189 



the researches of Messrs. Hofmann and Cahours on allylic alcohol. 

 These researches have established the most perfect parallelism be- 

 tween the two classes of radicals and their derivatives. Both the 

 radicals CH( W +i) and C^H^" 1 ) are monatomic, i.e. molecules capable 

 of replacing 1 equiv. of hydrogen. 



These two classes stand in the closest relation to each other, and 

 it is by no means improbable that one class may pass over into the 

 other, for instance, that the radical propyl C 6 H 7 , or a propyl-com- 

 pound, may be converted into allyl or an allyl-compound. 



There exist a third series of hydrocarbons, which, again, both by 

 composition and origin, are closely allied to the former two. They 

 are represented by the general formula C n H n ; and methylene, C 2 H 2 , 

 ethylene, C 4 H 4 , and propylene, C 6 H 6 , are well-known terms belonging 

 to this series. These hydrocarbons are also radicals ; they differ, 

 however, in their nature essentially from those of the former groups, 

 inasmuch as they are oiatomic molecules, i. e. molecules capable ef 

 replacing 2 equivs. of hydrogen . 



There exist parallel with these three series of radicals which form 

 alcohols, three other groups of radicals, which in acids play exactly 

 the same part that in the alcohols is assigned to the hydrocarbons. 

 These acid-forming radicals contain, in addition to carbon and hy- 

 drogen, oxygen and other elements belonging to the oxygen group. 

 They are closely connected with the radicals of the alcohols, and 

 this close connexion is particularly well established between the first 

 series of alcohol-forming radicals and the corresponding series of acid- 

 forming radicals. 



Methyl, C 2 H 3 -2H + 20=Formyl, C 2 HO 2 

 Ethyl, C 4 H 5 -2H + 2O= Acetyl, C 4 H 3 O 2 

 Propyl, C 6 H 7 2H + 2O = Propionyl, C 6 Hj O 2 . 



Formic, acetic and propionic acids are formed by the imperfect 

 oxidation of methyl-, ethyl- and propyl-alcohol, and we may con- 

 sider them to be simple substitution-products of these alcohols. 



By means of the electric current we are able to produce ethyl, 

 methyl and hydrogen from propionic, acetic and formic acids, and 

 these acids we may reproduce again by the action of hydrate of 

 potassa on the cyanogen compounds of hydrogen, methyl and 

 ethyl. 



VOL. VIII. R 



