S. H. Freeman—F lectrification by Evaporation. 429 
. From solutions of sei solids the water evaporated 
carries away a negative c e. 
. From solutions of winds acids or salts the water carries off 
a positive charge. 
Tait and Wanklyn repeated Pouillet’s experiments with a 
much more sensitive electrometer. They detected electrifica- 
tion where Pouillet had failed to do so, e. g., in the evaporation 
of distilled water; and in some other cases the effects obtained 
were totally different in kind and degree from those obtained 
by Pouillet and earlier experimenters. 
In these experiments a few drops of liquid were dashed on a 
red hot platinum dish insulated and connected with an electro- 
meter. So long as the spheroidal state continued, little or no 
electrification was observed; but as soon as violent vaporization 
began, decided deflections were obtained. This fact and other 
circumstances about the experiments indicate that friction was 
the chief source of electrification and make it doubtful whether 
TT had any part in producing the observed electrifica- 
tion. Tait and Wanklyn recognized the fact that to friction 
was aie a large part of the ae which they obtained. 
Still, in his lecture on Thunder Storms,* Professor Tait, speak- 
ing of atmospheric electricity, says: ac ae alm, clear weather 
the atmospheric charge is usually positive. This is very com- 
monly attributed to evaporation of water, and I see no reason 
to doubt that the phenomena are closely connected.” After 
reading these lectures the writer of this article decided to inves- 
is sufficient to account for the phenomena of atmospheric elec- 
tricity. In this connection it will be remembered that Faraday 
traced the electricity, produced by the escape of steam or water 
from orifices, to friction, and concluded it was not due to evap- 
oration, nor r did it have any mae on atmospheric electricity. 
he investigation was begun with the expectation on the 
part of the writer of finding electrification, Professor Row- 
land, to whom the author is much indebted, believed that no 
electrification would be found. sh aan case the subject seemed 
important enough to warrant experiments which were free from 
the objections which hold against Ftioee already described. At 
the very beginning of the investigation it was found that at 
most the electrification due to evaporation would be extremely 
small and very great caution would be necessary to eliminate 
various sources of error. The apparatus finally used consisted 
of an evaporating dish 19™ in diameter and 1™ deep, insulated, 
and connected with one pair of quadrants of a Thomson’s quad- 
rant electrometer. The other pair of quadrants and the case of 
* Nature, vol. xxii, p. 340. 
