468 Prof. Williamson on Chemical Nomenclature. 



distinctive name should be given to the bodies K 2 0, BaO, &c, 

 formed by dehydrating the so-called bases. The absence of any 

 such term is a deficiency sufficiently grave to make one pause in 

 adopting the term anhydride in systematic language, until the 

 idea which it represents is duly applied to the other great class 

 of chemical compounds ; but I cannot, with Mr. Foster, call it a 

 "limitation"; and as I have not said that Gerhardt imposed any 

 " limitation " in the matter, I may fairly be excused from accept- 

 ing Mr. Foster's challenge to show where Gerhardt imposed it. 

 If Mr. Foster were to deny my statement that the anhydrous bases 

 are unprovided by Gerhardt with a name corresponding to that 

 of anhydride for the acids, I might probably beg the favour of 

 his quoting chapter and verse, in support of his denial. But as 

 matters now stand, the two great classes of chemical compounds 

 are called acids (such as CO 2 , SO 3 , SiO 2 , &c.) and bases (such 

 as K 2 0, CaO, Fe 2 3 , &c). Whoever wants to take their 

 names from them for the use of their hydrates must at least give 

 them new names which will do as well. And he will certainly 

 not be permitted to take the two names from the two classes of 

 bodies, and put them off with one name between them. Ger- 

 hardt seems to have thought that he would be permitted to do 

 so, but the single substitute (anhydride) which he offered is ad- 

 mitted to be not only insufficient but absolutely unacceptable. 



Perhaps the most important advantage which chemists have 

 gained by representing all substances of known composition by 

 typical formula?, has been the increased clearness with which 

 they have been able to compare the properties of bodies with 

 one another, without the mind being encumbered by conven- 

 tional differences of form. Even elements are now for the most 

 part represented by formulae analogous to those used in repre- 

 senting compounds; free hydrogen being HH like HC1, free 

 oxygen being 00 like CaO, free phosphorus being P 3 P like 

 H 3 N, &c. The one great difference which stands forth above 

 all other chemical differences, is that which is described in various 

 terms, all more or less similar in import to acid or acid-like and 

 basic or base-like. We have long since admitted that this fun- 

 damental difference is a difference in the degree in which various 

 substances exert analogous effects, a weak acid acting like a base 

 under the influence of a very strong acid, and a weak base 

 acting like an acid to a very strong base. Among simple and 

 well-known compounds this difference is most markedly repre- 

 sented by oxides such as SO 3 , P 2 5 , SO 2 , CO 2 , CaO, K 2 0, 

 PbO, Bi 2 O 3 , &c. ; and every chemist knows that compounds of 

 the former class are electro-negative to those of the latter class, 

 electro-negative oxides being called acids, and electro-positive 

 oxides being called bases. It is admitted that hydrogen- salts 



