Hartshorn, (Spirit of,) is now usually obtained by the distillation of bones, hoofs, horns, and in general the refuse of slaughter-houses. An iron still or retort is generally used with a pipe leading from it into a worm condenser. The retort is filled with bones roughly broken, or other materials, and a strong heat applied. Water, and a tar-like oil, accompanied with a foetid inflammable gas, result; carbonic acid also comes over, but this is mostly taken up by the ammonia, which is formed at the same time, and received in the state of carbonate of ammonia. When the different substances have been condensed in the worm, they should pass into a receiver, which has no communication with the open atmosphere, (on account of the overpowering nuisance of its odour,) but which should have a pipe inserted into the upper part of it, and connected with the ash-pit of the still. The inflammable gas and the smell are conveyed to the fire, where the former ignites; but care must be taken to avoid any explosion, for when the evolution of the inflammable gas becomes slow, or ceases .entirely, the common air passes along the pipe into the close receiver, which is filled with the same inflammable gas; and, under these circumstances, an explosion will take place, which will not only burst the receiver, nut do other injury.

This evil, Mr. Gray observes, may he avoided by placing a valve in the pipe opening outwards, to allow the passage of the gas; and another valve into the receiver, opening inwards; by this means the flaming gas will be stopped in its passage to the receiver; as the valve into the receiver opening, will admit the common air to fill up the vacuum. Thus, by means of this apparatus, if it be well constructed, and proper luting be employed, the distillation of hartshorn may be carried on almost without any smell, although the odour of animal oil is so remarkably offensive. The first product consists of water, animal tar, and volatile salt. A great part of the tarry oil may be separated mechanically; the rest, in a great measure, by a second distillation with a gentle heat. The liquid which comes over consists of a solution of sesquicarbonate of ammonia, with a fetid animal oil, which gives it a peculiar odour. This liquid is still sold in the shops under the name of spirit of hartshorn, as the alkaline liquor obtained from that substance was at one time thought to possess certain medical virtues, not to be found in the alkaline liquor obtained from other animal matters.