42 CELL-CONTENTS AND CELL-WALLS. 



cooling. (3) Add nitric acid a white precipitate, which dissolves 

 on heating, the liquid turning yellow, and reappears on cooling. 

 (4) The Biuret test a rose pink colour. (5) Add acetic acid and 

 potassium ferrocyanide, (6) saturate with common salt in each 

 case a precipitate, which disappears on heating and reappears on 

 cooling. 



Now add ammonium sulphate to saturation to the remainder of 

 the solution, filter, and to the filtrate (which contains peptone but 

 not proteose) apply the general protein tests xanthoproteic, 

 Millon's, biuret (rose pink colour given) ; note also that the filtrate 

 gives no precipitate with acids, or with acetic acid and potassium 

 ferrocyanide. 



44. Dialysis Experiments with Albumin and Pep- 

 tone. Fit up two dialysers (Fig. 20), each floating in a 



dish of distilled water. 

 Into A place some of 

 the albumin solution, 

 into B some peptone 

 solution ; to each add 

 a little thymol or other 

 antiseptic. Let the two 

 dialysers stand for 

 three days ; then test 



Fig. 20. A Dialyser, made by binding parch- " 1G water in 6aC J 1 J 

 ment paper over a hoop of rubber. proteins, USHlg ( With 



different samples) the 

 xanthoproteic, Millon's, biuret, and other tests. 



Note that albumin is indiffusible, while peptone is diffu- 

 sible, though somewhat slowly, through a membrane. 



45. Proteins in Pea Flour. Pea flour contains starch, 

 dextrin, and several proteins. The chief protein is a globulin 

 (legumin), but there is also another globulin (vicilin) and an albu- 

 min (legumelin). 



(a) Place 10 grams of Pea flour with 50 c.c. of water in a flask, 

 shake vigorously, let it stand for several hours, and filter. Test 

 the residue tor starch with iodine. Divide the clear filtrate, con- 

 taining the albumin, into several parts and apply to these the chief 

 protein tests : (1) Xanthoproteic test ; (2) Millon's test ; (3) Biuret 

 test ; (4) acetic acid and potassium ferrocyanide ; (5) heat and note 

 the coagulation of the albumin, especially if a few drops of acetic 

 acid be added. 



