THE EFFECT OF HYDROGEN-SULPHIDE ON THE UNI- 
LATERAL CONDUCTIVITY OF ZINCITE- 
COPPER CONTACTS. 
R. B. DODSON. 
Of the many experiments concerned with the unilateral con- 
ductivity of the so-called crystal rectifiers very few have had to 
do with the effect of gases. 
The experiments described in this paper show that an artificial 
rectifier can be produced through the action of hydrogen-sulphide 
upon zincite-copper contacts. Such contacts show little or no 
unilateral conductivity in vacuo but possess the property to a 
considerable degree in an atmosphere of hydrogen-sulphide. 
In air the behavior of such contacts is extremely erratic. The 
greater current is as likely to pass from zincite to copper as from 
copper to zincite. Often there is no difference between the two 
currents. Sometimes the greater purrent may flow from copper 
to zincite for a few days and at the end of a week the greater 
current may pass from zincite to copper. 
The zincite and copper were placed in a glass tube with suit- 
able electrical connections and the tube evacuated with a Gaede 
mercury pump to as low a pressure as could be obtained with- 
out freezing mixtures. A piece was then broken off the zincite 
and the end knocked off the copper point. The two freshly 
made surfaces were then brought together and a direct electro- 
motive force impressed on the contact for fifteen or twenty min- 
utes in one direction and then in the other. Readings were taken 
at the end of every minute and curves plotted from the points 
so obtained. In order to economize space the curves are plotted 
with the same origin instead of consecutively with respect to 
the time. 
Curves No. 1, figure 41, show the flow of current shortly after 
the two substances were brought into contact in air. It will be 
noted that the greater current flows from copper to zincite. After 
a few days the amount of rectification began to fall off and at 
the end of three days the situation was as shown in No. 2. Curves 
No. 3 show the same contact at the end of a week. There is now 
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