396 JOSEPH STRUTHERS 



have a black or dark brown color and a peculiar characteris- 

 tic pitchy odor when rubbed. 



Asphaltum breaks with a more or less splintery fracture 

 and does not soil the fingers. It is very brittle at low temper- 

 atures, but upon being warmed, although it remains suffi- 

 ciently hard to be broken by a sharp blow, at the same time 

 it yields to a steady pressure or tread. Asphaltums differ 

 much in their properties, and all do not possess the binding 

 power so necessary for a lasting pavement; they shade by 

 insensible gradations into brittle asphaltic coals. The melting 

 point of asphaltum is usually low. It is very inflammable, 

 burns with a 3'ellow, smoky flame, and when pure leaves very 

 little if any residue. It is insoluble in water, slightly soluble 

 in alcohol and fixed and essential oils, and readily soluble for 

 the greater part in ether, oil of turpentine, naphtha, and carbon 

 bisulphide. With benzole it forms a solution of an intense 

 black color, used as a varnish. When subjected to destruc- 

 tive distillation, asphaltum is decomposed into a distillate 

 of oils and a tarry residue which becomes solid when cold. 



The chemical composition of asphaltum is so complex 

 that elementary analyses throw little light on the subject. It 

 still remains an open question whether important groups of 

 definite and characteristic hydrocarbons can be separated 

 and recognized. 



Many chemical analyses of asphaltum from various local- 

 ities have been published from time to time which, however, 

 are of scientific value only. 



Means other than chemical analysis are generally used 

 to ascertain the commercial value of asphaltum. The first 

 of these is a solubility test of the sample dried at 212° F. in 

 various solvents, as carbon bisulphide, alcohol, turpentine, 

 ether, petroleum, naphtha, etc. Distillation is often used and 

 the losses at various temperatures are recorded. The quantity 

 and quality of mechanical impurities (water, clay, earthy 

 matter) contained in the sample are also determined; finally, 

 the best test of its applicability for pavement purposes is its 

 viscosity at various temperatures. In some cases the value 

 of an asphaltum for use in pavement construction is determin- 

 ed by an actual trial. 



