EXAMINATION OF BITUMINOUS ROAD MATERIALS. 



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Since bitumens are mixtures of various organic compounds, they 

 can have no true melting point, but an arbitrary method for deter- 

 mining the so-called melting point of those materials sufficiently solid 

 to maintain their form for some time under normal conditions is of 

 value as a means of identification and for control work. A number 

 of methods have been tried, but the following has been selected as 

 the most convenient and accurate for such materials. 



The material under examination is first melted in the spoon by the 

 gentle application of heat until sufficiently fluid to pour readily. 

 Care must be taken that it suffers no appreciable loss by volatiliza- 

 tion. It is then poured into the ^-inch brass cubical mold, which has 

 been amalgamated 

 with mercury and 

 which is placed on an 

 amalgamated brass 

 plate. The brass may 

 bo amalgamated by 

 washing it first with 

 a dilute solution of 

 mercuric chloride or 

 nitrate, after which 

 the mercury is rubbed 

 into the surface. By 

 this means the bitu- 

 men is, to a consider- 

 able extent, prevented 

 from sticking to tho 

 sides of the mold. The 

 hot material should slightly more than fill the mold and, when cooled, 

 the excess may be cut off with a hot spatula. 



After cooling to room temperature, the mold is placed in a bath 

 maintained at 25° C. for one-half hour. The cube is then removed 

 and fastened upon the lower arm of a No. 12 wire (Brown & Sharpe 

 gauge), bent at right angles and suspended beside a thermometer in 

 a covered Jena glass beaker of 400 cubic centimeters capacity, which 

 is placed in a water bath, or, for high temperatures, a cottonseed-oil 

 but li. Tho wire should be passed through the center of two opposite 

 of the cube, which is suspended with its base 1 inch above the 

 bottom of the beaker. The water or oil bath consists of an 800-cubio 

 centimeter low-form Jena glass beaker suitably mounted for the 

 application of beat from below. The beaker in which the cube is 

 ii pi nded is of the tall-form Jena type without lip. The metal cover 

 has two openings as shown in figure H-d. A cork, through which 



Fig. 8.— Melting point apparatus. 



