82 PROPERTIES OF CERTAIN AMINO-ACIDS. [CH. IV. 



Properties of Aspartic Acid. It crystallises in small 

 rectangular plates. It dissolves in about 360 parts of 

 cold water and 19 parts of boiling water. Like glutami- 

 nic acid, its aqueous solutions are markedly "acid to litmus. 

 Solutions in alkalies are laevorotatory, those in hydro- 

 chloric acid are dextrorotatory. 



The copper salt is very characteristic. It can be 

 obtained by the method given in Ex. 79, or more readily by 

 boiling a solution with some solid cupric acetate, and filter- 

 ing the hot liquid. On standing, beautiful blue needles 

 separate. This copper salt, which contains 4! molecules of 

 water of crystallisation, is so sparingly soluble that it 

 serves for the estimation of aspartic acid. 



Cystine. 



83. Preparation from hair (or wool) by Folin's method. 



(i.) Heat 500 cc. of pure concentrated hydrochloric acid in a 

 litre round-bottomed flask on a water bath. 



(ii.) Add 250 grms. of human hair (the sweepings from a hair- 

 dresser's shop), or of washed wool (a piece of a pure 

 woollen blanket). If hair is used it must be added in 

 portions of about 50 grams, at a time, the hot mixture 

 being well agitated after each addition. 



(iii.) Boil under a reflux condenser on a sand bath for 5 to 6 

 hours, or until the mixture no longer yields the biuret 

 reaction. 



(iv.) To the hot mixture add solid sodium acetate to remove the 

 free hydrochloric acid. The point is reached when a drop 

 of the mixture added to about 2 cc. of water gives a 

 reddish violet or brown, and not a deep blue with a few 

 drops of a dilute (0-2 per cent.) solution of Congo red. 

 Usually 500 to 600 grams, of the solid are required. Allow 

 the mixture to stand over-night. 



(v.) Filter on a Buchner. The precipitate consists of cystine, 

 together with a considerable amount of dirt and in- 

 soluble debris. 



