properties, and among those which are most marked in this particular may be mentioned cottonseed oil, sesamé oil, maize or corn oil, and rapeseed oil. Types of the oils which have the least drying properties and which are regarded as types of non-drying oils are olive oil and peanut oil. The castor oil group is distinguished partially from the other vegetable oils because it contains, or is likely to contain, more or less of a somewhat poisonous substance, namely, ricinolein, which is peculiar to castor oil and to which its purgative value as a medicine is due. The castor bean also contains a very poisonous nitrogenous base, ricin, very small quantities of which may be incorporated in the oil itself.

Melting Point and Solidifying Point.-The oils and fats differ greatly among themselves in the temperature at which they become solid or liquid. If a solid fat or oil is subjected to a gradual rise of temperature it does not pass at once or suddenly from a solid to a liquid state, but there is a gradual liquefying, thus olein first becomes liquid and the stearin and palmitin become liquid at a higher degree of temperature. The same phenomenon in its inverse order occurs when a liquid fat is cooled until it solidifies. The moment at which the fats become semi-liquid, liquid, or semi-solid, therefore, is not to be determined with absolute precision, but only approximately, and that temperature is designated as the melting or solidifying point respectively. When the process is carefully conducted under standard conditions the different fats and oils have very definite melting or solidifying points, as determined in the manner described above, and these temperatures should be sufficient to make the melting and solidifying points valuable indications. of the character or kind of oil.

Physical Characteristics.-The difference in the physical characteristics of vegetable fats and oils is even greater than in their chemical composition. Unfortunately for the chemist, the vegetable fats and oils naturally have about the same color or at least very slight variations therefrom, namely, an amber tint, so that, as a rule, it is impossible to discriminate between these oils by their mere color alone. The edible oils also have very much the same taste, so that this physical property is not of any very great diagnostic value. Some of the more important physical properties by which the oils are distinguished are the following:

Refractive Index. The well-known phenomenon which is shown by water of bending sharply a ray of light falling upon it in a direction oblique to its surface is known as refraction, and the degree of deflection of the ray is a measure of the refractive index. This is easily illustrated by putting a straight stick or rod into still water at an angle to its surface. The stick or rod will appear to be broken or bent at the surface. Oils have a higher faculty of deflecting the ray of light than water. For instance, if in round numbers the refractive index of water is represented by 1.33, the refractive

SPECIFIC GRAVITY.

393 index of cil may be represented by 1.44. The oils differ greatly among themselves in the magnitude of the refractive index, but these indexes are all approximately of the magnitude last mentioned. Hence a determination of the refractive index is a valuable means of helping to discriminate between oils of different kinds.

Reichert-Meissl Number.-Attention was called above to the fact that in addition to three special forms of fatty acids there were many others present in oils in small quantities. Among these are found acids which are volatile in a current of steam, which is not the case with the oleic, palmitic, and stearic acids. Among the most important of the volatile acids is the one which exists in large quantities in butter, namely butyric acid. The quantity of volatile acid is determined arbitrarily by the amount of a standard alkali solution which will be neutralized by the volatile acid from five grams of fat. In the case of butter, for instance, it may be said that in round numbers it requires 28 cubic centimeters of standard alkali to neutralize the volatile acid produced according to the above method of procedure. In cottonseed oil the amount of standard solution required to neutralize the volatile acid obtained in the same way is extremely minute, amounting to less than one-half cubic centimeter.

I have given above a brief description of some of the physical and chemical characteristics of oils and fats in order that the reader not specially trained in chemistry may understand thoroughly the references made to these properties in the general description given of vegetable fats and oils. It is not necessary to be a skilled chemist in order to have a general knowledge of some of the points which are of most interest in this respect.

Saponification Value. As is well known, one of the most common uses of oils and fats is in soap making. Soap consists of the products of chemical reactions by means of which the glycerine contained in an oil or fat are set free and a mineral or other base substituted therefor. For instance, lye consists of the hydrate or carbonate of potash and soda. When an oil is heated with a lye the fatty acid leaves the glycerine in the oil and combines with the potash or soda of the lye. The number of milligrams of potash or soda required to saponify one gram of fat or oil is called its saponification value. For instance, in the case of cottonseed oil it requires, in round numbers, 190 milligrams of potash or hydrate of potash (KOH) to replace the glycerine in one gram of oil. The quantity of potash required for an edible oil to make a complete saponification varies, and hence this number becomes one of the means of distinguishing between them.

Specific Gravity. The relative weight of a given volume of oil compared with the weight of the same volume of water at the same temperature or at some standard temperature is known as its specific gravity. The oils and fats are universally lighter than water, and in the comparison the unit weight

of water is assumed to be unity or 100 or 1000-usually unity or 1000. If the relative weight of water is unity, then the relative weight or specific gravity of oil is expressed as a decimal fraction. For instance, if water is taken as unity the specific gravity of oil equals .912; if the relative weight of water is assumed to be one thousand then the specific gravity expressed above is 912. Unless it is stated otherwise, in all references to specific gravity of these oils it is assumed that the comparison is between the unit weight of water and oil at the same temperature. This is the most convenient form for comparison for general use, though for strictly scientific purposes it is customary to refer all specific gravity numbers to water at the temperature of its maximum density, namely 4 degrees C. (39 degrees F.). At this temperature a given weight of water has its smallest volume, in other words its greatest density. When water is raised to a temperature above that mentioned, it expands and its volume becomes larger. When it is cooled to a temperature below four degrees C., its volume also expands.

The variations in the specific gravity of the common oils is not very great, and therefore the specific gravity is not the most valuable indication in discriminating between these oils.

EDIBLE VEGETABLE OILS.

While there is very little chemical difference between the fats of animals and the oils of plants, the difference is sufficiently distinguished to secure a proper degree of identification and classification. Both classes of bodies are composed of the fatty acids combined with glycerine. The three fatty acids which are most important from the edible point of view and also from the chemical are oleic, stearic, and palmitic. When these acids are united with glycerine as the basic element, they form three classes of oils or fats to which the names olein, stearin, and palmitin are respectively given. A distinction may also be made between a fat and an oil by observing its physical consistence at ordinary room temperature of approximately from 70 to 80 degrees F. It is usual to speak of the bodies which are liquid at such temperature as oils, while those that are solid under like conditions are known as fats. A compound of this description does not pass suddenly from one state to another. In the case of a fat, for instance, which is solid at ordinary temperature, it passes by gradual stages from that condition to a slowly softening mass and then to a complete liquid as the temperature is raised. On the other hand, an oil passes gradually through the same stages to the condition of a solid body as the temperature is lowered. Of the different constituents the olein has the lowest melting point, pure olein being still liquid at quite a low temperature, approaching even the freezing point of water. Stearin and palmitin on the contrary, if in a pure state, are solid at a temperature even above that of the room and above that of blood heat.

In the mixture of these bodies it is evident that a complicated structure must be present which is composed of different bodies of varying melting points and passing through all different degrees of temperature from a solid to a liquid state or vice versâ. It is evident that an oil has a larger proportion of olein in its composition and a fat a larger proportion of stearin and palmitin. Animal fats are composed chiefly of olein and stearin, while strictly vegetable oils are principally olein, and palm oil is composed chiefly of stearin and palmitin.

In butter fat there is introduced an important additional compound of a fatty acid with glycerine, namely butyrin, which is made up of a union of glycerine with butyric acid. Butter also contains other components or glycerids, but in small quantities. Oleic, stearic, and palmitic acids are insoluble in water and not volatile at the boiling point of water. Butyric acid is soluble in water and is volatile at the boiling point of water. The first kinds of acid are therefore called "fixed" and the second "volatile."

The edible vegetable oils like the animal fats are highly nutritious in the sense that they afford to a greater degree than any other kind of food product the elements necessary to the production of heat and energy. The average number of calories to one gram of edible oil is in round numbers 9,300. When this number is compared with the average number of calories in one gram of sugar or starch, namely 4,000, it is seen that fats and oils are two and onefourth times as valuable as sugar in the production of heat and energy. Since the greater part of the food consumed by an animal is utilized in the production of heat and energy, it is seen that the fats and oils must be classed as the most concentrated and in that sense the most valuable human foods.

The use of edible vegetable oils is also advisable for hygienic purposes. They are readily assimilated and digested, and they produce a physical effect upon the process of digestion which is a matter of importance. The free use of edible vegetable oils is to be recommended in cases of constipation or where there are mechanical difficulties in the digestive process. In these cases it is consumed in larger quantities than would ordinarily be the case. Use of Edible Oils.-The edible oils are used most extensively on the table as the base of salad-dressing. Many succulent vegetables, as has already been stated, are eaten very commonly with condimental substances such as vinegar, salt, spices, etc., and as a vehicle for these condimental substances there is nothing superior or even equal to the edible vegetable oils. Vinegar, itself, owes its active principle, namely, its acid, to a member of the fatty acid series, so that the mixture of vinegar with oil is not a bringing together of two wholly different substances but of two substances belonging to the same general family. Vinegar itself has no value as a food, but is useful solely for condimental purposes. On the other hand the edible oil is not only condimental, increasing the pleasant taste of the compound, but also has a

high food value. Edible oils may also be used in the place of lard and other animal fats in the preparation of bread and pastry, serving the purpose of shortening. Edible oils are also highly useful as a vehicle for frying foods, such as oysters, croquettes, doughnuts, etc.

The heating of an oil or fat to a high temperature produces a certain degree of decomposition with a development of an aromatic and sometimes unpleasant product known as acrolein. It is not believed that this change is as detrimental to digestion as is commonly supposed. Products which are fried in oil, or boiled in oil, which is probably a better term, as described above, are not to be considered wholly indigestible, though it cannot be denied that they are not the best things for delicate stomachs or those which are in any way weakened by disease. In the case of a healthy individual, however, a moderate quantity of such products may be eaten without any great danger of producing a derangement of digestion. If these bodies are found to be indigestible, it is probably not due to the fact that they contain large quantities of oil but rather to the decomposition effected by the high temperature and the hardening of the periphery of the bodies to such an extent as to make them difficultly amenable to the activities of the digestive ferments.

Acorn Oil. The oil of the acorn is sometimes used for edible purposes. It is extracted by pressure, and the nature of the product depends upon the variety of the acorn. Acorn oil has at 15 degrees a specific gravity of .916 and an iodin number of 100. It is not of any commercial importance as an edible oil.

Almond Oil.-Almond oil is not so commonly used for edible purposes as it is for pharmaceutical preparations. By reason of its flavoring properties, however, it may sometimes be used for food purposes, and a brief description, therefore, is advisable.

Almond oil is obtained from the seed of the bitter almond, a variety of Amygdalus communis L. It may also be extracted from the seeds of the sweet almond, but these contain less oil than the bitter almond seed and the oil is not so useful for flavoring purposes. The bitter almond whose seeds are used for the extraction of oil are grown chiefly in Morocco, the Canary Islands, Portugal, Spain, France, Italy, Sicily, Syria, and Persia. The almond kernel contains about 40 percent of oil. Almond oil is said by most observers to be free from stearin, and it is therefore an oil which is composed almost exclusively of olein. The specific gravity of almond oil at 15 degrees C. is almost exactly that of rapeseed oil, being only a trifle higher. The average number expressing the specific gravity at that temperature is .918. Its iodin value is slightly lower than that of rapeseed oil, being about 97.

Adulterations.-Almond oil is often adulterated with other cheaper oils. Among these those which are principally used are cottonseed oil, walnut oil, poppyseed oil, sesamé, peanut, apricot-kernel and peach-kernel oil, and lard oil.