TUN
TUN
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filter, carbonat of foda is to be added to thefolution in order to precipitate the lime: this,when wafhed and dried, is pure carbonat, fromwhich the amount of pure lime may be deducedby the common rule of proportion.
The ammoniacal folution contains only am-monia and oxyd of tungften ; it is therefore tobe evaporated to drynefs, and the refidue gentlyignited in a platina crucible; by this procefs theammonia will be deftroyed and driven off', anda pure yellow oxyd of tungsten will be leftbehind.
2. The analyfis of Wolfram is to be con-ducted nearly in the fame manner as the pre-ceding. Having reduced the ore to fine powder,it is to be digefted with nitro-muriatic acid ;a pretty copious difengagement of nitrous gaswill eniue, part of the powder will be diflolved,and the remainder will be of a yellowifh colour:the nitro-muriatic folution being poured off", therefidue is to be treated with liquid ammonia;thus alternately making ufe of thefe two men-ltrua till nothing but a few grains of quartzremains behind.
The muriatic folution, containing the oxydsof iron and manganefe, is to be miked withperfedily neutralized carbonat of potafli, till theliquor begins to grow turbid ; being then gentlyboiled for a minute or two, a copious precipi-tation of oxyd of iron will take place. Theclear liquor being then neutralized with a folu-tion of pearlafh, will depofit a cream-colouredprecipitate, confifting of carbonated manganefe,with a little oxyd of iron, which is to befeparated as already defcribed in the articleiVJ ANGANESE.
The ammoniacal folution contains the oxydof tungften, which may be procured in theform of a yellow powder, by evaporating todrynefs and fubfequent ignition in a platinacrucible.
3. It remains to make a few remarks on theparticulars of the analyfes quoted in the pre-ceding fediion.
The analyfes of tungften by Scheele and theElhuyars agree very nearly with each other,though- they differ very widely from thofe byKlaproth . It is to be obferved however thatthe analyfis attributed to Scheele is merely aninference from a fingle experiment, in which 80grains of tungften were alternately treated withnitric acid and ammonia; the nitric folution,when faturated by carbonated potafh, afforded45 grs. of carbonat of lime; but no mention is
made of the proportion of tungften contained inthe ammoniacal folution. The particulars ofthe analyfis by the Elhuyars we have not feen ;but thofe by Klaproth are ftated at length in hisAnalytical Effays, and appear to be liable to noobjedtions.
With regard to the four analyfes of Wolfram ,it is remarkable that in thofe by Wiegleb andKlaproth there is a deficiency amounting to be-tween 21 and 22 per cent. The particulars ofthefe two analyfes we have not been able tomeet with, and therefore can only account forthe deficiency by fuppofing that the old methodof decomposing this fubftance by fufion withnitre or fixed alkali has been reforted to ; inwhich cafe the oxyd of tungften being renderedfoluble in water by combination with alkali andthe precipitating acid, may have partly efcapedin the wafhings.
The method employed by Vauquelin c andthe Elhuyars d was the alternate application ofmuriatic acid and liquid ammonia, and the fol-lowing was the Jlate in which the componentparts were eftimated, viz. yellow oxyd of tung-ften, magnetic oxyd of iron, and black oxyd ofmanganefe. But though thefe metals were ob-tained from the ore at the above-mentionedftates of oxydation, it does by no means followthat they exifted in this ftate in the ore itfelf.Firft with regard to the iron ; this it is evidentdoes not exift in the Wolfram as black oxyd ;for the mineral is wholly incapable of afte&ingthe magnetic needle. Secondly, with regard tothe manganefe; this probably exifts in thewolfram at a low ftate of oxydation, for whendigefted with muriatic acid there is no percepti-ble odour of oxy-muriatic acid, and its colouris very confiderably deepened by gentle calci-nation. Thirdly, with regard to the tungften ;in the analyfes both of Vauquelin and the El-huyars it is mentioned, that the colour of therefidue after digefting wolfram with muriaticacid, was yellow ; from which it would appearthat the tungften exifted in the ftate of yellowoxyd in the ore. It is with'the utmoft diffi-dence that we oppofe our own experiments tothofe of fo accurate and able a chemift as Vau-quelin, yet as they were carefully made wecannot avoid ftating them. The wolfram thatwe operated on was from Cornwall , and of adark liver colour. When digefted with nitro-muriatic acid, there was a copious productionof nitrous gas, the liquor became of a high winecolour, and had taken up oxyd of iron and
u No. 19. p, 17.
: Elhuyars, tranflated by C. Cullen, p. 30.