178 ELEMENTS OF MATERIA MEDICA.

large manufactory (fig. 44) in this metropolis, the retort (which is mideof Welch bricks) is placed perpendicularly in the furnace. Its shipe

Fig. 44.

Manufacture of bone spirit (Carbonate of Ammonia ) and animal charcoal.

is a right rectangular prism, the height being twenty feet, the lengthabout three feet, the breadth two feet: it is closed at both top andbottom by a moveable iron plate, and the fire is made around it. Thebones are introduced at the upper end of the retort. The volatile pro-ducts are conveyed (by an iron pipe, which opens into the upper part ofthe retort) first into water, and then into an iron receiver (in some places anold steam boiler is employed as a receiver) where the brown ammoniacalliquor (bone spirit) and the empyreumatic oil (animal oil) are deposited.The non-condensable portion is a foetid inflammable gas: this, after pass-ing through water contained in a second receiver (a cask or vat), is con-veyed into a chimney, or is burned. The solid residue in the retort isremoved, while red hot, through the lower and underground end of theretort into wrought-iron canisters, which are instantly closed by ironcovers, luted to make them air tight, and then raised to the surface by acrane. When cold, it is powdered and sold as ivory black. A coarsepowder is employed by sugar refiners for decolorizing saccharine liquids.

The products of this operation are easily accounted for. When bonesare heated, their cartilaginous or gelatinous portion undergoes decompo-sition, and its elements (carbon, hydrogen, nitrogen, and oxygen) enterinto new combinations. Some of the oxygen and hydrogen unite toform water. Carbon and oxygen, combining in different proportions,furnish carbonic oxide and acid. Carbon with hydrogen forms carbo-hydrogen; while nitrogen uniting with hydrogen produces ammonia,which, with some carbonic acid, forms carbonate of ammonia. Theempyreumatic oil consists of carbon, hydrogen, and oxygen, with pro-bably some nitrogen.

The carbonate of ammonia contained in the bone spirit is converted