GALL OF ANIMALS, or OX-GALL, purification of. Painters in water colors, scourers of cloth, and many others, em ploy ox-gall or bile ; but when it is not purl tied, it is apt to do harm from the green ness of its own tint. It becomes therefore an important object to clarify it, and to make it limpid and transparent like wa ter. The following process has been given for that purpose. Take the gall of newly killed oxen, and after allowing it to *Settle for 12 or 15 hours in a basin, pour the supernatant liquor off the sediment into an evaporating dish of stone ware, and expose it to a boiling heat in a water bath, till it is somewhat thick. Then spread it upon a dish, and place it before a fire till it becomes nearly dry. In this state it may be kept for years in jelly pots covered with paper, without undergoing any alteration. When it is to be used, a piece the size of a pea is to be dissolved in a tablespoonful of water.
Another and probably a better mode of purifying ox-gall is the following. To a pint of the gall boiled and skimmed, add an ounce of fine alum in powder, and leave the mixture on the fire till the alum be dissolved_ When cool, pour into a bottle, which is to be loosely corked. Now take a like quantity of gall, also boiled and skimmed, acid an ounce of common salt to it, and dissolve with heat ; put it when cold into a bottle, which LS likewise to be loosely corked. Either of these preparations may be kept for several years without their emitting a bad smell. After remaining three months, at a mode rate temperature, they deposit a thick sediment and become clearer, and fit for ordinary uses, but not for artists in water colors and miniatures, on account of their yellowish-green color. To obviate this inconvenience, each of the above liquors is to be decanted apart, after they have become perfectly settled, and the dear portion of both mixed together in equal parts. The yellow coloring matter still
retained by the mixture coagulates im mediately and precipitates, leaving the ox-gall perfectly purified and colorless. If wished to be still finer, it may be passed through filtering paper; but it becomes clearer with age, and never acquires a disagreeable smell, nor loses any of its good qualities.
Clarified ox-gall combines readily with coloring matters or pigments, and gives them solidity either by being mixed with or passed over them upon paper. It in creases the brilliancy and the durability of ultramarine, carmine, green, and in general of all delicate colors, whilst it contributes to make them spread more evenly upon the ivory, &c. When mixed with gum-arabic, it thickens the colors without communicating to them a disagreeable glistering appearance ; it prevents the gum from cracking, and fixes the colors so well that others may be applied over them without degradation. Along with lamp-black and gum, it forms a good imitation of China ink. When a coat of ox-gall is put upon drawings made with black lead or crayons, the lines can be no longer effaced, but may be painted over safely with a variety of colors pre viously mixed up with the same ox gall.
Miniature painters find a great ad vantage in employing it; bypassing it over ivory it removes completely the unctuous matter from its surface; and when ground with the colors, it makes them spread with the greatest ease, and renders them fast.
It serves also for transparencies. It is first passed over the varnished or oiled paper, and is allowed to dry. The colors mixed with the gall are then applied, and cannot afterwards be removed by any means.
It is adapted finally for taking out spots of grease or oil.