PROTEINS. I I I 



(1) Coagulation Test. Heat some of the solution to boiling 

 in a test-tube. Does it coagulate? 



(2) Biuret Test. 



(3) Influence of Protein Precipitants. Try a few protein pre- 

 cipitants such as picric acid and mercuric chloride. How do the 

 results obtained compare with those from the experiments on egg 

 albumin ? (See page 97. ) 



ALKALI METAPROTEIN (ALKALI ALBUMINATE). 



Preparation and Study. Carefully separate the white from 

 the yolk of a hen's egg and place the former in an evaporating dish. 

 Add concentrated potassium hydroxide solution, drop by drop, stir- 

 ring continuously. The mass gradually thickens and finally as- 

 sumes the consistency of jelly. This is solid alkali metaprotein or 

 " Lieberkiihn's jelly." Do not add an excess of potassium hydrox- 

 ide or the jelly will dissolve. Cut it into small pieces, place a cloth 

 or wire gauze over the dish and by means of running water wash 

 the pieces free from adherent alkali. Now add a small amount of 

 water, which forms a weak alkaline solution with the alkali within 

 the pieces, and dissolve the jelly by gentle heat. Cool the solution 

 and divide it into two parts. Proceed as follows with the first part: 

 Neutralize with dilute hydrochloric acid, noting the odor of the 

 liberated hydrogen sulphide as the alkali metaprotein precipitates. 

 Filter off the precipitate and test as for acid metaprotein, page 1 10, 

 noting particularly the sulphur test. How does this test compare 

 with that given by the acid metaprotein ? Make tests on the second 

 part of the solution the same as for acid metaprotein, page no. 



Coagulated Proteins. 



These derived proteins are produced from unaltered protein 

 materials by heat, by long standing under alcohol, or by the con- 

 tinuous movement of their solutions such as that produced by 

 rapid stirring or shaking. In particular instances, such as the 

 formation of fibrin from fibrinogen (see page 191), the coagula- 

 tion may be produced by enzyme action. Ordinary soluble proteins 

 after having been transformed into the coagulated modification 

 are no longer soluble in the ordinary solvents. Upon being heated 

 in the presence of strong acids or alkalis, coagulated proteins are 

 converted into metaproteins. 



Many proteins coagulate at an approximately fixed temperature 



