EXAMINATION OF BITUMINOUS EOAD MATERIALS. 29 



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 cubic centimeters is then added, 

 and the flask is twirled a moment in order to mix the contents thor- 

 oughly, after which it is corked and set aside for 30 minutes. 



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 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 mate- 

 rial is merely washed until free from soluble matter, and the flask is 

 dried with the crucible at 100° C. for about one hour, after which it 

 is cooled and weighed. The percentage of bitumen insoluble is re- 

 ported upon the basis of total bitumen taken as 100. 



The difference between the material insoluble in carbon disulphide 

 and in the naphtha is the bitumen insoluble in the latter. Thus, if 

 in a certain instance it is found that the material insoluble in carbon 

 disulphide 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 9.9 ,_ 

 lotal bitumen 100 — 1 99 L 



USE OF NAPHTHA INSOLUBLE BITUMEN DETERMINATION. 



This test' is made on all petroleums, malthas, asphalts, and other 

 solid native bitumens and their products. 



It should be noted that petroleum naphthas arc by no means defi- 

 nite compounds, but are composed of a number of hydrocarbons 

 which vary in character and quantity according to the petroleum 

 from which they have been distilled. Their solvent powers also vary 

 greatly. Tims naphthas produced from asphaltic petroleums, con- 

 -i ting mainly of naphthene and polymethylene hydrocarbons, are 

 much more powerful solvents of the heavier asphaltic hydrocarbons 

 than are the paraffin naphthas. The density of the naphtha also 

 affect it solvent power, for those of high specific gravity dissolve the 



