LECTURE X.] HISTORY OF CHEMISTRY. 179 



Liebig's relations to them. His opinion concerning Laurent's 

 nucleus theory must not guide us here. The discovery of 

 trichloracetic acid had not been without effect upon him also, 

 and he not only admits the replaceability of hydrogen by nega- 

 tive elements, but he also agrees with Dumas in his views 

 respecting these facts. This is seen from the following : 9 



"The remarkable observation has been made in inorganic 

 chemistry, that the manganese in permanganic acid may be 

 replaced by chlorine without altering the form of the com- 

 pounds which permanganic acid can produce with the bases. 

 There can scarcely be a greater dissimilarity in chemical pro- 

 perties than that between manganese and chlorine. . . . 

 Chlorine and manganese can replace each other in certain 

 compounds without alteration in the nature of the compounds. 

 I do not see why a similar behaviour should be impossible 

 with other substances with chlorine and hydrogen, for example, 

 and this very view of these phenomena, in the form in which it 

 has been advanced by Dumas, appears to me to furnish the 

 key to most of the phenomena of organic chemistry." 



Dumas, it is true, goes too far for him. Liebig will not 

 admit, for example, the replaceability of carbon, and he prints 

 in his journal the well-known letter of S. C. H. Windier 10 which 

 makes sport of Dumas in a somewhat harsh manner. However 

 this may be, it might appear from these statements that Liebig 

 had materially contributed by his views to the further develop- 

 ment of the radical theory. This is not my belief, and I find 

 support for my view in a paper on the theory of ether, which 

 he published in the year i839. n Liebig here endeavours 

 to solve the difficulties of the question as to the constitution of 

 ether, by the assumption of the radical acetyl ; and, in doing 

 so, he proves to us that radicals, with him, still retain their old 

 signification. The whole plan of his Hand-book also shows the 

 same thing. 12 



9 Annalen. 31, 119, Note. 10 Ibid. 33, 308. n Ibid. 30, 129 ; 



compare p. 137. 12 See Liebig's Handbuch der Chemie, Heidelberg 

 (1843), especially 2, I etc, 



