202 Hydrolysis of the Soluble Protein of Swede Turnips 



The mixture may be looked upon as made up of 10-09 grms. of valine 

 and 15* 14 grms. of alanine. The mixture was dissolved in 353 c.c. of 

 hot 10 per cent, sulphuric acid, 35 c.c. of acid for every gram of vaUne 

 being used. 283 grms. of purified phosphotungstic acid were added, 

 this quantity being equal to 14 grms. for every grm. of alanine present, 

 and enough to make the solution to contain a 20 % excess of phospho- 

 tungstic acid. A precipitate was formed but this was dissolved by 

 heating on the water bath. The flask was placed in ice in the ice chest 

 and allowed to stand for twenty-four hours. A thick crust of crystals 

 had formed round the sides of the flask. The supernatant solution 

 containing the vahne was poured off carefully, and the crystals dissolved 

 by heating with a volume of 10 per cent, sulphuric acid equal to that 

 originally used. Purified phosphotungstic acid was also dissolved in 

 the acid in the ratio of 1 grm. for every 5 c.c. The solution was then 

 allowed to crystaUise again for twenty- four hours at 0° C. The crust 

 of crystals was loosened by means of a glass rod and poured into a 

 Buchner funnel, and washed with a small volume of ice-cold 20 per 

 cent, phosphotungstic acid in 10 per cent, sulphuric acid. 



Determination and isolation of the jjrecipitated alanine. 



The alanine phosphotungstate was at once dissolved in hot water, 

 the solution given being rather turbid. The solution was made up to 

 2000 c.c. on cooling and an amino nitrogen determination made on 

 10 c.c. by Van Slyke's method. 



10 c.c. of the solution gave 13-15 c.c. N at 17-5° C. and 764 mm. 

 = 0-007655 grm. N in the amino form. 



The 2000 c.c. of solution contain 1-53 grms. of nitrogen. A duphcate 

 gave exactly the same result. This means that only 9-73 guns, of 

 alanine were present instead of 15-14 grms. as stated above. 



The remainder of the alanine hquid (1980 c.c.) was heated to boihng 

 on a water bath and 20 per cent, purified lead acetate solution added 

 until excess was present as shown by a sulphuric acid test in a drop 

 removed from the surface of the solution. The heavy precipitate of 

 lead phosphotungstate and sulphate was filtered ofE and thoroughly 

 washed in the usual way. The filtrate was concentrated to a volume 

 of 500 c.c. ; during this concentration a bulky precipitate separated 

 out which was filtered off. An equal volume of 95 per cent, alcohol 

 was now added to precipitate any lead sulphate left in solution. The 

 mixture was allowed to stand for an hour to complete the precipitation. 



