NOVEMBER 15, 1935
ANALYTICAL EDITION
manganese phosphates, it may be more convenient to ignite the precipitate to the pyrophosphates, weigh, and then fuse the pyrophosphate with sodium carbonate and proceed with the bismuthate method for mangansse.
385
gether, after which the manganese present is determined by means of the bismuthate method, and the amount of magnesium is obtained by difference. In a number of tests this procedure has given satisfactory results.
Summary
The precipitation of manganese by oxidation with bromine or persulfate in the regular course of analysis of rocks and soils has not been satisfactory because of incompleteness of precipitation of the manganese, and a t times contamination of the manganese precipitate with magnesium and the magnesium precipitate with manganese. To overcome these difficulties, it is suggested that the manganese be precipitated with the magnesium as the phosphate. The phosphates of manganese and magnesium are then weighed or titrated to-
Literature Cited (1) ASSOC.Official Agr. Chem., Official and Tentative Methods of Analysis, 2nd ed., p. 30 (1930). (2) Chapman, H . D., Soil Sci., 26, 479 (1928). (3) Handy, J. O., J . Am. Chem. SOC., 22, 31 (1900). (4) Hillebrand, W. F., and Lundell, G. E. F., “Applied Inorganic Analysis,” p. 743, New York, John Wiley & Sons, 1929. ( 5 ) Park, B., IiYD. EKQ.CHEM., 18,597 (1926).
RECEIVED July 22, 1935. Published with the permission of the director of t h e Wisconsin Agricultural Experiment Station.
Refractometric Estimation of the Total Solids Content of Whole Eggs and of Yolks M. IRENE BAILEY, Columbia University, New York, N. Y.
A
CORRELATION between the total solids contents and the indices of refraction of whole egg and of yolk magma obtained from hens’ eggs shows that an estimation of the per cent total solids may be made by the use of a refractometer. A study made a t the California Agricultural Experiment Station (1,s) has shown that the total solids content of egg white may be estimated refractometrically. In the study herein reported, the eggs were taken from carload deliveries received a t an egg-freezing plant in Jersey City, from various parts of the United States during the eggproducing season of the year 1931. KO storage eggs were used. Yolks were separated from whites in commercial fashion by girls accustomed to the work of a commercial egg-breaking plant supplying bakers and confectioners with whole egg, yolks, or whites according to demand. This plant prepared commercially two types of yolks, one known as “commercial yolk” and the other as “dry yolk.” In the preparation of the latter, extra care was exercised to remove as much of the egg white as was practically feasible. Consequently, all the yolk samples studied contained some adhering whites. This paper, therefore, does not attempt to record the total solids in the egg yolk entirely free from egg white but nevertheless presents a method by which such determinations may be made if desired. A method for completely separating the egg white from the yolk is given by Pennington (4). The whole egg magmas were prepared in the laboratory. Two grades were studied, U. S. Extras and U. S. Standards, the selection according to grade having been made by expert egg candlers. Samples were prepared for analysis in the following manner:
of refraction was read in an Abbe type refractometer around the prisms of which water a t 25 * 0.01” C. was circulating. A drop or two of the remixed egg magma was pipetted onto the prism of the instrument. (Owing to danger of “creaming” of the fatty matter, the magma was always carefully mixed in the sample bottle immediately prior to placing it in the refractometer.) The prism was then closed and the index of refraction was read exactly one minute later. This procedure was adopted for two reasons, in order to allow time for temperature equilibrium and because the reading changes with time. Egg white gives a sharp and easily read line of demarcation between the illuminated and dark segments of the field. I n the case of yolk magma, the line of demarcation is less distinct, while whole egg magma in general gives a poorer boundary line than yolk magma. The distinctness varies with different specimens. However, with a little practice operators can readily learn to check each other to about 3 units in the fourth decimal place of refractive index in the case of whole egg magma and better in the case of yolk magma. A dipping or immersion refractometer was tried on yolk and whole egg magma. Owing to its greater sensitivity, the line of demarcation was too blurred and consequently this type of refractometer was found inapplicable for the purpose of this study.
Six (or three) eggs at about 5’ C. were removed from the shells and then disrupted to a uniform magma by the operation of a typical malted milk mixer. (In the early part of the work a composite sample was made from six eggs, or yolks, but later the sample was reduced t o three.) The yolks as received from the plant were disrupted and mixed in the same manner, in all cases, six yolks constituting one sample.
The number of specimens of fresh eggs examined is given in Table I according to the months of the year they were received and analyzed. When the total solids contents were plotted against the indices of refraction, the distribution of points indicated a straight-line relationship. On the assumption of this indication, the several sets of data were subjected to mathematical analysis by the method of least squares which produced the following equations, where R equals index of refraction and S equals per cent total solids:
The magma was then submitted to analysis. The determination of total solids was carried out according t o the Association of Official Agricultural Chemists method ( 2 ) . The index
TABLEI. NUMBERS OF SPECIMENS STUDIED Whole egg, U. P. Extras Whole egg, U. S. Standards Commercial yolks D r y yolks
(Spring 1931) March April 38 14 38 13 19 20 9 17
May 10 9 16 17
June 15 9 9 9
Total 77 69 64
52
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VOL. 7, NO. 6
INDUSTRIAL AND ENGINEERING CHEMISTRY
Whole eggs, U. S. Extras Whole eggs, U. S. Standards Commercial yolks Dry yolks All yolks (combination of data on '(dry" and %ommercial" yolks) "
S = 497.0R - 658.29 S = 439.9R - 579.49 S = 503.1R - 663.15 S = 542.4R - 718.19 S
=
565.4R
- 750.76
After having derived these equations, the total solids content for each specimen included in the data was calculated by substitution of the observed values for R. The differences, d, between the observed and calculated values for the per cent total solids were then used to calculate the standard deviation, 8. D., by means of the formula X.D. = d y w h e r e n equals the number of cases, with the following results:
Whole eggs, U. S. Extras Whole eggs, U. S. Standards Commercial yolks Dry yolks All yolks
S. D. = '0.30 = *0.31 S. D. = *0.59 S. D. = '0.45 S. D. = *0.55
S.D.
The standard deviations for the yolks are seen to be higher than those for the whole eggs, despite the more distinct line between light and shadow in the refractometer observed in the case of the yolks. Thus the relationship between refractive index and total solids is more variable with yolks of commerce than with whole eggs. This is to be expected in view of the fact that the yolks measured contained variable amounts of whites. Since a large fraction of the total solids of whole eggs and an even larger one in case of yolks is fatty matter emulsified in the continuous aqueous phase, it is remarkable that the refractometric method works a t all. Since it does, there is evidently a relationship between the total fatty matter and the water-soluble matter, as is the case in cows' milk where a high fat content is accompanied by a high protein content and vice versa. An examination of the data obtained in this study revealed an indication of a seasonal variation in the case of yolks and to a less extent in the case of whole eggs. The determined
values for total solids of late June eggs were lower than those calculated by means of the equation, and to a smaller extent early March eggs showed calculated total solids lower than those actually determined. However, the number of specimens analyzed was insufficient to give more than a general trend. Further study is necessary to determine the extent of this seasonal variation. For the benefit of those who may wish to apply the data a t temperatures other than 25" C., temperature coefficients were determined by measurements upon 7 specimens of whole egg and 7 specimens of dry yolk. These showed that there is a straight-line variation between the temperatures of 20" C. (68" F.) and 30" C. (86" F.) The method cannot be applied outside of this temperature range. In the case of the refractive index of whole egg, 0.0001 should be added (or subtracted) for each degree Centigrade above (or below) 25" C. (77" F.) in order to reduce the reading to the 25" C. (77" F.) basis. The corresponding correction for dry yolk refractive index is 0.0002. While the number of cases studied is small, the application of the equations derived from them to 1932 spring eggs and yolks gave such satisfactory results that it was decided to publish the results herein given as a rapid method for the estimation of the total solids content.
Acknowledgments The author is indebted to M. E. Pennington for the suggestion of this study, to A. W. Thomas, in whose laboratory the work was done, and to the Borden Company for its material codperation.
Literature Cited (1) Almquist, H. J., Lorenz, E'. W., and Burmeater, B. R., IND. ENQ.CHEM., Anal. Ed., 4, 305 (1932). (2) Assoc. Official Agr. Chem., Official and Tentative Methods, 3rd ed., p. 244 (1930). (3) Holst, W. F., and Almquist, H. J., Hilgardia, 6, 45 (1931). (4) Pennington, M. E., J. Biol. Chem., 7, 109 (1910). RECEIVED August 13, 1935.
A Short Method for Calculating Delta D in a Crystal Growth Process J
RIOSES GORDON,' University of North Dakota, Grand Forks, N. D.
I
N ORDER to predict the screen analysis of the product
from the analysis of seed it is necessary to calculate AD, the increase in size of opening (mesh) through which a crystal will pass after the growing process is completed. McCabe (9, S) does this by integrating the following equation graphically : where W , and D,give the screen analysis of the seed W , = weight of crystal product
(
Values are assumed for AD, a curve of 1
>:,
+-
against
W , is plotted for each value of AD, and the area under each curve measured. The A D giving the proper value for W, is then used in calculating the final screen analysis. The purpose of this paper is to eliminate the cut-and-try 1
Present address, University of Minnesota, Minneapolis, Mian.
graphical integration by substituting for it a rapid method of finding A D . The method will be illustrated by applying it to the example on the crystallization of potassium chloride worked out by McCabe ( I ) . The screen analysis of the seed (D. and WE) is given. Calculations made from solubility data show that 155 pounds of product will be obtained per 100 pounds of seed. From these data A D may be calculated as follows: To integrate Equation 1 it is necessary to obtain an expression for D, in terms of WE. This is done by plotting D, against W, and drawing the best straight line through the points. (The straight line is an approximation, since the cumulative screen analysis plot will curve a t either end, but the approximation is sufficiently accurate for practical purposes.) This will give
D, = b
+ mW,
(2)
where b is the intercept on the D, axis and m is the slope.
