Prof. W. A. Miller on Chemical Nomenclature. 17 



Dipotassic dichromate . . (K 2 0, 2Cr0 3 ), 

 Dipotassic trichromate . . (K 2 0, 3Cr0 3 ), 

 Dipotassic tetrachromate . (K 2 0, 4Cr0 3 ). 



And in order to point out the unusual nature of these salts, a 

 corresponding alteration in the mode of writing the formula? 

 should be adopted. 



A similar principle, both of nomenclature and of notation, 

 would be usefully applied in representing the composition of the 

 silicates and borates. 



Cases like these are not of unfrequent occurrence, though 

 they are on the whole comparatively rare and exceptional ; but 

 upon their existence Professor Williamson originally founded his 

 chief argument in support of his proposal to limit the use of the 

 term acid to the anhydrous electro-negative oxides. 



While admitting the ingenuity of his arguments, I do not 

 share the views adopted by Professor Williamson in this restric- 

 tion of the term acid. It is true that the use of so awkward a 

 word as anhydride is objectionable, though it has been to some 

 extent adopted from Gerhardt as a substitute for what appears 

 to me still more objectionable, the phrase "anhydrous acid/' 



The difficulty which really is felt in the use of the word acid 

 at all arises from its ambiguity, inasmuch as it has been loosely 

 and indiscriminately applied to two different sets of bodies, — one 

 set consisting of the electro-negative oxides of Berzelius, such as 

 CO 2 , SO 3 , N 2 5 ; the other set, the compounds of a halogen 

 with hydrogen, such as HC1, HI, and HBr. The compound 

 HC1 was regarded as possessing in an eminent degree the pro- 

 perties of an acid, long before its chemical composition had been 

 ascertained ; and it certainly has as good a right to be described 

 as an acid as any known substance, so long as chemists regard as 

 an acid compound which possesses a sour taste, reddens vegeta- 

 ble blues, and neutralizes the alkalies. Hydric chloride has pro- 

 perties exactly answering to this description, which, if not strictly 

 expressive of the scientific sense of the term acid, unquestionably 

 expresses the sense in which it is understood in ordinary cases. 

 CO 2 , SO 3 , and N 2 O 5 possess none of these properties until they 

 have become dissolved in, or till they have combined with water. 

 The use of the term acid for bodies which possess properties like 

 those of hydric chloride cannot, as it seems to me, be displaced 

 from our popular language ; and chemists of late years have been 

 gradually accepting the necessity, and have adopted Gerhardt's 

 definition of an acid, as a salt whose base (or rather basyl) is hy- 

 drogen — a definition which includes all the substances popularly 

 known as acids, and others which are chemically analogous to 

 them. 



Phil Mag. S. 4. Vol. 30. No. 200. July ]865. C 



