50 BULLETIN 1216, U. S. DEPARTMENT OF AGRICULTURE. 
the precipitate too tightly. The material on the felt should never 
he allowed to run entirely dry until the washing is completed, as 
shown by the colorless filtrate. When considerable insoluble 
matter adheres to the flask no attempt should be made to remove 
it completely. In such cases the adhering material is merely 
washed until tree from soluble matter and the flask is dried with 
the crucible at 1<><>° O. for about one hour, alter which it is 
cooled and weighed. The percentage of bitumen insoluble is 
reported upon the basis of total bitumen taken as 100. 
.'!. The difference between the material insoluble in carbon 
disulphido and in the naphtha is the bitumen insoluble in the 
latter. Tims, if in a certain instance it is found that the ma- 
ferial insoluble in carbon disnlphide amounts to 1 per cent and 
that 10.9 per cent is insoluble in naphtha, the percentage of 
bitumen insoluble would be calculated as follows: 
Bitumen insoluble in naphtha_10.9— 1_9 I 9_ 
Total bitumen ~ " 100^1 ~ 99 ~~ 10 per cent ' 
TEST FOR LOSS ON HEATING OF OIL AND ASPHALTIC 
COMPOUNDS. 
(A. S. T. M. standard method, serial designation D 6-20, slightly modi- 
fied.) 
1. This test is used to determine the loss in weight (exclusive 
of water) of oil and asphaltic compounds when heated as here- 
inafter prescribed. The material under examination must there- 
fore first be tested for water, and If water is found to be present 
it must be removed by suitable methods of dehydration before the 
material is subjected to the loss-on-heating test, or another sam- 
ple obtained which is free from water. 
I. APPARATUS. 
Oven. 2. The oven may be either circular or rectangular in form and 
may be heated by either gas or electricity. Its interior dimen- 
sions shall be approximately as follows: Height, not less than 
40.04 centimeters (1(5 inches); width and depth or diameter, at 
least 5.08 centimeters (2 inches) greater than the diameter of 
the revolving shelf. 
It shall be well ventilated and shall be fitted with a window in 
the upper half of the door, so placed and of sufficient size to per- 
mit the accurate reading of the thermometer without opening the 
door. It shall also be provided with a perforated circular shelf, 
preferably of approximately 24.8 centimeters (0.75 inches) in 
diameter. This shelf shall be placed in the center of the oven and 
shall be suspended by a vertical shaft and provided with me- 
chanical means for rotating it at the rate of five or six revolu- 
tions per minute. It shall be provided with recesses equidistant 
from the central shaft in which the tins containing the samples 
are to be placed. 
Thermometer. 3. The thermometer shall be between 12.7 centimetres (5 
inches) and 15.24 centimeters (0 inches) in length, and the mer- 
cury bulb shall be from 10 to 15 millimeters ((I..".!) to 0.59 inch) 
iti length. The settle shall be engraved on the stem, shall be clear 
out and distinct, and shall run from 150° to 175° C. (302* to 
347° F.) in 1° C. divisions and shall commence substantially 3.81 
centimeters (13 inches) above the top of the bulb. Every fifth 
graduation shall be larger than the Intermediate ones and shall be 
numbered. The degrees shall be substantially 3.17 millimeters 
(one-eighth inch) apart. The thermometer shall be furnished 
with an expansion chamber at the top and have a ring for at- 
taching tags. It shall be made of a suitable quality of glass and 
shall be so annealed as not to change its readings under condi- 
tions of use. It shall be correct to 0.25° (\ (0.45° P., as deter- 
mined by comparison at full immersion with a similar thermom- 
