Molybdoena, a mineral that is frequently confounded with black-lead ; though possessing properties widely different from the latter -It is of a laminated texture, or formed of plates which slightly cohere ; are somewhat greasy to the touch, and soil the fingers ; leaving, on paper, marks or traces of a dark-grey colour.
This metal has, hitherto, been found only in Sweden, Germany, Carniola, and the Alps. It is of a light lead-grey Shade, sometimes shaded with red, or streaked with a blueish.grey. It is insoluble in the sulphuric and muriatic acids ; though, in a boiling heat, it tinges them green ; effervesces with warm nitric acid, leaving a grey oxyd.or powder undissolved; and also with soda, to which it imparts a reddish pearl-colour.
Molybdoena is at present extremely scarce; but, should it ever be found in abundance, it will certainly be of great utility both for dyeing and painting. If one ounce of the perfect oxyd of molybdoena, be boiled with sixteen ounces of water, till the liquor is reduced to one-third ; then filtred, and half an ounce of it poured into a small glass vessel, containing ten grain's of tin-filings; and next, if four drops of the muriatic acid be added to this mixture, and the whole be suffered to stand at rest, a fine blue colour will be speedily produced, which rises from the bottom; gradually acquires a deeper shade ; and is, at length, deposited in the form of a blue powder.
A beautiful blue lake may likewise be obtained, by precipitating the solution of muriat of tin, by means of dissolved molybdat of pot-ash, if both solutions be previously diluted with a considerable proportion of distilled water -This precipitate is called by RicHter blue carmine; and, we conceive, might be of eminent service to portrait-painters.