THE ESTIMATION OF SODIUM HYPOSULFITE.1
Journal of the American Chemical Society
The usual methods of determining the degree of purity of sodium hyposulfite are unsatisfactory for ordinary laboratory work because they require either extreme care to exclude air or the use of uncommon reagents. Direct titrations 'with ferric3 or cupric4 salts were very inaccurate when performed without keeping the air away from the easily oxidized hyposulfite solution. The use of an excess of standard dye solution to oxidize the hyposulfite, the excess of dye being titrated with titanium
... with titanium trichloride,6 requires reagents that are uncommon. In the average laboratory a dye of standard purity is di8ticult to obtain. Hence a method was looked for which requires no extraordinary pains in the exclusion of air, uses only common reagents and which is fairly rapid. Seyewetz and Bloch6 oxidized the hyposulfite with ammoniacal silver chloride, reducing the silver salt to metallic silver as follows. The silver was collected and weighed in a Gooch crucible. In principle this method is superior to the direct titration methods in that the easily oxidized solution of the hyposulfite is eliminated. The solid hyposulfite is flooded with the oxidizing solution, thus excludmg the effect of the air. Another advantage recommends this method, viz., that the impurities sulfite and thiosulfate, do not affect the silver salt as they do such reagents as iodine, permanganate and ferric alum. The method, however, has two drawbacks : First, the gravimetric procedure is slow; second, it is inaccurate because of the insoluble impurities in the hyposulfite which are caught in the Gooch crucible and weighed. For these reasons we sought a method which would use the above principle but eliminate its disadvantages. Both faults can be remedied by solution of the silver on the Gooch crucible in nitric acid and titration of the silver nitrate by the Volhard method. A minor modification was made in the use of silver nitrate instead of the 1 Sodium hyposulfite is more commonly, but incorrectly, known as sodium hydrosulfite. *This work was carried out by me as chemist in the employ of the U. S. Public Health Service, under the direction of J. Stieglitz in his capacity of adviser to the Hygienic Laboratory of the U. S. P. H. S. The work was done a t the University of Chicago and is published with the consent of the Surgeon General.