V O L U M E 2 3 NO. 3, M A R C H 1 9 5 1
48 1
of magnesium, the pH of the solutions should be much closer t o the neutral point than is required for lithium determinations. The intensity of the fluorescence of the magnesium-oxine complex decreases rapidly on standing, in contrast to that of the lit’hium oxine complex, which is very stable. The nieasurement of the fluorescence of the magnesium-oxide complex was used to determine the amounts of magnesiuni left in solution after an oxine separation. The results so obtained checked very closely those obtained spectrographically on the same sample. The fluorometric method found 1 niicrogram of magnesium oxide per ml., as compared to 0.9 microgram per ml. found with the spectrograph. If the distillation method of separation is used, magnesium is effectively eliminated. Calcium. Calcium oxide in amounts as large as 30 micrograms in 25 ml. had little or no effect upon the fluorescence of lithium t;olutions. Greater quantities caused a steady increase in the intensity of the fluorescence, but the increases were not sufficiently great to allow for a method for the accurate determination of calcium. The quantity of calcium left in solution after the oxalate separation amounted to about 0.3 mg. of calcium oxide. K i t h the dilution technique, therefore, calcium does not constitute an interference. I n fact, as much BS one tent,h of the original sample could be wed before calcium would cause any apprrciable error in the detcwiiiiiation of lithium.
to remove the hydrochloric acid. Both amyl alcohol and nbutyl alcohol formed highly fluorescent substances on heating in the presence of the lithium chloride. If the solution w3s taken nearly to dryness, a tar was formed, and a t 70” the n-butyl alcohol turned brown. I t was found that by reducing the pressure and keeping the temperature below 50” C., the hydrochloric acid could be renioved without formation of these objection:ii)le materials. However, the process was too time-consunling for practical analysis. Ninety-five per cent ethyl alcohol as a separation solvent did not produce consistent results. The etheralcohol separation, as outlined by Scott ( 7 ) ,gave excellent result.. I n this method, it was found that if less than 2 ml. of water were required to dissolve the initial precipitate, a second precipitation was not necessary. COMPOUNDS TESTED A S REAGENTS
The compounds tested for color or fluorescence reactiwi3 with lithium were: 1,4-,1,s-, and l,Mihydroxyanthraquinones, 1,25,&tetrahydroxyanthraquinone, 1-amino-4-hydroxyanthraquinone, p - nitroazoresorcinol, 2 -naphthylamine, corhineal, I-aniino-2-naphthal-4-eulfonieacid, p-nitrobenzeneazoresorcinol, morin, and quercetin. None of these proved sensitive enough for either qualitative or quantitative reagents for lithium. ACKNOWLEDGMENT
The study reported in this paper was completed under the general direction of Paul h m b r o ~ e ,chief, College Park Branch, Metallurgical Division, Bureau of Mines, and under the iinniediate supervision of Alton Gabriel and Howard Carl. The authors wish to express their appreciat,ion to M. J. Peterson for the spectrographic analysis and to H. TT’. Jaffe for the spectroscopic chrclr of residues for lithium. LITERATURE CITED
0.4
0.8
Mg. NoCl ADOEO
Figure 4. Effect of Sodium Chloride
0.4
0.8
MQ. K C I ADDED
Figure 5. Effect of Potassium Chloride
(1) Caley, E. R., and Elving, P. J., “Inorganic Synthesis,” Vu1 1, p. 1, New York, McGraw-Hill Book Co., 1939. (2) Fletcher, M.H., ANAL.CHEM.,21, 173 (1949). (3) Fletcher, 11. H., White, C. E., and Sheftel, M. S.,IND. ENG. CHEM.. ANAL. ED.. 18. 1’79 11946). (4) Zbid., p . 204. ( 5 ) Kallmann. S., Ibid., 16, 712 (1944). (6) Merritt, L. L., Ibid., 16, 758 (1944)
(‘7) Scott, W. W., “Standard Methods of Chemical .%nalysia.” ed. by N. H. Furman, Vol. 1, 5th ed.. p. 890, New Yoik, D. (8)
Van Nostrand Co., 1939. TT’hite, C. E., and Lowe, C. S..IND.ENG.CHEX.,ANAL.ED., 13, 809 (1941).
Zinc. Merritt ( 6 ) has shown that oxine is a very sensitive quantitative reagent for zinc. It is necessary, therefore, that the zinc be renioved as far as possible. Experiments showed that on starting with 0.046 gram of zinc, about 400 miwograms remained in solution after a hydrogen sulfide precipitation; after precipitation of 0.046 gram of zinc with oxine only 7 3 micrograms remained in solution. Tests also showed that if residues from these separations were made up to 100 ml. with alcohol, aliquots of the solution from the hydrogen sulfide separation greater than 0.2 ml. would disturb the lithium determination; more than 1 ml. of the solution from the oxine separation could be tolerated. I n an actual determination not over 0.3 ml. of the sample solution would be used; therefore, oxine provides a safe separation. The amount of zinc left in solution by the hydrogen sulfide separation is much greater than the solubility product would indicate. This may be d u to ~ colloidal zinc sulfide passing through the filter; however, usual care was used in this procedure. SEPARATION OF LITHlUM
Several so1vent.s were investigated for the separation of lithium chloride from the chlorides of sodium and potassium. After extraction with the solvent, it was necessary to heat the mixture
RECRIVLD
AIas 18. 19.50.
Determination of Nitrate in Plant Material-Correction In the paper “Determination of Nitrate in Plant Material” by C. 31. Johnson and Albert Ulrich [ A N ~ LCHEM., . 22, 1526-9 (1950)], the folloiving errors in statistical terminology appear: In TaLle I and also in Tahle 11, footnote should read, u = ____ iristcad of standard yi.cc’y3, 1;. The remainder of the footnote is correct.
st,andard deviation = I ---= deviation = __
v‘;
7 1 - 1
u =
In Table 111,footnote d l a portion should read, C.L. = niean * t
z,
rather than C.L. 4%
=
mean *t%.
The remainder of the
footnote is correct. All calculations were hased on thc correct formulas and are correct. C. M. J O H N ~ O N
