The structure of Na2[Zr(SO4)3].3H20 has been determined'~y single-crystal X-ray analysis and refined by least-squares. The crystals, which are orthorhombic with space group P21212t, have the unit-ceU dimensions a=22.16, b=7.73, c=7.08 /~. The structure consists of spirals of composition [Zr(SO4)a(H20)2], extending in the [001] direction which are held together by the sodium atoms and a single lattice water molecule. Two of the sulphate groups form bridges between the zirconium atoms while two more sulphate groups are each doubly bonded to each zirconium atom. All sulphate groups have two terminal oxygen atoms. There are two water molecules coordinated to each zirconium atom. The hydrogen atoms of these water molecules bridge to oxygen atoms of sulphate groups and probably give rigidity to the spiral structure.

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For nearly spherical molecules the x-ray scattering from liquids yields structure and correlation functions for molecular scattering centers. The distribution of electron density in a water molecule is very nearly spherical, and orientational correlation between molecules in the liquid is not ``seen'' by x rays. Structure and correlation functions for molecular scattering centers are derived from x-ray data on water and tabulated. They provide a sensitive test for future work on a molecular theory of liquid water.

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