Abstract
On the determination of the weight of tin coating on tinplates, alkali electrolytic method, rapid alkali electrolytic method and iodometry are formulated in JIS H 0402. Since each of these methods, however, has some drawbacks, electrolytic iodometry which has been suggested by G. H. Bendix, W. C. Stammer and A. H. Carle was reinvestigated to remove these drawbacks. Fundamental experimentations were carried out on the following points: (1) Determination of current density and acid concentration; current density 3 A/dm2 and concentration of hydrochloric acid 1:7 are most suitable. (2) Bath voltage-time curve; when Sn and Fe in the bath are measured after initial electrolysis for 40, 55, 90, 120 sec, the amounts correspond to weight losses of panels. Microscopic structures on these panels are observed. (3) The end point of electrolysis; electrolysis for 60∼90 sec under maximum bath voltage is enough for complete dissolution of sn. (4) The effects of metallic irons upon iodometry; the effects of iron and other ions are negligible. It is found that the amount of iodine adhered to the surface of porous filter and panel is the blank source. On the basis of the results above mentioned, this electrolytic iodometry is compared with alkali electrolytic method and usual iodometry. The weight of tin coating obtained by alkali electrolytic method is 0.05 lbs/B.B. higher and that by usual iodometry is equal to the value obtained by this method.
