the flash point of the oil as shown by the previous test. With cold water of nearly constant temperature it will be found that a uniform amount will be required to reduce the temperature of the water bath to the required point. Place the oil cup back in the bath and measure into it a 50 cc charge of fresh oil. Destroy any bubbles on the surface of the oil, put on the cover with its thermometer, put in the heating lamp, record time and temperature of oil and water and proceed to repeat test as described above. Introduce test flame for first time at a temperature of 5° C. below flash point obtained on the previous test.
Precautions.--Be sure to record ,barometric pressure either from laboratory barometer or from nearest Weather Bureau Sta tion. Record temperature of room. Note and record any flicker ing of the test flame or slight preliminary flashes when the test flame is introduced into the cup before the proper flash occurs. Record time and temperature of such flickers or slight flashes if they occur.
With the Cleveland open-cup tester, the oil is poured into the oil cup within 5 mm. of the top. The flame is then applied to the air bath in such manner that the temperature of the oil in the cup is raised at the rate of 5° C. per minute. The testing flame is made from a piece of drawn glass tubing, making a flame about 5 mm. in length. This flame is applied to the surface of the oil every half minute. distinct flicker or flash over the entire surface of the oil shows that the flash point is reached and the temperature at this time is recorded.
Table 8 gives figures for the conversion of barometric pres sure in centimeters to inchesa and Table 9 gives corrections of the flash point for normal barometric pressure.a