30 



PRACTICAL PHYSIOLOGY. 



[IV. 



ethereal solution fall on paper, e.rj.^ a cigarette paper = a greasy 

 stain on the paper, which does not disappear with strong heat. 



{d.) To ohve oil or suet add caustic potash, and boil. Stearin is 

 present in the suet and is glycerin-stearate, while olein in olive 

 oil is glycerin-oleate. When stearin is boiled with a caustic 

 alkali, e.g.^ potash, a potassic stearate or soap is formed, and 

 glycerin is set free. This is the process of saponification. 



Tri-Stearin 

 3C18H35O 



'^ lo 



Potash. Potassic Stearate ^Soap). Glycerin. 

 ,3|}0 = 3C:sH.0j03 + C3H.|03 



(?.) Heat lard and caustic soda solution in a capsule to form a soap; decom- 

 pose the latter by heating it with dilute sulphuric acid, and observe the 

 liberated fatty acids floating on the top. 



(/.) Proceed as in ('/.), and add to the soap solution crystals of sodium 

 chloride until the soaps separate. 



(^.) Shake oil containing a fatty acid, e.g.^ De Jongli's cod-liver 

 oil, with a few drops of a dilute solution of sodic carbonate. The 

 whole mass becomes wliite = emulsion. Examine it microscopi- 

 cally, and compare it with milk, which is a typical emulsion. 



In an emulsion the particles of the oil are broken up into 

 innimierable finer particles, which remain discrete, i.e., do not run 

 together again. 



(/i.) Shake up olive oil with a solution of albumin in a test- 

 tube = an emulsion. Examine it microscopically. 



(/.) Gad's Emulsion Experiment. — Place in a watch-glass a solution of 

 sodic carbonate (.25 per cent.), and on the latter place a drop of rancid oil. 



The drop comes to rest, but soon the oil 

 drop shows a wliite rim, and at the same 

 time a white milky opacity extends over 

 the soda solution. With the microscope, 

 note the lively movement in the neighbour- 

 hood of the fat-droplet, due to the separa- 

 tion of excessively minute particles of oil. 

 The white fluid is a fine and uniform 

 emulsion (fig. 15). This experiment has 

 an important bearing on the formation of 

 an emulsion in the intestine in connection 

 with the i^ancreatic digestion of fats. 



(j.) Ranvier's Emulsion Experiment. — 

 Ranvier has shown that if a drop of lymph 

 taken from the peritoneal cavity of a frog 

 be mixed on a microscopical slide with a 

 Fro. i5.-Gad'3 Experiment. drop of olive oil, on examining with a 



microscope where the two fluids come into 

 contact, one sees emulsification going on before one's eyes, with the forma- 

 tion of fine particles of oil like the molecular basis of chyle {Comptes reiidics, 

 1894). 



