U L T

( 455 )

URA

u

ULTRAMARINE. Outrtmere. Fr. where it Is ufed in the manufacture, or more

This precious colour fo remarkable for itsbeauty and durability is a pure deep fky blue.

It is capable of bearing a low red heat withoutinjury, and it is not fenfibly impaired by theaction of the air and weather. It is the colour-ing matter of the mineral already defcribed un-der the name Lapis Lazuli , and appears accord-ing to an analyfis by Klaproth , to confift oflittle elfe than oxyd of iron. The method inwhich this pigment is feparated from the earthyparts of the above mineral is as follows. Letthe lapis lazuli be heated juft to rednefs, andthen fuddenly quenched in cold water, and letthis be repeated two or three times, till theftone becomes almoft friable; then let it beground down with a few drops of water in aclean iron mortar, or ftill better, in an agateone till it is reduced to a perfectly impalpablepowder. Then take one pint of linfeed oil,warm it over the fire in a clean veffel, and addone pound of bees-wax, one pound of turpen-tine, half a pound of rofin, and half a pound ofgum maftich : keep the ingredients over the fire,with conftant ftirring til! they are melted andthoroughly incorporated together; the refult■will be a tenacious adhefive mafs. Of this takeany quantity, 6 oz. for example, melt it andpour it into a warm clean mortar; then fprinkleupon it 3 oz. of pulverized lapis lazuli, and in-corporate it thoroughly by long beating withthe peftle ; this being done pour in fome warmwater, and again work it about in the famemanner as before: in a Ihort time the waterW'ill become charged with the blue colouringmatter ; it muft then be poured into a clean tallglafs, and replaced by frefh, proceeding in thismanner till the pafte will give out no morecolour on the addition of frefh water. ByHanding a few days the colour will fubfidefrom the water in which it was fufpended; theclear fluid being then decanted off, and the reftgot rid of by evaporation, there will remain adeep-blue powder which is ultramarine.

UMBER.

There are two kinds of umber, the onetailed Cologne Umber , is a variety of peat or ofearthy brown coal. There are large beds of itwrought in the neighbourhood of Cologne,principally as an article of fuel; a pretty confi-derable quantity is alfo imported into Holland,

• Analyt. Eff.

properly in the adulteration of fnuff, for whichpurpofe it appears to be better than the com-mon peat of the country; a ftill fmaller quan-tity is confumed by the paint-makers.

The colour of this vegetable umber is awarm fomewhat pinkifh brown, and is an ufefulingredient to the painter in water colours.

The fecond kind of umber goes by the nameof Twkifl) umber, and appears to be a variety ofthe iron ore called brown ironftone ochre Afpecimen from Cyprus was analyfed by Klap-roth, " and afforded him,

48 Oxyd of iron20 Oxyd of manganefe

13 Silex

5 Alumine

14 Water

ICO

URANIUM.

Uranium is a brittle hard metal, of ex-tremely difficult fufibility. It is foluble innitro-muriatic acid, and is precipitable from itsfolution of a yellow colour by cauftic alkali,and of a brownifh-red by pruffiated potafh.

§ 1. Ores.

Sp. I. Black Uranium. Pecherz , Wern.Pechblende , Widenm, &c.

Its colour is velvet black paffing into iron-grey and brownifh black; it is fometimes fuper-ficially tarnifhed like tempered fteel. It occursin mafs, difleminated, and in fmall reniformpieces. Internally it has ufually a glifteningfemi-metallic luftre; its fracfture is impelfefllyconchojflal, paffing into granular uneven. Itfometimes occurs in thick lamellar or granulardiftintt concretions. It is moderately bard,paffing to foft, is brittle and eafilv frangible.Sp. gr. — y.y.

It is infufible per fe before the blowpipe ;,with foda or borax it forms a dull greyifh flag,,and with the alkaline phofphats a clear greenglafs. It is foluble in nitric acid, giving outabundance of nitrous gas.

A fpecimen from Bohemia was analyfed byKlaproth , (to whom the difeovery of the newmetal which it contains is owing) with the fol-lowing refult.xoL ii. t>* ro6-