THE PROTEINS. 21 



-the former sub-group belong the albumins, the globulins, 

 histones, and protamines; to the latter the keratins, 

 elastins, collagen, recticulin, and the skeletins. 



ALBUMINS. 



The albumins present the most characteristic type of the 

 proteins since they give a positive response to all the typical 

 protein reactions. 



Remember that an albumin (egg-white) solution was 

 employed for all the protein tests. 



(a) To 10 c.c. of the albumin solution add (NH 4 ) 2 SO 4 to 

 saturation. Note result and compare with experiment (c) 5, 

 p. 20. Filter off the precipitate and test the filtrate with the 

 biuret test. 



(6) To 10 c.c. of the albumin solution add MgS0 4 to sat- 

 uration. Compare this result with that of experiment (c) 4, 

 p. 20. Now add 2 drops of acetic acid. What is the precipi- 

 tate? 



(c) Test the albumin solution for lead-blackening sul- 

 phur. 



Coagulation. 



Certain of the proteins in the presence of water and heat 

 undergo a change which is confined to an intramolecular 

 rearrangement of the atoms in the molecule. This trans- 

 formation, which is termed coagulation, brings about physical 

 differences in the behavior of the proteins. They become 

 insoluble in all of the ordinary protein solvents. Under simi- 

 lar conditions the degree of temperature at which a definite 

 protein will coagulate is fairly constant, a fact which is 

 employed to ascertain not only the character but also the 

 purity of an unknown protein. 



