hydrogen, ct irre-pt Hiding with tin- amount of the metal taken, mav be 

 difectlv obtained. < )nc i_;ram of hvdro^vn. occupying' a \olmiic of 



ll'lt* litre-, at () and <<>(>nim.. is evolved jicr -"i! 1 plains of i>< itassium, 

 or _!"> u'i'am- of sodium. Tin- phenomenon niav lie observed in tlie 

 following way :a solution of sodium in mercurv or ' sodium {inuilgain, ; 

 as it is "jeiierallv called i- poured into a vessel containing water, and 

 ownm' TO its weight sinks to the bottom : the -odium held in the 

 nierciir\" 1 hen acts on the water like pure sodium, liberating hydrogen. 



liif 1 1 n MTU i v doe- not act here, a i id the sail it 1 amount of it as \vas taken 

 for dissolving the sodium i- obtained in the residue. The hydrogen i- 

 evolved little by little in the form of bubbles, which pa-- through 

 the liquid. 



]>evoiid the hydrogen evolved and a -olid substance, which remains 

 in solution (it may be obtained by evaporating the iv-ultant solution), 

 no other products are here obtained. Consequently, from the t wo sub- 

 stances (water and sodium) taken, the same number (if new substances 

 (hvdrogen and the substance dis-<il\ed in water) have been obtained, 

 'fi'oin \\hieh we ma\" conclude that the reaction which here takes place 

 i- a reaction of double decomposition or of substitution. The sub- 

 stance- taken were, sodium in a. free -late, and water, which consists of 

 two ^'ases, hydrogen and oxygen. r l'he pnduct- obtained \\cre. 

 hvdro^en in the free state and a solid, which i- nothing else lr,;t the so- 

 ealled dtisticsoda (-odium hvdroxide), \\hich is made ti] of sodium. 

 oxvgen. and half of the hydrogen contained in the water. Therefore, 

 the -ubstitution took" jilace between the hydrou'en and the sodium, 

 namely half of the hvdrogen in the water was replaced bv the sndiuin. 

 and was evolved iii a free state. < >n this basis it mav be said that 

 ca.u si ic soda is nothing else but \\ater. in \\'hich half the hvdrogen 

 is replaced bv metallic sodium. The reaction which Takes place 



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