It is evident that the commercial form and the high price of this drug favor fraud, and the desire to illicitly introduce foreign substances into the paste. It is important, therefore, that the purchaser should carefully ascertain the actual value of the article which he is to use. He should know not only the proportion of indigotine contained, which varies in the commercial indigoes from twelve to seventy-five per cent, but the hardness and density. A good indigo ought to have qualities which can be recognized by the eye and touch alone. The first and the only examination ordinarily made by purchasers is in respect to the physical qualities of the article. Different pieces are selected, and their fresh fracture is attentively observed. The purchaser observes whether the squares are like each other, and if the parts of the same piece present the same tint. He determines the porosity by the simple means of applying his tongue to the fresh fracture. The more rapid the adherence of the tongue, the more porous the indigo. By scratching the piece with his finger-nail, he determines the extent of the coppery reflection,—an important test. From all these characters, taken together, the purchaser can form quite a correct idea of the value of indigoes in general; and the greater number of dyers, both in Europe and this country, are satisfied to make their purchases with only this physical examination. The most experienced dealers in this country make no other examination than the physical one. An eminent indigo broker in Boston has permitted me to copy the following memoranda for the physical examination of indigo from his notebook. The chief signs of good indigo are its lightness, feeling dry when touched, and, when broken, appearing of a beautiful violet blue. Good indigo swims in water; if thrown upon burning coals it emits a violet-colored smoke, and leaves but little ashes. In selecting indigo the large regularly formed cakes should be preferred,—those of a fine, rich blue color, extremely free from the white adhesive mould[1], and of a clean, neat shape. When broken, it should be of a bright purple cast, of a close and compact texture, free from specks or sand, and when rubbed with the nail should have a beautiful shiny coppery appearance; when burnt in a candle it should fly like dust; that which is heavy and dull colored should be rejected. Indigo is estimated and classed in commercial language, as follows: fine blue, ordinary blue, fine purple, inferior purple, and violet, strong copper, and ordinary copper. It is purchased by the factory maund (74⅔ lbs. The Bazaar maund is 82²⁄₅₀ lbs.), packed in cases containing on an average 2¼ cwt., dammered (pitched) and covered with gunny bagging. ------------------------------------------------------------- [1] Many experienced purchasers in this country pay no regard to this mould, as it weighs scarcely any thing.—Ed. -------------------------------------------------------------