EMULSIONS AND FOAMS 541 



(8) 400 500 c.c. of cottonseed oil. i'lacc in slialiow dishes. Note rigidity. 

 What happens when the optimum concentration of oil has been passed. 



(e) Divide an emulsion of oil in water — (soap), {i.e. 120 c.c. oil in 20 c.c. 

 7 per cent, soft soap) into nine [)ortions. No. (i.) will serve as control. 

 To the others add a few drops of one of the foUowinjj; N solutions, (ii.) HV\, 

 (iii.) NaOH, (iv.) Ca(OH).,, (v.) CaCl.,, (vi.) NaCI. (vii.) Alcolu.l, (viii.) (TIC^, 

 (ix.) Ether. 



Instead of soap any hydrophilic colloid may be used, e.g. albumin, 

 casein, acacia, dextrin, starch. The carbohydrate-stabilised emulsions are 

 the hardest to break. 



43. Foams. 



{a) Place about 10 c.c. of distilled water, absolute alcohol, and jiiacial 

 acetic acid in separate test tubes and shake vigorously for two minutes. Does 

 a foam appear ? Now mix 5 c.c. of water with 5 c.c. of the alcohol ; and also 

 with 5 c.c. of the acetic acid ; and the remaining 5 c.c. of the alcohol with 5 c.c. 

 of the acetic acid. Again shake vigorously. {Caution. — Release pressure 

 occasionally.) Do foams appear ? How long do they last ? Dust a little 

 lycopodium powder on to the aqueous alcohol, and a little finely powdered 

 lamp-black on to the surface of the aqueous acetic acid. Again shake for 

 two minutes. The foams last much longer. 



(6) Shake up some protein sol, e.g. diluted blood serum, 1 per cent, egg 

 albumin, or 1 per cent. Witte's peptone in 0-5 per cent. NaCl. Touch the 

 froth with a glass rod on which is a drop of either olive oil, caprylic acid or 

 cheese. Why does the froth subside. 



(c) Put 5 c.c. of a rennin solution into each of three test tubes. Leave 

 tube 1 as control. Add a trace of saponin to tube 3. Shake tubes 2 and 3 

 vigorously for two minutes. Withdraw 2 c.c. from each tube and compare 

 their activity in curdling a calcified milk (see Experiment 47). Why has 

 the saponin prevented the inactivation of the enzyme produced by shaking. 



44. Conditions Governing Enzyme Action. 

 Collect 10-20 c.c. saliva, filter. 



(1) Optimum temperature for the action of ptyalin on starch. Measure 

 5 c.c. of 1 per cent, boiled starch solution into a test tube and add 1 c.c. of 

 saliva. Set up the tubes at the following temperatures, {a) 0° C, {b) 20° C. 

 (c) 40° C, {d) 60° C, (e) 100° C. Test every minute with dilute iodine solu- 

 tion until the achromic point is reached. Note the time taken. 



(2) Optimum pH. One cubic centimetre of 1 per cent, starch solution, 5 c.c. 

 of a buffer solution, 1 c.c. of 0-9 per cent. NaCl solution, 1 c.c. saliva and 4 c.c. 

 distilled water are measured into a test tube, the tube is set in a water bath at 

 37° C. Note the time taken to reach the achromic point. Buffer solutions 

 of the following pR values to be used : {a) 8, {h) 7-4, (c) 6-8, {d) 5-8, (e) 4-8. 



(3) The action of salts in enzyme action, {a) Take 1 c.c. of starch solution, 

 1 c.c. of distilled water, and 1 c.c. of dialysed saliva. 



{b) Take 1 c.c. of starch solution, 1 c.c. of 0-9 per cent. NaCl solution, and 

 1 c.c. of dialysed saliva. 



Set the tubes in a water bath at 37' C.. and note the time taken to reach 

 the achromic point. 



(4) Effect of boiling on saliva. To 1 c.c. of starch solution add 1 c.c. of 

 boiled saliva. Does the saliva have any action when placed at 37° C. ? 



(5) Effect of boiling on starch. Add a little raw starch to 10 c.c. of 

 water. Divide into two equal portions, boil {a) and allow to cool, then add 

 1 c.c. of saliva to each portion and ])lace the tubes in a water bath at 37° C, 

 Note the tiine taken to reach the achromic ])oint. 



