513 
some minutes, a small quantity of a dark blue liquid will appear 
on the surface of the crystal in which small gasbubbles rise. In 
one case e.g. the strength of the current was 6 milliampères, the 
impressed EK. M. F. being 3 volt. If this E. M. F. between crystal 
and platinum fell to below 1,8 volt then the disengagement of gas 
could no longer be seen. If the B. M. F. of 3 volt was reversed, 
the current was only 0,5 milliamperes, the disengagement of gas 
became less and could no longer be seen when the E. M. F. fell 
to 2 a 2,5 volt. By these experiments it is proved that in the 
contact molybdenite-metal, opposite to the direction of the primary 
current, an E. M. F. exists, due to polarisation, in consequence of 
electrolysis; the value of this KE. M. F. of polarisation differs ac- 
cording to the direction of the primary current. By this the unipolar 
conduction has been reduced to well-known phenomena. 
The inquiry into the electrolysis as appearing here, is not yet 
complete; though it has been found that the phenomena as described 
here, exactly agree with those obtained if the platinum point is 
brought into contact with the molybdenite not directly, but by 
means of a drop of acidulated water. Again the resistance is least 
in the direction from MoS, to Pt; on the outer edge of the drop 
one can at first observe a green, after some time a dark-blue change 
of colour; without doubt an oxidation product of the mineral. In 
order to get the disengagement of gas the EK. M. F. must be at least 
1,2 volt; at the platinum point the colour of the liquid is somewhat 
brownish. If the current is reversed, then its strength possesses a 
greater value for some seconds, only to fall suddenly to a very 
small value. The disengagement of gas may be best seen on the 
side of the crystal and the liquid will also assume a brown colour 
on that side. In this case the disengagement of gas will only take 
place with an E. M. F. of 2 volt. 
The intention is to extend the investigation to other combinations. 
Physical Laboratory 
of the University Groningen. 
33 
Proceedings Royal Acad. Amsterdam, Vol. XIX. 
