TANNING AND DYE MATERIALS
Tannins are organic compounds, chiefly glucosidal in nature, which have an acid reaction and are very astringent. Their biological function is problematical. They may be concerned with the formation of cork or pigments, or with the protection of the plant. Tannins are of interest economically because of their ability to unite with certain types of proteins, such as those in animal skins, to form a strong, flexible, resistant, insoluble substance known as leather. Because of this property of "tanning" hides, tannin-containing materials are in great demand. Tannins also react with salts of iron to form dark-blue or greenish-black compounds, the basis of our common inks. Because of their astringent nature they are useful in medicine. Tanning materials are often utilized in oil drilling to reduce the viscosity of the drill without reducing the specific gravity.
Although nearly all plants contain some tannin, only a few species have a sufficient amount to be of commercial importance. Tannins are found in the cell sap (Fig. 3) or in other definite areas in bark, wood, leaves, roots, fruits, and galls. In most cases these structures are of little value otherwise, so the extraction of tannin is usually incidental to other industries.
Tanning is a very old industry, dating back possibly 5000 years. The Chinese tanned leather over 3000 years ago. The Romans used oak bark for tanning skins. In more recent times the American Indians utilized several native plants in curing their buffalo hides. The first tannery in the United States was established in Virginia in 1630. Twenty years later there were over 50 in New England alone. The industry developed in this region because it was here that the chief raw material, hemlock bark, was most abundant and cheapest. By 1816 the business was worth over $200,000,000, and Boston had become one of the chief leather markets of the world. Fifty years later the industry began to shift westward and southward, as the hemlock became scarce, and many tanneries were established in Pennsylvania. Here oak was used extensively. Still later other tanneries sprang up in the Southern states, using chestnut