420 



SCIENCE 



[N. S. Vol. L. No. 1296 



activation — a condition which, has many gen- 

 eral biological analogies and suggests that the 

 basis for many phenomena of sensitization 

 and memory in organisms may consist in a 

 deposition of speciiic materials in the surface- 

 films of the sensitive elements. In other 

 words, some specific and lasting change in 

 composition is the direct result of the response 

 to stimulation, and increases the sensitivity 

 to a subsequent stimulation of the same kind. 



Antagonisms. — In general any condition 

 that confers increased stability upon the sur- 

 face-film prevents or retards its destruction in 

 an activating solution and hence preserves 

 passivity. Accordingly strongly oxidizing 

 compoimds like peroxides, bichromates, per- 

 manganates, osmium tetroxide, salts of noble 

 metals (Hg, Ag, An, Pt) antagonize the 

 activating effects of sodium nitrate and other 

 salt solutions upon passive iron. The addi- 

 tion of one mol of AgNOg to 100 mols of 

 IN'aN'O, in a solution of the latter salt entirely 

 prevents spontaneous activation. The antag- 

 onism between ISTa and Ca salts, however, 

 which is so characteristic of biological sys- 

 tems, is not exhibited by passive iron, or only 

 slightly. It is also difficult to antagonize the 

 activating effect of chlorides; for example, in 

 m/60 NaCl the addition of K^Cr^O^ to a total 

 concentration of 0.08 m. was found to preserve 

 passivity indefinitely, but 0.04 m. proved in- 

 sufficient, although it prolonged the time of 

 activation from one or two seconds (the time 

 in pure m/60 ISTaCl) to about 30 seconds. 



The activating influence of the 01-ion is 

 thus counteracted only by a great excess of 

 the oxidizing agent. A less strongly oxidizing 

 salt like ISTaNOj has only a slight antagon- 

 izing effect with chlorides; thus in a series of 

 mixtures of m/50 ISTaCl and w/50 NalSTOg in 

 all proportions, using passive wires which 

 underwent activation in pure m/50 'NaGl in 

 2 to 3 seconds, the activation-time was pro- 

 longed to only 7 or 8 seconds in a solution 

 containing 1 part ISTaCl to 4 parts ISTalSTOj, 

 and to 20 or 25 seconds in a solution of 1 part 

 NaCl to 9 parts NaNO,. In the pure m/50 

 NaNOj activation requires five minutes or 

 more. The prepotent action of the Cl-ion is 

 thus evident. 



The action of AgNO^ in solutions of sodium 

 nitrate, chlorate, sulphate or acetate affords a 

 typical instance of ion-antagonism in which 

 the protective effect is due to the cation of the 

 added salt. Many biological antagonisms are 

 of this class. The following brief summary 

 of typical experiments will illustrate. Passive 

 wires were placed in solutions of the four 

 sodium salts named, both pure and with the 

 addition of AglSTO, as indicated. 



Solution 



Pure m/10 NaNOs, 



NaClOs, Na-SOj, or 



NaCOOCHs 

 99 vols, m/10 Na-salt 



phis 1 vol. m/10 



AgNOs 



98, 97 96 and 95 vols. 

 m/10 Na-salt plus 



Result 

 Wires are all active 

 ■within 30 minutes or 

 less. 

 Wires in NaN03, NaSOj 

 and NaCOOCH^ re- 

 mained passive indefi- 

 nitely; in NaClO, 

 they became active in 

 respectively 1 hour, 2J 

 hours, and 50 minutes 

 in three successive 

 trials. 

 All wires remained pas- 

 sive indefinitely, 

 (respectively) 3, 3, 

 4 and 5 vols, m/10 

 AgNOs 



Salts of other noble metals (Hg, Au, Pt) 

 similarly prevent spontaneous activation in 

 solutions of l^alSTOj. Of the two mercuric 

 salts, chloride and nitrate, the former proved 

 ineffective in the three mixed solutions used, 

 viz., 95, 90 and 80 vols, m/10 JSTal^Oj plus 

 (respectively) 5, 10 and 20 vols, m/10 HgCla; 

 in these solutions the action of the Cl-ions 

 overbalances that of the Hg-ions; but in cor- 

 responding solutions containing Hg(N'03)2 

 instead of HgCl, passivity was preserved in- 

 definitely. Similarly a slight addition of 

 AuClj or PtCl^ to m/10 ]Sra]Sr03 prevented 

 spontaneous activation and preserved passivity 

 indefinitely (e. g., 2 or 4 c.c. of a 1 per cent, 

 solution of either salt to 100 c.c. of m/10 

 NaNOg). 



It is significant that such salts exhibit pro- 

 tective action only if the metal is nobler than 

 passive iron; similar addition of Ca(N03)2, 

 Pb(No3)„ or Cu(K03)„ to m/10 ]SroIsr03 had 

 no such effect. Apparently the metal of the 



