BY-PRODUCTS

secondary produced in the course of manufacturing a principal product. The utilization by-products, formerly allowed to to waste, is e entially a modern ment, and in certain industries products now form the main source profit. ‘The importance of by-products dates from the artificial production aniline coloring matter from coal by the Eng. chemist Perkin in Other examples of profitable ucts are: industrial alcohol made waste sulphite liquor in manufacturing paper from wood; tar and ammoniacal liquor got by distilling coal for nating gas. Besides dyes, many drugs and flavoring agents are obtained from coal tar ucts; tar, ammonia, and potash recovered from blast furnaces jron ores, while the slag is useful for ing, cement, and road metal; basis a ol roduct in steel manufacture, valuable manure. Glycerine is a by-product of soap and candle