22 LABORATORY WORK IN PHYSIOLOGICAL CHEMISTRY. 



(d) Heat 5 c.c. of the albumin solution to boiling and 

 then add one or two drops of very dilute acetic acid. The 

 albumin separates out in an insoluble, flocky (coagulated) 

 form. Why is the addition of the acetic acid necessary and 

 why is it added after boiling? Try to dissolve the coagulum 

 in some of the ordinary protein solvents. Make 5 c.c. of the 

 albumin solution faintly alkaline, and heat. Note differ- 

 ences. 



(e) The temperature of coagulation is determined as 

 follows:' 



Fill a test-tube (one-third of its capacity) with the clear, 

 very slightly acidulated solution of the protein. By means 

 of a bored cork fasten into the test-tube a thermometer in 

 such a manner that its bulb is entirely immersed in the solu- 

 tion. Suspend the test-tube in a large beaker of water which 

 rests upon a wire gauze. By cautious heating, the tempera- 

 ture of the water in the beaker may be raised slowly and the 

 point on the thermometer noted at which the first flocks of 

 coagulated protein appear in the solution. This point is 

 considered as the coagulation temperature of the substance 

 under these conditions, but it varies with the reaction of 

 the solution and the nature and quantity of the salts 

 present. 



Another form of coagulation is induced by the action of 

 certain ferments, such as the fibrin ferment of the blood, by 

 the action of which the soluble fibrinogen is transformed into 

 insoluble fibrin. 



(/) Heat some dried albumin in a dry test-tube to about 

 100 C. After cooling the tube try to dissolve the substance 

 in water. Why does not the albumin coagulate by the 

 heat? 



