THE PROTEINS. 29 



with acids or alkalies. In the formation of alkali albuminate 

 neutral sulphur is split off from the protein molecule. 



To 25 c.c. of the albumin solution add 5 drops of very 

 dilute HC1 and warm for 15 minutes at 40 C. Cool. 



(a) Exactly neutralize one-half of this solution with very 

 dilute NaOH. What is this precipitate? Shake up the pre- 

 cipitate and divide the solution into two parts. To the first 

 add a drop of NaOH and heat. Heat the other part and 

 then add a drop of NaOH. Explain the differences in results. 



(6) Try three characteristic protein tests on the remain- 

 ing half of the solution. 



To 25 c.c. of the albumin solution add 10 drops of NaOH 

 and warm for 15 minutes at 40 C. Cool. 



(c) Try the effect of heating some of this solution. 



(d) Neutralize the solution and repeat the procedure 

 employed under (a), using HC1 instead of NaOH. 



(e) Try three characteristic protein tests. 

 Explain the results. 



(B) Coagulated Proteins. Insoluble products which result 

 from (1) action of heat on their solutions, (2) action of alco- 

 hols on the protein. Heat coagulation has been considered 

 on p. 21. 



2. SECONDARY PROTEIN DERIVATIVES. 

 Products of a more pronounced hydrolytic cleavage of 

 the protein molecule. 



(A) Proteases, see p. 52. 



(B) Peptones, see p. 53. 



(C) Peptides. These are definitely characterized com- 

 binations of two or more amino-acids, the carboxyl group of 

 one being united with the arnino group of the other with the 

 elimination of a molecule of water. Some of the more com- 

 plex polypeptides give the biuret reaction. 



