18(i8.] 455 [rcckhaui. 



.aspiifiltum by docomposition, it does not contain paraffme, 

 neither do the distiUates from any of its derivatives ; this group 

 I shall call the class />', and it may be represented by the petro- 

 leums of Southern California. The derived forms of these 

 different classes are designated, asphalts of the class A, pyro- 

 asphalts of the class />', etc. 



The word naphtha is used to designate the most volatile pro- 

 ducts of the distillation of wood, coal or petroleum. "When 

 restricted in its use to this class of substances, it indicates an 

 extremely volatile product of distillation, composed of carbon 

 and hydrogen. The loose manner in which this term has been 

 applied to products of exceedingly unlike chai'acter, has led to 

 much confusion in description. I propose in this connection to 

 limit its nse to those extremely volatile and slightly colored 

 mineral oils, which are occasionally met with in different local- 

 ities, and which are evidently the product of a distillation car- 

 ried on by natural processes.* 



Gaseous carbides of hydrogen almost invariably accompany 

 deposits of l)itumen of every variety. 



Maltha or mineral tar is, as its name implies, more nearly 

 allied to tar in its ph^'sical properties than to oil. It is usually 

 described as distinguished from petroleum b}^ its viscidity, but 

 a more marked dissimilarity is found in the manner in which the 

 two are separated from mechanical admixture with either gaseous 

 or licjuid impurities. When petroleum is mingled with either water 

 or air, they readih^ separate, as soon as the mixture is allowed 

 to remain at rest, leaving the petroleum in a state of purity. 

 With the more dense varieties this separation ma}^ be assisted 

 b}^ the aid of a gentle heat. Petroleum which has been thus 

 separated from these impurities may be heated to its boiling- 

 point, when gentle ebullition ensues. If however an attempt is 

 made to boil petroleum before such separation is complete, the 

 water will subside as the temperature is raised, until at 100° C, 

 the ebullition will become explosive from the escape of inter- 

 mittent puffs of steam. 



Crude maltha which has escaped from a fissure in a rock, or 

 has been pumped from a well accompanied b}' water, in falling 

 into a tank, entangles air in its descent. Manj^ of the larger 

 bubbles of both air and water readil}' separate, but the separa- 



* See Humbolt's Travels, 1. 19S ; III. 113, Bohn's Ed. 



