August, 1944
ANALYTICAL E D I T I O N
and phosphate present was being checked. This provided no interference. I n the case of biological materials, phosphate should be completely removed. Chloride should not be present in amounts such that the weight ratio of chloride to sulfur exceeds 30; else, precipitation of benzidine sulfate is not complete. The method is accurate in a range extending from 0.05 to 0.150 mg. of sulfate with a maximum error of 2%. The results obtained on pure sulfate solutions are summarized in Table I. Each value is the mean of triplicate determinations.
537 LITERATURE CITED
(1) Bratton, A. C., and Marghall; E. K., J . Biol. Chem., 128, 537 (1939). (2) R *s.,Ibid**74, (lgZ7). (3) Kahn, B.S.,and Lieboff, S.L., Ibid., 80, 623 (1928). J. G,,Ibid., 114, 147(1936). (4) Lentonoff,T,V,,and (5) Looney, J. M., and Dyer, C. G., J . Lab. Clip. Md., 28, 355 (1942). (6) Shinn, M., IND. ENQ.cHEM,, A N A L . ED.,13,33 (1941). (7) Wakefield, E.G., J . Bi02. Chem., 81,713 (1929). (8) Yoshimatsu, 5 . I., Tdhoku J . Ezpt. Med., 7,553 (1926). Hubbardl
NOTES ON ANALYTICAL PROCEDURES Improved Distillation Receiver
A n Observation of Possible V a l u e
HOWARD M. WADDLE1
for Sugar Determinations
State Engineering Experiment Station, Georgia School of Technology, Atlanta, G a .
DANIEL LUZON MORRIS, The Putney School, Putney, V t .
I
S AT\’ attempt to modify the Sichert and Bleyer reagent (1)
for micro use, potassium iodide was included in the reagent. When this reagent was heated with glucose, a precipitate formed which was identified as cuprous iodide. The presence of the iodide ion speeds up the reduction reaction, presumably because of the removal of the cuprous ion from solution as cuprous iodide. The observation may have value for the determination of sugars, for the cuprous iodide can be determined iodometrically in the solution or separated and weighed directly. I t s weight is of the order of ten times that of the glucose taken. The reagent may be made up as follows: To 250 cc. of water are added 500 grams of hydrated sodium acetate, 75 cc. of 5% acetic acid, and 5 grams of potassium iodide. The solids are dissolved by warming the solution, and 25 grams of crystalline cupric sulfate are added as a 10% solution. About 40 grams of glucose are now added, the volume is made up to 1 liter, and the mixture is heated in boiling water for 45 minutes, let cool slowly, and filtered to remove the crystalline precipitate of cuprous iodide which had separated during the heating. For the determination, the solution is heated for 30 minutes a t 100” with an equal volume of glwose solution. Further work on this reagent is not contemplated. Lowering of the pH by the addition of more acetic acid results in the formation of less precipitate for a given amount of glucose; if the amount of acetic acid is decreased, a white precipitate (apparently cupric hydroxide or a basic cupric salt, as it is nonreducing) is formed on heating, even in the absence of glucose. Omission of the preliminary heating with glucose causes a slight black precipitate to form during the determination if the quantity of glucose being determined is very small. The use of more than 5 grams of potassium iodide per liter increases the speed of the reaction, but makes iodometric estimation of cuprous iodide in the solution difficult. Less than 0.2 gram of glucose will give no reduction. The reagent is affected by maltose, whose reduction, under the conditions mentioned, is about l / g that of an equal weight of glucose. The maltose reduction is not complete even after 50 minutes of heating, whereas the glucose reductionshows no increase after 30 minutes.
THE
uiual variety of cow’s-udder fraction cutter ( 1 ) has the inherent disachantage that each drop of distillate must be collected in one of the receivers attached to the cutter. The modification described makes it possible to interrupt the flow of a distillate while the operator follows the course of a temperature change in the fractionating column. Since the fraction cutter can be clamped in a stationary position, it is possible, in the caie of low-boiling fractions, to surround the entire receiver with a freezing mixture. FROM DISTILLING FLASK
In practice bulb F is approximately 10 mi. in diameter. Ground joint C has a standard taper 14/35, and the body, A , is made from a 50-ml. Erlenmeyer flask. All glass tubing, B , is 8 mm. The inside rod that conducts the distillate to the receivers must rotate freely and must not leave the surface of the tube coming from stopcock D, 2-mm. bore. LITERATURE CITED
LITERATURE CITED
(1) Sichert and Bleyer, 2.anal. Chem., 107,328 (1936). Txie work waa aided by a grant iron] hIead Johnson and Co.
(1) Reilly and Rae, “Physico-chemical Methods”, 3rd ed., Vol. I1 p. 94, New York. D.Van Nostrand Co., 1939. 1 Preaent address, Rwearch Divieion, West Point Manufacturing Co., Shawmut, Ala.
