264 Mr. G. C. Foster on Chemical Nomenclature, 



acid, SO 3 sulphuric acid, &c. Among the arguments urged by 

 Professor Williamson in support of this proposal, one of the 

 most forcible is founded upon what he says was the original 

 meaning of the word. "There are perhaps no words in use 

 among chemists of which the original meaning was so clear as 

 the word acid, and the correlative word base. They were intro- 

 duced to describe bodies of opposite properties, which are more 

 or less completely lost in the salt or compound of acid and 

 base" (page 423). And again, "I submit that it is not allow- 

 able to use any word in a sense inconsistent with its established 

 meaning and use, unless one has the most ample evidence that 

 it cannot again be wanted, and will not again be used, for its 

 original pupose. Words may. be considered as the property of 

 the ideas which they are used to denote, and the words ' acid ' 

 and f base ' belong to the idea of compounds of fundamentally 

 opposite properties, which unite to form one or more molecules 

 of a comparatively neutral compound " (page 424) . 



No doubt Dr. Williamson's definition of the words acid and 

 base would have met with very general, though not universal, 

 acceptance fifty years ago ; but if we wish to ascertain the " ori- 

 ginal " meaning of these words, we must go much further back, 

 and then that meaning becomes anything but particularly clear. 

 There can be no doubt that sourness was the property whose 

 possession in common by different substances first led to the 

 use of the term acid as a generic name for a class of bodies. 

 Corrosiveness came afterwards to be regarded as an important 

 mark of acidity; but at no time previous to Lavoisier does it ap- 

 pear that the meaning of the word acid was defined with anything 

 like precision. In addition to sourness and corrosiveness, the 

 power of reddening many vegetable blues, of precipitating sulphur 

 from solution of liver of sulphur, of causing effervescence with 

 alkaline carbonates, and of destroying more or less completely 

 the causticity of alkalies, was considered characteristic of acidity \ 

 but how far chemists were from using the word acid to denote 

 any very clearly definable idea, is sufficiently proved by the fact 

 that, in the latter half of the last century, limestone was sup- 

 posed to become caustic when burned by absorbing an acid 

 {acidum pingue) from the fire, and that its power of rendering 

 the " mild alkalies " caustic was due to its imparting to them 

 this same acid*. 



Until the time of Lavoisier, the substances known as acids 

 were regarded as members of the general class of salts, which 

 was commonly divided into salia acida, salia alcalina, and salia 



* The acidum pingue of Meyer was the last form of an idea which had 

 been previously put forth by Van Helmont and by Stahl. (See Watts's 

 'Dictionary of Chemistry/ vol. i. pp. 40 & 115.) 



