The indigoes of the inferior qualities, characterized by a salt-like color, bordering more or less upon green; by a coarse, uneven, and very dense paste; by not adhering to the tongue, and by not showing a coppery color when scratched,—can never be employed to advantage, notwithstanding their low price. The purchaser of these qualities must be guided solely by the results of analysis; for an article is found in commerce whose richness in indigotine does not exceed twelve to fourteen per cent. The presence of so high a proportion of foreign matter prevents the chemical change which the indigo ought to undergo in the dyeing vat; and this foreign matter, added to the deposits of the dyeing vats, causes great loss of the coloring matter. These indigoes should be used as little as possible, especially in the cold vats used for dyeing cotton and linen. The middle varieties of the Bengal and Guatemala indigoes, and, above all, the red varieties, produce in the cold vats the most advantageous results. The lower qualities above spoken of present less inconvenience in the hot vats used for dyeing wool; and it is for this purpose that they are generally used. In considering the previous observations, the wool manufacturer may arrive at this conclusion: that while he can, with less loss than the maker of cotton fabrics, make use of the lowest qualities of indigo, he will obtain _the best results from the middle qualities of the reddish Bengal indigoes_. The skilled dealers in indigo recognize not only the above distinctions, founded upon the country of production, color, and physical qualities, but they observe whether the article has any of the following defects, which are designated by certain well-understood terms: such as whether the indigo is _sandy_,—when brilliant points are observed in the interior, which are in reality particles of sand; _spotted_, that is to say, of unequal tint, and marked by small blackish points; _ribboned_, marked by transversal bands of a paler, and sometimes red color; _burnt_, the pieces having a scorched appearance, due to rapid drying, and separating into small black fragments under the pressure of the hand; _crumbly_, when in pieces of irregular figure, proceeding from fractures of the squares; _cold_, when the indigo does not adhere to the tongue. The above classification is presented with a full knowledge that these distinctions are by no means recognized in the ordinary commerce in this article. It is not, however, without interest as an illustration of the minute attention given to this subject in Europe, where a higher manufacture requires a nicer investigation of the qualities of materials employed. DETERMINATION OF THE RICHNESS AND PURITY OF INDIGOES.