

96 Prof. Louis Henry on the Polymerization 



usually represented by their anhydrides. In addition to these 

 general facts, it is important to observe not only the nature of 

 the anhydrides thus obtained, but also the connection which 

 underlies the two distinct chemical phenomena, viz. dehy- 

 dration and molecular condensation. Wiirtz developed this 

 principle in one of his lectures before the Chemical Society of 

 Paris in 1863. The elimination of water usually depends not 

 on one but on several molecules of the hydroxide, the residues 

 of which become soldered together, as it were, by the atoms of 

 oxygen ; we therefore get an accumulation of the radicals of 

 these hydroxides in the products formed — a veritable molecular 

 condensation proportional to this accumulation. This principle 

 applies to all hydroxides indiscriminately, not only to the 

 normal hydroxides B^OH)*, but to the oxyhydroxides or 

 incomplete anhydrides ITO n (OH) x ~ 2 n- It therefore follows 

 that the compounds formed under these conditions become 

 more and more complex, in proportion as this dehydration 

 itself is more or less complete. 



These general facts apply to all hydroxides, both organic 

 and mineral. The following are illustrations from organic 

 chemistry: — 



The acid alcohols are the most interesting in this connection. 

 The most simple, and therefore the most conclusive cases are 

 furnished by the glycollic and lactic acids. When heated, 

 these compounds lose successively a half and then a whole 

 molecule of water, forming finally glycollide and lactide. I 

 have shown (Bull. Acad. Belg. xxvii. p. 409) that lactide in 

 the state of vapour ought to be represented by the formula 

 [(C 3 H 4 0)0] 2 , and not by the usual formula (C 3 H 4 0)0. The 

 same thing applies also to glycollide, which is nonvolatile. 

 If w r e represent the radicals glycollyl (C 2 H 2 0) and lactyl 

 (C 3 H 4 0) respectively by Gl and La, the action of heat on 

 glycollic and lactic acids will be expressed thus*: — 



OH /Gl-OH Gl 



G1 <OH' °<Gl-OH' °<G1>°' 



.OH y La— OH y La Xr . 



La< OH' °<La-OH' °<La >a 



* The following considerations prove that glycollide cannot be 2 H 2 2 , 

 but is really a polymer (C 2 H 2 2 ) n . The minimum molecule of glycollic 

 acid is represented by CH 2 OH . COOH, and contains therefore the tetra- 

 valent radical (~ C . CH 2 — ). The corresponding chloride OCl 3 . CH 2 C1 is 

 a liquid, b.-p. 102°. Consequently the oxide, or glycoll, 0=C . CH 2 . O, 



ought to be still more volatile, just as the oxide of methylene is gaseous, 

 whilst the chloride CH 2 C1 2 is a liquid, b.-p. 40°. In reality, however, this 

 is not the case, for glycollide is a fixed solid. 



