42 



BULLETIN 949, U. S. DEPARTMENT OF AGRICULTURE. 



Highly volatile and nonvolatile materials should not be subjected to this test at 

 the same time in the same oven owing to a tendency on the part of the latter to absorb 

 some of the volatile products of the former. 



24. FLASH AND BURNING POINT 

 TESTS. 



The open-cup oil tester consists of a brass 

 oil cup, a, (Fig. 20) of about 100 c. c. 

 capacity. The outer vessel, b, serves as 

 an air jacket. No glass cover is used in 

 the open-cup method. A suitable thermom- 

 eter, c, is suspended from the "wire support, 

 d, directly over the center of the cup so 

 that its bulb is entirely covered "with oil 

 but does not touch the bottom of the cup. 

 The testing flame is obtained from a jet of 

 gas passed through a piece of glass tubing, 

 and should be about 5 millimeters in length. 



The test is made by first filling the oil 

 cup with the material under examination to 

 within about 5 m. m. of the top. The Bun- 

 sen flame is then applied in such a manner 

 that the temperature of the material in the 

 cup is raised at the rate of 5° C. per minute. 

 From time to time the testing flame is 

 brought almost in contact with the surface 

 of the oil. A distinct flicker or flash over 

 the entire surface of the oil shows that the 

 flash point is reached and the temperature 

 at this point is taken. It will usually be 

 found that the flash point as determined 

 by the open-cup method is somewhat higher 

 than by the closed-cup method, for the same 

 material. 



The burning point of the material is ob- 

 tained by continuing the test and noting that 

 temperature at which it ignites and burns. 

 The flame should then be extinguished by 

 means of a metal cover supplied with the 

 instrument. 



'-•'i ■. 20. — Open-cup oil tester. 



