xix BALANCED ACTIONS 509 



entire of the carbonic acid, the decomposing substance must 

 be used in quantity somewhat greater than that necessary to 

 produce saturation." 



" If concentrated sulphuric acid be poured on desiccated 

 muriate of soda, the affinity of the muriatic acid is diminished ; 

 and that acid assumes the gaseous state in consequence, 

 and acts no longer by its mass : but if an aqueous solution 

 of muriate of soda be employed, or a diluted acid, whether 

 the sulphuric, or any other, then the muriatic acid may be 

 retained in the water ; in which case it can act by its mass " 

 (Chemical Affinity, pp. 46-48). 



Berthollet shows that a weak fixed acid may displace 

 a stronger volatile acid. " It is to this effect of elasticity 

 that the decompositions produced by the most fixed acids 

 ... are to be attributed . . . ; it is thus that sulphuric 

 acid, by means of heat, decomposes the muriates and the 

 nitrates with a fixed base." 



" I distilled a mixture of oxalic acid and muriate of soda, 

 and the liquor which passed over contained much muriatic 

 acid" (Chemical Statics, I. 192-193). 



In the latter case the weak oxalic acid displaced the 

 strong muriatic acid because of its greater fixedness : 



H 2 C 2 4 + 2NaCl H> Na 2 CA+ 2 HC1. 



(weak (strong 



fixed acid) volatile acid) 



Again, phosphoric acid is a very weak acid, since nearly 

 all its salts are decomposed by acetic acid even though 

 insoluble in water ; but sulphuric acid, which " expels 

 entirely the muriatic and nitric acids from their combina- 

 tions, with the assistance of a sufficient degree of heat . . . 

 is itself expelled from its combinations by phosphoric acid, 

 independently of affinities" (Chemical Affinity, p. 54). 



"Therefore when, by the aid of heat, one body has 

 separated another from its combination, it must not be 

 inferred that its affinity is greater at an ordinary tempera- 

 ture" (Chemical Affinity, p. 55). 



In fact, if mere fixedness were the real test of affinity, 

 ordinary sand must be regarded as one of the strongest 



