294
OWE BERG, GAUKLER, AND SQUIER
hold such bound hydrogen in their interiors but much less at their sur-
faces owing to transformation of the carbide at the surface. Pickling
or abrasion_of steels B and C removes the surface layers and exposes
the hydrogen-bearing carbide. It makes little difference in this respect
what acid is used.
Pickling of steel A in 2N H,SO, or tumbling it in sand causes the
steel to pick up hydrogen, either from the H,SO, or from the water
present. Pickling of steel Ain 2N HNO, and 12N HNO; (for a sufficient
time) removes the dissolved hydrogen partially and completely, respectively, for the pickling times used.
It follows from these arguments that steel A should give rapid
wetting after pickling it in 2N H,SO,, somewhat less rapid wetting after
tumbling it in sand, and slow wetting after pickling it in 2N or 12N HNOs3.
It also follows that steels B and C should give comparatively rapid
wetting after all these treatments. These expectations are partially
verified by the data. However, steel C was not attacked by 2N H,SQ, or
2N HNO; and was not wetted in 7 msec after treatments with them.
It appears, therefore, that wetting is promoted by a reaction be-
tween hydrogen in the steel and water in the drop. The mechanism of
this reaction is discussed later. However, if this concept holds true for
steel, it may hold more generally; therefore any rapid reaction between a solid and water would cause rapid wetting. This concept does
not include electrolytic decomposition of the water because no current
can flow prior to wetting.®
Experiments were undertaken with sheet copper and drops of 12N
HNO, to follow up this concept. Since these two materials react very
rapidly, wetting by 12N HNO; was expected to be more rapid than wetting by pure water. The results of these measurements are presented
in Fig. 17. They are quite different from those obtained with pure
water, which are shown in Figs. 12 and 13. The product tV is constant
for 12N HNO3;, whereas the product tv *is constant for water.
DISCUSSION
There are two conceivable ways for the formation of bonds between a metal and water, namely, with or without decomposition of the
water. Without decomposition the water is held physically adsorbed;
with decomposition the water is held chemically adsorbed, notably as
OH. Decomposition of water on a metal surface may occur by two
mechanisms:
H2O,as a Habs + OH ads
and
(3)