336 THE POPULAR SCIENCE MONTHLY 



contains less than 15 per cent, of asphaltenes will lack cohesiveness and 

 stability or body, while, on the other hand, if it contains less than 70 

 per cent, of petroleum it will not be sufficiently adhesive. Even with 

 the proper proportion of petrolenes and asphaltenes a bitumen may still 

 be valueless as a cement, if the petrolenes are not of a proper ch^aracter, 

 that is to say, not sticky. These are all facts to be determined by the 

 chemist, and his contributions to the subject have been of the greatest 

 importance to the development of bituminous highway construction. 

 The characteristics which he determines may be summarized as follows : 



1. General Characteristics. — The series of hydrocarbons of which 

 the bitumen is composed for the purpose of comparing it with those 

 in standard materials. 



2. Purity. — The amount of bitumen apart from the mineral or other 

 matter, with which it may be contaminated, to regulate the amount of 

 it which should be used under various conditions. 



3. Adhesiveness. — Arrived at from a determination of the specific 

 gravity of the bitumen, its solubility in naphtha, the amount of paraffine 

 scale which it contains, this being evidence of the facts that paraffine 

 petroleums are present in the material or absent, and its ductility or 

 extent to which a small test piece can be elongated under tension with- 

 out fracture. 



4. Cohesiveness. — Determined by the percentage of asphaltenes 

 which the material contains, and by the residual coke remaining after 

 ignition of the material in absence of air, which bears a close relation 

 to the percentages of asphaltenes present. 



5. Consistency. — Determined by the depth to which a weighted 

 needle will penetrate into the material, under a definite weight, at a 

 definite temperature, during a definite period of time. 



6. Viscosity. — Determined by the rate at which the material will 

 flow through an aperture of definite size, at a definite temperature, in a 

 definite period of time. 



7. Capacity to Resist Temperature at Which it Becomes Suffi- 

 ciently Liquid to ie Used in Actual Construction. — Determined by the 

 volatilization of the material when exposed for a definite length of time 

 in a definite amount, to the high temperature at which the materials 

 would be used. 



8. Safety. — Determined by the temperature at which the vapor aris- 

 ing from the material at high temperatures, such as those used in 

 manipulating it, will flash or take fire. 



Determination by the chemist of the above characteristics and com- 

 parison of them with well-known standards enables him to say whether 

 the bitumen in hand possesses those which have been recognized as de- 

 sirable in similar materials which have been subjected to service tests in 

 actual work with successful results. 



