THE ELECTEOLYTIC METHOD OF CLEANING SILVER. 9 



tration of the solution on the rate of cleaning. It was found, for 

 example, that with a solution of one-tenth teaspoonful of washing 

 soda to 1 quart of water the time of cleaning was approximately six 

 times as long as when 1 teaspoonful was used. Conversely, the in- 

 crease in the rate of the reaction when concentrations of the electro- 

 lyte as high as 1 tablespoonful to 1 quart of water were used was not 

 sufficient to warrant the use in practice of larger amounts than 1 

 teaspoonful. 



As a result of these tests it is believed that a teaspoonful of sodium 

 carbonate to 1 quart of water, with or without the addition of about 

 1 teaspoonful of sodium chloricl, is the most satisfactory concentra- 

 tion of the cleaning solution for general use. 



RELATrVE EFFICIENCY OF ZINC AND ALUMINUM. 



A study of the tables with reference to the time required for clean- 

 ing the silver with aluminum and with zinc indicates that in general 

 there is little difference in the efficiency of th6se metals. In some 

 instances alimiinum and in others zinc cleaned the silver more rapidly. 

 This apparent inconsistency is probably due to the fact that in some 

 cases the metals became corroded or that tile tarnish in some series 

 of tests was slightly heavier than in others. Although the zinc 

 cleaned very efficiently when first put into the solution, it soon became 

 corroded and its efficiency thereby greatly reduced. For example, in 

 tliree tests it was found that spoons having a uniform tarnish were 

 not cleaned at the end of four, five, and four minutes, respectively, 

 by a piece of zinc which had become corroded. After a new piece 

 of zinc was substituted the spoons were cleaned in as many seconds. 

 After the corroded zinc had been cleaned by immersing for about 

 one minute in a sokition of hydrochloric acid (one part HCl sp. gr. 

 1.2 to 10 parts of water) it cleaned practically as well as the new 

 metal. Attempts were made to restore the efficiency to the corroded 

 zinc by cleaning it with vihegar and also by rubbing it with various 

 abrasives such as sand soap and emery paper, but without success. 



EFFECT OF TEMPERATURE OF CLEANING SOLUTION. 



A few experiments were made to determine whether tliis method 

 of cleaning is efficient below boiling temperatures, since under house- 

 liold conditions it might be desirable to clean very large pieces of 

 silver, wliifli could lie boiled only with difficulty, by immersing them 

 in th(! hot cleaning solution contained in a tub or bucket. It Avas 

 fonnd. on an average, that at temperatures as low as 40° C. the silver 

 was f^lcjined only after being IirirricT-sed sevei-al minutes; at ternperii- 

 tures from 50 to 00' ('. in al)Out ten seconds; and at temperatuivs 

 from GO to 100° C. in about five seconds. At temperatures much be- 



