Platinizing glass

The glass tubes contain mercury and are firmly fixed in the ebonite cover of the cell so that the distance between the electrodes may not change during the experiment. Contact with the platinum electrodes is made by dipping the copper wires of the circuit in the mercury contained in the tubes. The coating of the electrodes with platinum black is carried out in order to inhibit polarization. When examining certain electrolytes, platinized electrodes cannot be used since platinum black may catalyze the decomposition or the oxidation of the electrolyte. The cell is maintained at constant temperature thermostatically, as conductivity increases rather significantly with temperature. 

The electrodes consist of platinum discs, slightly platinized and mounted in glass tubes which are placed in the glass vessels. The types of Wheatstone bridge commercially available for conductometry and known as conductivity bridges can be used in either the resistance mode or the conductance mode the choice between these modes depends on the character of the solution under investigation and on the performance of the conductance cell. 

Electrical conductance The conductance measurements were made in a glass cell consisting ot two equivalent electrode sections. Circular platinized platinum electrodes parallel to the plane of the membrane were embedded in each section. The membrane area was 0.98 cm2. Resistance measurements were made with and without the membrane in O.IN NaCl solution. 

Figure 17.36 Cyclic voltammograms of (a) naked and (b) platinized conductive glass (FTO) in the presence of 5 mM EMISeCN and 5 mM K(SeCN3) in acetonitrile/0.1 M TBAPF6. Reprinted with permission from Ref. 70. Copyright 2004 American Chemical Society.

Prepare platinized asbestos as follows put 5 g of purified asbestos into a bowl and pour a 1-2% cbloroplatinic acid solution over it. Transfer the fibres impregnated with the solution into a porcelain crucible and roast them first carefully, and then strongly on a blowtorch. Store the prepared catalyst in a jar with a ground-glass stopper. Roast the platinized asbestos -without fall before each experiment. 

Six conductance cells, LC-1 through LC-7, each constructed of borosilicate glass with platinized platinum electrodes, are shown in Figure 5 (LC-7 is similar to LC-5 and... 

The residue free from ammonium salts may be weighed to obtain the total alkali chlorides. The residue is then evaporated almost to dryness with platinic chloride solution, 90-96% alcohol being then added the whole is well mixed with a glass rod and the potassium platinichloride collected on a tared filter (the filtrate should be deep yellow), washed well with 80-90% alcohol, dried at 130° and weighed, The weight found, multiplied by 0-194, represents potash (Kt0). The soda may be found from the weight of total alkali chlorides, by difference,... 

Apparatus. A pyrex tube D, 50 cm. in length and 4 cm. in diameter (Fig. 29), is filled with approximately 300 g. of platinized silica gel packed at each end with a plug of glass wool. The catalyst tube is wrapped with asbestos paper and placed in the electric furnace E. The tube is drawn down at each end, and a 200-ml. distilling flask B... 

A solution of 4.15 g. (0.01 mol) of potassium tetrachloro-platinate(II) in 50 ml. of water is shaken vigorously in a 250-ml., glass-stoppered Erlenmeyer flask with 4.31 ml. (3.61 g. = 0.04 mol) of diethyl sulfide (density, 0.837) until the originally deep red supernatant liquid has become colorless (ca. 15 minutes). The mixture is allowed to remain in the stoppered flask for about 24 hours, whereupon the yellow precipitate of trans isomer initially formed above dissolves. The resulting clear yellow solution is filtered if necessary, transferred to an evaporating dish, and evaporated to dryness at room temperature, f Caution. A hood should be used. This evaporation can be accomplished in about 10 to 20 hours if a constant flow of air is maintained above the dish. 

At Hanau the method adopted is similar to the foregoing. The crude Russian platinum is treated with a mixture of aqua regia (one part) and water (two parts) in a glass retort under a pressure of 12 inches of water. The resulting solution is evaporated to dryness and heated to 125° C., whereby the palladium is converted to the palladous condition. The product is extracted with water, and acidified with hydrochloric acid. On addition of ammonium chloride a precipitate of ammonium chlor-platinate is obtained, contaminated with some ammonium chlor-iridate. On concentration of the mother-liquor a further small amount of ammonium chlor-iridate separates out. The liquid is now treated with scrap-iron, which precipitates all the other platinum metals, together with any platinum and iridium not hitherto precipitated. The deposit is washed free from undissolved iron by treatment with hydrochloric acid, and in turn dissolved in aqua regia. From this... 

A more satisfactory method consists in dissolving platinum sponge in hydrobromic acid saturated with bromine. This may be effected in a sealed glass tube at 180° C., but that is not necessary. If the platinum sponge is simply boiled for a short time with an excess of bromine and hydrobromic acid in a flask with a reflux condenser, the whole is dissolved,8 yielding a solution of brom-platinic acid. 

The capacity of the cell is 450 cc. It is constructed of silica, the adsorption of water on borosilicate glass being too troublesome. The electrodes are made of platinized platinum and have been calibrated with an aqueous solution of potassium chloride O.OIN at 0°C. Introduction of alkali metal and ammonia is made in a similar way to that used in kinetic studies. The formation reaction of the alkali amides is catalyzed by the electrodes. Various concentrations are studied with the same preparation of alkali amide. After ammonia has been removed, the alkali amide is hydrolyzed in the cell. The amounts of alkali ammonium hydroxides are determined by conductimetric titration. 

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