PART II 

 PHYSICAL CHEMISTRY OF CELLS 



A. SOLUTION AND DIFFUSION 

 A. GENERAL PHENOMENA. 



The purpose of the following experiments and simple observa- 

 tions is to enable the student to form a concrete idea of the reality 

 and character of diffusion and solubility, and to work out some of 

 their general laws for application later to organic processes. 



105. Fill a test-tube, supported on a clamp, to within an inch 

 from the top with distilled water. Place in a position where it can 

 remain entirely undisturbed. Then with a long pipette drawn to a 

 slender -point, place in the bottom of the test-tube 2 cc. of potassium 

 permanganate solution, in such a way as not to disturb the water 

 and to leave all the purple solution at the bottom. On the outside 

 of the tube mark the level of the potassium permanganate solution. 

 Observe that it very slowly rises, by diffusion. Mark the position 

 reached by the end of the laboratory period, and leave the experi- 

 ment in progress until the next period. Mark the point to which 

 the fluid has then risen. What is the approximate rate of diffusion ? 



106. Seal off a glass tube at one end and fill with hot 1.570 

 agar-agar, colored red with neutral red solution. Set in an upright 

 position to solidify. When solidified, place in a bottle of 0.2', 

 KOH open end down. Measure by the change in color of neutral 

 red, the amount of diffusion during the laboratory period. Set 

 aside for measurement next day. What is the rate of diffusion 

 of KOH as thus measured ? 



107. Fill a petri dish with warm agar-agar solution (1.5% ) and 

 allow to cool. When solidified place one drop of each of the fol- 

 lowing solutions on the agar-agar : a. Saturated CuSO 4 ; b. 

 KoCr..O 7 ; c. KMnO 4 ; d. aqueous neutral red ; e. aqueous 

 methylene blue ; f . haemoglobin ; g. chlorophyll solution. Com- 

 pare the rates of diffusion. Is there any difference? Is it related 

 to the molecular weights of the substances? Cover and leave until 

 the next day when the diffusion may be again noted. 



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