V O L U M E 2 3 , NO. 10, O C T O B E R 1 9 5 1 it was necessary to look for a spectroscopic buffer. Langstroth and hIcRae ( 6 ) , after a study of transport phenomena in the arc, outlined the requirements of a good buffcr. After a study of these requirements and attempts to use previously reported buffers, it was decided to attempt the use of lithium tartrate. Lithium tartrate prepared from reagent grade lithium carbonate and tartaric acid and recrystallized was sufficiently pure for these experiments.
.
, 0-0-
1469 The elements included in this study may be listed qualitatively with respect to their effects on each other in the direct current arc BB follows: tin, potassium, cobalt, calcium, phosphorus. In this list any element will depress the intensity of lines of elements to its right and enhance the lines of elements to its left. This is similar to the arrangement given by Brode and Timma (9), who assigned quantitative values to their series. The data reported here confirm the relative positions of tin and calcium as observed by Brode and Timma. The other three elements were not included in their report.
0
LITERATURE CITED
(1) Brode, W. R., and Hodge, E.
S.,J. OpticaL
Roc. . 4 m , 31, 58
(1941).
LOG MICROGRAMS CALCIUM Figure 6. Effect of Calcium on Spectral Line Intensities of Cobalt and Phosphorus in Presence of Lithium Tartrate Buffer Cobalt present, 0.10 mg. Phosphorus present, 0.03 mg.
Results shown in Figures 5 and 6 indicate the effectiveness of the lithium tartrate buffer when used a t a concentration of 35 mg. of lithium tartrate per milliliter of test solution. The buffer has the added advantage of not flaking off during euritation of the sample, with increased precision as ii result.
(2) Brode, W.R.,andTimma, D. L., Itrid., 39,478(1949). (3) Ells,V. R.,Ibid., 31,534 (1941). (4) Langstroth, G.O., and Andrychuk, D., Can. J . Research, 26A. 39 (1948). ( 5 ) Langstroth, G. O., and hIcRae, D. R., Ibid., 16A,61 (1938). (6) Melvin, E. H., and O'Connor, R. T., IND. ENG.CHEM.,ANAL. ED.,13,520(1941). (7) Morris, V. H., Pascoe, E. D., and ;ilexander, T. L., Cereal Chem., 22,361 (1945). ( 8 ) Parks, R. Q., J.Optical Soc. Am., 32,233(1942). (9) Slavin, M., IND. ENG.CHEM.,ANAL.ED.,10,407(1938). (10)Smith, F. M., Schrenk, 1%'. 0.. and King, H. H., A N ~ LCHEM., . 20,941(1948). i l l ) Zehden, W., J. Sac. Cheni. I i d . , 59,236 (1940). RECEIVEDMay 7, 1951. Presented before the Division of Analytical Chemistry a t the 119th Meeting of the AMERICAX CHEMICALSOCIETY, Cleveland, Ohio. Contribution 438, Department of Chemistry. From a thesis submitted as partial fulfillment of the requirements for the drgrre a t Kansas Statc College.
M.S.
Determination of lanthanum in Rare Earth Mixtures F. T. FITCH AND D. S . Kt'SSELL Ilictional Research Laboratories, O t t a w a , Canada Lacking any absorption lines, lanthanum cannot be determined colorimetrically like most other rare earths. Although i t can be estimated spectrographically, a simple method of determining semimicro quantities would be preferable. Several iminodiacetic acids were found to be effective eluting agents for the rare earths. In general, they commenced removal of the earths almost immediately and could be operated a t higher concentrations than the usual citric acid solutions. Conditions could be chosen for hydrazinodiacetic acid where lanthanum was left on the resin bed even when washing was w n -
C
HROSf ATOGRAPHIC techniques utilizing an ion exchange resin adsorbent have been applied successfully to the separation of the rare earth mixtures (4, 12). The elements TI ere resolved into bands by the citrate complexing technique and then eluted in succession from the resin bed. Careful control of pH and ion concentrations was required for maximum exploitation of the slight differences between these clements. However, the separation still remained both laborious and time-consuming, because of the large volume of eluate required and its fractional nature. Most di- and trivalent cations readily form complex ions M ith the partially neutralized iminodiacetic acids, RN(CH*COOH)*, and differences in the stability of the rare earth complexes with some of these acids have been indicated by Beck (2),Schwarzenbach and Biedermann (IO), and Marsh ( 7 ) . Differences have
tinued after the other earths were eluted., The lanthanum was then removed by treatment with a stronger eluting solution and determined gravimetrically by ashing the oxalate. This gravimetric procedure is simple, requires no special equipment, and has the advantage of removing one of the major components of the usual rare earth mixtures, so that the remainder may be dealt with more easily. Application of ion exchange resins may possibly be extended through use of substituted iminodiacetic acids to separate other members of the lanthanide and actinide series more completely.
also been noted in amino acid complexes by Vickery ( I S ) . Some substituted iminodiacetic acids, particularly nitrilotriacetic acid, have been found effective in the elution of the rare earths from synthetic cation exchangers (S). These compounds are weak acids; considerable difference exists in the dissociation of the acid groups, probably due to zwitterion formation. As hydrogen ion is liberated from them during complex formation, some indication of the type of ion formed and extent of reaction (11) may be obtained by titrating the acid with base in the presence of the rare earth elements. It was possible from this information to determine the iminodiacetic acids which exhibited pronounced differences in the stability of the complexes with the different rare earths. To some extent the conditions necessary for satisfactory elution were also indicated.
I470
ANALYTICAL CHEMISTRY
The titration curves of hydraziriodiacetic acid, in the presence of lanthanum or neodymium chloride as representative elements, indicated that appreciable differences in the extent of complex formation existed between members of the cerium group. Further preliminary column experiments showed that while the hydrazino compound produced sharp banding, it also had a tendency to elute the lanthanum only very slowly. I n the present work, conditions have been determined for the separation of lanthanum from the other elements of the group by its selective retention on a cation exchange bed during elution with this reagent. MATERIALS
Hydrazinodiacetic Acid. This acid was prepared from hydrazine dihydrochloride by the method of Bailey and Read (I). The use of excess potassium carbonate just sufficient to neutralize the acid salt required the removal of crystallized potassium chloride prior to recovery of the product with hydrochloric acid. Rare Earth Oxides. The rare earth oxides of samarium, neodymium, praseodymium, and lanthanum used in the preparation of standard solutions had been purified from crude di dymium oxide (Lindsay Light and Chemical Co.) by repeated column elution procedures with nitrilotriacetic acid. No absorption lines of contaminating rare earths were detected on examination of the absorption spectra of these materials as described by Rodden (9) and Ptloeller and Brantley (8). RESERVOIR
Some difficulty had been experienced in determining the rare earth content of samples with oxalic acid due to very small irregular losses in the filtrate (6, I 4 ) , but this was overcome to a large degree by controlling the amount of oxalic acid and carefully cooling the solutions to about 0" C. rapidly with stirring befoie filtration. However, the presence of either hydrazinodiacetic acid or nitrilodiacetic acid did not decrease the sensitivity of the oxalate precipitation in slightly acid solution. The progress of the elution of the colored elements was followed by their characteristic absorption spectra, except in the case of small samples, where visual inspection of the oxides gave a rough indication of their composition. ELUTION PROCEDURE
A long resin bed, supported on sand or ground glass to obtain an even interface, was prepared by settling the resin under water in a tube of the indicated diameter. The resin was conditioned before use by repeated treatment with 100 ml. of hydrochloric acid followed by 100 ml. of 15% ammonium chloride solution FinaIly the ammonium form of the resin was treated with 75 ml of stripping solution and washed with distilled water. A rare earth chloride solution (approximately 50 ml.) of known earth content was prepared from standard solutions and the cations were adsorbed on the upper sections of the resin bed b j slowly passing this solution through the column and washing the system with 75 ml. of distilled water. The eluting solution of hydrazinodiacetic acid, neutralized to the indicated pH with ammonium hydroxide, was passed through the resin bed a t a controlled rate by adiusting the reservoir level. On completing the elution, the remaining rare earth, usually lanthanum, was removed with 150 ml. of stripping solution. The resin bed wae treated with 150 ml. of hydrochloric acid ( 1 to 3 ) and then converted to the ammonium form with 150 ml of 15% ammonium chloride solution with washing before further use. The distribution of the rare earths in the eluting, stripping, and hydrochloric acid solutions wa9 determined as described. When required for an elution curve, numerous consecutive samples of approximately 25 ml. were collected by means of an intermittent siphoning pipet. In this way a series of about 10 or more samples of nieasured volume could be taken without the attention of an operator The samples v ere found to be regular within 0.1 ml.
RECEIVER
Figure 1. Column fof Elution of Rare Earths
Nalcite (Dowex 50), National Aluminate Corp., 40- to 100mesh pellets. Amberlite I R 120, Resinous Products and Chemical Co. The bulk of this resin was 20- to 35-mesh and was passed through a 20-mesh screen. In Some cases 48- to 60-mesh resin was alvo used. Distilled Water. A11 distilled R-ater used in the preparation of standards and solutions in contact with the resin bed was first passed through a cation exchanger (ammonium form to remove traces of inorganic cations. Stripping Solution, 1%;; nitrilotriacetic acid-2s ammonium chloride a t pH 7.5 to 8.0. This solution was used for the rapid removal of Fare earth and most other cations from the resin bed. RARE EARTH ANALYSIS
Add 10% weight per volume oxalic acid solution (4 ml. per 100 ml. of sample) to the sample heated just to boiling and keep warm for approximately 2.5 hours on a steam bath. Cool the sample ra idly to about 0" C. in a salt-ice bath, filter, and wash with a 2% ammonium nitrate solution. Ignite the precipitate a t 800' C. and weigh as the sesquiouide. For samples containing acid or buffered complexing agent, adjust acidity with methyl red (pH 4.5) before the addition of oxalic acid. As a further precaution, evaporate the filtrates from samples of appreciable volume to dryness and destroy the organic material by repeated digestion with nitric acid before determining, in a small volume, the slight quantities of rare earth sometimes present after precipitation.
U Figure 2.
Sampling Pipet
I
V O L U M E 23, NO, 10, O C T O B E R 1 9 5 1 Talrle I.
Elution of Rare Earths at Different Flow Rates Elution Required,
La209 Recovered, hlg. 20.9 300 18 325 21 .o 29 20.9 345 50 Vsing columns of IR 120 (48- t o 60-mesh), 7.5 X 0.6 cm. sample, 76.3 mg. of RtOa in approximately equal quantities of Sm. Nd, and Pr, and 20.7 mg. of LatOa. F l o w Rate. hll./Hour,
MI.
SAMPLING PIPET
The sampler shonn in Figure 2 consists of a glass pipet, A , whose discharge tube moves about in an arc as it fills the different receivers. The pipet is held upright by a glass tube n-elded to the bottom, which just fits over a metal rod secured to the base. The pipet is free to move smoothly on the rod both vertically and also as it rotates about it. ,4light spring is attached securely to both the pipet and the base. The tension of this spring must be wfficient to hold the weight of the enipty pipet, but allow the pipet to drop when it has become partly filled. A pointer, D, 1s connected to the pipet so that the free end engages with the teeth in the brass strip, C.
/-
/
1471
cated, with the latter predominating a t increased concentrations and a t higher pH values as shon-n in Figure 3. The existence of the mono- complex is suggested by the fact that all the rare earth is complexed a t least to some degree a t pH 5 , as it is not easily precipitated from solution. The neodymium tended to react more completely R-ith the hydrazinodiacetic acid, an indication of greater stability for the rare earths of higher atomic number. FACTORS INFLUENCING ELUTION OF RARE EARTHS
Preliminary elution experiments with hydrazinodiacetic acid as coniplexing agent were made with cerium-free crude didymium samples on w i n beds, 25 X 1 cm., of both Amberlite IR 120 and Dones 50. Little difference in behavior w f the two resins was noted, although Dovex 50 appeared to retain the rare earth somewhat more tenaciously. Finer resin particles (-48- +60mesh) were found to sharpen the concentration bands and to increase the rate of elution noticeably, as shown in Figure 4. With eluting solutions containing ammonium acetate as buffer, a pH range and ion concentrations could be selected which permit the rctention of lanthanum after the removal of the other rare earth elements. Optimum conditions for a lanthanum separation were determined with Amberlite IR 120 resin beds, 75 X 0.6 cm., employing known mixtures of lanthanum, praseodymium, neodymium, and samarium.
A
Nd
--I
E
5
6
PH
Figure 3.
Acid Neutralized per Mole of Rare Earth by Complex Formation
-48
Rare earth, 0.33 millimole Initial volume 100 m l . Hydrazinodiacetic acid 1. 4 millimoles 2. 1 millimole
When A becomes partly filled with liquid, the spring is compressed enough to allow the pointer to slide under the tooth against which i t rests. The slight torsion provided by the spring is sufficient to rotate the whole assembly in a counter clockwise direction until the pointer rests against the next pin, B. The discharge tube should now be in a position to diTect the liquid into the next empty recriver when the level has risen sufficiently to start the siphon. As the liquid empties, the indicator slides over the pin and comes to rest against the next tooth and the cycle is ready to be repeated. TITRATION O F HYDRAZINODIACETIC ACID
Psing a Model G Beckman pH meter, weighted samples of hydrazinodiacetic acid were titrated with sodium hydroxide solution (0.1 N or 0.5 Ai) in the presence of lanthanum and neodymium chloride as representative elements. The acid produced by the complexing of the rare earths was determined from the rcsulting neutralization c u r w s by comparing them with curves n hrre the rare earth vias not present. Because in this pH range the hydraziuoacetic acid can furnish onlv one molecule of acid hydrogen in the complexing process, the number of molecules of hydrazinodiacetic acid associated with the rare earth could be determined. The value was measured for both lanthanum and neodymium over a wide pH range. A mixtiire of mono- and dihydrazinodiacetate complex ions was indi-
I
I
I
I
I
I
100
200
300
400
500
VOLUME
Figure 4.
OF
E L U A T E , ML
I
Effect of Particle and Sample Size on Elution
Resin beds I R 120, 75 X 0.6 om. Flow rate approximately 10 to 18 ml. per hour Eluant, 0.5% hydrazinodiacetic acid and 1.5% ammonium acetate, buffered to pH 5.5 Samdes 1. 5. 76.3 m g . of R O a with approximately equiralent quantit i e of Sm. hd, and Pr, and 20.7 mg. of Lap08 7. 203 mg. of R:Oa with approximatel) equivalent quuntities of Sm, Kd, and Pr, and 124 mg. of L a d s Particle size 1 , 3 . -48 +60 2. -20
The addition of ammonium acetate a8 a buffer to the eluting solution both lowered the pH range necessary to remove the rare earths from the resin bed through increased ammonium ion concentration (3, 5 ) and appeared to increaae the separation of the elements in the eluate. The fluctuations in the pH of the eluate due to complex formation were decreased and the more uniform exchange conditions resulting throughout the resin bed appeared necessary to maintain thE! conditions required for the retention of
1472
lanthanum during the relatively rapid removal of the other elements. The selection of a suitable p H for an elutriant was important to avoid either the rapid removal of the elements with little separation a t a high pH, or prolonged elution a t diminishing concentrations for low pH values. The influence of ammonium acetate, hydrazinoacetic acid, and pH on the elution of the rare earths is demonstrated in Figures 5 and 6. The rare earths were eluted in order of decreasing atomic number with concentration bands appearing in the elution curve for each element present in sufficien& quantity. The changes in sample composition were definite a t the boundaries of these concentration bands. The rate of elution was influenced only to a limited extent by the sample size, so that large samples required much longer elution to be removed from the column, as shown in Figure 4. The process was not particularly sensitive to flow rate, and even a t the high rates indicated in Table I the separation was effective, and the characteristics of the elution curves remained unchanged. I n each case 150 ml. more were tested after the praseodymium had been eluted, and in each instance no weighable quantity of rare earth was found to be present.
-
a
z o.2
-
0
-I
I \
0.3
v
?]y$&
z
W Ia l0
0.1
2 0
I
I
I
I
TOP
BOTTOM
..\
0.4
Rz03 DISTRIBUTION ON COLUMN
2. p H 5.75
0.3
0 -
1
0
-
Nd V / / L P I llllllll LO \\Y
4. PH 5.25
100
200
VOLUME
300 OF
400
E L U A T E , rnl.
Resin bed IR 120.75 X 0.6 om. Flow rate approximately 10 ml. per hour Acid concentration 0.5%. curves 2 to 4 buffered with 1.5% ammonium acetate Sample. 94.9 mg. of RzOs with approximately equivalent quantities of S m , Nd, Pr, and La
The distribution of the rare earth along the resin bed during elution was investigated by dividing into sections a column which had been frozen with a dry ice-acetone mixture. The rare earth was removed from the resin sections with stripping solution and determining by oxalate prec*ipitation, Figure 7 shows the rare earth distribution when the elution had been interrupted just after the removal of samariuni. The bulk of the rare earth re-
Separation of Lanthanum from Rare Earth Mixtures
Oxide Composition as Prepared Total (Sm, Nd, Prhweight, 0 8 , La&, mg. mg. mg. 84.5 103,7 19.2 53.7 102,4 48.7 52.7 48.7 101.4 77.8 21.5 99.3 77.0 21.1 98.1 77.4 21.1 98,5 105.0 249.3 144.3 144.3 105.0 249.3
Oxide Composition as Determined Total (Sm, N d , Pr)zweight, Oa. LazOa. mg. w . mg. 103.9 19.9 84.0 102.2 48.5 53.7 101.2 48.6 52.6 21.1 98.3 77.2 98.0 77.6 20.4 20.5 98.8 78.3 248.7 143.9 104.8 250.6 146.0 104.6
0
10
20
30
40
50
60
D I S T A N C E ( C M . UP COLUMN 1
500
Figure 5. Elution Curves with Hydrazinodiacetic Acid as Complexing Agent at Different pH Values
*
pdA Sm
0 -
0 0
0.0
Table 11.
A
Q
0.I
0
-
N
Figure 7 .
Rare Earth Distribution of Column Bed during Elution
mained still in the top section of the column arranged in sequence, with neodymium extending downward through the greater portion of the resin bed at low, diminishing concentrations. Under these conditions of relatively rapid elution, the elements seemed to band in order in a region of high concentration in the upper section of the column, with the element of highest atomic number being washed rapidly through the remainder of the resin bed. Similar experiments with pure lanthanum samples indicated that 500 ml. of 0.5% hydrazinodiacetir acid solution and 1.5% ammonium acetate a t pH 5.5 moved the bulk of earth about one third the length of the column and that greater volumes of this elutriant could be used safely before a lanthanum breakthrough. SEPARATION AND DETERMINATION OF LANTHANUM IN RARE EARTH MIXTURES
The quantitative separation and subsequent determination of lanthanum under these conditions were checked in a series of experiments with rare earth samples of known com osition on Amberlite IR 120 resin beds, 75 X 0.6 cm., using an eruting solution of 0.5% hydraxinodiacetic acid and 1.5% ammonium acetate, a t pH 5.5 with a flow rate of 10 ml per hour. I n later esperiments similar beds of IR 120 resin, 48- to 6@mesh, were found to be better, and were operated a t flow rates up to 40 to 50 ml. per hour. The other elements of the group were removed from lanthanum with 300 and 500 ml. of eluting solution for 100and 300-mg. samples, respectively. An additional 50-ml. portion of eluting solution was used to check the completeness of this operation before the remaining earth was removed from the resin with 100 to 150 ml. of stripping solution. The complete removal
V O L U M E 2 3 , NO. 10, O C T O B E R 1 9 5 1 of rare earth was confirmed with additional stripping solution :md hydrochloric acid (1 to 3). The rare earth was precipitated \vith oxalic acid and it was found necessary to examine, as described, the filtrates from these complexing solutions for small quantities of unprecipitated earth. Interference from traces of inorganic cations in the reagents and solutions employed and the quantitative recovery of the earth appeared to present the greater difficulties in obtaining quantitative values for the rare earth mixtures. I n Table I1 are shown typical valuesobtained in the separationof lanthanum from several ixre earth mixtures. Because the presence of cerium in samples required some addit,ional elut,ion, its removal by chemical means is recommended twfore this procedure is used for the separation of lanthanum. LITERATURE CITED t
1I
Bailey, J . R., and Read. IV. T., J . A m . Chcm. SOC.,36, 1747 (1914).
1473 ( 2 ) Beck, G., Helv. Chirn. I c t a , 29,357 (1946). (3) Fitch, F. T., and Russell, D. S.,Can. J . Research, 29,363 (1951). (4) Johnson, W.C., Quill, L. L., and Daniels, F., Chem. E u y . S r t c s , 25, 2494 (1947). ( 5 ) Ketelle, B. H., and Boyd, G. E.. J . A m . Chtm. SOC., 69,2800 (1947). 161 Knlthoff. I. hI.. and Elmouist. It.. Ibid.. 53. 1217 119311. (7) hIaish, J K., J . Chem Sic., 1950,1819. (8) Moeller, T., and Brantley, J C , A V ~ L CHEW,22,433 (1950). (9) Rodden, C. J., J . Research .Vat[ Bvr Standards, 26,557 (1941) (10) Schwarzenbach, G., and Biederniann, IT., HeZv. Chtm. Acta, 31, 331 (1948).
(11) Schwarsenbach, G.. Kampitsch, E.. and Steiner, R., Zhid.. 28, 828. 1133 (1945). (12) Tompkins, E'. R., Khym, J. X , and Cohn. W. E., J . A m . Chem. SOC.,69, 2769 (1947). (13) Vickery, R. C., J. Chem. SOC.,1950, 2088. (14) 1-ost, D. M.. Russell, H., and Garner, C. S., "Rare Earth Elements and Their Compounds." p. 59, S e w York. John Wiley & Sons, 1947. RLC>.ITLD December 4, 1950
Determination of Acetaldehyde and Acetone by the Iodoform Reaction Determination of 1,Z-Propylene Glycol STEPHEX DAL NOGARE, T. 0. NORRIS, AND JOHN MITCHELL, .JR. I'olychemirals Department, Chemical Dixision, E. I . du Pont de Nemours & Co., Inr., Wilmington, Del. The procedure described was developed to fill the need for a method applicable to the determination of very low concentrations of acetaldehyde or acetone in solution. The method is based on the reaction of these carbonyl compounds with hypoiodite to give iodoform which is measured spectrophotometrically at 347 mp. Under controlled conditions acetaldehyde and acetone give reproducibleiodoform yields of 58 and l08%, respectively, on a mole per mole basis. By means of this procedure 0 to 0.4 mg. of these compounds may be determined. In the development of the iodoform method a study was made of the reaction conditions necessary for reproducible results. The observation that iodoform in solution can be measured spectrophotometrically is a marked improvement over gravimetric and titrimetric means previously used. Specific applications of the method are reported for acetone in cyclohexanol and 1,2-propylene glycol in ethylene glycol.
0
NE of the oldest and best known qualitative tests for organic
compounds containing the aceto group, or a group capable of easy oxidation or hydrolysis bJ- alkaline hypoiodite to the ucaeto group, is the iodoform reaction. The specificity of this iraction and the low solubility of iodoform in water were properties early utilized for the determination of ethyl alcohol in water ( I f , 1 2 ) and acetone in methanol (9). The most widely used adaptation of the iodoform reaction, however, was that made bv JIessinger ( I S ) to the iodometrlc determination of acetonr. Some of the reported modifications of hleseinger's technique (1-3, 7') indicate the widespread utility of this procedure. In the course of research on the determination of small quantities of acetaldehyde and acetone in various solvents the authors btudied the iodoform reaction. I t was found that iodoform ab-
wrbs in the ultraviolet region from 400 to 260 m p . This absorption is characterized by three well defined maxima occurring a t 347, 307, and 274 mp, as shown in Figure 1. The absorption peak a t 347 mp is the most sensitive to changes in iodoform concentration and shows good agreement with Beer's law for amounts of iodoform from 0 to 3 mg. Ultraviolet absorption by iodoform thus gives a sensitive and accurate means for determining acetaldehyde and acetone in very l o a concentrations. This observation has made it possible to study the reaction variables, in order to obtain the optimum conditions for the conversion of acetaldehvde and acetone to iodoform. €3evious studies of iodoform reaction conditions include the u-ork of Hatcher and Mueller ( 5 ) , Iiolthoff ( 8 ) ,and van der Lee (IO). I n general, the observations of these n orkcis indicated that the ieaction as written CH3CH0 4NaOH JIi --+ CHI3 3 S a I HCOOXa 3HaO
+
+
+
+
+
does not reveal the critical role played by excess alkali and iodine in determining the yield of iodoform. Their work also showed that acetaldehyde and ethyl alcohol gave low yield.5 of iodoform, possibly due to side reactions involving the formation of aldol and resins. The observations of Houghton ( 7 ) indicated that yields of iodoform in excess of theory are obtained with acetone, presumably through partial conversion of acetic acid t o iodoform. However, acetic acid alone did not react (see Table I). Quantitative observations in the authors' laboratory which utilized ultraviolet absorption for the study of iodoform reaction conditions led to the development of a method capable of determining 0 to 0.4 mg. of acetaldehyde or acetone. A N 4 L Y T I C A L P R O C E D U R E FORACETALDEHYDEANDACETONE
Apparatus. A Beckman Xodel DU spectrophotometer or other equivalent instrument may be used for absorbancy measurements. Either the hydrogen discharge or the tungsten lamp can be used to make measurements a t 347 mp.
