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Calculated diffraction profiles for interstratified kaolinite and montmorillonite have been used to determine the composition of clays reported from Poland, Japan and Mexico. The predicted layer proportions determined from the curves and by other methods are in close agreement for the first two but a higher kaolinite content than that originally proposed is obtained for the Mexican clays.

The crystal structure of the title compound has been determined by Patterson and Fourier methods using threedimensional X-ray data and has been refined by a full-matrix least-squares procedure to R = 0.029 for 2 546 observed reflections. The crystals are hexagonal, space group P63 with a = 16.1 07(2), c = 12.378(2) A, Z = 6. The transformation of the structure to that of anhydrous aluminum iodate (hexagonal, a = 8.97, c = 5.25 A) is considered. The structure can be formulated as [Al(OH,)63+] [103-]2[H1,06-]*H10, and contains a very short non-bonded oxygen-iodine contact of 2.476 A. Institute for Soil Research, Craigiebuckler, Aberdeen AB9 2QJ PREPARATION of the mixed anion salt A1[I03],[N0,]-6H,O using an A1 : [IOJ-ratio >1 : 3 (or better, 1 : 6) results in the crystallisation of the acid salt Al[IOJ,-2HI03*6H20 after all the nitrate salt has been removed from the solution. The crystal structure of aluminium iodate nitrate has already been reported and the structure of the acid iodate is of interest because of the different behaviour of the two compounds on heating. AlJII0,],[N03]*6H,0 loses six water molecules and 20% of the nitrate (by analysis) at 200 "C. The remainder of the nitrate is removed between 300 and 340 "C and the [103]-decomposes at 425 "C. Up to the decomposition temperature, the powder diffraction pattern is not noticeably altered; a result of the fact that the positions of the iodate ions, which contain 60% of the scattering material, are unaltered. A1[I0,],~2HI0,*6H20, on the t Present address .-N.Z. Fertiliser Manufacturers Research Association,

The crystal structure of the title compound (I) has been determined by symbolic-addition and rotation-function procedures and refined by full-matrix least-squares methods to R 0.063 for 568 observed reflections. Crystals are triclinic, space group P i , with Z = 2 in a cell of dimensions a = 5.83(2), b = 5.78(2), c = 7.31 (2) 8, a = 79.0(3), p = 99.5(3)", y = 107.2(3)". Analysis of the molecular structure suggests that maleic hydrazide could act as a pyrimidine or a purine analogue.

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