138 HISTORY OF CHEMISTRY. [LECTURE VIII. 



Three views respecting the ammonium salts and the com- 

 pound ethers had thus been advanced, and these differed from 

 one another merely in the number of hydrogen atoms which 

 were assumed in the radical. These were : 



1. The ammonia theory of Lavoisier, corresponding to the 



etherin theory of Dumas and Boullay ; 



2. The ammonium theory of Davy, Ampere, and Berzelius, 



corresponding to the ethyl theory of Berzelius and 

 Liebig; and 



3. The amide theory of Davy and Liebig, corresponding to 



the acetyl theory of Regnault and Liebig. 



Liebig believed that, by his new theory, he had overcome 

 all difficulties, and had settled all contentions with respect either 

 to the ethyl theory or the etherin theory. He closes his paper 

 with the following words : " From this point of view, both of 

 the formerly opposed theories possess, as may easily be observed, 

 the same kind of basis, and all further question as to the truth 

 of the one view or of the other is thereby settled." 



In a certain respect, Liebig was right ; the.question whether 

 ethyl or etherin was present in alcohol was no longer discussed ; 

 not, perhaps, because ace.tyl was preferred, but because chemists 

 now began to attach another signification to the radicals. The 

 phenomena of substitution, which were already known, gradu- 

 ally became of general applicability, and, after the discovery of 

 trichloracetic acid, the hypotheses which Dumas and Laurent 

 had advanced, acquired great influence. Not only was the 

 radical theory, in the form in which it was then stated, threat- 

 ened by these hypotheses, but dualism and the electro-chemical 

 theory the very foundations of the entire mode of viewing 

 chemical matters were attacked by them, and were eventually 

 driven out of the science. These hypotheses led to the recog- 

 nition of the radicals as variable and of chemical compounds 

 as possessed of an individual or unitary character; and to the 

 abandonment, as arbitrary, of the division of the latter into two 

 parts. At a later period, in conjunction with the conceptions 

 derived from the theory of the polybasic acids, they led to a 

 revision of the size of the atoms in the case of compounds, to 



