620 SCIENCE PROGRESS 



the term "isomeric" to the cases in which no such difference was 

 present, and to describe those substances in which the relative 

 numbers of the atoms were the same, but the absolute numbers 

 unequal, as Polymeric. 



Metamerism or Isomeric Change. — The same decade which 

 witnessed the discovery of isomerism by Wohler and Liebig, 

 and of polymerism by Davy, was rendered memorable by a 

 further discovery arising out of Wohler's work on the cyanates. 

 After investigating a number of the metallic salts of cyanic acid, 

 he attempted to enlarge their number by the preparation of an 

 ammonium salt by the action of ammonia on lead cyanate. A 

 soluble substance was formed, but after evaporating to dryness 

 the product was identified as urea. This preparation attracted 

 great attention at the time, and for many years afterwards, as 

 a conversion of mineral matter into a typical organic product : 

 how far this view was legitimate in view of the animal sources 

 (" horns, hoofs, and hides " — to quote the conventional statement 

 of the textbooks) from which the cyanides were invariably 

 prepared, is open to question, but the observation was at least 

 of striking importance as the first known example of Isomeric 

 Change. 



Substances such as ammonium cyanate and urea which could 

 thus pass over into one another, by keeping or by change of 

 temperature, without any change of composition or any alteration 

 in the size of the molecule, Berzelius proposed to call metameric, 

 using (as he says) the prefix " meta " as in " metamorphosis " 

 to indicate change. As illustrations of this relationship he 

 quoted two examples, one from inorganic and the other from 

 organic chemistry. The former of these — the isomerism of 

 basic stannic sulphite (SnO)S0 3 , with stannous sulphate SnS0 4 

 — appears to be entirely hypothetical. The organic example 

 of cyanic and cyanuric acids, another quotation from Wohler's 

 fruitful work on the cyanates, has since been shown to be 

 vitiated by an alteration in the size of the molecule, so that the 

 conversion of cyanuric acid by distillation into cyanic acid, and 

 of cyanic acid by keeping into cyamelide, are really cases of 

 depolymerism and of polymerism rather than of metamerism 

 or isomeric change. 



It is altogether unfortunate that the word thus excellently 

 chosen and defined by Berzelius should have been diverted 

 from its original meaning and attached to other phenomena — 



