170 PRACTICAL LESSONS IN SCIENCE. 



and zinc the hydrogen set free from the acid replaces the oxygen 

 of the nitrobenzole as follows: C 6 H 5 (N0 2 )+6H=C 6 H 5 NH 2 or 

 C 6 H 7 N aniline, -j-2H 2 0. Aniline is colorless when pure, becom- 

 ing brown if exposed to the air. Aniline mixed with a little tolui- 

 dine derived from toluole, and treated with chloride of lime, 

 yields a beautiful violet dye. What share the toluidine has in 

 the production of the color is not known, and the chemical 

 changes are not understood, but it is known to be an oxida- 

 tion. Red, blue, green, black, yellow, etc., in varying shades 

 may be obtained from these substances by the action of various 

 chemical agents. 



Carbolic acid (C 6 H 6 2 ) makes up the greater part of commer- 

 cial kreasote, which is extensively used as an antiseptic to pre- 

 vent the decay of wood. Carbolic acid is much used as a 

 disinfectant. The value of aniline dyes and other products from 

 coal tar manufactured in Europe amounts to about $30,000,- 

 000 annually. The recovery of the materials for aniline dyes, 

 carbolic acid and other substances from the waste products of 

 gas manufacture is a striking example of the utility of purely 

 scientific work. 



While aniline dyes have superseded many of those formerly used, 

 yet a few are worthy of mention. Madder, furnishing beautiful 

 red and purples, is derived from the root of a plant much grown in 

 Europe. The essential ingredient of madder is alizarin, which 

 has been prepared artificially from coal-tar products, so that the 

 madder industry is fast passing away. Brazil wood and log- 

 wood, quercitron from oak bark, fustic and indigo are important 

 dyes. Indigo is prepared from various species of plants by al- 

 lowing them to ferment in water, and when a blue scum appears 

 on the surface of the water a little lime is added, when the indigo 

 is precipitated. Cochineal, a dye prepared from an insect, gives 

 a beautiful red. 



The art of coloring fabrics of various kinds has been practiced 

 by man everywhere from the earliest times. The process varies 

 with different colors and different fibers. To obtain the finest 

 shades of mauve, magenta, purple and many other colors on 



