Lessons in Community and National Life; Series A, for the Upper Classes of the High School

This historic book may have numerous typos, missing text or index. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. 1918. Not illustrated. Excerpt: ... SYNTHETIC DYES. The dyes made from coal tar are called synthetic dyes. This means that they are made by synthesizing, or putting together under proper conditions, substances which unite and produce a new chemical compound. The best example of synthesis is exhibited by nature in the growth of a plant. The roots take up elements from the coarse dark soil and the plant combines these elements with others drawn from air and water, and under the influence of sunlight synthesizes all into the green leaves and colored blossoms. ARTIFICIAL SYNTHESIS. The synthesizing of substances by plants is imitated in some measure in the dye factory. As a visitor goes into such a factory he is shown a great retort or closed vessel in which one of the coaltar crudes is being mixed with sulphuric acid. Inside the retort are rotating paddles or agitators as they are called. The retort and its contents are raised to a high temperature, for heat helps to bring about the chemical change desired in the mixture. This high temperature can be compared to sunlight acting on a plant. Sometimes the heat necessary for the artificial synthesis is so great that it can not be produced by ordinary means; then coils of pipe containing superheated oil pass through the walls of the retort. Sometimes the synthesizing is of a very different type. A strong nitric acid, for example, is slowly poured into a retort containing a coal-tar product. The temperature is kept very low by means of a freezing mixture, which passes through the coils of pipe in the walls of the retort. Agitators keep the mixture in constant motion. If the temperature begins to rise, it means that the acid is coming in too rapidly or that it is acting too vigorously, and the operator shuts it off. If the temperature still continues to ri...