TUN
TUN
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To a folution of it in water was added lime-water as long as any precipitation enfued : theprecipitate being wafhed and dried, was foundto be pure tunftat of lime: the refidual liquorbeing then evaporated, afforded on cooling,'cryftals of nitre.
Tunftat of potafh is decompofable by everyother acid as well as by the nitric, and the whiteprecipitate is in all thefe cafes a triple fait, com-pofed of potafh, oxyd of tungften, and the pre-cipitating acid.
If the yellow oxyd of tungften is digeftedwith carbonated inftead of cauftic potafh, aneffervefcence is produced by the difengagementof carbonic acid, and the refulting tunftat ofpotafh is the fame as that already defcribed.
Tunftat of foda is produced by digefting theyellow oxyd with cauftic or carbonated foda, andevaporating the liquor, which depofits the fait inqueftion in the form of lengthened hexahedralplates. The tafte of this fait is acrid and metal-lic; it changes the colour of red vegetable infu-fions. as the alkalies do : it is foluble in fourtimes its weight of cold, and in twice its weightof boiling water: it is decompofable by the acidsforming with them triple falts analogous to thofeof tunftat of potafh: the phofphoric acid how-er^r occafions no precipitate, forming with it avery foluble triple fait, which is not decompofedeven by fulphuric acid.
Tunftat of foda is not rendered turbid by thefulphats either of potafh or of magnefia ; butalum and the muriats of lime and barytes throwdown a white precipitate: alkaline pruffiat of pot-aflr occafions no turbidnefs in this ialt, but on theaddition of a little muriatic acid a brown preci-pitate falls down, which is foluble in a largeproportion of water. Neither the fulphuret ofammonia, nor folutions of oxyd of arfemc orcorrofive muriat of mercury occafion any pre-cipitate ; the latter fubftance however changesthe colour of the folution to yellow. Withfulphat of iron there is formed a brown pre-cipitate, which by digeftion in muriatic acid isdecompofed, the oxyd of iron being taken up,and yellow oxyd of tungften remaining behind.Tindture of galls, when mixed with tunftat offoda, occafions an abundant Hocculent precipi-tate ftraw of a pale colour.
Ammonia combines readily with the yellowoxyd, forming tunjlat of ammonia ; which crys-tallizes from its lolution, by evaporation andcooling, in the form of fhining plates likeboracicacid, or in (lender tetrahedral prifms. Its co-lour is very pale yellowifti brown. It has a
* An. de Chin*.
metallic tafte, is foluble in water, is not deli—quefeent, and exhibits with the various reagentsanalogous properties to thofe of the precedingfalts. By a red heat the ammonia is totally de-compofed ; leaving the tungften behind in theftate of yellow or blue oxyd, according as theprocefs has been performed in an open crucibleor in a retort.
The only ufe that has hitherto been fug-gefted of tungften in any form, is as a mordant.The triple acidulous tunftat when digefted, ac-cording to Morveau, h with the red juices offruits, and with infufions of turmeric and tour-nefol, forms with them coloured lakes of re-markable fixity, and hence may be of confider-able ufe in the arts. Thefe experiments, how-ever, on repetition in this country, have notbeen attended with the fuccefs that would na-turally be expected from the reprefentations inthe memoir referred to.
TURBITH MINERAL. See Mercury.
TURMERIC. Terra Merita. (Curcumatonga, Linn.)
The root of the turmeric, which is cultivatedlargely in the Eaft Indies, confifts of a largeoval bulb, from which fpring two or three tor-tuous proceffes three or four inches long. Thisroot is of a dulky brown externally, and of adeep orange yellow within, of a fomewhat fra-grant fmell, and a bitterifh aromatic tafte. Theyellow colour is extracted eafily, both by waterand alcohol, and is fometimes ufed in dyeing,but the dye is extremely fugitive, and cannot befixed on cloth by any known mordant, which isa lofs to the dyer as there is no vegetable fub-ftance that gives fuch a rich orange yellow.When employed in dyeing it is chiefly to givea finifhing glofs to the more folid colours,which foon fades. The yellow- of tumeric isrendered fomewhat paler by acids, but. ischanged to a brick-red by the alkalies and alka-line earths, and it is the latter property thatrenders it of ufe to the chemift, as its fenfibi-lity to alkaline tells is fo great as to indicate afmaller quantity of thefe fubftances than can bedone by any other method, and hence the exaclpoint of faturation may be hit, which is of im-portance in many experiments of refearch. Toapply it, either a fpirituous tincture or a wateryinfulion may be ufed, or more fimply, a frefn-cut lurface of the entire root may be wettedwith diftilled water, and by being rubbed onwhite paper, a very vifible yellow mark will bemade, on which a drop ol the liquor to be
vul. XXX. p-123.