Carbon, lamp, and vegetable blacks consist almost entirely of carbon, containing usually from 98 to 99½ per cent. of that substance, the residue consisting of a little ash, water, and occasionally unburnt oil. Bone and ivory blacks, on the other hand, are chiefly composed of mineral matter, which may amount to 65 or 75 per cent. and is mainly represented by phosphate of lime. Their actual colouring matter, the carbon, only constitutes 15 to 30 per cent. of the mass. The balance is water and unburnt animal tissue. Blacks prepared from animal matters other than bone and ivory carry 40 to 80 per cent. of carbon, and their mineral matter is generally in the form of carbonates of lime and of the alkalies. The principal impurity to be watchful of in the vegetable and lamp blacks is a small quantity of oily matter which may seriously interfere with their drying qualities. They should leave very little ash after being burned in a crucible. Bone and ivory blacks are sometimes valued as much for their mineral matter as for their colouring matter. The proportion of this mineral matter is ascertained by heating a certain weight of the black to red heat in a crucible till every trace of black has disappeared, and then weighing the residue. The residue should next be boiled in strong hydrochloric acid till it is dissolved; if there is any which will not dissolve it is most probably barytes, which has been added as an adulterant and to make the black weigh heavy. When the solution is complete, the addition of ammonia will throw down a precipitate of phosphate of lime, which should equal 60 to 70 per cent. of the original weight of mineral matter. If much less than this, it is likely that whiting or gypsum has been mixed with the pigment. As carbon is not acted upon by acids or alkalies, it follows that all pure carbon blacks are in themselves perfectly stable and permanent pigments, and that they exert no influence on other pigments with which they may be mixed. =Animal-black.=--This substance is almost identical with bone-black, but is generally in a more finely divided state. Any animal refuse matter may be used in its preparation, such as albumen, gelatine, horn shavings, &c. These are subjected to dry distillation in an earthenware retort. An inflammable gas is given off, together with much oily matter, ammonia, and water, while a black carbonaceous mass is left behind. This is washed with water and powdered in a mill, the product being animal-black. It is largely used in the manufacture of paint, printing ink, and blacking.