DIGESTION AND ABSORPTION 163 



finally to a temperature of 100 C., 'by dipping the tubes into water- 

 baths of the temperatures named: 



(a) Dilute egg albumin. 



(b) Saline solution of myosin. 



(c) Syntonin in acid solution. 



(d) Acid albumin in acid solution. 



(e) Gelatin in aqueous solution. 

 (/) Proteoses. 



(g) Peptone. 



Record results in a table and formulate conclusions. 



(2) The Cold Nitric Acid Test. Subject the same series of proteids 

 to the cold nitric acid test by first pouring 1 c.c. or 2 c.c. of strong 

 nitric acid into a test-tube; then, with pipette, carefully floating 

 the proteid liquid upon it. In the case of the dilute egg albumin, 

 a characteristic white ring forms between the acid and the albumin. 

 Note in each case whether or not a typical ring is formed. 



(a) Dilute egg albumin. 



(b) Saline solution of myosin. 



(c) Syntonin. 



(d) Acid albumin. 



(e) Gelatin. 

 (/) Proteoses. 

 (g) Peptone. 



Tabulate results and formulate conclusions in a concise statement. 



(3) The Xanthoproteic Test. Use the tubes and materials already 

 prepared in the cold nitric acid test. Shake the tubes to mix the 

 acid with the proteid. In some cases a coagulum will be formed, and 

 this coagulum turns yellow on boiling if the tube is held in a Bunsen 

 flame. After the coagulum has been boiled in the acid, cool under 

 the hydrant or in a pail of ice-water and add strong ammonia to 

 alkaline reaction. The light-yellow coagulum which forms in the 

 case of the egg albumin turns to an orange color. This test is usually 

 given as a universal proteid test. Tabulate results on the above 

 suggested series (a) to (g), noting any variations of the reaction with 

 different proteids. Note variations in the reaction with different 

 strengths of solution of the same proteid. 



(4) Millon's Test. A general test for proteids is to heat a proteid- 

 containing liquid with half its volume of Millon's reagent. A pre- 

 cipitate appears, which is yellowish at first, but turns red under the 

 influence of heat. Test each of the above list of proteids (a) to (g) 

 with Millon's reagent. Record results. 



(5) The Biuret Test. To a suspected liquid add an excess of sodic 

 hydrate; shake well, and to the mixture add one or two drops of a 

 very dilute solution of cupric sulphate. A violet color appears, which, 

 on heating, becomes deeper in shade. 



A most convenient reagent for this reaction is a mixture of the 



