New Volumetric Method for Determination of Sulfate V. R. DAMERELL AND H. H. STRATER, Western Reserve University, Cleveland, Ohio
I
tion (0.02 $0 0.07 M ) was added T HAS long been k n o w n A direct volumetric method is described. Standto the sotut o potassium s u l f a t e solution that when sulfate solutions ard barium chloride solution is (0.005 to 0.02 M ) from a buret, are added to mercuric nition containing sulfate, using mercuric nitrate as both solutions being at trate solutions under the proper conditionsayellow colored, basic an outside indicator. A technic is described in temperature. T h e initial which a preliminary end point is reached several volume of the sulfate solution m e r c u r i c s u l f a t e , known as cubic centimeters in advance of the j n a l end was in most cases 100 CC. I n “turpeth,” precipitates (2). It point, enabling the analyst to add the bulk of the titration 0ask a medicine occurred to one of the authors dropper w i t h an e x t r a - l o n g that this might serve because Of the barium chloride solution rapidly. glass tube (22 cm.) was used its color. as an indifor obtaining test ‘ p o r t i o n s . cator in a v o l u m e t r i c sulfate analysis. It could not be used successfully in the titration The titration mixture was vigorously swirled before taking mixture, but when employed as an outside indicator the re- out test portions. The barium chloride solution was added sults were of such accuracy that the authors believe the method slowly (about 15 cc. per minute), and in the case of very to be of value. dilute solutions the titration mixture was allowed to stand This paper describes the titration, together with experi- after each addition for at least a minute (Table 11) before ments designed to determine favorable conditions under taking out test portions. which it should be carried out. A drop of mercuric nitrate solution was put in each of the outer depressions of a clean spot plate with another dropper. EXPERIMENTAL I n each of the two inside depressions were put 4 drops of well-mixed color standard from a third dropper. The color PREPARATION OF REAGENTS. Good grades of potassium sulfate and barium chloride dihydrate were further purified tests were made by allowing a drop of the titration mixture by recrystallization, and solutions of the two salts were made to fall into a drop of the mercuric nitrate solution on the spot plate. The time was then noted, by counting slowly, in distilled water. Mercuric nitrate solution was prepared by dissolving mer- or with a watch, when the color of the mixture just exceeded curic oxide in nitric acid. After some experiments the fol- that of the standard in intensity. When the tests were made in this manner the color exceeded that of the standard lowing preparation was used : Twenty grams of mercuric oxide were treated with 18 cc. of almost immediately up to within a few cubic centimeters nitric acid, made by diluting 10 cc. of strong acid (s ecific gravity, of the end point. At this stage the amount of titration 1.42) with water. The mixture was stirred wit[ a glass rod, mixture was increased to 3 or more drops per test. Upon and the reaction allowed to take place until the solution became the addition of more barium chloride solution the time strongly turbid. It was then filtered, and to the filtrate were interval before the appearance of the proper yellow color added 6 cc. of water. The solution was allowed to stand several hours before using. During this time a light-colored, crystalline rapidly increased, as shown in Figure 1. An interval of 30 precipitate of basic mercuric nitrate separated out. For best seconds was chosen as the end point. The buret volume results it was found essential to have the acidity of this indicator corresponding to this time was calculated by interpolation solution as low as possible, and to insure this the presence of between the two time intervals on either side of the 30-second the basic nitrate precipitate wa8 required. point, although a fair degree of accuracy could be obtained A color standard was used in determining the end point, by calling that reading closest to 30 seconds the end point. Spot plates were cleaned with cleaning solution and water, and after a number of experiments the following simple dried with filter paper, and preparation was employed: then rinsed with ether. It Potassium sulfate (4.3grams) was found helpful to remove and 0.2 gram of potassium all grease, so that the drops dichromate were dissolved in of l i q u i d f l a t t e n e d out a liter of water. Eight grams properly. Experiments were of barium chloride dihydrate were dissolved in another liter carried out using a spherically of water, To make u p t h e s h a p e d d r o p , such as decolor standard 10 cc. of the scribed by Pond (1) for the sulfate-dichromate s o l u t i o n were p i p e t t e d into a small zinc ferrocyanide titration] flask, and 10 cc. of the barium but satisfactory results could chloride solution were added not be obtained in the present with swirling. Fresh standard determination. was made up each day from A daylight-type e l e c t r i c the stock solutions. lamp was used in the work. All f l a s k s , . p i p e t s , a n d I n determining the time interb u r e t s u s e d In t h e w o r k vals] a greater accuracy rewere c a l i b r a t e d a t l e a s t sulted if the spot plate was twice. moved around so that the test TECHNIC USED IN TITRAmixture was always on the TION. Barium chloride soluFIGURE 1. EFFECT OF ORDER OF ADDITION OF REAGENTS same side of the standard. ,
Y
19
@
ANALYTICAL EDITION
20
ORDEROF ADDITIONOF REAGENTS.Four experimental procedures were tried in determining the best order of addition of reagents. Barium chloride solution was added to potassium sulfate solution, and vice versa, and on the spot plate the titration mixture was added to mercuric nitrate solution, and the reverse. An experimental curve for each of these titrations is given in Figure 1. TABLEI. EFFECTOF ORDEROF ADDITIONOF REAGENTS UPON SENSITIVITY SENSITIVITY (Mean of several)
ORDDROF ADDITION 0.0501 M potassium sulfate solution added to 100 00. of 0.0155 M barium chloride solution. Mercuric nitrate solution added to titration mixture on spot plate 0,0601 M potassium sulfate solution added to 100 ,cc. of 0.0155 M barium chloride solution. Titration mixture added to mercuric nitrate solution on spot plate 0.0621 M barium chloride solution added to 100 cc. of 0.0125 M potassium,sulfate solution. Titration mixture added to mercuric nitrate solution on spot plate 0.0621 M barium chloride solution added to 100 cc. of 0.0125 M otassium sulfate solution. Mercuric nitrate solutior) a&ed to titration mixture on spot plate
90 140 200 150
The sensitivity at the end point will be defined as the reciprocal of the number of milliequivalents of reagent being added from the buret necessary to cause the time interval (before the appearance of the proper yellow color) to change from 25 to 35, or from 35 to 25 seconds. Thus the larger the sensitivity the sharper the end point. The sensitivity for each of these procedures is given in Table I. The average deviation from the mean for these sensitivities is about ~ 3 0 .It was decided from the results in Table I that procedure 3 was the best, and this was used for all later work. Many concentrations of merSTRENGTH OF INDICATOR. curic nitrate were tried. Among the higher concentrations very little difference in behavior was observed, but with dilute solutions a definite drop in sensitivity was apparent. Sensitivities obtained with three concentrations were as follows: 6 M, 210; 3 M, 220; 0.2 M, 130. Approximately 3 M mercuric nitrate solution was used for most of the later work. REACTION TIME. The authors mere uncertain as to the length of time necessary for the completion of the barium sulfate reaction at room temperature, since it is generally believed that precipitation takes place slowly, even in hot solution. The point was cleared up by mixing various quantities of barium chloride and potassium sulfate solutions, and then noting whether the time interval before the appearance of the proper yellow color (in test portions) changed with time. The results are given in Table 11. TABLE11. EFFECTOF CONCENTRATION UPON REACTION TIME 0.0050 M KzSOc 0.0025 M Kzsoc 0.0152 M &so4 23.33 cc. Seconds for yellow color t o appear 33 37 37 34 40 35
.. *.
,
BaClz Minutes after adding BaCln 1.6 3 6 14 15 21
.. ..
7.63 cc. BaClz Seconds Minutes after for yellow adding color t o BaClz appear 4 0.6 9 1 27 2 27 3 26 5
.. .. ..
.... ..
3.70 cc. BaClz Seconds Minutes for yellow after color t o adding BaClz appear 0 1 3 1 5 12 2 18 3 5 32 5 7 27 25 12 30 23
100-cc. samples of potassium sulfate.solution used. 0.0621, M barium chloride solution added. Titration carrled out in neutral solution.
Vol. 6, No. 1
so far worked out. Thus when 0.0621 M barium chloride solution was added to 100 cc. of 0.0125 M potassium sulfate solution (neutral), 19.16 cc. were required, while the stoichiometrical amount necessary was 20.13 cc. The error may of course be overcome by standardizing the barium chloride solution with an easily purified sulfate, such as potassium sulfate. This procedure should be followed in any event, since both barium chloride dihydrate and anhydrous barium chloride are poor standards. EFFECTOF ACIDITY. The acidity of the titration mixture was found to affect markedly the position, sensitivity, and reproducibility of the end point. Results of experiments on this phase of the work are given in Table 111. A neutral or slightly acid solution appears to be the best in running the titration. Experiments carried out a t higher acidities and alkalinities than those of Table I11 gave, in general, more erratic results and lower sensitivities. TABLE111. EFFECTOF ACIDITY SOLUTION BEINQTITRATED 0.0501 M 0.1 N KzSOa Water Acid or base
cc.
a
0.0621 M BaClz REQUIRED MEAN FROM B U R B T ~SENSITIVITY
cc.
25.00 73 2 cc. NaOH 20.02 f 0 . 0 4 25.00 75 None 19.16 fO.O1 25.00 73 2 cc. HC1 18.91 * 0 . 0 1 26.00 70 5 cc. HC1 18.86 f O . O 1 25.00 65 IO cc. HC1 18.74 f 0 . 0 5 Average of four determinations in each case.
170 200 190 200 130
EFFECTS OF OTHERIONS.Titrations of potassium sulfate solutions were carried out in the presence of five times the amount (equivalents) of other salts, in neutral solution. The results are given in Table IV. The errors are seen to be smallest, on the whole, when the solutions were most dilute. Nitrates caused large errors in dilute solution, although in more concentrated solution the error due to calcium nitrate was smaller and different in sign. The results can be explained, for the most part, by assuming precipitation of complexes of the type (Ba, K)SOc when the results were low, and Ba(S04, NO,) when the results were high. TABLEIV. EFFECTOF IMPURITIES MOLALITY~ BaClz O F B ~ C I ZSoLuSOLUTIONTION Cc.
IMPURITY
Grams
604 904 NATUREOF IMPURITY PRESENT FOUND Gram
Gram
0.0482 0.0482 0.0219 2 2 . 9 None None 0.0482 0.0478 0.0219 22.7 0.24 MgClz 0.0482 0,0482 0.0219 22.9 0.24 MgClz 0,0482 0.0480 0.0219 22.8 0.24 MgCIz 0.0482 0.0476 0.0219 2 2 . 6 0.29 NaCl 0.0482 0.0476 0.29 NaCl 0.0219 2 2 . 6 0.0482 0.0482 NaCzHsOz 0.41 0.0219 2 2 . 9 0.0482 0.0476 0.41 NaCzHaOz 0.0219 2 2 . 6 0.0482 0.0478 XI 0.83 0.0219 2 2 . 7 0.0482 0.0476 KI 0.83 0.0219 2 2 . 6 0.0482 0.0471 LiCl 0.21 0.0219 2 2 . 4 0.0482 0.0476 LiCl 0.21 0.0219 2 2 . 6 0.1202 0.1202 None 0.0600 20.86 None 0.1202 0.1170 NaCl 0.0600 20.30 0 . 7 3 0.1202 0.1166 NaCl 0.0600 2 0 . 2 4 0 . 7 3 0.1202 0.1202 19.16 None Npne 0.0653 0.1202 0.1173 LlCl 18.70 0.51 0.0653 0.1202 0.1169 LiCl 0.0653 18.63 0 . 6 1 0.1202 0.1169 LiCl 0.0653 18.64 0.51 0.1202 0.1175 LiCl 18.73 0 . 6 1 0.0653 0.1202 0.1190 Ca(N0a)z 18.97 1 . 0 3 0.0653 0.1202 0.1184 Ca(N0s 2 18.87 1.03 0.0653 0.1202 0.1181 Ca(NOdi 1.03 18.83 0.0653 0.1202 0.1182 Ca(N0a)z 18.85 1.03 0.0653 0.0482 0.0482 None None 0.0219 2 2 . 9 0.0482 0.0490 Ca(N0a)a 0.41 0.0219 2 3 . 3 0.0482 0.0499 Ca(N0s)a 0.41 0.0219 2 3 . 7 0.0482 0.0516 NaNOa 0.43 0.0219 2 4 . 5 0.0482 0.0505 0.43 NaNOs 0.0219 2 4 . 0 0.0482 0.0560 Al(N0a)s 0.36 0.0219 26.6b a Solutions standardized against potassium sulfate. b Solution acid.
ERROR Gram
....
-0.0004 0.0000 0.0002
-
-0.0006 -0.0006 0.0000 -0.0006 -0.0004 -0.0006 -0.0011 -0.0006
....
-0.0032 -0.0036
....
-0.0029 -0.0033 -0.0033 -0.0027 -0.0012 -0.0018 -0.0021 -0.0020 f0:bO~s +0.0017 +0.0034 +0.0023 f0.0078
Even when using as dilute a potassium sulfate solution as 0.0025 M the reaction is essentially complete in about 5 It is to be noted that while some of the errors involved minutes. Titration at room temperature therefore appears to be entirely feasible. However, it is probable that certain are rather serious, they can be largely corrected by having an approximately equal amount of the impurities in the types of impurities cause a slower reaction rate than this. RELATIONOF ENDPOINTTO STOICHIOMETRICAL POINT. sulfate solution used to standardize the barium chloride. INTERFERING SUBSTANCES.The titration cannot be carThe 30-second end point and the stoichiometrical point do not coincide under the (otherwise) most favorable conditions ried out in the presence of appreciable amounts of ammonium
January 15, 1934
INDUSTRIAL AND ENGINEERING CHEMISTRY
compounds, as they prevent the formation of basic mercuric sulfate. The titration is also unsuccessful in the presence of ions that cause precipitates with mercuric nitrate, or with barium chloride, such as tartrates, phosphates, etc. Potassium iodide is an exception (Table IV) . The insoluble mercuric iodide could be made t o dissolve in excess mercuric nitrate solution by stirring the color test mixture with a glass rod, and the end point could then be determined as usual. Colored substances may also make the end point difficult or impossible to detect.
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can then be produced with a smaller amount of titration mixture.
DISCUSSION The method is recommended for routine analysis, rather than for single determinations. All the solutions involved are of stable inorganic compounds, and can be made up in large quantities and kept for long periods of time. The biggest advantage of the method is that it is timesaving. The authors are able to finish an ordinary titration, working individually and not knowing the sulfate content, in TABLEV. EFFECT O F SOLID BARIUM SULFATE UPON ENDPOINT about 10 minutes. This is possible, in spite of the outside indicator, because the method is a direct one, and because a 0.0207 M BttClz SOLUTION NEEDEDPER MILLIMOL Bas01 .TITRATION MIXTURE 100 cc. NEUTRAL KzSO4 SOLUTION preliminary end point is reached (using one drop of titration PER DROP About 0.12 g. About 0.24 g. About 0.36 g. Hg(N0a)z Bas04 formed Bas04 formed Bas04 formed mixture) several cubic centimeters in advance of the final end Drops CC . CO. cc. point (using several drops of titration mixture). Thus the 2 42.2 44.0 44.3 barium chloride solution can be added 2 or 3 cc. a t a time 3 44.7 45.2 45.3 4 45.5 45.8 45.7 until the final end point is nearly reached. The apparatus 6 46.0 46.2 45.9 necessary is also simple and inexpensive. No attempt will be made here to give further procedure EFFECT OF BARIUMSULFATECONCENTRATION ON END for the method other than that connected with the titration POINT. The effect of concentration of barium sulfate, and itself, because of the great variety of substances and solutions of the number of drops of titration mixture per drop of mer- in which sulfate may be determined. curic nitrate on the position of the end point was deterAside from any analytical considerations, the method mined in neutral solution, using 0.02 M barium chloride employed in obtaining Table I1 seems to be useful in measursolution. The results, given in Table V, indicate that the ing the rate of formation of barium sulfate under various error due to difference in concentration of barium sulfate conditions. may be minimized by taking a sufficient number of drops of LITERATURE CITED titration mixture near the end point. This is also recommended because the end point is then more sensitive and (1) Pond, Chemist-Andust, 22 (2), 4 (1933). closer to the stoichiometric point. A small-sized drop of (2) Ray, Trans. Chem. Soc., 71, 1098 (1897). mercuric nitrate is also advantageous, since the same effect RECEIVEDAugust 12, 1933.
Chemical Examination of Trichloroethylene for Anesthesia HERMANL. TSCHENTKE, American Medical Association, Chemical Laboratory, Chicago, Ill.
A
MONG the various chemical compounds recently used for local anesthesia is trichloroethylene, CHCl=CClg. This compound has been described in the literature since 1864; it is not, therefore, a new substance. During the World War, Plessner (8) found symptoms of poisoning in men using trichloroethylene for removing grease from metal parts of machinery, and noted that the poison had special affinity for the sensory fibers of the trigeminal nerve. Oppenheim (1) recognized the possibility of lessening sensitiveness of the diseased trigeminal nerve in cases of facial neuralgia by giving the patient small doses of this compound to inhale. Trichloroethylene has also been developed commercially as a low-boiling, noninflammable solvent for extracting oils, fats, and waxes, for degreasing metals, and for purposes of dry cleaning. For these uses, a rather impure “factory” grade ordinarily has been sufficient. For therapeutic purposes, only a much more refined product is suitable. Several firms have been supplying medicinal trichloroethylene under various brand names, such as Westrosol, Gemalgene, Chlorylen, and Trethylene. Trichloroethylene was presented to the Council on Pharmacy and Chemistry of the American Medical Association for inclusion in “Kew and Nonofficial Remedies” and the Chemical Laboratory was asked to make an examination of the product. Accordingly, examination was made of two brands of trichloroethylene preparations presented; a specimen of Eastman grade and
of a practical grade purchased from Eastman Kodak Co.; and another brand used medicinally, obtained on the open market. The results of this investigation are given in Table I, which includes qualitative and quantitative determinations. The boiling point range of Chlorylen and of Trichloroaethylen zu Chlorylen was determined after extraction of the preparation with an equal volume of water to remove any interfering substances such as alcohol, and subsequent drying of the trichloroethylene layer with anhydrous sodium sulfate. After being notified of the results of the investigation of Chlorylen, the firm indicated a desire to investigate further, and to submit the product again in the future. Based in part on the information in the literature and on the results of the work reported herein, somewhat rigorous standards for identity and purity were elaborated. These were sent for comment to the firm which submitted the product; then in due time the following standards were adopted by the Council on Pharmacy and Chemistry for inclusion in “New and Nonofficial Remedies.” STANDARDS TRICHLOROETHYLENE.~ Trichloroethylenum, trichlorethylene, CHC1:CC12, 1-chloro-2-dichloroethylene. 1 Solutions referred to in the descriptions of qualitative and quantitative teats are, unless otherwise stated. of the strength described in the current U. S. Pharmacopeia.
