BULLETIN 449, U. S, DEPARTMENT OF AGRICULTURE. 



minum was the active metal, in others zinc was used, and in a few 

 cases an alloy, which was prepared in the laboratory by melting to- 

 gether zinc and aluminum. Two cleaning solutions were used : One 

 contained 1 teaspoonful of washing soda per quart of water, and the 

 other was made up of 1 teaspoonful each of washing soda and salt to 

 every quart of water. The results obtained are given in Table II. 



Table II. 



-TJie effect of varying the concentration of the electrolyte by the 

 addition of sodium chlorid. 



Solution. 



Time required for 

 cleaning. 



Remarks. 





Observed. 



Average. 





Series IS. 



Washing soda 



Do 



Seconds. 

 3 

 6 

 3 

 2 

 1 

 1 



10 

 4 

 6 

 3 

 3 

 3 



3 



2.5 



2.5 



1.5 



1 



1 



3 ' 

 2.5 

 3 

 2.5 



1 

 2 



160 

 15 

 15 



WO 

 12 

 10 



Seconds. 



\ ' 



1 ' 



} ' 

 } ' 



^ 



3 



1 



3 



2 



1 '' 

 1 ". 



Aluminium was the active metal used in series 13 



Do 



Washing soda+salt . 

 Do 





Do 





Series I4. 



Washing soda 



Do 



fin series 14, 15, and 16 zinc was the active metal, which was 

 \ cleaned frequently with dilute HCl. 



Do 



Washing soda+salt . 

 Do 





Do 



- 



Series 15. 



Washing soda 



Do 





Do 





Washing soda+salt . 

 Do 





Do 





Series 16. 



Washing soda 



Do 





Do 





Washing soda+salt . 

 Do 





Do 





Series 17. 



Washing soda 



Do 



Do 



Washing soda+salt. 



Do 



Do 



(The alloy of zinc and aluminum was used in series 17. The 

 1 exceptionally long time ohserved in two instances was neces- 

 1 sary to clean two parts of the same silver buckle, badly tar- 

 l nished by use. 



The data recorded in Table II indicate that the average time re- 

 quired for cleaning the silver was less when sodium chlorid was added 

 to the solution. For all practical purposes, however, the difference 

 is so slight as to be of little or no consequence. It is reasonable to 

 assume that by increasing the concentration of the electrolyte, as is 

 the case when sodium chlorid is added, the cleaning reaction will take 

 place somewhat more rapidly. This conclusion is strengthened by 

 further experiments carried out to study the effect of the concen- 



