INDUSTRIAL A N D
January 15, 1931
ENGINEERING CHEMISTRY
I n order to obtain the Lintner’s value for 1 per cent enzyme solution for any given solutions, multiply 2542 by per cent of solution. Table I1 represents complete data for the three diastasesnamely, taka-diastase (A), malt diastase (B), and pancreatic
-
55
60
>- .
45
40
TKA-DIASTASE
hULTqlffiTA6E
PmTICDlASTA&
-%--*-
3s
3
30
0 2 . 5 20
15. IO
3
The relations between starch titration and calculated Lintner’s values to 1 per cent enzyme solution of these three enzymes are also given in the figure. In testing taka-diastase, the data of Table I may also be used a t 50” C. where digestion is carried on under the same conditions except that the starch solution is buffered a t pH 5.4 and is made by using 250 cc. of 0.2 M acid potassium phthalate and 177 cc. of 0.2 M sodium hydroxide solution. The calculation is not altered. I n routine practice it is possible to be more economical and use more dilute buffer solutionsthat is, one-fifth of the amount of each buffer solution for the starch solution. Ten cubic centimeters of 0.2 M sodium hydroxide solution instead of 0.25 M sodium hydroxide are sufficient to stop further reaction. The last column in Table I1 gives the percentage of pure glucose which corresponds to the observed starch titration. Literature Cited
1-
0
20
40
60
00
100
120
140
180
I
180
I
200
L. v.
I
220
I
1
1
240 260 l&2
I
I
I
300 320 340 L O
Starch Titration against Calculated Values i n Terms of L. V. t o Per Cent Enzyme Solution
(1) Clark, “The Determination of Hydrogen Ions,” Williams and Wilkins, 1928. (2) Euler, “General Chemistry of the Enzymes,” p. 290, Wiley, 1912 ~. ._
diastase (C)-where the observed titration values were obtained by the above described method. The references (a) data Obtained by repeating with represent various Der cent enzvme solutions. Unmarked numbers are interpolated data obtained from the curve.
(3) Lintner, J . prakl. Chem., 34, 386 (1886).
i:; , “ h “ , 4 i ~ ~ ~ ; ’ ~ ~ D , k ~ a ~ d c ~ ~ ~ ,
3a, 1082 (1910). (6) Waksman and Davison, “Enzymes,” p, 154, Williams and Wi]kins, 1926 _ .__
(7) Wohlgemuth, Biochem. Z., 9, 1 (1908).
Quantitative Determination of Potassium b y Sodium Cobaltinitrite Method’ Pierre J. Van Rysselberge STANFORD UNIVERSITY, CALIF.
HE precipitation of potassium by the sodium cobaltinitrite reagent, studied by de Koninck ( 5 ) ,Gilbert (4), Adie and Wood ( I ) , Cunningham and Perkin (3)) Vurtheim ( 7 ) , and others, has recently been thoroughly investigated by Bonneau ( 2 ) . The difficulties of the method are reviewed in some of the bulletins of the U. S. Department of Agriculture (8). Bonneau’s work confirms the results obtained by Adie and Wood, who showed that the formula of the potassiunisodium cobaltinitrite is KzNaCo(NOz)a.nHsO. According to Bonneau, a constant composition of the precipitate (disregarding the amount of water of hydration) is obtained only if the ratio of the concentration of sodium to that of potassium is larger than 25. Below that ratio the molecule of potassium-sodium cobaltinitrite contains more potassium and less sodium than indicated by the formula given above, the composition tending towards the limiting formula KsThe the temperature at which N~CO(NO~)~.~H ~ Ohigher . precipitation takes place, the higher the amount of potassium in the molecule. The formula found by Vurtheim is K1.5Nal.6Co(NOz)~.nHz0, a result that the work of Bonneau contradicts. Gilbert gives the same formula as Viirtheim. The results of Adie and Wood and those of Bonneau show that the number of water molecules attached to each molecule of KzNaCo(NOz)6is usually one. According to Adie
T
1 Received
July 30, 1930.
and Wood, drying the precipitate below 130” C. has a negligible influence on the final composition. After a long series of determinations of potassiucm in mixed solutions of potassium and sodium chlorides, the writer was able to draw a few interesting conclusions in regard to the sodium cobaltinitrite method, which are presented here as a complement to the work of Bonneau. The reagent was the same as that used by Adie and Wood (1). Bonneau (9) used cobalt nitrate instead of cobalt acetate, The writer usually had to determine small changes of concentration of potassium resulting from electrolytic migration (6). Those changes were determined by comparing the unknown samples with samples of the original solution for which the amount of potassium was known. It was necessary to use samples having equal volumes and to add to all of them the same amount of reagent. If, moreover, the time during which the precipitates were allowed to settle was exactly the same for all the samples to be compared, satisfactory results could be obtained. The influence of the time of settling seems to have been overlooked by all the authors who investigated this method, with the exception, perhaps, of Vurtheim. He allowed the precipitates to settle for 18 hours, a time after which no increase of weight of the precipitates could be detected. Adie and Wood let the precipitates settle overnight. Bonneau few hours.” speaks of
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
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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 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
