36 BULLETIN 314, U. S. DEPARTMENT OF AGRICULTURE. 
heavier hydrocarbons more readily than those of lower specific gray- 
ity. As the main object of this test is to separate the heavier hydro- 
carbons of an asphaltic nature from the paraffin hydrocarbons, a 
paraiiin solvent should be employed, and for ordimary purposes a 
paraffin naphtha of 86° to 88° B. as described Has been found to be 
readily obtamable and fairly satisfactory. 
The determination is also frequently made with heavier naphthas, 
such as 66° B. and 72° B., for the purpose of grading the character 
of the bitumen present in the compound. A report should therefore 
always distmctly state the gravity and character of the solvent used. 
DETERMINATION OF BITUMEN INSOLUBLE IN CARBON TETRACHLORIDE. 
EQUIPMENT. 
The apparatus is the same as for bitumen soluble in carbon disulphide. 
METEOD. 
This determination is conducted in exactly the same manner as 
described under “‘ Determination of bitumen soluble in carbon disul- 
phide,’”’ usmg 100 cubic centimeters of chemically pure carbon 
tetrachloride in place of carbon disulphide. 
The percentage of bitumen imsoluble is reported upon the basis 
of total bitumen taken as 100, as described under “‘ Determination of 
bitumen insoluble in paraffin naphtha.” 
USE OF DETERMINATIGN GF BITUMEN INSOLUBLE IN CARBON TETRACHLORIDE. 
The bitumen insoluble in carbon tetrachloride, but soluble in car- 
bon disulphide, is commonly known as “carbenes.” The test is 
occasionally made on petroleums, asphalts, and other solid native 
bitumens and their products, for the purpose of identification, or 
when there is any reason to suspect that the material under exami- 
nation has been injured by overheating durmg the process of manu- 
facture. 
DETERMINATION OF FIXED CARBON. 
EQUIPMENT. 
1 iron ring support (ring 7.5 cm. in diameter). 
1 platinum or nichrome triangle. 
1 Bunsen burner and rubber tubing. ; 
1 platinum crucible with a tight-fitting cover (weight complete, from 20 to 30 grams). 
1 crucible tongs. 
1 desiccator with calcium chloride. 
J analytical balance, capacity 100 grams, sensitive to 0.1 milligram. 
METHOD. 
This determination is made in accordance with the method de- 
scribed for coal in the Journal of the American Chemical Society, 
