950 EDWARD DIVERS AND TAMEMASA HAG A ; 



off. The temperature rising, the liquid becomes quite thin, while tine 

 effervescence and free ebullition set in ; probably, colloids have now 

 changed to crystalloids by hydration. On removing the flame, the 

 boiling quickly stops, but the effervescence continues for some 

 time. The vapours evolved at first are dense white and apparently 

 contain much sulphur trioxide, besides dioxide diluted with much 

 nitrogen ; but, as the temperature rises and decomposition gets more 

 rapid, the vapours become almost transparent. They can then be 

 copiously condensed on a glass plate held over, but not touching, the 

 mouth of the crucible, and form on it a dense white, crypto- crystalline, 

 dry, coherent, non-deliquescent film, neutral or even slightly alkaline 

 to litmus. The substance thus deposited is ammonium pyrosul- 

 phite. Towards the end of the decomposition, with farther rise 

 of temperature, ammonium hydrogen sulphate condenses from the 

 vapours. 



If the liquid is allowed to cool when something like a fourth of it 

 only has been driven off, large prisms shoot right across the solidifying 

 mass, suggesting the crystallisation of a less fusible salt out of its 

 solution in a more fusible one. These prisms are probably ammonium 

 hydrogen sulphate. When the heating is not arrested till half or more 

 of the liquid has been volatilised, the mass on cooling consists of brilli- 

 ant prismatic plates. 



The decomposition induced by the higher heating is an interesting- 

 sequel to the primary decomposition of the acid by heat. That 

 consisted in a part of the elements of water and ammonia becoming 

 available in hydrating und forming salts out of the acid. The suc- 

 ceeding change proceeds with the same consequences, but the water 

 and ammonia are now obtained only by sulphur oxides, nitrogen, and 

 a little ammonia being lost by the mass. The pyro-salts become 

 ordinary salts in the following way, as closely as can be traced : — 



