IVORY-BLACK. When bones are subjected to destructive distillation in close vessels, the substance of the bone is resolved into its constituent elements, which recombine and form new compounds. Some of these escape in the form of vapour or gas, such as carbonic acid and various hydro-carbons. Water holding carbonate of ammonia in solution is also formed, and an oil, which is collected and used for feeding the lamps, which, being burnt in close chambers, with a very limited access of air, the oxygen of which is just sufficient to combine with the hydrogen of the oil, but not sufficient to form any compound with the carbon, the results of the combustion are water and carbon, in a minutely divided form, which collects on the walls of the chamber, and forms lamp-black. In the distillation of bones muriate of ammonia and sulphate of soda are formed towards the end of the process; the latter is separated by solution and crystallization, and the former by sublimation.1 When all the volatile products are separated, the mass which remains in the retort, consists of the earthy and saline portions of the bone, blackened by the carbon of the animal matter, and forming what is called ivory-black, bone-black, or animal charcoal. In this condition, from its strong attraction for animal colouring matters, it is employed in the refining of sugar for bleaching the syrup, and in other arts for similar purposes. If the bone-black be exposed to a red heat, with access of air, the carbon passes off as carbonic acid, and the bone-ash is left of a light colour, which ash is useful in making cupels for the assayer; it is also a good polishing powder for plate, and is the raw material for the manufacture of phosphorus.
When the material for the production of bone-black consists of ivory dust or shavings, the calcined matter is called ivory-black; it is ground and levigated on a porphyry slab, and produces a beautiful velvety black, which forms the chief ingredient in the ink of the copper-plate printer. Ivory black may be prepared on a small scale in a covered crucible at an ordinary fire. (C.T.)