Silver-Silver Chloride Electrodes Using Optical Silver Chloride Crystals

Abstract

For a c u r r e n t inves t iga t ion of m e m b r a n e potent ia ls , we r equ i r e s i l ve r s i l ve r chlor ide e lectrodes which can m a i n t a i n s tab i l i ty for long t ime per iods even w h e n subjec ted to f r e q u e n t moves f rom one d i lu te (less t h a n 1M) aqueous chlor ide solut ion to another . A ve ry s imple p r epa ra t i on which requ i res on ly rou t ine l abora to ry p recau t ions and yields elect rodes wi th exce l len t s tab i l i ty is descr ibed in this note. Electrode Preparation Si lver chlor ide optical c rys ta l sheet, 1 1 m m thick, is cut in to smal l sections abou t 0.5 cm on an edge. A piece of 0.030-in. s i lver wi re ~ is hea ted over a b u n s e n f lame un t i l the end mel ts to a smal l sphere and whi le hot is pressed in to an edge of one of the sections. The wire mus t be hot enough to me l t the crys ta l a r o u n d itself to secure an adequa te e lec t r i cal and mechan ica l connect ion. A piece of glass tubing , somewha t shor ter t h a n the s i lver wire, and p rev ious ly filled wi th Apiezon W is w a r m e d to soften the filling. The wire is pushed th rough the tube d r a w i n g the crys ta l as close to the end as possible. Af te r the a s sembly has cooled, the crys ta l is r insed severa l t imes successively and b r ie f ly in r eagen t g rade concen t ra t ed n i t r i c acid, water , and concen t ra t ed a m m o n i u m hydroxide , and is f inal ly washed for severa l m i n u t e s in dis t i l led water . Using the crystal as the cathode and p l a t i n u m wire or foil as the anode, a deposi t of meta l l ic s i lver is developed on the crys ta l surface by i m m e r s i n g it in a 0 .05-0.IN redis t i l led hydroch lor ic acid solu t ion and then slowly w i t h d r a w i n g it whi le pass ing about I0 ma of cu r rent . The s i lver deposit forms at the contact of the crys ta l and the wi re and grows down the surface in a t h in jagged l ine. Af te r ob t a in ing the in i t i a l deposits, a group of electrodes are cathodized in the same solu t ion for 30-40 rain at a c u r r e n t of 2-3 ma per electrode. D u r i n g this per iod the in i t i a l deposits b roaden and become more diffuse. The c u r r e n t is r eversed on comple t ion of ca thodiz ing and the elect rodes are anodized at 0.2-0.3 m a / e l e c t r o d e for 2-3 rain. They are then washed for a few m i n u t e s in dis t i l led wa te r and can be used.