418
ANALYTICAL EDITION
usual manner and compared with freshly prepared solutions.
No change whatsoever was observable. One year later (August, 1932), standards were again made from these solutions and compared with those freshly prepared and no change was noted. This fact appears t o contradict t h e observations reported by Atkins (6),who noted a change in 3 months, but the authors have likewise observed that continual exposure of the diluted solution to the dust of the air, etc., may cause a fading in color within the period mentioned by Atkins. However, these diluted solutions may be kept for a considerable period in stoppered tubes, the stoppers being removed only when comparisons are to be made.
USE OF COLORIMETRIC METHOD As the result of a detailed study of the method used in the laboratory and aboard ship, the following notes summarize certain observations and precautions necessary in the application of the method: 1. A greenish tinge is sometimes obtained with water having more than 0.07 mg.-atoms of silicon per kg., especially if Nessler tubes are employed. This interference may usually be eliminated by the use of the colorimeter or by the reduction of the size of the sample to 25 ml. es, 100-ml. sam les should 2. With waters of low si1 be utilized. A sensitivity is with Nessler tuge series of 2 parts of silicon to 100,000,000 parts of water. 3. An excess of sulfuric acid causes a diminution in the color intensity, but no effect is noted with slight excesses of the molybdate solution. The yellow color of the hetero oly acid reaches its maximum intensity within 5 minutes after t f e addition of the reagents and remains constant for nearly 3 hours. However, the samples should be compared with the standards as soon as possible to avoid any increase in silicates caused by the dissolving action of the sea water on the glass container. 4. A maximum probable error of 5 er cent occurs when Nessler tubes are employed and this may ge reduced by the employment of the colorimeter. 5. Dissolved compounds containing iron or phosphorus in sufficient quantities to affect the determination are not encountered in sea water (1, 15). 6 . Organisms and finely divided inorganic material, if present in sufficient quantities, may be removed by filtration or centrifuging. 7. Contamination from glass bottles containing the sea water samples is ver marked, as shown by Atkins (2) and Thompson Thus water that has been ex osed to glass and Johnson 6‘7). for some length of time should not be analyzed &r silicon. If containers other than glass are employed, they soon corrode and the sediment settling to the bottom may absorb silicates. Thus for reliable results analyses should be performed only on freshly sampled sea water. 8. The c. P. picric acid contains varying quantities of water, and such material should never be used for the preparation of standards without recrystallization and drying.
Vol. 5 , No. 6
9. Picric acid standards should never be prepared with sea water, as the dissolved salts have a very pronounced “salt effect.” 10. Should it be deemed advisable to dilute samples with distilled water, an examination of the latter for silicon should first be made. 11. To insure concordant results on long trips, it is advantageous to prepare two standard stock solutions from two different batches of pure picric acid. The comparison standards are made from one of these solutions and these are checked occasionally against the second standard. 12. Various means of reporting the quantit of dissolved silicates in sea water occur in the literature. T l e authors feel that the most logical form of reporting the results is that recommended by a committee of chemists representing the different marine and oceanographic institutions on the Pacific Coast of Canada and the United States. The committee recommended that the constituents of sea water be reported as milligram-atoms of the element determined per kilogram of water. A milligramatom is defined as the result obtained when the number of milligrams of the determined element per kilogram of sea water is divided by the atomic weight of the element ( 5 ) . 13. The silicon content varies considerably in sea water ranging from less than 0.01 mg.-atom of silicon per kg. in surface waters where there is marked plankton growth to as hi h as 0.3 mg.-atom in the bottom ocean waters. Generally speafing, the silicon content increases with depth, and coastal waters as well as those of estuaries will show a seasonal fluctuation.
LITERATURE CITED Asoh, W., “Silicates in Chemistry and Commerce,” p. 16, Constable, 1913. (2) Atkins, W. R. G., J . Marine Biol. Assoc. United Kingdom, 13, (1)
154 (1932): 14, 89 (1926): 15, 91 (1928): 16, 822 (1929).
(5) Bergman, T., “De aquis Upsaliensibus,” Upsala, 1770. (4) Bunsen, R., Liebigs Ann. Chem., 62, 49 (1847). (5) Carter, N. M., Moberg, E. G., Skogsberg, T., and Thompson, T. G., Proc. Fifth Pacific Sci. Congr., 1933 (in press). (6) Dienert, F., and Wandenbulke, F., Bull. soc. chim., 33, 1131-90 (1923).
Forohhammer, G., Proc. Roy. SOC.Edinburgh, 2, 38, 303 (1850). (8) Jolles, A., and Neurath, F., 2. angew. Chem., 1, 315 (1898). (9) King, E. J., and Lucas, C. C., J. Am. Chem. Soc., 50, 2395 (7)
(1928).
(10) Lincoln, A. T., and Barker, P., Ibid., 26, 975 (1904). (11) Murray, J., and Irene, R., Proc. Roy. SOC.Edinburgh, 18, 229 f1891). (12)
Riben,‘ E., Wiss. meersuntersuchungen (KieE), 8, 100, 287
(13)
Salvadoni, R., and Pellini, G . , Chem. Zentr., 71, Pt. 1, 834
(14) (15) (16) (17)
Sohreiner, O., J. Am. Chem. Soc., 25, 1056 (1903). Sund, O., J. conseil intern. ezploralion mer, 6, 24-245 (1931). Thayer, L. A., IND.ENG.CHEM.,Anal. Ed., 2, 276 (1930). Thompson, T. G., and Johnson, M. W., Pub. Puget Sound
(18) (19)
Wells, R. C., J . Am. Chem. Soc., 44, 2187 (1922). Winkler, L. W., 2. anorg. Chem., 27, 511-12 (1914).
(1905); 11, 319 (1910); 16, 226 (1914).
(1900).
Bid. Sta., Univ. Wash., 7, 345 (1930).
RECEIVED August 16, 1933.
Note on Shaffer and Hartmann Combined Carbonate-Citrate Method for Determination of Glucose J. 0. HALVERSON AND F. W. SHERWOOD, Nutrition Laboratory, Agricultural Experiment Station, Raleigh, N. C.
I
N MANY respects one of the most rapid and convenient
methods for the determination of dextrose after the hydrolysis of starch by a malt solution is t h a t of Shaffer and Hartmannl in which the “combined carbonate-citrate solution” is used. This is a single stable alkaline copper solution to which is added sufficient potassium iodide and potassium iodate to yield a 0.1 N iodine solution when acidified. With this combined reagent i t is necessary only to add the dextrose solution, boil, cool, acidify, and titrate the excess iodine liberated. I n checking this method with a washed starch and also 1
Shaffer, P. A., and Hartmann, A. F., J . E d . Chern., 46, 365 (1921).
against dextrose (No. 41, Bureau of Standards), the amount recovered for the latter, calculated from the copper : glucose ratios of Shaffer and Hartmann, averaged 2.3 mg. more than that started with. In other words, in the authors’ hands and under their conditions, with the standardization of uniform heating by an electric hot plate2 in bringing the solution to a boil, there was somewhat more reduction from a given amount of glucose than t h a t reported by Shaffer and Hartmann. A preliminary examination of the data showed t h a t there 2 I. D. Jones has found that the rate of heating by the slightly fluctuating electric current may be readily controlled by the use of an ammeter and rheostat.
November 15,1933
I N D U S T R I A L A N D E N GI N E E R I N G C H E M I S T R Y
was a linear relation between the amounts of dextrose present and the amount of copper reduced. I n order to derive an expression of this relation which would be more applicable under the authors' conditions than the published ratios, a straight line was fitted by the method of least squares to the results of 46 determinations (omitted). This linear estimating equation was found to be: Mg. of glucose = 0.458 (mg. of copper reduced) - 1.546, with a standard error of 0.74 mg. of glucose, over the range between 35 and 125 mg. of glucose.
Continuous Liquid Extractor ABRAHAMMAZUR,ROBERTROSENTHAL, AND BENJAMIN HARROW College of the City of New York, Convent Ave. and 140th St., New York, N. Y.
A
CONTINUOUS liquid extractor for solvents having a lower specific gravity than the liquid to be extracted is shown in the figure. The receiving flask A , containing the solvent, can be made from a 250-cc. Erlenmeyer flask. The container D consists of a large test tube constricted a t both ends, the size of the tube varying with the quantity of liquid to be extracted. The side tubes G and F for filling the receiver and container. a s well a s H , a r e made by constricting the mouth of a 15 X 1.5 cm. t e s t t u b e . The glass stopcocks I a n d J a r e u s e d to drain the apparatus. If a glass-blower i s available, H may be made with a mercury s e a l connecting t h e c o n d e n s e r and the container, thus doing away with a stopper. The tube E is joined to D a t the upper end by an inner seal and G extends down almost to the bottom of the tube; or, to do away with this inner seal, E can be joined to D by a stopper at the upper end. The circuit is completed by the tube L which joins the receiver A and the container D. The solvent (ether) is placed in A by means of the side tube G. The ether is boiled on the steam bath K , vaporizes up B, condenses in C, and flows down E, bubbling up to extract the liquid (some aqueous solution). The ether extract forms a layer on top of the liquid and when it reaches tube L flows back into the receiver. Pure ether boils again to extract continuously. After complete extraction, the ether extract may be drained by means of I and the liquid removed from D by means of J . The apparatus is absolutely stationary and never has to be moved or adjusted. It may be taken apart but can be filled and drained without disassembling very easily. A series of three or four of these extractors may be set u p on a steam
d!kF
419
These data indicate that the combined carbonate-citrate method gives results closely paralleling those published by the authors, but because of the number of factors which affect the reduction each analyst should carefully standardize his technic and for the more accurate work should derive an expression of the relation between the amount of dextrose present and the amount of copper reduced (or set of copper: glucose ratios) which is applicable under the conditions prevailing in his laboratory. RECEIVED June 7, 1933. Published with the approval of the Director of the North Carolina Agricultural Experiment Station as Paper 72 of the Journal Series.
bath in a small hood. Both receiver and container may be varied in size, depending upon the quantities to be used. The container D, however, should be kept narrow, so as to have as much surface of the liquid as possible exposed to the ether bubbles. Complete extraction of a compound difficultly soluble in ether is accomplished in 5 to 10 hours. RECEIVED July 31, 1933.
Apparatus for Filling Large ClosedEnd Manometers ANGUS E. CAMERON School of Chemistry, University of Minnesota, Minneapolis, Minn.
T
HE ordinary method of filling a closed-end manometer
and boiling out gases from the mercury during evacuation is attended with considerable danger of breakage when the manometer is of large bore and sufficient length to enable one to read pressures over a range of one atmosphere. Distillation of mercury into the manometer through a side tube seemed to permit trapping of gas or vapor below the wall of mercury vapor in the tube and result in unsatisfactory manometers. The apparatus shown in the figure overcomes both difficulties. The purified mercury was placed in the bulb and the upper end of the short water-jacketed condenser sealed t o a high-vacuum line. The s y s t e m w a s evacuated and the manometer flamed. The mercury in the bulb was boiled with an electric heater or with a Bunsen burner. The mercury vapor condensing above the jet was delivered into the manometer tube and water vapor and gas passed up through the condenser. Once set in operation the system required no attention until sufficient mercury had accumulated in the manometer and then the closed end was sealed off a t the s t r i c t u r e d portion. Evacuation w i t h a good oil pump should be sufficient to give a well evacuated manome duce the mercury is essentially a diffusion pump. RECEIVED August 26, 1933.
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