Volume 1

Fownes' manual of chemistry : theoretical and practical / [George Fownes].

  • George Fownes
Date:
1877
Catalogue details

Licence: Public Domain Mark

Credit: Fownes' manual of chemistry : theoretical and practical / [George Fownes]. Source: Wellcome Collection.

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    out. A cover made of another piece of lime fits on tlie top of this basin; it is also hollowed to a small extent, and has a conical perfora- tion at the top, into which is inserted the nozzle of an oxy-hydrogen blowpipe. The whole arrangement is firmly bound with u'on wire To use the apparatus, the stopcock supplying the hydrogen (or coal gas) is opened, and the gas lighted at the notch in the crucible: the oxygen is then gradually supplied; and when the furnace is sufficiently hot, the metal is introduced in small pieces through the orifice. By this arrangement as much as 50 pounds of platinum and more may be fused at once. All the impurities in the platinum, ex- cept the ii-idium and rhodium, are separated in this manner : the gold and palladium ai-e volatilised; the sulphur, phosphorus, ai-senic, and osmium oxidised and volatilised ; and the iron and copper oxidised and absorbed by the lime of the crucible. Platinum is a little whiter than iron : it is exceedingly malleable and ductile, both hot and cold, and is very infusible, melting only before the oxy-hydi'ogen blowpipe, or in the powerful blast fiu-nace ]ust described. It is the heaviest substance known, its specific gravity being 21-5. Neither aii-, moisture, nor the ordinary acids attack platmum in the slightest degree at any temperature: hence its great value in the construction of chemical vessels. It is dissolved by nitro-muriatic acid, and superficially oxidised by fused potassium hydroxide, which enters into combination with the oxide. The remarkable property of the spongy metal to determine the union of oxygen and hydrogen has been already noticed. There is a stUl more curious state in which platinum can be obtained—that of platmum-hlack, in which the division is carried much further It IS easily prepared by boiling a solution of platinic chloride to which an excess of sodium carbonate and a quantity of sugar have been added, untU the precipitate formed after a little time becomes perfectly black, and the supernatant liquid colourless. The black powder is collected on a filter, washed, and dried by gentle heat. Ihis substance appears to possess the property of coudensiiier aases naore especially oxygen, into its pores to a very great extent: when placed m contact with a solution of formic acid, it converts the latter, with copious efi'ervescence, into carbonic acid ; alcohol dropped upon the platinum-black, become^ changed by oxidation to acetic acid, the rise of temperature being often sufficiently great to cause mflammation. When exposed to a red heat, the black substance shrinks in volume, assumes the appearance of common spongy platinum, and loses these peculiarities, which are no doubt the result of its excessively comminuted state. Platinum forms two series of compounds : the platinous compoiindi3, m which it is bivalent, e.g., ViCl^, PtO, and the P O <=o™Pounds, in which it is quadrivalent, e.g., VtC\, Chlorides.—The dichloride, or Platinous chloride, PtClo, is pro- iced when platinic chloride, dried and powdered, is exposed for