Solid solutions with the general formula Bil-,Ca&O, (0.2 5 x 5 1) are found to possess the perovskita structure. The phase diagram based on X-ray diffraction studies involving cubic, orthorhombic and monoclinic modifications is constructed. It is concluded from conductivity and X-ray data that the transition into the monoclinic I1 modification is connected with some type of electron ordering on manganese ions. The changes in the paramagnetic Curie temperature resulting from these structural transitions are discussed. The magnetic ordering occurring in the system a t about 110 O K can be explained if Zener's double exchange interaction Mns+-02--Mn4+ is assumed to occur only in modifications in which electron ordering does not exist. The antiferromagnetic exchange interaction Mn4+-02--Mn4+ and the weak exchange interaction Mns+-O*--Mns+ (the latter being ferromagnetic at a > 3.8 A or antiferromagnetic a t a < 3.

Some series of solid solutions with perovskite-type structure are synthesized and investigated, viz. the binary systems Ndl-,, Me,MnO, where Me = Ca2+, Sr2+, Ba2+, and the ternary systems (Bi1-.La,)o.5Cao.5MnO3 and Bio,5(Cal -.Me,)0.5MnO3 where Me = = Sr2+, Pb2+, Ba2+. Distortions from the cubic perovskite structure are detected at room and liquid nitrogen temperature. Magnetic measurements are made in the temperature interval 77 to 800 OK. For all the compounds, a correlation between lattice distortions and magnetic behaviour is observed; 1. cubic and slightly distorted compounds exhibits a pure ferromagnetism; 2. distortions from the cubic structure give reduced spontaneous moments and in some cases antiferromagnetism developes. The ferromagnetic nature of the Mn3+-02--Mn3+ and Mn3+-02--Mn4+ interactions which are found in the non-distorted compounds is interpreted according to the Goodenough-Kanamori rules assuming that the quasi-static hypothesis is satisfied. The lattice distortions observed are thought t o give rise to a static distortion in the Mn3+ ion environment and an ordering of covalent bonds. As a result, some part of exchange couplings becomes antiferromagnetic. The influence of tJhe decreased subtended angle in the Mn-02--Mn linkage is discussed. This angle decreases from 180" when the lattice becomes distorted and this fact disturbs the orbital orthogonality. This results in a n increase of the antiferromagnetic t2g-t,g interaction via a-bonding and in the occurence of the other superexchange antiferromagnetic interactions which couple both the eg and t2g orbitals and the t2g and tZg orbitals via n-bonding. The contribution of double exchange to the ferromagnetism of mixed manganites is believed to be not important.

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The incubation of adrenal ferredoxin with various detergents in the presence of oxygen or ferricyanide leads to bleaching of the protein. The bleached preparation has the properties of apoferredoxin and it can be reconstituted with high yield by conventional methods.

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