430 
The distance at which the disc, doing duty for an impediment, 
is arranged, has an influence upon either. 
In the case of spray-electricity there is an optimal and a critical 
distance. According to LeENARD *) waterfall-electricity augments with 
the distance of the disc. 
However, the liquid medium and tle small chemical additions 
are of consequence. In most experiments water was the medium, 
but paraffinum liquidum will also generate spray-electricity, while 
waterfall-electricity can be obtained also with mercury. We have 
chiefly noted the influence of small additions of known chemical 
nature. 
Spray-electricity is markedly raised by the addition of substances 
that lower the surface-tension and are moreover volatile (odorous 
matter, antipyretica, narcotica, alkaloids). It may thereby rise to 
an amount which waterfall-electricity cannot approach by far. 
Perfectly pure water does not yield spray-electricity that is distin- 
guishable with an ordinary electroscope. *) 
Traces of odorous matter are capable of rendering it excessive. 
Spray-electricity, therefore is a means to detect the presence of small 
amounts of odorous matter otherwise than by the sense of smell. 
Pure water of itself generates waterfall-electricity, as the water 
becomes positively electric at the moment of its collision. 
Minute additions of odorous matter, gustatory substances, colloidal 
substances, modify the charge of the water considerably, now in a 
positive, now in a negative sense. 
LrNARD was the first who studied this problem in 1892, and im- 
mediately put forward an interpretation *), which he altered a little 
and extended in a subsequent publication. *) 
In our experiments we made use of LeNnarp’s apparatus, with 
slight alterations. 
A strong metal cylinder of + 24 liter capacity, with the lid 
attached to it hermetically by three screws, is provided at the bot- 
tom with a metal pipe with a tap. The pipe terminates in a glass 
tube with a fine outlet (1 mm. in diameter). In the lid there are 
two apertures, one of which is connected with the supply-pipe of 
the compressor with a gas-chamber of 2 m.’ capacity, while the 
other which is closed with a screw-stopper, subserves the filling of 
the cylinder. 
1) P. Lenarn: “Ueber die Elektricität der Wasserfalle’’. Wied. Ann. 46 p. 584. 1892 
*) Unless in the presence of an electric field. 
5) P. LENARD: ‘Ueber die Elektricität der Wasserfille’. Wied. Ann. 46—1892, 
4) Id. id, “Ueber Wasserfallelektricitét’’, Ann. der Physik. Bd. 47—1915. 
