On first mixing digested sewage sludge with soil the proportions of the Cu and Zn in the sludge that are extractable to conventional extractants fluctuate considerably. Thus Cu extractable from sludge alone shows a marked initia fall to a minimum at 8–29 days and then rises to near its initial value; from a sludge—soil mixture there is a less marked decrease (over 8–16 days) and the extractable Cu returns to near its initial value over 90–100 days. The Zn extractable from sludge alone falls to a minimum at 8–16 days and then rises to near the initial value, but the Zn extractable from sludge-soil mixtures rises sharply over 2–4 days and then falls to near the initial value over 50–100 days.

During pot trials, germination of barley and ryegrass seeds appeared to be inhibited by the presence of sewage sludge. Laboratory experiments confirmed this effect and showed that germination was not permanently inhibited but merely delayed. The lag period was dose-dependent, increasing in proportion to the amount of sludge added. A similar effect was induced by heavy metals (Cu, Ni, Zn) in aqueous solution but only by concentrations much higher than those in sludge, considering that most of the total metal load in sludge is in insoluble or unavailable forms. Results showed that the effect was more closely related to the organic matter (OM) content of sludge-soil mixtures on which the seeds were incubated. When sets of old and new mixtures differing only in OM content were tested, the delay in germination was greatest in the new mixtures which contained higher amounts of organic matter. When sludge is freshly incorporated with soil, intense microbial activity is to be expected leading to reduced oxygen tensions and conditions which favour the formation of volatile inhibitors such as ethylene and ammonia. Preliminary tests established that volatile inhibitors were involved in the effect.

Theupper critical level of a potentially toxic element is its minimum concentration in actively growing tissues of a plant at which yield is reduced.

An exploratory examination of the use of rye grass as an indicator of environmental accumulation of minor elements confirmed that natural grass is contaminated by soil or airborne dust, and that this contamination cannot be washed off sampled grass with water without also removing elements from within the leaves, to an extent that varies with the age and/or environment of the grass. This reduces the suitability of natural grasses as indicators of pollution, and alternative procedures are required and proposed.

The magnetization density induced in palladium by an applied magnetic field was measured by polarized neutron diffraction. The measurements were taken with the sample at 4.2 K in an applied field of 57.2 kOe and include the innermost eleven Bragg reflections. The observed density is contracted by about 15% relative to that calculated for ${\mathrm{Pd}}^{+2}$ by the Hartree-Fock method, and shows an asphericity similar to that of isoelectronic Ni.

We report neutron measurements of the magnetic disorder scattering cross section for ${\mathrm{Ni}}_{0.8}$${\mathrm{Cu}}_{0.2}$. These indicate that the magnetic moment disturbance produced by Cu in Ni is essentially limited to first-neighbor effects.

The magnetic coupling properties of the Ni-Pd alloy system are considered in terms of a molecular-field solution based on a Heisenberg type of interaction for spin \textonehalf{}. The unpaired electrons in Ni are assumed to be part of a band of mainly ${t}_{2g}$ character in which the totality of interactions leads to an interatomic ferromagnetic coupling. The unpaired electrons in pure Pd are assumed to be part of a narrow, weakly interacting band with more nearly ${e}_{g}$ symmetry. In the alloy, the Pd band structure becomes progressively more like that of Ni. The magnetic energy is then calculated in terms of the probability of finding unpaired electrons in the overlapping orbitals of the Ni and Pd atoms. The probability is determined from the average moment curve on the assumption of $3{d}^{9}$ and $3{d}^{10}$ states only. A fit to the data on the Curie temperature and average magnetic moment then gives the following relative values for the exchange constants (molecular-field coefficients); $A$ for Ni-Ni, $\ensuremath{\alpha}A$ for Ni-Pd, and ${\ensuremath{\alpha}}^{2}A$ for Pd-Pd, with $\ensuremath{\alpha}\ensuremath{\cong}0.8$.

Neutron diffraction measurements were made on a single crystal of gadolinium at sample temperatures from 10 to 350\ifmmode^\circ\else\textdegree\fi{}K to investigate the possible occurrence of a spiral spin structure. The measurements show that Gd is a normal ferromagnet with a rather complex temperature dependence of the spontaneous moment alignment. Between ${T}_{C}=294$ and 232\ifmmode^\circ\else\textdegree\fi{}K the moment is parallel to the $c$ axis; below 232\ifmmode^\circ\else\textdegree\fi{}K it moves away from the $c$ axis to a maximum deviation of about 65\ifmmode^\circ\else\textdegree\fi{} near 180\ifmmode^\circ\else\textdegree\fi{}K and then back to within 32\ifmmode^\circ\else\textdegree\fi{} of the $c$ axis at low temperatures.

Alloys of the heavy rare earth metals with La have been studied by neutron-diffraction methods. For alloys with 15 at.% or less of La the alloys have the simple hcp structure. The influence of La on the magnetic structures of the metals is such as to enhance the stability of a ferromagnetic configuration relative to an oscillatory one. The transition temperature is lower and the initial turn angle (when it exists) smaller in a lanthanum alloy than in the corresponding yttrium alloy. In the lanthanum-rich region, the system La–Tb has been most extensively studied with five compositions ranging from Tb0.10La0.90 to Tb0.75La0.25 having been investigated. Of these, the compositions Tb0.20La0.80, Tb0.40La0.60 and Tb0.50La0.50 formed a single phase alloy with the double hexagonal lanthanum structure (dhcp). The 4.2°K diffraction patterns of these three alloys exhibited a number of broad diffraction maxima rather similar to those found for Nd in the antiferromagnetic region. Néel temperatures of approximately 50°, 68°, and 75°K, respectively, were estimated for the three specimens. The specimen Tb0.75La0.25 exhibited lines from the hcp and dhcp structures as well as of a third phase which is probably the δ phase. In the Tb0.10La0.90 alloy both a dhcp and fcc phase were observed at room temperature; the low-temperature pattern exhibited magnetic reflections characteristic of the dhcp alloys. The La-rich Tb alloys thus are antiferromagnetic, rather than ferromagnetic as had been proposed previously.

Neutron-diffraction measurements have been made on single-crystal holmium at temperatures ranging from 4.2 to 120\ifmmode^\circ\else\textdegree\fi{}K in applied magnetic fields up to 22.3 kOe in order to study the magnetization process of this material. At low temperatures, the $b$ direction in the basal plane is an easy axis. For a field applied parallel to an $a$ direction, the moments are aligned parallel to the closest $b$ directions. At higher temperatures the effect of a field applied parallel to a $b$ direction is to transform the system to a $b$-axis ferromagnet after causing it to pass through one or two (depending upon the temperature) intermediate fanlike oscillatory structures. Similar oscillatory configurations are produced by the application of a field parallel to an $a$ direction. The $a$-axis ferromagnet is not produced in fields up to 22.3 kOe. A characterization of the four intermediate structures observed at 50\ifmmode^\circ\else\textdegree\fi{}K was made and schematic phase diagrams in the $H\ensuremath{-}T$ plane were extracted from the diffraction and magnetization data. Studies of the remanent state at 4.2\ifmmode^\circ\else\textdegree\fi{}K were made, and are reported.

The alloys of the heavy rare earths with scandium have appreciably lower magnetic ordering temperatures than the metals themselves and their alloys with yttrium. The difference between these systems appears to be associated with the effect on the magnetic coupling of the smaller atomic volume of scandium. The Curie temperatures ${T}_{C}$ of the Gd-Sc and the Gd-Y alloys are compared over the composition range for which they are ferromagnetic. The coupling energy per gadolinium atom $\frac{{T}_{C}}{x}$ in the Gd-Y system is found to be essentially independent of composition whereas there is a linear decrease in this quantity for the Gd-Sc system. The rate of decrease of $\frac{{T}_{C}}{x}$ with volume for the alloy system is compared with the corresponding decrease of ${T}_{C}$ for pure gadolinium as determined in measurements at high pressures, and the results are found to be in good accord. The N\'eel-temperature data for the Tb-Sc system are also discussed.

The Curie-temperature and average-magnetic-moment data for the NiCu alloy system are considered in terms of a generalized Heisenberg exchange model in which, as pointed out by Van Vleck, only $3{d}^{10}$ and $3{d}^{9}$ states are involved. On this model the magnetic energy per spin should be a linear function of the average moment per atom, and the data bear out this relation, when a small correction is made for fluctuation effects in the magnetically dilute alloys. It is difficult to see how the data can be fitted on the basis of the commonly made assumption that the ferromagnetic energy arises primarily from the Hund's-rule coupling of two electrons simultaneously occupying orbitals on the same atom, $3{d}^{8}$ states.

Neutron-diffraction measurements have been made on single-crystal specimens of holmium at temperatures ranging from room temperature to 4.2\ifmmode^\circ\else\textdegree\fi{}K. Below the N\'eel temperature of 133\ifmmode^\circ\else\textdegree\fi{}K, the moments order in a helical structure in which the $c$ axis is the screw axis. The interlayer angle varies from about 50\ifmmode^\circ\else\textdegree\fi{} per layer at ${T}_{N}$ to 30.0\ifmmode^\circ\else\textdegree\fi{} per layer at 4.2\ifmmode^\circ\else\textdegree\fi{}K. Below about 20\ifmmode^\circ\else\textdegree\fi{}K the structure is a conical configuration in which there is a net moment of $1.7{\ensuremath{\mu}}_{B}$ parallel to the $c$ axis. The configuration of moments in the basal plane at 4.2\ifmmode^\circ\else\textdegree\fi{}K is a distorted helical one in which moments of $9.5{\ensuremath{\mu}}_{B}$ are bunched around the easy $b$ directions in the plane.

Neutron paramagnetic scattering measurements were for metallic palladium at sample temperatures of 15, 77, and 298\ifmmode^\circ\else\textdegree\fi{}K. Within experimental error the paramagnetic scattering cross section is the same for these temperatures and is only about 5 mb/sr atom. It is concluded that the Pd $4{d}^{9}$ spin states exist for a time short relative to the time of passage of a neutron over an atom (\ensuremath{\sim}${10}^{\ensuremath{-}13}$ sec for a 1-\AA{} neutron).

Neutron-scattering and magnetization measurements were made on a series of face-centered cubic $\mathrm{P}\mathrm{d}\ensuremath{-}3d$ and $\mathrm{N}\mathrm{i}\ensuremath{-}3d$ alloys to determine the distribution of magnetic moments in these ferromagnetic binary alloys. The specific alloys studied were: ${\mathrm{Ni}}_{3}$Co, NiCo, ${\mathrm{Pd}}_{3}$Co, PdCo, ${\mathrm{Pd}}_{3}$Fe (ordered and disordered), PdFe, ${\mathrm{Pd}}_{0.93}$${\mathrm{Fe}}_{0.07}$, and ${\mathrm{Pd}}_{0.97}$${\mathrm{Fe}}_{0.03}$. Magnetic moments of about 3.0, 1.8, and 0.6 Bohr magnetons per atom were found for Fe, Co, and Ni, respectively, and these were essentially independent of concentration. The average Pd moment varies with concentration and approaches a maximum of about 0.4 Bohr magnetons per atom in the concentrated alloys.

A neutron-diffraction study of the heavy rare earths Tb, Dy, Ho, Er, and Tm diluted with yttrium and of Tb with lutetium is reported. The modulated antiferromagnetic structures of the rare-earth metals are found to exist in the alloys, but the ferromagnetic phases of Tb and Dy are destroyed with small admixtures of Y. The N\'eel temperatures of the alloys and the pure metals are found to be a universal function of the average of the square of the spin projection on $J$, given for these heavy-rare-earth alloys by $\ensuremath{\xi}=c{(g\ensuremath{-}1)}^{2}\ifmmode\times\else\texttimes\fi{}J(J+1)$, where $c$ is the atomic concentration of rare earth. The value of the interlayer angle $\ensuremath{\omega}$ at ${T}_{N}$ which is related to the wavelength of the modulation of the magnetic structure is also found to be a universal function of $\ensuremath{\xi}$, and the temperature variation of $\ensuremath{\omega}$ decreases with decreasing $\ensuremath{\xi}$ so that $\ensuremath{\omega}$ approaches a temperature-independent value of about 50\ifmmode^\circ\else\textdegree\fi{} per layer for small $\ensuremath{\xi}$, regardless of the magnetic ion in the alloy.

The magnetic properties of chromium alloys with small amounts of manganese (0.5%, 0.74%, 2.1%) and vanadium (1.0%, 1.9%) have been investigated by neutron diffraction, and these results and others involving higher manganese concentrations are compared with theoretical calculations by Tachiki and Nagamiya. The addition of vanadium tends first (1.0%) to destroy the long-range modulation of the moment configuration and then rapidly to eliminate the magnetic moment of the system. The addition of manganese progressively modifies the temperature-dependent properties of the modulated-moment structure of pure chromium and the temperature of the spin-flip transition. Over a small composition range both the simple antiferromagnetic and the modulated-moment structures appear to be stable. Above 2.1% manganese only the simple antiferromagnetic structure is observed. The changes in the magnetic properties of the alloys have a qualitative relation to the theoretical calculations.

Neutron diffraction measurements were made on polycrystalline samples of a 75% Pd---25% Mn alloy. It was found that long-range positional order could be obtained by appropriate heat treatment and that this order was of the one-dimensional antiphase domain type with a period of 4 cubic unit cells. Below 170\ifmmode^\circ\else\textdegree\fi{}K antiferromagnetic reflections were observed for this ordered alloy. A magnetic structure is proposed which satisfactorily accounts for the observed magnetic reflection intensities. On the basis of this structure the atomic magnetic moments are $(4.0\ifmmode\pm\else\textpm\fi{}0.2){\ensuremath{\mu}}_{B}/\mathrm{Mn}$ and $(0.2\ifmmode\pm\else\textpm\fi{}0.1){\ensuremath{\mu}}_{B}/\mathrm{Pd}$.

In order to account for the magnetic properties of alloys it becomes important to determine the individual magnetic moments of the constituent atoms. This determination can be accomplished by the combination of neutron diffraction and magnetic induction measurements. Such measurements were made on the following ferromagnetic alloys: Pd3Fe, PdFe, Pd3Co, PdCo, Ni3Co, and NiCo. The average moment values were obtained from magnetic induction measurements while the differences in the atomic moments were determined from either the ferromagnetic diffuse scattering of the disordered alloys or the superlattice reflections of the ordered alloys.

Neutron diffraction studies on polycrystalline and single-crystal specimens of thulium have been made at temperatures ranging from room temperature to 1.3\ifmmode^\circ\else\textdegree\fi{}K. The results are interpreted by means of a method which exhibits explicitly the Fourier components of the distribution of magnetic moments on the lattice sites. At about 56\ifmmode^\circ\else\textdegree\fi{}K, the N\'eel temperature, a simple oscillating $z$-component-type antiferromagnetic structure is developed. At approximately 40\ifmmode^\circ\else\textdegree\fi{}K, nonzero Fourier coefficients of overtones of the fundamental observed at higher temperatures are first detected. At 4.2\ifmmode^\circ\else\textdegree\fi{}K the magnetic structure of thulium is a type of antiphase domain structure in which several layers of moments parallel to the $+{a}_{3}$ direction are followed by several layers in which the moments are oppositely directed. The sequence in thulium is -4, +3, -4, +3,... etc. Each atom has, within the precision of the experiments, an ordered moment of $7{\ensuremath{\mu}}_{\mathrm{B}}$, and the ferrimagnetic structure has a net moment, parallel to the $c$ axis, of $1{\ensuremath{\mu}}_{\mathrm{B}}$ per atom. The fundamental period of the modulation remains constant over the whole range of temperatures at a value corresponding to $3.5 {a}_{3}$ periods. In the course of this study the scattering amplitude of thulium was determined to be ${b}_{\mathrm{Tm}}=(0.69\ifmmode\pm\else\textpm\fi{}0.02)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}$ cm.