4 REPORT 1859. 



can in their turn take up other substances in exchange for their chlorine, 

 while the remainder of their elements (carbon, or carbon and hydrogen) 

 pass into new compounds with the properties of polyatomic radicles. 



These relations may be stated still more generally as follows : — compounds 

 formed upon the molecular type CH 4 are either incapable of undergoing 

 double decomposition, or are monatomic, diatomic, triatomic, or tetratomic, 

 according to the number of atoms of hydrogen which are replaced, and to the 

 nature of the substance by which it is replaced*. 



A remarkable instance of a series of compounds presenting precisely 

 similar relations has recently been pointed out by Bayerf, in his researches 

 upon the compounds of methyl with arsenic. 



If we now consider some of' the most important reactions by which com- 

 pounds are converted into others of greater atomic value, we shall find that 

 in almost all cases the process is essentially the same as in those already 

 referred to. 



1. Acetic acid, C 2 H 4 O 2 , which in most of its reactions behaves as a 

 monatomic hydrate, is converted by the action of chlorine into chloracetic 

 acid J, C 2 H 3 CI O 2 . This substance can easily be made to part with its 

 chlorine and to take up in its place other elements. For instance, when 

 heated with an alkaline hydrate, it exchanges its chlorine against an atom of 

 hydrogen and an atom of oxygen, thus — 



C 2 H 3 CI 2 + KHO = C 2 H l 3 + KCl, 



Chloracetic acid. Glycolic acid. 



giving rise to an alkaline chloride and a biatomic acid, glycolic acid§. 

 Again, chloracetic acid is decomposed by ammonia into hydrochloric acid 

 and glycocol||, also a biatomic substance: — 



C 2 H 3 C10 2 + H 3 N=C 2 H 5 N0 2 + HC1. 



Chloracetic acid. Glycocol. 



In these two cases it admits of question whether the change from a mon- 

 atomic to a diatomic compound takes place when the acetic acid is converted 

 into chloracetic acid, or in the subsequent metamorphosis of the latter body. 

 But at whatever stage of the process the change occurs, it is essentially the 

 same, and consists in the replacement of an atom which, in ordinary double 

 decompositions, acts as a constituent part of the radicle of the acid, by an 

 atom or group which, in similar circumstances, acts as though it were ex- 

 ternal to the radicle. 



2. Chloride of kakodyl, As Me 2 CI, is a monatomic chloride, but, acted 

 upon by chlorine at the temperature of 40° to 50° C, it is converted into 

 bichloride of arsenmonomethyl, As Me CI 2 , a diatomic chloride (Bayer). 

 Here, again, the change may be described as the replacement of an atom 

 (methyl) which is inactive with regard to double decompositions, by an 

 atom (chlorine) which is active. 



3. An increase in the quantity of oxygen contained in a compound gene- 

 rally increases its atomic value. An instance of this has already been re- 

 ferred to in the case of acetic and glycolic acids. We may mention as 

 further examples — 



Alcohol C 2 H 6 O Tritylic alcohol. . C 3 H s O Monatomic. 



Glvcol C 2 H 6 2 Tritylic glycol . . C 3 H 8 2 Diatomic. 



Ethyl-glycerine(?) C 2 H 6 3 Glycerine C 3 H 8 3 Triatomic. 



* Comp. Odling, Journ.Roy. Instit., March 16th, 1855. 



t Ann. Chem. Pharni. cv. 265 ; more fully, cvii. 257. 



t R. Hoffmann, Ann. Chem. Pharm. cii. 1. § Kekule, ibid. cv. 286. 



|| Cahours, Ann. Chim. Phys. [3] liii. 355. 



