208 ASPHALT. 



this paper, and for this purpose these petroleums may be sub- 

 divided into asphaltic, semi-asphaltic, and non-asphaltic. The 

 latter are the products from the oil fields of Russia, the Eastern 

 and other isolated fields of the United States of America, 

 Borneo, etc. 



The asphaltic and semi-asphaltic petroleums only are used for 

 making the oil asphalts. The latter are found in the eastern fields 

 of Mexico, some of the American States, as Texas, Kansas, 

 Oklahoma, while the true asphaltic petroleums are found in the 

 Island of Trinidad, British West Indies, the Western American 

 States of California, Wyoming, and others. 



All these differing petroleums are found singly in fields, or 

 even doubly, as no field, territory or state has a monopoly of one 

 variety. As a matter of fact any oil well in any field may differ 

 in point of gravity from the well next adjoining it. This may, 

 and probably will, result in non-uniformity of the asphalt pro- 

 duced in any refinery, and especially if it is supplied with 

 petroleum from different fields. 



From wherever obtained the petroleum is received at the 

 refinery into a storage tank holding perhaps 55,000 barrels. This 

 is usually provided with steam coils in order to heat the oil and 

 to facilitate the settling out of the water that is nearly always- 

 present. From here it is pumped into a cylindrical iron still holding 

 from 125 to 350 barrels fitted with perforated steam pipes along 

 the bottom, and a fire is kindled under the still. Now petroleum 

 is a mixture of various complex hydrocarbons having different 

 boiling points. The effect of the heat is to drive off those hydro- 

 carbons having the lowest boiling points which pass as vapour 

 from the still to the condenser, where they resume the liquid phase; 

 thus the temperature gradually rises. At about 300° F. steam 

 is admitted through the perforated pipes to agitate the oil, and 

 assist in the removal of the distillates. As the temperature rises 

 the distillates evolved get heavier, and the residue in the still 

 becomes more concentrated until a temperature of about 700° F. 

 is reached. At this temperature the material in the still is thinly 

 liquid, and the vapours, assisted by the steam, come off as a heavy 

 yellow gas, which, when cold, yields lubricating oils. It is accom- 

 panied by a copious evolution of sulphuretted hydrogen, indicating 

 the decomposition of the sulphur compounds. On account of the 

 increasing weight of the distillates the steam has been gradually 

 increased until three or four times as much is used as at first. By 

 increasing the agitation this tends to prevent excessive decomposi- 

 tion of the oil against the hot bottom of the still heated by the 

 fierce flame of the fire, which has also been gradually increased. 

 The increased steam is not entirely successful, and a certain amount 

 of coke collects on the bottom of the still, and the fire-line carries 

 a black scum of decomposition products. This stage of the process 

 requires great skill to keep the temperature ahead of the boiling 

 point as a drop in temperature of only a few degrees would result 

 in the condensation of the vapours inside the still which would 

 drop back into the hot oil ; increased decomposition ensues 



