1398
ANALYTICAL
solution is introduced into the distillation vessel, followed by aqueous washings of the funnel. With a t the bottom of its runners, the receiving flask containing 10 ml. of 4% boric acid and 3 drops of indicator is placed on K . Ai is then slid up its runners until R engages and holds it in position. The bottom of the condenser tube should now be just ])elow the surface of the liquid in the receiver. If necessary both H and the rod of J can be adjusted in their base collars until the correct height is attained. The taps on E and G and the screi? clip on C are closed. Dry steam enters the sample liquid through the branch of F and distillation ensues. Because A is surrounded by a steam jacket, very little increase in volume occurs. I s the volume of distillate increases, K is depressed until 1.I closes, operating 0 and switching off J . In the construction, the ratio of spring extension of L to the height which the distillate will rise in the receiver (allowing adequate volume for complete distillation) can be so arranged that at least the last 5 ml. of the distillate enter the receiver after the bottom of the condenser tube has come above the surface of the distillate. Larger volumes of distillate can be received by lowering d l in its adjustable slot. R allows iV to slide down its runners and the receiver can then be removed from the pan and its contents titrated. Steam distillations, not requiring the interception of gases as in the Kjeldahl distillation, may be carried out with A: a t the bottom of its runners. Any desired volume of distillate, within limits, can be collected. The salient features in the design and use of the apparatus may be summarized as follows: The glass section of the apparatus can be made in one piece if desired. The ground joint between the distillation head and the condenser is provided merelv for convenience.
CHEMISTRY
Increase in volume due to condensation of steam within the distillation vessel is reduced to a minimum. The steam boiler is heated rapidly and effectively by electricity with very little heat loss. When, however, the circuit is automatically broken on receipt of the desired volume of distillate, the cooling of the element is rapid and the distillation vessel empties itself in about 20 seconds. The single rod stand and clamp are neat and permit rapid adadjustment. The apparatus can be adjusted to receive, within limits, any desired volume of distillate. The operator is free to carry out other duties, knowing that the receiver cannot overflow if neglected and that audible warning will be given a t the end of the experiment. The apparatus is best suited t o employment in banks of four or six units when large numbers of distillations are required. The device for controlling the volume of distillate and time of distillation may well suggest to the reader similar laborsaving devices in his own laboratory. ACKNOWLEDGJIENT
The authors wish to acknowledge the assistance provided in the design and construction of the apparatus by J. C. Button, E. Mears, and J. Nicholson and to thank “Shell” Refining & Marketing Company, Ltd., for permission to publish this paper. LITERATURE CITED (1) Cox, Chemistry & Industry, 56, 913 (1937). (2) Hoskins, J. L., Analyst, 69, 271 (1944).
(3) Kirk, P. L., IND.ENG.CHEM.,BXAL. ED.,8, 223 (1936). (4) Parnas-Wagner (Pregl-Roth) , Mikrochemie, 23, 218 (1937).
Calcium in High=Purity Sodium Salts Determination of Microgram Amounts by the Oxine-Oxalate Method JOSEPH RYNASIEWICZ AND MURIEL E. POLLEY Knolls Atomic Power Laboratory, General Electric Company, Schenectady, N . Y . As little as 0.1 mg. of calcium can be determined in high-purity sodium chloride and sodium nitrate by separating the calcium with 8-hydroxyquinoline (8quinolinol), followed by an oxalate precipitation and titration with 0.01 N potassium permanganate.
0
KLY two chemical methods for calcium in sodium salts could
be found by the authors in the literature ( 1 , d ) . Both methods depend upon the precipitation of calcium oxalate from concentrated salt solutions. The Association of Official Agricultural Chemists (1)describes a method for calcium in sodium chloride of “average” purity. Shuman and Berry ( 4 ) modified this procedure and “calibrated” it by using empirical corrections for varying amounts of calcium in high-purity sodium chloride (above 99.90%). For example, correction factors of $0.006 to -0.003% were added in the case of samples containing 0.02 t o 0.2% calcium. As a 50-gram salt sample is usually taken for analysis, this means corrections of $3 mg. to -1.5 mg. of calcium for 10 to 100 mg. of calcium analyzed. However, Shuman and Berry reported good accuracy for calcium above 0.02% using these correction factors. Tanne (6) found that low results were obtained for calcium and magnesium in proportion to the amount of salt taken for analysis and ascribed this fact to “something which complexed with calcium and magnesium, but did not react with the oxalate and phosphateions.” In another paper (e)he attributed the low recoveries of magnesium to water-insoluble magnesium hydroxide which was formed on hydrolysis. The low results are more understandable in view of the work of Rlaljaroff and Gluschakoff (Z), \Tho deter-
mined the solubilities of calciuin oxalate in the concentrated salt solutions of ammonium, sodium, and magnesium. They found that 36 mg. of calcium oxalate would dissolve in 1 liter of 10% sodium chloride a t 18”to 20” C. The method described below eliminates the undesirable effect of concentrated sodium salt solutions on the solubility of calcium oxalate. As little as 0.1 mg. of calcium can be separated from the sodium salt by precipitation as 8-hydroxyquinolate (calcium oxinate) a t pH 9.5 to 10 along x i t h %hydroxyquinoline (8quinolinol, oxine). After the oxine-calcium oxinate is ashed, calcium is precipitated as oxalate in the absence of high salt concentrations, and measured by titrating with 0.01 iV potassium permanganate. The method assumes the absence of large amounts of cations which would be separated as oxinates and included in the calcium oxalate precipitation. PROCEDURE
Solutions Required. 8-Hydroxyquinoline solution, 2.5% in 5% acetic acid. Ammonium oxalate solution, 0.5 N . Potassium permanganate solution, 0.01 S. Method. Dissolve enough sodium salt in water (up to 50 grams) to give 0.1 to 5 mg. of calcium and make the solution slightly acid with hydrochloric acid. Adjust the volume to a t
1339
V O L U M E 21, NO, 1 1 , N O V E M B E R 1 9 4 9 Table I. Recovery of Calcium from 100 311. of 20% Solutions of Sodium Nitrate and Sodium Chloride by the Oxine-Oxalate 3Iethod Calcium Recovered"
Calcium Added ~
0.09 0.18 0.28 0.37 0.46 0.92 4 GO
0.0005 0.0009 0.0014 0.0019 0.0023 0.0046 0.0230
g
0.07 0.17 0.28 0.33 0.47 0.94 4.66
.
70
0.0004 0,0009 0.0014 0.0017 0.0024 0.0047 0.0233
.\iter
subtrarting blank \.alceq. and 0.03 n ~ g C . a for S a C I .
Table 11.
S o . of
LIg. % Uetns. 0 . 0 8 0.0004 0 . 2 0 o nolo 0 . 2 6 0.0013 0 . 3 8 0 0019 0 . 4 5 0 0023 0.94 4.68
A v Deviation f r o m ]lean
B
3 1 ~
*0.02 *0.04
.to rn
10.03 10.02 +0.02 +=O, 07
*0.0001 = o , 0002 0.0002 +n no02 1Q 0001 1 0 0001 1 0 0004 3
Blank \ya- 0.02 nip. C a fur S n S O , .
Analysis of Calcium in Different Grades of Commercial Sodium Salts
+
Descriiition of Sample l l e r c k ' s h-aCl h-0. 41748 Baker's C.P. KaCI A-0. 6648 Baker's reagent grade T\TaNOa No. 12644 Baker's C.P. S a S O a KO.22445
Ca L!g, Mfrs. Analysis"
Saiupli.
0.01 0.003 0.0003
60 ;i0 50
0.005
30
~
Two grades of comniercial sodium nitrate and oi mlium chloride were analyzed for calciuni by the oxine-oxalate prowdure. The results are reported in Table 11. To check the calcium analysis of the high-purity sodium salt-, 0.28 mg. of calcium was added to 50-gram salt samples. Calcium was determined by t,heoxine-oxalate procedure, and the rcsults :ire rcported in Table 111.
Calciuiii Found 0,002~
< 0 . 000J < 0.0005 < 0.0005
.Inalyses by J. T. Baker a n d Rlerck chemical companies are: Calciuni a n d magnesium are precipitated together in a n ammoniacal solution with oxalate and phosphate. The precipitate is filtered, ignited, weighed, and reported as a single value.
DISCUSSION OF PROCEDURE
Hefore arriving at the oxine-osalate method for calcium i n high-purity sodium salts, an attempt was made to precipitato calcium oxalate without a preliminary scparation from the sodium salts. I t was found that a minimum of 3 mg. of calcium in 20 grams of salt (0.015%) could be determined. This valup xva- in accord with the smallest amount measurable by Shunian arid Berry and is confirmed in Table IFr, which s h o w the recoveries of various amount,s of added calcium from 50 ml. of a 4070 sodium nitrate solution (20 grams of total sodium nitrate) by a direct precipitation of calcium oxalatc from an acetic acid medium (p11 ra. 4.2).
'Table Ill.
Recoveries of 0.28 \Ig. of Calcium iclded t o .io-Gram Samples of Sodium Salts Calcium Found I n salt 0.28 mg. calcium I n salt along added
+
least 100 nil. to give an approximately 2OYOsodium salt) solution. Add 15 ml. of 2.5Y0 oxine solution, and precipitate the osinecalcium oxinate by slowly adding ammonium hydroxide and adjusting to pH 9.5 to 10 using a pH meter. rlvoid an excess of ammonium hvdroxide, as this may redissolve some of the voluminous prec"ipitate. Allow the precipitate to stand for a t least 3 hours, filter through ashless retentive filter paper, taking care that a minimum of cold water is used in transferring the precipitate, and wash once with a 5-ml. portion of cold water. Allow the bulky precipitate t o drain completely, transfer the filter paper and precipitate to a platinum crucible, and dry thoroughly on a moderate hot plate or in a drying oven. If the oxine recipitation was made in the presence of nitrate, great care shouPd be exercised in ashing, for the gases formed during initial charring may expel the m-ad of filter paper from the crucible. The filter paper should be charred from the top to the bottom of the crucible, and when the burning has started, the crucible should be removed from the flame and the filter paper allowed to burn by itself. Ashing should be completed over a burner until a clear melt is obtained. Cool the melt, make i t slightly acid with hydrochloric acid, and transfer to a 50-ml. beaker. Any acid-insoluble material should be removed by filtration. The calcium is precipitated as oxalate from an acetic acid medium ( 3 ) . Make the hydrochloric acid solution slightly ammoniacal and then slightly acid to methyl red with glacial acetic acid. Heat the solution to boiling, add 1 to 3 ml. of 0.5 S ammonium osalate depending upon the amount of calcium present, and allow the precipitate to set'tle ( a t least 30 to 40 minutes). Filter t'he calcium oxalate through a sintered-glass microfilter tube using suction, and wash with small quantities of hot water. Aft,er attaching a clean suction flask to the filter tube, dissolve the precipitate by pouring hot 10% sulfuric acid through t,he filtrr. Transfer the solution to the beaker in which t,he original precipitation was made, heat to about 65" C., and titrate with 0.01 S potassium permanganate. A correction for the oxine reagent i* unnecessary, as it contains less than 0.00470 calcium. RESULTS
Table I show3 the recoveries of 0.1 to 5 mg. of calcium froin 100 nil. of 20% solutions of sodium nitrat,e and of sodium cliloridc. The values given in Table I were obtained by two independrnt analysts. Of 35 determinations made, only 6 exceeded a11 average deviation of +=0.04mg. of calcium. The results indicate that whereas small amounts of calcium are lost in the range 0.1 to 0.4 mg., the average deviation is not prohibitive in estimating 0.1 mg. of calcium. This is equivalent to 0.0005~ocalcium, which value is 40 times more sensitive than hithrrt? rrI1ortcd results.
Salt
l l e r c k ' s C.P. S a C l No. 4 1 i 4 8 Baker's C.P. NaCl h-0. 6648 Baker's reagent grade NahOs No. 12644 a
Rrcovery of 0.28 M g . Calcium Added
1.03 0.03"
1.29 0.27
n. yf,
0.03"
0.28
1-1.
(1.2%
2.5
Figures represent blank values for respective salts.
Table IV. Recovery of Added Calcium from 50 M I . of 4070 Sodium Nitrate Solutions by Direct Precipitation as. Calcium Oxalate Calcium Added Mg.
0.09 0.4G 0.92 4.60 0.46 0.00
SaSOa Present Grams 20 20 20 20 Sone 20
Calcium Recovered MQ.
0.09 0.03 0.63 4.58 0.48 0.03
The method of Marsden (3') has a 2% accuracy for 0.1 to 5 rng. when calcium is precipitated as oxalate in 20 ml. of acetic acid solution. Apparently there are two factors which cause loiv results: the concentration of sodium saks on the solubility of calcium oxalate as reported by Maljaroff and Gluschakoff, and the cffect of the increased volume of solution from which calcium oxalate is precipitated. The mechanism of the osiiie scparation is not clear. Calcium is probahly precipitated as the osinate and i s occluded, coprrcipitated, or ahsorbed by the flocculent oxine precipitate. Cntloubtedly the solubility of calcium oxinate would be prohibitive in rlctermining microgram quantities of calcium were it not for the tii:neficial effect of the large excess of precipitated oxinr. The low results reported for less t'han 0.4 mg. of calcium may tJe :tscribed in part to operative errors in transferring the precipitates, ashing, etc., but it is more probable that this is caused tly the solubility of the calcium osinate-oxine precipitate in the watcr \\ash solution. Tracer experiments with radiocalcium ( C a ' j ~ showed that 3 mg. of calcium (microgram amounts of this carrier could not be used because of low specific activity) were precipit ated quantitatively as calcium oxinate-oxine from a 20% sodium nitrate solution, but that about 5y0calcium was lost in two washings. Therefore, a minimuni amount of washing is advisable,. Because magnesium can be Precipitated under the sanic roii-
1400
ANALYTICAL CHEMISTRY
ditions as calcium, i t is entirely possible that magnesium can be estimated in the filtrate from the calcium oxalate precipitation. ACKNOWLEDGMENT
The authors wish to express their appreciation to L. P. Pepkowitz and J. F. Flagg for helpful suggestions during the course of this work and for reviewing the manuscript. LITERATURE CITED
(1) Assoc. Offic;,Agr. Chemists, “Official and Tentative Methods of Analysis, 6th ed., p. 664, 1945.
Maljaroff, K. L., and Gluschakoff, A. J., 2. anal. Chem., 93,265 (1933). Marsden, -4. W., J . SOC.Chem. I n d . , 60, 20 (1941). Shuman, A. C., and Berry, N. E., IXD. ENG.CHEN.,ANAL.ED.,9, 77 (1937).
Tanne, Carl, Chem. I b i d . , 63,93 (19391.
Ztg., 62, 572 (1938).
>larch 15, 1040. The knoll^ .itoInic Power Laboratory is operated by the General Electric Research Laboratory for the Atomic Energy Commission. The work reported here was carried out under contract 50.\T-31-109 Eng.-52.
RECEIVED
Determination of Unsaturation by Microhydrogenation Method and Apparatus CLYDE L. OGGAND FRANCES J. COOPER Eastern Regional Research Laboratory, Philadelphia 18, P a . A n apparatus and method for quantitative microhydrogenation are described. The simple design of the apparatus is made possible by use of magnetic stirring to agitate the reaction mixture. Data are presented to indicate the precision and accuracy of the method.
Q
UANTITATIVE hydrogenation as a means of measuring unsaturation has several advantages over the halogenation methods commonly used. This method is not subject to the errors resulting from the presence of two or more conjugated double bonds or from complex molecular structure. Except for choosing the correct catalyst for determining aromatic or aliphatic unsaturation, conditions for hydrogenation do not have to be empirically adjusted to the material being analyzed, as do those for halogenation. I n general, hydrogenation is more reliable, for it eliminates the necessity of previous knowledge of the molecular structure, Another important advantage is that a high catalyst-to-sample ratio can be used. This aids in obtaining complete hydrogenation and in overcoming the effects of poisoning the catalyst by small amounts of sample impurities. Halogenation micromethods are seldom used because of the many inherent errors. Several authors have described hydrogenation microapparatus that have given reliable rrsults. Among them are Johns and Seiferle ( I ) , whose relatively simple apparatus was mounted on a plywood board and shaken as a single unit to agitate the reaction mixture. The apparatus of Prater and Haagen-Smit (3) was also mounted rigidly and rocked by an eccentric driven by a motor. It had two completely symmetrical systems, which were connected; one served as the reaction system and the other as the compensator. When no temperature compensation was necessary, tn o determinations could be run simultaneously. The apparatus described here is more simply constructed and much more easily assembled than the two just mentioned, for a stationary reaction vessel is used and agitation is produced by magnetic stirring. This type of agitation for hydrogenation Kas first desciibed by Keygand and Werner ( 4 ) and more recently by Zaugg and Lauer (5),whose semimicroapparatus was designed for both Grignard and hydrogenation determinations. Blthough Weygand and Werner’s apparatus is the simplest yet described, the manometer-buret assembly with rack and pinion device for
leveling bulb adjustment described here makes possible more accurate volume measurements. This part of the apparatus is adapted from the Soltys’ active hydrogen apparatus sold by Arthur H. Thomas Company. The ball joint connection gives the apparatus greater flexibility, and the detachable reaction vessel with standard-taper joint is easily accessible for cleaning. APPARATUS
Figure 1 shows the apparatus and hydrogen purification train. The purification train consists of a standard micro electric combustion furnace, A , heated to approuimately 750” C. so that the platinum star contact catalysts, C, in the 8-mm. inside diameter quartz combustion tube, B , will effectively remove the oxygen from the hydrogen gas, The water so formed is absorbed by indicating Drierite in the inner tube of the Prater ( 2 ) semimicro absorption tube, D. If the hydrogen gas is wet, it is advisa-
Figure 1. Hydrogenation Microapparatus
