A new crystalline form of polyoxymethylene is described with an orthorhombic unit cell, space group P212121, and lattice constants a = 4.77 A., b = 7.65 A., c = 3.56 A. The chains are helicoidal with the axis of the helix parallel to c. The period of identity of 3.56 A. comprises two monomeric units and one turn of the helix. The lattice of orthorhombic polyoxymethylene is made up of isomorphous helicoidal chains.

The products obtained by sublimation or radiation of trioxane by high energy radiations have been examined by X-ray diffraction analysis.It has been possible to demonstrate that they consist of twinned crystals of hexagonal polyoxymethylene. By using rotating and WEISSENBERG photographs, the geometric correlations between the elements of the twins have also been definitely established. ZUSAMMENFASSUNG:Durch Analyse von Rontgendiagrammen werden die Produkte uutersucht, die bei Sublimation oder Bestrahlung von Trioxan mit energiereiehen Strahlen entstehen.Man kann zeigen, daf3 diese Produkte aus Zwillingskristallen von hexagonalem Polyoxymethylen bestehen. Mit Hilfe von Drehkristall-und WEISSENBERG-Aufnahmen konnen die geometrischen Beziehungen zwischen den Zwillingselementen gesichert werden. c y-3.563 A and helicoidal chains of the 211 type12). 171 G. CARAZZOLO, S. LEGHISSA, and M. MAMMIBoth structure analyses of these POM modifications were carried out by using X-ray diagrams of powders or stretched fibers.On the contrary, X-ray diffraction patterns of the single-crystal type are shown by POM when it is formed either by repeated sublimations of trioxane (first obtained by HAMMICK and B O E R E E~~) in 1922) or from radiation of trioxane with high energy radiations (HER) (prepared in 1961 by HAYASHI et al.I4)).

Ricerche Resine CasteZcanza (Varese) , ItalyWe have ascertained that aqueous solutions of formaldehyde absorb hydrogen sulfide proportionally to the formaldehyde present in solution. The highest molar ratio obtainable in solution is equivalent to the value CHzO/HzS = 2. When this ratio is reached, regardless of the initial concentration of formaldehyde, if the solutions are maintained constantly under pressure of hydrogen sulfide, separation of a solid product begins. Varioua chemical and physical studies indicate that the first solid separated from this system ia HSCH~SCHZSCHIOCH~OH. A possible mechanism of formation of this compound from the liquid phase is discussed.Many investigators have studied the interaction of hydrogen sulfide with aqueous solutions of formaldehyde in the presence of strong acids, which leads to formation of the cyclic trimer of thioformaldehyde (1,3,5,-trithmne) .Hofman' first reported this reaction, while Bonst and Constable2 described conditions leading to high yields (92-94%) of the trithiane.Baumana proposed that the intermediate I plays an important role in the reaction :In the presence of strong acids, I may react giving trithiane (11) with elimination of three molecules of water. Bogdanski and Chrzaszcrewki* ascertained that the reaction proceeds essentially as proposed by Bauman and while reaction (1) is fast, reaction (2) is slow. Therefore the intermediate obtained by reaction (1) may react to form such other intermediates as CHZ(SH)Z (111) and (H0CH2)8 (IV).We have ascertained that the reaction of hydrogen sulfide with aqueous formaldehyde, under suitable conditions616 in the presence of sulfuric acid, gives rise to a polymer with a polythiomethylene structure.On the other hand, few investigations have been carried out on the reaction of hydrogen sulfide with aqueous solutions of formaldehyde at normal pH (2.5-3.5). These investigations are summarized in the patent of Marks,' according to which a white solid having a sulfur content of about 51.5% and a melting point of 8OOC. separates out on saturating commercial solutions of formaldehyde with hydrogen sulfide. No further data regarding the solid so precipitated and the progressive uptake of hydrogen sulfide by aqueous solutions of formaldehyde'were available to date.Therefore, it was in our purpose to study the reaction between hydrogen sulfide and aqueous solutions of formaldehyde. The conditions that give rise to the formation of a solid product were investigated and the properties of this compound determined.. RESULTSIn order to study this reaction we allowed aqueous solutions of formalde hyde (at their standard pH) to absorb hydrogen sulfide and determined the content of formaldehyde and hydrogen sulfide in the liquid phase. All our

A new crystalline form of polyselenomethylene is described with an orthorhombic unit cell space group P2,2,2, and lattice constants a = 5.37A, b = 9.03A, c = 4.27 A. The chains are helicoidal with the axis of the helix parallel to c. The identity period of 4.27 A comprises two monomeric units and one turn of the helix. ' ZUSAMMENFASSUNG:Eine neue Form von Polyselenomethylen mit or thorhombischer Elementarzelle, Raumgruppe P2,2,2,, und den Gitterkonstanten a = 5,37 A, b = 9,03 A, c = 4,27 A wird beschrieben. Die Ketten sind spiralformig mit der Schraubenachse parallel zu c angeordnet. DieIdentitatsperiode von 4,27 A enthat zwei CH,Se-Gruppen in einem Schraubengang.

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