U R A

U R A

( 455 )

$ 3. Chemical and Phyf.cal Properties.

The method of obtaining reguline uranium,according to Klaproth , though Ample, is notvery eafy, on account of the high heat requiredfor this purpofe; it being greater than that ne-ceffary for the reduction of oxyd of manganefe;50 grs. of the pure yellow oxyd being made upinto a ball with wax were placed in a clofecrucible lined with charcoal, and expofed forfome hours to the mod intenfe heat of the Berlinporcelain furnace, equal to i7o°Wedg. Therewas thus obtained a metallic button weighing28 grs. of an iron-grey colour and metallicluftre, compofed (*f hard minute grains, firmlyadhering to each other. Its fp. gr. was=8.i.Other attempts to reduce the yellow oxyd bythe affiflance of borax and other faline fluxesentirely failed; the refult being only a blackvitreous fcoria.

Uranium is foluble with effervefcence in ni-

tric acid, nitrous gas being at the fame tim#given out, but the other Ample acids appear tohave little or no aftion on it, neither does itappear to be affected by the alkalies. It is noteaftly oxydized by expofure to air and heat, atleaft no change is produced in it by the blow-pipe on charcoal.

Uranium appears capable of two ftates ofoxydation; the method of procuring the yellowor per-oxyd, we have already mentioned in thepreceding fedtion. The black or fub-oxyd maybe procured by mixing the yellow oxyd withoil, and then gently burning it off on a teft;from 120 grs. of yellow oxyd treated thus,Klaproth procured 85 grs. of black oxyd. Thislatter differs from the former, not only in co-lour, but in its producing nitrous gas whendigelted with nitric acid. The relative compo-Ation of the two oxyds, as deduced from theabove fadts, is,

56 metal -f- 44 oxygen = 100 of yellow oxyd,79.9 metal -{- 20.1 oxygen = 100 of black oxyd.

The yellow oxyd is readily foluble in acids.When digefted with diluted fulphuric acid itreadily diffolves, and by evaporation and cool-ing depofits fulphat of uranium in the form offmall prifms of a lemon yellow colour. Dilutenitric acid diffolves the oxyd of uranium withfacility, and the fait hence refulting cryftallizesin oblong hexagonal tables of a light greencolour. Muriatic acid in like manner takes upthis oxyd and cryftallizes in the form of rhom-boidal tables, of a greenifh yellow colour. Con-centrated diftilled vinegar takes up the oxydof uranium by digeltion, and forms cleartopaz-yellow cryftals in the form of tetrahedralprifms terminated by tetrahedral pyramids;when thefe cryftals are very flowly ignited, theacid is driven off, and nothing but the oxydremains, without the form of the cryftals beinginjured. Phofphoric acid is capable alfo of dil-folving this oxyd hut the folution in a fhorttime becomes turbid from the precipitation of aflocculent fub-phofphat of a yellowifh whitecolour.

All the above folutions are decompofable bycauftic alkali, a lemon yellow oxyd beingthrown down. Carbonated alkali throws downa yellowifh white precipitate which is partlyrefoluble in an excefs of mild alkali. Pruffiatof potafh throws down from thefe folutions acopious brownifh red precipitate refemblingkermes mineral. Hydrofulphuret of ammoniaeccafions a brownifh yellow precipitate; and

tin&ure or infufion of galls a copious chocolatebrown one.

The affinity of this oxyd for the acids is foconftderable that its falls are not decompofedby the addition of zinc or of any other metal.

The following vitrefcent mixtures were madeby Klaproth , to afcertain the power of thisoxyd as a colouring fubftance.

Silex — — — 2 drachms

Carb. potafh —■ — 1 drachm

Yellow oxyd — 10 grs.

produced a clear light brown glafs.Silex — — — 2 drachms

Carb. foda — — 1 drachm

Yellow oxyd — — 10 grs.

produced an opake blackifh grey glafs,.Silex — — — 2 drachms

Glafs of borax — — 2 drachms

Yellow oxyd — — 20 grs.

produced a clear glafs of a fmoke-brown colour.

Silex — — — 2. drachms

. Vitreous phofphoric acid

(from bones) —— 2 drachms

Yellow oxyd — — 20 grs.

produced an opake apple-green glafs, likechryfoprafe

Vitreous phofphoric acid 2 drachms

Yellow oxyd — — 10 grs.

produced a clear emerald-green glafs.The glafs produced by the two latter experi-ments was however in fome degree deiique-fcent.