Inasmuch as the aim of this little volume is to interest other than those who are directly associated with the petroleum industry, I shall endeavour in this chapter to refer to the refining of petroleum in a manner which shall be readily understood by the reader, and shall, wherever possible, refrain from entering into those highly technical matters which do not lend themselves to popular expression. The refining of crude oil as it is produced from the earth, consists in the classification of its various hydrocarbons by means of fractional distillation, into the various products which so largely enter into our commercial and domestic life of to-day. The refined products, in the order in which they are received by distillation, are: motor spirit, illuminating oils, solar oils, lubricating oils, fuel oils, residuum, etc.--the first mentioned being the lightest and the last the heaviest in specific gravity. Almost simultaneously with the discovery of petroleum, there sprung up the first attempts to refine Nature’s product, and though these early experiments were of a most primitive character, they doubtless served their purpose admirably. In this respect, probably the most primitive oil refinery in the world was built near the Tigris, in Mesopotamia. Crude petroleum varies in its character, for while certain crudes are pale in colour and almost transparent, others are almost black and viscid. Some, indeed, would appear to have undergone a course of refining by Nature itself, for in some fields the crude oil will freely burn in lamps without any refining treatment: in the vast majority of cases, however, the crude oil, as withdrawn from the producing wells, represents a liquid somewhat like molten tar.