1. Materials

Olive oil, cream, butter, and cotton-seed oil.

2. Experiments And Observations. - (1) The Osmic-Acid Test

Place in test-tubes a small amount of each of the above foodstuffs; add to each a few cubic centimeters of osmic acid. A characteristic reaction takes place, the result of which is a deep brown coloration of the fat. If the conditions are favorable the stain deepens into a sepia black. The cream has protein admixtures; note the variation of the reaction.

(2) The Solubility Of Fats And Oils

Prepare two tubes each of olive oil and of tallow; treat each material with absolute alcohol and with ether. It will be found that both of these 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 1 to 2 volumes of a 25-per-cent solution of sodic hydrate. Shake the mixture vigorously; it is evident that a chemical reaction is in progress. The fat is undergoing the process of saponification. A complete and typical saponification requires a more careful apportionment of the amount of oil and of alkali used, and an application of heat.

(b) 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 ?

(d) Write the reaction which takes place in saponification of palmitin; of olein. Note the ready solubility of the products of this reaction in water. (Soaps of the alkalies are soluble.)

(4) Insoluble Soaps

To a solution of soap add any aqueous solution of a calcium, magnesium, or barium salt soluble in water - e. g., calcium chlorid; a curdy, white precipitate separates out. Write the formula of the reaction.

(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, and finally into larger and larger globules, then 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 subdivision 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 emulsion unlike milk?

(6) To 2 c.c. of olive oil add 2 c.c. of syrupy solution of any gum - e. g., gum acacia; shake the mixture thoroughly. An emulsion will be formed. What characteristics has this emulsion in common with emulsion (a) ?

(c) To 5 c.c. of cotton-seed oil containing a little free fatty acid add 10 drops of strong sodium carbonate solution and shake. A good stable emulsion is made in this way.

In what way is this emulsion different from those which precede? Which one of the emulsions given above is most like the emulsions formed in the small intestine?

(d) What materials present in the small intestine tend to promote emulsification of fats?

(6) The Diffusibility Of Fats Or Their Derivatives Or Modifications

Fill five dialyzers as follows:

(a) Milk.

(b) Solution of soap.

(c) Ten-per-cent glycerin.

(d) Emulsion (5, a).

(e) Emulsion (5, c).

Complete the observations on the following day, determining what derivations or modifications of fat or oil are diffusible. How may the presence of soap in the diffusate be determined ?