��Popular Science Monthly
���more volatile gases first and the heavy ones afterward. This treatment of coal tar is combined with alternate treatment by certain chemicals, commonly referred to as reagents. These reagents consist of dilute caustic soda, dilute acid and con- centrated sulphuric acid.
When distilled up to 252 deg. Fahr., ben- zene, more frequently referred to as benzol, is obtained. It is the first to pass over. By further distillation , up to 306 deg. Fahr., sol- vent and burn ing- naphtha are also driven out. Still further heat- ing from 414 deg. to 486 deg. Fahr., results in the formation of creosote and other oils, referred to as the heavy oils.
Beyond these are obtained anthracene oil and anthracene, both used in making dyes. Other products are lampblack, used in making printer's ink; pitch, employed for roofing, road-building, water-proofing; and coke, used instead of coal for obtaining intense heat without smoke, especially in blast furnaces. In 1916, 54,200,000 tons of coke were manufactured in the United States.
��A beehive coke oven. The coal is admitted at the top and the coke removed through the side openings. By this crude method, the tar and ammonia are entirely wasted, passing off into the air
��Benzol Obtained from Gas or Tar
In the case of coke oven gas, benzene (or benzol) is obtained by a direct recovery method. The recovery of benzol is limited almost entirely to the coke oven plant and to the tar distiller. The chart on page 874 shows how benzol can be obtained directly from raw gas or indirectly from the raw tar. During the distillation of tar the so- called light, middle and heavy oils which come off give us the first nine dye"crudes," such as ben- zol, toluol, xylol, naph- thalene. By addition and subtraction of various chem icals, and by cer- tain chemical changes-, these crudes make up the 300 dye "inter- mediates," such as phenol, aniline, cresol, etc. These, by further addition and sub- traction, make the 1200 different coal tar derivative dyes.
These colors range from black up through the rainbow colors and other shades, such as the browns and grays. In fact, to tell the difference between two similar shades is like splitting hairs. In the chart, page 879, I have shown only the production of basic reds.
����A battery of by-product ovens. Observe two trams, the upper one for depositing coal in the ovens and the lower one for ramming the -coke out on the farther side. The ovens are sealed with a clay-packed lid. Half the gas formed is consumed in heating the coal. The remainder, as well as the tar and ammonia, is conducted away through pipe lines to the receiving tanks