July, 1923
ISDCXTRIAL A S D E-‘GI-I’EERISG
CHEMISTRY
Values of a Single Paint Yield value Dynes/sq. cm. End point -Constants of capillaryf p Q Rf Capillary PQ Rf 2 21 1B 21,300 0 . 0 0 8 4 14 4.000 22.4 z p 13,600 0.01564 4.390 24.2 ,‘3B 15,000 0 . 01300 4,000 24.4 4R 11,500 0.01654 4,000 23.8 6 l: a 19,100 0.Oll50 5,156 21.3 Average 23.2 e These capillaries were not cut off flush with the ends of the mounting block.
729
Table 11-Yield
-
of the curve used. The higher this portion is, the higher will be the calculated yield value. Experimentally I t is difficult to obtain accurate results near the yield value nith ordinary methods, consequently the Buckingham formula also gives high results, though not so high as the Binghani formula. In paint work, the authors feel that the Buckingham formula when practically *applied will give results for yield values 100 to 300 per cent too high and the original Bingham formula several hundred per cent higher than this. In the average of seven paints the yield values of which were determined, the Bingham method gave results 600 per cent higher than those obtained with the microplastometer. When these excessively large deviations from the right order of magnitude are considered, then the microplastometer seems justified, even though it does not duplicate results precisely.
Per cent deviation from av. of all capillaries 3.4 4.3 5.2 2.6 , 8.2 4.7
Extreme per cent variation in detns. on individual capillaries 3.4 5.9 4.0 11.8 7.7 6.6
,4s yield value is only one of the two factors controlling plasticity, its determination alone is insufficient to give a complete idea of the consistency of a paint. But if we did have the second factor, mobility, consistency even then would not be obtained as a comparable quantity, such as viscosity, for instance. Both yield value and mobility give information concerning consistency; hence, each one possesses a certain value of its own to the paint technologist. ,4t present the microplastometer cannot determine the mobility of materials that are relatively opaque. The solution of this problem will depend on whether light can be used of sufficient intensity to reveal the flow along the axis of the capillary. If this can be accomplished the microplastometer will be completely satisfactory for the study of plastic flow.
Effect of Sodium Carbonate Concentration in the Benedict Sugar Method‘.’ By Armand J. Quick S C H O O L OF hfEDICINl?, U N I V E R S I T Y OF P E N N S Y L V A I I I A , P H I L A D E L P H I A , PA
I
S APPLYING the Benedict quantitative sugar method to
the determination of glycuronic acid, the oxidizing value of the reagent was found to vary with the concentration of the sodium arbo on ate.^ Further investigation shoaed that this same variation occurs in the titration of glucose solutions, thus introducing an error which becomes increasingly more marked the more dilute the sugar solution employed. According to the directions of Benedict4 10 to 20 grams of crystallized sodium carbonate, or one-half that amount of the anhydrous salt, should be added to the reagent before titrating. For glucose solutions stronger than l per cent entirely satisfactory results are obtained, since the volume of the liquid added in the titration is so small that the concentration of sodium carbonate is very little altered. With a 1 per cent solution, however, a difference of 0.1.5 cc. in the titration is obtained by using 5 grams of the anhydrous sodium carbonate instead of an equivalent amount of the hydrated salt. With more dilute solutions the error due to the alteration of the final concentration of sodium carbonate becomes so great that the method becomes very unsatisfactory for sugar solutions containing less than 0.2 per cent glucose. This influence of the sodium carbonate concentra1 Presented under the title “A Study of the Effect of the Concentration of Sodium Carbonate in the Renedict Quantitatire Sugar Method” before the Division of Biological Chemistry at the 69th Meeting of the American Chemical Society, Baltimore, Md , April 6 to 10, 1925. 2 -4 part of this work was carried out in theLaboratoryof Pharmacology, University of Wisconsin, during the summer of 1924 The author wishes to acknonledge the courtesy o f Dr. Loevenhart in placing at his command the facilities of the laboratory. 2 Quick, J Biol Chem , 61, 667 (1924). 4 Ibid 9, 57 (1911)
tion on the accuracy of the method has recently also been observed by woke^.^ Since the Benedict method is one of the simplest and handiest titration methods available, and has the further advantage of being more specific for glucose than the methods using sodium hydroxide, it seemed well worth while to investigate the effect of varying concentrations of sodium carbonate with the view of making the method more accurate, especially Then applied to dilute sugar solutions. In developing a modification of the method, all unnecessary changes were avoided. The reagent was prepared exactly according to the directions of Benedict, although it was later found that the potassium ferrocyanide could be omitted without producing any perceptible changes in the results. Benedict’s procedure was followed, but the titration was carried out in a 100-cc. Erlenmeyer flask instead of a porcelain dish, in order t o minimize both the loss of water by evaporation and the reoxidation of the reduced copper. In studying the effect of the sodium carbonate concentration on the oxidizing power of Benedict’s reagent the final concentration of the salt was caused to vary by titrating with glucose solutions of different strengths, with consequent variation of the amount of liquid added from this source, by adding definite volumes of water, and by adding varying amounts of the salt. These variations and the results obtained are recorded in Table I. The relationship between the sodium carbonate concentration and the glucose equivalent of Benedict’s solution is best brought out by the chart. For any concentration of sodium 6
Pharm J , 113, 117 (1924).
INDUSTRIAL A N D ENGINEERING CHEMISTRY
730
carbonate greater than 25 grams per 100 cc. of the final solution, Benedict’s reagent has a constant and minimum oxidizing value, but for lower cmcentrations the value increases as the concentration of sodium carbonate decreases. The factors concerned in the oxidation of glucose are too complicated to be discussed in this paper, but the relationship between the oxidizing power of Benedict’s solution and the concentration of sodium carbonate presents an interesting physicochemical problem. The hydroxyl-ion concentration rather than the sodium carbonate itself seems to be the real factor, for a decrease of the glucose equivalent can also be brought about by increasing the alkalinity in other ways, as for instance, by adding trisodium phosphate to the reagent. This substance, however, as well as dilute sodium hydroxide, will cause the cuprous thiocyanate to dissociate with the precipitation of red cuprous oxide. Table I Concn. of glucose soh. Per cent 2.0
NazC03 added Grams 10
? 5
5 10 5 5 5 5 5 10 5
1.0
0.5
Final Water TitraFinal concn. of added tion volume XarC08 cc. Cc. Cc. G . /lo0 cc. 25 cc. Benedict’s Solution 0 2.35 27.36 45.7 0 2.35 27.35 27.4 15 2.50 42.50 17.7 25 2.65 52.60 14.2 50 2.70 77.70 9.i 0 4.75 29.66 42.1 0 4.75 29.70 25.2 5 4.85 34.85 21.4 10 4.95 39.95 18.6 25 5.15 55.15 13.6 50 5.60 80.60 9.3 0 9.50 34.50 36.2 0 9.65 34.65 21.6 5 9.85 39.85 iS.8 10.05 45.05 16.7 10.40 60.40 12.4 0 18.80 41.10 28.4 0 20.00 45.00 16.7 5 20.30 50.30 14.9 10 20.65 55.65 13.5 I O cc. Benedict’s Solution 19.40 56.6 0 9.40 0 9.45 19.45 30.8 19.50 25.6 0 9.50 0 9.70 19.70 20.3 0 10.10 20.10 14.9 0 10.50 20.50 9.6 0 12.60 22.60 48.6 0 12.60 22.60 26.6 0 12.80 22.0 22.80 0 13.30 17.2 23.30 0 13.80 12.6 23.80 0 14.20 8.3 24.20 0 18.90 38.0 28,90 0 19.40 29.40 20.4 0 20.00 30.00 16.r 13.2 0 20.40 30.40 0 21.20 31.20 9.6 6.3 0 22.00 32.00
18
0.20
0.15
10 5 4 3 2 1 10 5
J. Biol. CkPm., 46, 365
(1921).
carbonate should be taken. In fact, 5 cc. of the reagent can often be employed to advantage. By using smaller quantities of reagents one cuts down the amount of material used, and also lowers the final volume of the solution, which assists in securing a better end point. Results are most satisfactory when the amount of reagent is so adjusted that the titration does not exceed 20 cc.
Glucose equivalent of Benedict’s s o h . Mg./cc. 1.88 1.88 2.00 2.06 2.16 1.90 1.90 1.94 1.98 2.06 2.24 1.90 1 . 9~. 3 1.97 2.01 2.08 1.86 2.00 2.03 2.06 ~
1.88 1.89 1.90 1.94 2.02 2.10 1.89 1.89 1.92 2.00 2.07 2.13 1.89 1.94 2.00 2.04 2.12 2.20
It should be noted that the constant and minimum value for the glucose equivalent of Benedict’s reagent is somewhat different from that given by Benedict. He states that 1 cc. of the reagent is equivalent to 2.0 mg. of glucose, whereas the values obtained in this work are 1.88 to 1.90 mg. To check this value several specimens of copper sulfate have been used and the glucose (Pfanstiehl’s pure anhydrous) analyzed polarimetrically and by the Shaffer-Hartmann method.6 From the experimental data obtained it is possible to formulate modifications which increase the accuracy of the method, especially when used with low concentrations of glucose. Since the glucose equivalent remains constant as long as the final concentration of sodium carbonate is kept above 25 grams per 100 cc. of solution, enough of the anhydrous salt should be added to the reagent to maintain the concentration above this critical level. For glucose solutions stronger than 0.25 per cent it is best to use 25 cc. of Benedict’s reagent and 10 grams of anhydrous sodium carbonate, although 5 grams are sufficient for glucose solutions stronger than 1 per cent.’ In titrating glucose solutions weaker than 0.25 per cent, 10 cc. of Benedict’s reagent and 10 grams of anhydrous sodium 6
Vol. 17, S o . 7
G r a m s of sodium carbonate added per 100 cc of final solution Variation of Glucose Equivalent of Benedict’s Solution with Different S o d i u m Carbonate Concentrations
.A commonly used micro Benedict method described by Hawk,? in which 5 cc. of the reagent and 1 to 2 grams of sodium carbonate are employed, is subject to even a greater error than the macro method, especially if the reagent is diluted to 25 cc. to retain the original volume of the macro method. As pointed out by Smith,8the micro method which has come into common use leads to an error of 15 to 30 per cent. By using only 1 cc. of the reagent without dilution and 0.2 to 0.7 gram of anhydrous sodium carbonate and carrying out the titration in a test tube, Smith has been able to increase the accuracy to that of the macro Benedict method, but, like the latter, it is unsatisfactory for the determination of solutions containing less than 0.17 per cent reducing sugars. It seems quite probable that with a slightly better adjustment of the sodium carbonate concentration the method could be extended to sugar solutions containing as little as 0.1 per cent glucose. 7
“Practical Physiological Chemistry,” 1923, p. 598, Philadelphia.
8
J . L.ab Clzn Mcd.. I , 364 (1922).
Cooperation with Libraries Again we are impressed by the cooperation which exists between the Cleveland Public Library and the Cleveland Section of the AMERICAN CHEMICAL SOCIETY. With the notices to members of the Cleveland Section announcing Professor Bogert’s address on “Science and Art in the Perfume Industry,” there was sent an announcement from the library giving authors and titles of books and magazine articles on the subject of perfumery. The other side of the notice carried a list of new books on chemical subjects t o be found in the library. Likewise, when Dr. Reese spoke on explosives, a separate notice carried a list of references t o recent magazine articles on the subject and again a list of new books of interest to chemists. In Indianapolis the public library frequently prints lists of books on special subjects, and distributes such lists a t meetings of the scientific and technical organizations of the city. The Accelerator, the bulletin of the local AMERICAN CHEMICAL SOCIETY section, regularly prints the list of new chemical books. I n addition, the library prepares an annual list of new chemical books for distribution among the members of the local section. Occasionally, lists are prepared to meet special demands and the patrons of the technical department are continuously urged to make suggestions for the purchase of new books. Similar plans may be in force elsewhere, but they have not come t o our notice. I t is an evidence of cooperation which should be appreciated by those able to use the information and displays a laudable purpose on the part of the library to increase its service. Both the chemists and the library profit by such cooperation.
