THE ELECTKOLYTIC 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 chlorid, is the most satisfactory concentra- 
tion of the cleaning solution for general use. 
RELATIVE 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 these metals. In some 
instances aluminum 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 the 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 
three 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 solution of hydrochloric acid (one part HC1 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 vinegar 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 this method 
of cleaning is efficient below boiling temperatures, since under house- 
hold conditions it might be desirable to clean very large pieces of 
silver, which could be boiled only with difficulty, by immersing them 
in the hot cleaning solution contained in a tub or bucket. It was 
found, on an average, that at temperatures as low as 40° C. the silver 
was cleaned only after being immersed several minutes ; at tempera- 
tures from 50 to 60° C. in about ten seconds; and at temperatures 
from 60 to 100° C. in about five seconds. At temperatures much be- 
