178 HISTORY OF CHEMISTRY. [LECTURE X. 



without our afterwards being able to recompound it from these 

 substances. The reason for this fact must be that, in the latter 

 mode of decomposition, the atoms of the elements are trans- 

 posed into other relative situations which are obstructive to 

 their reuniting." 



These ideas are as clear, as impartial, and as unprejudiced 

 as could possibly be desired. The same holds also for the 

 following statements of Liebig : 7 



" A theory is the explanation of positive facts, which does 

 not permit us, from the behaviour of a substance in various 

 modes of decomposition, to make deductions backwards as to 

 its constitution, with conclusive certainty, simply because the 

 products vary with the conditions of the decomposition. 



" Each view as to the constitution of a substance, is true 

 for certain cases, but unsatisfactory and insufficient for others." 



Even if I also admit that the principles of the newer radical 

 theory are expressed in these statements of the two great 

 teachers, 8 still it would appear to me presumptuous that any 

 one should declare the latter, on this account, to be the authors 

 of the views which are now to be discussed. By their activity 

 in other directions in the domain of theoretical chemistry, they 

 have shown that, with them, the radical is a definite, unchang- 

 ing group, and that they only considered a single view as to the 

 constitution of compounds to be admissible. I would recall 

 the numerous discussions regarding the conceptions of alcohol 

 and its derivatives. Would these have been possible if opinions 

 such as those quoted above had been guiding and predominant 

 ideas with Berzelius, Liebig, and Dumas? Prior to the dis- 

 covery of the phenomena of substitution, this certainly was 

 not the case. In treating of Berzelius and of Dumas, we have 

 already discussed the influence which these facts exerted upon 

 the conception of the radicals. We have still got to consider 



7 Annalen. 26, 176-177. 8 Thus Gerhardt, for example, begins. the 

 exposition of his theoretical views by directing attention to the various 

 formulae that are possible for sulphate of baryta ; that is to say, he adduces 

 considerations quite similar to those quoted above as advanced by Ber- 

 zelius. See Gerhardt, Traite de Chimie. 4, 561. 



