32 
CHEMISTRY: D. P. SMITH 
Proc. N. A. S. 
proximately 4 milliamperes, and the intermediate one with a current of 
half this intensity. 
The potentiometer employed was a low-resistance "Type K" instru- 
ment by Leeds and Northrup, with which was used a suspended coil 
galvanometer by the same makers. The latter was adjusted by means 
of*a shunt until its vibrations were aperiodic, and had under these condi- 
tions a sensibility more than adequate. Care was taken before the beginning 
of an experiment to bring the potentiometer battery to such constancy 
of e. m. f. that errors from this source were negligible, and this constancy 
was checked at least once in the course of each series of observations by 
comparisons with a set of standard cells. 
The ten-ohm comparison resistance used was not a precision coil, so that 
the resistances found are only relative. Their relative accuracy may be 
estimated at 0.02% in the least favorable instances. 
Results. — The results of one experiment are recorded in table I, and dis- 
played graphically in figure 2. Before this run the wire had been several 
times saturated with hydrogen, and immediately before the interruption 
of electrolysis the current had been maintained over night at a value of 
2.3 milliamperes, corresponding to a cathode current density of about 
1.4 amperes per square decimeter. 
In the table below, column 1 shows the measuring current in milli- 
amperes; column 2 the time elapsed from the first reading in seconds; 
and column 3 the interval between successive observations. The un- 
enclosed numbers in the column headed Eiq give the observed fall of 
potential across the ten-ohm resistance, and the numbers in parentheses 
are interpolated from the preceding for the time at which E x was read. 
E x is the observed fall of potential across the cathode wire; and R x is the 
resistance of the latter calculated from the relation R x = 10'E x /(Eio). 
In figure 2 the values of t from table I are plotted as abscissae, and those 
of R x as ordinates. If the resistance were independent of the measuring 
current, the values for all three series of the table should lie upon an un- 
broken curve which is very nearly rectilinear; but it will be seen that the 
points for the intermediate series, taken with a measuring current only 
half as great as that used in the two end series, fall far out of line. A 
diminution of current of 50% has produced a diminution of resistance of 
some 30% o . 
This result was confirmed by that of an entirely similar experiment in 
which the changes of current and of resistance were, respectively, fifty 
and forty- two per cent; and finally by that of an experiment in which the 
electrolyte was withdrawn from the cell, before the resistance of the wire 
was observed, and in which the corresponding decrements were fifty and 
twenty-six per cent. It should be pointed out that only qualitative 
agreement between the several experiments was to be expected, since 
the magnitude of the effect is dependent both upon the quantity and 
