ANALYTICAL EDITION
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Vol. 3, No. 1
With mixtures of potassium and sodium chlorides of a total concentration varying from 0.5 to 5 gram-equivalents per liter, the ratio of the concentration of sodium chloride to that of potassium chloride varying from 9 to 49, th,e writer obtained ratios of the weight of potassium-sodium cobaltinitrite to the weight of potassium varying from 5.56 to 6.43. The time of settling was a t least 4 hours, and in some cases reached 66 hours; in a few exceptional cases ratios in the vicinity of 8 were obtained. The ratio given by Adie and Wood, and Bonneau, corresponding to the formula KzNaCo(N02)6.H20, is 5.81 (1:0.172), a ratio which the writer frequently obtained for a time of settling of about 24 hours. The ratio 5.58 corresponds to the formula K2NaCo(NOa); the ratio 6.28 to the formula KzNaCo(NO&.3H20. I n general, the weight of the precipitate increases with the time of settling and seems to tend towards a certain limit; the value of that limit and the time after which it is reached are exceedingly variable and seem to depend on the volumes of the samples, their concentration, the way in which the reagent is added the excess of reagent used, etc. Another point noticed is that, even in the case of low NaC1:KCl ratios, high values of the ratio complex nitrite:K can be obtained. Those high ratios are evidently due to gradual hydration. Samples containing approximately the same amounts of potassium, when treated in strictly identical conditions, usually give identical ratios complex nitrite :K; sometimes, however, differences occur, They correspond as a rule to a variation of 1.3 per cent, which the writer empirically ascribes to a difference of one-third of molecule of water in the composition. Indeed, most of the results could be explained by assuming the formula [KzNaCo(N02)sla.nH~0. Suggested Method for Determination of Potassium
(2) Several samples, known and unknown, are treated together in exactly the same conditions: the volumes must be the same (independently of the actual amount of potassium they contain, provided the order of magnitude be constant). The same amount of reagent is added to all of them, preferably with a pipet, stirring all the time; this amount should constitute an excess such that, after settling of the precipitate, the supernatant liquid has a dark brown color. To analyze a solution which contains about 0.1 gramequivalent of potassium chloride per liter, a 10-cc. sample should be diluted to about 30 cc. and from 20 to 30 cc. of the cobaltinitrite reagent should be used. The ratios Na:K of the solutions to be analyzed should be of the same order of magnitude for all the samples. The actual value of that ratio is not of primary importance. I n order to obtain a constant composition of the complex nitrite, for all concentrations of potassium, one should, after Bonneau (W), use a ratio Na:K larger than 25. (3) The precipitates are allowed to settle for 24 hours. They must all be filtered a t the same time, on weighed filters, washed with equal amounts of water 'acidified with acetic acid, then washed again with alcohol. (4) The filters are dried, all of them for the same length of time, a t about 120" C., then weighed. (5) The ratio complex nitrite:K is deduced from the analysis of the known samples. Very satisfactory results are obtained in this way. The accuracy of the method is 1.3 per cent, although in most cases the variations do not exceed a few tenths of one per cent.
(1) The reagent is prepared according to the directions of Adie and Wood (1). Two solutions having, respectively, the compositions 220 grams of sodium nitrite in 440 cc. of water, 113 grams of cobalt acetate in 300 cc. of water and 100 cc. of glacial acetic acid, are mixed, thoroughly stirred, and filtered just before use.
(1) Adie and Wood, J. Chem. SOC.,I?, 1076 (1900). (2) Bonneau, Bull. sot. chim., 46,798 (1929). (3) Cunningham and Perkin, J . Chem. SOC.,95.1562 (1909). (4) Gilbert, 2. anal. Chem., 35, 184 (1899). (5) Koninck, de, Ibid., 20, 390 (1881). (6) McBain and Van Rysselberge, J . A m . Chem. Soc., 52, 2336 (1930). (7) Vtirtheim, Rec. Irov. chim., 40, 593 (1921). (8)See particularly: U.S. Dept. Agr., Bur. Chem. Bull. 187, 152.
Literature Cited
Micro-Absorption Tube with Mercury Seals' Ralph T. K. Cornwell NATIONAL INSTITUTE OF HEALTH (HYGIENIC LABORATORY), U. S. PUBLICHEALTH SERVICE, WASHINGTON, D.
HE first absorption tube for organic microcombustions in the determination of carbon and hydrogen, which could be sealed, was designed by Blumer. The Blumer tube is described and discussed by Pregl (2). Later a microabsorption tube was made so that the capillary ends could be sealed by drops of mercury ( I ) . An objection to the Kemmerer-Hallett micro-absorption tube is the fragile nature of the ends of the tube, This objection is overcome in the new micro-absorption tube reported here (Figures 1 and 2). Two2hollow glass stoppers were ground to fit the ends of a piece of Pyrex tubing about 14 cm. long and 1cm. in diameter. The mercury trap and seal were then placed on the inside of - the stopper as shown in the diagram. In this way the original
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1 Received August 21, 1930. Publication authorized by the Surgeon General of the U. S. Public Health Service. a The writer wishes to thank Arthur Shroder, director of Technical Service, Fisher Scientific Co., Pittsburgh, Pa., who had an experimental tube made for him. The apparatus can now be purchased from this company.
c.
straight design of the Pregl micro-absorption tube was retained. To fill the tube, one of the glass stoppers is attached in the usual manner with Kronig's cement (3). A small layer of cotton (about 5 mm.) is then pressed against the stopper and the absorbing material added. This is followed by another layer of cotton and the second glass stopper is sealed to the apparatus in such a manner that the mercury traps in both stoppers occupy the same relative positions. If the Kronig cement is used correctly the ground-glass ends will be transparent. A small drop of clean mercury is then introduced into one end of the tube. This is drawn into the mercury trap by slight suction applied from the Mariotte flask. I n the same manner a drop of mercury is placed in the other end. The mercury falls into the two traps, shown in Figure 1, allowing free passage of the gases during the combustion. When the tube is rotated 180 degrees, the mercury falls into the small tubing as shown in Figure 2, and thus protects the
INDUSTRIAL AND ENGINEERING CHEMISTRY
January 15, 1931
contents of the tube from the air. Just enough mercury is used to seal the tubes. The tube for the absorption of water was filled with Anhydrone. Ascarite, followed by 3 to 4 cm. of Anhydrone, was
Figure 1-Position
Figure 2-Tube
of Tube during Combustion
Rotated 180° and Sealed
used to absorb the carbon dioxide. Both tubes were kept cool during the combustion by wrapping them in wet flannel. No disadvantage resulted from having one of the sealed glass stoppers next (4) to the electric furnace. ~ ~ l preglrs l ~directions ~ h emctly, ~ but using the new micro-absorption tube, very satisfactory carbon and hydrogen determinations have been made in this laboratory for a period
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of 6 weeks. Practically theoretical figures can be obtained. One illustration might be of interest: 4.570 mg. (pyrogallol); 1.95 mg. HzO, 9.583 mg. Con. Calcd.: H, 4.79 (8), C, 57.12. Found: H, 4.79 (2); C, 57.19. The advantages of the micro-absorption tube here described over those already recorded are: (1) Since both ends can be removed, the cleaning of the tube is greatly facilitated. (2) While standing on the rack and during the weighing, the tube is sealed-yet, because of the shape it can be wiped before each weighing and handled in the manner so carefully worked out by Professor Pregl. (3) The tube can be weighed when iilled with oxygen or air. Literature Cited (1) Remmerer and Hallett, IND. END.CAEM.,19, 173 (1927). (2) Pregl, “Quantitative Organic Microanalysis,” translated by Fyleman, (3) Ibid., p. 42, p. 63. Blakiston, 1924. (4) Ibid., p. 87.
Hydrogen-Ion Determinations with Low-Resistance Glass Electrodes’ G. Ross Robertson UNIV~RSITY OF CALIFORNIA AT Los ANGELES, CALIF.
A description is given of glass electrodes which have HE estimation of hymay accordingly be connected resistances of but 2 t o 3 megohms, and are made of drogen ion by standand used in a glass electrode a commercially available glass. Such electrodes permit ard methods becomes apparatus in the same manner the use of a d’Arsonva1 galvanometer in hydrogen-ion difficult or impossible when which one would employ with estimation with fair accuracy. Their use requires little the solution under examinaa q u i n h y d r o n e electrode. more skill than is needed with an industrial quinhytion contains certain active Furthermore, since the resistdrone apparatus. Electrometers are eliminated, ajld oxidizing or reducing agents. ance of the glass electrode is electrostatic shielding becomes of little importance. I n such situations the glass so low, static charges do not Directions for construction and use of the apparatus electrode invites consideraaccumulate and disturb the tion. Although this device are given. galvanometer as they do an has been known for over electrometer which by its very twenty years (2), it has been generally overlooked in Ameri- nature has no current “leak.” can laboratories. Thanks largely to the recent work of The sharpness of estimation of the null point is of course MacInnes and Dole (4, 5 ) , and Elder and Wright (I), it is not so great as in a common potentiometer circuit in a hydronow attracting considerable attention. gen-ion determination. It is, however, sufficient to serve orA serious drawback of the glass electrode has been its very dinary purposes, as seen in the following illustration: large electrical resistance. Values of 20 to 100 megohms are Assume 3 megohms resistance, and the normal galvanometer commonly reported in the literature. When such a device is deflection of 1 mrn. for 10-lp amperes current. Suppose the placed in the ordinary potentiometer circuit in place of the potentiometer adjustment has come within just one millivolt common hydrogen or quinhydrone electrode, the current of the null point. The current which is to actuate the galvanometer upon depression of the contact key is, therefore, by Ohm’s becomes too small for detection on a common galvanometer law at adjustments near the null point. A quadrant electrometer, or vacuum-tube potentiometer ( I ) , 3 O.x Ool1 0 6 = 3 x 10-10amperes is accordingly used instead of the galvanometer. More or Such a current deflects the No. 2500-f galvanometer marker less electrostatic shielding and special insulation are necessitated in such apparatus, I n any case the exacting technic 3 mm., and thus one may locate the null point to the accuracy required in the use of these physical instruments is discourag- of one millivolt with ease. This indicates a maximum error of ing to an ordinary chemist who is seeking only an approxi- *0.02 pH in this part of the operation. On account of the relatively long period of the galvanometer any greater premate estimation of pH value, I n the present work the resistance of the electrodes was cision in estimation requires more time than one would care cut to values from 2 to 3 megohms, the bulbs being blown to take in rapid commercial work. thin. It was then found that Leeds and Northrup type R Preparation of Electrode galvanometer, model No. 2500-f, an instrument of moderate cost, became useful. This galvanometer, while not of preCorning No. 015 glass, as suggested by MacInnes and Dole cision grade, has a sensitivity of 0.0001 microampere. It ( 5 ) , proved to be suitable for the purpose. It is obtainable from the manufacturer. A piece of 10-mm. tubing of this 1 Received May 23, 1930.
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