﻿MERCUROUS PERCHLORATE VOLTAMETER 



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in this research was prepared by dissolving freshly precipitated 

 mercurous oxide in the perchloric acid. The mercurous oxide wa^ 

 , made by precipitating a solution of pure mercurous nitrate with 

 sodium hydroxide. The precipitate was filtered and was washed 

 until free from nitrates. This solution always gave low results in 

 the voltameter. Analysis showed the presence of small amounts of 

 mercuric mercury. Mercurous oxide is unstable and easily decom- 

 poses into mercuric oxide and metallic mercury. The low values in 

 the voltameter are explained b}^ the fact that mercuric mercury has 

 an electrochemical equivalent which is just one-half that of mercur- 

 ous mercury. Pure mercurous perchlorate was prepared by an elec- 

 trolytic method. The pure perchloric acid was electrolyzed in a 

 small beaker with mercury in the bottom as anode. A small piece 

 of platinum gauze, reaching just below the surface of the elec- 

 trolyte, was used as the cathode. Connections were made to the 

 anode by means of a platinum wire fused into a glass tube contain- 

 ing some mercury. The solution was stirred occasionally — just 

 enough to break up the layer of crystallized salt which tended to 

 form on the surface of the anode. The dense mercurous perchlo- 

 rate solution remained in the bottom of the beaker on the mercury 

 anode, and so hydrogen and only small amounts of mercury were 

 precipitated upon the cathode. As the quantity of mercurous per- 

 chlorate increased, the stirring and diffusion brought mercury ions 

 to the cathode in gradually increasing quantities, where they were 

 precipitated. The electrolysis was terminated when large amounts 

 of mercury began to be deposited upon the cathode. Water was 

 added and the solution was stirred until the crystallized mercurous 

 perchlorate dissolved. This solution, after filtration, was ready for 

 use as a voltameter solution. The amount of free acid which always 

 was present in the solution was about the quantity that was re- 

 quired to make a good voltameter electrolyte. 



Conductivity Experiments. A good voltameter solution should 

 have a low electrical resistance, so conductivity measurements were 

 made to determine the best conducting solutions of mercurous per- 

 chlorate and perchloric acid. The determinations were made at 

 40° by the Kohlrausch method. The data for solutions of per- 

 chloric acid and of mercurous perchlorate were taken by starting 

 with solutions of definite strength, and by adding 1 cc. portions of 

 water until 10 cc. had been added to 10 cc. of the solution; and vice 

 versa, by adding 1 cc. portions of the solution to 10 cc. of water 

 until 10 cc. had been added. Data for the mixture of mercurous 

 perchlorate and perchloric acid were obtained by the use of the 



