Page:Foods and their adulteration; origin, manufacture, and composition of food products; description of common adulterations, food standards, and national food laws and regulations (IA foodstheiradulte02wile).pdf/109

 to produce ebullition in the mass, causing it to foam up and fill the tube. To avoid this, smaller quantities of acid should be used or the oil in question be diluted with a less thermogenic one, so that the maximum temperature may not be high enough to produce the effect cited.

Chemical Properties.—Volatile Acids.—The quantity of volatile acid arising on the decomposition of a soap made by the saponification of lard is very minute in lard of high quality. The total amount of volatile acid should not be in excess of that necessary to saturate .2 cubic centimeter of deci-normal alkali solution.

Fixed Acid.—The quantity of fixed acid, consisting principally of oleic and stearic, in pure lard should not be less than 93 percent. The total quantity of free acid in lard, that is, acid uncombined with the glycerine, should not exceed one-half of one percent, and in neutral lard should be much less than this.

Quantity of Iodin Absorbed.—All common fats and oils have the property of absorbing, under given conditions, certain quantities of iodin. Lard of the highest quality should not absorb more than 60 percent of its weight of iodin. The lard made from the feet and certain other parts of the animal, however, may have a larger iodin number, rising as high as 75 or even 80.

Properties of Lard.—The average properties of different classes of lard in relation to physical and optical conditions are shown in the following table:

.9053            40.7        1.4620           41.5            .077      62.48

The above table is the average composition of nineteen samples of lard furnished under affidavits of purity and which appear from their chemical and physical properties to be composed purely of the fat of swine taken from those parts of the animal usually devoted to lard making. The average data may be regarded as representing the properties of the ordinary pure commercial lard on the market.

—Below is given the average composition of eleven samples of steam lard furnished under affidavit and, apparently, as judged by their chemical and physical properties, composed solely of the fat of swine. Steam lards are not of as high a quality as the lards contained in the preceding table. They have usually a distinctively strong odor, quite different from that of lards which are rendered in open kettles at low temperature and from selected portions of fat.

.9055            37.0        1.4623           39.9            .109      62.86