1894.] Specific Resistance of Pure Electrolytic Copper. 69 



The method of making a determination was as follows : 1st, C^ 

 was placed in the position which made the galvanometer circuit a 

 shunt of the standard ohm. RB was adjusted so as to make the de- 

 flection of a convenient amount by placing in a resistance R r (R r 

 having been determined by means of preliminary experiments). Then 

 K was pressed down and a deflection of the galvanometer " a " ob- 

 served. The current was then reversed, and a deflection " b " 

 observed, (a + fc) wa.s then placed in the observation table under the 

 heading G R . The key opened. The temperature of B observed and 

 noted (T B ). 2nd, Ci was then placed in the position which made the 

 galvanometer circuit a shunt to X. RB adjusted to make the 

 deflections of a suitable size by putting in a total resistance of R x 

 (determined by previous experiment). Then K was pressed down, 

 and the deflection a l observed, the current was then reversed, and a 

 deflection bi observed, (a^ + bi) was then put down in the table under 

 the heading Gr x . The temperature of X observed and noted (T x ). 



3rd observation. No. 1 repeated. 



4th 2 



A set of measurements like these were made in 20 seconds, thanks 

 to the dead-beat quality of the galvanometer, and the easy manipula- 

 tion of the mercury switches. It is evident that, if the galvanometer 

 deflections were exactly proportional to the current, and if the resistance 

 of the galvanometer circuit ivas sufficiently high to be neglected, and also 

 if the potential difference of the accumulator did not alter between 

 observations 1 and 2, the resistance X can be put 



CM 

 - G5 



S = resistance of the galvanometer + resistance of galvanometer 

 leads. 



The proportionality of the galvanometer deflections with the 

 limited range employed was, as previously stated, experimentally 

 proved. The conductivity of the galvanometer as a shunt was 

 negligible, as is evident from the fact that it was more than 2000 

 ohms resistance (when a minimum), and then diminished the total 

 resistance of the main circuit about 1/8000 ohm (it was shunted 

 round ^ ohm), the resistance of the main circuit amounting to 8 

 )hms. The fall of potential of the accumulator was very seldom 

 appreciable during one set of measurements. This will be seen from 

 the identity between observations 1 and 3 and 2 and 4 respectively in 

 the tables. When appreciable a correction was applied. When all 

 the arrangements were completed, a determination of the specific 

 resistance of the best specimen of copper (marked " A ") was 

 made. 



Origin of the Copper. The copper was deposited in a large rocking 



