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sium, and by the same means, that is, by theelectro-chemical action of a powerful galvanicbattery acting on solid caustic hydrat of soda.The mode of preparing sodium therefore isprecisely the same as that of potassium, substi-tuting one alkali for flic other. Sodium mayalso be readily prepared by igniting commonsalt and then beating it to redness with potas-sium in a close vessel. The salt is immediatelydecomposed, and the sodium rises very pure.No hydrogen is disengaged in this process, andtwo parts of potassium produce rather morethan one of sodium."
Sodium is also prepared by the process dis-covered by Messrs. Gay Lussac and Thenard,for obtaining potassium, the apparatus beingprecisely similar, and no other difference beingrequired than to substitute soda for potash asthe alkali to be passed through the ignited ironturnings. As solid hydrat of soda containsmuch more water of composition than hydratof potash, it should be kept for some time infusion at a low red heat just before it is putinto the gun barrel apparatus. In the distilla-tion, a still greater heat is required to obtainsodium than pota-asium, and the transmissionof the soda through the heated barrel should beslower.
Pure sodium is an opnke substance with awhite silvery lustre. It melts at about 200°Fahr. if unalloyed with potassium, and it risesin vapour at a strong red heat. It is exceedinglymalleable and soft like wax so as readily to bepressed out into thin leaves. Portions of sodiummay .Easily be united into one mass by strongpressure, a species of cold welding. Sodium is avery powerful conductor of electricity. Smallglobules of it inflame by the Voltaic spark,and bum with bright explosions. The specificgravity is given by Davy at 0.9348 (water being1.0) and by the French chemists at 0.97 223.
Before we describe the chemical propertiesof sodium we shall notice its alloy with potas-sium, as this very materially alters its fusibilityand specific gravity. These two substancesunite perfectly, and indeed the alloy is alwaysproduced whenever the soda employed for theproduction of sodium is mixed with any por-tion of potash. This is the case with allthe common soda or carbonat of soda that isused when prepared from barilla, unless parti-cular pains be taken to purify it by repeatedsolution and cryftallization ; so that wheresodium is to ba obtained directly from the de-
composition of soda, the alkali manufacturedfrom common salt is perhaps the surest.
When the soda contains as little as five orsix per cent, of potash the mixed alkaline me-tal thence obtained becomes fluid at a tempera-ture little above that at which pure potassiummelts, and when the alloy contains more potas-sium it remains fluid at a common temperature.Three parts of sodium and one of potassiumfrom an alloy fluid at 30°, and which cryftal-lizes into a bright brittle mass when surroundedby salt and ice. Even a thirtieth part otpotassium in the alloy materially encreases itsfusibility.
An alloy of 10. parts of potassium and I. ofsodium is also fluid at 32°, and is lighter thanrectified naphtha. These alloys therefore are inall cases more fusible than pure sodium, andoften more so than pure potassium, and theyare also always brittle and crystallizable. Thealloys may be made either by heating the alka-line metals under naphtha, or even by simplepressure without heat. It should be observedthat these alloys are gradual y oxydated evenunder naphtha when exposed for some time tothe air, and that it is the potassium which firstundergoes this change, and by ( this meanssodium may be purified from a small admixtureof potassium, the latter being entirely oxydatedbefore the former is altered.
When sodium is exposed to the atmosphereit immediately tarnishes and gradually becomescovered with a crust of soda which deliquesces.Sodium confined in oxygen gas combines withit slowly and without any luminous appearanceat a common temperature, but when heated itburns with a very white brilliant sparkling flame.In common air the flame is yellow.
When sodium is thrown on water it producesa violent effervescence of hydrogen with a hiss-ing noise, the globules run about in all directionson the surface of the water, rapidly lessenwithout flame or explosion, and gradually dis-appear, leaving the water alkaline by the sodaproduced. The quantity of hydrogen producedby a given weight of sodium in water is thusgiven by Messrs. Gay Lussac and Thenard,whose experiments very closely coincide withthe results adopted by Sir H. Davy . The modeof conducting the experiment was exactly thesame as with potassium. 2.486 grammes ofsodium decomposed by water gave 1.2525 litresof hydrogen gas at 15° centigrade Th. and 0.75.9metre Bar.; whence it follows that 100. parts