894
ANALYTICAL CHEMISTRY
these two methods, together with one of the tapered-hole diJk a ithout added load. The Potter-McLennan disk gives good sensitivity up through grease E, but strikes bottom on all the softer greases. The 30gram cone measures all the greases, but owing to bouyancy, its sensitivity is low compared with the disk methods. There i3 a total spread of only 108 points over the nine greases tested, and there is a definite tendency for the sensitivity to decrease among the soft gremes. The data spread with the tapered-hole disk without load i J 233 points over the same range of consistencies. Its sensitivity is substantially tbe same as that of the 30-gram cone in the harder greases, and it is increasingly sensitive in the more fluid range. The Precision penetrometer timer was used for all data presented in this paper. Reproducibility was greatly improved over manual timing in the soft greases, wherein the disk moves continuously over the 5-second period. It was also found essential that the penetrometer cup be level full (except when the beakets were used) for each determination, in order to obtain good reproducibility with any of the instruments. The new disk-type penetrometer having tapered holes ha3 proved useful for grading semifluid greases. It is used in (>onjunction with the ASTM penetrometer, and it can be fabricated simply and cheaply. Its use requires no special skill or training other than that required for operation of the ASTJI penetrometer. LITERATURE CITED
A
B
C
D
E
F
C
~
I
GREASE
Figure 4.
Comparison of Penetration Methods
( 2 ) Brunstrum, L. C., A S T M Bull. 154, 66-7 (1948). 1 3 ) Brunstrum, L. C., and Steinbruch, R., Inst. Spokesman (Satl.
Lubricating Grease Inst.), 8, No. 8, 10 (1949). :4) Buchdahl, R., Curado, J. G.. and Braddicks, R., J r . , Rev. Sci. Instruments, 18, 168 (1947).
6 )Combes, K. C., Ford, C. S., and Schaer, W. S., IXD. Esc. CHEY.,AKAL.ED.,12, 285-7 (1940). ( 6 ) .\lacMichael, R. F., J . Ind. Eng. Chem., 12,817-8 (1920). (7) Potter, R. -1..and McLennan, L. W.,Inst. Spokesmn?r ( S a t l . Lubricating Grease Inst.),8, S o . 9. 16 (1949). ( 8 ) JVicker, R . C., and Geddes, J. A , . dSTMBulZ. 120, 11-15 (1943).
(1) Am. SOC. Testing Materials, "Standards on Petroleum Products
Lubricants," Designation D 217-48, November 1950.
R E C E I V Efor D review M a r c h 23, 1951. A i c e p t d Soveiiiher 13, 1951.
Spectrophotometric Study of Cadmium-1,lO - Phenanthroline System COE WADELIN WITH M. G. SIELLON Purdue University, Lafayette, Ind.
X
VIEW of the successful use of 1,lO-phenanthroline as a
I reagent for the determination of iron (6),an investigation of the spectrophotometric properties of the cadmium-1,lO-phenan-
throline system was undertaken to determine the feasibility or' using it for the determination of cadmium. The possibility of such a method was indicated in the earlier work by the strong interference of cadmium in the determination of iron. The dissociation constant of the cadmium-tris-l,lC-phenanthroline complex was recently reported to be 6.4 X 10-'6 ( 4 ) . As the complex is colorless in solution, the ultraviolet region of the spectrum was scanned in order to see if any absorptive characteristics there could be used. It was found that 1,lO-phenanthroline itself absorbs radiant energy in the region from 200 to 300 mp and that the curve is modified by the presence of cadmium salts. Typical curves are shown in Figure 1. REAGENTS
Doubly distilled water x a s used throughout. I n order to ensure the absence of iron, a standard solution of cadmium chloride was prepared by electrolyzing a solution of J. T. Baker Chemical (20,'s C.P. cadmium chloride according to an ASTM method ( 2 ) , using a xeighed platinum cathode. The electrode ivas dried and rexveighed, then the cadmium deposit was dissolved in a minimum amount of reagent grade hydrochloric acid and diluted to 1000 ml. All other chemicals used wexe of reagent grade, no further puriEcation being made. APPARATUS
Measurements of the absorption of radiant energy were made with a Beckman quartz spectrophotometer, Xlodel DU. The
wave-length scale w-as calibrated frequently with a mercury arc using the lines at 546.1 and 135.8 nip. The instrument i v m operated a t a constant slit width of 2 mm. when quantitative measurements were being made. This slit width gives a hslfintensity band width of 2.5 mp at 211 mp. Matched 1-cxn. cells were used. pH measurements were made fiith a Beckman pH meter, Model G. It was calibrated several times each day with a Clark and Lubs buffet of pH 7.00 prepared from sodium hydioxide and sodium dihydrogen phosphate (3) Volumetric flasks were calibrated by M eighing. Pipets were not calibrated, exce t for a 5-ml. Nohr pipet used t o measure the cadmium chlorife solution, since all other constituents ere added both to the blank solution and to&e solution containing cadmium. EFFECT O F 4CIDITY
Consideration of the fact that 1,lO-phenanthroline exhibits basic properties attributable to the nitrogen atoms contained in pyridinelike rings indicates that changes in hydrogen ion concentration might be expected to affect the properties of the compound, including the absorption of radiant energy. In order to study the effect of acidity, a series of curves correlating transmittancy and wave length was made a t pH's ranging from 3.0 to 8.0, covering the wave-length range from 200 to 300 mp. Two curves were determined at each pH value, one using a solution which was 2 X 10-5 M in 1,lO-phenanthroline, the other using a solution which contained the same concentration of 1,lO-phenanthroline, and also 1 X 10-5 -11' cadmium chloride. The pH was adjusted with 0.02 V hydrochloric acid and 0.02 AI' sodium hydroxide. Since the system nas not buffered, the pH was again measured after the curves xere run, in order to detect any change. J\'ater was used as the blank solution in each case, it having been determined in advance that hvdrochloric acid and
V O L U M E 2 4 , NO. 5, M A Y 1 9 5 2
895
Effect of Diverse Ions
Table I.
(All solutions 2 X 10-4 .If in 1,lO-phenanthroline, 6.7 p.p.ni. cadmiuii~,pH 5.9, meaqrired a t 241 nip, 2.5-nip band x i d t h , 1-cin. cell;;) M a x . Concn. Direrae .4dded Concn., Error, for 2% Error. Ion as P.P.31. 70 P.P 11.
XI14 Fe--
-
SHaCl FeCIz
Sa-
En-Zn+Br ;LO3
-
KHzOH SO4--
Sad04
Fe--Li 3Ig + Hg++ CrzO;-+
Ion-
INO3 ClOI IO, -
500 500 250 IO
SaCl HzBnClc ZnClz KBr NaCl KClOa KaF SHzOII.IIC1
+
.io0 500
3
0 500
500
?on-L 500+
500 0 12 50 Ions Absorbing at 241 m p
FeCla LlCl MgCh HgCh Ion+
0 Ppt. 90 0 0
jno
NaS08 KC104
vas-
500+ 0 500
83 0
4
KCI
Ii-
c1-
Ions Not Absorbing a t 241 m p 500 0
0.100 -11 potassium dihydrogen phoiphate and 1 ml. of 0.193 M .odium hydroxide and, were diluted to a final volume of 50 ml. The resulting solutions had a pH of 5.85 zkO.05 (3).
I
Reproducibility and iccuraq
Amount of cadmium taken in each sample was 5 p.p.rn.1 Cadmium Pound, P.P.XI. Sample No. 1 5 03 .5 00 2 3 5 20 4 5 06 5 f 86 o 06 4 94 4 97 9 4 97 10 5 00 Xumber oftests, n 10 Averaee. 5.009 n.o.m. ~, X < I S % confidencelimits for 5,009 h o 061 p.p.rn. Standard deviation 0.0850 p.p.m. .%rerage de\.iation 0 063 p.p.rn.
: h
~
~~
F
1
.
EFFECT OF CADMlUhI COYCESTRATION
In order to determine whether the syst,em follow Beer’s lam-, t\To series of solutions were measured. In the first series the concentration of 1,lO-phenanthroline was 1 X 10-4 M in each solution. The concentration of cadmium chloride was varied ironi zero to 5.3 X 10-5 M . I n the second series, the 1 , l O phenanthroline concentration was 2 X 10-4 M and the cadmium chloride concentration was varied from zero to 2 X 10-4 M. Beer’s law is folloxed in the first series up to a cadmium concenrration of 4.5 X 10-5 ;If and in the second series up to a cadmium Concentration of 8 X 10-5 111. The latter case corresponds to a :iiaximum cadmium concentration of 0 p.p.ni. The molar absorbancy index in the range of Concentration where Beer’s law holds is 3980. The molar ratio of 1,lO-phenanthroline to cadmium a t the point where negative deviation from Beer’s law first appears is 2.5 to 1. Maximum absorbancy is attained within 10 :>:inUtes and t.he solutions are stable for at least 5 hours before the aimrbancy decreases by more than 1% of the initial value. EFFECT O F DIVERSE IONS
The diverse ions studied are listed in Table I, which is divided into two general classes, ions that do not absorb radiant energy oi wave length 241 mp and those t,hat do. This classification is based on experiments in which solutions containing 500 p.p.ni. of diverse ion were compared with water. 200
I 225
1
I
I
250
2 75
scn
L I a r e l t r i g t h , rnM
Figure 1. .4bsorbanc>-of 2 X M 1,lO-PhenanthroM 1,lO-Phenanthroline with 1 X line and 2 X M Cadmium Chloride pH 5.84 1-cm. oells
Water blank
2 - m p band width
The general procedure I n s t o add t o 26 ml.of buffer solut,ion, contained in a 50-ml. volumetric* flask. the desired amount of a solution containing 10 mg. of diverse ion per ml., and 3 nil. of 3 x 10-3 M cadmium chloride solution. Then 10 ml. of 1 X 10-8 .If l,lO-phenant,hroline solution were added and the solution was diluted to 50 ml. This made the final concentration 2 X M in I,lO-phenant,hroline and 6.7 p. p, m. of cadmium. The absorhancy, det,ermined in the manner already described, R-as t,hen compared 1vit.h 0.239, the ahsorbancy of :I similar solution which
896
ANALYTICAL CHEMISTRY
contained no diverse ion. For each diverse ion a concentration of 500 p.p.m. was tried first. If this gave more than 2% relative error in absorbancy, another solution was prepared containing half as much diverse ion. This process was repeated until an absorbancy error not exceeding 2% was obtained. The data in Table I were chosen t o give some idea of the magnitude of the interference. Of the ions that do not absorb radiant energy a t 241 mp, ammonium, potassium, sodium, bromide, chloride, chlorate, and fluoride ions and hydroxylamine may be present in concentrations of more than 500 p.p.m. without interference. Iron(I1) and zinc ions must be absent. A precipitate forms when the concentration of tetrachlorotin(I1) ion exceeds 3 p.p.m., or that of sulfate ion exceeds 5 p.p.m. The ions that absorb radiant energy a t 241 mp must be absent from the solution, except for lithium, magnesium, mercury, and iodate ions. These are weak absorbers and may be present in the concentrations indicated in Table I. Reproducibility and Accuracy. A solution containing 250 p.p.in. cadmium was prepared by dissolving 0.1043 gram of anhydrous cadmium chloride in 250 ml. of water. One milliliter of this solution was used for each of ten samples to test reproducibility and accuracy. The measurements were made as described above, the total volume of each solution being 50 ml ThiE made the concentration of cadmium 5 p.p.m. The results of this series of measurements are shown in Table I1 (1).
CONCLUSIONS
An interesting revelation of the diverse ion study is that some ions, such as nitrate and iodide, which are colorless and usually considered harmless so far as interference is concerned, absorb radiant energy in the ultraviolet region of the spectrum and must be dealt with accordingly. This phenomenon makes it necessary to exercise care in selecting reagents for the dissolution of samples, for the preparation of pH buffers, and for other purposes incidental to the procedure. The method described is capable of rapid, reproducible determinations of cadmium up to 9 p.p.m. It is useful for certain applications, such as rate studies, although the interference of many ions makes it impractical for general use. LITERATURE CITED
(1) Am. SOC. Testing Materials, Philadelphia “A.S.T.M. Manual on
Qualit) Control of Materials,” p. 46, 1951. Am. SOC. Testing Materials, “Methods of Chemical Analysis of hIetals,” p. 178, 1946. (3) Clark, “Determination of Hydrogen Ions,” Baltimore, Williams and Wilkins Go., 1929. ( 4 ) Douglas, Laitinen, and Bailar, J . Am. Chem. SOC.,7 2 , 2 4 8 4 (1950). (5) Fortune and hlellon, IND.ENG.CHEM., ANAL.ED.,10, 60 (1938). (2)
RECEIVEDfor review August 23, 1951. Accepted November 21, 1951. Taken from a thesis submitted to t h e faculty of Purdue Cniversity by Coe Wadelin in partial fulfillment of t h e requirements for t h e degree of master of science, January 1951.
Precipitation of Calcium from Homogeneous Solution with Methyl Oxalate LOUIS GORDON
AND
’
K A recent paper Holth ( 4 ) presented a critical study of pro-
cedures that have been suggested for the separation of calcium from magnesium by precipitation as the oxalate. Both his examination of the various methods and his own investigation indicated that inverse precipitation was desirable when more than 25y0 magnesium is present in a solution containing calcium and that a standing period of 4 hours is necessary. Holth’s study did not include the urea method ( 2 , 5, 7 ) for the precipitation of calcium from homogeneous solution. This method accomplishes a satisfactory separation from magnesium, even in dolomite, with one precipitation. However, it also requires a 3- to +hour standing period; longer standing is not permissive because magnesium may coprecipitate. Oxalate ion produced by the hydrolysis of organic esters has been used to precipitate thorium and the rare earths (8), magnesium (S), and zinc ( 1 ) from homogeneous solution. The use here of methyl oxalate to precipitate calcium results in wellformed crystals which can be filtered and washed with ease. PROCEDURE
Dilute the solution containing calcium and magnesium chlorides to 150 ml., and then adjust the pH to 4.7 with dilute ammonium hydroxide or hydrochloric acid. Add 100 ml. of ammonium acetate-acetic acid buffer, 2.5 M with respect to each. Then add 10 grams of pure methyl oxalate; the latter if partly hydrolyzed should be recrystallized from methanol. Cover the beaker, then heat on a regulated hot plate a t 90” C. for 2.5 hours. Stir occasionally. As a precautionary measure, especially if there is doubt as to the full maintenance of the proper temperature throughout the period of precipitation, add, 10 minutes before filtration, 10 ml. of a solution containing 0.5 gram of ammonium oxalate. Cool the solution rapidly to room temperature. Filter through previously weighed Selas crucibles of medium porosity and wash with 1% ammonium oxalate solution. Dry the precipitate for 1 hour a t 110” C., then ignite a t 500” C. for 2 hours. After cooling, moisten the precipitate with several drops of saturated 1 Present
A. F. WROCZYNSKI1
Syracuse University, Syracuse, N. Y .
address, Imperial Paper and Color Corp., Glens Falls, N. Y.
ammonium carbonate solution, then heat in an oven a t 110’ C. for 1 hour and weigh as calcium carbonate. PRELIMINARY INVESTIGATIONS
Materials Used. C.P. calcium carbonate, Iceland spar quality, was dissolved in hydrochloric acid and the resulting solution was standardized according t o the conventional method ( 7 ) of adding ammonium hydroxide to an acid solution containing ammonium oxalate. Methyl oxalate, Paragon, was recrystallized from methanol and stored in a dry atmosphere. All other chemicals used were C.P. quality. Effect of pH. Calcium oxalate can be quantitatively precipitated a t p H 4 (7). Because hydrogen ion is a product of the hydrolysis of methyl oxalate, it was necessary to utilize an equimolar mixture of acetic acid and ammonium acetate as a buffer. It is not necessary to maintain the pH a t one level, but simply to prevent the solution from becoming too acidic. The choice here of final pH control a t 4.2 to 4.4 was based on the characteristics of the buffer system selected. The effect of pH, as is shown in Table I, is not critical. Effect of Excess Methyl Oxalate. The use of 3 grams of methyl oxalate, which furnishes the approximate quantity of oxalate ion
Table I.
Effect of pH on Precipitation of Calciumu so.
(Ca taken, 0.0503 gram) Difference, Final pHb Gram
4 Recommended procedure with modified amounts of buffer constituents t o obtain varying final pH values. b Initial p H of 4.7 for all determinations.
