Electrolysis with Alternating Currents

If the polarity of the current is not allowed to change too rapidly, it is possible, since oxidation and reduction occur successively at each pole, to accomplish electrolyses with alternating currents. Experiments with this end in view have been made b Drechsel.1 Dehydration is a case of simultaneous reduction and oxidation. The supposition that in living organisms carbamide is produced from ammonium carbamate by the splitting off of water prompted Drechsel to make experiments in this direction. When an aqueous solution of ammonium carbamate is electrolyzed with a current from a battery of 4-6 Grove cells, and platinum electrodes used, carbamide is obtained independently of the electrode material when alternating currents are employed. The reactions are supposed to be either 

The observation that the platinum electrodes were strongly attacked, with the formation of platinum salts, caused Gerdes2 to investigate the platinum bases. As the principal product he found a compound to which he gave the following formula  

2 Joum. prakt. Chem. 26, 257 (1882) see also Inaug-Dissert., Leipzig 1882. 

Gerdes also examined the nitrate and sulphate of this base. 

In the course of further researches 1 Drechsel found that when alkaline solutions were used platinum was present in the electrolyzed fluid. Copper when used as electrode showed a similar behavior lead was less attacked, gold hut very slightly, and palladium not at all. 

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In a still later research on the electrolysis of phenol with alternating currents Drechsel1 detected phenylsulphuric acid, dioxybenzenes, a number of acids of the fatty acid series, and in addition to these an oil which he identified as hydropheno-ketone,... 

A variation of the bromine oxidation process which seems to be particularly feasible for the commercial production of aldonic acids involves the electrolysis between carbon electrodes of solutions containing sugars, small amounts of bromides, and a buffer such as calcium carbonate 179), Presumably the reaction takes place by the formation of free bromine at the anode the bromine oxidizes the aldose to the aldonic acid and is reduced to bromide. Yields are almost theoretical in many cases. If the electrolytic method is not well controlled, saccharic acids and 2-keto and 5-keto aldonic acids may be produced 180), Whereas the normal electrolytic oxidation is conducted with direct current, a yield of 55 % of gluconic acid has been obtained with alternating current 181) and platinum electrodes a very low efficiency was observed with graphite electrodes. 

Apart from use in metallurgical research and measurements, solid electrolytes have also been put to use as heating elements in electrical resistance furnaces. In order to prevent electrolysis from occurring, alternating currents must be used. In contrast to metallic heating elements, they may be used in air at around 2000 °C. In view of the fact that their conductivity must be very low at room temperature, there is a need for them either to be kept continuously warm, or to be preheated with an auxiliary heating element. 

The condition of specific and complete conversion of the analyte means for alternative 1 an exclusive and complete electrolytic reaction of the analyte at the working electrode with 100% current efficiency (exhaustive electrolysis), and for alternative 2 preferential and detectable complete conversion of the... 

J. Tafel found that while nitric acid is reduced only to hydroxylamine q.v.) by mercury or well-amalgamated electrodes, a copper cathode reduces it to ammonia and at the same time has no action on hydroxylamine. A. Brochet and J. Petit studied the electro-reduction of nitric acid by an alternating current. T. H. Jeffery described the electrolysis of nitric acid with a gold anode, and obtained from the anode liquor crystals of aurinitric acid, HAu(N03)4.3H20. R. Ihle s observations on the oxidation-potential of nitric acid have been discussed in connection with nitrous acid (q.v.). He found that if the cone, of the nitric acid be expressed by... 

Sodium hypochlorite is also manufactured by the electrolysis of sodium-chloride solution without a diaphragm (p. 97), the solution being less concentrated than that prepared by the chlorine process from sodium hydroxide, but free from the excess of alkali characteristic of that prepared by the older method.2 The process is carried out either in the apparatus designed by Kellner,3 or in that of Haas-Oettel,4 sodium chlorate being a by-product (v. infra). It is noteworthy that electrolysis of sodium-chloride solution with an alternating current also produces sodium hypochlorite.5... 

A simple conductivity cell is shown in Fig. 31.2. Two platinum electrodes are sealed in the ends of the cell. These are usually coated with a deposit of finely divided platinum, platinum black, to eliminate some of the effects of electrolysis. The cell is filled with the solution, and the resistance is measured by placing the cell in one arm of the alternating current version of a Wheatstone bridge. The frequency ordinarily used is about 1000 Hz. 

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