THE volume of literature relating to the cracking of petroleum is enormous and ever increasing. Presentation of this paper requires, therefore, no small amount of audacity, especially as no attempt will be made to contribute any information new to those familiar with the art. The author's sole justification is a belief that a rapid review of the subject may prove of some interest to those outside the petroleum industry.
Petroleum is a term often used, in a broad sense, to designate not only crude petroleum but also the products derived therefrom. Crude petroleum may be defined 1 as: "A naturally occurring mixture consisting predominantly of hydrocarbons, or of sulphur, nitrogen or oxygen derivatives of hydrocarbons, which is removed from the earth in liquid state, or is capable of being so removed." Crude petroleums show extreme variations in properties, both physical and chemical. These differences are reflected to a considerable degree in the products obtained from the crude and the differences are both qualitative and quantitative. Nevertheless all crude petroleums are initially refined by a distillation process conducted under conditions adapted to the particular crude handled. Such primary distillation results, broadly speaking, in the separation of the crude petroleum into three products; first, a mixture of gases which are not condensed; second, a series of liquid or semi-liquid distillates, and third, a residuum left in the still.
The usual major products of the primary distillation are shown in the chart on the following page.
The quantity and quality of the products named depends, first, upon the nature of the crude petroleum and, second, upon the method of distillation. Two factors are of prime importance in the primary distillation of crude petroleum, namely, the distillation temperature and the duration of exposure to such tempera-* Presented at a meeting held Thursday, March 25, x926.