A manual of practical medical electricity : the Röntgen rays and Finsen light . ng much moresoluble, the solution can be made much stronger in regardto its depolarizing power; half the sulphuric acid added toa bichromate solution is required to combine with thepotash to form sulphate of potassium ; the chromic acidsolution is thus stronger m its excitant action ; lastly, thedouble salt chrome alum is not formed when chromic acidis used. The bichromate of soda may be used instead of thepotash salt. A convenient means of preparing the solution, and ofavoiding the trouble of handling the corrosiv
A manual of practical medical electricity : the Röntgen rays and Finsen light . ng much moresoluble, the solution can be made much stronger in regardto its depolarizing power; half the sulphuric acid added toa bichromate solution is required to combine with thepotash to form sulphate of potassium ; the chromic acidsolution is thus stronger m its excitant action ; lastly, thedouble salt chrome alum is not formed when chromic acidis used. The bichromate of soda may be used instead of thepotash salt. A convenient means of preparing the solution, and ofavoiding the trouble of handling the corrosive sulphuric Forms of Primary Cells 39 acid, is afforded by the crystals of the combination of theacid with the bichromate of potash ; seven ounces of thecrystals should be dissolved in two pints of water, and thesolution is ready. The crystals can be purchased at mostelectrical instrument makers. As a result of the mixture of bichromate of potash, sul-phuric acid and water, we obtain potash sulphate andchromic acid. The chemical action wlien the circuit is closed is that the. Fig. 17.—Bottle Bichromate Cell. sulphuric acid reacts with the zinc to form zinc sulphate,liberating hydrogen ; this is oxidized by the chromic acid,in the presence of sulphuric acid, into water, with theformation of chromic sulphate, and, if the potash salt hasbeen used, later of chrome alum. The principal reactions may be expressed as follows : (a) Zn + H2S0, = ZnS0, + H,. (b) K.,Cr207 + 4H,SO, = Cro(S04)3 + KoS04+4H,0 + 03. (c) B., + 0 = ;. {d) Cr2(S04)3K2S04+24H20 = chrome alum. 40 A Manual of Practical Medical Electricity This cell is frequently sold in a bottle form, with anarrangement for lifting out the zinc (Fig. 17), and it isuseful for furnishing strong currents for short periods,, as in working an induction-coil. It is also one of the most suitable primary cells wepossess for heating the cautery or lighting small incan-descent lamps. For these purposes several cells areusually co
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