ANALYTICAL EDITION
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air-carbon monoxide analysis did not vary significantly from those which were made when the acid was fresh. We conelude, therefore, that no appreciable error was introduced by the returning of carbon monoxide from the scrubbing train to mixtures t o be analyzed. Similarly, in the case of ethylene-monoxide mixtures there
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was no tendency for the blank determinations to increase as the number of analyses increased. The acid in the scrubbers was changed between the air analyses and the ethylene analyses, and the same acid was used throughout the series of ethylene analyses. The experimental results are given in Tables I and 11.
Use of the Refractometric Method in Determination of Oil in Avocados' B. E. Lesley a n d A. W. Christie FRUITPRODUCTS LABORATORY, UNIVERSITYO F
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HE oil content of avocados is a valuable index of maturity and market value in determining the proper time of picking and shipping. Furthermore, the California Fruit and Vegetable Standardization Act (Chap. 350, see. 11) states that "Avocados shall not be considered mature when the edible portion shows an oil content of less than eight per cent by weight by chemical analysis." The California Avocado Growers Exchange found it necessary to have frequent oil analyses made by the ether extraction method, which was so expensive and time consuming that they appealed to the University of California to develop a rapid and inexpensive method suitable for their purpose. The method developed by us and described in this paper is not only suitable for the determination of oil in avocados but also, if a suitable factor is used for its determination, in other materials high in moisture content. Wesson2has described a method for determining oil in oil mill materials based on the extraction of the oil from the material by means of a measured amount of a suitable solvent having a refractive index sufficiently different from that of the extracted oil to produce relatively large changes in the refractive index with small amounts of oil dissolved in the
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5 milliliters of Halowax oil into the mortar. Grind carefully for about 5 minutes. The oil quickly separates from the mass, so that a drop can be conveniently picked up on a stirring rod. Separate a drop of the oil mixture, and determine the refractive index, observing the temperature also. Grind for about 1 minute more, and repeat the refractive index determination. Continue grinding and reading until a constant value is obtained. Correct the reading to 25" C. by adding 0.0004 for every degree above 25" C., or subtracting 0.0004 for every degree below 25" C. Application of Method
This method was applied to several samples of avocado paste on which the oil had already been determined by the official ether extract method. A graph was prepared by plotting the percentage of oil by ether extract and refractive indices of mixtures at 25" C. The result was practically a straight line. This graph is presented in Figure 1. By drawing this graph to a larger scale than here presented and extrapolating it was observed that the theoretical refractive index which would be obtained from a sample of avocado containing 0 per cent oil would be 1.63215, whereas the refractive index of the Halowax oil used was 1.63535. This difference of 0.00320 is probably due to the presence of some substance other than oil, which will dissolve in Halowax oil, lowering the refractive index. It is believed that this figure is correct for all samples within the limits of error of the method, which is not greater than 1.0.3 per cent. Unfortunately, all shipments of Halowax oil do not have the same refractive index. Variations in refractjive index as high as +0.002 have been noted by the authors. For this reason the use of the graph in converting refractive indices to percentage of oil may be inconvenient or cause error. The following formula was considered more correct and convenient : (a - 0.0032) - b = c d where a = refractive index of Halowax oil a t 25" C. b = refractive index of mixture oil a t 25' C. c = per cent oil in sample d = change in refractive index per per cent of oil in sample
From the slope of the line (Figure 1) it is seen that cl 0.001555 per cent oil.
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Practically all Czechoslovakian producers of potato starch are included in an organization which has recently been formed in that country. The uncertain outlook for the industry in general, together with a poor crop of potatoes in Slovakia and good crops in neighboring countries, hastened the formation of the cartel.
