igo THE POPULAR SCIENCE MONTHLY. 



became so completely saturated with it that the innermost fractures 

 resembled the natural asphalt-stone; but it differed from the latter in. 

 this most important property, that it did not crumble to a powder 

 when heated. On the contrary, the absorbed bitumen was expelled 

 by heat, leaving a hard limestone, instead of a calcareous powder. 

 From this it seems probable that the particles of the natural asphalt- 

 stone are simply cemented together by the bitumen, and both must 

 have been deposited at the same time. 



In most mines the strata dip slightly toward the horizon. They 

 vary greatly in thickness ; sometimes there is only one stratum, at oth- 

 ers there are several superimposed on each other or separated by strata 

 of harder limestone or shale. At Val de Travers the strata that are 

 worked are from two to six metres thick, and rest on hard, non-bitumi- 

 nous limestone. 



In some places it is mined in open trenches, in others by means of 

 shafts and subterranean tunnels. At Val de Travers, Seyssel, and 

 Lobsann, the latter alone are employed. The rock is blasted out 

 with powder, which works better in soft rock than dynamite. The 

 holes are bored with an ordinary hand-auger. At Limmer, owing to 

 the water in the mines, it is necessary to use dynamite. 



The percentage of bitumen in the different varieties of asphalt- 

 stone is as follows : That from Limmer, 14*3 ; Val de Travers, 10*15 ; 

 Lobsann, 12-32 ; Ragusa, 8'92 ; Seyssel, 815 ; Vorwohle, 8*50.' It is 

 estimated by extracting it from the finely pulverized mineral with 

 carbon disulphide, benzene, or other solvent, and weighing the resi- 

 due after the solvent has evaporated. The quality of the bitumen is 

 determined by heating it to 430 or 440 Fahr. ; the less it loses by 

 evaporation the better its quality. The powdered mineral from which 

 the bitumen has been extracted should be white and soft. If it has a 

 gray color, and feels harsh or sticky, it is of poor quality. Too much 

 dependence can not be placed on chemical analyses, for much depends 

 on the physical properties as well. 



The larger portion of the asphalt-stone used in Europe comes from 

 Val de Travers, which produces about 25,000 tons a year ; Limmer is 

 not much inferior in its yield, which amounts to about 21,500 tons ; 

 Seyssel furnishes 13,000 tons, and Lobsann about 9,000 tons. That 

 which is mined at Limmer and Vorwohle, being very rich, is only used 

 for making mastic. 



The first operation to which the asphalt-stone is subjected, when it 

 reaches the factory, is pxilverization. For this purpose several differ- 

 ent machines are in use, the ordinary stone-breaker being unsuited to 

 the purpose. Four or five of these are figured in Professor Dietrich's 

 new work on " Asphalt Streets," * to which we are indebted for many 

 of the facts in this article. 



The powder thus obtained may be employed directly for the com- 



* " Die Asphalt-Strassen, ' E. Dietrich, Berlin, 1882, pp. 207. 



