I N D V S T R I A L A N D ENGINEERING CHEMISTRY
January, 1925
The results in Table I1 show that the free insoluble acids of the decomposed butter fat contain oleic acid in almost exactly the same proportions as in the neutral fat, thus confirming the experiments made by the authorl9in 1899 and the findings of ThiimZ0upon rancid vegetable oils and of Spaethzlupon rancid lards. It seems reasonable from this to suppose that the insoluble acids of butter fat are liberated during spontaneous decomposition ifi approximately the same proportions in which they occur in the neutral fat, the oxidation of the oleic and other acids proceeding a t the same rate in both the free and combined condition. While the double bonds of the unsaturated fats are the first points of attack during decomposition, the liberated atoms of active oxygen cause a general disruption of both the saturated and unsaturated glycerides. Changes in Acids Formed
VOLATILE ACIDS-with regard to the changes in the character of the volatile acids, which, as shown in Table I, are formed in increasing amounts during the spontaneous decomposition of butter fat, the mean molecular weights were determined upon the free and combined volatile acids of a butter fat, both when fresh and after 17 years' exposure to the air and light, with the results shown in Table 111. TABLE 111-EFFECT
AGEUPON THE MEANMOLECULAR WEIGHTOF THE VOLATILE ACIDSO F BUTTERFAT FRACTION Mean molecular weight 98.00 Total volatile acids of fresh butter fat 99.50 Total volatile acids of butter fat after 17 years 105.40 Free volatile acids of butter fat after 17 years 91.70 Combined volatile acids of butter fat after 17 years OF
The results in Table 111show that the increase in the volatile acids of the decomposed butter fat is due to the formation of a mixture of acids of somewhat higher mean molecular weight than those occurring in fresh butter fat. INSOLUBLE AcIDs-lVith regard to the changes in the character of the insoluble acids of decomposed butter fats, the following results in Table IV are given for two butter fats which had been exposed to the air and light for 17 years. TABLEIV-EFFECT
AGE U P O N CONSTANTS OF INSOLUBLE ACIDS OF BUTTERFATAFTER 17 YEARS Fresh Sample I Sample I1 17 years CONSTAXT OF INSOLUBLE FATTY ACIDS butter fat 17 years 209.4 A Acid number 214.5 211.3 219.6 218.0 B Saponificatlon number 214 5 C Ester number (23-A) 0 0 8.3 8.6 37.0 35.7 D Acetyl number 4.0 E Mean molecular weight, calculated 257.3 261.0 255.5 from B F Fatty acid anhydrides, calculated from C as stearolactone, per cent 0.0 4.2 4.3 G Hydroxyacids, calculated from D as 2.2 20.4 19.6 monohydroxystearic acid, per cent H Hydroxyacids, calculated from D as di10.3 hydroxystearic acid, per cent 1.2 10.7 OF
The distinguishing characteristics of the insoluble acids of the two old samples of butter fat in Table IV, as compared with those of fresh butter fat, are the presence of pronounced ester numbers due to the formation Qf fatty acid anhydrides (calculated conventionally as stearolactone), and the marked increase in the acetyl numbers due to the formation of hydroxy acids (calculated conventionally both as mono- and dihydroxystearic acids). The table shows that the lowering in the mean molecular weight, which would be occasioned by the decomposition of a part of the insoluble acids into products of lower molecular weight, has been largely counterbalanced by the formation of hydroxy acids of higher molecular weight. Conclusion and Suggestion for Further Work
The spontaneous decomposition of fats, as previously indicated, does not proceed uniformly but is periodic in character, the monthly changes in weight rising and falling in a J . A m . Chem. Soc , 21, 982 (1899). Z. angew. Chem., 3,482 (1890). 2 1 2. a n d . Chem., 36,471 (1896). 19
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sinusoidal curve according to the relative humidity of the air. The decomposition of the fat into free fatty acids no doubt proceeds most rapidly a t the season of highest humidity when the percentage of moisture absorbed by the fat is the greatest. Unfortunately, the quantities of material used in this investigation were not sufficient to permit frequent determinations of the free acids and other constants of the fats with t h e periodic fluctuations in weight. If the theory of spontaneous deterioration of fats proposed in this paper is correct, then a saturated glyceride, such as stearin or palmitin, should show a much higher stability in the pure condition than when exposed to the air in contact with an unsaturated glyceride, such as olein. A periodic study of the action of air and light upon saturated and unsaturated glycerides of known composition, both singly and in mixture, would seem a t least to offer the best means of determining the exact nature of the chemical changes which take place during the spontaneous decomposition of oils and fats.
The Rhe as the Absolute Unit of Fluidity' By Eugene C. Bingham LAFAYETTE COLLEGE, EASTON, PA.
T H E disadvantages of relative units such as the Saybolt seconds and Engler degrees are obvious, although they; are being overcome to some extent by the conversion formulas. Specific viscosities, while convenient for dilute solutions, are nevertheless awkward to compare, particularly when water is taken as a standard a t various temperatures, such as 0') 20°, 25" C., etc. To get around this difficulty the author suggested the use of the centipoise, as all viscosities would then be in absolute units and a t the same time specific, since the viscosity of water a t 20" C. is almost exactly unity. The absolute unit of fluidity has no name, and since fluidities are additive rather than viscosities, the awkward term "reciprocal poises" is coming into use. In order to avoid this, the author suggests the term "rhe" from the Greek rheo, ($ow) to be pronounced ree, as in rheostat and the various human ailments which terminate in "rhoea." The term "isorrheic" for mixtures having equal fluidity has already been suggested by the author and S. B. Stone.2 In considerably over a thousand investigations on fluidity, only a few dozen have obtained fluidities by absolute measurement of the dimensions of the apparatus. In most cases the instrument was calibrated by use of some standard substance, usually water. But there has been no agreement as to the viscosity of water or as to the temperature at which the viscosity should be taken. It seems logical to take for comparison water at 20" C. But even if this were done, we would find that the data on the viscosity of water given in the literalure is of a sort which does not recognize all the corrections which are now familiar; "hencethere is an uncertainty of 0.3 per cent even in the viscosity of water at 20" C. This is an extraordinarily large error and doubtless an apparatus can be devised to give a closer value than this. It seems desirable that a commission be chosen to measure the viscosity of water with precision in order to establish the viscosity of water a t 20" C. This value should then be taken as standard for calibration purposes, just as we take as our unit of weight, not the weight of 1 cc. of water a t 40" C., but 0.001 of the standard kilogram. 1 Presented before the Division of Physical and Inorganic Chemistry a t the 68th Meeting of the American Chemical Society, Ithaca, N. Y . , September 8 t o 13, 1924. * J . Phys. Chem , 27, 736 (1923).
