505. Errors Due to Poor Glass.—The easy solubility of the glass holding the reagents is the cause of some of the difficulties attending the determination of the saponification value. The separated silica tends to carry down, mechanically, a part of the alkali. This is shown by the fact that after the color has been discharged by titration with acid and the flask set aside a reappearance of the red color is noticed, after a time, beginning at the bottom of the flask.[506] In order to avoid difficulties of this nature, either cold saponification should be practiced or the digestion vessels used for moist combustion in sulfuric acid be employed.
Errors may also be easily introduced by the use of uncalibrated burettes and from the employment of varying quantities of the phenolphthalein solution.
506. Estimation of the Molecular Weight of Butter and Butter Substitutes.—Garelli and Carono have proposed a method for discriminating between butter and its substitutes by the kryoskopic determination of molecular weights.
The molecular weights of stearin, palmitin and olein are 890, 806 and 884, and of butyrin, caproin and caprylin 303, 386 and 470 respectively. Pure butter, therefore, has a lower mean molecular weight than margarin.
The method and apparatus of Beckmann are used in the determination, fifteen grams of benzol being employed as a solvent.
The constant for the molecular depression of the benzol is found to be 53.
The molecular weight obtained with samples of pure butter varied from 696 to 716, and for oleomargarin from 780 to 883.
The figures obtained with mixtures of twenty, twenty-five, thirty-three and fifty per cent of margarin with butter were 761, 720, 728 and 749 respectively. The method can be relied upon to classify samples as follows:
- 1. Pure butter.
- 2. Butter containing margarin.
- 3. Suspicious butter.[507]
507. Substitutes and Adulterants of Butter.—In this country, butter is never adulterated with cocoa or sesame oil, as is sometimes the case in other lands. The common substitute for butter here is oleomargarin, and the most common butter adulterant, neutral lard. The methods of analyses, by means of which these bodies can be identified, have already been sufficiently described. By the use of certain digestive ferments and other bodies, butter may be made to hold an excessive quantity of casein, sugar and water in the form of a somewhat permanent emulsion.[508] This form of adulteration is revealed at once on melting the sample.