INDUSTRIAL AND ENGINEERING CHEMISTRY
414
TABLEV. PRECISION OF METHOD APPLIEDTO TYPICAL SAMPLES Deviation from Mean
Deviation Bismuth from Mean
Sample Designation
Copper
Commercial lead Av.
0.065 0.063 0.064
4-0.001 -0,001 *0.001
0.014 0.015 0.0146
-0.0002 -0,0002 -0,0002
Av.
0,056 0.056 0.056 0.057 0.0562
0.124 0.124 0.122 0.122 0.123
%
%
No 1 i%'antimony lead
+0.0008
+=0.0004
-0.0005 +0.0005 t0.0005
fO.001
+0.001
-0.001 -0.001 tO.001
fO.001
0.064 0.060
Av.
0.059 0.059 0.0593
fO.0007 -0.0003 -0.0003 *0.0004
0.065 0.063
4-0.002 h0.002
-0.001 +0.001 *0.001
0.038 0.034
Av.
0.022 0.024 0.023
+0.002 -0.002 t0.002
No. 2 l%'antimony lead
0.060
40-60 lead-tin solder
0.036
-0.003
VOL. 8, NO. 6
The data presented in Tables I to V indicate that there are no significant constant errors in the method. The precision of Procedure B, in which hydrofluoric acid is used, is somewhat lower than Procedure A because of the poorer character of the plates obtained in this solution. I n Procedure B there is also more danger of loss of metal by re-solution during the washing of the plate. The precision limits of Procedure A are as follows: bismuth, *50 parts per thousand when the bismuth content of the sample is 0.05 per cent; copper, *30 parts per thousand when the copper content is 0.05 per cent. The precision limits of Procedure B are as follows: bismuth, * 100 parts per thousand when the bismuth content is 0.05 per cent; copper, *75 parts per thousand when the copper content is 0.05 per cent.
Literature Cited were boiled to remove nitrous acid fumes, and were then diluted to approximately 300 ml., cooled to 65' C., and analyzed as described in Procedure A. The results are shown in Table
111. Ten grams of a 50:50 lead-tin alloy were dissolved in a nitric-hydrofluoric acid mixture as recorded in Procedure B. The solution was diluted, 2 grams of tartaric acid were added, and the solution was electrolyzed a t 65" to 75' C. in the leadplatinum cell. The plate was discarded. Known amounts of copper, bismuth, and silver as nitrates were added to the purified solution. Copper and bismuth were then determined as described in Procedure B. (See Table IV.)
(1) Collin, Analyst, 55, 312 (1930). (2) Ibid., 55, 495 (1930). (3)Ibid., 55, 680 (1930). (4) Ibid., 56,90 (1931). (5) Francois, Ann. chim., 191 12, 178 (1919). (6) Hollard, Bull. soc. chim. de Paris, [3]29, 116 (1903). (7) R.Norton and Co., Worcester, Mass. (8) Sand, Analyst, 55, 309 (1930). (9) Schleicher, 2. anal. Chem., 83, 127 (1931). (10) Tutundzic, 2. anorg. allgem. Chem., 190, 59 (1930). (11) Ullgren, 2. anal. Chem., 7,442 (1868). RECEIWD August 11, 1936. Presented before the Division of Physical and Inorganic Chemistry at the 91st Meeting of the Amerioan Chemical Society, Kansas City, Mo., April 13 to 17, 1936.
Separation of Strontium, Barium, and Lead from Calcium and Other Metals By Precipitation as Nitrates HOBART H. WILLARD AND EDWIN W. GOODSPEED, University of Michigan, Ann Arbor, Mich.
I
3 T H E quantitative separation of strontium from calcium
there has always been considerable difficulty due to the fact that most of the properties of strontium are very closely related to those of calcium. Thus, although the determination of either strontium or calcium alone is easily carried out, the task of determining them when taken together presents greatly increased difficulty. By extracting the mixture of anhydrous nitrates with absolute alcohol, in which strontium nitrate is not very soluble, Stromeyer (5) separated strontium from calcium. Rose (4) improved this method by using a mixture of equal parts of absolute alcohol and anhydrous ether, in which strontium nitrate is much less soluble than in alcohol alone. With certain modifications introduced by Fresenius (I), this method is the one most used today. Rawson (3)suggested the use of concentrated nitric acid as the extracting solvent. Since precipitation methods are known to be superior to extraction methods, both in accuracy and ease of manipulation, it seemed desirable to develop such a method for the separation of strontium from calcium and other metals.
Preparation and Standardization of Solutions c. P. strontium nitrate was dissolved in water and filtered to remove any insoluble impurities. The strontium was precipitated as the nitrate by the slow addition, with stirring, of enough 70 per cent nitric acid to bring the acid concentration of the solu-
tion up to about 40 per cent. The strontium nitrate was filtered off, washed with 40 per cent nitric acid, dissolved, and then reprecipitated a second time in a similar manner. The solution of strontium nitrate was standardized by pipetting 10-ml. samples into weighed crucibles, adding a few drops of nitric acid, and evaporating to dryness on a very low-temperature hot plate. The strontium nitrate was then dried 2 hours at 130' to 140' C., and weighed. This standardization was checked by precipitating 10-ml. samples as the sulfate with a tenfold excess of sulfuric acid from a 50 per cent alcohol solution. After standing 12 hours, the precipitate of strontium sulfate was filtered throu h a Gooch crucible and dried 1 hour in a muffle heated to 500" The results obtained by the two methods agreed within 0.1 mg. Solutions of barium nitrate and lead nitrate were purified in a similar manner and standardized by evaporating to dryness and weighing as the nitrates. The calcium nitrate solution was prepared from reagent quality calcium carbonate by dissolving it in dilute nitric acid. It was purified by adding 100 per cent nitric acid until the acid concentration was 80 or 81 per cent, the volume being such that a small amount of calcium nitrate was precipitated. After standing 0.5 hour the precipitated calcium nitrate (along with any barium or strontium nitrates that might have been present) was filtered off and discarded. The filtrate was evaporated t o dryness t o remove the nitric acid, and the calcium nitrate was then dissolved in water. The solution was standardized by precipitating IO-ml. samples as oxalate, followed by ignition at 500' C. to the carbonate. Although fuming nitric acid as purchased could be used SUCcessfully for obtaining the desired acid concentration, in most of this work freshly prepared 100 per cent nitric acid was employed. This was prepared by distilling a mixture of c. P. sodium nitrate
8.
NOVEMBER 15, 1936
ANALYTICAL EDITION
and c. P. concentrated sulfuric acid in an all-glass distilling apparatus, the flask having a capacity of 2 liters. A convenient charge consisted of 500 grams of sodium nitrate and 500 ml. of sulfuric acid.
Experimental Attempts were f i s t made to precipitate strontium nitrate from solution in an organic solvent. The general method used was to evaporate a sample of strontium nitrate to dryness with a n excess of perchloric acid and dissolve the strontium perchlorate in the organic solvent. Strontium was then precipitated as the nitrate by the slow addition of a mixture of the solvent and 100 per cent nitric acid. The solvents tried were a mixture of absolute alcohol and anhydrous ether, normal butyl alcohol, a mixture of normal butyl alcohol and anhydrous ether, tertiary butyl alcohol, carbitol, and butyl carbitol. Incomplete precipitation and the formation of slimy, unfilterable precipitates caused this work to be abandoned. It was found that dry strontium nitrate could be dissolved in a very little water and was precipitated in a dense granular form by the addition of nitric acid, whereas calcium nitrate proved to be much more soluble. The precipitate showed no tendency whatever to stick to the sides of the beaker, and was readily washed into the filtering crucible with a few jets of acid of the same concentration as that used for the precipitation. The wash bottle was a 250-ml. Erlenmeyer flask fitted with a two-hole rubber stopper. A rubber bulb furnished the necessary air pressure. The rubber bulb and stopper are attacked slowly by the nitric acid vapors but, if rinsed after being used, they last a long time. The solutions were filtered through Gooch crucibles with rather thick pads. The recipitates were dissolved out and the pads used repeatedly. n! dissolving the precipitates, hot water with a little nitric acid roved to be more satisfactory than hot water alone, especially if metals other than strontium were present. The strontium nitrate precipitate was dried 2 hours at 130" to 140' C , but longer drying does no harm. The concentrations of the nitric acid solutions were obtained from tables (d), after determining the specific gravity of the pure solutions by means of a hydrometer having 8 range of 1.4 to 1.6. (For concentrations below 70 per cent a hydrometer with a range of 1.2 to 1.4 was used.) A few specific gravity determinations were made with a pycnometer and the values were found to check those obtained by the hydrometer method within 0.002. We may assume, then, that the acid concentration is always within 1 per cent of the stated value, and usually within 0.5 per cent. Precipitations were first made by dissolving the dry salts in a definite volume of water, adding a known amount of 70 per cent (ordinary concentrated) nitric acid, which caused most of the strontium nitrate t o precipitate, and then adding a definite amount of 100 per cent nitric acid to bring the acid concentration to the desired value. It was simpler, however, to dissolve the dry salts in a definite volume of water and add enough 100 per cent nitric acid, drop by drop, with constant stirring, to bring the acid concentration up to the desired value. This was determined by adding to the proper volume of water increasing amounts of acid and determining the specific gravity with a hydrometer, applying a temperature correction. It is convenient to make all the additions from a buret. If 70 per cent nitric acid is used, each bottle must be tested, likewise the c. P. fuming nitric acid of commerce. Precipitation was complete within 30 minutes, except that for very small amounts i t was necessary to stir the solution mechanically for 45 minutes. EFFECT OF VARYING ACIDCONCENTRATION. I n determining the effect of acid concentration all precipitates stood 0.5 hour or more before filtering, were transferred and washed with about 18 ml. of acid of the same concentration as that used during the precipitation, were then dried for 2 hours a t 130" to 140" C., and weighed. The volume during precipitation was about 18 ml. The results are shown in Table I. As an additional check the filtrates and washings were evaporated to dryness and taken up with water. Any barium
415
or strontium present was precipitated as sulfate, the latter from a 50 per cent alcohol solution. No barium sulfate could be detected in the filtrates from acid concentrations of 76 per cent or higher. With strontium a very faint turbidity was noticed with 70 per cent acid, less with 80 per cent, and none with higher concentrations. I n the case of lead, noticeable precipitates were obtained with ammonium sulfide in all filtrates up to, and including, the 80 per cent acid. In the others no precipitate settled out, but the solutions darkened considerably. .There was no difference in the amount of darkening between those obtained with the 83 per cent and the 87 per cent acids, but that with the 82 per cent was somewhat darker. In general, the solubility of lead nitrate in 84 per cent nitric acid corresponds to about 0.1 mg. of lead per 20 ml. The solubility increases considerably with higher temperatures, but is reduced to a negligible amount when the solution is cooled in ice. It would seem, then, that 76 per cent nitric acid suffices for barium, but 80 per cent acid is required for strontium, and 84 per cent for lead. TABLEI. EFFECTOF ACID CONCENTRATION ON PRECIPITATION OF STRONTIUM, BARIUM, AND LEADNITRATES (All prec.ipitations were made in a volume of about 18 ml. a t 20' t o 25" C. The precipitates were transferred and washed w,ith about 18 ml. of acid of the same concentration as that used for the precipitation.) Acid, per cent 66 69 74 78 80 83 85 87 Sr found, error mg. (67.9 mg. t a i e n i n -1.3 -0.3 o o +O.I o . , . each case) -1.7 -0.3 -0.1 0 0 0 ... Ba found, error, mg. 0 0 (56.6mg. taken in -0.8 0 0 0 each case) -0.9"... -0.1 -0.1 -0.1 -0.1 ,. -0.1 P b found. RTPOP. m n . -1.3 - 0 . 9 (10i.7mg.-G-kenk -8.8 -0.2 -0.2 -0.1 each case) -9.5 -1.4 - 0 . 7 -0.4 -0.1 .. -0.1
... ...
..
.. . .... ..
..
Using 77 per cent nitric acid, in which the solubility of strontium nitrate is appreciable, a comparison of the solubility of strontium nitrate in both the precipitating and the wash solutions was made. About 140 mg. of strontium nitrate were dissolved in a little water and the acid concentration was brought up to 77 per cent, the volume being 100 ml. After standing 0.5 hour the precipitate was filtered off and the strontium in the filtrate was determined as sulfate. The precipitate in the crucible was then washed with 100 ml. of 77 per cent nitric acid, and the strontium determined in the washings. The strontium sulfate in each case weighed 0.7 mg., indicating that the wash solution becomes saturated with the nitrate. EFFECT OF TEMPERATURE. Since the separation of strontium from certain metals might be improved by an increase in temperature, a few determinations were made a t 50" and 70" C., these temperatures being maintained for 0.5 hour after precipitation, when the solution was filtered and washed with acid a t room temperature. The results in Table I1 show that temperatures up to 70" C. may be used without causing loss of strontium nitrate. Temperatures above 70" C. were not tried, because above this the nitric acid fumes off rather rapidly. TABLE11. PRECIPITATION OF STRONTIUM NITRATE AT VARIOUS TEMPERATURES FROM 80 PERCENTNITRICACID
-
[Sr(NOa)z taken, 149.3 mg. 61.8 mg.of Sr] Temperature Sr(N0a)l Found Error, Sr 0
c.
Me.
25
149.6 149.4
50
149.2
70
149.2 149.5 149.4
MB. +O.l 0
0 0
+O.l 0
EFFECT OF OTHERANIONS. KO effort was made to determine an all-inclusive list of anions that might be present in the determination of strontium. However, as it was felt that chloride and perchlorate would be frequently encoun-
VOL. 8, NO. 6
INDUSTRIAL AND ENGINEERING CHEMISTRY
416
tered, tests were made in their presence. The amounts of these acids taken were greatly in excess of that required to convert all the strontium to chloride and perchlorate, and were added after evaporation to dryness, so that the full amount of acid was present during precipitation. Precipitation was made in 80 per cent nitric acid in a volume of 18.2 ml. Upon taking 0.76 ml. of concentrated hydrochloric acid and 139.9 mg. of strontium nitrate, 140.0 and 140.1 mg. of strontium nitrate were found. When 149.3 mg. of strontium nitrate were taken with 0.75 ml. of 70 per cent perchloric acid, 149.5 and 149.3 mg. of strontium nitrate were found. Evidently these ions exert no harmful effect on the determination of pure strontium. TABLE 111. SOLUBILITY OF CALCIUM NITRATEIN NITRICACID Acid Concentration
% 77 79 81 83 85
Calcium Dissolved Mg./ml. 26.5 10.0 6.0 1.9 1.1
SOLUBILITY OF CALCIUM NITRATEIN NITRIC ACID. The solubility of calcium nitrate in nitric acid of various concentrations was determined by putting an excess of finely pulverized calcium nitrate in glass-stoppered cylinders containing the nitric acid. The mixture was kept in a thermostat a t 25' C. for several hours with frequerzt shaking. Samples of 50 ml. were pipetted out, the nitric acid was evaporated, and the calcium determined by precipitation as the oxalate followed by ignition a t 500" C. to the carbonate. The results, shown in Table 111,indicate that as low an acid concentration as possible should be used in separating strontium from calcium.
As was to be expected, the lower acid concentrations gave better separations, but any concentration in the range of 79 to 81 per cent is satisfactory. Above 81 per cent the solubility of calcium nitrate is too small, and below 79 per cent the solubility of strontium nitrate becomes appreciable. Table IV shows the results of some separations of strontium from calcium. The dry nitrates were dissolved in 10.0 ml. of water, and the strontium nitrate was precipitated by adding 26.0 ml. of 100 per cent nitric acid drop by drop with mechanical stirring. This gave an acid concentration of 80 per cent. After the addition of the acid the solution stood 0.5 hour, before filtering through Gooch crucibles, the precipitate being transferred with jets of 80 per cent nitric acid, then washed 10 times in the crucibles with approximately 1-ml. portions of 80 per cent nitric acid. The strontium nitrate was dried 2 hours a t 130" to 140" C. In making double precipitations the precipitates were dissolved directly into a beaker placed under a bell jar, using hot water which had been slightly acidified with nitric acid. In each case pure strontium was carried through the same process to ensure that the results obtained were not due to compensating errors. TABLE Iv. Sr
Me. 2.14 2.l"Pb 2.1"
It was found essential to add the nitric acid drop by drop with constant stirring, in order to avoid carrying down appreciable amounts of calcium. Separations of strontium made by the addition of the acid in a stream from a buret with a little stirring gave results 1.7 mg. too high, while identical separations made with drop-by-drop addition of the acid with constant vigorous stirring gave correct results. The greater the volume of the solution a t the time of precipitation, the better are the separations obtained. However, because of the slight solubility of strontium nitrate and the greater ease in transferring the precipitate from a small beaker, total volumes under 40 ml. were usually employed and a 50-ml. beaker was used. Best results were obtained by precipitating the bulk of the strontium with 70 per cent nitric acid and then using 100 per cent acid to bring the concentration up to the desired value. However, it is simpler to eliminate the use of the 70 per cent acid, and results practically as good may be obtained using only 100 per cent acid, provided it is added very slowly and with vigorous (preferably mechanical) stirring. A solution in which the acid concentration is 80 per cent may be obtained by dissolving the salt in 10.0 ml. of water and adding 26.0 ml. of 100 per cent nitric acid. Separations were made in which the time of standing after precipitation was varied from 0.5 to 5 hours. There is a slight downward trend in the amount of calcium carried down as the time of standing is lengthened. Evidently on standing some of the co-precipitated calcium nitrate is gradually dissolved. Separations were tried a t elevated temperatures, but no appreciable advantage is gained by precipitating hot. Separations were made using various acid concentrations.
SEPARATION O F STRONTIUM FEOM CALCIUM
Ca
Mo. 50 600
None
12.4
50
12.4
None
61.7
50
61.7
None
First Precipitation Found, Sr Error, Sr
Mo
.
2.8 2.8 3.2 4.0 2.1 2.1 12.9 12.8 12.4 12.3 62.0 61.9 61.7 61.7
154.6
Second Precipitation Found, Sr Error, Sr
Mo.
Ma.
Mo .
$0.7 +0.7 $1.1 fl.9 0 0 $0.5 1-0.4
2.0 2.0 2.3 2.3 2.0 2.0 12.4 12.3 12.3 12.3 61.5 61.6 61.6 61.7 154.2 154.2 154.4 154.3 928.7 928.7 928.7 928.6
-0.1 -0.1 f0.2 $0.2 -0.1 -0.1 0
0
-0.1 $0.3 $0.2 0
0
$0.2
-0.1 -0.1 -0.1 -0.2 -0.1 -0.1 0 -0.2 -0.2
154.5 $0.1 154.4 0 0 154.4 0 None -0.1 154.4 929.7 +l.O 0 $1.2 929.9 50 0 928.7 928.8 $0.1 0 -0.1 928.6 -0.1 None 928.7 0 61.7 Second pptn. not needed 0 25 61.7 61.7 62.7 11.0 61.6 -0.1 62.7 $1.0 61.7 0 125 61.7 +4.0 65.7 61.8 $0.1 $3.6 65.3 61.7 0 600 61.78 -0.1 61.5 -0.2 61.6 -0.1 61.6 61.6 None -0.1 61.7b a Mechanically stirred for 45 minutes after precipitation. 6 30 ml. of water and 78 ml. of 100 per cent n1tri.c acid, giving 80 per cent acid for the first preci itation; second precipitation, 10 ml. of water, 26 ml. of 100 per cent a c X 154.4
Separation of Strontium from Calcium
Taken
50
Various amounts of strontium may be separated from 25 mg. of calcium with only one precipitation. If more than 25 mg. of calcium are present double precipitations are necessary, and if the amount of calcium is very large the volume of the solution must be increased.
Separation of Strontium from Metals Other than Calcium Solutions of many metals were made up, usually from the nitrates. The solutions were made from c. p. chemicals, and as first prepared were not purified in any way. If high results were obtained in a separation, the solution of the metal was purified by treatment with 80 per cent nitric acid, fiItering off any precipitate that was obtained. The solutions were not analyzed as t o metal content, but were probably accurate to within 10 per cent. Generally the dry salts were dissolved in 3.0 ml. of water and precipitated with 5.5 ml. of 71 per cent nitric acid, and the concentration was brought t o 80 per cent by the addition of 10.0 ml. of 100 per cent nitric acid. The precipitate was allowed to stand 0.5 hour, and then was transferred and washed with about 18 ml. of 80ger cent nitric acid, after which it was dried for 2 hours at 130 to 140" C . Solution of the salts in 3.0 ml. of water was readily accomgl'ished. by adding 1.0 ml. of 71 per cent nitric acid and heating a ew minutes. In the list of metals separated from strontium, the
ANALYTICAL EDITION
NOVEMBER 15, 1936
TABLEV. SEPARATION OF STRONTIUM FROM VARIOUS METALS [In each case Sr(X0a)z taken, 149.3 mg. Salt Added Metal C o n t e n t
61.8 mn. of Srl Error. Sr
Mo.
MU.
Al(N0a)a
25
+0.2 0
.41( NOa)a
750
0
NHiNOa
b
-
-0.1 0 -0.1 +0.1 $0.1 0 -0.1 +0.2 $0.2
500
SbCls
500b
HaAsO4
500
Be(N03)~
500
Bi(NOd3
500
0
Ca(N0s)z
25
Cd(N0a)z
500
-0.2 $0.2 +o. 1 0 -0.1
Ce(N0d.r
500
+0.5 +0.5
Cr ( NOda
100
Co(N0s)z
500
Cu(N0a)z
250
Cu (NOa)z
500" 500
La(N0a)a
500
LiNOa
150
Mg(N03)Z
500
$0.1
+O,l 0 0
$0.1 $0.1 0 -0.1 -0.1 0 $0.1 0 -0.1 -0.1
Determination of Barium and Separation from Other Metals
0
+O.l
Mn(NOa)z
500
Hg(N0a)z
500
Ni(N0a)z
2000
0
$0.1
The precipitate of barium nitrate is of the same dense crystalline form that characterizes strontium nitrate, and it is reasonable to assume that barium may be separated from all the metals from which strontium may be separated. Since a lower acid concentration may be used for barium, even better separations would probably be possible. Table VI shows the results of a few separations that were made.
0 0
n
$0.5
+0.4
KNOa
500
HzSeOa
500
0
AgNOa
150
$0.2 $0.2
NaNOa
300
HzTe03
75
$0.1
$0.3
+0.2 0 0 0
TlCls
500
TlNOa
500
+0.1 +0.1 +0.2
SnCh
500
-0.1
UOz(NOa)z
500
0 $0.1
500
0
The dry salts were dissolved in 5.0 ml. of water. The barium nitrate was partially precipitated by the slow addition, with stirring, of 3.0 ml. of 70 per cent nitric acid, after which 11.0 ml. of 100 per cent acid were added in the same manner to bring the acid concentration up to 76 per cent. After standing 0.5 hour the barium nitrate was filtered off, washed ten times with 76 per cent nitric acid, and dried for 2 hours at 130' to 140' C.
0
0
Zn(N0a)z Precipitated a t 70' C. 1.5 ml. of HCl added.
separations from these metals were made a t 70" C. The solutions were allowed to stand for 0.5 hour a t the same temperature, after which they were filtered through a warm crucible and washed with acid a t room temperature, The metals from which separations were made, as shown in Table V, are the largest amounts possible in a volume of 18.5 ml. of 80 per cent nitric acid, with the exception of those metals from which the separation of 500 mg. or more was possible. No amounts greater than 500 mg. were tried except in the case of nickel, where the maximum used was 2000 mg. If larger volumes were used, separations from larger amounts of the metals would be possible. The only metal tried from which strontium could not be separated was titanium (except for barium and lead which were quantitatively precipitated). RECOMMENDED PROCEDURE. Evaporate the metallic chloride, perchlorate, or nitrate (preferably the latter) to dryness; dissolve in 10.0 ml. of water; precipitate the strontium nitrate by adding 26.0 ml. of 100 per cent nitric acid, drop by drop, with constant (preferably mechanical) stirring; allow to stand 0.5 hour; filter through a Gooch crucible, transferring the precipitate with a jet of 80 per cent nitric acid, and washing ten times with acid of the same concentration, using about 1ml. each time; dry at 130" to 140' C. for 2 hours; weigh as Sr(NO&. Larger volumes and double precipitations may be used if necessary.
$0.1
Fe(NO3)s
417
It did not seem necessary to try other separations. Barium can undoubtedly be separated from all the metals from which strontium was separated (Table V).
TABLEVI. SEPARATION OF BARIUMFROM VARIOUS METALS [In each case Ba(N0a)z taken, 107.7 mg. = 56.6 mg. of Bal Metal Ba(N0s)z Error, Salt Added Content Found Ba
MO.
1x0.
Mg.
500
107.7 107.6 107.9
0
Bi(N0a)a Ca(N0a)z Cd(N0s)a
125 500
Ni(N0dz
500
Pure Ba(N0a)a
...
lo!.!? 1UI.Y 107.7 107.8 107.8 107.6 107.5
0
$0.1 0 $0.1 0 0 0 0
-0.1
only ones which could not be dissolved in this volume were 500 mg. of beryllium nitrate, 500 mg. of ferric nitrate, and 2000 mg. of nickel nitrate. For these amounts of beryllium, iron, and nickel, larger initial volumes were used, the amount of 71 per cent acid being decreased, and the 100 per cent increased, in order t o keep the final volume the same. In the case of antimony and tin, as it was found advantageous t o have some hydrochloric acid present, the salts were dissolved in a mixture of 1.5 ml. of water and 1.5 ml. of concentrated hydrochloric acid. Nearly all precipitations were made a t room temperature but in some cases a large temperature effect was noticed. This was especially true with copper and aluminum, so a few
Determination of Lead and Separation from Other Metals Table VI1 shows the results of a few separations of lead from various metals. The dry salts were dissolved in 2.5 ml. of water, and the acid concentration was brought to 84 per cent by the drop-by-drop addition of 5.0 ml. of 70 per cent nitric acid and 13.0 ml. of 100 per cent acid. After standing 0.5 hour at room temperature, the lead nitrate was filtered off, washed ten times with small portions of 84 per cent nitric acid, and dried for 2 hours at 135' c. Because the presence of chloride gives low results in the determination of lead, this must be absent. This fact prevents the separation of lead from antimony and tin. A separation from all the other metals shown in Table V would no doubt be possible. In some cases a t least, separations are made from highly supersaturated solutions of the metals. For instance, in the separation of lead from copper, a crystal of copper nitrate was added to the filtrate and caused a large amount of copper nitrate to precipitate. This was filtered, dried, and with an indefinite amount of water of crystallization weighed 0.7 gram.
INDUSTRIAL AND ENGINEERING CHEMISTRY
418
TABLEVII. SEPARATION OF LEADFROM. VARIOUS MBTALS [In each case Pb(N0a)z taken, 162.5 mg. = 101.7 mg. of P b ] Salt Metal Pb(N0a)z Error, Added Content Found Pb Mg.
HaAsOa
500
Bi(N0s)a
500
Ca(N0a)a
15
Cd(NOd2
500
Cu(N0a)z
300
Hg(NOs)z
500
Pure Pb(N0da
...
Mo.
Mo.
162.3 162.4 162.7 162.9 163.0 162.9 162.2 162.3 162.2 162.2 162.4 162.5 162.4 162.4
-0.1 -0.1 f0.l +0.2
+0.3 +0.2 -0.2 -0.1 -0.2 -0.2 -0.1 0
-0.1 -0.1
Summary Attempts to separate strontium from calcium by precipitation of strontium nitrate with nitric acid in organic solvents resulted in incomplete precipitation and slimy, unflterable precipitates Strontium nitrate can be completely precipitated in a dense, crystalline form from a water solution, and separated from twenty-eight metals by the very slow addition of 100 per cent nitric acid until the resultant solution contains not
.
VOL. 8, NO. 6
less than 79 per cent: to separate barium from the same metals, 76 per cent acid suffices; to separate lead, 84 per cent is necessary, but chloride makes impossible a separation of lead from tin and antimony. The precipitate should stand a t least 30 minutes before filtering; if it is very small, the solution should be stirred mechanically for 45 minutes. The nitrate is dried 2 hours at 130" to 140" C. Temperatures up to 70" C. do not increase appreciably the solubility of strontium nitrate but may increase that of other nitrates. The solubility of calcium nitrate decreases rapidly with increasing acid concentrations. A maximum of 80 per cent acid is recommended.
Literature Cited (1) Fresenius, 2.anal. Chem., 32, 189 (1593). (2) Lange, "Handbook of Chemistry," p. 853, Sandusky, Ohio, Handbook Publishers, Ino., 1934. (3) Rawson, J. 8oc. Chem. Ind., 16, 113 (1597). (4) Rose, Ann. Physik. C h m . , 110,296 (1860). (5) Stromeyer and Pfaff, "Handbuoh der analytiaohen Chemie," Vol. I, p. 412, 1821. REICEIVED August 26, 1936. Presented before the Diviaion of Physical and Inorganic Chemistry a t the 87th Meeting of the Amerioan Chemical Society, St. Petersburg, Fla., March 26 to 30, 1934.
Determination of Phthalate Plasticizers FRANCIS C. THAMES, Naval Powder Factory, Indian Head, Md.
W
HEN the diamyl, dibutyl, diethyl, and dimethyl esters of phthalic acid are used to plasticize cellulose nitrate they may be determined by extraction and saponification. However, if the cellulose nitrate plastic also contains aromatic nitro derivatives, such as those of benzene, toluene, and xylene, the determination of the phthalate plasticizer becomes more difficult. These nitro compounds are soluble in the plasticizers and are also mutually soluble with them in solvents. They therefore cannot be separated by difference in solubilities. When the alkali is added for the saponification of the ester plasticizer, in the presence of these nitro compounds, colored additive compounds of the alkali and nitro derivatives are formed (4). These colored compounds cannot be separated from the plasticizer by solvents and only a trace of them is necessary to interfere with the titration of the alkali after saponification. Therefore, a method for the determination of the phthalate plasticizers, in the presence of aromatic nitro derivatives, was sought.
Experimental Unable to determine the phthalate esters in this mixture by saponification, a gravimetric method was developed. Barium phthalate is regularly referred to in organic chemistry texts (1, 2) as an insoluble salt of phthalic acid. It will not precipitate when barium chloride is added to acid solutions of phthalic acid, but phthalic acid itself is precipitated. The solution must be neutral to precipitate barium phthalate. Following the procedure of Ekeley and Banta (S), barium nitrate was added to a solution of sodium phthalate. On boiling, a barium salt was precipitated, which analyzed 51.41 per cent barium oxide compared with 50.89 per cent barium oxide theoretical. In 100 cc. of water a t 20" C., 0.2760 gram of this salt was found to be soluble, in spite of the constant reference to barium phthalate in the literature as an insoluble salt of phthalic acid. Since barium phthalate
precipitates only in neutral solutions, allowing the precipitation of other barium salts, and because of its solubility, it was eliminated as a means of precipitating phthalic acid. Precipitation of phthalic acid as lead phthalate proved to be more favorable than the barium precipitation. Lead phthalate was prepared from phthalic anhydride and lead nitrate, and analyzed 56.55 per cent lead compared with 55.82 per cent lead theoretical. It was also made from saponified dibutylphthalate and lead nitrate and upon analysis gave 55.94 per cent lead. Lead phthalate is a white crystalline compound, of which 0.0020 gram is soluble in 100 cc. of water a t 20" C . It is soluble in nitric acid but insoluble in dilute acetic acid. Because of its low solubility and ease of formation, lead phthalate was adopted as a means of precipitation of phthalic acid. Lead acetate was later used in place of lead nitrate, as the nitric acid left from this reagent interfered with the precipitation of lead phthalate. It was also decided to reprecipitate lead phthalate as lead sulfate to eliminate errors that might be introduced by insoluble organic compounds. The phthalic acid could not be liberated quantitatively by the saponification of the ester in the presence of nitro compounds, therefore i t was liberated from the ester plasticizer by the oxidation of the aliphatic side chains by nitric acid. Crystals were obtained by adding 30 cc. of concentrated nitric acid to approximately 1 gram of dibutylphthalate and evaporating to dryness on the steam bath. These crystals were identified as phthalic acid, according to Mulliken (6),by being converted to o-phthalanil, melting a t 205" C. A trace of nitrophthalic acids was also formed. Oxalic acid was found to be present as a product of the side-chain oxidation of the phthalate esters of the higher alcohols. Oxalic acid must be removed before the lead precipitation because lead oxalate has properties similar to those of lead phthalate. This removal of oxalic acid was accomplished by a second oxidation, using potassium permanganate.
