Lessons in elementary physics / by Balfour Stewart.

  • Balfour Stewart
Date:
1895
Catalogue details

Licence: Public Domain Mark

Credit: Lessons in elementary physics / by Balfour Stewart. Source: Wellcome Collection.

    475/502 page 455
    LI-SS. 1.1 This f;ict h:is sjivon riso to mimorous iiulustriiil and artistic applications. -V thin but adlieslve layer ot metal may be deposited on an interior metal. This is the process of clcci)o^ fUitittg. Again a metal, usually copper, may be deposited on a prepared concluctmg mould so as to reproduce with accuiacy the form from which the mould was taken. This is ckclro- Ivpiitg. We may also use electrol3'tic methods to extract a metal from an ore or to obtain :i pure from an impure metal. The metals which are usually deposited by the electro-plater are copper, nickel, gold, and silver. For the deposition of copper on all articles which are less electro-positive than copper, a solution of cop- per sulphate made acid with sulphuric acid is em- ployed. If it is desired to deposit copper on metals such as zinc and iron which are more positive than cop- per, a bath of double cy- anide of copper and po- tassium is employed, for on these metals a non-ad- hesive deposit of copper would be immediately produced if placed in a sulphate bath. Nickel is usually deposited from a bath of the double sulphate of nickel and ammonium, whilst gold and silver are best obtained from the double potassium cyanides. The arrangement of a plating vat is seen in Fig. 152. The vat, often made of well enamelled iron, has three brass rods, a /;and c, placet! across the top. The two outer are con- nected together and have suspended from them plates of the pure metal called the anodes. fhe middle rod supports the article to be plated which is named the cathode. The anotles .are connected with the positive pole of ;i b.atlery or djaiamo, .and the cathode with the negative pole. The .anodes dissolve .and keep the solution of constant stiamgth whilst metal is deposited on the cathode. 44-5. Secondary or Storaere Batteries. — If lifter a voltameter h.as been used for the decomposition of water the battery be removed and the voltameter connected with a galvanometer a current will be indicated due to the
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