A laboratory manual of electrotherapeutics . scause it to be much less used than other forms of E. M. F. is volts. The Bichromate Cell.—The elements in this cellare zinc and carbon plates immersedin a fluid composed of bichromate ofpotassium, (or chromic acid), sulphuricacid and water. When a solution of potassium bichro-mate is treated with sulphuric acid, apurely chemical reaction takes place,resulting in the formation of chromicacid. Thus: — K., Cr2 0,+ H2 S04 = K2S04+H2 O + 2 Cr Os. Bichromate Cell. Trie chromic acid, Cr 03, is the use-ful agent to effect depolarizatio
A laboratory manual of electrotherapeutics . scause it to be much less used than other forms of E. M. F. is volts. The Bichromate Cell.—The elements in this cellare zinc and carbon plates immersedin a fluid composed of bichromate ofpotassium, (or chromic acid), sulphuricacid and water. When a solution of potassium bichro-mate is treated with sulphuric acid, apurely chemical reaction takes place,resulting in the formation of chromicacid. Thus: — K., Cr2 0,+ H2 S04 = K2S04+H2 O + 2 Cr Os. Bichromate Cell. Trie chromic acid, Cr 03, is the use-ful agent to effect depolarization by the oxidation of hydro-gen. The process is supposed to be represented in thefollowing reaction: — 6 H + 2Cr 03-f-3H2 S04 = 6 H2 0+Cr2 (SO,),. The final result is, therefore, the production of thesulphate of zinc (at the positive plate), the sulphates of po-tassium and chromium, and water. The cell should be so constructed that both the zincand carbon plates can be removed from the liquid whennot in use. The E. M. F. is two i8 LABORATORY MANUAL Battery Fluid.—The following formulae are gener-ally employed in the preparation of the battery fluid: No. i. Sulphuric acid (commercial) 3 fluid oz. Potassium bichromate (powdered) 2 oz. Water 16 fluid oz. *(Bisulphate of mercury 2 drachms. First dissolve the bisulphate of mercury and then the potassiumbichromate in the water, and then slowly add the sulphuric acid withconstant stirring. Allow the liquid to cool before using. No. 2. Chromic acid (Cr 03) 2 oz. Water 16 fluid oz. Sulphuric acid 1J/3 (Bisulphate of mercury .. 2 drachms.) This fluid is much to be preferred to the former, since the absence of potassium salts prevents the formation of chrome alum, K^C^fSO,)^, which is very difficult of removal from the bottom of thebattery jar.
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