_ W A -V- ' * «k •»-X' VKAv.\L|. 1- 
.1 \ . , « -- <ll» 
[J. Am. Chem. Soc. 76, 3015 (1954)]. The following ions 
at a concentration of 10 -3 molar had no inhibitory effect; 
ferrous, ferric, ferricyanide and ferrocyanide. Six pen- 
tacyano iron compounds, tested at 10~ 3 molar concentra¬ 
tion inhibited hydrogenase about 50 percent. In a particu¬ 
lar compound, nitroprusside inhibits 69 percent at 10 ~*M, 
56 percent at 10 ~ S M, and 46 percent at 10 -~M. 
During the experiments in which nitroprusside was 
tested for its inhibitory effect, it was observed that the 
solution of nitroprusside changed from its original faint 
orange to blue-green and finally to a yellowish-brown. 
Quantitative determinations show that 1 mole of hydrogen 
was consumed per mole of nitroprusside. 
The blue compound formed after partial reduction is 
bleached by air to yield a compound other than nitro¬ 
prusside. Nitroprusside is not reduced by hydrogen acti¬ 
vated by platinum. 
Uranium-Lead Method of Age Determination 
J. Laurence Kulp, Columbia Unviersity 
The absolute geologic time scale has been inferred from 
age measurements by the uranium-lead method. New in¬ 
vestigations have elucidated the factors that produce 
anomalies among the various isotopic ratios that are used 
for the age measurement in this method, that is 
Pb 200 
Pb 206 Pb 207 
i 
Pb 210 U 235 Pb 
Pb 207 Pb 20S 
, and 
200 
rpp232 
Correction for common lead contamination is improved 
if the isotopic composition of the common lead of a dis¬ 
trict is known. Radon leakage occurs in all radioactive 
minerals, but this phenomenon can be measured and its 
effect calculated. Leaching of lead in preference to ura¬ 
nium also appears to occur under certain conditions. The 
agreement in the isotopic and chemical assays from vari¬ 
ous laboratories suggests that the analytic, procedures are 
not a significant source of error. 
An attempt is made to illustrate each of these effects 
with new data, to show which age determinations can be 
accepted with a high degree of confidence, and to pro¬ 
pose the experimental program required to fill out the 
geologic calendar. 
Velocity Distribution Measurements in 
Atomic and Molecular Beams 
P. Kusch and R. C. Miller, /Columbia TJnviersity 
A high-resolution spiral rotor velocity selector has been 
built for study of the/velocity distribution of the par¬ 
ticles in atomic and ltfolecular beams. For atoms effluent 
from an oven with slits designed to approximate as nearly 
as possible an ideal aperture of infinitesimal thickness, it 
is found that the/velocity distribution is that to be ex¬ 
pected from a Maxwellian velocity distribution within the 
oven. In the ca/e of the alkali halides the velocity distri¬ 
bution indicates the presence of polymers of the diatomic 
molecule. Tlpe polymers are principally dimers and are an 
important /Component of the lithium halides. They de¬ 
crease in/abundance, under our experimental conditions, 
with increasing atomic number of the alkali and are un¬ 
observable for the cesium halides. An observation of the 
abundance of the dimers as the temperature and pressure 
of the gas in the oven are varied yields the heat of dis¬ 
sociation of the dimeric molecule into two monomeric 
molecules. 
Rate of Evaporation of Water throu; 
Monolayers of Fatty Acids 
Victor K. LaMer and Robert J. Archer, 
Columbia Unviersity 
The control of evaporation fronyreservoirs is a problem 
of economic importance. The influence of monolayers lias ; 
been investigated by measuring the rate of absorption of 
water vapor by a desiccant surface 2 mm above the water 
surface. The rate of evaporation is reduced by a factor of 
10* by these monolayers. The data are reported as specific 
resistances of the,monolayers to evaporation for the satu¬ 
rated fatty acids, C 17 , Cj 8 , C I3 , and Coo. They were measured 
as a function of surface pressure, chain length, monolayer 
phase, subphase composition, and temperature. 
For a liquid condensed phase, the logarithm of the re¬ 
sistance of a monolayer is independent of the surface 
pressure and pH of the subphase but is a linear function 
of the chain length and the reciprocal of absolute tem¬ 
perature, which substantiates the description in terms of 
an exponential energy barrier. 
A theory is proposed for the source of the energy bar¬ 
rier; calculation of its magnitude agrees w r ell with known 
data on heats of vaporization. A full discussion will ap¬ 
pear in the Journal of Physical Chemistry. 
Temporal and Intensity Limits of the 
Flicker-Fusion Threshold 
Carney Landis, Columbia University 
When the eye is stimulated by intermittent light, any 
of several sensory experiences may result. The experience 
of flicker may change to fusion, or vice versa; that is, a 
critical flicker-fusion threshold (CFF) may be estab¬ 
lished. The basic considerations are successive pulses of 
light having measurable duration; the pulses are sepa¬ 
rated by measurable intervals of reduced light or absence 
of light. In most experiments the duration of the light 
pulse and darker interval bear some regular relationship 
to each other, which usually has been expressed as a light- 
dark ratio. It is of interest to consider the boundaries in 
time and luminance within which the CFF has been found 
to occur. The luminance limits are approximately — 6.67 
log millilamberts to 5.5 log millilamberts. The pulse dura¬ 
tion limits extend from 8 x 10 -3 to 2.5 x 10 5 p sec. The 
darker interval duration limits extend from 0.6 to 2.5 x 10 5 
u sec. A three-dimensional graphic representaion of these 
boundaries which gives rise to a “solid” is shown. Within 
these boundaries the interaction of the effects of the ten 
or more known determinants of the CFF may be system¬ 
atically located and their effect on the temporal and 
luminance components may be apportioned. 
Model for Multiple Meson Production 
T. D. Lee, Columbia University 
A Blocli-Nordsieck type treatment of multiple meson 
production is presented. In this treatment the physical 
nucleon is regarded as a composite system composed of a 
core surrounded by a meson cloud. The collision of two- 
nucleons is assumed to consist of a sudden exchange of 
spin, isotopic spin, and momentum between the cores of 
these two nucleons; these, in turn, shake off part of the 
surrounding mesons as radiation. This treatment is ap¬ 
plied to both the symmetrical scalar meson theory and the 
neutral pseudoscalar theory for arbitrary values of the 
coupling constant. 
9 ‘ 
r > / 
