Prof. Thomson , Electrification produced by heating Salts. 107 
dentally got on the wire enormously increased the discharge of 
positive electricity. 
Nitrates. 
The nitrates when heated get rapidly converted into oxides, but 
in the early stages they give off positive electricity. 
Chlorides. 
Give a small excess of positive but nothing like so much as 
the phosphates. 
Oxides. 
These when heated give out an excess of negative electricity, 
the most copious streams coming from the oxides of calcium 
and barium. 
Connection between electrification by heating and electrification 
by friction. 
If a salt when heated gives off an excess of positive electricity 
the salt itself will be negatively electrified, while if it gives off 
an excess of negative the salt will be positively electrified. I have 
found that the sign of the electrification produced by heating is 
the same as that produced by friction of the dry salt when cold 
and finely powdered. To test the electrification produced by 
friction the salt was placed in a mortar and rubbed with a dry 
pestle, the salt was then poured into an insulated cylinder con- 
nected with an electroscope, and the sign of the electrification 
given to the gold leaves tested, the substances on which the salt 
was placed while being rubbed and the substance with which it 
was rubbed were changed without making any difference in the 
sign of the electrification of the salt. 
The results are shown in the following table : 
Phosphates. 
Electrification by heating. Electrification by friction. 
A1 
— 
_ 
Ca 
— 
— 
Zn 
- 
Pb 
- (slight) 
- 
Sn 
Mcc 
(slight) 
— 
IVig 
Fe 
Hg 
- 
Ag 
- (slight) 
