PROTEINS 275 



sodium chloride, or on half saturation with ammonium sulphate. 

 If the solution is acid, however, in these latter cases some albumin 

 is precipitated. Recall also that albumin is coagulated by heat 

 and is precipitated by various reagents such as alcohol, mineral 

 acids, etc. 



19. Recall the color reactions of the albumins as determined 

 under general protein tests. 



20. Coagulation Temperature of Egg Albumin Solution. Fill 

 a large beaker half full of tap water. In this beaker place a 

 smaller beaker or an Erlemeyer also about half full of water. If 

 the inner vessel is not supported by fitting into the large beaker, 

 arrange the amount of water in this inner vessel so that it will 

 not sink to the bottom of the large beaker. Place a test tube 

 containing about five cubic centimeters of clear, fresh albumin 

 solution in the inner vessel, and add to the albumin solution 

 about 1 c.c. of saturated sodium chloride and a few drops of 1% 

 acetic acid. While your partner carefully warms the water in 

 the outer beaker, observe the thermometer and the albumin solu- 

 tion. The point at which it becomes cloudy is taken as the coagu- 

 lation temperature of the protein under examination. 



Globulins. As has been observed above, globulins, at least 

 those of animal origin, are precipitated from neutral solution by 

 saturating with MgS0 4 or half saturating with (NHJ 2 S0 4 . 



21. Plant Globulins. Globulins are found in many plants and 

 may be extracted with dilute salt solutions. An example of this 

 class is Edestin, which may be prepared by extracting hemp 

 seed with 5% sodium chloride solution. 



22. Globulins of tlie Blood Plasma. If time permits, the vari- 

 ous blood globulins may be fractionally precipitated from blood 

 plasma. Quarter saturation brings down fibrinogen, half satura- 

 tion precipitates practically all the remaining globulins of which 

 there may be several. The filtrate from the globulins still con- 

 tains serum albumin, which may be precipitated by acidifying 

 slightly, or by saturating with ammonium sulphate. Fibrinogen 

 also may be precipitated by half saturating with NaCl, differing 



