EXAMINATION OF BITUMINOUS ROAD MATERIALS, 15 
| METHOD. 
Since bitumens are mixtures of various organic compounds, they 
-ean have no true melting pomt, 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 normai 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 3-inch brass cubical mold, which has 
been amalgamated 
with mercury and 
which is placed on an 
amaloamated brass 
plate. The brassmay 
be amalgamated by 
washing it first with 
a dilute solution of 
mereuric 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 the 
sides of them old. The Fig. 8.—Melting point apparatus. 
hot material should shghtly 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 m a water bath, or, for high temperatures, a cottonseed-oil 
bath. The wire should be passed through the center of two opposite 
faces 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-cubic 
centimeter low-form Jena glass beaker suitably mounted for the 
application of heat from below. The beaker in which the cube is 
suspended is of the tall-form Jena type without lip. The metal cover 
has two openings as shown in figure 8-d. A: cork, through which 
