1890.] 



The Passive State of Iron and Steel. 



119 



For each experiment a pair of polished steel bars, 8^ inches long, 

 and 0'261 diameter, were cut adjacently from a long steel rod to 

 insure practical uniformity of structure and composition. The steel 

 and iron rods were of the chemical composition and physical proper- 

 ties given on previous page. 



The apparatus will be understood on reference to fig. 1. 



FIG. l. 



A pair of bars, supported in a wooden frame, W, were immersed. 

 in lj fluid oz. of cold concentrated nitric acid, sp. gr. 1/42, contained 

 in the (J-tube, A being the magnetised bar, and B the unmagnetised 

 one, and allowed to remain therein for periods stated on the Table I. 

 The bars were in circuit with a delicate astatic mirror galvanometer, 

 the telescopic observations of the deflections of which were carefully 

 taken. In some cases the bar A was previously permanently mag- 

 netised by hand, and in other instances the bar was magnetised in the 

 coil C for a short time. In the latter instances the subsequent 

 results were due to the residual permanent magnetism. The mag- 

 netising coil, C, was a powerful one, and was worked in connexion 

 with a bichromate battery in cases where the magnetisation of the 

 metal was made in the coil. 



A considerable number of experiments were made in the above 

 manner, those sets recorded on the Table I being selected as average 

 typical ones. In all the following experiments a new wooden stand 

 and a fresh pair of bright polished steel or iron rods were prepared 

 for each set of observations. 



VOL. XLVIII. K 



