While the study of the kinetics of reactions between the iodate and various other ions has always proved to be of special interest, there is no record of any detailed study of the reaction between iodate and thiosulphate ions.

Normal trisodium phosphate forms three hydrates-a hemihydrate, a hexahydrate, and an oetahydrate-which can be identified by their optical properties and melting points. All higher hydrates were found to be complex salts.Trisodium phosphate forms hydrated complexes with the sodium salts of monovalent ions. These complexes are of two types. The first is represented by the formula raNasPOi.NaF.-XH20 where = 1 or 2, Y is a monovalent anion, and X = 18 or 19. The best known member of this type is the fluorine complex, 2NaaPC>4.NaF.19H20. The type formula for the second group is ra(Na3P0i.XH20)NaF where = 4 to 7, X = 11 or 12, and F is a monovalent anion. Two complexes are formed by some members of this series, both of which fall within the limits of the type formula. The crystal structure and optical properties of the complexes of the second type are very similar, all of them being trigonal and optically positive, and having similar refractive indexes. Some of the members of this group form an isomorphous series. The best known member of the second type is the hydroxide complex with the formula 5 (NasPOi. 12H20) NaOH, representing the common form of commercial trisodium phosphate. ACKNOWLEDGMENTThe author wishes to thank Howard Adler and W. H. Woodstock for many helpful suggestions, L. P. Audrieth for assistance in preparing the paper for publication, and A. R. Wreath for some of the analyses reported.

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