PHYSIOLOGICAL CHEMISTRY 



301 



EXPERIMENT VI. Fill a narrow glass tube with some egg-white 

 solution, faintly acidulated with acetic acid, and fasten off one end. 

 Now fix this to the lower end of the thermometer by means of small 

 elastic bands. Gradually heat in a test tube placed in a water bath and 

 observe the temperature at which the albumin becomes opaque and set. 



IV. Crystallisation. Most proteins crystallise with difficulty; the 

 blood pigment of certain animals, however, crystallises readily. (See 

 later under Blood, Chapter VIII.) Egg albumin and serum albumin 



FIG. 224. Crystallised albumin. X600. 



have, however, been crystallised. Certain vegetable proteins, e.g. the 

 globulin of hemp seed (edesbin), crystallise more easily. 



DEMONSTRATION. Some hemp seed has been thoroughly pounded, 

 extracted with warm 5 % sodium chloride (50C.) and placed in a dialyser 

 overnight. As the result of dialysis, crystals of edestin have become 

 deposited in the tube. Examine those placed under the microscope. 

 Crystals of edestin may also be obtained, on standing, by cooling with 

 ice the extract of hemp seed. 



To obtain crystals of egg albumin the whites of several eggs are mixed with an 

 exactly equal amount of a fully saturated solution of ammonium sulphate. This 

 precipitates the globulins. The ammonium sulphate solution must be exactly 

 neutral in reaction and should be added to the egg-white in small quantities at a 



