KRYPTOPHANIC ACID. 137 



adding no excess, and filter. Evaporate the filtrate to 

 a thick syrup, precipitate with 90% alcohol, wash the 

 precipitate with a little more alcohol, and dry the 

 pure kryptophanic acid at a very gentle heat, or in 

 vacuo. 



3. The acid is very soluble in water, nearly in- 

 soluble in alcohol, insoluble in ether. 



4. Dissolve a portion in water : the solution has a 

 pleasant acid taste. Use it for the following experi- 

 ments. 



5. Add a little saturated lead acetate solution : a 

 white precipitate will fall, redis solved by excess, and 

 again precipitate by alcohol. 



6. Add copper acetate : a green precipitate will 

 form, behaving like the lead compound. 



7. Dry a portion of the green precipitate at 100 C., 

 and distil with a small quantity of water. The sub- 

 stance will turn dark green, and alcohol will be found 

 in the distillate, proved by a diminished sp. gr. and 

 by its reducing a drop of potassium bichromate and 

 sulphuric acid. 



8. Add copper sulphate in excess, then excess of 

 caustic potash : if on long boiling the copper is reduced, 

 the acid is yet impure ; the pure acid does not reduce 

 copper solution. 



9. Add mercuric nitrate, or acetate, or silver 

 nitrate. A white precipitate will fall, soluble in nitric 

 acid. 



10. Add ammonio-nitrate of silver : the solution will 

 become dark and will gradually deposit black metallic 

 silver. 



