6 HYPONITRITE FROM NITRITE THROUGH 



be added without effect, good or bad, unless the solution of the 

 salts is weaker than it is here advised to be, for in that case 

 additional potassium hydroxide must be taken to bring its con- 

 centration to the right point. 



Treatment with a silver salt is the only way of separating 

 the hyponitrite from the other salts, and for this purpose the 

 presence of the alkali is essential, together with large dilution 

 when precipitating. The best way is to use the silver solution 

 exceedingly dilute, because this checks the precipitation of sil- 

 ver oxide and sulphite until some time after hyponitrite has 

 been all separated. Now, the need for large dilution and the 

 advantage of still larger dilution remove the only objection 

 that can be raised to the use of silver sulphate instead of sil- 

 ver nitrate ; and since it is generally important to feel assured 

 that no trace of nitrate or nitrite can have been added to the 

 hyponitrite, the sulphate should have the preference, although 

 the nitrate can almost certainly be used with as good results. 

 A cold saturated solution contains only 5 or 6 grams of the 

 sulphate to the litre, and is most easily prepared by boiling 

 excess of the salt with water and pouring the solution into an 

 equal volume of cold water. 



Whichever salt is used, the contents of the basin having 

 been washed into a very capacious precipitating vessel, the 

 highly dilute silver solution is poured in until it ceases to pro- 

 duce any more black precipitate. When this is at all abun- 

 dant, as it sometimes is in winter weather, an hour's interval is 

 given for subsidence of most of it, the still dark solution 

 decanted, and the precipitate washed by décantation before 

 rejection. With or without this interruption, the addition of 

 the silver solution is continued until the bright yellow hypo- 



