524 PRINCIPLES OF CHEMISTRY 



forms the hypochlorite, NaClO. In the same way, by the action of 

 sodium hydroxide on sulphur, hydrogen sulphide is formed, which acts 

 on the soda forming sodium sulphide, in addition to which sodium 

 thiosulphate is formed (see sulphur). In virtue of the possibility of 

 similar reactions, sodium hydroxide acts on many metals and 

 non-metals. Such action is often accelerated by the presence of the 

 oxygen of the air, as by this means the possibility of the formation of 

 acids and oxides rich in oxygen is increased. Thus many metals and 

 their lower oxides, in the presence of an alkali, absorb oxygen and 

 form acids. Even manganese peroxide, when mixed with caustic soda, 

 is capable of absorbing the oxygen of the air, because sodium manga- 

 nate is formed. Organic acids, when heated with caustic soda, give up 

 to it the elements of carbonic anhydride, forming sodium carbonate, 

 and separating that hydrocarbon group which exists, in combination 

 with carbonic anhydride, in the organic acid. 



Thus sodium hydroxide, like the soluble alkalis in general, ranks 

 amongst the most active substances in the chemical sense of the term ; 

 but few substances are capable of resisting it. Even the rocky siliceous 

 substances, as we shall see further on, are transformed by it, forming 

 vitreous slags with it, at all events on fusion. Sodium hydroxide, as a 

 typical example of the basic hydrates, in distinction from many other 

 basic oxides, easily forms acid salts with acids (for instance, NaHSO 4 , 

 NaHCO 3 ), and does not form any basic salts at all ; whilst many 

 less energetic bases, such as the oxides of copper and lead, easily 

 form basic salts, but acid salts only with difficulty. This capability 

 of forming acid salts, particula.rly with polybasic acids, may be ex- 

 plained by the energetic character of the basic properties of sodium 

 hydroxide, and the small development of these properties in the 

 bases which easily form basic salts. These latter bases are even 

 capable of combining with such bases as sodium hydroxide and 

 ammonium hydroxide. An energetic base is capable of retaining a 

 considerable quantity of acid, which a slightly energetic base would 

 not have the power of doing. Certain feeble bases, particularly inter- 

 mediate ones (like alumina) are not at all capable of retaining such feeble 

 acids as carbonic, or, if they form compounds with them, they are very 

 unstable and basic. The formation of acid salts with such acids as 

 carbonic, oxalic, sulphuric, phosphoric, <fcc., which contain two or 

 more atoms of hydrogen, capable of being replaced by metals, is 

 explained by the fact that the normal salt represents the substi- 

 tution of sodium for all the atoms of hydrogen. Such monobasic 

 acids as nitric, hydrochloric, fec., do not form any stable acid salts 

 (although they form unstable compounds of the normal salt with the 



