enon observed by Davis and Schuhmann (Q), who found that tertiary amines give colors different from secondary amines in nonaqueous solutions containing bromophthalein magenta. They noted that the wave length of maximum absorption with tertiary amines was approximately 40 mp lower than that with secondary amines. The molar absorbance was less for the tertiary amines than for secondary amines. Table V lists the rcsults obtained with the proposed method on known mixtures and commercial samples. The reproducibility of the outlined procedure is estimated a t 50.05% absolute. The method should also be applicable to low molecular weight amines, if equivalently smaller sample sizes are used. The method was applied to a sample of n-butylamine of unknown purity and to mixtures containing this amine and di-la-butylamine. The re-
suits indicated thRt di-la-butylamine gives absorbance vaiues close to those obtained with the same equivalents of didodecylamine. On the other hand, aromatic secondary amines are apparently too weakly basic to be de-
Table
V.
Analysis of Purified and Commercial Amines
Samp1ea 1. Dodecylamine
+ +
Secondary Amine Found, yo 0.727’
didodecylamine 0.66 2. Dodecylamine 0.29% Didodecylamine 0.28 3. Dodecylamine 0.10 4. Dodecylamine 0.50 5. Octadecylamine 0.30 6. Tallow primary amine 0.80 7. Tallow primary amine 0.10 8. Tallow primary amine 0.48 a 1 and 2, purified amines; 3 through 8, commercial distilled amines.
tectra :his method. l\ilixttriws containing slethybniline and aniline gave no m o r . LITERATURE CITED
( I ) Ilritchiield, F. E., Johnson, J. A N A L .CHEM.28, 430 (1956). (2) [bid., 2 9 , 957 (1957). (3) Crilles, E. C.. Waddington, D. . -4naI. Chim. Acta 15, 158 (1956). (4) Davis, M. M., Schuhmann, P. J. Research Natl. Bur. Shndarda
B.. J., J., 39,
221 (19471. ( 5 ) Hershenson, H., Hume, D., ANAL. CHEM.29, 16 (195i). (6)Jackson, J., Ibid., 25, 1764 (1953).
(7) Stanley, E. I,., Rmim, H., Gove, J. L., Ibid., 23, 1779 (1951). (8) Wagner, C. D., Brown, R. H., Peters, E. D., J. Am. Chem. SOC.69,
2609 (1947). (9) Wagner, C.
D., Brown, R. H., Peters, E. D., Ibid., 69, 2611 (1947).
RECEIVEDfor review .4pril 10, 1959. Accepted June 22, 1959. Paper 236 Journal Series, Research Laboratories, General Mills, Inc.
Steam Distillation of Fluorine from Perchloric Acid Solutions of Aluminiferous Ores E. J. FOX and W. A. JACKSON Fertilizer Investigations Research Branch, Soil and Water Conservafion Research Division, U. S. Department of Agriculture, Beltsville, Md.
b An all-glass multiple-unit fluorine distilling apparatus equipped with automatic temperature controls was developed in a study of factors affecting the volatilization of fluorine during the acidulation of phosphate rock. Results obtained with this equipment indicate that the interference of aluminum in the steam distillation of fluorine from perchloric acid solutions of aluminum-bearing rocks is caused by the formation of acid-soluble complex ions of aluminum, fluorine, and possibly other elements that greatly reduce the partial pressure of fluorine compounds in the gas phase above the distilling acid solution. A procedure for simultaneous double distillation to speed up the operation is described.
T
HE interference of aluminum and
silicon in the determination of the fluorine content of rock by distillation from perchloric acid solution and in the titration of the distillate with thorium nitrate has long been recognized (25). The exact nature of the interference, however, is not apparent from a perusal of the several procedures that have been suggested to overcome the di5culties
engendered by the presence of these elements in fluorine-bearing materials. Dahle and Wichmann (3) found that aluminum salts retard the rate of fluorine distillation, while Reynolds (16) found that hydrous silica adhering to the walls of distilling flasks above the level of the acid solution retains fluorine during distillation from fluorine-rich samples, only t o give it up during the distillation from fluorine-poor samples, thus vitiating the results of both. Willard and Winter (25) attributed interference in the titration with thorium nitrate to the precipitation of a nondissociakd aluminum salt. Hoskins and Ferris (9) determined the permissible limits of concentration of such ions in solution in which fluorine was 50 be titrated. The use of a multiple-unit distilling apparatus such as that described by Reynolds, Kershaw, and Jacob (18) made control of the temperature of the distilling acid difficult, while the use of rubber stoppers and hose connections with perchloric acid was recognized as potentially dangerous ( 1 7 ) and a possible source of error due to their sorption and desorption of hydrogen fluoride. Some of the more recently proposed
procedures for the determination of fluorine in rocks that require fusion prior to distillation are reviewed by Hollingsworth (8) and a high ternperature pyrohydrolysis method especially designed for the assay of aluminum fluoride is described by Haff, Butler, and Bisso (6). A procedure applicable to the analysis of aluminifwous ores decomposed by acid digPstion is described ip. this article. The influcnce of the s l u ~ i n u mion on the distillation cf fluorine from materials decomposed by alkali fusion is also indicated. EXPERIMENTAL PROCEDURE
Improved Bluorine Distillation Apparatus. A sectional drawing of one of the units comprising a multipleunit still is shown in Figure I . .!IC arrangement for mounting the several unit,s i s likewise suqgc,stcd by the cross-sectional outline of the wooden framework of the apparatus in this figure. Castalloy clamps were used to fasten the steam-generator flasks to the frame. The distilling flasks 5 cm. in diameter were blown from the female sections of 29/42 standard-taper borosilicate glass ;oink to F,t 50-ml. Mas-Col heating mantles. The 7-mm. outside diYOL. 31, NO. 10, O C T O B E R 1959
e
1657
timeter steam-inlet tube was. drawn down to a 1-mm. opening at the tip to create a slight back pressure in the steam iine. Because two distilling flasks are served by one steam generator, the tips of the steam-inlet tubes must be matched to deliver equal rates of flow. This may be done by drawing the taper of the tip and dropping a 1-mm. steel drill into the tube as an internal gage. I n fire polishing the tip, care should be taken not to alter the dianieter of the 4)pening. .\fercurj.-filled thermoregulators were chstendeci verticdly downward through the still heads, made from the male scctions of the standard-taper joints. The still head was made integral with tiit: condenser tube. It is recominended, however, that ball and socket or standard-taper joints be used to coniiwt the distilling flasks to the con_Iensers. Dual condensers (only one h b e is shown in the drawing) were used to make more work space available for iiiountiiig and dismounting the distilling flasks. This arrangement saves space h u t makes repairs and replacements inore difficult. The wiring circuit for the heating iiiantles and thermoregulators (Figure 2 ) shows a i35volt autotransformer divided into three 45volt sections, each of which serves a pair of flasks. This arrangement gives maximum Hexibility in the operation of one, two, or three pairs of flasks simultaneously. The 2 h h m resistors shunted across the reiay switches reduced the current density when the switch was open to a mint slightly below tha.t needed to iriaintain the desired temperature, while the current density with closed switches was slightly higher than that required to maintain the set temperature. With this arrangement temperature fluctuations were reduced from +1.5' to riLo.2" C. a t 125" C. This is an unnecessary refinement for ordinary anaiytical purposes, but is a decided improverne:it in temperature control for research purposes. ?est Materials. I n addition to the Yiuminum, sodium, and calcium fluo:ides and a specially prepared dihydrate of ,:alcium fluosilicate, the materials Ksted in Table I have been *elected for specific reasons for in..lusiou in :his study. 38tionai 3ureau of Standards opal glass :XBS 91) reprrsents one of the a(,,(i-insc:lu!)ll, rnateriais that need to be ;used \c:th alkali before fluorine s~paration i)y distillation. Furnace
Table I.
Sample Nu. - .. 3 HS SI
-1.
P
-5"'
%
~
1658
-
ANALYTICAL CHEMlSTRl
d
1 :
"c
/
i
i
I
Tnblc Top S E C T I O N AA
Figure I. Sectional drawing of fluorine distilling apparatus showing asseml y of a single unit
14°C
Figure 2. Wiring diagram for automatic temperature control of a six-unit assembly
slag (No. 2548) is an example of a glassy type of material amenable to acid digestion in which a high degree of interference with fluorine distillation is Indicated, while Pembroke clay (No. 2335) is a naturally occurring material
Analyses of Selected Test Materials
.%OI, % CaO, % F, % ' Opal giass6.01 10.5 5.72 Li48 Furnace slagk 9.82 2 79 44.8 "a,',? Pembroke clay" 29.0 8.92 1.25 :i7- l.24 Synthetic product 17.9 21 1 21 . 0 - C#.nstituentsnot listed include 8.4870 N*O, 3.25% KZO. Anhiyses furnished by producer. ' From phosphate deposit near Pembroke, Fls. (1'
I
P435, % 0.22 1.12 24.9 12.1
SiO,, % 67.5 40.4 17.5 19.2
containing hignly complex fluoride ions that are readily extracted by acid digestion. The soluble constituents of some silicates may be extracted without sltering the silica skeleton. Thus, acid extraction of greensand leaves a rugged silica residue that has the dimensions and markings of the original glauconite grains and the adsorptive properties of silica gel (2.9). A distinguishing test for this type of silica is its adsorptive capacity for indicator dyes, such as methyl red. A drop of alkali solution added to tinted particles on a microscope slide will reveal the changing color line from surface to center of porous material in contrast t, nonporous quartz sand. Pembroke clay is described by Hill,
carricd over into the condrnser tub(,. Aftcr the danger of frothing has passed. the rate of steam generation should b(. regulated to yield about 100 ml. o! condensate per hour. Afwr 10 to 15 minutes, when the temperature and distillation rate have reached a steady state, samples of the condensate may be taken for the purpose of determining the rate of fluorine distillation a t constant ternperaturo. The equation for the distillation ratc under thrse conditions would take t,he form of - d z / d t = k (a - X )
Figure 3. The system, H4SiFB. 12H20 boiling point
I l l I I I 0 0 0 ~ 0 00
9-m
o m e
4 d
4.0+0*
1 1 1 1 1 I
-
*I
HgF?.2H20 - H Q at the
I N
lm?+an+
c)
lo
N
p + o l $0 y 'ruiionid ionp!say
Figure 4. Steam distillation of fluorine from perchloric acid solutions of sodium fluoride, calcium fluoride, and calcium fluosilicate a t 125" C.
Titration. I n the titration, using sodium alizarin sulfonate (Alizarin Red S) as indicator, the end point is reached slightly below the exact thorium nitrate equivalence of thorium 5uoride. In a least squaresderivation of the, constants for the equation,
y=a+bz
Armiger, and Gooch (6) as pseudomavellite and its silica content was originally considered as a physical impurity consisting of quartz sana. But, upon examination, the perchloric acid-insoluble residue appears to be the porous silica residue of clay The composition of Pembroke clay suggests that it may be formed by h reaction between water-soluble calcium phosphate, clay residued, and waterborne fluoride ions that, replace hydroxyls in the silicate cornpiex. It is a common impurity of phosphate rock, with which it is admixed in natural deposits and probably represents the end product of phosphate fixation in clay soils (20). This thought prompted an attempt to synthesize such a product. The reactants consisted of calcium silicate, aluminum fluoride trihydrate, and phosphoric acid. The water-
insoluble product is listed in Table I BS NO.67-124. Analytical Procedure. A weighed sample containing 10 to 25 mg. of fluorine is placed in the distilling flask and washed down with about 5 ml. of water, after which 10 ml. of about 50% perchloric acid solution is added. Then the flask is connected t o the still head and t o t h e steam generator. The temperature of the acid solution is raised to the boiiing point, preferably by admitting steam before the heating current is turned on, especially if the sample contains fluosilicate. If the accuniulation of condensate in the flask appears to be too great, however. the heat may be turned on earlier, but heating the solution to the set temperature before steam ie ready to be passed should be avoided. I n the beginning, care should be taken to avoid a too rapid evolution of carbon dioxide to prevent froth from bein,
i,1 )
\Therc a - z reprcsents the rrsitiuc of undistilled fiuorine a t any time during thr. distiilation period. Fluorine Determination. I n (listillation rat(, studies, samples arc' taken t>y c1i:inging receivers a t frcqucnt. intervals, whereas i n ordinary analyticni practice samples of 100 mi.. representing a n hour's distillatior,, would be collected. l f iess than 11)O mi., tlie distiliate is diluted t,o this voiume with distilled \vai,er and neutralized with sodium hydrosiw, using sodiuni alizarin sulionate as indicator. It is then bufferrd t o a pH of 3 by the addition of I mi. of 0.851' acetic acid solution and titrated with standardized thorium nit,rate soiutiori. Reagents. I'erchioric acid, SOYo solution. Indicator, 0.1% sodium alizarin sulfonate solution. Buffer, 50 mi. of glaciai acetic acid per liter. Tliorium nitrate, 0.0525 (1 m;. = 1 mg. F). Thorium nitrate solution is standardized b:; precipitating the thorium as hydroxide or peroxiae and igniting the precipitate to thorium oxitie.
(2)
where z ant1 y represent milliliters of 0.lX sodium fluoride and 0.1N thorium nitrate solution, respcctively, the results obtained were as follows: Direct titration, a = 0.17, b = 0.983 Recovered by distillation, a = 0.06, b = 0.985
which compzres with similar data obtained by Nichols and Kmdt (15) using a photoriectric titrator in which a =' 0.03 iinci b = F.995. From. thesis data, the sodium fluoride equiva!cncr 0;' thorium nitrate msy '0- derived in th!. form of the equatim, 2
= (y - a)/b = c
(sr
.- r '
!:1
I
in which c = l ! b = 110.985 = r . O l E . The constant, a. in Eqiiation 3 re:-)resents the composiie of tht- blank to:. thorium nitrate equivai-cce of ttii. i-:dicator in solutiolj and the corre VOL. 31. NO. 10, OCTOBER ' ~ ' $ 5 5 r
1659
Figure 5. Relative rates of fluorine distillation from perchloric acid solution of sodium fluoride and various aluminiferous materials at 125' C.
factor for residual fluorine left u n d i s tilled in the flask (a 2 , Equation 1). These two corrections are about equal in value, but opposite in sign, so that in the titration of fluorine separated by distillation, the blank, u, may be ignored. But, in the case of direct titration, the blank of 0.17 ml. of 0.1N thorium nitrate solution should be subtracted before the correction factor (c = 1.018) is applied to the titer. Fluorine Distilled as Hydrofluoric Acid. Willard and Winter (85),and most of those who have proposed various modifications (13) of their procedure, state that fluorine is distilled as fluosilicic acid in the steam distillat i m process. A study of the molecular species in the hydrogen fluoride&icon tetrafluoride-water system, however, indicates that the composition of the invariant solution (14) in this system corresponds to the compound 12H20, a hydrated bifluoride of silicon produced by the reaction of hydrofluoric acid with silica, as follows,
-
diOt
+ 4HrFp.3Hp0 e Si(HFt .~ H I O +) ~ 2H20 (4)
Equilibrium between it and fluosilicic acid in solution with silicon tetrafluoride in the gas phase is given by Fox and Hill (4) as
-
2B9siF~. 6H20
188iFI. 12 HtO
+ SiF4(5)
The partial pressure of silicon tetrafluoride above fluosilicic acid, deter1-
ANALYTICAL CHEMISTRY
mined by Whynes and Dee (84) at 75" C., may be expressed by the equation, Log p (siF4)x"C. = 2.934
+ 0 . 1 0 1 8 ~ (6)
where w represents weight per cent fluosilicic acid in solution (4). m'h.ynes and Dee (84) also report that silicon tetrafluoride is the only form of fluorine found in the gas phase above fluosilicic acid. This report is in line with the observations of Baur (1) who found that the ratio, silicon tetrafluoridehydrogen fluoride in the gas phase increased rapidly over the range, 15 to 30% of fluosilicic acid in solution (4). From these observations, i t appears that fluosilicic acid is an unstable compound and would not be distilled as such. Nor does it seem likely that the invariant complex, H$iFs. 12H20, could be distilled from dilute solutions under the conditions necessary for substantially complete recovery of the fluorine in the distillate. But, in the steam distillation process, the equilibrium expressed by Equation 4 is shifted toward the left, silica is precipitated in hydrated form in the solid phase, and the fluorine is distilled as the tetrahydrate of hydrogen fluoride ( 4 , as shown in Figure 3. In this graph, representing a part of the transposed data of Brosheer, Lenfesty, and Elmore (8) and of Munter, Aepli, and Kossatz ( 1 4 , the circled
points rcpresent the solution coniposition after distillation n liile the arrow tips represent the composition of the distillate (gas phase). From these data, it is evident that fluorine is distilled mostly as a hydrate of hydrogen fluoride or hvdrofluoric acid. Thus, in the case of fluosilicate samples, the silica remains as a hydrated solid residue in the distilling flask (16). Consequently, the addition of quartz or other materials to the distilling flask as a source of silica for the production of fluosilicic acid is unnecessary. This practice undoubtedly arose from the need for silica in procedures designed to volatilize fluorine as silicon tetrafluoride (22) and the erroneous impression that fluorine is steam distilled as fluosilicic acid (81,25). W O F-
CHEMICAL COMPOSITION ON STEAM DISTILLATION OF FLUORINE
Simple Compounds. The sodium and calcium fluorides, or even the slightly more complex calcium fluosilicate dihydrate, show little difference in the rate of fluorine distillation from perchloric acid at 125' C., as shown in Figure 4. A rate of about 15% per minute for each of these salts is indicated by the slope of the main branches of the curves. At this rate about 99.8% of the fluorine in the original charge is steam distilled in about 40 minutes, so that, an hour of distillation should be ample, including the time required for the system to reach a steady state. Phosphate Rock. While phosphate rock may not be regarded as a simple compound (10, l a ) , the fluorine in the
rock, for the most part, behaves as calcium fluosilicate (4) (Figure 4) while s relatively small proportion of it behaves like fluorine in Pembroke clay (Figure 5). Complex Compounds. Those containing aluminum show a much lower rate of fluorine distillation under similar conditions (Figure 5). The initial rate for the first and second fluoride ions of aluminum fluoride trihydrate is about one third the rate for fluorine in sodium fluoride, or approximately 5% per minute. If this rate were maintained, a period of 3 to 4 hours of distiition at 125" C. mould be indicated. But this initial rate is not maintained and the third fluoride ion of aluminum fluoride is distilled a t a much slower rate, so that a period of about 9 hours of distillation h a m perchloric acid a t 125" C. is indicated (Figure 5). Dahle and Wichmann (3) determined the effect of a large excess of aluminum added as aluminum sulfate on the rate of fluorine distillation from sodium fluoride in sulfuric acid at 130" C. A comparison of their results with the authors' results from aluminum fluoride in perchloric acid is shown in Figure 6. From this comparison it is apparent that sodium fluoride and aluminum sulfate react to form a complex which is very effective in reducing the partial pressure of fluorine in the gas phase (Figure 5). The stability of a subfluoride, AlF, is indicated by the fact that it can be volatilized at about 700" C . in vacuum without dissociation (If). Bands appearing in the absorption spectrum of aluminum fluoride vapor at 1300" C. near 2300 A. have been ascribed to ALF (f9). In the case of opal glass (NBS 91, Table I), distillation of fluorine from the u n f u d glass (-90 mesh) in perchloric acid at 125" C. yielded less than 18% of the total in 1 hour, and about 1.6% more during the next 2 hours. These results indicated that only the fluorine-bearing component exposed at the fractured surface of the glass particles was accessible to attack by the acid. A sodium carbonate fusion opened u p the silicate glass, b u t the rate of fluorine distillation from the melt was still retarded by the presence of aluminum in the sample, as shown in Figure 5. The phosphate reduction furnace slag (No. 2548,Table I) was amenable to acid digestion with fluorine distillation at a still lower rate. The rate of distillation of the first 85% is substantially the same as from the (Am) ++ complex (Figure 5), but the remaining 15% was distilled at a much slower rate. Extrapolation of the lower portion of this curve back to zero time would suggest that the complex responsible for this lowering may be A@, since the
point of interception is about one third of the total fluorine, the initial fluorine distillation rate of which corresponds to that of the third fluoride ion of ALF,. In the case of Pembroke clay (No. 2335,Table I) the initial rate of distillation was approximately the same as the final rate of the phosphate reduction furnace slag. It, too, exhibits a transition from the initial to a still lower rate. The question of the completeness of the acid extraction naturally arises in the case of both the phosphate furnace slag and the day. This question was answered in the case of Pembroke clay by removing the insoluble residue after one hour's distillation. After this, the rate of distiliation from the liquid phase continued as before, whereas the insoluble residue yielded no appreciable amount of additional fluorine upon further distillation with a fresh supply of perchloric acid, nor did the insoluble silica have any significant effect on the distillation of fluorine from sodium fluoride. These results indicate that the interference of aluminum with the fluorine rate was due to the lowering of the partial Dressure of fluorine in the vapor phase by the formation of complex ions in the liquid phase. The attempt to synthesize a complex of calcium aluminum phosphatefluosilicate (No. 67-124,Table I) was not entirely successful but resulted in the unusual and interesting effect of delaying the attack of the perchloric acid on the aluminum fluoride, as shown in Figures 5 and 7. A similar effect is also evident in the case of the phosphatereduction furnace slag (No. 2548, Figure 5), a material that is quite different from the synthetic product. The explanation of this effect is not immediately apparent, but undoubtedly is connected in some way with the phosphate-silicate complex. In Figure 7, the magnitude of this effect is more clearly indicated by the enlarged scale of the graph on which the initial rate data are plotted. The similarity of results from alunlinum fluoride and the synthetic product after the delaying action shown in Figure 7 is over is illustrated in Figure 5. Measures that have been proposed to overcome the interference of aluminum and silica with fluorine distillation fall into two categories. One of these includes the separation of fluorine from aluminum after dccomposition by fusion as in the Berselius (7) method. This mould seem to be an acceptable procedure where fusion is necessary as in the case of opal glass (Figure 5). Shell and Craig (21) as well as Hollingsworth (8) suggest the use of zinc oxide in the fusion mixture to effect a separation of the fluorine from soluble silica, but it is doubtful that this would be of any benefit in nonfused samples.
.. '..\ \
23
0
2'0
40
\
\
6'0
Distillotion
lbc
80 Time
Minutes
Figure 7. Delaying action of a combination of calcium silicate and phosphoric acid on the distillation of fluorine from aluminum fluoride
The other procedure involves doubie distillation, first from sulfuric or perchloric acid at high temperature (160"C.),followed by concentration by evaporation after neutraiisation of the first distillate and a secondary distillation at a lower (135" C.) temperature ($). The latter procedure is about as time-consuming as the fusionextraction method. SIMULTANEOUS DOUBLEDISTILLATION. Uncondensed ggs from the first still maintained a t 1 0 " passcd through a solution of perchloric acid held at 125" in the second distilling flask, gave the results shown by dotted curve in Figure 5 for Pembroke clay. By this procedure, the distillation time required for complete recovrry was 1.5 hours compared with only 90% recovery in 14 hours a t 125" C. The scrubbing action of perchloric acid held at 125" in removing volatile subsianres that interfere in the titration step is just as efficacious as successive double distillations, whereas the time required is cut to that needed for a single high temperature distillation. LITERATURE CITED
(1) Bmr, E., Ber. deut. chem. Ges. 36, 4209 (1903); 2. physik. Chem. 48, 483 (1904). (2) Brosheer, J. C . . Lmfesty, F. .4.. Elmore. K. L.. In& Ena. Chem. 39, 427 (1947). ' (3) Dahle, D., Wichmxnn, H. S.,J. Assoc. OB. Agr. Chemists i F , 320 (1986). (4) Fox, E. J., Hill, W.L., J . Agr. Food Chem. 7, 478 (1959). (5) Haff, L. V. ButIrr, C . P., Bisso, J. D., ANAL.CKEM.30, 984 (1958). ( 6 ) Hill, R. L., Armiger, W. H., Gooch, S. D., Trans. A m . inst. Mming Met. Engrs. 187, 699 (1950!. (7) Hillebrand, W. F., Lundell,,G. E. F., "Applied Inorganic Analyss," 2nd ed., p. 919, Wiley, New York, 1953. VOL. 31, NO. 10, OCTOBER 1959
0
1661
IS! Hollingsn-orth, R. P.. -Lx.\L. CFEU. 29, 11.30 ( 1%; J .
\V. X.,Ferris, C. -1.ISD. ESG. &EX, -\SAL. ED.8, 6 (1936;. (10; Jacob, K. D., Hill, K. L., Marshall, H. L.. Reynoidc, D. S..U. S. Dept. Agr.. Tech. Buli. 364 (1933). ( 1 1 ) Klemm, K., Voss, E., Z . anorg. u ( 9 ) Hoskins,
allgem. Chem. 251, 233 (1943). (is) IIcConnell, D., A m . Jlineralogist 23, 1 (1938). (13) McIienna, F. E., Xuclwnics 8, S o . 6, 24-33; 9, KO.1, 40-9; S o . 2, 51-8 (1961). (14) Slunter, P. h.,Aepli, 0. T., Boesatz, R . .I.,I d . Eng. Chem. 39,427 (1947 I .
(16) Sichols, \I.L., Kindt, B. E.. .%SAL. CHflI. 22, 'is5 (1950). (16~~ Reynolds, D. S.,J. Assoc. O@. Agr. Chemists 17, 323 (1931j. (1;' Reynolds, D. 5.. Hill, K. L., ISD. ESG.CHEU.,- 1 s ~ED. ~ .11, 21 (1939). (1s: Reynold-., E. S., Kershan, J. B., Jacob, B. D., J. -4sscrc. O B . I g r . Chevzists 19, 1% (1936). (19) Rochester, G. D., Phys. Rec. 56, 305 (1939). (20) Scarseth? S. D.. Better Crops W i t h Plan: Food, 24, 10 (1940); T h o & phates in Agriculture," rev. ea., p. 89, Darison Chemical Corp., Baltimore, lid., 1951.
R., Crsig, E:. L.! .\s.*L. Cmx. 26,996 (19%). ( 2 2 ) Wagner, 6.R., Ross. K. E.: 3. It!i. (21) Sneli, E.
Eng. chem. 9,1116 (1917;. (23) Khittaker7 (2. Vi'., Fox,
E.S., Zbid., (21)Wh-ynes, A. L., Dee,T. P., Specis! 19, 46i (19'27:.
Rept. Tech. Meeting, Intern. Superphosphate Slanufacturers , . k o c . , London, September 1953; Inst: Chem. Eng., Graduates & Students Section, Februarv 19%. ( 2 3 ) Kilia&, E. H., Winter, 0. E.. Iso. ESG.CHEU.,.LuL. ED.5, i (1933 j. RECEIVEDfor review January 14, 1850. Accepted June 26, 1959.
Colorimetric Determination of Chloride in Concentrated Hydrogen Peroxide ISIDORE GELD and IRVING STERNMAN Metal Chemistry Section,
U. S. Naval
Material laboratory, New York,
b Aluminum containers, commonly employed for storage of concentrated hydrogen peroxide, exhibit accelerated corrosion in the presence of traces of dissolved chloride. To study this effect, development of a sensitive method was necessary for determining chloride in concentrated hydrogen peroxide. A colorimetric method, based on the reaction of mercuric thiocyanate with chloride ion to release thiocyanate, which forms a reddish orange complex with iron(lll), is capable of determining chloride in 90% hydrogen peroxide, up to 4 mg. per liter with a sensitivity to 0.01 mg. per liter and an accuracy equal to or better than 0.1 mg. per liter. Variables are studied with respect to hydrogen peroxid e decomposition, rea gents, temperature, and interferences
D
of a method for determination of trace quantities of chloride in concentrated hydrogen peroxide was undertaken in conjunction with studies of the corrosive effect ( 6 . 7 ) of such chioride on aluminum containers. The government specificatioxi for hydrogen peroxid? (JIIL-H16005C) pernlits a maximum chloride content of 1 mg. per liter (1 p.pm. on a n.eight-\-olume basisj. The method described is a niodfication and extension of that proiiond by Zall? Fisher! and Garner is:. anri is intended for the determination of 0.01 to 4 mg. per liter cf chloride in co'icentrat,ed 1907G)hydrogen peroxide. EVELOPMEST
REAGENTS AND STANDARD SOLUTIONS
Mercuric thiocyanate, saturated solu1662 *
ANALYTICAL CHEMISTRY
N. Y.
tion in deionized water ( O . O i 5 a t C.). Filter to remoi-e excess. Ferric Perchlorate. Dissolve 14.0 grams of pure iron mire in dilute nitric acid. Add 120 mi. of perchloric acid (70%) and heat to fumes of perchloric acid. Continue fuming for 30 minutes. Cool, add 100 d.of hot deionized water, and boil for 5 to 10 minutes to remove chlorine. Cool and dilute to 1 liter with deionized water. Composite Reagent. Prepare as needed by mixing 2.00 parts by volume of ferric perchlorate solution n-ith 1.00 part by volume of mercuric thiocyanate solution. The rea-gent is stable for approximately 8 hours. Standard Solutions. By suitable dilution. of a sodium chloride master solution (0.1 nip. of C1- per ml.) prepare standard solutions ranging from 0 to 40 y of C1- per mi.. in increments of 2 y per d. These will be employed in preparation of thr calibration curve. 23'
CALIBRATION , Pipet 5.00 m!. of each standard solution into 10-ml. volumetric flasks and add 1.0 nil. of 6-j- sodium hydrosjde and 0.6 ml. of perchloric acid (iOYc). Add 3.00 ml. of the composite reagent and fill to the 10-ml. mark with deionized water. Mix. transfer to a testtube colorimeter cell, and compare the yellow-orange color against Rater a t approximately 460-mp wave length (KS-47 filter is satisfactory). The color is stable for approximately 1 hour, Kith gradual increasing absorbance thereafter. Plot the colorimeter readings, or absorbances. against the corresponding micrograms of chloride present. Make a separate calibration for each nen- solution of mercuric thiocyanate reagent prepared. Conduct the calibration a t approsimately the ambient temperature expected during the actual analysis. -4 representative
curve [Figure 1) indicates that Beer's law is not obeyed. The curve shows an approximate sensitivity of 0.5 y in the lorer portion of the curre-beloK 30 7 of chloride. The sensitivity decressec: a t higher chloride concentrations. PROCEDURE
Transier 50 mi. of the hydrogen peroxide sample into a covered 500-nii. tall-form borosilicate glass beaker. Carry along duplicate reagent blanks. Add 10 ml. of deionized water and 1.0 d.of 6-\- sodium hydroxide. Place on a steam bath to initiate a rigorous reaction. Maintain the temperature of the solution between 75' and 90" C. until decomposition is almost complete, then evaporate to dryness on the eteani bath. Dissolve salts and r i w . inside of beaker n-ith 1 to 2 mi. of tipionized water. Add 0.6 ml. of pcrchlorir acid (707,) and 3.00 ml. of the composite reagent. Transfcr the s o h tion to 3 10-ml. volumetric flask, rincing the beaker at least tlvice with c i t ionized water. Dilute to the 10-mi. mark, mix, and compare against n-nter Kith the photoelectric colorimeter. a: described under calibration. Obtair the quantit- of chloride from the calibration curve and deduct the aver'!g;c of the blanks. Several samples may be run simultaneously, escept for peroxide drconiposition, which should preferably be conduct,ed in pairs. Suitable safety precautions should be talien when handling concentrated hJ-droge:> peroxide, especialiy.during decomposition. PRECAUTIONS AGAINST CONTAMINATION
Decomposition and evaporation should be conducted in a hood with suction off to minimize motion of at-
