THE MODERN THEORY OF CHEMICAL TYPES. ^57 



Dutch liquid C4H4CI2 — (C4H4)Cl2 



1st substitution C4H3CI3 = (^4 { Qi^Gh 

 2d " C4H2CI4 = (C4 1 ^^Qoh 



3d " C4H CI5 = fCi I ^JC12 



4tll " C4CI6 — (C4Cl4)Cl2 



If upon the members of this series an alcoholic solution of potassa act, one 

 equivalent each of hydrogen and chlorine is separated, and we obtain the fol- 

 lowing compounds ; 



TT \ 



From Dutch liquid C4H4C12 we obtain C4^,,^ > 



" 1st substitution O4H3CI3 " C47,j | 



" 2d " C4H2CI4 " C}^^^ I 



" 3d " C4HCI5 " C4Cli; 



which demonstrates that in Dutch liquid and its chlorine compounds the latter 

 element exists in two conditions : one in which it takes the place of hydrogen, 

 atom by atom, and another in which it unites with carbon and the compound 

 atom thus formed. In other words, the negative atom of chlorine drives out 

 and takes the place of the positive atom of hydrogen. To bring these phe- 

 nomena in accord with the former electro-chemical theory, we would have to 

 assign to the atom of chlorine a preponderating positive and a negative charac- 

 ter at the same tim:-, which was deemed inadmissible. 



The same difficulty occurred with respect to the negative atom oxygen, to 

 which, according to some, a place had to be assigned sometimes inside of the 

 positive I'adical. 



The behavior of acetic acid with chlorine gas in sun-light affords a strik- 

 ing example of the substitution of CI for H. By this reaction, from C4 H4 O4 

 (acetic acid) there arises, by the substitution of chlorine for hydrogen, chlor- 



acetic acid, ( C4 pi ? O4 I and between the two acids there is a great chemi- 

 cal similarity. They each saturate the same amount of base, and when acted upon 

 by the same reagents, give rise to analogous products. Thus, by heating with 

 excess of alkali, acetic acid becomes carbonic acid (2 C Oo) and light carburetted 

 hydrogen, (O2 H4,) while by the same treatment chloracetic acid becomes 



2 C O2 and C2 pi [ or chloroform, Avhich may be regarded as light carburetted 



hydrogen, in Avhich a portion of the hydrogen is replaced by chlorine. By the 

 action of nascent hydrogen, chloracetic acid is regenerated to acetic acid. It 

 is true that these difficulties might be reconciled by the assumption of both a 

 negative and positive character being assumed under different circumstances 

 by the same atom. This must be done in certain instances to bring the mod- 

 ern type theory in accord Avith the electro-chemical theory, and, indeed, the 

 experiments of Schoenbein upon ozone, and the phenomena of the action of 

 certain bodies in the " nascent" state, would render this assumption not un- 

 likely ; but the immediate result of the experiments cited was to hold the 

 electro-chemical theory in abeyance, and to develop the theory of types. 



The first type theory was a theory of the classification of chemical com- 

 pounds, and was analogous to the natural history system of classification into 

 orders, genera, and species. There was a "molecular" or "mechanical" type 



