A knowledge of the mechanism of the degradation of triglycerides at temperatures from 190ŶC. is important in predicting the type of breakdown products likely to be formed in processing oils at elevated temperatures, or in the usage of oils and fats in frying or baking. The effect of heat on tricaprin and 2‐oleo‐dipalmitin has been studied both in the absence and in the presence of oxygen. The results show that even a pure fully saturated triglyceride is rendered organoleptically unacceptable, due to breakdown in the temperature range studied, although the mechanism differs according to whether oxygen is present or not. Unsaturated glycerides are more readily degraded, fission at or near the double bonds being superimposed on the processes previously established for saturated triglycerides. Many of the degradation products have been identified. Degraded triglycerides can be refined to an acceptable standard by conventional means but their keeping times, in the refined state, are considerably less than those of the original pure materials. Hence, it is inferred that precursors of off‐flavors persist in the products and survive the refining operations.

Early studies of human depot fat were limited by available analytical techniques and investigations into the fatty acid composition of the depot fat did not begin until about 1925. Eckstein (1925) reported 1% of myristic acid and traces of lauric acid, 26% of saturated and 63.6% of unsaturated acid, and 0 5, 0 03 and 0.33% of acids with two, three and four double bonds respectively. The dienes and tetraenes, but not the trienes, were confirmed by Wagner (1926), and 60% of unsaturated acids and 25 8-31 % of saturated acids were found by Telfer (1928) and McAmis & Anderson (1930). Cramer & Brown (1943) published the results of analyses made by fractional distillation of the methyl esters of fatty acids from depot fat, together with their new technique of low-temperature crystallization. These authors were the first to report the presence of mono-unsaturated C14 and

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A4-tetrahydrobenzene, CMe2CH. The ketonic nature 0 f this substance is shown because it readily yields a semicarbazone ; and its constitution is proved by the facts t h a t (i) on hydrolysis with potassium hydroxide it is reconverted into dimethyldihydroresorcin ; and (ii) on oxidation i$ gives a small quantity of as-dimethylsuccinic acid, hut principally PP-dimethylglutaric acid and the lactone of a-hydroxy-P/3-dimethylglutaric acid. These are the same oxidation products a s mere obtained from 5-bromo-1 : 1-dimethyl-A3-tetr:thydrobenzene, CMe,CH (Trans., 1902, 81, 824, 834), and afford additional proof of the correctness of the formula assigned to this substance. The chloroketone and the tetrahydrobenzene derivative should therefore have very similar constitutions, and t h e oxidation would seem to take place on the same lines. A part of the chloroketodimethyltetrnhydrobenzene, for example, is oxidised, yielding PP-dimethylglutaric acid, CH-CH 2 as the solution becomes alkaline, it is probable t h a t the elements of hydrogen chloride are removed from a fresh portion of the chloroket,one, partial oxidation taking place a t the double bond so formed, giving rise to a n intermediate oxidation product. From this the lactone of a-hydroxy-PP-dimet hylglutaric acid would readily be obtained which, on further oxidation, would give as-dimethylsuccinic acid (ibid., page 835), Chloroketodimethyltetrahydrobenzene appears to be very susceptible to t h e action of moisture, for on standing, especially if exposed t o air, it slowly deposits crystals of the hydrochloride of dimethyldihydroresorcin. This is evidently a case of hydrolysis, the chloride CMeh2