in the presence of these small quantities of soaps, the fats are subdivided, and pass through the bowel-wall and are absorbed.

Take

Saponification; Preparation of Fatty Acids. -Take about 5 grams of mutton- or beef-fat in a small flask, add 25 c.c. of strong alcohol, and 5 c.c. of a concentrated solution of potassium hydroxid. Fit the flask with a cork, through which passes a piece of glass tubing about 100 cm. long (Fig. 6). Heat the flask gently over an asbestos board for fifteen minutes. care that the vapors of the alcohol are condensed by the air-cooling of the long tube, and do not escape. At the end of fifteen minutes dilute the mixture with 100 c.c. of water, and carefully add dilute sulfuric acid till the contents of the flask react acid.

Note the formation of solid fatty acids. Filter these off through a small filter, and wash with water. Dissolve the acids in a small quantity of alcohol, using heat.

Pour

FIG. 6.

off a few drops into a watch-glass, and allow the solvent to evaporate. Examine the residue left, with the microscope. Sketch some of the crystals formed.

Test the reaction of the alcoholic solution of fatty acids with a few drops of phenolphthalein, made slightly red with a drop of very dilute alkali.

Volatile Fatty Acids.-Saponify 5 grams of

butter-fat, using the same apparatus as was employed in the case of the beef-fat. Make the mixture acid with dilute sulfuric acid as before, and distil the contents of the flask, arranging a distilling apparatus as shown in Fig. 2.

Put into the distilling apparatus a few pieces of porous tile or pumice-stone, to prevent the mixture bumping.

Collect about 10 c. c. of the distillate. Note the odor and taste of the distillate. Test its reaction with litmus-paper. What are the acids which have come over?

Write the equations of the reactions occurring in the process.

Formation of Acrolein (Acrylic Aldehya) from Fats. Take a small quantity of tallow, and mix with an equal quantity of acid potassium sulfate in a mortar. Transfer about 2 grams of the mixture to a test-tube, and heat the contents of the test-tube over a flame. (This operation should be performed in the draught cupboards.) Note the odor of the acrylic aldehyd formed by the dehydration of the glycerol :

CH,OH.CHOH.CH,OH - H2O=CH2: CH.COH.

Emulsification.-Take a small quantity of olive oil in a test-tube. Shake with 10 c. c. of water. Observe that the oil separates almost immediately on ceasing to shake the tube. Add 1 c. c. of a dilute solution of sodium carbonate. Shake again. Note that the oil does not settle readily, but that a certain amount remains in the aqueous layer in a

very finely divided state. Allow the tube to stand for an hour. Examine at the end of this time. Describe the appearance.

THE PROTEIN SUBSTANCES.

The proteins are the most important series of substances dealt with in physiological chemistry. They make up a large part of the food which is used by animals, and form the greater part of the solid material of the body. They are also characterized by containing an amount of nitrogen which averages about 16 per cent.

An average of analyses of protein substances gives the following numbers in percentages:

In many of the proteins other elements enter, such as iron and phosphorus. A large percentage of the proteins are insoluble in water. Those which are soluble do not form a true solution, as, for example, sugar does, but exist, as do the soaps, in a colloidal or jelly-like condition. For this reason the molecular weight of these compounds has not been ascertained, and hence no formula can be given to them. Those determinations which have been made lead to the assumption that the molecular weight of egg-albumin is about 15,000, and that of vitellin 5513 with the formula

C292H481N9S2O3. These formulæ have as yet no real scientific foundation. The molecular weight of these substances is, however, undoubtedly high. The proteins as a whole are uncrystallizable. Recently a number of plant and animal albumins have been made to crystallize in microscopic crystals, but in the majority of cases this occurs only with the greatest difficulty.

In contradistinction to the crystalloids, the proteins are not dialyzable, and this property is used to separate them from substances, like the inorganic salts, which dialyze readily.

Aqueous solutions of protein substances have the property of being precipitated when their solutions are saturated with easily soluble salts, such as the sulfates of ammonium and magnesium, and the chlorids of sodium and iron.

Many of the proteins react differently with the salt employed, and hence this property is in common use to separate mixtures of these substances. All the members of this series are insoluble in strong alcohol, and may be precipitated out of solutions containing them by it. On long-continued treatment with alcohol the proteins are modified, so that they do not redissolve in the solvent from which they were precipitated. When this occurs the phenomenon is called coagulation, in contradistinction to precipitation, where on the addition of the original solvent the substances are redissolved.

One of the most characteristic reactions of many of the proteins is the change which they undergo

when their solutions are heated. This coagulation inay occur either in neutral, acid, or alkaline solution, according to the protein with which one has to deal. In neutral or alkaline solution the coagulation is, as a rule, only partial. In acid media the protein may be entirely thrown out of solution under favorable circumstances. When the acid is employed in too great or too small a quantity the coagulation may here be also partial.

The following is the classification of protein substances according to Neumeister:

The

The Albumins.-1. The true albumins. members of the following groups are differentiated by their coagulation-temperatures, their specific indices of refraction, and their behavior toward certain reagents.

a. The albumins. Serum-albumin, egg-albumin, lactalbumin, and plant-albumins.

b. The globulins. Fibrinogen (metaglobulin), serum-globulin (paraglobulin), fibrinoglobulin (from the digestion of fibrin), plant-globulins, and myosin.

c. Vitellins. Phytovittellin and crystallin.

2. Albumins formed from true albumins by fermentative action. Fibrin, formed from metaglobulin by the action of the fibrin-ferment.

3. Artificially changed albumins.

a. Albuminates, formed by the action of alkalies or acids on albumins.

b. Coagulated albumins.

The Proteids.-Compounds formed from the union of an albumin with some other substance.