540 ILLUSTRATIVE EXPERIMENTS 



5. Potassium . 3 c.c. 6 per cent, gelatin -\- 3 c.c. N. K28O4. 



6. Ammonium . ,, ,, + 3 c.c. N (NH^)., .SO4. 



7. Iron . . „ „ + 3 c.c. N. FeoCSO^).. 



41. Study of Syneresis. 



(a) Make up about 30 c.c. each of 3 per cent., 1-5 per cent., and 0-75 per 

 cent, gelatin. Add a drop of thymol in chloroform to each sol, and place in 

 stoppered weighing bottles for three or four days. Note contraction of the 

 gel with expression of clear fluid. Examine both gel and fluid in each case 

 and note that qualitatively they are alike. That is, the separated phases 

 contain gelatin and salts dispersed through water and the gels, water and 

 salts dispersed through gelatin. 



(b) A similar series of experiments may be performed with 4 per cent, and 

 2 per cent, starch. 



(c) Examine the curd and the whey produced (a) by the addition of essence 

 of rennet, or (b) by a drop of acid to 20 c.c. of warm (30-38° C.) milk. 



(d) Put about 5 c.c. of freshly drawn blood into each of a pair of centrifuge 

 tubes and spin gently for about 10 minutes. Remove from centrifuge, add a 

 drop of preservative, cork firmly and allow to stand overnight. Draw of? the 

 clear fluid (serum) and test for proteins and chlorides. Examine the clot. 

 Note clear layer on top — the buffy coat. Cut this part away and test it for 

 proteins and chlorides. Put the lower red portion in a fold of muslin and 

 knead it in a little 0-9 per cent, saline in a small evaporating basin. Note 

 (1) emergence of red corpuscles, (2) residue of tough fibrin. Treat the 

 remainder of the buffy coat in the same way and note the fibrin residue. 



42. Emulsions. 



(a) (i.) Take four test tubes and place in each 10 c.c. of olive oil. In 

 addition add to (a) a few drops of oleic acid and a drop of alcoholic NaOH : 

 to {^) some (soft) soap solution : to (y) a few drops of oleic acid and about 

 the same quantity of cone. Ca(0H)2 solution, shake and allow to stand. 

 Which give the best emulsions ? 



(ii.) Another method of preparation. Place some gum acacia in a large 

 mortar. Powder it thoroughly. While continuing the rotatory movement of 

 the pestle, add the oil to be emulsified in a very slow stream. Keep the pestle 

 going, always in the same direction. After a thorough mixture has been 

 produced add sufficient water to emulsify the gum, starting with a few 

 cubic centimetres and gradually increasing the rate at which the water is 

 run in. Keep the pestle going. When the emulsion gives forth a cracking 

 sound, the rest of the water may be added in one lot. 



{})) To determine the optimum concentration of colloid for the stabilisation 

 of an emulsion. Into each of three mortars introduce 20 c.c. of water, 

 (a) containing 1-25 per cent, of commercial soft soap, (/3) 1-875 per cent., 

 and (y) 2-5 per cent. To each slowly add 120 c.c. of, say, cottonseed oil, 

 stirring regularly but not too vigorously meanwhile. If possible, put on 

 a mechanical shaker for half an hour. Pour into tall cylinders and allow to 

 stand for some days. 



(c) To determine the effect of the pR of the colloid on the stability of the emul- 

 sion. To 5 gm. of drv casein in each of three mortars add slowly (a) 50 c.c. 

 N/20NaOH, '(^) 50 c.c. water, and to (y) 50 c.c. N/20HC1. Allow to stand 

 overnight and then slowly stir 75 c.c. of cottonseed oil into each. Pour 

 into clean jars and allow to stand. Why does (jS) separate out ? 



(d) Effect of concentration of oil on rigidity. Stir into four lots of 25 c.c. 

 of 25 per cent, soft soap in mortars, (a) 50 c.c, (j8) 100 c.c, (y) 200 c.c, 



