This substance, which is now much used for tanning, is obtained from the bark of the Hemlock Spruce (Tsuga Canadensis, Carriere = Abies Canadensis, Linnaeus), a tree 70 to 80 feet high, found over a very extensive area in North America, extending from Nova Scotia, Hudson's Bay, and New Brunswick, through Canada and the United States, as far south as North Carolina. The tree yields Canada pitch, used for similar purposes as Burgundy pitch in Europe. Oil of Spruce, or oil of Hemlock, is also distilled from the leaves, and used in medicine. The bark contains 14 per cent. of tannin. In the southern parts of the United States the stripping of the bark commences in the spring, and continues during April and May. In New York, Michigan, and Wisconsin, the bark is collected in June and July, and further north it is still later; that obtained furthest south is said to be of the best quality. In consequence of the demand for Hemlock bark, the forests are said to be fast disappearing. The extract, which has superseded the export of the crude bark, contains from 18 to 25 per cent. of a deep red tannin, which gives considerable weight and firmness to leather.

The following is given as the mode of preparing the extract: - "The bark, in pieces 1/2 to 1 inch thick, and several inches long, is soaked for about 15 minutes in water at 93° Cent. (2000 Fahr.); it is then fed into a hopper, which conducts it to a 3-roller machine, something like a sugar-cane mill, through which it passes. Coming out lacerated and compressed, it next falls into a vat of hot water, where it is agitated by a wheel, that the tannin from the crushed cells may be dissolved in the water; hence it is raised by a series of buckets on an endless chain, somewhat in the manner of a grain elevator, to another hopper, whence it is fed into another 3-roller mill; here it receives its final compression, and comes out in flakes or sheets like coarse paper, and almost free from tannin. The buckets are made of coarse wire that the water may drip through during the elevation. In order to avoid the blackening action of iron whenever this metal is brought into contact with the solutions, it is thickly coated with zinc. The solution is evaporated to a solid consistency generally by vacuum pans.

About 2 tons of bark are represented by one bar (of less than 500 lb?.) of extract." The total production of extract is probably over 10,000 tons annually, ranging in value between L17 and L 23 per ton.

No returns are available as to the quantity and value of the extract imported into Britain, as it is included under barks and extracts used by dyers and tanners. Neither is there any record of the cost of extraction; the profits, however, must be sufficient to maintain a large plant and a considerable number of hands.

From the general use of the extract, it would seem that it is applicable to most, if not to all, kinds of leather. It also has a medicinal value, in consequence of its having similar properties and effects to extract of Rhatany (Krameria trian-dra), and consequently applicable as a medicine where that drug is applied - John R. Jackson, Museum, Kew, in Gardeners' Chronicle.