SPECIFICATIONS FOR BITUMINOUS EOAD MATERIALS. 53 



bitumen, and organic and inorganic matter insoluble, on the basis of tbe weight 

 of material taken for analysis. 



This method is quite satisfactory for straight oil and tar products, but where 

 certain natural asphalts are present it will be found practically impossible to 

 retain all of the finely divided mineral matter on an asbestos felt. It is, there- 

 fore, generally more accurate to obtain the result for total mineral matter by 

 direct ignition of a 1-gram sample in a platinum crucible. The total bitumen is 

 then determined by deducting from 100 per cent the sum of the percentages of 

 total mineral matter and organic matter insoluble. If the presence of a car- 

 bonate mineral is suspected, the percentage of mineral matter may be most 

 accurately obtained by treating the ash from the fixed carbon determination 

 with a few drops of ammonium carbonate solution, drying at 100° C, then 

 heating for a few minutes at a dull red heat, cooling, and weighing again. 



When difficulty in filtering is experienced — for instance, when Trinidad asphalt 

 is present in any amount — a period of longer subsidence than 1.5 minutes is 

 necessary, and the following method proposed by the Committee on Standard 

 Tests for Road Materials of the American Society of Testing Materials is 

 recommended : ^ 



From 2 to 15 grams (depending on the richness in bitumen of the substance) 

 is weighed into a 150-cubic centimeter Erlenmyer flask, the tare of which has 

 been previously assertained, and treated with 100 cubic centimeters of carbon 

 disulphide. The flask is then loosely corked and shaken from time to time 

 until practically all large particles of the material have been broken up, when 

 it is set aside and not disturbed for 48 hours. The solution is then decanted 

 off into a similar flask that has been previously Aveighed, as much of the sol- 

 vent being poured off as possible without disturbing the 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 48 hours. 



At the end of this time the contents of the two flasks are carefiilly decanted 

 off upon a weighed Gooch crucible fitted with an asbestos filter, the contents of 

 the second fiask being passed through the filter first. The asbestos filter shall 

 be made of ignited long-fiber amphibole, packed in the bottom of a Gooch cru- 

 sible to the depth of not over one-eighth of an inch. After passing the con- 

 tents 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 continued 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. 



BITUMEN INSOLUBLE IN NAPHTHA. 



[Bulletin 314, p. 28.] 



GOOCH CKTJCIBLE METHOD. 



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

 determination, except that 100 cubic centimeters of 86° to 88° B. paraffin 

 naphtha, at least 85 per cent distilling between 35° C. and 65° G., is employed 

 as a solvent instead of carbon disulphide. Considerable difficulty is sometimes 



1 Proc. Am. Soc. for Testing Materials, 1909, Vol. IX, p. 221. 



