Page:International Library of Technology, Volume 93.djvu/108

 other causes the density of the gasoline as actually purchased is likely to be somewhat greater than its nominal rating, and may test as low as 68°. The vapor of gasoline that forms over the liquid consists chiefly of pentane, C5H12„ having a specific gravity of .628; but the liquid gasoline consists of a mixture of hexane and heptane, the composition varying with the specific gravity of the gasoline.

A gasoline with a specific gravity of .683 and a boiling point of 154° F., has shown the following composition by analysis: hexane, 80 per cent.; heptane, 18 per cent.; pentane, 2 per cent. The chemical composition is 83.8 per cent, carbon and 16.2 per cent, hydrogen; and the chemical formula is 41.86C6H14 + 6.48C7H16 + C5H10 This formula will serve for use in calculating the fuel value.

Commercial gasoline evaporates very readily at ordinary temperatures, but quite slowly in cold weather, and leaves small percentages of a heavier oil, which evaporates slowly or not at all. The vapor tension varies considerably with the temperature, but at 60° F. the vapor of commercial gasoline represents about 130 volumes of the liquid and sustains a water pressure of from 6 to 8 inches. An explosive mixture of gasoline vapor and air is composed of the vapor of 1 part of liquid gasoline to from 8,000 to 10,000 parts of air by volume. The volume of the vapor will vary, but an average proportion will be 2.15 of gasoline vapor to 100 parts of air.

So far as their heating value per pound goes, there is not much to choose between kerosene and gasoline, each developing about 19,800 British thermal units per pound. Kerosene, however, is about 10 per cent, heavier, so that a gallon of kerosene has more fuel value than a gallon of gasoline.

Ordinary kerosene varies in specific gravity (at 59° F.) from .760 to .820. Exceptionally light kerosene, such as the Pennsylvania light oil, has a specific gravity below .760. The boiling point of kerosene of .760 specific gravity is