386 ORGANIC CHEMISTRY. 



posed by heat. Shoemakers wax is made by a similar 

 process. 



What are the ^67. ROSIN OIL AND GAS. Rosin is 



products of partially converted by dry distilla- 

 te dry distil- \ . . . , . 



lation of tion into an oil, which is largely 



used for adulterating other oils, and 

 also for purposes of illumination. A black pitch 

 remains in the retort. The oil has the advan- 

 tage of extreme cheapness, but owing to its 

 large proportion of carbon, can only be burned 

 in lamps furnished with tall chimneys. At a 

 still higher temperature rosin is converted into 

 gas, with a residue of carbon. 



What is as- 968. AspHALTUM. Asphaltuni or bi- 



phaltum? tumen is a mineral resin, similar to the 

 black pitch which remains from the distillation of coal 

 tar. This material is found on the shores of the Dead 

 Sea, in the island of Trinidad, and in several European 

 localities. It is extensively employed for hydraulic 

 cements, roofing, and pavements. 



969. PETROLEUM. Petroleum is a liquid 



What is said . 



of the source, hydrocarbon, also known as rock oil. It is 

 often found u P on standing water, in bitu- 

 ofpetrole- minous coal districts. Pits are also dug 

 for the purpose of collecting it. These 

 become filled with water, upon which the oil rises, more 

 or less abundantly. The rectified petroleum is called 

 naptha, and is a nearly colorless and highly volatile 

 fluid. The entire absence of oxygen in its composi- 

 tion, adapts it perfectly to the preservation of the metals 

 potassium, and sodium, in their metallic condition. 



