210 
Proceedings of Royal Soeiety of Edinburgh, [sess. 
III. Resistance of Hydrogenised Iron. 
In this part of the experiment I measured the change of resist- 
ance due to the hydrogen charged. The charge, when too small 
to be measured by weight, was roughly measured by the time 
of electrolysis, the strength of the current being kept practically 
constant. When iron is put into an electrolytic bath, the hydro- 
gen liberated upon its surface is gradually absorbed by it, though 
some portion, of course, escapes through the water. Thus the 
duration of electrolysis can give only a very rough measurement 
of the charge. 
When the duration of electrolysis is short, say twenty or thirty 
minutes, the surface of the wire remains bright when it is allowed 
to dry j but when the duration is much longer, say a day or two, 
the surface becomes covered with black dust which adheres to the 
cloth when it is wiped, while the wire is still wet. The amount of 
this dust, though small, affects the weight of the vure to the extent 
of some milligrammes. 
In the experiment, a hard-drawn iron wire ~ mm. in diameter 
and 1 metre in length was taken, and, after being rubbed with 
emery-paper, was put into the electrolytic bath. The current was 
supplied by three Daniells, and was measured on a tangent galvano- 
meter. The wire was taken out every ten minutes, and was care- 
fully wiped with a soft cloth. Its resistance was then measured by 
an ordinary resistance box and a delicate galvanometer. The fol- 
lowing are the results of the measurement, the temperature being 
that of the room, 25° C. : — ■ 
After 
Eesist. in Ohms. 
After 
Resist, in Ohms. 
0 min. 
4*176 
50 min. 
4*235 
10 „ 
4*186 
60 ,, 
4*244 
20 „ 
4*204 
70 „ 
4*257 
30 „ 
4*214 
00 
o 
4*268 
40 „ 
4*224 
These figures show (see also the curve) that the resistance 
increases steadily with the time of electrolysis. Hence, assuming 
the charge of hydrogen to be proportional to the duration of electro- 
lysis, we may regard the change of resistance for such small charges 
