COB

( 306 ) COB

The colour of this is the fame as that of thepreceding variety. It occurs in a pulverulentor indurated ftate, difieminated through orinvefting other minerals, and occafionally inmafs. It is dull, opake, and has an unevenearthy fratfture. In other refpects it agreeswith the preceding.

Sp. IV. Native Sulphat of Cobalt . Natur-Ucher Koboltvitriol. Sulfate de Cobalt natif.

At Herrengrund, near Neufohl in Hungary ,is found a faline fubftance in the form of tranf-lucid ftaladfites of a pale rofe red colour : itwas at firft fuppofed to be fulphat of manganefe,but from an analyfis by Klaproth it appears tobe a pure fulphat of cobalt.

ReduElion of the Ores and Analyfis.

Cobalt is never employed in the regulineftate for any purpofe of manufactory, the foielife of this valuable metal being to give variousfhades of blue colour to glafs, porcelain, andother earthy mixtures, and when thus employedit mull be in die ftate of oxyd. But the inten-fity of colour given by the oxyd in very fmallproportion is fo great that it is found more con-venient, after due calcination, to mix and diluteit with a quantity of vitrifiable earth, and in thisftate it is generally fold, that is, either limplymixed with earth, when it appears as a browngritty powder called Zaffire, or elfe alreadymelted with a portion of vitrifiable materialswhen it becomes a glafs of a moft intenfe bluecolour, which, when properly ground and fifted,forms the Smalt of the (hops.

The preparation of thefe two articles of com-merce will be mentioned, after the analyfis ofthe cobalt ores has been defcribed.

Many of thefe ores are complicated and diffi-cult to analyze. The natural metallic admix-tures with cobalt hitherto difcovered are thefollowing:

1. Arfenic, generally in very large quantity,part of which is in the ftate of reguline arfenic,and as it appears, another part is in the ftate ofarfenic acid, or at leaft is brought to this ftatein the procefs of analyfis. This unites withpart of the cobalt forming an arfeniat of cobalt,which has often been miftaken for the pureoxyd. The entire feparation of the two isattended with much difficulty.

2. Nickel is abundantly mixed with many ofthe cobaitic ores, and not eafily feparated, beingfoluble in the fame menftrua.

3. Iron, in variable quantity, generally ad-heres to the natural cobalts, and is a hurtfulingredient, as it much alters and impairs the

* Klaproth.

beautiful blue colour for which alone cobalt isvalued.

4. Manganefe, which now and then is mixedwith the cobalt ores, has a ftill worfe effect thaniron on the colouring power.

5. A little copper is contained in fome ofthe ores of cobalt, but does not much injuretheir quality.

An imperfect analyfis of the cobalt oresrefembling that of Tunaberg, and confiftingchiefly of arfenic and cobalt is made in the dryway, by mixing the ore with charcoal, 5 orbetter with faw-duft, and roafting it to expelthe arfenic, with the precautions defcribed underthat metal. The remaining oxyd, after thoroughcalcination, fhould be mixed with about fourtimes its weight of an equal mixture of carbonatof potafli and tartar (or with any other falinereducing flux), and heated intenfely for about15 minutes in a heat fufficient to melt call iron.A button of reguline cobalt is found beneaththe fcoria, which laft are always of an intenfeblue almoft black, owing to the folution of partof the cobalt-oxyd. From 100 grains of theore of Tunaberg Klaproth obtained in this way44 grains of regulus of cobalt, but this wouldobvioufly be impure whenever the ore containediron, or copper, or nickel, nor is it quite certainthat every atom of the arfenic would be ex-pelled.

The reducing flux employed by Beaume isthe following: mix one ounce of roafted ore ofcobalt with three ounces of black flux and halfan ounce of potalh, cover it when in the cruciblewith about one ounce of fait, and heat at firftflowly, afterwards very brilkly for about a quar-ter of an hour.

For the mere purpofes of analyfis the follow-ing laboured and accurate analyfis of the fameby Taffaert is much preferable, 6 the particu-lars of which may be given, as the whole isextremely inftradtive.

That the reader may better underftand theprocefs it may be premifed, that when regulinearfenic is boiled with a little nitric acid it is dif-folved and converted into white oxyd, all of.which is depofited by mere evaporation to afmall bulk of liquid : but when much nitric acidis ufed, the arfenic is more or lefs acidified,becomes thereby much more foluble in water,and then adting as an acid, it readily diffolves co-balt, iron, &c. forming arfeniats of thofe metals,which are decompofable by the fixed alkalies.It may be alfo added, that oxyd of cobalt isfoluble in ammonia, but oxyd of iron is not, and‘An. Chim. tom. 38.