42 HYPONITRITES ; PROPERTIES AND PREPARATION BY 



which is of somewhat thick consistence, being generally a little 

 turhid, has to be passed through a Gooch asbestus filter, well 

 covered from the air. It consists of one molecule of sodium 

 hydroxide to only 3 mois, water and is just saturated with 

 liydrated sodium hydroxide, while there are about 2I2- atoms 

 of sodium present as hydroxide to one present as hyponitrite. 

 Cooling alone will cause some of the hyponitrite to separate 

 and the solution readily loses water in a vacuum over sulphuric 

 acid until it retains only about 2 molecules to one mol. sodium 

 hydroxide, when almost all sodium hyponitrite will have sepa- 

 rated out. At a temperature of 25-30° this will happen in 

 al)0ut 40 hours, the salt separating as minute crystalline, round 

 granules, some scattered over and adhering to the w^alls of the 

 dish but most of them united into a thick crust on the surface 

 of the solution. Below 15" the mother liquor readily deposits 

 crystals of the mouohydrate of sodium hydroxide. As also 

 evaporation is slower in the cold, it is better for both reasons 

 to evaporate in a warm room. 



The only effective way of separating the salt from its viscid 

 mother-liquor is by the pump and a Gooch crucible unlined 

 with asbestus ; draining on the tile is impossible. By the same 

 apparatus it is washed with absolute alcohol and then transferred 

 to a basin and gently rubbed up with fresh portions of alcohol, 

 till all sodium hydroxide has been removed. Drained now on 

 a good tile it is for the time being nearly the pnre hydrated 

 salt, very unstable, losing both water and nitrous oxide, and 

 consequently acquiring sodium hydroxide again. But, placed 

 promptly in a vacuum desiccator, it becomes anhydrous before 

 it has very much decomposed and is then quite stable in dry 

 air. The amount of the hydrated sodium hyponitrite should be 



