172 Gerhard? s Organic Chemistry. 



are able to exchange themselves for hydrogen, equivalent for equiv- 

 alent. The acids are then to be regarded as salts of hydrogen, 

 and the view which regards them as compounds of an anhydrous 

 acid with water, is inadmissible, as the monobasic acids contain 

 bat one equivalent of hydrogen, which is replaced by a metal, 

 while water contains two equivalents of that element. A second 

 mode of combination is that designated by title of metalepsis or 

 equivalent substitution. In these as in the salt compounds, cer- 

 tain elements are capable of being replaced by others, without 

 altering the molecular constitution of the organic substance. The 

 phenomena of metalepsis are divided into two classes, those in 

 which hydrogen is replaced by chlorine, bromine or iodine, and 

 those where oxygen is exchanged for sulphur, selenium/or tellu- 

 rium. The two metaleptic groups are illustrated by the follow- 



exam 



tf Hyd 



\ 



C H 4 Forme ne, (marsh gas.) 



C (H 3 CI) Chlorinized formene, (chlorid of methyle.) 



C (H 3 Br) Brominized formene, (bromid of methyle.) 



C (H 3 I) Iodized formene, (iodid of methyle.) 



C (H 2 Cl 2 ) Bichlorinized formene. 



C ( HC1 3 ) Trichlorinized formene, (chloroform. ) 



CC1, Q,uadrichlorinized formene, (chlorid of carbon.) 



C 2 H, 2 Normal acetate, (acetic acid.) 



C 2 (HC1 3 ) 2 Trichlorinized acetate, (chloracetic acid.) 



Metalepsis of Oxygen. 



C 4 H, O Ether, (sulphuric ether.) 

 C 4 H t S Sulphuretted ether, (sulphuret of ethyle.) 

 C 4 H I0 Se Seleniuretted ether, (seleniuret of ethyle.) 

 C 4 H, Te Telluretted ether, (telluret of ethyle.) 

 In these reactions the substitutions are always equivalent, and 

 since one equivalent of chlorine corresponds to one of hydrogen, 

 and one of oxygen to two of hydrogen, it follows that oxyg en 

 cannot like chlorine replace hydrogen. 



' The metaleptic hydrogen is to be carefully distinguished from 

 that which is replaceable by a metal. The action of chlorine 

 upon acetic acid, removes three equivalents of its hydrogen and 

 substitutes three of chlorine in their place, forming chloracetic acid 

 C 2 (HCl 3 ) 2 , but the fourth equivalent can only be removed by 

 substituting a metal in its place. 



Substitution of Residues. — The action of nitric acid upon m a ' 

 ny organic substances, results in the formation of water and a ne# 

 compound which contains the elements of the acid ; thus benzene 

 C 6 H 6 , with nitric acid NH0 3 forms an equivalent of water ana 

 the new substance C 6 H 5 N0 4 . In this and analogous com- 



