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driven off (which is known by a paper dippedin turmeric liquor no longer turning brown) inthis ftate, if potafh is added, and diluted withmuch water, the whole of the nickel is precipi-tated very fpeedily, but the cobalt remains fuf-pended for a confiderable time.

If copper be contained, after the arfeniat oflead is precipitated, as in the laft procefs, letthe copper be feparated by a bar of iron beforethe nitric folution is decompofed by alkalies.

In the large way cobalt and nickel may beconfulerably feparated by fcorification with nitre,the oxyd firft produced being chiefly cobalt. d

Cobalt was fuppofed by Brugnatelli e to becapable of acidification. This was found byDarracq f to be a miftake, but fome of the parti-culars will (hew fome further circumftances re-lative to the union of arfenic acid and cobalt. Ifzaffre is digefted in ammonia for fome time, ared folution is formed, which when much eva-porated depofits a yellow oxyd. The clear fo-lution, after drynefs, is again foluble in water,but not the yellow oxyd. If zaffre is boiled inWater, a folution is alfo obtained, which whenevaporated depofits a whitilh oxyd, after whichit cryftallizes. The folution is fenfibly acid,but is not a cobaltic acid as was fuppofed, but anarfeniat of cobalt with excefs of acid. Theoxyd in both cafes is not a pure oxyd of cobalt,but a mixture of cobalt with arfenic in fomeHate of oxygenation.

The pureft poflible regulus of cobalt obtain-able by any yet known procefs, is certainly thatwhich is got from the ammoniated folution inthe way above deferibed, but as this is veryexpenfive, chemifts have endeavoured with fomefuccefs to purify this metal by fufion. Lam-padius’s procefs s is the following. Projedt ina red-hot crucible a mixture of 4 ounces offmalt, 2 ounces of nitre, and half an ounce ofcharcoal. A ftrong fmell of arfenic is perceivedin the procefs, and a blackifh grey mafs remains,which is to be again mixed with nitre and char-coal, and deflagrated as before : then throw intothe crucible 2 ounces of black flux and heat it-ilrongly for an hour. This gives a tolerably pureregulus, weighing 6 drams. Powder it, and mixit with 1 dram of nitre and as much manga-nefe, then put it in a luted double crucible, andheat it for an hour in a forge-furnace. Themetal lofes by this operation all its iron, and isnearly pure, excepting a fmall portion of arfenic,which may be further feparated if neceffary.

Tromfdorf’s procefs is nearly fimilar. h The:

1 Trotnfdorf.

zaffre or fmalt is to be twice detonated withnitre, wafhed in hot water to carry off thearfenic now united with the alkali of the nitre,and the refidue digefted in nitric acid, whichwill only touch the cobalt, leaving the iron inthe higheft ftate of oxidation. The purifiedoxyd of cobalt may then be reduced in the com-mon way.

It may be obferved on the fubjedl of repa-ration of iron from cobalt (as this is of con-fequence for manufacturing the fineft pofliblecolour from it) that when an alkali is addedgradually to a mixed folution of the two metals, •much of the iron precipitates before the cobaltfalls, and this diftinftion is very obvious by thecolour. Thus if carbonated potafh be flowlyadded to nitrat of cobalt and iron, the firft pre-cipitate is a dull ochery flime, chiefly iron, afterwhich the cobalt ftiews itfelf by a violet colouredprecipitate, and thus a judicious addition ofalkali (flopping when the violet colour is per-ceived) will alone purify the folution to a con-fiderable degree.•

Preparation of Zaffre, Smalt, and Azure .

All the zaffre and fmalt of commerce is pre-pared in the large way in feveral parts of Ger-many, and particularly at Schneeburg in Mifnia,which affords a very lucrative trade to Saxony .

The cobalt ore is put on the hearth of a fur-nace like a baker’s oven, ’ fo conftructed that-the flame of wood is reverberated on all fidesover the furface, and foorr heats it red-hot. Avery denfe arfenical vapour then begins to begiven out, which is conveyed through a verylong horizontal wooden fquare trough or chim-ney, fometimes as much as a hundred fathomsin length, where the arfenic is chiefly condenfed,though Kunckel remarks that notwithftanding-this enormous length of chimney, fome of thevapours ftill efcape through the further opening?The cobalt ore is calcined for fome hours till it.fcarcely emits any more vapours, after which it-is ground to powder, calcined- a fecond- time,again ground and pafled through a very fine-fieve. This powder is then-mixed with twoparts of powdered flints or quartz, moiftened,and put in barrels, where it grows exceffively-hard. This forms the zaffre in the ftate inwhich it is exported. The real reafon of adding-the flints appears to be for fome purpofes of'concealment, the exportation of the Ample cal-cined oxyd being forbidden under heavy penal-ties.

Smalt, fometimes alfo called zaffre^ and when-.

h Ph.Jovtr. vol. ix.

* An. Chim. torn. 33. r An. Chim. tom. 41. » An. Chim. tom. 26. p. 89.

‘ Kuackd in a note to Neri’s Art dc la Verraie, p. £1.