SAMPLING AND TESTING HIGHWAY MATERIALS. 49 
treated with fresh carbon disulphide and shaken as before, when 
it is put away with the second flask and not disturbed for 48 
hours. 
8. At the end of this time the contents of the two flasks are 
carefully decanted oft' upon a weighed Gooch crucible fitted with 
an asbestos filter, the contents of the second flask being passed 
through the filter first. The asbestos filter shall be made of 
ignited long-fiber amphibole, parked in the bottom of a Gooch 
crucible to the depth of not over one-eighth of an inch. After 
passing the contents of both flasks through the filter, the two 
residues are shaken with more fresh carbon disulphide and set 
aside for 24 hours without disturbing, or until it is seen that a 
good subsidation has taken place, when the solvent is again de- 
canted off upon the filter. This washing is continued until the 
filtrates or washings are practically colorless. 
9. The crucible and both flasks are then dried at 125° C. and 
weighed. The filtrate containing the bitumen is evaporated, the 
bituminous residue burned, and the weight of the ash thus ob- 
tained added to that of the residue in the two flasks and the 
crucible. The sum of these weights deducted from the weight 
of substance taken gives the weight of bitumen extracted. 
Note. — This method for recovery of mineral material should also 
be used in case of asphalt topping and rock asphalt if analyzed as 
previously described. 
DETERMINATION OF BITUMEN INSOLUBLE IN CARBON 
TETRACHLORIDE. 
1. This determination is conducted in exactly the same manner 
as described under " Determination of bitumen soluble in carbon 
disulphide," using 100 cubic centimeters of chemically pure carbon 
tetrachloride as a solvent in place of carbon disulphide. 
2. The percentage of bitumen insoluble is reported upon the 
basis of total bitumen taken as 100, as described under " De- 
termination of bitumen insoluble in paraffin naphtha." 
DETERMINATION OF BITUMEN INSOLUBLE IN PARAFFIN 
NAPHTHA. 
1. This determination is made in the same general manner as 
the total bitumen determination, except that 100 cubic centimeters 
of 86° to 88° Bauine paraffin naphtha, at least 85 per cent dis- 
tilling between 35° and 65° C, is employed as a solvent instead 
of carbon disulphide. Considerable difficulty is sometimes ex- 
perienced in breaking up some of the heavy semisolid bitumens; 
the surface of the material is attacked, but it is necessary to re- 
move some of the insoluble matter in order to expose fresh ma- 
terial to the action of the solvent. It is, therefore, advisable to 
heat the sample after it is weighed, allowing it to cool in a thin 
layer around the lower part of the flask. If difficulty is still 
experienced in dissolving the material, a rounded glass rod will be 
found convenient for breaking up the undissolved particles. Not 
more than one-half of the total amount of naphtha required 
should be used until the sample is entirely broken up. The bal- 
ance of the 100 cubic centimeters is then added, and the flask 
is twirled a moment in order to mix the contents thoroughly, 
after which it is corked and set aside for 30 minutes. 
2. In making the filtration the utmost care should be exercised 
to avoid stirring up any of the precipitate, in order that the filter 
may not be clogged and that the first decantation may be as com- 
plete as possible. The sides of the flask should then be quickly 
washed down with naphtha and, when the crucible has drained, 
the bulk of insoluble matter is brought upon the felt Suction 
may be applied when the filtration by gravity almost ceases, but 
should be used sparingly, as it tends to clog the filter by packing 
67006°— 24 4 
