PAINTS 203 



Since cellulose combines with very few dyes directly, it and the 

 dye must be held together by a third substance, which can unite with 

 the cellulose on the one hand, and with the dye on the other. Such 

 a substance is called a mordant. Here, also, we can look upon the 

 dyeing process as a reaction between acids and bases; only there are 

 three substances in the reaction instead of two. The final, complex salt 

 is the dyed fabric itself. 



Aluminum hydroxide is a common mordant. It is insoluble, and it 

 is sticky, like boiled starch. It is formed in the fibers of cloth when we 

 soak the cloth in aluminum acetate, and then in ammonia water. In the 

 making of calico the pattern is first printed on cotton cloth with a 

 mordant, and the cloth is then soaked in a dissolved dye. The dye com- 

 bines with the mordant, but not with the cloth alone. The uncom- 

 bined dye is washed out. If different parts of a pattern are printed 

 with different mordants, a number of colors can be made from 

 the same dye. 



229. Paints. Common paint consists of linseed (flax 

 seed) oil and turpentine, mixed with " white lead/' or 

 " zinc white/' and a pigment to give color. White lead, 

 etc., are compounds used to give the paint " body " or 

 "covering power." The turpentine not only thins the 

 paint, but assists in drying the oil. 



When paint dries, its linseed oil is oxidized by the air to 

 a hard gum. Considerable heat is given off in the process; 

 hence heaps of cloths containing paint or linseed oil often 

 take fire without an apparent cause (" spontaneous com- 

 bustion "). Such cloths should never be left about a 

 building except in covered metal boxes. 



To remove a paint stain from a fabric we need usually 

 remove only the linseed oil. This is soluble in benzine, 

 gasoline, etc. When we have removed the oil, we can 

 generally remove the white lead by brushing or rubbing. 



