STEATITE is a kind of saponaceous stone, which is sometimes found of a white colour, at others grey or green, and but rarely red or yellow. Its specific gravity varies from 2.60 to 2.66.
This substance is composed of a mixture of silex, alumine, magnesia, oxide of iron, and water ; but it differs according to the localities in which it is found. It is very c ommon in Germany, and in Cornwall ; and we have no doubt that it may also be found in the western parts of France.
As steatite is not fusible excepting at a very high temperature, and as it can be worked with the great est facility, so it forms excellent crucibles, which harden in the fire, and which litharge penetrates with great difficulty. It also serves as a facing to protect moulds for casting iron, and other metals.
Viscot, of Liege, made a great number of ex periments to prove that this substance might be em ployed by the lapidaries. He formed cameos with it, to which he gave a fine polish, after exposing it to the action of the fire ; and it becomes so hard, as to give sparks like flint, when struck upon hardened steel.
By polishing it, he gave the appearance of agate, and even obtained some pieces which perfectly re sembled the onyx ; hut this appearance was quickly destroyed by the fire, and he found it impossible to restore it.
Having a great affinity with glass, the steatite, when reduced to a very fine powder, and mixed with the colours, becomes exceedingly convenient in paint ing upon it. It is also used as a kind of sympathetic crayon, for drawing or writing with upon glass, and on which it leaves no apparent trace, after the draw ing or writing has been wiped over with a woollen cloth. However, the marks are rendered instantly visible, by breathing upon them ; but they disappear anew, when the glass becomes dry.
The embroiderers and tailors prefer steatite to chalk, to make traces with ; as they are more durable, and do not affect the colours of their cloth.
As steatite has the property of combining with oil or grease, so it enters into tilt composition of the great er part of the balls, which are used for cleaning silks and woollen cloths from oil or grease spots. It also serves as a basis, in the preparation of certain co lours for painting with.
It is employed to give a fine polish to marble, ser pentine, and other gypseous stones. Mixed with oil, it is used to polish glass and metallic mirrors.
If the surface of newly prepared leather be sprink led over with it ; and if, when it has become dry, it be rubbed with a piece of horn, it will give the leath er a fine gloss.
Steatite is also employed to glaze paper, upon the surface of which it is sprinkled, when it is reduced to a very fine powder ; or, which is much better, when mixed with the colouring materials. To glaze the paper, it must be rubbed over with a hard brush.
The powder of steatite, owing to its unctuosity, is one of the substances employed in lessening the fric tion of screws, toothed wheels, and other metallic con tacts.
Steatite is a mineral, which belongs to the primary or secondary formations. It often constitutes beds of great extent, but when pure, it usually forms lumps of greater or less magnitude. That variety of it termed Venice talc, abounds in the Tyrol and the Valteline. The Briancon and the Spanish chalks are found, the one in the Alps of Dauphiny, near Brian con, and the other in the mountains of Arragon. The Venice talc affords a powder, which renders the skin smooth and shining, and is employed as a cos metic. The lard stone is also another kind of graphic talc, and is used in China, to form small grotesque figures.
Fat, and fixed oils, have long been used to lessen friction in machinery. But their bad properties, and the ill scents of these matters, ought to induce us to abandon their employment, and to substitute others for them. And we may likewise add, that the ema nations which they diffuse in the workshops or mills, are frequently inconvenient ; and it would, therefore, be much better to sell them to the manufacturers of oil gas. !lumbago, or the carburet of iron, has been successfully used for diminishing friction in machine ry; but this material is too rare and costly to be or dinarily used. There arc, however, other unctuous minerals to which we may recur, and amongst these, steatite seems to hold the first rank.