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: 



Dilute solution of white of egg with several volumes of .4 per cent, hydro- 

 chloric acid. Allow it to stand for some time at 40 Centigrade. Filter and 

 neutralize the filtrate. A precipitate of acid metaprotein is obtained. The 

 acid albuminate then is insoluble in neutral dilute salt solutions, but it dis- 

 solves in acidified solutions. Filter off some of the precipitated acid albumin- 

 ate 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 sodium hydroxide solu- 

 tion slowly with constant stirring. The mixture forms a stiff gel known as 

 Lieberkuhn'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 water 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- 



