GB191512599A — Improvements in the Process for the Manufacture of Sodium Thiosulphate.

USPTO Abstract

12,599. Hutchins, T. W. S., Hargreaves, L., and Dunningham, -A. C. Sept. 2. Sodium thiosulphate is obtained from sodium sulphite and sulphur in a solution sufficiently concentrated to allow of crystallization without evaporation, by digesting the reagents and water in the requisite proportions. Theoretical proportions of sodium sulphite and sulphur, or a small excess of either may be used; or a large excess of one or the other so as to form a paste or magma, or a large excess of both in proportion, to the water, may be used. When excesses are employed, the sulphur and sodium sulphite may be used in excess alternately, to allow of the separation of both soluble and insoluble impurities. The reaction may be facilitated by adding a small proportion of a hydrate or sulphide of an alkali or alkaline earth, the product being finally treated with sulphurous acid or sodium bisulphite. The sodium sulphite may be made as described in Specification 10,556/15, by the reaction of sulphur dioxide on hydrated or anhydrous and hydrated sodium carbonate, sulphur being mixed with the carbonate; or by the reaction of sodium bisulphite on a soda ash, in which case the sulphur is mixed with soda, agitated with water, and the bisulphite added. In another modification, a hot saturated solution of sodium sulphite is passed through a solid mixture of sodium sulphite and sulphur, and this process may be continuous. The mixture is placed in a vessel a connected by pipes g, i with another vessel d having a louver plate f. Hot sodium sulphite solution is admitted by a pipe c up to the level of the overflow e. Then the valve is closed, and a pump h is operated so as to pass the solution from d to a through the pipe i and from a to d through the pipe g. Solid matter passing into d is deflected to the bottom by the louver f, and so returns to the vessel a. From time to time, further sodium sulphite and sulphur are charged into the vessel a, and further hot liquor is admitted, by the pipe c, thus displacing thiosulphate solution, which leaves by the pipe e and is filtered andcrystallized by cooling. The vessels a, d may be steam-jacketed.