Clark and Weston standard cells . ed into the lowerends and filled with mercury. To prevent the possible formationof basic compounds and mercuric sulphate, the solution near thesurface of the anode was stirred continuously. In this way, and witha current density not greater than ampere per square decimeter,the surface of the anode was kept in motion and the mercuroussulphate was swept over the edges of the plate as rapidly as it was TABLE Method, Old Apparatus. Sample Mad e Cone, ofH0SO4 Remarks *i Jan., 04 5% +5% CdS04 a,1 Mar., 04 a5 a6 Apr.,Apr., 0404 5%5% I Slightl
Clark and Weston standard cells . ed into the lowerends and filled with mercury. To prevent the possible formationof basic compounds and mercuric sulphate, the solution near thesurface of the anode was stirred continuously. In this way, and witha current density not greater than ampere per square decimeter,the surface of the anode was kept in motion and the mercuroussulphate was swept over the edges of the plate as rapidly as it was TABLE Method, Old Apparatus. Sample Mad e Cone, ofH0SO4 Remarks *i Jan., 04 5% +5% CdS04 a,1 Mar., 04 a5 a6 Apr.,Apr., 0404 5%5% I Slightly brownish on exposed surfaces 06 a7 May, 04 1:6 at May, 04 1:6 a7 digested with 25% H2S04 a8 May, 04 1:6 aa May, 04 1:6 From top of cover dish a9 June, 04 1:6 aio Sept., 05 1:6 From inside dish a 10 Sept., 05 1:6 From outside dish an Sept., 05 1:6 From inside dish an Sept., 05 1:6 From outside dish ai2 Oct., 05 1:6 ai3 Oct., 05 1:6 1 Samples a2 and a3 not preserved. i8 Bulleti7i of the Bureau of Standards. [ Vol. 4, No. formed. To prevent mechanical loss the inner dish was coveredwith a perforated crystallizing dish, through which the glass stirrerand anode connection passed. A metallic shield attached to theshaft of the stirrer prevented possible contamination by oil andparticles of metal from the bearing. Nine samples, of which seven were preserved, were made in 1904,and four others in 1905, using this form of apparatus, which was designed to give a whiteproduct free from finelydivided mercury, as perTable I. The currentdensity was kept ampere per squaredecimeter in the prepa-ration of all the sam-ples. (b) Electrolytic meth-od, new apparatus.—Inthe preparation of theremaining samples ofelectrolytic mercuroussulphate, the apparatuswas so modified as toperm it the use of greatercurrent densities, whichnecessitated more effi-cient stirring. A layerof mercury 3 to 4 cmdeep, purified as de-above, was h2so4 Hg<
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