112 THE CHEMICAL COMPOSITION OF THE BODY 



white precipitate shows the presence of sulphate. Neutralize to litmus-paper 

 with solid potassium or sodium hydroxide and test for sugar with Fehling's 

 solution (see Experiment 12, d). The mucoid has been split by boiling with 

 acid into protein, protein cleavage products, and carbohydrate or a reducing 

 substance. The presence of oxidized sulphur in the molecule has also 

 been shown. 



DERIVED PROTEINS. 



10. Metaproteins. a. Acid Metaproteins or Acid Albuminate. Acid 

 metaprotein or acid albumin may be prepared as follows: 



To some chopped lean meat in a flask add .4 per cent, hydrochloric 

 acid. Allow it to stand for some time, shaking it occasionally. Filter 

 and neutralize the nitrate. A precipitate of acid metaprotein is obtained. 

 The acid albuminate then is insoluble in neutral dilute salt solutions, but 

 it dissolves in acidified solutions. Filter off some of the precipitated acid 

 albuminate and test it for loosely combined sulphur. 



b. Alkali metaprotein is formed on treating proteins with alkali. To 

 some undiluted egg white in an evaporating dish add some protein hy- 

 droxide solution slowly with constant stirring. The mixture forms a 

 stiff gel known as Lieberkiihn's jelly. Wash the gel, which has been broken 

 into small pieces, with running water until the excess of alkali is removed. 

 Warm it in a small amount of \vater and dissolve by heating gently. 

 Neutralize the solution carefully with acid, noting the odor of the hydrogen 

 sulphide that is given off. The precipitate which appears when the neutral 

 point is reached is alkali metaprotein or alkali albuminate. Filter off the 

 precipitate, wash it in water, and try the test for loosely combined sulphur. 

 A weak reaction or negative result shows that the loosely combined sulphur 

 has been split off by treating the protein with the alkali, a change which has 

 not occurred in the formation of the acid albuminate above. 



SECONDARY PROTEIN DERIVATIVES. 



11. Proteose and Peptone. Commercial proteose-peptone prepara- 

 tions, such as Witte peptone or Armour's peptone, may be employed for 

 the separation of proteoses and peptones. 



a. Take about 5 grams of the proteose-peptone mixture and dissolve it in 

 100 c.c. of water. 



Try the biuret reaction, Millon's reaction, and Heller's ring test. Do 

 the proteoses and peptones coagulate on heating ? 



b. Place the remainder of the solution in the beaker and add dry ammonium 

 sulphate in excess. Note that before the solution is completely saturated with 

 the salt, the precipitation of the primary proteoses (proto proteose and hetero 

 proteose). Completely saturate the solution with the ammonium sulphate, 

 warming it gently to facilitate the separation. At full saturation the second- 



