ANALYTICAL CHEMISTRY
1878 Table 11. Titration of Iron(II1) with Uranium(V) in Presence of Nitrate (Iron taken, 28.6 mg. I = 10 ma.) PH NO*-, .lf % Error 2 0
0 0 0 0
1.5
1 5 0 04
+o +O
2, +O 6, +O
reaction with generated uranium(T’). I t follows from these data that a t p H 2, uranyl nitrate can be used directly as the source of uranium(V), provided its concentration does not exceed about 0.03Af. At higher pH’s more concentrated uranyl nitrate solutions could no doubt be used.
2 8
*o.o
ACKNOWLEDGMENT
The authors wish to express their gratitude to the Research Corp. for financial assistance.
+1.1
LITERATURE CITED
Mg. of Fe = Z(ma.) X t(seconds) X 55.84/96,493 I n only the last run was the precise determination of the end point felt to be the major source of error. Further refinement of procedure and apparatus might reduce the small errors observed to even lower values. Although there is evidence ( 5 ) that sulfate catalyzes uranium(V) disproportionation, the effect is not sufficient to interfere with the iron determination, as is evident from the third entry in Table I. The effect of nitrate ion i j s h o m in Table I1 for the electrolysis of 2.86 mg. of iron with a 10-ma. current. Positive errors a t high hydrogen and nitrate ion concentrations may be due either to direct cathodic reduction of nitrate, or to its
(1) Belcher, R., Gibbons, D., Wert, T. S., ANAL.CHEM.26, 1028 (1964). (2) Bradbury, J. H., Trans. Faraday SOC.50, 959 (1964). (3) Cheng, K. L., Bray, R. H., Kurtz, T., ANAL.CHEM.25, 347 (1953). (4) Kern, D. AI., Orlemann, E. F., J . Am. Chem. Soc. 71, 2102 (1949). (5) Kolthoff, I. bl., Harris, W. E., Ibid., 68, 1175 (1946). (6) Kraus, K. A . , Nelson, F., Johnson, G. L., Ibid., 71, 2510 (1949). (7) Lingane, J. J., Iwamoto, R. T., Anal. Chim. Acta 13,465 (1955). (8) Orlemann, E. F., Kern, D. >I., J . Am. Chem. Soc., 75, 3068 (1953.) (9) Schmid, R. W., Reilley, C. N., ANAL.CHEM.28, 520 (1956). (10) Shults, W. D., Thomason, P. F., Kelley, AI, T., Ibid., 27, 1751 (1955). RECEIVED for review May 15, 1956.
Accepted August 11, 1956.
Determination of Chloride in Titanium Sponge by the Rapid Potentiometric Method H. V. MALMSTADT, E. R. FETT’, Department
and
J. D. WINEFORDNER
o f Chemistry and Chemical Engineering, University o f Illinois, Urbana, 111.
Two procedures are presented for the rapid, precise, and accurate determination of 0.001 to 0.5% chloride in titanium sponge, requiring only about 7 minutes per determination after dissolution of the sample. The chloride analysis involves a final measurement of the voltage difference between two silver-silver chloride electrodes in a concentration cell, one arm of which contains the unknown chloride solution and the other a standard chloride solution. Prior to the potentiometric measurement the unknown chloride solution must be prepared to prevent interferences from substances in the titanium samples. In one procedure the chloride is removed from an aliquot of a sulfuric acid solution of the titanium sample by a rapid distillation (about 5 minutes). In the other, the titanium sponge is dissolved in a measured quantity of either sulfuric or fluoboric-sulfuric acid mixture and prepared for the potentiometric measurement by selective oxidation with hydroxylamine sulfate.
T
H E quantitative determination of chloride in commercially produced titanium sponge is an important routine determination, and a rapid and accurate procedure is desirable. Several methods are used currently for the chloride determination, but most of them are time-consuming and some are rather inaccurate for the low concentrations of chloiide which are usually present in titanium sponge. The gravimetric (6) and colorimetric (3) chloride procedures give reliable results, but both methods involve a precipitation in which the precipitate must stand overnight. Some labora1
Present address, Union Oil Co., Fullerton, Calif
tories use titration procedures (6) m-hich are more rapid than the gravimetric and colorimetric procedures but are not very reliable for samples containing less than 0.1% chloride. The concentration of chloride in titanium sponge is usually in the range of 0.01 to 0.57,, and under the best conditions for dissolving the titanium samples, solutions containing about 20 mg. of titanium per ml. of solution are obtained. Therefole. the concentration of chloride in solution would usually be in about the range G X 10-E to 3 X 10-3X. An ideal method for determination of chloride in titanium sponge should make it poasible t o determine a loiv concentration of chloride rapidly and accurately in a very acid solution containing relatively large quantities of titanium and small quantities of iron, magnesium, manganese, vanadium, and other trace elements. Blaedel, Len-is, and Thomas ( 1 ) have s h o m that high ionic strength renders turbidimetric, nephelometric, and direct titration procedures using adsorption indicators very unreliable. I n addition, the direct visual color indicator titrations by the Mohr and mercurinietric methods do not have sufficient sensitivity. and the \-olhard method is reliable for only relatively high pelcentage chloride samples (6). Potentiometric titration of the chloride in the strong sulfuIic acid and fluoboric-sulfuric acid mixture has not been too reliable, partly because of the erratic behavior of the silver indicator electrode in these solutions. Direct polarography and amperometric titration methods do not give good precision at the low chloride concentrations encountered in the titanium samples. Conductometric titintion methods are useless because of the high ionic stlength. Ordinary potentiometric measurement of chloride concentration using a concentration cell generally involves consideration of and correction for liquid junction potential and ionic strength
V O L U M E 2 8 , NO. 12, D E C E M B E R 1 9 5 6 effects, but Furman and Low (4, 6) and more recently Blaedel, Lewis, and Thomas ( I ), have devised a simple differential method tvhich eliminates errors from these two effects. The method was conceived primarily for measuring low chloride concentrations in solutions of high ionic strength, and is readily adaptable for routine analysis. The procedure consists of measuring the voltage of a silver-silver chloride electrode immersed in the unknown solution against an identical electrode immersed in a standard chloride solution. Both solutions must have practically identical composition, except for chloride concentration, which should contribute negligibly t'o ionic strength. From the voltage of the cell the unknon-n chloride concentration is easily determined. Considerat,ion of the characteristics of the acid titanium solutions containing low concentrations of chloride leads to t n o OSsibilities for utilizing the rapid potentiometric concentration cell method. One obvious general procedure is to remove, quantitatively, the chloride from the acid titanium solution and transfer it to a solution of knon-n ionic strength which is free from possible interferences. Another general procedure is to dissolve each titanium sample in the same quantity of acid, treat the solutions so as to prevent interference from certain constituents likely to be present in titanium sponge, and measure the potential of the unknown solutions against a standard solution prepared in the same way. The first general procedure can be carried out rapidly and accurately by dissolving the titanium sample in sulfuric acid, diluting to volume, rapidly distilling t'he chloride of an aliquot sample into a sulfuric acid solution of known concentration, and measuring the final unknoivn chloride solution in one arm of a concentration cell against a standard chloride-sulfuric acid solution in the other arm. The second procedure consists briefly of dissolving the titanium sample in a measured quantity of sulfuric or fluoboric-sulfuric acid mixture, diluting to volume, treating an uliquot of the solution viith hydroxylamine sulfate to oxidize the titanium to titaninm(IV), not oxidizing ferrous iron to ferric iron, and finally measuring in a concent'ration cell against a specially prepared standard. Both procedures have been developed to provide rapid, precise, nnd accurate results. The total analysis time after dissolution of the sample is only about 5 to 7 minutes per sample by either procedure. EQUIPMENT
The concentration cell used n-as similar to the one described by Blaedel and coworkers ( I ! , The dimensions of the cell were chosen 80 that each arm had a capacity of about 15 ml. Therefore, 25 nil. of unknown chloride solution were sufficient to provide initial rinsing of the unknown arm prior to filling for a measurement. The cells were coated wit,h Desciote, and one rinse was found to be sufficient. The silver-silver chloride electrodes \?-ere prepared by the method of Brown ( 2 ) . Square plate platinum electrodes, 4 sq. cm. in area, were used for most of this work, although wire electrodes, 2 em. long and 1 mm. in diameter, were also satisfactory. The electrodes are stable for many months and last for hundreds of determinations. A thermostat was used which controlled the solution temperature a t 25' =t0.1" C. An L and S type K potentiometer was used to make the voltage measurements of the cell, and a nomogram similar to the one described bj- Blaedel, Lewis, and Thomas (Ij was used to convert the voltage - readings - to concentration values rapidly. A simale distillation setuo was used with which the chloride was removed quantitativel? from the titanium sample. h 50ml. distillation flask was used, and a condenser with a condensing tithe 7-nlnl. in inner diameter, and 70 em. long, surrounded by a water jacket, Tvas attached to the side arm. h condensing tube with small diameter n-as used so that it could be easilj- rinsed down with a small volume of n-ash water. A 0" to 200" C. thermometer x a s inserted into the top of the distillation flask so :hat the tip IT-as immersed in the solution. A glass tube adapter mm. in inside diameter v-as made for the end of the condenser Ivhich fitted into the 25-ml. volumetric receiving flasks. The distillation flask Iyas heated with a Meker burner.
1879 DETERMINATION OF CHLORIDE I N TITANIURI SAMPLES BY DISTILLATION TECHNIQUE
Titanium sponge is often dissolved in sulfuric acid and the dissolved sample is diluted to be about 421 in sulfuric acid and to contain 20 mg. of sample per ml. of solution. Experiments were conducted, therefore, to determine the feasibility of rapidly and quantitatively removing the chloride from about a 431 sulfuric acid solution. Preliminary Distillation Tests. Preliminary experiments showed that known amounts of chloride added to reagent grade 4 M sulfuric acid could be rapidly and quantitatively distilled off and collected wit,h a simple distillation setup as described above. A 25-ml. aliquot of 4M sulfuric acid containing a known quantity of chloride was added to the distillation flask, the tip of the condenser adapter was immersed in 2.50 ml. of 10.0JI sulfuric acid contained in a 25-m1. volumetric receiving flask, and the chloride was distilled off by heating the distillation flask with a Meker burner until the solution temperature reached 130" to 140" C. The distillation was then stopped, the condenser was washed down with a fine jet of distilled water, and the distillate was diluted to volume with distilled water. After dilution to volume the chloride distillate was almost exactly 1Jf in sulfuric acid. X very small quantity of sulfuric acid was carried over from the distillat,ion to the receiving flask during the distillation, but the quantity \vas not significant compared with the large known quantity of sulfuric acid added to the receiving flask to adjust the ionic strength. The chloride concentration in the distillate was determined in the concentration cell as described beloK. Dissolution of Titanium Sample. h solution containing about 10 ml. of concentrated sulfuric acid and 25 nil. of distilled water was used to dissolve each gram of titanium sample. Immediately after addition of the titanium sample t o the cool sulfuric acid solution contained in an Erlenmeyer flask, a reflux condenser n-as connected to the top of the flask to prevent' loss of any chloride during dissolution of the sample. The solution was heated gently on a hot plate until the sample was dissolved, usually about 4 hours. The solution was then cooled and quantitatively transferred to a 50-m1. volumetric flask and diluted to volume x i t h distilled water. Titanium samples larger than 1 gram are often used for analysis when the samples are nonhomogeneous, and proportionately larger quantities of acid solution and larger volumetric flasks are used, so that the final titanium concentration is the same .regardless of sample size. I n all cases, a 25-ml. aliquot of the final titanium solution, containing 0.500 gram of sampIe, is used for analysis. Distillation of Chloride from Titanium Samples. The distillation of 25-ml. aliquots of titanium sponge solutions can be performed by the same basic procedure as for the sulfuric acid solutions, but the heat,ing of the distillation flask must be carefully regulated, and the solution temperature raised to 150" C. to assure quantitative transfer of chloride. Local heating of the distillation flask must be eliminated to prevent severe bumping, and the solution must be heated so as to prevent condensation of solution in the neck of the flask. 1Iost of the hydrochloric acid is distilled over near the end of the distillation, and condensate in the neck of the flask results in absorption of a considerable amount of hydrochloric acid. However, both of these difficulties can be readily prevented and a rapid distillation effected by adjusting a Lleker burner as shonx in Figure 1. Several other methods of heating the di.stil1ntion flask Kere attempted hut none proved as simple, rapid, and effective as the 1leker burner. S o trouble was experienced n-ith this distillation method of rapidly removing chloride from the titanium samples when the hurner n-as adjusted a s rhon-n in Figure 1, and no attention wns required except to turn off the flame n-hen the solution temprrature reached 150" C. The position and adjustment of the flame should approximate those sh0n.n in Figure 1. The 25-1111. volumetric receiving flask sho~ilclcontain 2.50 nil. of 10.0J1 sulfuric acid before the distillation is started. Measurement of Chloride Concentration. After being diluted to the mark and thoroughly mixed in the 25-ml. volumet,ric receiving flask, the chloride distillate \vas 1.00.1lin sulfuric acid and ready to be transferred to the concentration cell. The unknown arm of the concentration cell \vas rinsed once with the distillate and then refilled. The chloride concentration was determined by measuring the voltage between the unknown solution and the chloride standard (a 1.000 X 10-3JI sodium chloride, 1.00M
1880
ANALYTICAL CHEMISTRY
sulfuric acid solution). The measured voltage was converted to molar concentration using a nomogram ( I ) , and then to percentage of chloride in the original titanium sample. The nomogram could, of course, be made to read directly in percentage of chloride.
Results. The method was first tested on a titanium sample which was analyzed by the gravimetric procedure (6) to give a result of 0.162% of chloride. The results of the distillationconcentration cell method are given in Table I. Each sample was an aliquot of a 20-gram sample of titanium dissolved in sulfuric acid solution as previously described. Prior to distillation] the iron content of aliquots 7 and 8 was increased from less than 0.1 to over lY0 by adding ferrous ammonium sulfate, and the chloride results TTere not affected.
1
&-THERMOMETER
I
P
3\
to be equivalent to less than 0.001% chloride in the titanium sample for all sulfuric acid solutions tested, and this quantity is generally insignificant for routine chloride determination of titanium sponge samples. Five titanium sponge samples issued to the chloride panel of the Metallurgical Advisory Committee on Titanium were obtained from Watertom Arsenal. The nominal chloride values were available n-ith which to compare the distillation results, but the arsenal samples were not checked by other standard chloride methods. The results in Table I11 illustrate the precision of the method for the arsenal samples. DETERMINATION OF CHLORIDE WITHOUT SEPARATION FROM ORIGINAL TITANIUM SOLUTION
Although the total analysis time required for determination of chloride after dissolution of the sample is less than 7 minutes by the distillation method, the time involved in dissolution of the titanium sample with sulfuric acid is about 4 hours. The dissolution of the titanium sample can be decreased to about 30 minutes or less by using a sulfuric-fluoboric acid mixture, but such a solution is not suitable for the distillation method because of evolution of hydrofluoric acid a t the temperature required to distill off hydrochloric acid quantitatively. Consequently, a second basic method xas investigated to enable chloride to be determined in the sulfuric-fluoboric acid solution of the titanium sponge. I n this method, the dissolved sample is treated to prevent interferences and the solution is measured directly in the concentration cell. Upon dissolving the sponge sample in sulfuric or a mixture of sulfuric-fluoboric acids, most of the titanium is in the trivalent state, and the strongly reducing solution destroys a silver chloride electrode surface almost immediately after contact. Therefore] it is necessary to oxidize the titanium to titanium(1V) before the
OUTER CONE
\
Table I.
Precision of Chloride Distillation Method
Aliquot NO. -+--MEKER
Chloride Determined,
%
BURNER
0.164
0.159
Av. Standard deviation
0.163 0.162 0.165 0.162 0.164 0.162 0.163 0.0018
Table 11. Determination of Chloride in Titanium Samples Containing Known Quantities of Added Chloride Figure 1. Flame adjustment and burner placement for rapid distillation of chloride
Chloride Added,Q
%
h-one (originally present in T i sponge)
The method of standard addition was employed next as a means of testing the method. -420-gram sample of titanium sponge containing only about 0.01 of chloride was dissolved as before. -4fter accurately determining the small quantity of chloride originally present in the titanium sample, known amounts of chloride were added to aliquots of the titanium solution prior to distillation. The results are given in Table 11. Khen the concentration of chloride is very low (about 0.03% or less), the solubility of the electrode must be considered] and it is necessary to know the value of electrode solubility, 8, which can be determined as described by Blaedel, Lewis, and Thomas ( 1 ) . illso, the chloride content of the sulfuric acid solution used in dissolving a titanium solution should be determined and corrected for by applying a blank correction. The blank was found
0.025
0.050 0,100
0.200
Chloride Found, 6
%
0 0 0 0
0108C
0108C 0099e
OlO5C 0.026 0.023 0,027 0.025 0.024 0.050 0.051
0.100 0.099 0,199 0.203
0.506 0.495 a Added as XaC1 t o aliquots of same titanium solution. b yo chloride found is equal to total chloride determined minus chloride originally present in titanium sponge sample, except where no chloride was added. C Yo chloride found in original titanium sample. 0.500
1881
V O L U M E 28, NO. 1 2 , D E C E M B E R 1 9 5 6 Table 111. Determination of Chloride in Watertown Arsenal Titanium Samples by Distillation Method" Sample WA46
Nominal Concentration, Chloride 0 09
WA-47 b
0.18
m7.4-47c
0.18
WA-48
0.05
Chloride Found,
70
0 108 0.108 0.108 0.203 0,203 0.203 0.182 0.183
0.0513 0.0513 0.0513 0.0502 WA-64 0.19 0,190 0,190 0,190 WA-65 0.16 0,171 0.171 0.171 0.171 a 5 grams of each sample were dissolved and several ZZ-ml. aliquots of each were individually distilled and concentration of the distillates mas determined in the concentration cell. b Results of this sample did not check closely with nominal value, so a second 5-gram sample, C , was dissolved a n d chloride determined. Results indicate t h a t sample was not very homogeneous.
solution can be transferred to the concentration cell. It is essential, hon-ever, that the iron, which is usually present in small but signscant quantities in the titanium sponge, remain in the ferrous state, because ferric iron interferes n ith the method a t concentrations greater than 10-4M ( 1 ) . In addition, a strong oxidizing agent could oxidize the chloride to free chlorine, which would be lost by volatilization. Hydroxylamine sulfate (Kodak, 99+%) fulfills the desired condition of selectively oxidizing the trivalent titanium and not the ferrous iron. Dissolution of Titanium Sample. I n the direct method for chloride determination it is necessary to dissolve all samples in the same way, so that all solutions have the same ionic strength. The method is applicable to either sulfuric or sulfuric-fluoboric acid solutions, but the latter was investigated most thoroughly because it dissolves the titanium much more rapidly than just the sulfuric acid solution
A solution containing 8.0 ml. of concentrated sulfuric acid, 2.50 ml. of 48 to 50% fluoboric acid, and 25 ml. of distilled mater was used to dissolve each gram of titanium sample. Xfter addition of the titanium to the acid solution contained in an Erlenmeyer flask, a reflux condenser mas immediately connected to the top of the flask, and the solution was heated gently on a hot plate until the sample was dissolved. One gram of hydroxylamine sulfate was then added to the dissolved sample and the solution mas diluted to 125 ml. with distilled water. Proportionately larger quantities of acid, hydroxylamine sulfate, and increased dilution volumes were used for larger than 1-gram samples. If the same titanium solution is to be used for determination of other elements, it might not be desirable either t o make such a large dilution of the dissolved sample or to oxidize the entire sample with hydroxylamine sulfate. In this case, a dissolved 1gram sample is quantitatively transferred to a 50-ml. volumetric flask and diluted to the mark with distilled n-ater, so that the solution contains 20 mg. of sample per ml. A 10-ml. aliquot of this solution is then transferred to a 25-m1. volumetric flask, 0.2 gram of hydroxylamine sulfate is added, and after being shaken and cooled to room temperature, the solution is diluted to the mark with distilled water. This solution is used directly in the unknown arm of the concentration cell. The remainder of the more concentrated solution, containing 20 mg. of sample per ml., can be used for determination of other elements. The double quantitative dilution, whereby an intermediate solution of 20 mg. of sample per ml. and a final solution of 8 mg. of sample per ml. are prepared, is also convenient in the preparation of the standard solution as described below. Experiments were tried using larger quantities of fluoboric acid to dissolve the titanium samples, and although the dissolution time was decreased by several minutes as compared with the above solution, two difficulties were experienced. The
solutions with larger quantities of fluoboric acid hydroljrzed readily, and because the fluoboric acid contained significant quantities of chloride, the blank correction was increased appreciably. Preparation of Standard Solution. I t is essential to prepare a standard solution which has nearly the same ionic strength as the samples and has an accurately known quantity of chloride. The most straightforward n-ay of preparing such a solution is to dissolve a titanium sample of knomn chloride concentration in exactly the same quantity of acid as for the samples. An amount of chloride is then added to give the desired chloride concentration and the solution is treated and diluted to volume as for the unknown samples. This procedure is very satisfactory, but several considerations and precautions are necessary to ensure an accurately known standard. There are several sources of chloride in a titanium sponge sample used as a standard; the titanium sponge and the sulfuric and fluoboric acids all contain small quantities of chloride. Very pure titanium sponge is preferably chosen for preparing the standard; it will usually contain a fen- hundredths of a per cent of chloride. The quantity of sulfuric and fluoboric acids used to dissolve the titanium samples was found, respectively, to be equivalent to 0.0003 and 0.0097, of chloride in the titanium sample for the particular batches of acid used in this work. S o significant quantity of chloride was found in the hydroxylamine sulfate. One method of accurately preparing a chloride standard is to determine individually the chloride in the titanium sponge and in the acid solution used to dissolve the sample, and then to add a k n o m amount of chloride to give the desired total concentration of chloride. The chloride in the titanium can be determined by the previously described distillation method or by the standard gravimetric procedure (6). The chloride in the sulfuric-fluoboric acid solution can be determined by preparing two identical acid solutions except that to one is added a known quantity of chloride. The two solutions are poured in opposite arms of the concentration cell and the potential is measured. From the potential reading and k n o m quantity of added chloride, the original concentration in the sulfuric-fluoboric acid solution can be readily calculated. A more rapid method of preparing a chloride standard is to dissolve a large titanium sponge sample in sulfuric-fluoboric acid and to dilute to volume to give a solution containing 20 mg. of titanium sample per ml., and then t o determine the total chloride in titanium sample and acid solution all at one time. This can be accomplished by the following method. Two 10-ml. aliquots of the above solution are put into two 25-ml. volumetric flasks; 0.2 gram of hydroxylamine sulfate and a known quantity of chloride are added to each flask and the solutions are diluted to the mark with distilled water so as to contain 8 mg. of sample per ml. The known chloride added to one flask should be about ten times greater than added to the other flask. After shaking the flasks, the contents are poured into opposite arms of the concentration cell and the potential is measured on a potentiometer. The potential can be expressed in terms of chloride concentration by Equation 1,
E
=
+
0.0591 loglo ki x k2
+2
where r is the unknown chloride resulting from the chloride in the titanium and in the acid used to dissolve the sample, E is the measured potential of the cell, kl is the known added quantity of chloride to one aliquot of solution, and kp is the known added quantity of chloride added to the other aliquot of solution, and, for convenience, is ten times greater than kl. It is assumed in making this calculation that the total chloride concentrations of both solutions are sufficiently great so that the solubility of the electrode is insignificant, which is the case when the total chloride concentration is greater than 0.25 X 10-3LTf. Equation 1 is rewritten to give Equation 2 for conveniently calculating x,
' = kt10E/0.0591 - 1
kl10E/0.0691
(2)
ANALYTICAL CHEMISTRY
1882
After the value of 2 has been determined, a large measured volume of the same titanium solution, containing 20 mg. of sample per ml., is treated with sufficient hydroxylamine sulfate (I gram per gram of titanium sample); and a known quantity of chloride is then added so that upon dilution to final volume (8 mg. of titanium sample per ml.) the total chloride concentration will be that chosen for the direct method standard (0.500 X lO-3M). The above methods of preparing the standards are illustrated a i t h the following experimental results: Chloride, kl (0.0100 mmole), was added to a 10-ml. aliquot of the sulfuric-fluoboric acid solution of titanium containing 20 mg. of sample per ml., 0.2 gram of hydroxylamine sulfate was added, and then diluted to volume in a 25-m1. volumetric flask. Then, 0.100 mmole of chloride, kp, was added to the other 10-ml. aliquot and the above process was repeated. The two solutions were poured into opposite arms of the concentration cell and the potential, E, was measured and found to be 53.55 mv. The values of k l , kp, and E were substituted into Equation 2, and z was calculated to be 2 . i i X mmole per 25 ml. of solution. The same measurement and calculation were performed for other pairs of the same titanium solution to which different amounts of chloride were added, and a n average value of 2.75 X 10-3 mmole per 25 ml. of solution was determined for z. This result compares favorably with that obtained by separately determining the chloride in the original titanium sample by the distillation method and the chloride in the acid solution by use of the concentration cell. The chloride in the same quantity of original titanium sample as used above m s determined mmole, and the chloby the distillation method to be 2.23 X ride in an amount of acid, equivalent to that used above, to be 0.50 X 10-3 mmole, or a total of 2.73 X mmole per 25 ml. of solution; which is nearly the same result obtained by the more rapid and single measurement method described above.
Table IV. Determination of Chloride by Direct Method in Titanium Samples Containing Known Added Quantities of Chloride Chloride Added,'
Chloride Found, b
%
%
0.0068 0.0071 0.014 0.014 0.034 0.036 0.071 0.071 0.140 0.140 0.356 0,347 0.712 0.712 Added a s NaCl to titanium solution. b % chloride found is equal t o total chloride determined by volt,age measurement minus chloride originally in titanium sample and in a r i d used to dissolve sample. Q
Table V. Determination of Chloride in Watertown -4rsenal Titanium Samples by Direct Method Sample W.4-46
Nominal Concentration, % Chloride 0.09
WA-47
0.18
W.4-48
0.05
W.4-61
0.19
WVA-65
0.16
Chloride Found,"
%
0.107 0.107 0.106 0.183 0.179 0.179 0,057 0.058 0,059 0.199 0.198 0.199
0.176 0.171 0.168 a % chloride found is equal to total chloride determined minus chloride present in acid used for dissolving sample.
MEASUREMEST OF CHLORIDE COhCENTRATION IN TITANIUM SAMPLES
The dissolved, treated, and diluted titanium sample is placed in one arm of the concentration cell and the standard chloride solution in the opposite arm. The measured potential is converted to concentration nith a suitable nomogram. A correction must be made for the quantity of chloride contained in the sulfuric-fluoboric acid solution used to dissolve the unknown sample. The chloride in the acid solutions used for this work was equivalent t o 0.009% in the titanium sample. The chlorid? should be determined for each new lot of acid used for dissolving the unknown titanium samples.
Results. The method was tested for accuracy by preparing a sulfuric-fluoboric acid solution of a titanium sample for which the chloride concentration was accurately determined by the distillation method. Known quantities of chloride were then added to aliquots of this solution and, after proper oxidation and dilution, the solutions were measured in the concentration cell against the standard chloride solution. The results are given in Table IV. The method was also tested by dissolving 5 grams of the KA4 samples in the sulfuric-fluoboric acid mixture; in general, the results agreed closely n-ith those obtained by the distillation method. The precision and apparent accuracy of the method indicates that differences in the results of the TT'A samples by
the distillation and direct methods are primarily the result of nonhomogeneity in the samples. The results for the WA samples by the direct method are given in Table V. ACKNOWLEDGMENT
The authors Fish to thank Craniet, Inc., for grants-in-aid in support of this project, and Katertoan Arsenal for the TVA titanium sponge samples. LITERATURE CITED
(1) Blaedel,
IT.J., Lewis, TV. B., Thomas, J. IT., AXAL.CHEM.24, 509 (1952). (2) Brown, A. S., J . Am. Chem. SOC.56, 646 (1934). (3) Codell, 31.,AIikula, J. J., ANAL.CHmr. 2 4 , 1972 (1952). (4) Furman, 4.H., Low, G. H., J . Am. Chem. SOC.57, 1585 (1935). ( 5 ) I b i d . , p. 1588.
(6) Thompson, J. II.,-4s.4~.C H E x 25, 1231 (1953). RECEIVED for review July 9. 1966. Accepted August 30, 1956. Presented in part before Division of Analytical Chemistry, Symposium on Analysis of Titanium and Its Alloys, 128th meeting, ACS. Ilinneapolis, hlinn., September 1935.
