210 CHEMISTRY OF THE PROTEIDS CHAP. 



case of As, Sb, Sn, and with the hydroxides of Titanium and 

 Germanium. 



With arsenic the following amphoteric reactions take place : 



As 2 (OH) 6 + 6H + 6Cr 2 2(AsCl 3 ) + 6H 2 0, 

 and As 2 (OH) 6 + Na + OH' ^ As 2 (OH) 5 0' + Na + H 2 0. 



3. Attach H and OH' ions to themselves and then form an-iom 

 and kat-ions. 



R - NH 3 + Na + OH' ^ R-NH 3 .OH 



COO COO' + Na, 



and 



R - NH 3 + H- + Cl' ^ R - NH 3 + 01' 



COO COOH. 



4. Give rise to ions which are simultaneously electro-positive anc 

 electro-negative (Bredig), and which Kiister l calls * Zwitter-ions,' i.e 

 hermaphrodite-ions. Thus the * Zwitter-ion ' of glycocoll is the grouj 

 H 3 N - CH 2 - COO : 



+ + 



HO . H 3 N . CH 2 . COOH ^ OH + H 3 N - CH 2 - COO + H. 



5. Undergo a peculiar intramolecular change (Davidson anc 

 Hantzsch), 2 whereby there is formed the an-ion of a dibasic acid, as ii 

 the di-azonium compounds, represented by di-azonium-sulphanilic acid 



C 6 H 5 N ! N + 2Na + 20H' ^ C 6 H 4 N + 2Na + H 2 



/ I II 



SO^ S0' 3 'ON, 



and 



c 6 H 4 N;N + H +cr ^ c 6 H 4 -N o + cr 



S0 3 H N. 



. 



The simultaneous presence of acid and of basic radicals in one and 

 the same molecule must of necessity lead to a weakening of the acid 

 or basic characters of the molecule towards other individual molecules, 

 and must also set up within the amphoteric molecule a tendency 

 towards ' internal salt-formation,' by which expression we mean that 

 the acid and the basic radicals of an amphoteric electrolyte will tend 

 to mutually satisfy one another. Whenever this tendency becomes an 



1 Kiister, Zeitschr.f. anorg. Chemie, 13. 136 (1897). 

 - W. B. Davidson and A. Hantzsch, Ber. d. deutsch. chem. Ges. 31. 1612 (1898). 



