690 
NATURE 
[May 19, 1923 

circuit is formed by these molecules being coupled 
with (distributed at) the electrode face and with the 
complex molecules. A similar interpretation is 
applied to aqueous solutions—R. W. Wood and 
A. Ellett: On the influence of magnetic fields on the 
polarisation of resonance radiation. In the case of 
the resonance radiation of mercury and sodium 
vapour, strong polarisation of the light can be pro- 
duced by weak magnetic fields properly orientated, 
and the polarisation of the light normally present 
can be destroyed by a magnetic field in a certain 
orientation. The field strength necessary for the 
destruction of the mercury vapour polarisation is 
less than one Gauss.—W. G. Palmer: A study of the 
oxidation of copper and the reduction of copper 
oxide by a new method. A film of copper about 
1/1000 mm. thick is prepared by chemical means on 
a china-clay rod, which is then clamped in a circuit 
carrying a small current at constant E.M.F. The 
film is oxidised at 130°-210° C. with gaseous oxygen 
at pressures up to 1 atmosphere, and the rate of 
oxidation determined by measurements of the 
resistance of the film. The rate of oxidation is 
proportional to the second power of the amount of 
metal in the film, and, for pressures up to 300 mm., 
to the square root of the oxygen pressure. Between 
170° and 190° C. the temperature-coefficient of the 
oxidation is negative owing to the simultaneous 
oxidation of cuprous oxide first formed. When 
hydrogen or carbon monoxide is mixed with the 
oxygen the rate of oxidation is greatly enhanced 
after a short initial period. In the reduction of 
copper oxide by hydrogen and by carbon monoxide, 
both gases are adsorbed on the metal and reduce 
adjacent oxide, but with hydrogen the water formed 
also adheres to the metal. The rate of reduction 
in both cases is directly proportional to the amount 
of metal present, an additional term in the case of 
hydrogen representing the action of the water.— 
E. A. Fisher: Some moisture relations of colloids. 
I1.—Further observations on the evaporation of 
water from clay and wool. The curvature occurring 
in the evaporation curves of clay soils, formerly 
attributed to shrinkage, is not found with ball clay, 
although this substance also shrinks on drying. 
This type of curvature appears only in the evaporation 
curves of such materials as soils, which are mixtures 
of colloidal and non-colloidal substances, and is due 
to the’simultaneous evaporation of imbibitional water 
held by the colloidal and of interstitial water held as 
water-wedges between the soil grains. The former 
evaporates at a practically constant rate, while the 
latter evaporates at a rapidly diminishing rate. The 
linear rate-curve of wool is not inconsistent with a 
real shrinkage occurring, although no such shrinkage 
has been demonstrated. 
Faraday Society, April 23.—Sir Robert Robertson 
in the chair—J. H. Shaxby and J. C. Evans: On 
the properties of powders ; the variation of pressure 
with depth in columns of powders. In the theoretical 
section an approximate mathematical solution is 
given of this problem for the case of powder in a 
cylindrical tube and in the absence of external 
pressure and where the surfaces of equal pressure 
are plane. The following equation is arrived at, 
P =p»(I—-e-**), where p is the pressure at depth x, 
Pm 1s equivalent to pgR/ze and » to 2c/R; p being 
the mass per unit volume of the powder, R the 
radius of the tube, and ¢ a constant depending on 
the coefficient of friction. In columns of lead shot and 
of powder, the absolute value of the pressure appears 
to depend on the state of packing of the column, 
and the resulting shape of the equal-pressure surfaces. 
—E,. E. Walker: On the properties of powders. 
NO. 2794, VOL. 111] 

(1) The compressibility of powders. The resistance 
offered by powders to static loads and to blows from 
a falling weight has been investigated. (2) The 
distribution of densities in columns of compressed ~ 
powders. Local densities in columns of compressed 
powder have been measured, and from the form of 
the density gradient curve “the distribution of 
pressure in a column of compressed powder has been 
deduced.—E. K. Rideal: On the rate of hydro- 
genation of cinnamic and phenyl-propiolic acids. 
Solutions of sodium phenyl-propiolate and sodium 
cinnamate undergo hydrogenation at equal rates of 
hydrogen uptake in the presence of palladium sol 
in large quantities. The rate of hydrogenation is 
governed by the rate of supply of hydrogen to the 
palladium in the liquid and is proportional to the 
square of the shaking speed, the reaction velocity 
being of zero order. Both old and fresh sols com- 
mence reaction with a velocity curve of zero order, 
but terminate in a reaction velocity curve of the 
first order. The salts undergoing hydrogenation as 
well as the hydrogen are adsorbed. The adsorbed 
salt remains on the surface until completely hydro- 
genated ; thus the rate of hydrogenation of phenyl- 
propiolate is the same as that of the cinnamate, the 
former taking up two molecules of hydrogen in the 
same time as the latter takes up one.—Leonard 
Anderson: Note on the coagulation of milk by acid. 
Addition of hydrochloric acid to milk of various 
dilutions causes precipitation of casein, the amount 
of precipitation increasing with increasing amounts 
of acid until a maximum rate of settling of the 
casein occurs which is inversely proportional to the 
dilution of the milk. The fat globules are mechanically 
carried down by the casein curd. At higher con- 
centrations of acid the casein goes into solution 
again, and at still higher concentration is again 
precipitated ; this is the salting out of the casein 
chloride by hydrochloric acid. Emulsions of benzene 
and olive oil in casein solution behave in an analogous 
manner to milk with respect to acid and alkali. 
Casein is probably the protective agent for the 
particles of fat in milk.—A. Taffel: The temperature 
of maximum density of aqueous solutions, The 
decrease in the total volume which occurs when 
41 eae of a substance is dissolved in water at a 
definite temperature has been termed the “ solution- 
contraction ’’ for that substance at that temperature 
and concentration. Solution-contraction increases as 
the temperature at which solution is brought about is 
lowered. With methyl, ethyl, and propyl alcohols, 
the solution-contraction decreases with the tempera- 
ture. The temperature of maximum density of the 
solution is below 4° C. The specific effect of ions 
and molecules on the depression of the t.m.d. of 
water results from their specific solution-contraction. 
Zoological Society, April 24.—Prof. E. W. MacBride, 
vice-president, in the chair.—Baron F. Nopesa: On 
the origin of flight in birds.—E. C. Stuart Baker: 
Cuckoos’ eggs and evolution. 
Royal Microscopical Society (Industrial Applications 
Section), April 25.—Prof. F. J. Cheshire, president, 
in the chair—W. N. Edwards: The microscopic 
structure of coal. The study of the microscopic 
structure of coal, though dating back to Henry 
Witham (1833), made rather slow progress until 
recent years owing to the difficulty of preparing thin 
sections. Much detailed work has now been done 
by Lomax, Hickling, Stopes, Thiessen, and others, 
which has considerably widened our knowledge of 
the mode of formation of coal, and has important 
economic bearings on questions of fuel economy, 
seam correlation, spontaneous combustion and in- 
