The ultracentrifugal procedure used by Lewis and coworkers (6) employing potassium bromide-sodium chloride (1.21 grams per ml.) and which involves ultracentrifuging a t 30,000 r.p.m. for 13 t o 17 hours a t temperatures between 16” and 18’ C. does not quantitatively recover all the serum lipoproteins. The lower viscosity of potassium bromidesodium chloride solution than that of sodium bromide solution at a density of 1.20 grams per ml. does not sufficiently compensate for the shortness of their preparative ultracentrifugal run, ahich also occurs at a lovc-er centrifugal field. Because of viscosity differences, lipoproteins in potassium bromidesodium chloride (1.21 grams per ml.) float a t a rate about 2OyO faster than in sodium bromide (1.20 grams per ml.). Considering this factor in potassium bromidesodium chloride (1.21 grams per ml.), i t is somewhat more difficult to study lipoproteins with flotation rates in the neighborhood of S , ( I 20) 802 (in 1.20 grams per ml. of sodium bromide) in the analytical ultracentrifuge without using an accurately determined acceleration picture taken considerably below 52,640 r.p.m. I n choice of salts for increasing solution densities, it is worthy of note that sodium bromide has a much higher solubility than potassium bromide.
Saturated aqueous sodium bromide a t 20” C. has a density of 1.543 grams per ml., whereas saturated potassium bromide has a density of only 1.371 grams per ml. Compared to the deuterium oxide-sodium nitrate system of deLalla ( 2 ) sodium bromide represents a simplification, as well as a further advantage of not interfering with a Kjeldahl nitrogen analysis, which may be desired. The analytical ultracentrifuge field a t 42,040 r.p.m. represents a reduction of 3GY0 in centrifugal force compared with 52,640 r.p.m., the speed a t 1%-hich lipoprotein runs have been customarily made. This change will certainly reduce analytical-cell breakage. Because flotation rates remain nearly constant within the concentration ranges normally encountered, the analysis is simplified because the Johnston-Ogston correction becomes negligible and therefore unnecessary. Moreover, it is possible to follow the previously established flotation classification of the lowdensity serum lipoproteins ( 2 ) . I n this procedure the S,(l.BO)0-8 class lipoproteins correspond to the total of the two principal high-density lipoproteins (HDL2 and HDL-3). This method provides a simplified procedure for complete ultracentrifugal analysis in essentially a one-salt system (sodium bromide) and uses only 2 ml. of serum.
ACKNOWLEDGMENT
The authors express appreciation to John W. Gofman for his many helpful criticisms and suggestions given during the course of this investigation. LITERATURE CITED
(1) Beams, J. W.,Dixon, H. hI., 111, R e v . Sci. I n s t r . 24, 228 (1953). (2) delalla, O., Gofman, J. I\’., in “Methods of Biochemical Analysis,” Vol. I (D. Glick, ed.), Interscience, Ti-ew York. - , 1954. ~ ~ (3) Gofman, J. W.,Lindgren, F. T., Elliott, H. A . , J . Bid. Chem. 179, 973 (1949): (4) Hanig, M., Shainoff, T. R., Ibid., 219, 479 (1956). (5) Johnston, J. P., Ogston, A. G., Trans. Faraday Soc. 42, 789 (1946). (6) Lewis, L. A., Green, A. A., Page, J. H., Am. J . Phys. 171,391 (1952). ( 7 ) Lindgren, F. T., Elliott, H. A , , Gofman, J. W., J . Phys. & Colloid Chem. 5 5 , 80 (1951). (8) Pickels, E. G., Methods of M e d . Research 5, 107 (1952). (9) Svedberg, T., Pedersen, K. O., “The Ultracentrifuge,” Oxford Univ. Press, Oxford, 1940. (10) Trautman, R., Schumaker, V., J . Chem. Phys. 22, 551 (1954). RECEIVED for review September 29, 1958. Accepted March 26, 1959. Luigi Del Gatto is a fellow of the Jane Coffin Childs Memorial Fund for Medical Research. Investigation aided by a grant from The Jane Coffin Childs Memorial Fund for Medical Research.
Determination of Titanium and Iron in Titaniferous Materials by Cerate Titrimetry J. 0.PAGE and A. 8. GAINER’ Agriculfural and Mechanical College of Texas, College Station, Tex.
b As all commercial titanium ores contain iron, it is frequently desirable to determine these two metals in a single titration. A simple, rapid, and accurate volumetric method has been developed for the simultaneous determination of titanium and iron coexisting in solution. Seven titaniferous ore samples were fused with potassium bisulfate and the melt was extracted with dilute sulfuric acid. The solutions containing titanium(1V) and iron(ll1) ions were reduced with aluminum foil or liquid zinc amalgam in a simple apparatus which provided for flushing of the solution with carbon dioxide to remove air, and quick, easy removal of the zinc amalgam before titration. After reduction, a quantitative determination of titanium and iron in the solution was made with cerium(lV) sulfate as oxidant, and with methylene
blue and N-phenylanthranilic acid as the internal indicators for the titanium and iron end points, respectively. Separate determinations were made for chromium and vanadium. Results compare favorably with those obtained on the same ore using two modified methods.
T
for a simple, rapid, and accurate method for the simultaneous determination of titanium and iron in titaniferous ores prompted the development of a method which answered these specifications. Before 1949, all methods for the determination of the titanium and iron content of titanium ores required separation of the iron from the titanium. I n 1949, Shippy (3) presented a procedure for the simultaneous determination of these metals HE NEED
coexisting in solution, using potassium permanganate as oxidant with methylene blue as internal indicator for the titanium end point and 1,lO-phenanthroline ferrous complex as the internal indicator for the iron end point. Reduction was accomplished by use of the Jones reductor. Certain volumetric methods were evaluated with the objective of replacing potassium permanganate by cerium(IV) sulfate, the Jones reductor by aluminum or liquid zinc amalgam, and 1,IO-phenanthroline ferrous complex by AT-phenylanthranilic acid. Reduction of titanium(1V) and iron(II1) by aluminum foil or liquid zinc amalgam is recommended by ease of handling and 1 Present address, University of Oklahoma, Norman, Okla.
VOL. 31, NO. 8, AUGUST 1959
1399
ability to keep the reduced ions under a n inert atmosphere. The 1,lO-phenanthroline ferrous complex requires a blank of about 0.25 ml. of 0.1000N oxidant for 8 drops of this indicator while N-phenylanthranilic acid does not need a blank. The possibility of separating the iron and titanium and then determining each element was first investigated. Ammonium bifluoride and sodium fluoride were used to complex the titanium and iron, and ferrous sulfide was precipitated while the titanium was held in solution. Iron(II1) ions were separated from titanium(1V) ions in hydrochloric acid solution by extraction of the iron(II1) with diethyl ether, isopropyl ether, or methyl isobutyl ketone. Good recoveries of the iron(II1) ions were made in both the complexation and the extraction methods, but the procedures were too long. To develop a more rapid method, separation of titanium and iron was avoided. Internal indicators were investigated, whose redox potentials mere close to that of the titanium(III/IV), or to the iron(II/III) end point. Experiments were conducted with cacotheline, sodium tungstate, indigo carmine, and methylene blue as indicators for the titanium end point and with 1,lO-phenanthroline ferrous complex and X-phenylanthranilic acid as indicators for the iron end point. Cacotheline and sodium tungstate exhibited fleeting end points with cerium(1V) sulfate, while indigo carmine was sluggish and appeared to be destroyed by the cerium(1V) sulfate. However, methylene blue gave a sharp end point a t 65" to 70" C. in 2N hydrogen ion concentration. The color change was from cclorless to blue. After titration to the titanium end point, the solution was cooled to 25" to 30" C. and N-phenyl-anthranilic acid was added. The titration was continued to the iron end point. The color change was from blue to purple-violet. 1,lO-Phenanthroline ferrous complex also gave a good end point at 25" C. with cerium(1V) sulfate, but because the indicator required a blank, Nphenylanthranilic acid was preferred. SPECIAL REAGENTS
Ceric Sulfate, 0.1N. Weigh out 105.7 grams of G. Frederick Smith reagent grade ceric sulfate [Ce(HS04)J,dissolve in 600 ml. of 6.66N sulfuric acid, and dilute to 2000 nil. Allow the solution to stand overnight so that insoluble phosphates and other impurities will precipitate out. Filter the solution through a fritted-glass crucible. Standardize the cerium(1V) sulfate solution with sodium oxalate by potentiometric titrations using a platinum-calomel electrode assembly. Ferric Ammonium Sulfate, Baker, ACS standard. Standardize the solution after reduction with liquid zinc 1400
ANALYTICAL CHEMISTRY
amalgam against standard cerium(1V) sulfate, using N-phenylanthranilic acid as indicator. Liquid Zinc Amalgam. Add 30 grams of Merck granular No. 20 to 30 mesh ACS standard zinc metal to 1500 grams of Schaar C.P. redistilled mercury metal. Heat on a steam bath in a 500-ml. Erlenmeyer flask under 20 ml. of 5% sulfuric acid for 45 minutes with intermittent shaking. Wash with 5% sulfuric acid and remove any solid portion of the liquid zinc amalgam with a separatory funnel. Keep the solid portion of the zinc amalgam under 2% sulfuric acid for future refortification of the liquid zinc amalgam. When not in use, keep the liquid zinc amalgam under 2% sulfuric acid. APPARATUS
Ore samples were fused with potassium bisulfate in 500 ml. borosilicate glass Erlenmeyer flasks for these reasons: 45 to 50 grams of potassium bisulfate were required to obtain a complete attack on a 0.2-gram sample of ilmenite ore; the high walls of the flask removed the danger of mechanical loss by spattering; the flasks suffered no harm from the 30- to 45-minute heating under the full heat of a Fisher burner; and only one transference of the solution was necessary in the entire experiment. After extraction of the melt in the flask Ivith dilute sulfuric acid, the solution was transferred directly to the reaction flask. Samples n-ere reduced by aluminum in a lOOO-ml., three-necked, roundbottomed flask. A 50-ml. buret containing the oxidant was fitted in the left neck; a KO. 9 rubber stopper with opening for a mechanical stirrer, in the center neck; and a KO.4 rubber stopper with holes for a thermometer and a carbon dioxide entrance tube, in the right neck. A 1000-ml. heating mantle connected to a variable Ponerstat provided the heat. Samples were reduced by liquid zinc amalgam in a lOOO-ml., three-necked, round-bottomed reaction flask with a sealed-in petcock a t the bottom of the flask serving as an exit for the liquid zinc amalgam after reduction. The same apparatus was fitted in the three necks as before. The stirrer was wide and flat, and adjusted as close to the bottom of the flask as possible without touching the flask. The stirrer was maintained at a high speed for 20 minutes to obtain maximum mixing of the liquid zinc amalgam with the solution. Reduction of the titanium(1V) to (111) and iron(II1) to (11) was complete. PROCEDURES
Weigh out 0.2000 to 0.2500 gram of ilmenite ore which has been previously dried at 110" C. for 12 hours into a clean 500-ml. Erlenmeyer flask. Add 50 grams of potassium acid sulfate and place the flask on a clay triangle supported by a ring stand. Heat gently with a Fisher burner until the potassium acid sulfate is melted and then heat the flask under the full heat of the burner for
45 minutes. Pick up the flask with tongs and swirl the contents of the flask every few minutes. After the ore is in solution, remove the flames and allow the flask to cool. To the melt add 170 ml. of distilled water and 30 ml. of sulfuric acid if reduction is to be made by liquid zinc amalgam, or 170 ml. of water, 35 ml. of sulfuric acid, and 3 ml. of hydrochloric acid if reduction is to be made by aluminum foil. Heat until complete solution of the melt is obtained. Liquid Zinc Amalgam. Add 115 t o 140 ml. of liquid zinc amalgam and 100 ml. of water t o the zinc amalgam reduction flask. Transfer t h e solution in t h e Erlenmeyer flask t o t h e reduction apparatus with three washings of water and dilute t h e solution to be reduced to 540 ml., making the solution 2.V with respect to sulfuric acid. Start a vigorous stream of carbon dioxide bubbling through the solution. The mechanical stirrer, which has been adjusted beforehand as close to the bottom of the flask as possible without touching the flask, is maintained at a high speed for 20 minutes. The violet titanous ions ill begin to show after about 5 minutes. Place a 1000-ml. heating mantle on the side of the reduction apparatus and adjust the variable Powerstat to obtain a temperature of 62" to 65" C. a t the end of the 20 minutes. Stop the mechanical stirrer, add 10 nil. of redistilled carbon tetrachloride as recommended by Smith (Q), and remove the liquid zinc amalgam through the petcock a t the bottom of the flask. The heavy carbon tetrachloride will go to the bottom of the flask as the zinc amalgam is being removed and prevent the loss of the reduced solution. Quickly add 4 drops of 0.5% methylene blue solution, start the mechanical stirrer again, and titrate with cerium(1T) sulfate to the titanium end point where the color of the solution will change from colorless to blue. The temperature of the solution should not be less than 65" nor more than 70" C. The indicator becomes sluggish below 60" and carbon tetrachloride fumes nil1 be given off if the temperature exceeds 70" C. Make sure that a vigorous stream of carbon dioxide is flowing through - the solution a t all times. Remove the heating mantle and cool the solution in an i c bath to 25" to 30" C. Add 4 drops of 0.005M N phenylanthranilic acid (Eastman) and continue the titration to the iron end point where the color of the solution will change from blue to purple-violet. From the volume of oxidant required for each end point, calculate the per c m t of titanium and of iron in the sample. JTash the liquid zinc amalgam three times with 57, sulfuric acid to remove all traces of carbon tetrachloride. Aluminum Metal. Weigh 1.0 gram of aluminum foil (Alcoa Wearever) on t h e analytical balance, wash, and t r a p the foil between t h e end of t h e stirrer and t h e bottom of the flask in the apparatus. Transfer t h e solution in the Erlenmeyer flask t o the reduction apparatus 115th three washings I
of water and dilute the solution to be reduced to 300 ml. Start a vigorous stream of carbon dioxide bubbling through the solution. Place a 1000-ml. heating mantle under the reduction flask, and adjust the variable Powerstat to obtain a temperature of about 95" C. Start the mechanical stirrer after most of the aluminum has been dissolved and continue heating until all the aluminum dissolves and the clear solution becomes violet. Quickly remove the heating mantle and cool the flask for a few seconds in cold water to 70" C. Titrate as previously described. KO blank was required for the titanium end point for any of the foils tested. Calculate the per cent of titanium and of iron in the sample, subtracting a blank of 0.55 to 0.70 ml. of titrant for the iron end point. Modified H o D e - M o r a n - P l o e t z Method ( I ) . Thesample was dissolved and reduced by amalgam as already described and then the titanium was oxidized with a ferric solution. Modified Kobayashi-Ogasawara Method ( 2 ) . After adding 10 ml. of 0.5% sodium tungstate (Baker) and 3 ml. of phosphoric acid t o the amalgam-reduced solution, titrate as directed, first to the colorless, then to the pink end point. Calculate the percentages of titanium and iron. Chromium and Vanadium Determination. A modification of the method of Willard and Young (5) was used in determining the small amounts of chromium and vanadium present in a few of the ores. Fuse a 0.2000gram sample of ilmenite ore as before. Cool the melt, add 80 ml. of concentrated perchloric acid, and boil for 20 minutes with mixing. Cool, add 100 ml. of water, and boil for 15 minutes. Add 500 ml. of mater, and place in an ice bath. Decant the supernatant liquid off the voluminous, white, crystalline titanium dioxide precipitate and filter. Yash the precipitate with water, adding the washings to the solution. Add 10 ml. of concentrated phosphoric acid and 5 ml. of O.lAVferrous sulfate solution. Add 5 drops of ferroin and titrate as directed with 0.05Y potassium permanganate, first to the chromium end point, and, after adjusting the p H to about 4.5, titrate a t 50" C. to the vanadium end point. Calculate the percentages of chromium and vanadium. RESULTS
The results of the analyses of the ilmenite ores are given in Table I. Recoveries of titanium and iron from solutions containing known quantities determined by the liquid zinc amalgam reduction, aluminum foil reduction, and modified Hope, Moran, and Ploetz (1) method are shown in Table 11. DISCUSSION
Chromium and vanadium are a source of error in the titanium determination.
Table 1.
Analysis of ilmenite Ores (Values given as percentages) A1 Foil H Mod.~ ~Na2W04 ~ , Zn-Hg TiO, Fe TiOz Fe Ti02 Ti02 Fe
Ore 64.2 Florida (Ti Metals Corp.) 62.3 Cone. No. 2 (Foote Mineral) Quilon No. 1 59.3 Florida c0nc.a 58.3 Can.slanNo.4
TO 1
Mod. Willard Cr83
21.00 64.3 21.05 6 3 . 9
64.5
22.19
0.00
Vz06 0.0
22.09 62.4 22.24 62.0
62.1
22.38
0.00
0.0
0.00 0.071 0.00 000 0 20 0 014
0.0 0.303 0.0 0 0 0 io 0 00
25.63 22.51 11 60 7 77 14 22 0 061
59.6 58.4 70.5 68 9 68 1 0 28
24.99 22.56 11.57 7 72 14 12 0 088
59.5 5 8 . 5 5 8 . 3 22.91 70.2 68 9 67 6 0 21 0 32 0 065
Can.slag9o 5 69 3 Sore1 slaga 67 1 Std. dev , 7ob 0 31 Ti02 values corrected for chromium and vanadium. b 17 of the Ti-Fe determinations were in duplicate, 7 in triplicate. Q
Table II.
Determination
Method Liquid Zn-Hg reduction, Ce( IV) A1 foil reduction, Ce(1V)
Mod. Hope, &loran,Ploetn method
of Titanium and iron
Ti,5 Gram Taken Found
Fe, Gram Taken Found
0,2088 0.2088 0.2089 0.2089 0.2387 0.2387
0.0882 0.0883 0.0883 0.0883
0.2087 0.2081 0.2082 0.2082 0.2390 0,2387
0.0888
0.0892 0.0887 0.0890
a In preparing the standard solutions the pure metal (Titanium Metals Corp.) wae dissolved in dilute sulfuric acid.
Titanous ions are extremely unstable, and chromium(I1) and vanadium(I1) ions are even more so; thus, the reduced solution must be kept under an inert atmosphere such as carbon dioxide. The accuracy probably is improved by speed and promptness in titrating after the reduction step. The iron results are more precise because ferrous ions are more stable to oxygen than titanous ions. The accuracy of methods for the determination of titanium in ilmenite ores would be greater if larger ore samples could be used. Fifty grams of potassium bisulfate under the full heat of a Fisher burner for 45 minutes is necessary for complete solution of a 0.2- to 0.25-gram sample of most ilmenite ores. If platinum or palladium flasks are available, the addition of a small amount of sodium fluoride will aid materially in dissolving the silica-containing ores by potassium bisulfate. One gram of boric acid should be added to complex the fluoride ions as fluoboric acid after extraction of the melt if sodium fluoride is used. Other reagents, except sodium peroxide, do not attack ilmenite ore. Sodium peroxide was not used after it was observed that the reagent pitted the Parr bomb in which the fusion was made. The accuracy probably was impaired by an excess of foreign matter in some of the samples, Quilon ilmenite No. 1 in particular. Some of the samples were not finely ground and should have bren reduced to a 200- to 400-mesh powdcr. The aluminum reduction method
gives results which average o.4yOhigher than the amalgam reduction methods. The reason for this difference is not definitely known, but will be investigated. The difference possibly is due to the behavior cf minor constituents present in the ore, because quantitative determinations of the pure titanous and ferrous ions were obtained by each method (Table 11). Aluminum foil and liquid zinc amalgam are excellent reducing agents. Aluminum foil is more convenient and easier to handle; it is preferred if titanium determinations only are made. However, it gives a fairly high blank of 0.55 to 0.70 ml. for the iron end point. Yo blank was required for the titanium end point for any of the foils used in the research. Pure (99.99%) aluminum notch bar ingot donated by Alcoa Aluminum Research Laboratories, Xew Kensington, Pa., was unsatisfactory as a reducing agent as the ultrapure aluminum mas not dissolved by hydrochloric and/or sulfuric acids, even in the presence of catalysts. Attempts to use magnesium metal as a reducing agent were unsuccessful; in an acid solution the metal gave off hydrogen with little reducing action. Methylene blue is the best internal indicator available for titanium. It is stable a t temperatures as high as 90" C. in sulfuric acid Concentrations as high as 4N, and the titanium end point from colorless to blue is always sharp a t 65" to 75" C. An ovidation potential of 0.354 volt wzs cnlculated for the system in lyhich 2.5 meq. of titaVOL. 31, NO. 8, AUGUST 1959
1401
nium(II1) ions were oxidized to titanium(IV) ions in 500 ml. of water 2 N in hydrogen ions. A titanium(II1) concentration of 1 X 10-6M was assumed a t theequivalence point. The calculated oxidation potential for the system of titanium(II1) to (IV) is very close to the potential of 0.52 volt for methylene blue a t p H 0. A'-Phenylanthranilic acid is very satisfactory as an indicator for iron. The indicator appeared to function best at temperatures of 25' to 30" C. and sulfuric acid concentrations of 2 to 3N. The color change of N-phenylanthranilic acid a t the iron end point is from colorless to red in the absence of methylene blue, but in the presence
of methylene blue, the color change is from blue to purple-violet. ACKNOWLEDGMENT
The pure titanium metal used in preparing the standard titanium sulfate solution was kindly supplied by Titanium Metals Corp. of America and John Hill. The authors especially thank F. S. Griffith, N. J. Zinc Co., Palmerton, Pa., and R. W. Brickenkamp, Manager of Research, National Lead Co., Titanium Division, South Amboy, Is. J., for their courteous and gracious cooperation in supplying the ilmenite ore samples for this work and giving information concerning methods.
LITERATURE CITED
(I) Hope, H. B., Moran, R. F., Ploetz, A. C., IND.ENG.CHEM.,ANAL. ED. 8.48 (1936). (2) 'Kobayashi, S., Ogasawara, I., Tokyo KGgyG Shikensho HGkoku 52,21 (1957). ( 3 ) Shippy, B. A., ANAL. CHEbf. 21, 698 (1444) ,(1949). - - ,. (4) Smith, G. F., I N D . ENG.CHEU., AKAL. ED. 14,854 (1942). (5) Willard, H. H., Young, P., Ibid., 6 , 48 (1934). I
1
RECEIVED for review October 13, 1958. Accepted A ril 29, 1959. Division of Analytical &hemistry, 14th Southwest Regional Meeting, ACS, San Antonio, Tex., December 1958. Experimental results taken from the thesis of A. B. Gainer, presented in partial fulfillment of the requirements for the M.S. degree to the A. and M. College of Texas.
Determination of p-tert-Butylbenzoic Acid in Coconut Oil-Type Modified Alkyds P. J. SECREST and BOGUMIL KOSCIESZA1 Analytical Research Deparfment, Sherwin- Williams Co., Chicago 28, 111.
A method for determining the amount of p-tert-butylberrzoic acid in alkyd resins is based on the difference in absorbance at 282.5 and 300 mp. Absorbance measurements are made of solutions of mixtures of p-tert-butylbenzoic acid and fatty acids which are separated from alkyd resins. The method is applicable only to alkyds containing coconut-type and similar acids which are only slightly unsaturated and exhibit only a slight difference in absorbance a t 282.5 and 300 mp. Accuracy varies with the unsaturation and oxidation of the fatty acids.
P
ARA-tert-butylbenzoic acid is used in alkyd resins. Substitution of this acid for part of the fatty acid portion of oil-modified alkyd resins results in harder baked films without appreciable change in the viscosity of the resin solution or undue decrease in the flexibility of the baked film. Use in alkyd resins has increased to the point that a method for its determination is desirable, both for quality control of alkyds containing this acid and for analysis of unknown alkyd resins. No report on the determination of pteTt-butylbenzoic acid in alkyd resins has been found in the literature. The object of this investigation was to Present address, Bell & Howell Co., 7100 McCormick, Lincolnwood, Ill. 1402
ANALYTICAL CHEMISTRY
develop a method for determining p tert-butylbenzoic acid in alkyd resins. In the usual analysis of alkyd resins ( I ) , p-tert-butylbenzoic acid is separated along with the fatty acids. I t s presence maj- be detected by a study of a n infrared spectrum of the fatty acid fraction, because this acid has characteristic absorption bands at approximately 11.65, 12.82, and 14.14 microns. The actual problem then was to determine the amount of p-tert-butylbenzoic acid in the fatty acid fraction. Because the solubility characteristics of the p-tert-butylbenzoic acid and the fatty acids were found to be so nearly the same, the approach by solvent extraction was abandoned. A study of ultraviolet spectra of p-tertbutylbenzoic acid revealed that its absorbance between 270 and 285 mp is appreciably higher than that of coconut-type fatty acids. Relatively highly unsaturated fatty acids such as linseed and soybean acids have considerable absorption in the ultraviolet region between 270 and 285 mp, Fortunately, p-tert-butylbenzoic acid is not normally used in alkyd resins containing highly unsaturated fatty acids. The presence of highly unsaturated fatty acids may be detected by a n iodine value determination. Most coconut-type fatty acids will have a n iodine value below 15. Transmittance spectra of p-tert-butylbenzoic acid in various solyents (made with a Beckman DK-1 spectrophotometer) are sholyn in Figure 1. I n a solution of cyclohexane containing fatty
acid, the acid exhibits small absorption peaks a t 282.5 and 272 mp, It has relatively very little absorbance at 300 mp. Measurements made a t 271.5 mp revealed that fatty acids lowered the absorbance of p-terf-butylbenzoic acidfor example, the absorbance of a cyclohexane solution containing 50 mg. of p-tert-butylbenxoic acid (1-cni. cell) is 0.335. Addition of 100 mg. of pelargonic acid to the solution lowers the absorbance to 0.318. The effect of lauric acid may be seen by referring to Figure 1. Measurements made a t 282.5 mp revealed that fatty acids did not affect the absorbance of p-tert-butylbenzoic acid. As shown in Table 11, fatty acids absorb at both 300 and 282.5 mp and therefore would interfere with any determination of p-tert-butylbenzoic acid based on its absorbance a t 282.5 mp. A partial correction for this interference can be made by subtracting the absorbance at 300 mp from the absorbance a t 282.5 mp, A method based on the difference in absorbance a t 300.0 and 282.5 mp was developed for quantitative determination of the acid. A Beckman Model DU spectrophotometer with a KO.4300 photomultiplier attachment \vas used TTith 1-cm. silica cells for all quantitative measurements. Practical grade cyclohexane (Eastman S o . PiO2) was used for all solutions. Absorbance of this soh-ent was checked and found to be 0.018 a t 282.5 mp for a thickness of 1 cm., and less at longer n-ave lengths. For the sample concentration used, this
