COLLOIDS 245 



Colloids 



12. Solation and Gelation. Cover a small amount of gelatin 

 in a test tube with water and warm. What happens? Allow 

 to cool. What happens? Repeat the process once or twice. 

 Is the process reversible? 



13. Imbibition. Cut two equal-sized pieces of sheet gelatin 

 about VixV^ inch. Put one in a test tube or small beaker of 

 cold water for some time. Compare its size with the piece which 

 has remained dry. Explain. 



14. Dialysis. In a parchment or collodion dialyzing tube 

 place some albumin solution and some sodium chloride solution. 

 Suspend the tube in a beaker of distilled water and let it stand 

 several hours or over night. Test the water in the beaker for 

 chloride (has the chloride dialyzed?), and for albumin by acidi- 

 fying with a drop or two of dilute acetic acid and boiling; a 

 cloudiness indicates albumin. Has the albumin dialyzed? 



15. Suspensoids and Emulsoids. Prepare two test tubes, 

 one containing 1-2 c.c. of colloidal iron (dialyzed iron) the 

 other 1-2 c.c. of albumin solution. To each add a drop of sodium 

 chloride solution. Which is more easily precipitated by elec- 

 trolytes? 



Emulsoids form gels, suspensoids do not. 



16. Reversibility. Prepare two test tubes, one containing 

 1-2 c.c. dialyzed iron, the other 1-2 c.c. gelatin solution. Evap- 

 orate both to dryness in a water bath or beaker of boiling water. 

 When dry, add water to each (1-2 c.c.). Explain. 



17. Diffusion. Prepare a 4-5 per cent solution of gelatin, 

 by dissolving in warm water. Half fill four or five test tubes 

 with the solution and allow to gel. Pour on the gel 1-2 c.c. of 

 colloidal iron, copper sulphate, congo red, beet juice and any 

 other colored salt solution available. Which are colloids? 

 (Holmes.) 



