40 BULLETIN 949, U. S. DEPARTMENT OF AGRICULTURE. 



residue. The first flask is again treated with fresh carbon disulphide and shaken as 

 before, when it is put away with the second flask and not disturbed for 4S hours. 



At the end of this time the contents of the two flasks are carefully decanted off 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, packed 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 decanted off upon the filter. This washing is con- 

 tinued until the filtrate or washings are practically colorless, 



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 obtained 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. 



21. DETERMINATION OF BITUMEN INSOLUBLE IN CARBON TETRA- 



CHLORIDE. 



This determination is conducted in exactly the same manner as described under 

 ' ' Determination of bitumen soluble in carbon disulphide, ' ' using 100 c. c. of chemically 

 pure carbon tetrachloride as a solvent in place of carbon disulphide. 



The percentage of bitumen insoluble is reported upon the basis of total bitumen 

 taken as 100, as described under "Determination of bitumen insoluble in paraffin 

 naphtha.'' 



22. DETERMINATION OF BITUMEN INSOLUBLE IN PARAFFIN NAPHTHA. 



This determination is made in the same general manner as the total bitumen 

 determination, except that 100 c. c. of 86° to 88° B. paraffin naphtha, at least 85 per 

 cent distilling between 35° C. and 65° C, is employed as a solvent instead of carbon 

 disulphide. Considerable difficulty is sometimes experienced in breaking up some 

 of the heavy semisolid bitumens; the surface of the material is attacked, but it is 

 necessary to remove some of the insoluble matter in order to expose fresh material 

 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 balance of the 100 c. c. 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. 



In making the filtration the utmost care should be exercised to avoid Stirling up any 

 of the precipitate, in order that the filter may not be clogged and that the first decanta- 

 tion may be as complete 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 the precipitate too tightly. The material on the felt should never be 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 free from soluble matter, and the flask is dried with the crucible at 100° C. 



