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CHAP. VIII.] stockings, and on analyzing these he discovered a compound of tin, which had been used as a mordant in fixing the dye. Each time articles dyed in this way are washed, the tin salt becomes more and more soluble. The skin excretions attack the oxide of tin, and thus a poisonous compound is formed. Some colouring substances unite directly with the fibres of the material to be dyed, and require no mordant to make them fast. Indigo is one of these so-called substantive colours, so indigo-blue is a very safe colour for your own or your children's clothes. But nearly all vegetable colours require mordants, and the principal mordants are salts of iron, tin, and alumina.

Notwithstanding the fact that salts of tin are commonly used in red dye, such is the general ignorance on the subject that it is frequently worn next the skin by preference. In underclothing shops, even in some of the most fashionable, red flannel vests and drawers are sold with the greatest complacency as being "very good," and "recommended by the faculty," or "anti-rheumatic," and in every chemist's shop we see dozens of "chest protectors," made of material dyed with this poisonous stuff, in spite of the fact that, so long ago as 1876, Dr. Richardson published a case of disease resulting from the wearing of such a "comforter," together with some strong censure of the use of the aniline dyes.

There is a sort of idea that red flannel possesses some mysterious curative properties superior to any other colour. As example of this popular error,