TO PRESERVE STEEL GOODS.-Caoutchouc 1 part; turpentine 16 parts. Dissolve with a gentle heat, then add boiled oil 8 parts. Mix by bringing them to the heat of boiling water; apply it to the steel with a brush, in the way of varnish. It may be removed with turpentine. The oil may be wholly omitted.

SIZE. Oil size is made by grinding yellow ochre or burnt red ochre with boiled linseed oil, and thinning it with oil of turpentine. Water size (for burnished gilding) is parchment size ground with yellow ochre.

SILICA AND CARBON.-Silica is the base of the mineral world. Carbon the base of the organized.

IVORY.

How to Soften it.-Take 3 oz. spirits of nitre, and 15 of spring water; mix together; drop in the Ivory, and let it soak. In three or four days it will be so soft as to obey your fingers.

How to Dye Ivory when Softened.—If you desire to dye Ivory when thus softened, dissolve, in spirits of wine, such colors as you wish to use. When the spirit of wine is sufficiently tinged with the color you have put in plunge in your Ivory, and leave it there till it is dyed to suit you. Then take out the Ivory and give it what form you please.

How to Harden Ivory.-To harden the Ivory afterwards, wrap it up in a sheet of white paper, cover it with dry, decrepitated salt, and lay it by for twenty-four hours, when it will be restored to its original hardness.

To re- Whiten Ivory which has Turned a Brown Yellow.-There are two ways of doing this, namely: 1. Slack some lime in water, into which drop the ivory; decant it gently, and boil till it looks quite white. 2. To polish it afterwards, set it in the turner's wheel, and after having worked it, take some rushes and pumice stone, mix a subtile powder with water, and rub till it becomes perfectly smooth: then heat it by turning it over a piece of linen or sheepskin, and when hot rub it with a little whitening diluted with olive oil; then rub it with a little dry whitening alone, and finally with a piece of soft white rag, and the Ivory will look remarkably white.

How to Dye Ivory Black.-Immerse the Ivory in a boiling solution of logwood, then take it out, and wash it in a solution of copperas Blue.-There are two ways of reaching this color. The first is to soak the Ivory in a solution of verdigris in nitric acid, which will make it green; then dip it into a solution of boiling hot pearlash, and it will turn blue. The second way is as follows: Immerse the Ivory in a solution of sulphate of indigo and water, partly neutralized with potash.

Green.-Steep blued Îvory in a solution of nitro-muriate of tin, and then in a decoction of fustic. Another and a more instantaneous plan is to immerse it in a solution of acetate of copper.

Yellow-Steep the Ivory in a bath of neutral chromate of potash, and afterwards in a boiling solution of acetate of lead.

Red.-Soak the Ivory for a short time in a solution of tin, and then in a decoction of cochineal.

Violet.-Moisten the Ivory with a solution of tin, as before; then immerse it in a decoction of logwood.

Purple.-Soak the Ivory in a solution of sal ammoniac into four times its weight of nitrous acid.

Fluid for Marking Ivory.-Take nitrate of silver, 2 parts; nitric acid, 1 part; water, 7 parts. Mix.

Etching Fluid for Ivory. Take of diluted sulphuric acid and diluted muriatic acid, equal parts. Mix.