ANALYTICAL EDITION
106
bituminous emulsion through a brass sieve on which an appreciable amount of separated asphalt will be collected. The same emulsion when poured through an iron screen of the same mesh will show no separation of asphalt. A satisfactory screen cgm be made by bending a piece of iron wire cloth (12 mesh; 0.028-inch diameter wire; 0.055-inch opening; this corresponds to a No. 14 standard test sieve) over the end of a cylindrical or spherical block forming a basket. A convenient size is about 3 or 4 inches (7.6 or 10.1 om.) in diameter and 1 to 2 inches (2.5 or 5.0 em.) deep. A piece of heavy iron wire can be caught through the upper edge to serve as a handle. No solder should be used. Repeated tests have failed to show any difference in the results when the emulsion and calcium chloride are allowed to
Vol. 4, No. 1
stand for a considerable length of time or the asphalt is drained at once through the screen. Emulsions which show high percentages of demulsification frequently separate the asphalt in the form of a large lump which is quite likely to entrain unbroken emulsion. The calcium chloride should be added slowly with vigorous stirring in order to keep excessively large lumps of separated asphalt from forming.
LITERATURE CITED (1) Am. SOC.Testing Materials, Tentative Method of Testing Bituminous Emulsions, D-244-28T (1928). (2) MoKesson, C. L., Am, SOC.Testing Materials, Preprint 84 (1931). (3) Myers, J. E., private correspondence. July R~CBIV E ~31, 1931.
A New Jelly-Strength Tester C; R. FELLERS AND J. A. CLAGUE, Massachusetts State College, Amherst, Mass.
M
EASUREMENT of jelly strength is of importance not only in the study of pectin but also in the manufacture of fruit and artificial jellies. The standardization of jellies and similar products with respect to consistency and jelIy strength is much to be desired. Paine ('7) in 1922 called attention to the need of a satisfactory method of measuring the jelly strength. Since that time several jelly-strength testers have been described by Sucharipa (9), Baker ( I ) , and Tarr (IO). Fellers and Griffiths (4) have shown that the Bloom gelometer (S), originally adapted for testing gelatin (8), could be used to measure the jelly strength of fruit jellies and similar products. But these instruments are either expensive, non-mobile, or of complex construction. Their use is limited almost entirely to the laboratory.
FIGURE1. DETAIL OF JELLY-STRENGTH TESTER
To overcome such difficulties and to supply the need for a simple tester of more general utility, the present instrument was devised. It operates on a principle similar to that utilized in several pressure testers which have been recently devised by Magness and Taylor (6), and Blake (d), for determining the maturity of pears, apples, peaches, etc. As illustrated in Figure 1, a detachable plunger, A , is attached to a metal rod, B, which runs through a hollow metal cylinder, C. Bearings, D, for the rod are provided a t either end of the cylinder. Within the hollow cylinder a spring is attached to the metal rod a t one end and to the bottom bearing at) the other, 'ebd. This- spring provides the necessary tension. An eyelet, E , attached to the plunger rod projects through a slot, F , in the cylinder and travels back and forth with the rod. On the outside of the cylinder the eyelet encircles a small rod, G, running parallel to the plunger rod. There is a leather washer, H , on this small rod which is pushed by the eyelet and marks the highest point reached by the latter. A scale registering the tension of the spring in
grams is stamped on the metal cylinder and the pressure necessary to break the jelly layer may be read directly. To eliminate the effect of the weight of the instrument tests must be made with the tester held horizontally, as shown in Figure 2. The plunger is placed on the surface or layer of the jelly to be tested and pressure is slowly applied until the surface is broken, when the plunger springs back to its original position. The leather washer marks the maximum pressure reached, which is read directly in grams from the scale. Because of the ease of making the pressure tests, fully eight or ten measurements may be made in a minute. Results of measurements made to test the accuracy of the instrument are shown in Table I. Apple jelly and strained cranberry sauce were prepared in quantity and poured while hot into a large number of 2-ounce straight-sided glass jars, These were paraffined to prevent surface evaporation and tested for jelly strength the following day. Several of the samples of cranberry sauce examined were from tin cans holding 21 ounces. The tests were made by cutting the jelly mass in two and determining the jelly strength of both cut surfaces. In general, the cut surface of a jelly gave more reliable pressure measurements than the outer surfaces-i. e., the top or bottom. In preparing the jellies a series was purposely included extending from soft to very firm consistency. The probable error was calculated by use of the formula (6):
-
P. E. = 0.6745
4%
where P. E. is the probable error, d. the deviation from the arithmetic mean, and N the number of determinations.
FIGURE 2. INSTRUMENT IN OPERATION
'
From Table I, the average per cent deviation from the mean in a large number of determinations is 3.51 to 4.7, indicating a reasonable accuracy for the instrument.
Janiinry 15, 1932
INDUSTRIAL AND ENGINEERING CHEMISTRY
107
TABLEI. ACCURACY OF JELLY-STRENGTH MEASUREMENTS PRODUCT Apple jelly Cranberry sauce A Cranberry sauce B Cranberry aauce C Cranberry sauce D
INVESTI- SAMPLEMEANJELLYSTREKQTH QATOR No. Top Bottom CRF JAC CRF JAC CRF JAC CRF JAC CRF JAC
34 32 70 70 60 60 10 10 10 10
86.1 88.3 122.6 123.9 174.1 172.8 233.1 234.0 251.4 256.0
68.5 71.6
176.4 155.9 161.8 162.5
ERROR OF MEANWHENTHREE TABLE11. PROBABLE MEASUREMENTS AREMADEON JELLY JELLYSTRENQTHS 255, 238, 256 247 257 250 237’ 260’ 245 84: 88: 82 85, 75. 85 160 180 170 165’ 179’ 170 129: 120: 115 125, 124, 130
MEAN 249.7 251.3 247.3 84.7 51 7 170.0 172.3 121.3 126.3
TOP
Grams 3.6 3.6 3.8 4~. .5 5.5 6.6 7.7 8.4 6.9 8.2
It was found that the best method of testing jellies was to make three or more measurements on a sample. The mean of the three determinations is then taken as the jelly strength, In order to determine the accuracy of this method, samples of jelly and strained cranberry sauce were measured by different investigators and the probable error of the mean calculated in each case.
SAMPLE No. XHVESTIQATOR 1 CRF 1 JAC 1 CCR 2 CRF 2 JAC 3 CRF 3 JAC 4 CRF 4 JAC
Av. DEYIATION FROM MEAN
PROBABLE ERROROF .MEAN &3.6 ztl.6 13.7 10.97 11.8 13.2 &?.8
&2.3 *l.O
Table I1 shows the probable error of the mean of three measurements on the same sample to vary from 0.97 to 3.7 where the jelly strengths varied from 82 to 260 grams. The
% 4.-2 4.1 3 ..I 3.7 3.4 3.8 3.3 3.6 2.7 3.2
Bottom
Grams 4.0 4.0
9.7 3.9 9.6 5.1
%, 5.8 5.6
5.5 2.5 5.9 3.1
PROBABLE ERROROF MEAN TOP Bottom 0.55 0.78 0.36 0.46 0.61 0.65 1.74 1.96 2.12 1.99
0.62 0.77
APPARENT CONSISTENCY Medium Medium soft Firm
2.88 1.70 2.26 0.92
Veryfirm Too firm, rubbery
personal error was likewise slight. Because of the small probable error, the mean of three determinations on the same sample may be considered reasonably reliable. The new jelly-strength tester combines low cost, adaptability, ease and speed of operation, mobility, and simplicity. It may be purchased from John Chatillon & Sons, 85 Cliff St., New York, N. Y.
LITERATURE CITED Raker, G. L., IND.ENQ.CHFIM.. 18,89-93 (1926). Blake, M .A., N. J. Agr. Expt. Sta., Circ., 212 (1929). Bloom, 0. T., U. S. Patent 1,540 979 (June 9, 1926). Fellers, C. R., and Griffiths, F. P., IND.ENQ.C H ~ M 20, . , 85762 (1928). ( 5 ) Gavett, G. I., “A First Course in Statistical iMethod,” 1st ed., p. 181, McGraw-Hill, 1926. (6) Magness, J. R., and Taylor, G. F., U. S. Dept. Agr., Circ. 350 (1925). (7) Paine, H. S., Am. Food J.,17, No. 3, 11-13 (1922). (8) Richardson, W. D., Chem. Met. Eng., 28, 551 (1923). (9) Sucharipa, R., “Die Pektinstoffe,” p. 81, Serger and Hempel, Braunschwcig, 1925 (10) Tarr, L. W., Del. Agr. Expt. Sta., Bull. 142 (1926). (1) (2) (3) (4)
RECEIYED August 12, 1931.
Determination of Phosphates in Waters JASONE. FARBER AND GUY E. YOUNGBURG, University of Bufflo Medical School, Buffalo,N . Y
T““
need for a more rapid, reliable, and simplified method for the determination of phosphates in certain waters is evident. In the biological field limnologists are giving attention to the relation of phosphates to plankton content, and although primarily interested in this field, the authors have noted the recent method of Scarritt (8) for the determination of phosphates in boiler water in the presence of silicates. This method has been tried and found to have some outstanding disadvantages which can be practically entirely eliminated by the method prescribed. Scarritt’s main disadvantages are that the amount of color is not sufficient; that some of the reagents are unstable; and that the color due to silicates is not obviated, the final solution not being acid. Truog and Meyer (3) have improved Denigb’ method for phosphorus analysis but have not presented it in detail for water, After considerable experience with phosphorus determinations, the Deniges principle, as outlined by Kuttner and Cohen (1) and further elaborated by Youngburg and Youngburg ( d ) , has been chosen for biological work. It is the colorimetric method whereby phosphomolybdate is reduced by stannous chloride to give an intense blue color. The concentration of the acid and the molybdate is much different from that used by Truog and Meyer, and sodium
molybdate is preferred to the ammonium salt, although either may be used. This method, here presented for waters, involves no deteriorating reagents except the dilute stannous chloride solution; the preparation of it, however, is extremely simple. The color development is immediate, the fading is slow (see Figure l), and the amount of color obtained is greater than has been found for any other phosphorus method. The method of Truog and Meyer, however, gives only 12.5 per cent less color. The reason for this is the lower concentration of molybdate and of acid which they use. Al-
Time, Min.
Tims,
Hrs.
OF BLUECOLOR FIGURE1. RATEOF FADIXG
though 12.5 per cent less color is not a major objection in itself, the greater the acidity of the solution the less interference of silica, and in the determination of total phosphorus,
