CRUDE PETROLEUM .'501 



changing receivers at any point in the boiling as many 

 fractions can be obtained as desired. 



At first there are obtained only three or four fractions, the 

 first one called benzine distillate or crude naphtha (sonic- 

 times light naphtha and heavy naphtha), with a density of 

 80° to 58° Be. 1 Then come burning oils or kerosene with a 

 density of 58° to 4o°. Tar or residuum is left in the stills. 

 The temperature of distillation rises gradually to 300° or 

 400° C. From the crude naphtha several colorless fractions 

 are usually obtained by distilling again and purifying with 

 strong sulphuric acid and caustic soda. The liquid to be 

 thus treated is agitated with sulphuric acid of 66° Be., 

 then washed with water, agitated with caustic soda of 

 4° to 10° Be., and finally washed with water. The 

 acid and soda decompose or dissolve various impurities 

 and coloring matters in the petroleum products other than 

 the paraffine hydrocarbons. The spent acid which settles 

 to the bottom is drawn off as "sludge" acid and is used in 

 some places for making phosphatic fertilizers. The various 

 fractions have different names, not alwavs uniform. Thev 

 are arbitrary at best, depending on the density. Some of 

 the names are gasoline; naphtha, A, B, C, grades; benzine; 

 petroleum ether, etc. It is not safe to buy by name for any 

 special purpose but by specific gravity (Baume scale) or by 

 boiling points. 



The kerosene is redistilled into two or more nearlv colorless 

 fractions, purified with acid and alkali as above described, 

 and sold as burning oils of various "tests." 2 Many of the 



1 Baume. This is an arbitrary standard of density for liquids. Hydrom- 

 eters are graduated for liquids heavier and lighter than water. For the 

 former, 0° on the Baume scale is where the instrument sinks in pure water, 

 and 10° in a 10 per cent, solution of salt. For the latter 0° is the point 

 to which the hydrometer sinks in a 10° per cent, salt solution, and 10° 

 in pure water. The graduation is extended uniformly in both cases. The 

 temperature is 17.5° C. 



2 For use in lamps particularly, kerosene must not be so volatile as to 

 cause an explosion when the wick is lighted. This volatility or "flash 

 point, " as it is called, is regulated by law. The flash point is the temperature 

 at which kerosene gives off enough vapor to ignite in a flash over the surface. 

 In most of our states 110° F. is the legal flash point. Flash tests are the 

 determinations which are made to show what the flash points are. Fire 

 tests, also made sometimes, are the determinations which show the tem- 

 perature at which the vapor will burn continuously. The fire point is 

 usually about 20° F. higher than the flash point. 



