106 THE CHEMICAL COMPOSITION OF THE BODY 



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2. Elementary Composition of the Proteins. a. Nitrogen. Make 

 an intimate mixture of some dry protein, preferably a casein preparation, 

 with sodalime and place it in a dry test-tube. Warm gently over a Bunsen 

 flame. Hold a piece of moistened red litmus-paper over the mouth of 

 the test-tube. The ammonia split off from the protein will color the 

 litmus blue. 



Warm together carefully in a dry test-tube a few particles of dry protein 

 and a small cube of metallic sodium. (Do not place the tube in the flame.) 

 When the fusion is complete and the tube is cooled somewhat, plunge the 

 end into a small amount of water in a casserole. The glass of the test-tube 

 will probably break. When the fused mass has dissolved, filter, and to the 

 filtrate add a few drops of ferric chloride and ferrous sulphate solution. 

 On acidifying with hydrochloric acid a precipitate of Prussian blue is ob- 

 tained. Sodium ferricyanide is formed in the reaction and in consequence 

 gives a Prussian blue with the excess of iron present. 



b. Carbon. Place some desiccated casein in the end of a piece of glass 

 tubing, tap it down gently so that the lumen of the tube will not be obstructed. 

 Heat the casein gently over a small Bunsen flame, inclining the tube so that 

 there will be a slight current of air passing upward through it. The casein 

 will char, indicating the presence of carbon. 



c. Hydrogen. Note the clear fluid that has condensed in the upper 

 portion of the tubing from the preceding experiment. If a little anhydrous 

 copper sulphate is introduced into the tube, the fluid of condensation coming 

 in contact with it will become blue, indicating that water has been formed 

 in the charring of the casein. Hydrogen in protein has been oxidized to form 

 water. 



d. Sulphur. Boil some casein or some egg-white solution with sodium 

 hydroxide after adding a few drops of lead acetate solution. The presence 

 of sulphur is shown by the formation of a black-lead sulphide. On adding 

 hydrochloric acid the lead sulphide formed will be decomposed and the odor 

 of hydrogen sulphide will be noted. 



e. Phosphorus. Heat some casein, preferably in a nickel crucible, with 

 a fusion mixture composed of three or four parts of caustic soda and one part 

 of potassium nitrate, warming cautiously until the mass becomes colorless. 

 Dissolve the residue when cool in a small volume of water, neutralize and 

 acidify with nitric acid slightly, and add about 5 c.c. of ammonium molyb- 

 date solution. Warm for some minutes at 80. A yellow precipitate of 

 ammonium phosphomolybdate is obtained. 



3. Color Reactions of the Proteins. a. Millon's Reaction. To about 

 5 c.c. of a dilute solution of egg albumin in a test-tube add a few drops of 

 Millon's reagent. A white precipitate forms which turns red when heated. 

 This test can be used with advantage on solid proteins. In this case the 



