668 BERZELIUS ON THE COMPOSITION OF 
This gave rise to a theoretical explanation of the phenomenon 
which he called the Theory of Substitutions; and as most fre- 
quently the elements are exchanged in equivalent quantities, he 
framed for it the name of Metalepsy. He showed that an or- 
ganic body, in which one or several equivalents of hydrogen had 
been exchanged for an equal number of equivalents of chlorine 
or bromine, retained its original saturating power, as well as 
several of its chemical properties, and that in many cases it 
could be proved to possess the same crystalline form. From 
these facts he came to the conclusion, ¢hat the salt radical plays 
the same part in the new compound as hydrogen played in the 
original one; and having discovered and analysed chloracetic 
acid (chloroxalic acid), he considered this view so thoroughly 
established, as to build upon it an entirely new theory of organic 
composition. In the electro-chemical theory chlorine is one of the 
most highly electro-negative bodies, hydrogen, on the contrary, 
electro-positive; and as, according to the view which he had 
taken, one element could play the same part in a chemical com- 
bination as another, Dumas concluded that the electro-chemical 
views were not sufficiently well-founded to find application in 
the scientific theory ; and with reference to this he settled, that 
the part which an element plays in organic composition, does 
not depend upon its original properties, but upon the position 
which it occupies in the compound ; thus then chlorine or any 
other element taking the position of the hydrogen can play ex- 
actly the same part as it does. 
This induced him to give up the idea of the organic radicals, 
which however, having previously so strenuously advocated, he 
avoided openly to dispute; he compared them now no longer to 
the simple elements, but to carbonic oxide, sulphurous acid, deut- 
oxide of nitrogen, and to the so-called hyponitric acid, NO*. He 
now took quite another view of organic composition. 
The elements combine in organic nature two or more with each 
other to form peculiar dypes, and in these types the atoms are 
arranged, for each particular type, in a fixed, and for those bodies 
belonging to the same type, in a similar manner ; the characters of 
the compound depend upon the arrangement amongst the com- 
pound atoms, so that it becomes quite immaterial what element 
it is that occupies a certain position in the compound. In this 
manner the possibility of substitution is extended to other bodies 
besides hydrogen and the salt radicals. “The law of substitu- 
