122 TRANSMISSIVITY IN PASSIVE IRON WIRES 



All these determinations were made at room temperature, and the 

 temperature of the acid was taken at the end of each series; in all but 

 seven of the 1 19 series summarized in the table the temperature was 

 between 19 and 21°; in the others it rose to 21.5 or 22° (in one case 

 22.5°). The irregular fluctuations in the series have, however, noth- 

 ing to do with temperature, but are to be referred chiefly to accidental 

 variations in the surface structure of the different wires. In order to 

 obviate this source of irregularity, as far as possible, a number of other 

 series of determinations were made later, using a somewhat different 

 plan. In each of these series eight wires were employed, designated 

 A, B, C to H; each wire during passivation was kept separately in a 

 long test-tube labeled with its letter, so that its individual behavior 

 could be observed. Eight separate series of determinations were 

 made as above in each of the following solutions of acid: 60, 65, 70, 

 75, and 80 volumes per cent, in such a manner that each wire was ex- 

 posed to each solution for each of the eight periods employed in the 

 series. For example, the times of exposure to 75 per cent HNO3 

 were 2, 4, 6, 7, 8, 9, 10, and 11 minutes; in the first series with this so- 

 lution the wires were arranged in the acid in the order A, B, C to H 

 corresponding to the above times; in the second series Wire H was 

 shifted from the end to the beginning of the series, so that it received 

 2 minutes exposure before reactivation. Wire A 4 minutes, and so 

 on; in the third series the wires were in the order G, H, A, B to F, 

 etc. In this manner a record of transmission distances was obtained 

 for each wire with each of the eight recovery intervals allowed. 



The results of these series were on the whole more regular than those 

 of the earlier series. The wires used were of the same kind as before, 

 but cut from a different roll (No. 25 thickness). The behavior and 

 the recovery times showed little difference from those of the earlier 

 series (made with No. 20 wire). Care was taken to keep the tempera- 

 ture constant between 19.5 and 20.5°. Table IV gives the complete 

 record of two typical series with 65 and 80 per cent acid respectively. 



These results are closely similar to those obtained in the earlier se- 

 ries, and no significant differences of behavior are observable in the 

 indi\'idual wires. It is apparent that each reaction means a renewal 

 of the reacting surface, since a thin layer of metal is dissolved each 

 time. The irregularities of behavior are therefore probably due to 



