Z I N

Z I N

( 502 )

according to Mufchenbroeck, is equal to about26 lbs. upon tV °f 311 inch in diameter. If,however, zinc is hammered at about the tem-perature of 300° F. its malleability is greatlyincreafed; it wdl now bear to be bent back-wards and forwards feveral times before itbreaks ; its fradfure is fibrous and fteel grained ;it may be reduced into thin leaves by lamina-tion, and may be drawn into wire not exceedingvrro of an inch in thicknefs, and pofleffingnearly the tenacity of filver. b The hardnefsof zinc is fomewhat inferior to that of copper :its fpecific gravity varies from 6.8 to about 7.1 ;by hammering it is increafed to 7.19. It yieldseafily to the file, but in a very fhort time en-tirely clogs up the teeth of this inftrument,rendering it quite fmooth. By friction, oreven when kept in a moift warm hand for afhort time, it gives out a very fenfible metallicodour, fomewhat refembling that of iron.When heated to 400° Fahr. and upwards, itbecomes perfectly brittle, and in this ftate maybe pulverized without difficulty in a heatedmortar. At about 700* Fahr. it melts, and ina full red heat is volatilized. It cryftallizes withdifficulty into tetrahedral or comprefied hexa-hedra! prifms.

The aftion of air upon zinc at the commontemperature is very flight; it acquires a verythin fuperficial coating of grey oxyd, whichadheres to the metal and prevents any furtherchange. But if the zinc is melted it foon be-comes covered with a pellicle of grey oxyd,and this being removed as fall as it forms, thewhole mafs of metal is in no very long timeentirely oxydated. If the grey oxyd thus formedis ftill further calcined at a red heat, it ac-quires a greeniffi-yellow colour, and increafes inweight: by a white heat it runs into a compactyellow glafs.

If zinc inftead of being merely melted isignited, it takes fire and burns rapidly, with anintenfe bluifh-white flame of great brilliancy:as the combuftion goes on, the metal is con-verted to a yellowifh-white flocculent oxyd, folight as to be thrown up into the air by theforce of combuftion, a peculiar odour which hasbeen likened to that of arfenic being given out.This fublimed oxyd is commonly known by thename of Flowers of Zinc , and in the writingsof the older chemifts by thofe of Nihil album ,Pomphalix , Philofophical IFool, &c. If this oxydas foon as prepared is put into a dark place, itwill be perceived to emit a bluifh phofphoriclight for the fpace of an hour or more. Another‘ Phil Mag, xxiii, p. z8z. c Opufcula, ii. p. 3>Z.

phenomenon which has probably fome relationto the above is, that, if a filter be filled withflowers of zinc, and water repeatedly palledthrough them, they will appear fuperficially ofa dazzling white, and internally of a pureflcy-blue, which laft however is replaced by thecommon yellowilh tinge in proportion as itbecomes dry. The flowers of zinc like theother oxyd are reducible by an intenfe heatinto a yellowilh glafs.

The compofition of the oxyds of zinc is byno means yet afeertained with the defired pre-cifion, we fhall therefore ftate the refults of allthe experiments that have been made on thisfubjedt, with fuch obfervations as may fuggeltthemfelves.

1. According to Bergman,' 100 parts of zinc,after being diflolved in dilute fulphuric acidand precipitated by cauftic foda, afforded i6tof oxyd dried at the temperature of boilingwater; therefore 100 parts of oxyd are com-pofed of 62 zinc and 38 oxygen. But the oxyddried at this low temperature muft necelfarilyretain a confiderable portion of water; indeedit is by ■ no means improbable that it wouldactually be in the ftate of hydrat, which, ac-cording to Mr. Smithfon, is compofed of 75oxyd and 25 water. If the necelfary corredlionbe made upon this fuppofition, 100 parts ofoxyd will confift of 83.3 zinc, and 16.7 oxygen.

2. According to Vauquelin, d (but from whatparticular experiments we are not informed)100 parts of oxyd of zinc produced by calci-nation of the artificial carbonat, are compofedof 69 of zinc and 31 of oxygen.

3. According to Clement and Deformes, e14.36 parts of zinc heated red-hot in a coatedglafs tube, with a ftream of air palling throughit, afford 17.48 parts of a white oxyd, thecompofition of which therefore per cent, is82,15 zinc, and 17.85 oxygen.

The fame chemifts found that 30 grammesof fublimed oxyd of zinc, by diftillation withcharcoal at a high heat were reduced to 21.82grammes of metallic zinc, according to whichipo parts of fublimed oxyd confift of 72.4 zinc,and 27.6 oxygen. In this however the amountof zinc is very probably under rated, as feveralminute particles might remain unperceived inthe charcoal.

It appears from another experiment of theabove chemifts, that the fublimed oxyd whenexpofed to a forge heat for a quarter of an hourlofes about 7 per cent, and at the fame time ac-quires a dull yellow colour; hence the compo-* An. de Ch. xxyiii. p.47. 'lb. xxxix.p, 3*.