TAN
TAN
( 401 )
it, which is by means of fulphuric acid. When,a refin is immerfed in tliis acid it is fpeedilydiflolved, forming a brown-red folution, whichby continuing the digeftion turns to black.Heat is not necefl'ary to effect the folution, buthaftens it. After a time much fulphureous andcarbonic acids are given out, and if after thisthe folution is copiously diluted with coldwater a black mafs fubfidys, which is partiallyfoluble in alcohol, and this alcoholic folution istotally decompofed by gelatin, and thereforecontains an artificial tannin. It is not necefl'aryhowever to make a compleat folution of therefin in this acid, for if it is long digefted witha fmaller quantity of the acid, the fame gaffesare given out, and the refidue becomes con-verted into a black charred mafs from whichtannin may be extratled by alcohol. Not onlythe refins, but oil, wax, camphor, and manyother inflammable fubftances will yield tanninby digeftion with fulphuric acid, but fome withmuch more eafe than others. The tannin ap-pears to be the fame in all, and there appearsto be a certain period of the procefs when theproduction of the tannin has arrived at itsgreateft quantity, after which a gradual dimi-nution of it takes place, and it finally difap-pears, and the fubfiance becomes mere coal.
There is therefore this difference betweenthe action of the nitric and fulphuric acid uponrefins and other inflammable bodies, which is,that the production of tannin by the formeracid is an ultimate effect, beyond which, nofurther change takes place by a continuation ofthe procefs; whereas with the fulphuric, it isonly an intermediate product, which is loft onfurther digeftion.
The tannin produced by fulphuric acid ap-pears alfo to be much weaker in energy thanthat formed by the nitric.
From all thefe original and truly valuableexperiments therefore, it appears that artificialtannin may be made in the following ways:
1. By limply diffolving in nitric acid, eitherpure charcoal, vegetable or animal, or vegetablecompounds that contain naturally any quantityof uncombined charcoal, or in which charcoalhas been produced by previous expofure toheat, or by fulphuric acid. In thefe the quan-tity of tannin is diredlly proportioned to thatof the charcoal folely.
2. By repeatedly abftradling nitric acid offmoft of the refins, and fome other vegetableinflammables, which is totally independent ofany uncombined charcoal that they may con-tain.
* Journ, de Phyf.
3. By long digeftion of refins, oils, and fomeother fubftances with fulphuric acid, floppingthe procefs before the ultimate effect of theacid is produced, and extracting the tanninfrom the half-charred mafs by alcohol.
Further experiments are required to after-tain what difference there may be betweenthefe varieties of artificial tannin, and betweenthefe and natural tannin. With refpedl to thelatter queftion, one ftriking difference appears,which is, that the natural fpecies is totally de-compofed by nitric acid, whereas the artificialis both produced byAt, and is not eafily, if atall, alterable by any continuance of its action.
Of this metallic fubftance, newly difeoveredby Ekeberg, the following are all the particular*that have hitherto been publifhed.
Sp. 1. Tantalite.
The external colour of this mineral is iron-black, that of a recent fradlure is fomewhatlighter with a bluifh tinge; when pulverized it isa blackifh grey. It occurs imbedded in detachedcryftals of the fize of a hazel-nut; the form ofthe cryftals is an ill defined otlohedron. Itsfracture is compact, and prefents a faint me-tallic luftre. It gives fparks when ftruck againftthe fteel. Sp. gr. 7.95.
Its component parts are tantalium, iron, andmanganefe.
It occurs near Brockaern in the pari fir ofRimito in the government of Abo in Finland ,in a vein of quartz and mica, traverfing a rockof granite.
Sp. 2. Yttrotantalite.
The colour of this mineral when recentlybroken is iron black. It occurs in nodules notlarger than a hazel-nut. Its fradture is com-pact granular with - a metallic luftre. It maybe fcratched, though with difficulty, by aknife. The colour of its ftreak is greyifh.Sp. gr. about 5.1.
It is compofed of tantalium and yttria.
It occurs at Ytterby in Sweden , in a graniterock, accompanied by gadolinite.
§. 2. Phyftcal and Chemical Properties.
Tantalium is obtained from its ores by treat-ing them alternately with cauftic fixed alkali,and muriatic or nitro-muriatic acid. The alka-line folution being fuperfaturated with an acidlets fall a white powder which is oxyd of tan-talium, the fpecific gravity of which after ig-nition is =6.5. This oxyd if ftrongly heated
vel. Iv. p. a8j.
3 *
VOL. II.