42 
BULLETIN 949, U. S. DEPARTMENT OE 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, 6, 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 nicker 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. 
? ig. 20. — Open-cup oil tester. 
