THE SOLUBILITY OF STEARIC ACID IN ETHYL ALCOHOL AT ZERO
Journal of the American Chemical Society
I t will be noted that in but three cases out of the forty-five last stated does the difference between the two methods exceed 0.05, which is certainly as close as one can expect ordinary technical work to be done, and as between two samples is undoubtedly within the limits of accuracy of sampling large lots. A still further test of the method was given by making a gliadin determination upon a gluten flour in which the Kjeldahl method showed 3-32 per cent. of gliadin nitrogen. The polariscopic
... . The polariscopic method showed 3.45 per cent, Considerable difficulty was experienced at the outset in securing a clean solution for filtration, but this was finally overcome by avoiding excessive agitation. Snyder remarks that in the case of flours analyzed by him, and probably grown in the middle west, the combined alcohol soluble carbohydrates and non-gliadin proteins of the alcoholic solution affect the polarization to only a slight extent," and states that after the gliadin protein was precipitated the non-gliadin rotary bodies showed a reading of less than 0 . 2 0 on the sugar scale. I n our experience with the method it was always found necessary to make two polarization determinations, the first of the original solution, and the second after separating the protein bodies by the use of a concentrated solution of mercuric nitrate, and then making the required correction to give the true gliadin reading. This was particularly true in the case of wheat meals where the average difference between the two polariscope readings was 1.05 on the sugar scale corresponding too.21 per cent. on thegliadin scale, the range of differences on the sugar scale being from 0.08 to 2.75. I n the case of flours, unless extreme accuracy is required, the correction could be neglected inasmuch as the error is much less, not exceeding 0.04 per cent. of the gliadin scale. T h e writer is strongly impressed with the idea that the method is vorthy of 3 much more! extended use than it hasso far had, and that if precautions are taken to correct for the effect of other optically active bodies, there are fewer opportunities for error than with the ordinary method of nitrogen determination.