January 15, 1935
ANALYTICAL EDITION
isolated and weighed, but it is assumed that the composition of each product is constant, at least to the degree of reproducibility obtained. Small constant errors in the composition of a product would not affect the comparative amount in different samples. The hope of increased precision rested on two refinements of manipulation-the close control of temperature during the ashing of the milk and during the ignition of precipitates, and the use of a balance with high precision and large capacity. A No. 10 Troemner balance was used. The sensitivity was increased by means of an auxiliary scale and telescope, so that weights could be read to 2 micrograms The reliability of these weighings was a t least within 10 micrograms. The temperature of the muffle furnace was recorded and controlled within about 2" C. by a Leeds & Northrup selfoperating potentiometer and a calibrated iron-constantan thermocouple. The beakers used during the formation and digestion of precipitates were of Pyrex glass. Platinum dishes were used for all. ashing and ignition processes. Before weighing an empty platinum dish, it was slowly warmed in 6 N hydrochloric acid to a temperature slightly below boiling. The dish was then rinsed with water and ignited to constant weight at the same temperature as that a t which the next ash was to be ignited. DETERMIXATIONS Into a weighed platinum dish about 50 grams of well-mixed evaporated milk were pipetted. The dish with contents was then weighed to 0.1 mg. and heated in an electric oven at 120" C. until the contents were dry and partly charred. The dish was then placed in a cool electric muffle furnace and heated to 550" C. in the courde of 1.5 to 2.5 hours. Heating at this tem erature was continued until constant weight was obtained, usuaiy from 14 to 20 hours. The dish with ash was then weighed to 2 micrograms. It WBS demonstrated that at temperatures of 490" C. or lower the ash would not become white in 72 hours. At temperatures above 560" C. the ash continued to lose weight for 72 hours. It was not possible to secure satisfactory checks at either too high or too low temperatures. The isolation of calcium involved precipitation as a mixture of oxalate and phosphate, ashing at 570" C.,conversion to a mixture of carbonate and phosphate, drying a t 150" C.,and weighing. This weighed mixture was dissolved in hydrochloric acid, and calcium phosphate precipitated from the solution and heated to constant weight at 535" C. The following calculations could then be made: weight of calcium Carbonate, weight of calcium in carbonate, weight of calcium in phosphate, total weight of calcium, and weight of phosphorus in calcium phosphate. Magnesium was removed as phosphate from the solution of ash from which calcium had been isolated, heated to constant weight at 585" C.,and weighed as magnesium pyrophosphate. The weight of magnesium and the weight of a second fraction of phosphorus were calculated from this weight. The remaining phosphorus was isolated with magnesia mixture, ignited at 585" C., and weighed as magnesium pyrophosphate. The results are shown in Table I. The three brands of milk used are designated as A, B, and C, the different tins of each brand being shown by the subscripts. DISCUSSION OF RESULTS The question whether or not there may be a serious loss of moisture in weighing the sample is answered by comparing the deviations in the per cent and ratio columns. For each of the three elements determined, the average relative deviation (f) as per cent of sample, and as ratio to ash, is between 5 and 6 in the fifth place. Since the deviation of ratios is not much less than the deviation of per cent we conclude that the weighing of samples involves no serious loss of water. This opens the way for the development of a correspondingly precise method for the determination of citrates. The deviation (e) of per cent corresponds to the addition of less than 2 parts of the element per million parts of the -evaporated milk. Analysis with corresponding precision of
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all the constituents affecting heat stability should settle the question whether or not the amounts of various minerals are an adequate criterion of heat stability. If citrates are the only additional important constituent, the task does not look impossible. A comparison of the amounts of the different significant salts will be much more valuable when data on citrates are available. In the meantime it may be observed that the relation of calcium to magnesium, the relation of the sum of these to phosphorus or to ash, and the relation of phosphorus to ash, all vary by about 10 per cent. There seems to be no systematic order in these variations.
CONCLUSION If a sensitive balance of large capacity is used, and if the temperatures for ashing the milk and for igniting the precipitates are properly chosen and closely maintained, it is possible to determine the calcium, magnesium, and phosphorus content of evaporated milk with a variation of less than 2 parts per million. Addition of one or more of these minerals in amounts up to about 10 parts per million frequently improves the quality of the product. LITERATURE CITED (1) Assoc. Official Agr. Chem., Official and Tentative Methods, 3rd ed., pp. 268-9 (1930). (2) Rogers, L. A., Deysher, E. F., and Evans, F. R., J. Dairy Sci., 4, 294 (1921). (3) Scott, W. W., "Standard Methods of Analysis," pp. 59, 106, 293, 367, New York, D. Van Nostrand Co., 1927. (4) Sommer, H. H., and Hart, E. B., J. D a i w Sci., 7, 525 (1932). RECEIVEDOctober 8, 1934. Presented before the Division of Agricultural and Food Chemistry a t the 88th Meeting of the American Chemical Society, Cleveland, Ohio, September 10 t o 14, 1934. Taken from the M.S. thesis of Harold L. Anderson submitted t o the graduate council of Kansas State Colege, June, 1934. Publication No. 182 from the Chemistry Department of the Kansas Agricultural Experiment Station.
Device for Holding Electrodes during Electrometric Titrations MILTONL. HERZOG Cellulose Research Corporation, East Alton, Ill.
A
VERY useful and convenient piece of apparatus for use
with the asbestos1 or similar electrodes is shown in the accompanying sketch. This device is particularly useful when making e l e c t r o m e t r i c t i t r a t i o n s , a s it always insures uniform spacing of the e l e c t r o d e s and offers a compact, rigid mounting for them, This m o u n t i n g allows the operator greater freedom while t i t r a t i n g a n d a l s o readily lends itself for rapidly changing the electrodes. tLLLTRCDL T h e a p p a r a t u s can very readily be made b y t h e amateur glass blower from two 1.25-cm.
