DIGESTION AND ABSORPTION 173 



reagents are solvents of fats and oils. The alcohol, however, dissolves 

 very much more of the fat or oil when warm than when cold, as may 

 be demonstrated by making the alcoholic solution with the tube 

 immersed in boiling water; after the alcohol seems to have reached 

 the limit of solution at that temperature immerse the tube in cold 

 water. A large part of the dissolved oil instantly separates out, but 

 will readily redissolve on again immersing the tube in the boiling water. 



(3) The Saponification of Fats and Oils, (a) To about 2 c.c. of 

 olive oil in a test-tube add one to two volumes of a 25 per cent, solu- 

 tion of sodic hydrate. Shake the mixture vigorously; it is evident that 

 a chemical reaction is in progress. The fat is undergoing the process 

 of saponiftcation. A complete and typical saponification requires a 

 more careful apportionment of the amount of oil and of alkali used 

 and an application of heat. 



(6) Repeat the experiment, substituting a 25 per cent, solution of 

 potassic hydrate. The result is similar. 



(c) What is the chemical formula of palmitin? Of stearin? Of 

 olein ? 



(3) Write the reaction which takes place in saponification of 

 palmitin; of olein. Note the ready solubility of the products of this 

 reaction in water. 



(4) To a solution of soap add any aqueous solution of a calcium 

 salt soluble in water e. g., calcium chloride; a curdy, white pre- 

 cipitate separates out. Write the formula of the reaction. 



May the reaction have any relation to hygiene or therapeutics? 



(5) The Emulsification of Oils. Gould defines an emulsion as 

 ''water or other liquid in which oil in minute subdivision of its 

 particles is suspended." One may add: more or less permanently 

 suspended. For if one shake together vigorously 2 c.c. of oil with 

 an equal amount of water in a test-tube he is able to bring about 

 a minute subdivision and temporary suspension of the oil in the 

 water. While the oil is in this temporary physical condition it has 

 the white color typical of emulsions in general. In a few minutes, 

 however, the particles as they rise to the top of the liquid coalesce 

 into minute globules; then into larger and larger globules, and finally 

 into a homogeneous, supernatant oil-layer. 



(a) Add to the mixture above described 2 or 3 c.c. of strained egg 

 albumin; shake vigorously. One observes the same minute sub- 

 division of the particles, but they show no tendency to coalesce on 

 standing; the suspension is more or less permanent. 



Why do not the particles coalesce? In what respects is this emul- 

 sion unlike milk? 



(6) To 2 c.c. of olive oil add 2 c.c. of sirupy solution of any gum 

 e. g. y gum acacia; shake the mixture thoroughly. An emulsion 

 will be formed. What characteristics has this emulsion in common 

 with emulsion (a)? 



