14 LABORATORY MANUAL OF GENERAL PHYSIOLOGY 



turbidity appears through the solution except near the surface fihn. 

 Examine with eye level with meniscus and a light behind the tube. Do 

 not disturb the tube. The reaction results in an increase of surface energy 

 (opposed at the surface) (cf. Bayliss, p. 54). The water polymers in 

 the film may also affect the reaction (cf. Barnes and Jahn, Quart. Rev. 

 Biol., 9: 300, 1934). 



16. Spreading of Film. — Sprinkle a little talcum powder on the 

 surface of distilled water in a wide dish. Add a drop of oil. Explain. 

 Obtain a tray of clean water. Make the surface visible with a little 

 powdered sulphur. Add a strip of paper (a little shorter than the width 

 of the tray). Add oelic acid to the water surface on one side of the strip. 

 Result? (Cf. Langmuir, Jl. Chem. Education, 8:850, 1931.) Text p. 61. 



17. Drop Method. — Fill a pipette to a given point with water. Slowly 

 expel and count drops. Repeat with alcohol. Explain the difference. 



18. Surface Tension Parabola. — With a stalagmometer determine the 

 surface tension of solutions of alcohol of the following per cent by volume. 



Surface tension 



Proceed with great care, making five determinations for each solution. 

 Plot results with concentration as ordinates and surface tension (Dynes 

 per cm.) as abscissae. Text p. 53. 



No. drops H2O X Density of solution X 73 

 No. drops of solution 



19. Surface Tension and Temperature. — With stalagmometer compare 

 the surface tension of water at about 5° and 60° (cf. Kopaczewski, Proto- 

 plasma, 19: 262, 1933). Text p. 64. 



III. IONS 



1. Ionic Antagonism. — (These experiments are introduced here so that 

 the results may be compared with later ionic effects.) Grow 4 wheat 

 seedlings in each of the following mixtures of two salts in proportion by 

 volume (0.1 M concentration): 



(1) NaCl 100 95 90 50 25 _0_ 



CaCls 5 10 50 75 100 



(2) A similar series of MgCl2 vs. CaClz 



(3) NaCl vs. KCl 



(4) Controls in distilled water and diluted sea water (sea water is 

 osmotically equivalent to 0.52 M NaCl) 



Place 150 cc. of solution in a tumbler. Pour on melted paraffin. 

 Puncture 4 holes with heated glass rod. Place roots in punctures. 

 Wash seedlings carefully in distilled water and keep in distilled water 



