PRINCIPLES OF DIGESTION 



XXIX. — Principles of Osmosis. 



Apparatus. — Potassium bichromate, raisins, white of egg, starch, 

 Fehling's solution, iodine solution, Millon's reagent, dialyzer. There 

 are several forms of dialyzer described by different authors, any one 

 of which will serve. The following form has been found very satis- 

 factory. Obtain from the butcher some skins such as are used to 

 hold sausage meat. Tie one of these 

 around the base of a student lamp 

 chimney as in Fig. 22, after cutting 

 off the chimney so that it is only about 

 six inches in height. Select a cork to 

 fit tightly in the top of the chimney 

 and, with a cork borer, puncture this 

 to fit an eighth-inch glass tube about 

 a foot in length. Arrange the whole 

 apparatus as in the diagram, support- 

 ing the chimney in an outer jar so 

 that it will not rest on the bottom. 

 To fill the chimney, remove the cork 

 and tube. The tube will serve as a 

 delicate indicator of the amount of 

 rise in the water. 



J 



/ 



sJi: 





Fig. 22. 



Directions. — A. Put into the 

 dialyzer some crystals of potas- 

 sium bichromate. Fill with water both the dialyzer and 

 the outer jar until the level is the same in each. Allow 

 them to stand for a short time. Then examine and note the 

 level of water in the two parts. What has been the pre- 



47 



