Chemical technology and analysis of oils, fats and waxes / by Dr. J. Lewkowitsch.

  • Julius Lewkowitsch
Date:
1914
Catalogue details

Licence: In copyright

Credit: Chemical technology and analysis of oils, fats and waxes / by Dr. J. Lewkowitsch. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

    224/980 (page 204)
    Hence the Halphen colour reaction can be obtained with lards etc wliicli are absolutely free from admixed cotton seed oil ' ' It should fm-ther be noted that failure to obtain the colour in the Halphen test does not prove the absence of cotton seed oil. For the chromogenetic substance is destroyed by heating cotton seed oil to 250 C, or even by keepmg it at 200° C. for some prolonged time i or by blowing cotton seed oil with afr {Lewhowitsch), or treating ^ith fuming hydrochloric acid/ sulphurous acid,3 and chlorine. Cotton seed oil so treated no longer gives the Halphen colour reaction. Blown th rl''^ '-i ^^.'i- ^'^^ ^^^^ --id oil cannot tJierefore be identified by the Halphen test. Hence a negative Halphen test in a suspected sample is no conclusive proof of the absence of cotton seed oil. Cotton seed oil fatty acids do not show the colour test as distinctly as the oil itself. Frequently the mixed fatty acids obtained by saponifying cotton seed oil give a very laint red colouration only, or even none at all, most of the colourincr matter having either been destroyed or washed away in the process of isolating the mixed acids (Lewkoivitsch). Finally Halphen's test can no longer be considered as exclusively due to cotton seed oil. Kapok oil and baobab oil* give the same colour reaction, and the last-named oil with even gi-eater intensity than cotton seed oil {Milliau). In case a negative Halphen test be obtained on examining a sample, and the presence of heated cotton seed oil be suspected, confirmation may in some cases be obtained by the nitric acid test. This test is best carried out with nitric acid of 1-375 specific gravity, as the author has ascertained by a number of experiments. A few c.c. of the sample are shaken energetically with an equal measure of nitric acid of the specified gravity, and the sample allowed to stand for some time, up to twenty-four hours. Cotton seed oil gives a coffee-brown colouration which is characteristic of this oil to such an extent that admixtiu-es of 10 to 20 per cent of cotton seed oil to olive oil can be detected in certain cases.5 But even here great circumspection is necessary, as the coffee- brown colouration given by some specimens of cotton seed oil is not characteristic of all cotton seed oils. Thus the author has met with many American cotton seed oils that gave the nitric acid test so faintly that oHve oils mixed with 10 per cent of this cotton seed oil showed no coffee-brown colouration. Important is the observation made by the author, viz. that a specimen of heated cotton seed oil which no longer gives the Halj^hen test still gives the brown colouration with nitric acid, and that also the fatty acids from this specimen of heated cotton seed 1 Oilar {Amer. Chem. Journ. 24, 355) states that heating for one hour to 140°-150° C. in a steel pan suffices to nullify the Halphen colour test. - Kuhn and Bengen, Zeils. f. Unlers. d. Nahrgs- u. Oenussm., 1906 (xii.), 149. •' Fischer and Peyau, ibid., 1905 (ix.), 81. ■* Compt. rend., 1904 (139), 807. ° Soltsien {Ohem. Revue, 1908, 29) raises a]i objection against this test on the ground that olive and hazelnut oils heated to 250 C. also give a brown colouration. This objection is quite unintelligible, for no nuuiufacturer would heat edible olive and hazelnut oils in order to substitute them for cotton seed oil.