Silver salvarsan / by William Herbert Gray.

  • Gray, William Herbert.
Date:
[1923.]
Catalogue details

Licence: Public Domain Mark

Credit: Silver salvarsan / by William Herbert Gray. Source: Wellcome Collection.

    5/12 (page 637)
    Inst, exper. Ther. Georg Speyer-IIause, 1919, 8, 25) could not, for this reason, elucidate the nature of a solution containing two mole¬ cular proportions of silver nitrate. It is now found that all the silver is removed from aqueous solutions of both silver salvarsan and sodium silver salvarsan by aqueous picric acid, owing to the simultaneous precipitation of the diaminodihydroxyarsenobenzene as an insoluble picrate. From the solid products so obtained, the picrate is readily removed by acetone, leaving solids rich in silver chloride and silver oxide, respectively, but containing only a small amount of arsenic. Like Paal’s colloidal silver, precipitated by acid from sols containing sodium protalbinate or lysalbinate (Ber., 1902, 35, 2224), these are insoluble in water but soluble in alkali. In the case of sodium silver salvarsan, it is probable that colloidal silver is present as well as silver oxide, for a comparatively large amount of arsenic is not precipitated by picric acid, indicating that oxidation of the salvarsan by the silver oxide has occurred; whereas in the case of silver salvarsan the percentage of arsenic precipitated is the same as in the case of salvarsan alone. The oxidation products of salvarsan, 3-amino-4-hydroxyphenylarsenious oxide and the corresponding acid, are not precipitated by picric acid under these conditions. The above results obtained with silver salvarsan and with sodium silver salvarsan, both in aqueous and alcoholic solution, seem to indicate conclusively that to the properties of diaminodihydroxy¬ arsenobenzene and its salts as protective colloids must be ascribed the phenomena observed in their reactions with silver nitrate. In the case of silver salvarsan, silver chloride is formed by double decomposition and remains in solution, being protected by the diaminodihydroxyarsenobenzene dinitrate, but not essentially in stoicheiometric proportions. In the case of sodium silver salvarsan, the silver is present as oxide and probably to some extent as metal, both again being protected by the colloidal sodium salvarsan as suggested by Raiziss and Gavron (loc. cit.), or by its hydrolytic product, “ salvarsan base.” The occurrence of some combination is not excluded by these results, but the double decomposition appears to form the predominating part of the reaction. Contrary to the representation by Ehrlich and Karrer of the material obtained by them as a silver nitrate additive product, it follows that it is a mixture of two molecules of silver chloride and one of diaminodihydroxyarsenobenzene dinitrate; such a mixture would have the silver content observed by them. The precipitate obtained from this by Karrer {Ber., 1919, 52, 2323) on addition of sulphuric acid and considered by him to be a sulphate of the co-ordination compound is equally well explained as a mixture of