Peckham.] 4^fi [September 18. 



tioii will not be complete if the maltha should remain at rest for 

 months. When placed in tanks and moderately heated for a 

 long time the separation is still incomplete. As the temperature 

 is raised the liquid commences to foam, the foam finally occupy- 

 ing many times the bulk of the maltha. A sample of California 

 maltha which I examined, appeared to be a pure black viscous 

 bitumen of uniform consistence. When heated it began to foam 

 perceptibly when the temperature was raised only ten degrees 

 Fahr., and at 100° it foamed so rapidly that retort and worm 

 were soon entirely filled. When heated in an open vessel the 

 foam occupied about twent}^ times the bulk of the maltha, and 

 the air and water were not expelled until the temperature had 

 reached 230° Fahr. 



The surface oils or tars obtained from the so-called surface 

 wells, bored in the superficial detritus at Enniskillen, were mal- 

 thas possessing this characteristic of viscidit}^, and presenting 

 the same obstacles to successful distillation encountered in those 

 from California. 



The same causes which produce the lighter varieties of maltha 

 from petroleum, whether it belong to the class A or />, if their 

 action be continued, will cause the bitumen to become more and 

 more dense, until it attains the consistencj'' of pitch and finall}' 

 hardens into solid asphaltum. The line of separation between 

 maltha and asphaltum is wholly arbitrary. 



Of the solid bituminous minerals which are derived from 

 petroleum, there are four distinct species, viz: asphaltum, pyro- 

 asphaltum, asphaltic schists and pyroschists. The first two are 

 pure bitumens, amorphous, with a brilliant conchoidal, sometimes 

 angular, fracture. Asphaltum is soluble in bi-sulphide of carbon, 

 pyroasphaltum is insoluble, but both yield a distillate soluble in 

 that menstruum. Asphaltic schists and pyroschists are pro- 

 duced either b}' the saturation of pervious strata with petroleum, 

 or by the admixture of organic and earthy matter during the 

 deposition of sedimentrary strata, and their subsequent trans- 

 formation into asphaltum. Under these two species may be in- 

 cluded as varieties, all those bituminous minerals in which the 

 earthy matter preponderates, whether it be sand, slate or lime- 

 stone. They ma}'" be distinguished from each other by the same 

 tests which serve to discriminate between asphalts and pyro- 

 asphalts. The pyroasphalts and schists are derived from the 



