20 LABORATORY MANUAL OF GENERAL PHYSIOLOGY 



(b) Set up another series of six tubes with 2 cc. of granulated gelatin. 

 Into the first place 15 cc. N/10 HCl; into next 15 cc. N/10 HCl diluted one 

 half; next 15 cc. N/10 HCl diluted one fourth; next etc. Observe effect 

 on imbibition. 



3. Reversal of Emulsion. — Place 3 cc. of olive oil (colored with 

 Sudan III) and 3 cc. of water into two test tubes. Place a crystal of 

 CaCl2 into one and a few crystals of NaCl into the other. Shake violently. 

 Examine microscopically. Note dispersion of substances. Make several 

 trials varying proportions of oil, water, and salt until good results are 

 achieved. Consult Clowes' paper, Protoplasmic Equilibrium, J. Phys. 

 Chem., 20: 407, 1916; Scarth and Lloyd, p. 156; Clayton, "The Theory 

 of Emulsions," 1935- Text p. 187. 



If time permits, determine the effect of electrical stimulation on the 

 emulsions (cf. Dixon and Bennet-Clark, Proc. Roy. Dublin Soc, 20: 

 211, 1932). 



4. The Tyndall Effect. — Project a powerful beam of light from some 

 source into a small flask containing AS2S3 sol and note whether the path 

 of the beam becomes strongly luminous. Luminosity of the path of the 

 beam is known as the Tyndall effect and indicates the presence of suspended 

 particles (if no fluorescent material is present). Text p. 81. 



Insert a Nicol prism between the light source and the colloidal suspen- 

 sion and rotate the prism. Note whether there is any change of luminosity 

 as the Nicol is rotated. Cf. Robertson, "Optics," p. 273, 1929. 



6. Solubility find the Colloidal State. — Pour 2 cc. of an acetone solution 

 of a liquid fat into 100 cc. of water and get a suspension of minute particles 

 of fat in water. It is a general principle that if A is soluble in B but insolu- 

 ble in C, A will be thrown into suspension (often colloidal) when a solu- 

 tion of A in B is added to an excess of C (C and B being miscible). 



6. Permeability Test for Colloids. — Make colloidal Fe(OH)3 by pour- 

 ing a concentrated solution of FeCls into a beaker containing 100 cc. of 

 boiling water. A rich red solution, which is very stable, is formed 

 instantly. Place the colloidal suspension in a dialyzer. Test the dialysate 

 for chloride (AgNOs test). Does the Fe(OH)3 pass through? Keep the 

 dialyzer set up for a week. Concerning dialysis (cf. Bayliss, p. 83)- 



7. Diffusion Test for Colloids. — Let solutions of Congo red, colloidal 

 Fe(OH)3, safranin, and fluorescein as well as CUSO4 (10%) diffuse into 

 jelly of 3% gelatin (use test tubes % full of gelatin). Which are colloids 

 as shown by speed of diffusion? For dimensions of particles in the col- 

 loidal state cf. Scarth and Lloyd, p. 156. 



8. Hardy's Rule. — To 20 cc. portions of AS2S3 add drop by drop solu- 

 tions of NaCl, BaCl2 and AICI3 provided. How many drops are necessary 

 to produce a cloudy precipitate in each case? What is the relation be- 

 tween the valency of ions and coagulation? Consider the adsorption 



