4"i6 M. Dumas on the Laxo of Substitutions, Sj-c. 



to the chlorine and to the hydrogen in acetic acid and in 

 chforacetic acid, in the chloroform and in marsh gas. 



Here, however, as it was easy to foresee, is the point which 

 particularly arrested the attention of M. Berzelius, and which 

 he combated by changing all my formula and substituting 

 new ones for them. 



Down to the present time I have made no reply. Indeed, 

 what could 1 have added to the following; note that M. Liebiff 

 authorized me to publish in his name ? 



'•' In my interest for the science," says M. Liebig, " I must 

 declare that I do not share the opinions of M. Berzelius, be- 

 cause they rest upon a mass of suppositions which cannot be 

 proved. 



" In mineral chemistry the singular observation has been 

 made that chlorine may be substituted for manganese in per- 

 manganic acid, without the form of the salts produced by 

 this acid being changed. Nevertheless it is hardly possible 

 to find two bodies between which there exists a greater dif- 

 ference in chemical properties than there is between chlorine 

 and mansanese. 



" An experiment of this kind is not to be discussed; we 

 must leave to the fact all its value, and say, chlorine and 

 manganese may take each other's place without the nature 

 of the combination being changed by it. From that time I 

 do not see why this manner of acting should be considered 

 as impossible for other bodies, such for example as chlorine 

 and hydrogen. 



" The interpretation of these phasnomena, such as it has 

 been laid down by M. Dumas, appears to me to give the key 

 to most of the phsenomena of organic chemistry. 



" Without denying that bodies take each other's places in a 

 great number of combinations, according to their place in 

 the electric order, I think, from the manner of acting of or- 

 ganic combinations, we should draw this conclusion; — that a 

 reciprocal substitution erf simple O)- compound bodies, acting in 

 the manner of ii.omorphous bodies, should be considered as a true 

 law of nature. This substitution may take place between 

 bodies which neither have the same form nor are analogous 

 in composition. It depends exclusively on the chemical 

 force which we call affinity." 



These opinions are, in fact, quite conformable to those 

 which I myself published, when I compared the principle of 

 substitutions to the principle of isomorphism, and the bodies 

 of the same chemical type to the isomorphous bodies them- 

 selves. 



1 do not pretend to say, that bodies of the same chemical 



