SODIUM OR POTASSIUM : EDWAPtD DIVEES. 49 



Leen reduced, the alkaline solution, diluted to three times its 

 volume or more, is mixed with 13 grams silver sulphate or 14 

 grams silver nitrate dissolved in abont 3 litres water, and the 

 mixture stirred vigorously at once and continuonsly for five 

 minutes, in order to convert the silver oxide into silver hypo- 

 nitrite. After subsidencîo of nearly all the })rccipitate, the tur- 

 bid liqnor, if bright yellow rather than brownish, is decanted 

 and more silver solution added to it until, after good stirring, 

 some brown silver oxide remains, Avhen the Avliole is ^^onred 

 back and stirred np with the main precipitate and then left to 

 settle. Good daylight is almost essential for judging the colour 

 of the precipitate when finishing, but no more exposure of the 

 precipitate to light than necessary should be permitted. 



After some washing by décantation the precipitate is stirred 

 up with successive portions of highly dilute sulphuric acid 

 (3 or 4 per mille) until this fails to get fully neutralised and 

 shows, therefore, when poured off and mixed v>^ith a drop of 

 sodium carbonate, a slight yellow opalescence of silver hypo- 

 nitrite. The precipitate is washed with water by décanta- 

 tion till it gives up no sulphate, stirred up with water 

 containing a trace of sodium carbonate, and finally again 

 washed with water. It is collected on a filter and dried 

 in the dark in a vacuum. When thus dried it mav be heated 

 for a time to 100° in dry air without harm and become still 

 drier. It is now often as pure as it can be got. Not always, 

 however, are the operations so perfectly carried out as to ensure 

 this degree of purity, and it is, therefore, sometimes desirable 

 to sulnnit the salt to further treatment, preferably before it has 

 been dried. In that case it is dissolved, in portions at a time, 

 in 3-per-mille, ice-cold sulphuric acid and is either expedi- 



