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Atomistry » Sodium » Preparation | ||||
Atomistry » Sodium » Preparation » |
Sodium Preparation
Davy's original method can be modified by electrolyzing a concentrated solution of the hydroxide in contact with mercury, the resulting sodium-amalgam being decomposed by volatilizing the mercury in an atmosphere of petroleum-vapour.
In another electrolytic method formerly worked commercially, fused sodium chloride was employed as electrolyte. There are several practical difficulties to be overcome in carrying on this process, due partly to the corrosive nature of the chlorine liberated, and partly to the tendency to form the so-called subchloride of sodium. Either the formation of this subchloride must be prevented; or, if produced, it must not be permitted to regenerate sodium chloride by interaction with the chlorine evolved at the anode. The chlorine can be removed by contact at the anode with a heavy metal, such as lead, copper, or silver. Lowering the temperature of fusion by admixture with chloride of potassium or of an alkaline-earth-metal, or with sodium fluoride, prevents the formation of the subchloride. Electrolytic processes are gradually displacing the older chemical methods of isolating sodium dependent on the reduction of the carbonate or hydroxide with charcoal or iron. On a small scale, magnesium can be employed as reducer. A laboratory method is the reduction of the peroxide with wood-charcoal, coke, graphite, or calcium carbide - 3Na2O2+2C = 2Na2CO3+2Na; 7Na2O2+2CaC2=2CaO + 4Na2CO3+6Na. Hydrogen is a usual impurity in metallic sodium, and is evolved when the metal reacts with mercury. It can be removed by prolonged heating in vacuum. |
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