vi CARBONIC ACID AND THE CARBONATES 103 



chalybeate waters, as discovered by the English apothecary % 

 Lane in 1769), and of dissolving zinc. 



(7) Its power of precipitating substances dissolved in 

 alkalis, e.g. sulphur dissolved in lime-water. 



On account of the acid properties of its solutions the 

 French chemists in 1787 gave to the gas the name CARBONIC 

 ACID. 



" As fixed air has been perceived to be produced by the 

 direct combination of charcoal with vital air, by the assist- 

 ance of combustion, the name of this gaseous acid can no 

 longer be arbitrary, but necessarily must be derived from its 

 radical, which is the pure carbonic matter ; therefore it is 

 carbonic acid and its compositions with different bases are 

 carbonates" (Chemical Nomenclature, tr. 1788, p. 32). 



But as Bergman recognised, this acidity belongs to the 

 solution rather than to the gas. For this reason the name 

 " carbonic acid " is now restricted to the solution of the gas 

 in water, whilst the gas itself 1 is called CARBONIC ANHYDRIDE. 

 The recognition of carbonic acid as an acid necessitated a 

 change in the classification of the mild alkalis, which were 

 now regarded as salts under the name of CARBONATES. In 

 later years the term ' alkali ' became associated almost ex- 

 clusively with the caustic alkalis, instead of the mild effer- 

 vescent salts to which the name had been applied for a 

 thousand years previously. 



Cavendish (1767) discovers that chalk and magnesia 

 are rendered soluble by fixed air. To Cavendish belongs 

 the credit of discovering that chalk is rendered soluble in 

 water by the presence of fixed air. This discovery was made 

 in the course of his " Experiments on Rathbone-Place 

 Water" (Phil. Trans., 1767, 57, 92). He found that 494 

 ounces of a water, which on boiling liberated one-seventh of 

 its volume of fixed air, 2 deposited 271 grains of a calcareous 



1 Following Laurent (1854) ; see Chapter XII. 



2 411 ounces of water liberated 66 ounce-measures of fixed air and 

 8J ounce-measures of common air. 



