TEL

TEL

( 412 )

(<’) Having thus feparated tlie lead, the re-mainder of the folution was largely dilutedwith alcohol, by which a white oxyd of Tellu-rium was thrown down. This oxyd being re-diffolved by muriatic acid, and again preci-pitated by cauftic foda, afforded 178 grs. ofoxyd, equivalent to 148 grs. of reguline tel-lurium.

( f ) The alcoholic folution was next diftilledby which the alcohol was feparated; the refi-dual fluid being diluted with water, was treatedwith nitrat of mercury, in the way already,de-fcribed, by which a button of gold, weighing41.5 grs. was obtained.

(g) 'fhe refidual fluid of f was faturatedwith carbonated foda and boiled, by which abliufh-grey precipitate was obtained : by digef-tion in muriatic acid it diffolved, and oxy-muriatic acid gas was produced: the muriaticfolution being then fuper-faturated with carbo-nated ammonia, there was depofited carbonated■manganefe, mixed with iron, to the amount of92 grs.

(h) The ammoniacal folution was of a bluecolour, upon which it was fuper-faturated withfulphuric acid, and a plate of iron being im-merfed in the fluid, there was depofited 6 grs.of copper.

§ 3. Ph^fical and Chemical Properties.

Reguline tellurium may be obtained byheating the white oxyd of this metal in con tactwith carbonaceous matter : but as' tellurium isboth eafily volatilizable and readily inflammable,certain precautions are neceflary to enfure thefuccefs of the experiment. If the reduction isattempted in a crucible, in proportion as themetal is deoxydated, it rifes in vapours throughthe luting, and burns with a blue flame •, fo thatby the time the oxyd is reduced, the metal willhave efcaped. In order to fucceed perfectly,the following method mull be purfued : theoxyd, being previoufly well mixed with 8 or 9per cent, of charcoal powder, is to be put into afinal! glafs retort with a receiver adapted, andheated gradually to a low ftate of ignition : asfoon as it arrives at this point, a fudden andconfiderable production of carbonic acid takesplace, a little of the mixture paffes into thereceiver, and metallic globules will be obfervedadhering to the neck of the retort, as in- thediftillation of mercury. The apparatus beingthen cooled flowly, the tellurium will be foundat the bottom of the veiled, with a clean brightcryftaliine furface, perfectly reduced and un-mixed with charcoal. 100 parts of white oxydafford about 83 parts of metal.

The colour of pure tellurium is tin-white,palling into lead-grey: it has a brilliant metalliclultre: its fra£iure is ftraight foliated, and by flowcooling it is fuperficially cryftallized : the formof its cryftals however has not been afeertained.It is very brittle, and eafdy pulverizable. Itsfp. gr. is =6.115. It melts at nearly the fametemperature as zinc does 5 and when ignited itbegins to be volatilized. By expofure to theblow-pipe on charcoal, it inflames with aviolence approaching to detonation, burningwith a vivid blue flame, light-green on theedges, accompanied by a heavy white fmoke,which is the oxyd produced by the combuftion.

Tellurium combines readily by fufion with itsown weight of fulphur, and the refult is a lead-coloured ftriated mafs, with a metallic luftre.

By ignition in a retort, a part of the fulphurfublimes, carrying with it a fmall proportion ofmetal, by which it acquires a blackiflr-browncolour.

Nitric acid diflolves tellurium, and the re-fult is a clear colourlefs folution, capable of af-fording, by concentration and cooling, flenderneedle-fhaped cryftals.

Nitrat of tellurium is not decompofable bywater.

Muriatic acid by itfelf has little or no actionon tellurium, but when aflifted by a fmall pro-portion of nitric acid, the folution goes onrapidly. The refult is a clear colourlefs folu-tion, from which a white muriated oxyd, orfubmuriat, is precipitable on the addition ofwater ; in a larger proportion, however, of thisfluid, it is again foluble. If, on the other hand,the concentrated rnuriat is diluted with alcoholinftead of water, no tellurium remains infolution.

Concentrated fulphuric acid, by digeftionwithout heat, takes up a fmall portion of tel-lurium, and acquires thereby a deep ame-thyftine red colour. On the addition ol a littlewater, a black flocculent precipitate takes place,and the folution lofes its colour. The colour ofthe folution is likewife deftroyed by mere heat,a white oxyd being feparated.

If, however, the fulphuric acid is previouflydiluted with water, and mixed with a few dropsof nitric acid, a confiderable portion of tellu-rium is taken up, and the folution is withoutcolour, and not decompofable by the additionof water.

The acid folutions of tellurium are all de-compofed by the alkalies •, but if thefe laft areadded in excels, the oxyd is again taken up,whether a pure or carbonated alkali is made uleof.