56 HYPONITRITES ; PROPERTIES AND PREPARATION BY 



tlio voliimo of tlie gases at the common temporaturo and pressure 

 should be a little less than the capacity of the bulb. The air 

 was removed from the bulb holding the salt by means of the 

 mercury pump while the bulb Avas kept in l)oiling water to 

 ensure the dryness of the salt. When evacuated of air, the 

 bulb was sealed off and the silver liyponitrite decomposed by 

 heating the bulb in a bath and not by the naked flame. 

 Thus heated in the absence of air and moisture, the salt ex- 

 hibits scarcely any change below 140° and only slow decom- 

 position bet^veen 140° and 160°, but above these temperatures 

 the change is soon complete. The metallic silver is slightly 

 caked together, presumably by the silver nitrate, and the gases 

 are faintly red between 140° and 150° and orange red at 160° 

 and above. On allowing the vessel to cool, the gases become 

 colourless but regain their colour just as l)efore when the vessel 

 is again heated, and these changes can be repeated any number 

 of times. 



To examine the contents of the bulb when cold, its point 

 was broken off under water and the small rise of water into 

 the neck of the bulb marked ; then the bulb w^as transferred 

 to a small trough of strong solution of sodium sulphite in order 

 to absorb the nitric oxide (this vol., p. 10). After an hour or 

 longer the residual gas was examined and measured, by bringing 

 the bulb mouth upwards, testing the gas as to odour and power 

 to support combustion, and then fdling it with water from a 

 burette up to the mark already made and to the mouth, in 

 order to learn the volumes of the gases when corrected for 

 temperature and pressure. The volumes could be only approx- 

 imately measured in this w^ay, but quite well enough for the 

 purpose. The metallic silver was weighed, and from its weight 



