CYSTINE. Ill 



Neutralise with carbonate of sodium, wash precipi- 

 tate, and dissolve in some carbonate of sodium. 

 Observe that the spectrum has the same two bands as 

 the hydrochloric acid solution. 



Cystine, C 3 H 6 NS0 3 . 1. A urinary calculus containing 

 cystine (see Calculi) is powdered, digested with am- 

 monia, filtered, and the filtrate allowed to evaporate and 

 to crystallise. The crystals must be washed with water. 

 They are insoluble in water and alcohol. 



2. Heat a little powdered cystine with potash solution 

 till dissolved, add acetic acid in slight excess. The 

 cystine will be slowly deposited in neutral six-sided 

 laminae. Examine microscopically. 



3. Dissolve a small quantity of cystine in dilute 

 hydrochloric, nitric, or sulphuric acid. Evaporate 

 the solution and set aside to crystallise. Grouped 

 acicular crystals of a cystine salt will gradually be 

 formed. 



4. To the solution in acid obtained in the foregoing 

 experiment add ammonium carbonate. The cystine 

 will be precipitated as a white powder. 



5. Heat some dry cystine in a tube. It will give off 

 a thick, fetid oil, hydrocyanic acid, and ammonia, and 

 leave a porous charcoal. 



6. Fuse with caustic potash in a tube. An inflam- 

 mable gas will be evolved forming sulphurous anhy- 

 dride when burned. Dissolve the residue in water and 

 add lead acetate; a black precipitate will appear, 

 proving the presence of sulphur. 



8. Heat on platinum foil. A peculiar, disagreeable 



