58 Mr. G. C. Foster on Chemical Nomenclature. 



HC1, H 2 SO 4 , &c. Hence I concluded that the original mean- 

 ing of the term was anything but particularly clear, and that pre- 

 viously to the time of Laurent and Gerhardt it could not be said 

 to have had a strictly scientific and logical sense at all. 



Professor Williamson pays me the unexpected compliment of 

 calling my discussion of what I conceive to be the original mean- 

 ing of the word acid "an elaborate exposition" ; and he so far 

 agrees with the conclusion arrived at as to admit that, instead of 

 that meaning having been particularly clear, I " might safely 

 have called it ' particularly cloudy \" 



This admission and the passage which immediately follows it, 

 seem to indicate that, in speaking of the " original meaning," 

 Professor Williamson did not intend to go further back than Ber- 

 zelius. He says : — . 



"Every chemist knows that the great Berzelius epitomized 

 the prevailing definition by saying that an acid is an electro- 

 negative oxide, and a base is an electro-positive oxide. No 

 definition is complete and perfect ; but this definition is certainly- 

 clear," &c. I have no desire to put upon the word "original" 

 a different interpretation from that intended by my distinguished 

 friend when he employed it, and am therefore willing to accept 

 it as referring to Berzelius's definition. I contend, however, 

 that this definition does not completely express the sense in 

 which the word was currently used; and maintain that the 

 term acid has always been considered applicable to such com- 

 pounds as those represented by the formula? HC1, H 2 S0 4 , HNO 3 , 

 &c, whereas many chemists of high authority have objected to, 

 and avoided, the application of it to such compounds as SO 3 , 

 N 2 O 5 , &c. It is admitted on all hands that this word cannot 

 consistently be applied to both these classes ; and if what is 

 urged in the last sentence is true, it must, I think, be also ad- 

 mitted that, if we are to retain it for either class, usage is in 

 favour of its application to the former. 



Professor Williamson further urges that Gerhardt's definition 

 of an acid as a salt of hydrogen involves the fallacy of arguing 

 in a circle. In this, doubtless, there is some truth; but the 

 objection does not lie to Gerhardt's definition alone. All the 

 definitions of acids, bases, and salts that I have ever examined 

 have appeared to me to amount to more or less direct statements 

 that " acids are bodies which form salts by acting upon bases"; 

 that "bases are bodies which form salts by acting upon acids"; 

 and that " salts are bodies formed by the mutual action of acids 

 and bases." The fact is, that acids, bases, and salts are so in- 

 timately related that no one class can be defined without refer- 

 ence to the other two ; and I do not see that the above defini- 

 tions would be much improved by reading " electro- negative " 



