510 Mr. R. Phillips on the passive state of Iron. 



about the same height as before, and the metals were clean 

 and similarly immersed. 



The acid was again diluted with six times its bulk of water. 

 The iron wire at the moment of its entering this acid moved 

 the needle 20°, which then rested at 0° ; a swing could only 

 be communicated with still greater difficulty than in the fore- 

 going experiment. The copper wire caused the needle to 

 mark permanently an angle of 12°. In these experiments with 

 chromic acid the iron remained perfectly bright. 



With nitric acid, specific gravity 1*39, instead of the chromic 

 acid, the needle of the galvanometer was permanently deflected 

 5°. I found it advisable to screen the galvanometer from the 

 violent initial current of the arrangement, by opening another 

 circuit besides the wire of the galvanometer for this first 

 current. 



40 grains of iodic acid and 65 grains of water were placed 

 in the crucible; and when the acid was dissolved and mixed, 

 the crucible was connected with the galvanometer as before. 

 The iron wire at the first moment of its introduction acted 

 very powerfully, and then the needle stood at 4°; the iron 

 remained perfectly bright. A copper wire of the size before 

 mentioned gave a permanent deflection of 45°, notwithstanding 

 a dense film which formed on the surface of the copper. 



The action of chloric acid on iron was best observed with a 

 galvanometer far less sensitive than that before used, which 

 consisted of a pocket-compass having a few turns of insulated 

 copper wire round it. The metals and acid were employed 

 as before; the chloric acid was a rather concentrated solution. 

 When the iron was put in its place in the acid the needle re- 

 mained quite stationary ; but on touching the iron with a piece 

 of active iron or a copper wire, the needle was strongly affected, 

 and ultimately stood at 4-0°. This is an example of the pro- 

 duction of passiveness without the powerful initial current 

 which is generated by iron and nitric acid. With the first- 

 mentioned sensitive galvanometer the needle stood at about 

 35° when the passive state existed, but was remarkably un- 

 steady. 



The foregoing experiments were performed without any 

 considerable interruption, and with the same piece of iron wire, 

 which was j^th of an inch thick. 



A dilute sulphuric acid consisting of one of acid and five of 

 water, when cold was mixed by degrees with moist hyd rated 

 peroxide of barium of the consistence of cream, until the bulk 

 of the acid had increased from one to three ; no gas was 

 evolved. The sulphate of baryta was isolated on a filter, and 

 the fluid evaporated in vacuo over sulphuric acid until it had 



