THE CHEMICAL ELEMENTS. 743 



third degree of oxidation of the same radical. It was left for 

 Davy to demonstrate the elementary nature of chlorine and to 

 discover the true relations of the hydrogen acids. Lavoisier re- 

 garded oxygen as the universal acidifying principle, and the facts 

 known in his day admitted of this interpretation ; and it is inter- 

 esting to see how they were worked up in the table ; but when a 

 class of acids containing no oxygen came to be clearly recognized, 

 they proved a serious embarrassment to the Lavoisierian system 

 as it was developed by Berzelius and his associates. 



With the exception of caloric and two of the radicals above 

 referred to, Lavoisier's list of elements includes no substance not 

 regarded as elementary at the present day; but the list is as 

 remarkable for what it omits as for what it includes. There were 

 then known, and had been known for a long time, two very well 

 marked classes of bodies called alkalies and earths which readily 

 combined with acids to form salts. In this respect these bodies 

 closely resembled the known metallic oxides, as they did also in 

 most cases in their general appearance, and they were classed by 

 Lavoisier with the oxides under the general term of " bases sali- 

 fiables." Still, they had never been decomposed, and, according to 

 the spirit of Lavoisier's philosophy, ought to have been classed 

 among elementary substances ; but Lavoisier's classificatory in- 

 stinct was altogether too acute to permit him to fall into any such 

 error. He enumerates these bodies, and, although he speaks doubt- 

 fully in regard to them, he never for a moment questions their 

 compound nature. In regard to the earths he says their composi- 

 tion is wholly unknown, implying, of course, that they were com- 

 pounds, and under the head of " Des Substances m^talliques " is 

 this significant paragraph : 



" It is probable that we only know a part of the metallic sub- 

 stances which exist in nature. All those, for example, which 

 have more affinity for oxygen than for carbon can not be reduced 

 or brought to a metallic state, and must appear to us as oxides 

 which we mistake for earths. It is very probable that baryta, 

 which we have classed as an earth, is a case in point. When 

 experimented upon, it exhibits characters which closely approach 

 those of metallic substances. It may be, indeed, that all the sub- 

 stances to which we give the name of earths are only metallic 

 oxides that can not be reduced by the means which we use." 



It will be noticed that the alkalies are not included under this 

 remark, for their active qualities are very different from those of 

 an insipid, earthy-looking, metallic oxide ; and their resemblance 

 to ammonia, the volatile alkali, a known compound of nitrogen, 

 was constantly a confusing circumstance. Lavoisier discusses the 

 question whether potash and soda pre-exist as such in the plants 

 from whose ashes they are procured, and makes the suggestion 



