Two hundred grams of cleaned and dried crab shells (Note 1) ground to a fine powder is placed in a 2-l. beaker, and an excess of dilute (approximately 6 N) commercial hydrochloric acid is added slowly to the powdered material until no further action is evident. Much frothing occurs during the addition of the acid, and care must be exercised to avoid loss of material due to foaming over the sides of the beaker. After the reaction has subsided, the reaction mixture is allowed to stand from 4 to 6 hours to ensure complete removal of calcium carbonate. The residue is then filtered, washed with water until neutral to litmus, and dried in an oven at 50–60°. The weight of dried chitin is usually about 70 g., but with some lots of crab shells it may be as low as 40 g.

To 40 g. of dry chitin in a 500-ml. beaker is added 200 ml. of concentrated hydrochloric acid (C.P., sp. gr. 1.18), and the mixture is heated on a boiling water bath for 2.5 hours with continuous mechanical agitation. At the end of this time solution is complete, and 200 ml. of water and 4 g. of Norit are added. The beaker is transferred to a hot plate, and the solution is maintained at a temperature of about 60° and is stirred continuously during the process of decolorization. After an hour the solution is filtered through a layer of a filter aid such as Filter-Cel. The filtrate is usually a pale straw color; however, if an excessive color persists, the decolorization may be repeated until the solution becomes almost colorless. The filtrate is concentrated under diminished pressure at 50° until the volume of the solution is 10–15 ml. The white crystals of glucosamine hydrochloride are washed onto a sintered-glass filter with 95% ethanol. The white crystalline product, after being washed with 95% ethanol and dried, weighs 24–28 g. (60–70% of the weight of the chitin used). The optical rotation of a stable solution of the product containing the α- and β-isomers at equilibrium, [α]^25.5D, varies from +68.8° to +70.1° (c = 4.75 in water).

The product is pure enough for most uses. If a purer product is desired, the crystals may be dissolved in the minimum amount of boiling water and treated with Norit. The resulting solution is filtered and added to a large excess of 95% ethanol and stirred vigorously for several hours. The product is collected after 4–6 hours. An appreciable amount of the β-form of the amino sugar remains dissolved in the alcohol and may be precipitated by adding ether.