- EXAMINATION OF BITUMINOUS ROAD MATERIALS, 4] 
meters above the top of the aggregate. The meniscus of the kerosene 
in each cylinder and the volume of aggregate is then noted. The per- 
centage of voids is calculated as follows: 
a equals initial volume of kerosene in small cylinder. 
_b equals final voiume of kerosene in small cylinder. 
¢ equals meniscus of kerosene in large cylinder. 
d equals apparent volume oi aggregate. : 
Percentage of voids equals @ al) a 
In some cases the kerosene fails to expel all the air from the agere- 
gate, and this fact will be evidenced by bubbles coming to the surface 
if the aggregate is stirred with a long thin metal rod after the final 
readings are taken. Accurate results under such conditions are 
obtained by stirring the aggregate until bubbles cease to appear. 
This will, of course, yield a lower reading on the meniscus of the kero- 
sene in the large cylinder, but the original reading on the volume of 
rock should be taken. 
METHODS OF EXAMINING BITUMINOUS EMULSIONS. 
‘The exact determination of the constituents of a bituminous emul- 
sion is usually attended with considerable difficulty and no predeter- 
mined scheme can be made applicable to all materials of this character. 
In a number of cases, however, the following method has yielded satis- 
factory and fairly accurate results. 
In order to break up the emulsion, a 20-gram sample is digested on 
¥ 
a steam bath with 100 cubic centimeters of : alcoholic potash. The 
digestion is carried out in a flask with a reflux condenser for about 45 
minutes. The solution is filtered and the precipitate washed with 95 
per cent alcohol. The filtrate is evaporated to dryness, after which 
the residue is taken up with hot water and any insoluble matter is 
filtered off. The aqueous solution, which contains the potassium 
soaps of the fatty acids, is acidified with dilute sulphuric acid and then 
shaken in a separatory funnel with petroleum ether. The aqueous 
‘portion is drawn off and the ethereal layer shaken up with cold water 
and washed twicc, after which it 1s evaporated in a weighed platinum 
or porcelain dish to constant weight, first over a steam bath and then 
in a drying oven at 105° C. The neeulas consists of the fatty and 
resin acids present in the emulsion. 
The percentage of water in the emulsion is determined by distilling 
a 100-gram sample in the retort used for the dehydration of tars. 
The distillation is carried out in exactly the same manner as described 
for crude tars until the volume of water in the receiver shows no 
further increase. Any oils that come over are thoroughly mixed with 
the material remaining in the retort. 
