The most common form is that of bone black (commonly called ivory black), made by distilling bones (from which the grease has been removed by boiling) in iron or earthen retorts, the ammoniacal liquor, etc, being collected in proper receivers. The residue is bone black. When used for the purpose of decolorization, further treatment is required: either the bone earth may be entirely removed by hydrochloric acid, as directed in the Pharmacopoeia; or more commonly, in the refining of sugar, and for other manufacturing purposes, this is only partially effected, in some such way as the following: Mix 8 lbs. of the bone black, coarsely powdered, with sufficient water to form a paste, and add 1 lb. of hydrochloric acid. In an hour pour boiling water on the mass, let it settle, pour off the liquid, add more water, and repeat this till the water comes off free from taste. Drain and press the black in a cloth, and dry it. Its power is increased by mixing it with a little potash, heating it to dull redness in a covered crucible, and again washing it.