Elements of chemistry, in two volumes / by John Murray.

  • Murray, John.
Date:
1828
Catalogue details

Licence: Public Domain Mark

Credit: Elements of chemistry, in two volumes / by John Murray. Source: Wellcome Collection.

    37/768 (page 25)
    galvanic action is essential to these changes, was soon after made by the French chemists, Gay-LusSac and Thenard, potash having been decomposed by them by the action of iron ; and as this method yields potassium in much great- er quantity than can be obtained by the galvanic action even of very powerful batteries, it is usually employed in procuring this substance. Clean ii'on-filings are put into an iron tube, bent so that the filings shall lie in the cur- vature towards the middle of the tube. To one extre- mity of it is adapted, by grinding, a smaller tube having a stopper inserted at its open extremity, and containing a quantity of pure potash ; the curved tube is placed across a small furnace, so that the iron-filings are raised to a white heat; the potash is then liquefied by applying to it the necessai’y degree of heat, and it is allowed to run through a small aperture on the filings. It suffers de- composition; the iron attracts its oxygen; and its base, the potassium, is sublimed to the other extremity of the tube, which is kept cold by a freezing mixture. A quantity of hydrogen gas is disengaged during the process, appa- rently derived from the water contained in the potash, and is allowed to escape by a tube of safety connected with the tube : it appears, by the affinity it exerts to the potassium, to assist greatly in separating it from the oxy- gen. The potassium adheres in brilliant plates to the sides of the extremity of the large tube, and when cold is de- tached. It is similar to that obtained from the decompo- sition of the alkali by galvanism, or, at least, is only a lit- tle heavier. The chief difficulty in performing this pro- cess is, to have the iron and potash perfectly pure, and to keep up the heat sufficiently without melting the tube. Some methods have been employed rather more simp's, particularly one by Mr Tennant, in which solid potash and iron-filings are merely mixed together in the extre-