Page:International Library of Technology, Volume 93.djvu/101

 Baumé's scale, this being the rating at which it is sold in the general market. For instance, "Gasoline 72 Baumé" means that the density of the gasoline is 72° of Baumé's hydrometer. Kerosene is generally rated by its flashing point. This point is the number of degrees of temperature to which it must be heated before the vapors given off from the surface of the oil will take fire from a flame held over the containing vessel. Thus, oil of 150° test is oil that will flash or take fire when heated to a temperature of 150° F. Kerosene, at ordinary temperatures, should extinguish a lighted taper when the taper is plunged into it.

CHEMICAL CONSTITUENTS OF PETROLEUM

43. Composition of Petroleum. — Chemically, petroleum consists of what are known as hydrocarbons — combinations of carbon and hydrogen. Carbon is best known, in its pure state, in the form of charcoal, in which condition it is practically pure. The two substances, carbon and hydrogen — one a solid and the other a gas — combine to form gases, liquids, and solids whose physical properties — that is, density, fluidity, etc. — vary from those of hydrogen to those of carbon. This is best explained by Table VII, which shows only one series of the compounds found in the crude oil.

44. Marsh-Gas Series. — The series given in Table VII is known as the marsh-gas series, being so named from the lightest gas in it, marsh gas being the popular name for methane. It will be noticed on examination of the chemical formulas for the various products, that the number of hydrogen atoms is twice the number of carbon atoms plus 2; so that, if n is the number of carbon atoms, the number of hydrogen atoms is 2n + 2. Thus, the general formula for the series is Cn H(2n + 2).

45. Other Series. — There are also other series of less importance, at least eight being found in various petroleums. The marsh-gas series is an example of these, each series containing gases, liquids, and solids.