18 
BULLETIN 102, UNITED STATES NATIONAL MUSEUM. 
sene, fuel oil, and lubricating oil — together with by-products, the 
process separating the crude oil into its natural components with the 
minimum of chemical change. The “straight-run” refinery lacks 
flexibility, because it has no power of producing, for example, 
more gasoline than the crude oil naturally contains . 1 Such plants 
are situated in the East and other parts of the country where the 
demand, especially for lubricants, justifies the expense of the practice. 
The third type of refinery is of recent birth, but has made rapid 
strides toward a great future ; it employs the so-called “ cracking ” 
process, which yields, like the “straight-run” plant, a full set of 
products, but a greater percentage of gasoline than the crude oil gives 
upon ordinary distillation. This is accomplished at the expense of 
the heavier component oils, whose molecules are broken or “ cracked ” 
into lighter molecules, which constitute just so much additional gaso- 
line. It is obvious that cracking has developed in response to 
a growfing demand for gasoline; its significance is apparent in the 
fact that it permits the production of a more valuable product from 
one less valuable. With an increasing call for gasoline and a de- 
creasing supply of petroleum, cracking may be called the hope of the 
future as regards refinery advance. 
If we pause for a moment to contemplate the consumption of 
petroleum in the crude condition, and then the three types of refin- 
ing — skimming, straight-run, and cracking — it becomes evident that 
each treatment represents a step in advance over the preceding, and 
that, while all four prevail to-da}^, the cracking refinery is in line 
with true progress and will eventually dominate the .situation. 
Befineries, whatever the type, employ the principle of distillation 
in their operations. The petroleum is heated in stills and the prod- 
ucts vaporize, pass off, and are condensed in fractions, representing 
roughly the materials in demand. These products are then purified 
by chemical treatment or transformed by chemical means into a 
series of secondary products. The production of the various kinds 
of lubricating oils needed for diverse uses represents an intricate, 
yet single, part of petroleum refining; and is merely one aspect of the 
many ramifications found in refinery technique. The refining of 
petroleum makes heavy drafts upon other chemical industries — for 
example, in normal times, about one-tenth of the sulphuric acid pro- 
duced in the United States goes into petroleum refining — but the 
refinery in turn contributes many essential products to other chemical 
manufacturing activities. These industrial interrelationships, oft- 
times overlooked, are of the utmost significance — a fact strikingly 
1 Such statements are true in a broad way only ; the reader will understand that 
rigorous scientific accuracy of statement must be partly sacrificed to gain simpleness of 
expression. 
