80 
exception, because it does not render water a good con- 
ductor, and does not prevent the hydro-electric machine 
from giving off electricity. In trying ammonia as an 
experimentum crucis, I found that it did not stop the mi- 
croscopic movement, and had almost an inappreciable effect 
in precipitating suspended matter. A solution of 10 per 
cent, of ammonia would have less effect than too per cent, 
of sulphuric acid. The proof is rendered practically certain 
by the fact that boracic acid which was also ascertained to 
be a non-conductor by Faraday, does not precipitate matter 
from suspension. 
It is right to add, however, that in the case of acetic acid 
there is a discrepancy; Faraday stated that it does not 
render water a conductor ; but I find that in common with 
the other vegetable acids which I have tried it occasions 
precipitation. The conducting qualities of the substance 
have not been determined with sufficient accuracy to render 
a mistake impossible. 
It is probable that silicic acid does not render water a 
conductor, as I find that silicate of soda tends to increase 
* 
rather than diminish microscopic movement, and is another 
remarkable exception to the general precipitating power of 
soluble substances. 
I entertain no doubt that microscopic movement is closely 
connected with the phenomena of osmose so fully investi- 
gated by the late Mr. Graham. The connection is that of 
action and reaction ; for if a liquid is capable of impelling a 
particle in a given direction, the particle if fixed is capable 
of impelling the liquid in an opposite direction by an equal 
force. The earthenware jars used by Graham in many of 
