BASES OF UNKNOWN CONSTITUTION 115 



until the filtrate is nearly neutral, i.e. until the yellow mercuric oxide 

 just fails to be permanent. The white flocculent precipitate formed 

 is collected at the pump, suspended in hot water, and decomposed by 

 hydrogen sulphide ; after neutralising and boiling off the hydrogen 

 sulphide the solution is filtered and then furnishes a strongly active 

 secretine solution. The active substance can further be precipitated 

 from this solution by excess of picric acid, but attempts to obtain it 

 chemically pure have so far been unsuccessful. 



