8 HYPONITRITE FROM NITRITE. 



The precipitate should be treated with the acid in portions at 

 a time, not all together ; and as far as possible undissolved 

 precipitate should be kept off the filter till the last. For so long 

 a filtration a Lunge's filter tube extension of the funnel is more 

 suitable than the filter pump. The filtrate is to fall direct into 

 excess of sodium carbonate solution. Working with these pre- 

 cautions, the silver hyponitrite can be dissolved and reprecipi- 

 tated, even in hot weather, with hardly appreciable loss. 



Having replaced the mother-liquor by water, dilute sul- 

 phuric acid is cautiously added until, after good stirring up of 

 the precipitate, the solution is no longer alkaline and some of 

 it filtered is found to contain dissolved a trace of the silver 

 hyponitrite, this being best ascertained by adding one or two 

 drops of sodium carbonate solution to about 100 cc. of it, which 

 should cause a permanent yellow, very slight opalescence. 



The precipitate, thoroughly washed by décantation and 

 dried on a filter at the common temperature in a desiccator in 

 the dark, and then at 100°, will give 78 per cent, silver (calc, 

 78.26). But in order to preserve the bright colour of the salt 

 and its entire freedom from nitrite, all work upon it should be 

 done with very little exposure to bright daylight. Its weight 

 should be not less than 17 grams. 



