LESSONS IN CHEMISTRY. 171 



silk or wool fiber the whole process consists in placing the ma- 

 terial in a solution of the desired color; it absorbs the color 

 becoming dyed. The color enters into such intimate combination 

 with the fiber that it cannot be washed out. There is probably 

 no chemical action between the fiber and the coloring matter, 

 although the union is very close and some have considered it a 

 chemical union. 



In the case of the same kind of fibers, with cochineal, logwood 

 or madder, there would be no permanent color. In such cases 

 another class of bodies called mordants is necessary. They in 

 some way help to make the coloring matters adhere to the fiber. 

 The substances commonly used as mordants are the salts of 

 aluminum, iron, tin, chromium, copper and a few other metals. 

 Woolen goods, after boiling in salts of tin, will take on a brilliant 

 scarlet in a solution of cochineal. The process of dyeing calico 

 with logwood is first to pass the calico through a hot solution 

 of sulphate of iron, then through lime water, which decomposes 

 the iron salts, setting free the iron oxide, which remains in the 

 fiber ; the excess of lime is then washed away, preparing the calico 

 for the logwood. The calico, now of a buff color from the oxide, 

 when placed in the hot solution of logwood, speedily acquires a 

 dark hue, and in about half an hour has become dyed a dense 

 black color. The above will give some idea of the methods em- 

 ployed in one of the most important industries we have, and 

 that at every step from the preparation of the dye or mor- 

 dant it is mainly a chemical process. And a very large propor- 

 tion of all the chemical elements are in some way used in this 

 industry. 



Some interesting products arise from the destructive distilla- 

 tion of wood. Wood and coal are both of vegetable origin, but 

 coal, having suffered partial decomposition, has lost much of its 

 original oxygen, so that the products of wood and coal differ 

 somewhat. The gases derived from wood are marsh gas, and 

 the carbon oxides. Among the liquids are toluole, kreasote, 

 acetic acid and wood spirit. Paraffin, a beautiful, semi-trans- 

 parent, waxy substance, is the most important solid. It is used 



