SEPTEMBER 15, 1936
ANALYTIC4L EDITION
with acid is preferable, because absorption of carbon dioxide from the air may otherwise introduce errors. To avoid this, it is best to make a preliminary determination first, and in a second test add almost the total amounts of titrating liquid at once, using the greatest possible precision in the final titration. The method has great elasticity. The two volumes need not be known, and the amount of indicator need not be known in relation to the volumes of fluids, except when compared with permanent standards. The concentration of the titrating liquid needs t o be only approximately known. The essen-
399
tial features are that the added volumes of indicator solution be strictly equal, that the added amounts of titrating liquid before comparisons be equal, and that loss or absorption of carbon dioxide be prevented.
Literature Cited (1) Acree, S. F., and Fawcett, E. H., IND. ENQ.CREM.,Anal. Ed., 2, 78-85 (1930). (2) Burton, J. O., Matheson, H., and Acree, S. F.,Ibid., 6, 79 (1934). (3) Fawcett, E. H., and .4cree, S. F., J. Bact., 17, 163-204 (1929). RECEIVED Maroh 11, 1936.
Sensitiveness of Magnesium Uranyl Acetate Reagent to Sodium and Potassium CHARLES H. GREENE, Harvard University and Radcliffe College, Cambridge, Mass.
I
T\T THE course of work upon a system for the analysis of
the alkali and alkaline earth groups a study was made of the sensitiveness of magnesium uranyl acetate reagent to sodium and potassium. Since such data do not appear to be available for different dilutions of the reagent, in spite of the numerous papers upon the analytical applications of the reagent which have appeared, the results of the study may be of general interest.
Experimental The reagent was prepared according to the directions of Noyes and Bray (f). Solutions of sodium and potassium nitrates containing 50 mg. per ml. of sodium and potassium were prepared from reagent chemicals and diluted as required. Redistilled 95 per cent alcohol was used. The experiments were performed by mixing in small test tubes 1 ml. of sodium or potassium solution with a volume of reagent ranging from 0.1 to 2.0 ml. In some experiments 0.5 ml. of alcohol was added to the solution before mixing with the reagent. The results of the experiments in which 0.5 ml. of reagent was employed are presented in Table I.
tests which were negative even with the addition of alcohol are indicated by open circles. To avoid confusion, only those tests which were critical a t any concentration of reagent have been plotted. The scales of Figure 1are logarithmic to permit the inclusion of results for sodium and potassium in a single figure.
Discussion It is evident from Figure 1 that the distinction between sodium and potassium is improved as the ratio of the volume of reagent to the volume of the solution tested is increased. I
'
v
r
v
r
T
.2
* .5
A I
T
,
,
*
I
e . z 0
E 1 d 3 v) 0
. 0.5.
U 0
-I
I
TABLE I. TIMEREQUIRED
FOR PRECIPITA4TION
(1 ml. of solution mixed with 0.5 ml. of magnesium uranyl acetate reagent) Without With 0.5 M1. Pptas- Without With 0.5 MI. Sodium Alcohol of Alcohol slum Alcohol of Alcohol Mg. Mg. Noppt. No ppt. 5 No ppt. 0.00 No ppt. 8 No ppt. No ppt. Noppt 24 hr. 0.01 10 No ppt. 20 hr. No ppt. 24 hr. 0.02 0.03 No ppt. 25-35min. 12 .... 2-50 min 0.04 No DDt. 25-32min. 14 Nouut. 1-5min. n n5 NO b i t . 3-5 min. 15 22 k i n . 0.06 Ni$pt. 2 min. 16 3-4 hr. .... 0.12 No ppt. ...... 18 8 min. . . . . 0.14 No ppt. ...... 20 1-7 min. . . . 0.16 3 hr. ...... 25
