Focus; and in the path of the light is placed a glass beaker containing a dilute solution of sodium thiosulphate (hyposulphite of soda).
The hyposulphite experiment here again affords an excellent illustration.
By acting upon a solution of sodium hyposulphite with potassium bisulphate, Gernez (Compt.
Rend., 1891, 112, p. 866) is obtained by mixing a solution of sodium hyposulphite with double its volume of hydrochloric acid, filtering and extracting with chloroform; the extract yielding the variety on evaporation.
In systematic chemistry, sodium hyposulphite is a salt of hyposulphurous acid, to which Schutzenberger gave the formula H 2 S0 2, but which Bernthsen showed to be H 2 S 2 0 4.
18, p. 806) a mixture containing sodium hyposulphite and sodium formate for nitrates.
If a solution of sodium thiosulphate (hyposulphite) is added to this solution, hydriodic acid, sodium iodide and tetrathionate are formed; and if a little starch solution has been added, the end of the reaction is indicated by the disappearance of the blue colour, due to the iodide of starch.
The use of sodium hyposulphite as solvent, and sodium sulphide as precipitant, was proposed in 1846 by Hauch and in 1850 by Percy, and put into practice in 1858 by Patera (Patera process); calcium hyposulphite with calcium polysulphide was first used by Kiss in 1860 (Kiss process, now obsolete); sodium hyposulphite with calcium polysulphide was adopted about 1880 by 0.
Hofmann (Hofmann process); finally, sodium hyposulphite with cuprous hyposulphite was first applied by Russell in 1884, who included in his process the acidulation of the first wash-water (to neutralize any harmful alkaline reaction), and the separation of lead with sodium carbonate from the silver solution previous to precipitating with sodium sulphide (see C. A.
Stetefeldt, The Lixiviation of Silver Ores with Hyposulphite Solutions, &c., New York, 1888).
This is a solution containing up to 2% of sodium hyposulphite, of which one part dissolves 0.485 part silver chloride, equivalent to 0.365 part metallic silver, to form double hyposulphites.
If the sodium cuprous hyposulphite was used as a solvent in addition to the simple sodium hyposulphite, cuprous sulphide will be precipitated with the silver sulphide, and the precipitate will be of lower grade.