ANALYTICAL CHEMISTRY
1490 Each sample was weighed carefully on a delicate quartz helix balance ( 7 ) and transferred to the digestion tube. A major advantage of the sealed-tube digestion with sulfuric acid is that it allows complete digestion in the absence of any catalyst and also prevents the loss of such volatile constituents as phosphoric acid which would be formed simultaneously. Thus, the sample may be digested and an aliquot for nitrogen determination taken while anothrr may be used for determination of phosphorus or other constituent. The procedure was actually followed in determination of phosphorus, as shown by the data of the last column of Table 11, in which good reproducibility is shown. As compared with the method of Tompkins and Kirk, this method suffers from the necessity of transferring the digest to the diffusion vessel, but the technique involved is not in any way difficult. The direct use of the digestion vessel as a diffusion vessel t o avoid transfer has been tried u-ith some success, though additional problems were introduced. The technique has received considerable study (by Wolfgang Kirsten while visiting this laboratory) and may be made the subject of a separate publication. The use of Desicote is almost essential in making operations smooth in the determination, not only in performing pipet measurements without rinsing but also in control of the neutralization of digest, and in suspending the boric acid as a seal in the neck of the diffusion vessel. In neutralizing the digest, the latter does not spread on the surface. When alkali is added underneath it, there is still little spreading until after the bulb is sealed and stirring is started. As soon as the alkaline solution is spread over the surface, it removes the Desicote and the surface wets, allowing the liquid t o form a thin film from which diffusion is rapid and stirring is effective. The method is sufficiently reliable and rapid for an operator to perform many analyses in a day without losing one of them. Digestions are performed in multiple (10 or more simultaneously), and diffusions are likewise made simultaneously, a single rotating
magnet serving t o stir as many as 13 a t once The range of analyzable nitrogen has not been shown to be lower than with other methods. Experience indicates that 1’1ith certain modifications of technique or method, the loner limit of range may be lonered very significantly. Studies are being made of this possihilitv. ACKNOWLEDGMEAT
Phosphorus analyses were performed by Jean Fong by a procedure t o be published. LITERATURE CITED
(1) Bruel, D., Holter, H., Linderstr$m-Lang, K., and Rozits, K., Compt. rend. trar. lab. Cadsberg, Ser. chim., 25, 289 (1946). (2) Chibnall, A. C., Rees, h1. 37, 354 (1943).
IT.,and Williams, E. F., Biochem. J . ,
(3) Gilbert, P. T., Jr., Science, 114, 637 (1951). (4) Jonnard, R., IND. ENG.CHEM.,ANAL.ED., 17, 246 (1945).
(5) Kirk, P. L., “Advances in Protein Chemistry,” edited by .4nSon, M. L., and Edsall, J. T., Vol. 111, p. 147, Kew T o r k ,
Academic Press, 1947. (6) Kirk, P. L., “Quantitative Ultramicroanalysis,” Sew T o r k , John Wiley & Sons, 1950. (7) Kirk, P. L., and Schaffer, F. L., Rev. Sci. Instmments, 19, 785 (1948).
(8) Lake, G. R., hlcCutchan, P., Van Meter, R., and Neel, J. C., ANAL.CHEM.,23, 1634 (1951). (9) Ma, T. e., and Zuazaga, G., ISD. EN. CHEM.,~ A L ED., . 14,
280 (1942). (10) Keedham, J., and Boell, E. J., Biqchem. J . , 33, 149 (1939). (11) Tompkins, E. R., and Kirk, P. L., J . B i d . Chem., 142, 477 (1942). (12) White, L. M., and Long, 31. C., ANAL.CHEM.,23, 363 (1951). RECEIVED for review February 2 5 , 1952. Accepted M a y 23, 1962. This investigation was made under contractual support b y t h e Veteran’s Administration a n d with aid of the University of California Committee o n Research, a n d t h e Office of S a v a l Research. The opinions contained herein are the private ones of the writer a n d are not to be construed as official or reflecting the views of the Navy Department or the naval service a t large.
Anhydrous Alumina as Adsorbent in Constituent Analysis of Asphalt RETHEL L. HUBBARD, K. E. STAKFIELD, AND W. C. KOMJIES Bureau of Mines, U . S . Department of the Interior, Laramie, F’yo. KHYDROUS aluminum oxide has been used as an adsorbent
A in constituent analyses of several hundred samples of as-
phalts from petroleum ( l a ) ,shale oil (8),native bitumen, and bituminous sandstone (6) by the method of Hubbard and Stanfield (4). This method involved removing pentane-insoluble asphaltenes from approximately 1.5 grams of asphalt, then dispersing the petrolenes on 25 grams of alumina to adsorb the resins and leave an oil fraction. The three different batches of alumina used in these analyses had similar adsorption properties, presumably owing t o the same method of preparation and t o comparable contents of alpha- and gamma-alumina. However, several subsequent batches of alumina procured under the same lot number and from the same supplier had variable adsorption characteristics. Accordingly, a study was made of several different batches of alumina and their use in the constituent analysis of asphalt. The study showed that different batches of anhydrous, crystalline alumina may have different adsorption characteristics. Therefore, samples of the same alumina adsorbent should be used to compare constituent analyses of a series of different asphalts. Preliminary attempts, involving blending or treating different samples of alumina, were unsuccessful for the purpose of preparing an adsorbent having adsorption characteristics which were intermediate between those of alpha and gamma forms of alumina. I n these tests, the utilization of adsorbentgrade aluminas commonly used for chromatographic analyses was not inveetigated.
Anhydrous alumina may consist of several crystalline forms, particularly the metastable gamma-alumina, which is highly adsorptive, and alpha-alumina, which is stable but less adsorptive ( 2 , 6, 13). These two crystalline forms were determined qualitatively in seven alumina samples by means of x-ray diffraction and by petrographic examination. By the latter method, it was possible to distinguish the isotropic alpha-alumina particles from the anisotropic gamma-alumina particles. Asphalt constituent anal>-sesusing the different aluminas as adsorbents (each adsorbent \$as graded to pass a 100-mesh-per-inch sieve and be retained on a 200-mesh-per-inch sieve) showed that the yield of resins was increased in proportion to the gamma-alumina content of the adsorbent. The x-ray and petrographic examinations showed the presence of alpha- and gamma-alumina in the adsorbents but were not a measure of adsorption. Accordingly, several methods of directly measuring adsorption were tried. The adsorbent was exposed to a benzene-saturated atmosphere for periods of 24 and 72 hours, and the adsorbed benzene was determined b y the increase in weight in accordance Lvith the method of Mair, Westhaver, and Rossini (IO). By the method of 1Iair and Forziati ( 8 ) , columns of the adsorbent m r e treated n ith n-heptane solutions of anthracene and of phenanthrene. The adsorption of anthracene and phenanthrene mas folloived by fluoreseence under ultraviolet light. Although the percentages of henzene, anthracene, and phenanthrene adsorbed per 100 grams of adsorbent ranged from 7.5 to
V O L U M E 2 4 , NO. 9, S E P T E M B E R 1 9 5 2 Table I. Constituent Analyses of Asphalt from Tampico, RIexico, by Use of ,iluminas from Alpha-Alumina Monohydrate _
condition^ for Dehydration of Alpha-Alumina _ Monohydrate ~ to 4lrimina Quantity Temp , Heating OC period nun treated, grams
Resin Content of Asphalt, %"
1491
analyses of thc asphalt by use of tlic initial lot of anhydrous alumina (4). The blend was then used for the constituent analysis of a low-asphaltene-t>Te asphalt from crude oil from Kern River, Calif. Based upon this asphalt, the alumina blend was less adsorbent than the alumina used in the initial analyses. This shows that, although a blend of alumina can beprepared that has siniilar adsorption characteristics to another alumina in analyses of a given asphalt, these aluminas may exhibit dissimilar adsorption characteristics in analyses of a different type of asphalt. .ACKNOWLEDGMENT
Average deviation =0.4370; former analysis of asphalt: 29.8% asphaltenes, 42.3% oils and 27.77' resins ( 1 9 ) . a
1 & O j 0.05 to 0.09, and 0.16 to 0.51, respectively, the results were not consist'ent enough t o measure the adsorbability of the alumina samples. Under certain heating conditions, alpha-alumina monohvdrate is converted t o variouh crystalline forms of anhydrous alumina (f-3,6 , 7 , 11, I S ) . To prepare products having different adeorption characteristics, samples of alpha-alumina monohydrate were heat,ed for periods raiiging from 10 minutes to 18 hours a t t,emperatures of 700" t o 1200" C. +Is shon-n in Tahle I, a yield of 36.0% resins vivas obtained from an asphalt of crude oil from Tampico, LIrtsico, by using an adsorbent prepared by heating 140 grams of alphn-:Lluinina monohydrate in a muffle furnace a t 1050" C. for 50 minutcs. By hcatiiig smaller samples, or by heating samples a t higher temperatures or for longer periods, the alpha-alumina moiiohydrate was converted into less adsorbent products containing greater proportions of anhydrous alpha-alumina. This dehydration process was very susceptible t o changes in the quantity of sample heated and to minor changes in the heating conditions. Accordingly, the adsorpt'ion characteristics of the products iverv not sufficiently reproducible for t,he analysis of asphalt. -111 anhydrous alumina adsorbent that was suitable for the constitueiit analysis of a standard asphalt sample from crude oil from Tampico! Llexico, was prepared by blending aluminas having higher and lower degrees of adsorption. Const'ituent analyses made ivith this blcmtl agreed n-ith values obtained in previous
Work was done under cooperative agreement between the University of Wyoming and the Bureau of Mines. Special acknowledgment is made to the Fisher Scient,ific Co. and to the Aluminum Co. of .Imerica for their cooperation in providing samples of alumina; also, t o H. S . Smith and Howard H. Heady, who assisted in making the petrographic and x-ray diffraction analyses. LITERATURE CITED ( 1 ) Beletzkii, AI. S., Legkie ;Metal (C.S.S.R.),5 , KO.2, 16-21 (1936).
( 2 ) Gorbunova, 0. E., and Vaganova, L. I., Khim. Referat. Zhur. (V.S.S.R.).2, NO.5, 31-2 (1939). ( 3 ) Heineman, H., Krieger, K. A, and AIcCarter, W. S. W., Ind. Eng. Chem., 38, 839-42 (1946). ( 4 ) Hubbard. R . L., and Stanfield. K. E., ~ A L CHEJI., . 20, 460-5 (1948). (5) Ihid.. C. S . Bur. Mines, R e p t . I n r e . s f . , S o . 4523 (1949). ( 6 ) Jellinek, & H., I.and Fankucheii, I., I n d . Eng. Chem., 37, 15863 (1945). ( 7 j Ibid., 41, 2259-65 (1949). (8) Kommes, W. C., and Stanfield. IC. E., Proc. Assoc. Asphalt Pacing Technol., 20, 473-89 (Febiuary 1951). (9) >lair, B. J . , and Foraiati. A. F., J . Reseurch, S u t l . Bur. Standards, 32, 165-83 (1944). (10) hlair, B. J . , Xesthaver, J . \I-., and Rossini, F. D., I n d . Eng. Chem., 42, 1284 (195Oj.
( 1 1 ) Xoiin, R . , G e d . F o w n . i. Stockholm Fo (12) Stanfield. K. E., and Hubhard. R. L., Paper, KO 717 (1949).
(13) Stumpf, H. C . , Russell, A . P., Sewaome, J . W., and Tucker, C.M., 1nd. Eng. Chr'm., 42, 1398-403 (1950). RECF:IVED for review l f a r c h 20, 1952, Accepted June 9 . 19.52.
Sulfamic Acid as a Standard Reagent for Alkalimetry W. F . WAGSER, J. A. WCELLSER,
AND
C. E. FETLER'
C-niuersity of Zcentucky, Lexington, Icy.
HE use of sulfaniic acid as a standard of reference in alkaliinretry has increased rapidly in recent years after its suitability for this purpose was reported by Butler, Smith, and Audrieth (1). At room temperature, solutions of sulfamic acid hydrolyze slowly, but as suggested bj- these authors a const,ant acid titer should be maintained because the hydrolytic product is the hydrogen sulfate ion LThich contains only one releasable proton. The present investigation was undertaken t o verify that solutions of sulfaniic acid retain a constant acid titer and t o study the use of sulfamic acid as a st,andard titrant for alkalimetry. Sulfamic acid may he compared with hydrochloric acid and sulfuric acid, for use as a standard solution. Reagent grade SUIfamic acid may be obtained at a modest price from the G. Frederick Smith Chemical Co., or t'he technical grade may be purified easily (1). It, is readily soluble in water, forming a st,rong acid only slightly weaker than sulfuric and hydrochloric acids and can be titrated with bases using indicators with transition ranges h ? t w w n a p H of 4 to 9. The pure solid acid is nonhygroscopic; r
1
Present address, S . i C . 1 , Leivi? Flight Propuiaion Laboratory. Cleveland,
Ohio.
thus a solution of known concenti,ation may he prepared easily by dissolving an accuratelJ- Reighed sample and diluting t o a known volume. Pract'ically all salts of sulfamic acid are soluble, thus eliminating the interference of precipitates during a titration. h possible objection t o the use of sulfamic acid lies in its relatively low molecular weight. REAGENTS
Sulfamic Acid, standard of reference for alkalimetry, G. Frederick Smith Chemical Co. Sulfamic Acid, reagent grade, G. Frederick Smith Chemical Co. Sodium Carbonate, anhydrous, primary standard grade, 1Iallinckrodt Chrmical Works. Acid Potassium Phthalate, National Bureau of Standards. Modilled Methyl Orange Indicator, aqueous solution, prepared by method of Hickman and Linstead ( 2 ) . Bromothymol Blue Indicator, aqueous solution, 0.1 %. EXPERIMENTAL
Stability of Sulfamic Acid Solutions. Six liters of approximately 0.1 A; solution were prepared by dissolving reagent grade sulfamic acid in carbon dioxide-frec distilled water. Six liters of approximately 0.1 N carbon dioxide-free sodium hydroxide solu-
