Volume 1
Chemical technology and analysis of oils, fats, and waxes / by J. Lewkowitsch.
- Julius Lewkowitsch
- Date:
- 1904
Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)
Credit: Chemical technology and analysis of oils, fats, and waxes / by J. Lewkowitsch. Source: Wellcome Collection.
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![i SIMPLE AND MIXED TRIGLYCERIDES the sodium (or silver) salts of the fatty acids with tribromhydiin {Guth ; Partheil and v. Velsen1). The property of exhibiting a so-called double melting point has been looked upon as characteristic of the triglycerides (as also of the natural fats which constitute mixtures thereof). A numbei o observers have stated that the triglycerides melt at a certain degree of temperature, then solidify at a higher degree, to melt again on further heating. This curious behaviour was hitherto explained by assuming the existence of two modifications {Duffy; Heintz). The matter has, however, been recently elucidated by Guth in the case of tristearin, for which the two melting points, 55 C. and 71 0., have been observed. Guth ascertained that well-crystallised tristearin has only one melting point, viz. 71 '5°, and shows the same point even after it has been melted, provided it be kept in the capillary tube for some time after melting. But, if the tristearin was tested shortly after having been melted in the capillary, or if it had been intro- duced in a liquid state into the capillary and then cooled too rapidly, it showed two melting points. He further ascertained that at the lower temperature the substance would only melt completely when the capillary tube was very narrow, and the quantity of the substance very small; on examining a somewhat larger quantity of tristearin in a comparatively wide capillary tube, complete melting did not occur at the lower temperature, the mass only becoming soft and translucent; it then solidified again and finally melted at 71 '5° Q. to a clear liquid. The different behaviour of the crystalline tristearin on the one hand, and of the once fused tristearin on the other, may be explained, as Guth suggests, by the melted (at 55° C.) and rapidly solidified substance not yet having passed into the crystalline state, and behaving somewhat similarly as would super-cooled water (which has remained liquid below 0° C.) or a super-saturated solution of sodium sulphate. If the substance be then shaken or disturbed by increasing the temperature, it solidifies again to its original state; the latent heat thus set free is sufficient to melt the whole mass, if the quantity be small. If, however, the quantity of the substance be large, the temperature does not suffice to effect the complete melting, since the surrounding water still absorbs the liberated heat. Crystallised tripalmitin, as also stearodipalmitin and palmitodistearin have, as Guth has shown, one melting point only, but under similar conditions as stated above for tristearin, they exhibited two melting points.2 In further confirmation it may be mentioned that well-crystallised brassidin showed one melting point only, even after it had been heated to about 40° C. above its melting point. The assumption of the existence of two modifications must therefore be rejected, and it may be accepted as proven that the triglycerides do not possess two melting points, but that the phenomenon of the so-called double melting point is due to a state 1 Arcliiv. d. Pliarmacie, 1900 [238], 267. 2 Kreis and Hafner confirm Gulh’s observations ; B&richte, 1903, 1125.](https://iiif.wellcomecollection.org/image/b28120620_0001_0029.jp2/full/800%2C/0/default.jpg)
