﻿MERCUROUS PERCHLORATE VOLTAMETER 



41 



5. Studies on Perchloric Acid: Mercurous Perchlorate 

 Voltameter^ 



By Fkank C. Mathers and Albert F. O. Germans. 



General Statement. Metals which are eiectrolytically deposited 

 for the purpose of measuring the amount of current passing through 

 an electric circuit, must give quantitative, adherent deposits upon 

 the cathode. Besides these essential requirements there are several 

 other desirable cjualities, such as convenience in using, cheapness, 

 permanence, capacity, and reliability. Silver, copper, lead and 

 mercury have been used. 



Silver, from a solution of silver nitrate and nitric acid, is recog- 

 nized as standard. However, accurate measurements require great 

 skill in manipulation, and close adherence to the exact directions. 

 The silver deposits upon the cathode in crystals, which are easily 

 dislodged and lost during the washing.^ Only small currents can 

 be measured. Silver from a silver perchlorate solution has been 

 used in a few experiments.^ 



Copper, from a solution of copper su.lphate, sulphuric acid, and 

 alcohol, is generally employed because of its cheapness and because 

 large currents may be measured. The results, however, are not as 

 accurate as when the silver nitrate voltameter is employed. 



The lead fluo-silicate voltameter has not received much atten- 

 tion, although accurate results are claimed* for it. 



Mercury, from solutions of mercury salts in both stages of oxida- 

 tion, has been employed at different times by experimenters and has 

 given accurate results. The electrochemical equivalents of these 

 metals, silver, copper, lead, and mercury (ous) are 107.93, 106.9, 

 31.8, and 200 respectively. Therefore, equal quantities of elec- 

 tricity will precipitate approximately twice as much mercury (ous) 

 as silver or lead, and about six times as much as copper. Other 

 things being equal, the accuracies of voltameters using these metals 

 will stand in this ratio. 



The most satisfactory form of the mercury voltameter is that in- 

 vented by Wright, of England, and used to some extent in that 

 country as a meter. The solution of mercurous nitrate and nitric 



1 From a thesis presented to the Faculty of Indiana University for the degree 

 of Master of Arts, hy Albert F. O. Germann, 1910. 



2 Richards, Proceedings American Academy of Arts and Sciences, XXXV, 12i 

 1 1899) and XXXVII, 413 (1902). 



3 Carhart, Willard, and Henderson, Transactions American Electrochemical So- 

 ciety, IX, 374 (1906). 



^ Belts and Kern, I'raiisaetions American ElectrvchemAcal Society, VI, 67 (1904). 



