Use of High Frequency Titrimeter Volumetric Determination of Beryllium KERMIT ANDERSON
DAVID REVINSON'
AND
Fairchild Engine and Airplane Corporation, Oak Ridge,. Tenn.
A new high frequency titrimeter using a grid dip-type oscillator was investigated as an instrumental method for assay of beryllium metaI and for determination of beryllium in beryllium oxide and beryllium carbide. The instrument proved to be adaptable to the titration of beryllium ion with sodium hydroxide. The titration of beryllium ion furnishes a new example in which the high frequency titrimeter has served to indicate the end point of a volumetric reaction involving an amphoteric substance.
B
ERYLLIUM has been one of the few remaining elements
that has successfully withstood an accurate analysis by volumetric means (a, 5, 6). Since a suitable method for the rapid volumetric assay of beryllium metal was needed in these laboratories, it was decided to investigate the use of the grid-dip oscillator-type titrimeter (3) for this purpose. Jensen and Parrack ( 4 )and West ( 7 ) have adequately reviewed the literature on the rapid development of this instrument. Since the great majority of modern developments in beryllium chemistry are under security restriction, it is somewhat difficult to give an adequate review of the analytical chemistry of this element. With the electronic titrimeter, reasonably satisfactory results could be obtained using either triammonium phosphate, ammo1 Present address, New York Operations Office,U.9.Atomic Energy Commission, New York,N. Y.
nium hydroxide, or sodium hydroxide as the titrating agent However, sodium hydroxide gave the sharpest breaks in the titration curve and hence R&S selected as the most promising for this work. Work is expected to continue with various reagents for volumetric analysis of beryllium in these laboratories. APPARATUS AND
The titrimeter used in this work was a grid-dip oscillator-type instrument developed and built in the NEPA laboratories. The instrument and its operating characteristics are more fully described in an earlier paper by Anderson, Bettis, and Revinson ( I ) . Standard 0.5 N sodium hydroxide was used. It was ke t in wax-lined bottles, free from carbon dioxide. Standard berykum solution was prepared by dissolving National Bureau of Standards beryllium metal No. 2700 in a slight excess of 1: 1 hydrochloric acid and then evaporating to near dryness. Distilled water was
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Figure 1. Titration of Beryllium with Sodium Hydroxide
Beryllium Titration in Air in Presence of Free Hydrochloric Acid
0.0302 gram of B e i n 100 ml. of solutian containing freeHCI titrated with0.4320 N NaOH i n air at 22 me.
100 ml. of solution titrated with 0.4320 N NaOH i n air a t 22 mc.
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V O L U M E 2 2 , NO. 10, O C T O B E R 1 9 5 0 added and evaporation was repeated. .-lfter adding more water and filtering if necessary, the solution was dilut,ed to a known volume, the p H of which was ahout 5.2. This procedure was followed in order to remove the free liydrochloric acid that was present. An aliquot was taken and a precipitation carried out using ammonium hydroside to gravimetrically determine the amount of ber>-lliumpresent. PROCEDURE
Preliminary work with the titration showed that the cntire system had to be kept free of carbon dioside. T h e analytical procedure was carried out in hydrochloric acid solution to eliminate all chance of dissolving carbon dioside, and the tit,ration was carried out under an inert atmosphere of nitrogen or argon. + 25
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Figure 1 shows the curves obtained when different :tmounts of beryllium were preseiit :ind the titration was carried out i n air. h definite relationship \\-as otxerved betn-eeri the aniour.t of Iicryllium present and the aniouiit of titr:iut required. Hoivrvrr, ~v acid was present, as must lie the case in routine s:iniple :meil> the curve in Figure 2 \vas obtained. The flatness of the acitl ncutralization curve invalidates this type titration. In order to ovcrcome this difficulty, the titreitions were performed uzing ceirbon t 25
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Figure 3. Beryllium and Free Hydrochloric Acid Titrated with Sodium Hydroxide 100 ml. of solution containing indicated weight of Be titrated with 0.4320 N NaOH a t 22 mc. u 4 n g carbon dioxidefree reagents i n nitrogen atmosphere
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Owing to the presence of hydrochloric acid in the solution to be titrated, two breaks in the titration curve were observed, the first for the free acid and the second corresponding to the end point for the beryllium titration. Care was taken to ensure that a reasonable amount of free acid was present in the solution, and a calibration curve was set u p plotting the quantity of sodium hydroxide used between the two breaks in the titration curve against quantity of beryllium present. The solution to be titrated was placed within the condenser plates in a 37-mm. test tube. After allowing the titrimeter 10 minutes to warm up, the range was first set t o obtain, over the whole galvanometer scale, the total current change given during the complete titration. This was obtained by preliminary runs and was satisfactory for other similar samples. Once the range was determined, the current from the battery was adjusted to balance the grid current a t whatever portion of the galvanometer scale the readings were t o be started. Upon titrating in the normal manner and plotting grid current against volume of reagent added, the end points could be detected by sharp breaks in the curve. Of the interchangeable coils available to give the necessary high
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I., Zacodskouo Loh., 12, 543-6 ( 1 9 4 6 ) . (6) Torley, R., and Waidbauer. L., Proc. Ioira A c a d . Sci., 48, 277 (1941 ). (7)
West, P. IT.,Burkhalter, T. S., and Broussard, L., . k s . i ~CHEU., . 22, 4G9 (19 5 0 ) .
RECEIVEDhIarch 2 , 1950. Presented before the Division of .inalytica! and Micro Chernistry a t the 116th Meeting of t h e . i \ r ~ ~ r c aCsH E \ I I C A L SOCIETY..itlantic City, S . J. This paper is based o n work performed under contract for the United Stater Air Force by the NEP.i Division, Fairchild Engine and Airplane Corporation a t O a k Ridge, Tenn.
Amperometric Titration of Fluoride with Lead HESRT G . PETROW AND LEONARD K. NASH Hurcurd University, Cambridge, Mass. The amperometric titration of fluoride ion with lead, in a solution of 0.1 M chloride ion, is described. Lead chlorofluorideprecipitates smoothly if the pH of the solution falls in the range 5.5 to 6.5 and if the ionic strength of the solution is not excessive. The difficult separation of this fairly soluble precipitate from its mother liquor is completely avoided. Simple equipment is sufficient, thermostating is unnecessary, the solutions need not be deaerated, small concentrations of anions other than sulfate do not interfere, and the complete determination takes less than 1 hour. Cnder favorable conditions the results are accurate to a few tenths of a per cent.
I
S A recent publication (4)Kaufman has called attention to some weaknesses in the determination of fluoride ion by a widely practiced volumetric procedure. This method ( 2 ) involves the precipitation of the fluoride as lead chlorofluoride, followed by a separation of the precipitate from the mother liquor and a Volhard titration of the chloride content of the precipitate. A difficult quantitative separation of a relatively soluble-0.32 gram per liter of water a t 25’ C. (2)-precipitate from its mother liquor is involved, and considerable experimental manipulation, including two quantitative filtrations, is required. The method involves the addition of large excesses of solid reagents, and the original precipitate must age overnight. Kaufman indicates the necessity for particularly precise p H control between the narrow limits of 4.60 and 4.70, but even then it is not possible to secure or to work with quantities results of an accuracy surpassing 17, of fluoride less than about 15 nig. There is also an indirect lead chlorofluoride method ( 7 ) in which this salt is precipitated by the addition of excess lead and a measured escess of a determinate chloride solution to a chloride-free solution of the unknowi fluoride. After filtration of the precipi-
tate the excess chloride is determined by argentometric titration of an aliquot of the filtrate. This procedure also requires that the primary precipitate be aged for 12 hours; also, quantities of fluoride less than 19 mg. have not been determined. The distinctive advantages of the clean lead chlorofluoride precipitation can be retained in a swifter and more generally satisfactory procedure based on the direct amperometric titration of fluoride with lead in a chloride medium. I n that it eliminates the necessity of making a quantitative precipitation and/or a quantitative separation of the precipitate, the amperometric, like the conductometric, determination of the end point is particularly valuable when, as in the authors’ determination, the precipitate is appreciably soluble. Langer reports (6) that in dilute fluoride solutions this titration fails because of the slowness with which the precipitate separates. However, after the authors initiated this investigation, Haul and Griess ( I ) , working with higher concentrations of fluoride, described both polarographic and amperometric titration procedures based on the precipitation of lead chlorofluoride. I n the polarographic procedure a determinate chloride-bearing
