of Chemical Philosophy and Nomenclature. 183 



culty of defining the terms acid, salt, and base, in any mode 

 consistent with nis classification, they are not met by any facts 

 or reasoning in the much-esteemed letter of my illustrious 

 correspondent. The impracticability of defining a salt, he 

 does not deny ; and with great candour he admits that, in his 

 definition of acidity, he has not been consistent. He concedes 

 that it would be preferable to give the syllable, indicating the 

 electro-negative ingredient, the precedence, as nothing but 

 unwillingness to innovate prevented him from pursuing that 

 course. 



He acknowledges that as combustion, in many instances, 

 takes place without the presence of oxygen, the application of 

 the word combustible, should not be confined to bodies which 

 are susceptible of oxydizement. 



My definition of acidity was as follows : — 



" When, of two substances capable of combining with each 

 other so as to form a tertium quid *, and having an ingredient 

 common to them both, one prefers the positive, the other the ne- 

 gative pole of the voltaic series, we must deem the former an 

 acid, and the latter a base. Also all substances having a sour 

 taste, or which redden litmus, must be deemed acids, agreeably 

 to usage" This definition I would now amend by leaving out 

 the last sentence, and substituting therefore, the following: 

 Also when any substance is capable of forming a tertium quid 

 with any acid or base agreeably to the preceding definition, it 

 must be considered as an acid in the one case, a base in the 

 other. The definition, thus amended, takes in the organic 

 acids and bases. In the form in which it was at first pro- 

 posed, it has not been alleged defective by Berzelius; but he 

 has striven to show an incongruity in the attributes of his 

 double salts, when contrasted with those resulting from the 

 union of some of the acids and bases of his amphigen class; 

 which incongruity is, in his opinion, a sufficient reason for not 

 considering them as simple salts, and their ingredients as acids 

 and bases, agreeably to the opinions of De Bondsdorff and 

 myself. 



Berzelius errs in confounding my opinions with those of 

 De Bondsdorff. However I may have admired the sagacity 

 with which that chemist investigated the pretensions of some 

 haloid salts to certain attributes of acidity or alkalinity ; in my 

 letter on the Berzelian nomenclature, I signified my unwilling- 

 ness to rest my opinions upon a basis so narrow, as that which 



• This term tertium quid has been used by chemists, more formerly than 

 of late, to designate a compound resulting from the union of two bodies, 

 but in its properties resembling neither. 



