CH. IV.] TRYPTOPHANE. 89 



(ii.) Measure the filtrate and to every 86 cc. add 14 cc. of 

 a 50 per cent, solution (by volume) of pure sulphuric 

 acid. (This is prepared by gradually pouring 500 cc. of 

 pure sulphuric acid into 500 cc. of distilled water, 

 cooling thoroughly under the tap until the whole of the 

 acid has been added. When quite cold the volume is 

 made up to 1000 cc. with distilled water.) The mixture 

 now contains 7 per cent, by volume of sulphuric acid. 



C. Separation of the mercuric sulphate precipitate, 



(i.) Add 250 cc. of a 10 per cent, solution of mercuric sulphate 

 in 7 per cent, sulphuric acid (by volume). Mix well, and 

 allow to stand over-night. (The mercuric reagent is 

 prepared by grinding 100 grams, of mercuric sulphate 

 with 500 cc. of distilled water, to which 70 cc. of pure 

 concentrated sulphuric acid has been added, adding 

 distilled water to make a volume of 1000 cc., and filtering 

 if necessary.) 



(ii.) Filter off the bulky yellow precipitate of the mercuric 

 sulphate compound of tryptophane on a Buchner funnel, 

 reserving the filtrate for Ex. 90. 



(iii.) Wash the precipitate on the Buchner with cold 5 per cent, 

 sulphuric acid (by volume) to remove the tyrosine. It is 

 not necessary to remove the tyrosine completely at this 

 stage. 



(iv.) Wash the precipitate with distilled water to remove the 

 greater part of the sulphuric acid. 



D. Decomposition of the mercuric sulphate precipitate. 



(i.) Transfer the precipitate and paper to a wide-necked 500 cc. 

 flask, washing the remainder of the precipitate in the 

 Buchner into the flask by means of about 200 cc. of 

 distilled water. Agitate thoroughly to get a good sus- 

 pension of the precipitate. 



(ii.) Add 100 cc. of boiling water, to which 3 grams, of crystalline 

 barium hydroxide has been added. Shake well. 



