chemical Agencies of Electricity. 35 
but after exposure to the atmosphere for a few minutes it 
wholly lost this power. 
When metallic plates were made to touch dry lime, strontites, 
or magnesia, the metal became negative ; the effect was exceed- 
ingly distinct, a single contact upon a large surface being suf- 
ficient to communicate a considerable charge. For these 
experiments the earths were carefully prepared ; they were 
in powder, and had been kept for several days in glass bottles 
before they were used : it is essential to the success of the 
process that they be of the temperature of the atmosphere. 
In some experiments which I made upon them when cooling, 
after having been ignited ; they appeared strongly electrical, 
and rendered the conductors brought in contact with them 
positive. 
I made several experiments in a similar manner on the 
effects of the contact of potash and soda with the metals. 
Potash in no instance afforded a satisfactory result ; its power- 
ful attraction for water presents an obstacle probably unsur- 
mountable to the success of any trials made in the free atmos- 
phere. Soda, in the only case in which electricity was 
exhibited, affected the metal in the same way as lime, stron- 
tites, and magnesia. Upon this occasion the soda had been 
prepared with great care, exposed in a platina crucible for 
nearly an hour in a red heat, and suffered to cool in the 
crucible inverted over mercury; when cool it was imme- 
diately removed, and the contact made with a plate of zinc : 
the experiment was performed in the open air ; the weather 
was peculiarly dry, the thermometer stood at 28° Fahrenheit, 
and the barometer at 30.2 inches ; six contacts gave a charge 
to the condensing electrometer in the first trial ; in the second 
ten were required to produce a similar effect ; and after this, 
F 2 
