CHEMISTRY OF THE EIGHTEENTH CENTURY. 31 



the lowest degree of oxygenation of iron, while peroxide of iron or 

 ferric oxide implies the highest degree. Similarly, suboxide of copper 

 or cuprous 'oxide has the less proportion of oxygen, while copper oxide 

 or cupric oxide has the greater. In some instances some characteristic 

 physical properties of the compound is used to mark it, thus : magnetic 

 oxide of iron, black oxide of manganese, red oxide of lead, etc. But 

 there is another class of compounds also, containing only oxygen and 

 another substance, which Lavoisier called acids. The solutions of these 

 substances are all sour, and redden blue vegetable colours. Acids are 

 distinguished also by their power of combining with oxides, and in 

 this way forming salts. The names of acids are given on the same 

 plan as those of oxides, and the like terminations are used to express 

 the degree of oxidation ; e.g., sulphur^.*- acid, sulphunV acid. Occa- 

 sionally Greek prefixes are employed when still higher or lower degrees 

 of oxygenation have to be expressed, as /$j/^<?sulphurous acid, etc. The 

 names of acids of oxides being thus arranged for, it remains to be seen 

 how salts are named. The name of each salt is duplex, one word indi- 

 cating the oxide, and the other the acid from which it is formed. The 

 name of the acid determines the class, that of the oxide the kind, of the 

 body. Many salts are formed from acids and substances which La- 

 voisier only supposed by analogy to be oxides, e.g., magnesia, lime, etc., 

 and in such case the magnesia, etc., was called the base. Examples 

 of names of salts : sulphate of lead = sulphuric acid + oxide of lead ; 

 nitrate of potash = nitric acid + potash; sulph/fe of lead = sulphurous 

 acid-foxide of lead ; nitrite of potash = nitrous acid-f-potash, etc. 



This nomenclature holds its ground to the present day with only 

 some slight modifications. It had the merit of simplicity, apparent 

 agreement with the facts, and it even suggested new views which the 

 progress of discovery confirmed. The view it presents of the consti- 

 tution of salts became a central idea, which still predominates in the 

 conceptions of chemists ; at least, with regard to a very numerous 

 class of compounds. That view considers all salts as the result of the 

 combination of two distinct and indeed contrasted principles, namely, 

 an acid and a base. Thus, for example, hme is a base which absorbs 

 and combines with the gaseous acid called carbonic acid, the resulting 

 salt being the substance called in common language chalk, but which 

 is chemically named carbonate of lime. The base and oaV/are supposed 

 to exist in this combination, and are said to neutralize each other be- 

 cause the compound has no longer either acid or alkaline properties. 

 Now, in the time of Lavoisier lime had as yet not been decomposed ; 

 but he, remarking the absence of any tendency of that substance and 

 of other alkaline .earths to unite with oxygen, sagaciously divined that 

 this proceeded from these substances being metallic elements already 

 saturated with oxygen. This surmise was soon afterwards completely 

 verified, and lime was proved to be the oxide of a metal, to which the 

 name of calcium was given. Carbonate of lime therefore contains the 



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