PART VII.
VEGETABLE OILS AND FATS, AND NUTS.
VEGETABLE OILS AND FATS.
The production of a substance known as fat or oil, composed of oxygen, hydrogen, and carbon in the form of a fatty acid and combined with glycerine, is a function of almost every plant. The fat acids are usually in combination with glycerine, which plays the part of a base and in so far as its proportion by weight is concerned is much less important than the fatty acid itself. In round numbers it may be said that nine-tenths of all glycerids or fats are composed of a fatty acid and one-tenth of glycerine. When at ordinary temperature this combination is in a liquid form it is called an oil, and when at ordinary temperature it is in a solid or semi-solid condition it is known as a fat. The term "ordinary temperature" means in this connection that of an ordinary living room and not the extremes of outside temperature. In general terms it may be said that the temperatures referred to are included between the minimum of 50 degrees and the maximum of 85 degrees F. In so far as chemical composition and dietetic properties are concerned, there is no distinction between the oils and the fats. The names are simply a means of ordinary discrimination which has assumed importance by reason of common usage.
There are three of the fatty acids which are particularly important from a dietetic point of view which go to make up the greater part of these fatty and edible vegetable oils and fats. These three acids are oleic, stearic, and palmitic. Of the three, oleic acid is by far the most important, as it constitutes the greater part of nearly all these bodies, especially of oils. In fact the term "olein" and oil are of common origin. Palmitic acid exists chiefly in certain forms of vegetable oil and fats, while stearic acid is a very important constituent of animal oils and fats.
These three acids uniting with glycerine form the glycerids which make up the great body of edible and animal oils and fats, and these principal glycerids are known as olein, palmitin, and stearin, respectively.
Chemical Characteristics.—The chemical composition of these bodies has been pointed out above. There is, however, in almost all cases, some
