168 SULPHOCYANIC ACID. 



3. It is soluble in water, alcohol, and ether. Dis- 

 solve in water, and use for the following reactions. 



4. Neutralise with soda, evaporate to crystallisation. 

 Heat a portion of the crystals in a tube ; it will 

 blacken, leaving a residue of sodium carbonate mixed 

 with charcoal. 



5. Neutralise with ammonia and add ferric chloride. 

 A bulky red-brown precipitate will be formed, easily 

 soluble in mineral acids. Add excess of ammonia, 

 boil, and filter. To the filtrate add baryum chloride 

 and a little alcohol ; a white precipitate will fall. Ben- 

 zoic acid will give no "white precipitate under these 

 circumstances. 



6. Add lead acetate ; a white precipitate will ensue. 



Sulphocyanic acid, CNSH. 1. Obtain by distilling 

 large quantities of saliva with sulphuric acid and neu- 

 tralising the distillate, or evaporate the saliva to dry- 

 ness and extract with alcohol ; evaporate the alcohol 

 and use the extract dissolved in little water. Most 

 sulphocyanides are soluble in water and alcohol. 



2. Fuse with caustic potash ; ammonium carbonate 

 will be evolved, and will turn red litmus blue. Dis- 

 solve the residue in water and add lead acetate ; a black 

 precipitate of sulphide will be formed. 



3. Heat 100 grammes of dry ammonium sulpho- 

 cyanide in a flask to 170C. in an oil bath for two 

 hours. Allow to cool to 100C., add twice its bulk of 

 boiling water, filter hot, and set aside to crystallise. 

 A network of long fibrous satiny crystals of sulphur 

 urea will be formed. Press, purify by recrystallisation 



