EXAMINATION OF BITUMINOUS ROAD MATERIALS. 41 



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 volume of kerosene in small cylinder. 



c equals meniscus of kerosene in large cylinder. 



d equals apparent volume of aggregate. 



„ , . , , (a-b) —(c-d) 

 Percentage of voids eqiials —j • 



In some cases the kerosene fails to expel all the air from the aggre- 

 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 



N 

 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 ])recipitate 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 <>fr and the ethereal layer shaken up with cold water 

 and washed twico, after which it is evaporated in a weighed platinum 

 or porcelain dish to constant weight, first over a steam bath and then 

 in a drying oven :il 105° C. The residue consists of the fatty and 

 resin acids present in flu- emulsion. 



The percentage of water in the < mulsion is determined by distilling 

 ;i 100-gram sample in the retort used for the dehydration of tars. 

 The distillation is carried out in exactly the same manner ;is described 

 for crude tars until the volume of water in (lie. receiver shows no 

 further increase. Any oils that come over are thoroughly mixed with 

 the materia] remaining in the retorl . 



