EFFECT OF HYDROGEN — SULPHIDE ON COPPER 
243 
to copper. The observations for curves No. 7 were taken two 
days after the previous curves. The difference is now about seven 
milliamperes. The observations for No. 8 were taken about ten 
days after No. 6 and show a difference of about seven mil- 
liamperes. 
These curves are typical of the behavior of zincite-copper con- 
tacts. Of the several contacts studied none departed from the 
results shown here to any extent. 
The behavior of zincite-copper contacts in vacuo and in 
hydrogen-sulphide has a bearing on the theories of rectifier ac- 
75 
NOv 
In 
Vacu 
0 
NO 6 
In Hj 
S 
73 
1 "I'zz*' 
V 

ZnO- 
C u 
63 
/ 
..ZnO 
■Cu 
71 
^ — 
\ 

— — 
Co-Zn 
O 
67 
\ 
\ 
4 
IN 
R 
& 
JO 
12. 
\ 
1 
3 
2 
7~' 
c 
0 
i-Zn 0 
u 
7ft 
t ^ 
o 
Z 
r 
ZnO 
-Cu_ 
2 fi 
NO 8 
X yd 
-N.. 
In 
h 2 s 
O-Cu 
74 
— • 
— ' 
74 
/ 
7? 
72 
\ 
70 
\ 
Cu-2 
1 NO 
70 
' 
- . 
\ 
a 
2 
S 
7 
9 
i2_ 
2- 
s 
7 
_^Ct7 
2 
‘ZfTO 
11 
Figure 42 
tion. It is direct evidence that unilateral conductivity is entirely 
a surface phenomenon so far as the so-called crystal rectifiers 
are concerned. 
There is considerable indirect evidence favoring a surface film 
theory of rectifier action. Unilateral conductivity is certainly 
not a volume effect for small thin pieces of crystal possess the 
property to as high a degree as large thick pieces. Again almost 
the entire resistance of the contact is concentrated at the sur- 
faces as is shown by the fall of potential across the contact. The 
fact that uot all points on a given crystal surface possess the 
