10 BULLETIN- 449, V. S. DEPARTMENT OF AGEICULTUEE. 



low the boiling point, although the tarnish was removed, the cleaned 

 silver had a somewhat dull appearance. From the results of these 

 tests it is evident that the cleaning solution sliould be kept at the 

 boiling point, since the tarnish is more quickly removed and the 

 silver has a much brighter appearance than when cleaned in cooler 

 solutions. In cases where it is not possible to boil the articles to be 

 cleaned very hot cleaning solutions can be used with fairly satisfac- 

 tory results. 



RELATIVE MERITS OF THE ELECTROLYTIC AND POLISHING METHODS OF 



CLEANING SILVER. 



From the theory of the cleaning process as formulated earlier in 

 the paper it would appear that there is practically no loss in weight 

 of the silver cleaned by the electrolytic method, since the tarnish of 

 silver sulphid is merely reduced to metallic silver. In order to verify 

 this, however, three sterling silver and three silver-plated spoons 

 were weighed, tarnished and cleaned 50 times, and weighed after the 

 final cleaning, zinc being used in a solution of 1 teaspoonful of 

 sodium carbonate in 1 quart of water at the boiling temperature. 

 During the 50 cleanings the three sterling silver spoons lost 0.0043, 

 0.0034, and 0.0034 grams and the three plated spoons lost 0.0026, 

 0.0019, and 0.0024 grams, or an average of 0.00006 grams in each 

 cleaning. This loss is insignificant when compared with the loss in 

 polishing with an abrasive silver polish which actually cuts away 

 the tarnish, as was shown by the following test. One sterling silver 

 and one silver-plated spoon were weighed, tarnished and cleaned 

 six times by rubbing with a paste of finely powdered whiting and 

 water, and weighed after the last cleaning. The spoons lost 0.0094 

 and 0.0087 grams, respectively, or an average of 0.0015 gTams in each 

 cleaning, about 25 times as much as by the electrohi;ic method. For 

 a further comparison three sterling silver spoons were weighed, tar- 

 nished, and cleaned six times with a 5 per cent solution of potassium 

 cyanid. By this method the spoons lost in weight 0.0135, 0.0129, 

 and 0.0123 grams, respectiveh^, an average of 0.0022 grams in each 

 cleaning, a greater loss than by either of the other methods. 



While the electrolytic method removes the tarnish effectively and 

 Avith practically no loss of metal, it gives the articles cleaned a satin 

 finish rather than the bright burnished appearance obtained when 

 abrasive polishes are used. After the spoons used in these experi- 

 ments had been cleaned a number of times by the electrolytic method 

 it was found necessary to rub them with the paste of whiting and 

 water to restore their original bright polish. In practice, therefore, 

 it may be found desirable to use the electrolytic method as frequently 

 as is necessarv to remove the tarnish and to rub the silver with some 



