1887.] Electrochemical Effects on Magnetising Iron. 461 



the coil surrounding the upper portion of the long bar requiring 

 magnetisation. The coil used in the experiments with apparatus fig. 1 

 consisted of six depths or wraps of the insulated copper wire, each 

 wrap having 81 turns, making in the whole a coil of 486 convolutions. 

 The other coil employed in the experiments with apparatus fig. 2 was 

 of similar construction, but had ten depths of insulated copper wire of 

 the same thickness, constituting a coil with a total of about 750 con- 

 volutions. 



A single cell bichromate battery, easily put in or out of operation, 

 was attached to the coil, and the battery was recharged with the same 

 strength of solution for each observation. After a suitable time had 

 been allowed in each experiment for steady galvanic equilibrium to be 

 established between the two iron rods, in the solution in the tubes, 

 which took place at periods varying with the nature of the solution, 

 the coil was put into operation. In the experiments with fig. 2 the 

 end of the bar in the solution was the S seeking pole. Ifc was most 

 interesting to observe the result. The rod A thus magnetised in most 

 of the solutions became the metal positive, the galvanometer indicating 

 its steadily increasing electrochemical positive position compared with 

 that of the unmagnetised bar B. Repeated careful experimentation 

 appeared to indicate that the increased positivity of the rod A ob- 

 served under these conditions was due to the increased action of the 

 acid or saline solution on the iron rod which was under magnetic 

 influence, owing to which it became surrounded by a slightly stronger 

 saline solution than the other unmagnetised rod B, which was appa- 

 rently less acted upon. In some cases in the more powerfully acid 

 solutions, Table A, columns 4, 5, 7, 8, a kind of maximum point 

 seemed to be generally reached, and after the more violent action of 

 the acid had expended itself, a reduction of the B.M.F. between the 

 rods was generally noticed as the solution in the B-tube gradually 

 approached an equilibrium of composition compared with the solution 

 in the A limb of the U-tube, and subsequently a reverse action in 

 some cases was observed. The unmagnetised rod B appeared to be 

 less rapidly acted upon than the one under magnetic influence. On 

 magnetisation of the bar the above full effect on the galvanometer was 

 not always of an instantaneous character, though a short time only 

 appeared requisite for its development. The solutions employed are 

 given in Table A, and the results therein recorded were derived from 

 a series of constant observations, a comparison in some instances being 

 afforded between the respective effects obtained by the two forms of 

 apparatus employed. 



It may be noticed that a fresh pair of the iron rods, cut adja- 

 cently from a long polished rod, were used for each experiment, and 

 123 pairs were used in course of this part of the investigation, the 

 whole of the experiments being many times repeated to ensure 



