V O L U M E 22, NO. 1, J A N U A R Y 1 9 5 0
185
method, and a sample containing 150 mg. of honey was used for the Quisumbing and Thomas method. The results are found in Table ir. LITERATURE CITED
(2) Ibid.. p. 565. (3) Ibid., p. 582. (4) Kuhn, Richard, and
Jerchel, Dietrich, Ber., 74B,949-52 (1941). (5) Mattson, A. M., Jensen, C. O., and Dutcher, R. A., Science, 106, 294 (1947).
Chemists, “Official and Tentative hlethods of Analysis,” 6th ed., p. 133, 1945.
( 1 ) Assoc. Offic. Agr.
RECEIVEDJune 20, 1949.
Determination of Certain NitrogeRContaining Functional Groups in Organic Compounds WALTER W. BECKER Hercules Experiment Station, Hercules Powder Company, Wilmington 99, Del. Nitrogen exists in a considerable number of combinations with oxygen, hydrogen, and carbon in organic compounds. It is often necessary to determine the specific nitrogen-containing functional group present. This paper presents a review of available methods for determining certain of these groups. Included are literature references and an outline of the procedures for the determination of the nitrate, nitro, diazo, azo, amino, amide, alkimide, and nitrile groups in organic compounds.
N
ITROGEN exists in organic compounds in probably more combinations with oxygen, hydrogen, carbon, and itself than any other element. Its several valences enable it to unite with these other elements to form a variety of nitrogen-containing functional groups. In early days only the total nitrogen could be determined by the Kjeldahl or Dumas methods; as time went on, methods for determining the specific groups began to be developed. This article presents a review of the available methods for the specific determination of certain of these groups, which have been arbitrarily divided into a number of classes for the purpose of presentation. The principle of the procedure, a few typical compounds which have been analyzed, and literature references are given. NITRATE NITROGEN (-ONOz)
The methods for determining nitrate nitrogen fall into three general classifications. By Nitrometer. The apparatus in general use today is the Du Pont compensating-type nitrometer (20), which is a modification of Lunge’s gasvolumeter (21). With the du Pont nitrometer, the nitric oxide generated may be readily brought to the volume it would occupy a t 20” C. and 760 mm.; this eliminates the need for temperature and barometric corrections. Elving and hfcElroy (IO)developed a semimicronitrometer of the compensating type, with a motor-driven shaker. The nitrometer is usually standardized with potassium nitrate, which reacts with sulfuric acid and mercury according to the following equation: 2ECX03
+ iHzSO4 + 3Hg +KzS04 + 3HgS04 + 4H20
+ 250
In assembling the nitrometer, care must be taken to dry all glassware and to use clean mercury. As a safety precaution, a cellulose acetate face mask must be worn during the generation of the nitric oxide, in case of an explosion. Khen carefully trained, the average analyst is able to operate the nitrometer safely. Complete directions for assembling and standardizing the Du Pont nitrometer, as well as the procedure for analyzing samples, are given by Scott (34) and by the American Society for Testing Materials ( 3 ) . The method can be applied to the analysis of nitroglycerin, nitrocellulose, pentaerythritol tetranitrate, and similar esters, or to compounds that liberate nitric oxide quantitatively. Ob-
viously, the method is inapplicable to nitrate nitrogen-containing compounds that liberate carbon dioxide, sulfur dioxide, or gases other than nitric oxide. Nitrogen in finished explosives usually cannot be determined by means of the nitrometer because they invariably contain stabilizers such as diphenylamine or diethyldiphenylurea. These stabilizers undergo partial nitration in the decomposing bulb, and cause low results. However, certain compounds undergo quantitative nitration under these conditions. For example, if weighed amounts of potassium nitrate and material containing mononitrotoluene are shaken with sulfuric acid in the decomposing bulb, quantitative nitration to dinitrotoluene takes place. The decrease in volume of the nitric oxide obtained is a measure of the mononitrotoluene present. Saponification Methods. The reduction of inorganic nitrates to ammonia by the use of Devarda’s alloy is well known (2). It would seem, then, that organic esters such as nitroglycerin and nitrocellulose could be saponified with sodium hydroxide, and then Devarda’s method applied. Unfortunately, when such esters are treated with sodium hydroxide, various reduction products including ammonia are formed. Muraour (24) avoided this difficulty by conducting the saponification in an oxidizing medium. He dissolved the sample in acetone, added sodium hydroxide, sodium perborate, and hydrogen peroxide, then let stand overnight for the saponification to sodium nitrate. He then added Devarda’s alloy, heated, and distilled the resulting ammonia into standard acid ( 2 ) . Considerable foaming occurs a t the start of the distillation, due to the presence of a floating layer of isophorone which is formed by reaction of acetone and sodium hydroxide. -4good distilling head must, therefore, be used to prevent entrainment of alkali during distillation. hfuraour’s procedure has been used in this laboratory for various products, with good results. It is particularly applicable to samples of lacquer containing nitrocellulose; in this case the nitrogen content of the nitrocellulose must be known or assumed in order to calculate the amount of the latter present. Volumetric Reduction Methods. Knecht (16) first determined nitric acid in aqueous solution by reduction to nitric oxide with ferrous iron in hydrochloric acid solution, then titrating the resulting ferric iron with a standard solution of titanous chloride, using ammonium thiocyanate indicator. In this laboratory, it was found that Knecht’s method could be used for the determination of the nitrate nitrogen in nitroglycerin and nitroglycol, after
ANALYTICAL CHEMISTRY
186 dissolving the sample in glacial acetic acid (4).The procedure could be applied in the presence of aromatic nitro compounds such as 2,4-dinitrotoluene; the stabilizers diphenylamine and diethyldiphenylurea did not interfere. The equations in the case of nitroglycerin are as follo\rs. C3Hs(OhTO2)3 S F ~ C I L 9HClC3H5(OH), YFeCI, 3S0 3H20 TiC18 FeCI3 -+ TiCll FeCl,
+
+
+
+
+
+
+
VITRO NITROGEN (-NO*)
The methods for determining the nitro group depend upon the three general types of organic nitro compounds; more than one method is applicable to each type. Nitro Aromatic Compounds. The reduction of the nitro group by means of titanous chloride solution was first developed by Knecht (16) and applied to various compounds by English (11j and Callan and Henderson (6). The compound is dissolved in water or alcohol and an excess of standard titanous chloride is added. After boiling, the excess is titrated with standard ferric iron solution, using ammonium thiocyanate indicator, thereby obtaining a measure of the nitro nitrogen present. Six equivalents of titanous chloride are required for each nitro group. Certain nitro compounds do not reduce in the orthodox manner with titanous chloride. For example, in hydrochloric acid solution, low results for a-nitronaphthalene are due to the formation of 1,4-monochloronaphthylamine. Xitroanisole becomes chlorinated in a similar manner. Using titanous chloride and sulfuric acid, English (11)obtained low results for nitro hydrocarbons such as the mononitro derivatives of benzene, toluene, and xylene. Callan and Henderson (6) shoxved that accurate results could be obtained on the foregoing types of mononitro hydrocarbons by using titanous sulfate in place of the chloride. and a reflux condenser to avoid loss of the sample by steam distillation. For compounds such as dinitrotoluene and trinitrotoluene, a 5minute boiling period is necessary in acid solution. TT’ith the use of an alkaline buffer such as sodium citrate, Kolthoff and Furman (17) state that the reduction will take place practically instantaneously a t room temperature. This shortened and equally accurate procedure was used a t ordnance plants operated by the Hercules Potvder Company (5) during World m a r 11. The polarograph may also be used to determine the nitro group; the reduction a t the dropping mercury electrode probably proceeds as follows in the case of nitrobenzene: C6HsK02 6Hf 6e +C5HsKH2 2H20
+
+
+
Shikata (36) and his associates measured the reduction potentials of mono- and dinitrobenzene, mono- and dinitrophenol, and the nitranilines, with satisfactory results. Kolthoff and Lingane (18) summarize the application of the polarograph to nitro compounds; the E. H. Sargent Company (33) publishes frequently a review of the literature concerning the applications of the polarograph. Nitro Aliphatic Compounds. The nitro group in this type of compounds is much more difficult to reduce. The total nitrogen rontent may be determined by the Dumas method or by suitable modifications of the Kjeldahl method. A study of the available references listed in the review article by Hass and Riley (14) did not reveal any reliable volumetric reduction methods for the specific determination of the nitro group in nitroparaffins. DeVries and Ivett (9) developed a polarographic method for the quantitative determination of several low-molecular-meight nitroparaffins, when present in dilute solution. A 0.05 W sulfuric acid solution was used as the supporting electrolyte. The half-wave potentials vs. a normal calomel electrode ranged from 0.60 to 0.72 volt, for the series nitromethane to nitrobutane. The half-wave potentials were not sufficientlyfar apart to determine the compounds separately in the presence of each other. Heyrovsk$ and Sovak (15) used the polarograph in connection with an investigation of the stability of smokeless powder, to determine
oxideh r ~ lr~itrogenand nitric acid. Sitroglycerin interfered but wuld tx removed by solvent extraction. Nitroamino Compounds. In connection with the analysis of newer explosives compositions during World K a r 11, this laboratory 1% orked on the development of methods for the determination of nitroguanidine and cyclotrimethylenetrinitramine, popularly known as RDX. In the analysis of nitroguanidine, the regular titanous chloride reduction method gave erratic results. On increasing the acidity and lengthening the boiling time to 15 minutes, it was found that 1 mole of nitroguanidine reacted with 4 moles of titanous chloride (19). Cottrell, MacInnes, and Patterson (8) determined the nitrogen content of nitroguanidine by dissolving the sample in concentrated sulfuric acid and titrating with ferrous sulfate solution. The visual end point was not sufficiently reproducible, but by using a platinum-tungsten electrode system, they mere able t o obtain concordant results by titrating potentiometrically. Apparently, when dissolved in sulfuric acid, the nitroguanidine yields nitrate ion under the given conditions. Cope and Barab ( 7 ) were able to analyze nitroguanidine and tetryl by the nitrometer method; Elving and XcElroy (10) also analyzed these two compounds. Cope and Barab postulated that the nitro or nitroso group must be attached to a second nitrogen atom, which in turn is attached to a carbon atom. For example, they were able to determine the nitroso group on diphenylnitrosoamine, which fulfills these conditions, but found that no reaction occurs in the nitrometer with p-nitrosodimethylaniline or nitromethane. Rathsburg (31) used titanous chloride to analyze “the nitration product of hexamethylenetetramine” (cyclotrimethylenetrinitramine or RDX) and formulated the reaction as follows: C3HeS,(S02)3
+ 12T1Clq +C?He?;c
He did not balance the equation. I n this laboratory, titanous chloride alone gave low results on RDX. Ferrous chloride was tried, but the reduction was negligible. However, by the addition of both reducing agents and a 30minute boiling period, reduction was complete, 4 equivalents of titanous chloride being required for each nitro group (19). In view of these results, it seems likely that Rathburg used titanous chloride which contained ferrous iron as an impurity. DIAZO AND AZO NITROGEN (rV=h’=
AND -N=N-)
Diazo. Knecht and Hibbert (16) successfully titrated benzenediazonium chloride with titanous chloride and found that 4 equivalents were required. Wienhaus and Ziehl (43) treated the ethyl ester of diazoacetic acid with hydrogen in the presence of palladium catalyst, and measured the nitrogen liberated. Pierce and Rising (68) modified Mehner’s (22) method and adapted it to a micro scale. The sample is heated with hydrochloric acid in a closed system, and the gaseous nitrogen formed is measured in an azotometer. On diazoaminobenzene and three substituted diazoaminobenzenes, they obtained values which agreed closely with the total nitrogen present as determined by another method. The method should be applicable to any substance that evolves nitrogen quantitatively under these conditions. I n this laboratory, methods for the determination of diazo and nitro nitrogen in diazodinitrophenol were devised (35). Rathsburg (31) had formulated the reduction of this compound by titanous chloride as follows :
+
C6H2O(NO2j2Sz 13TiCId+C6H?O(SH2)JSHz The author’s results confirmed the stoichiometry of Rathsburg’s equation, but no differentiation between the diazo and nitro nitrogen could be calculated. On treating diazodinitrophenol with hydrochloric acid or sodium hydrosulfite and measuring the evolved nitrogen gasometrically, low results were obtained, However, when a large excess of titanous chloride was added to the sample, the mixture heated, and the evolved nitrogen
187
V O L U M E 2 2 , NO. 1, J A N U A R Y 1 9 4 9 measured, quantitative results were obtained on diazodiinti ophenol. Rathsburg’s unbalanced equation is apparently in erior, Azo Nitrogen (-N=N-). Knecht (16) was able to analyze a variety of “azo dyestuffs” with titanous chloride, either by titrating directly, or by adding an excess of the reducing agent, boiling, and back-titrating with ferric solution or a dye solution such as methylene blue. He gave the general reaction as folloirs:
R‘ S : S R ”
+ 4 TiCla + 4 HCI +R’. KH2 + R ” .S H , +
4 TiCl, hzobenzene and its derivatives are reduced a t the dropping niercury electrode in neutral, acid, and alkaline media. Using the polarograph, Tachi (39) measured the reduction potentials of azobenzene, p-aminoazobenzene, and dimethylaminoazob~nzene in dilute ethanol solution a t 0.001 JI concentration. AMINO hITROGEN (--NHz)
A widely used method applicable to the determination of many
aliphatic primary amino groups is that developed by Van Slyke (40). The general reaction is:
RNHz
+ “02 +ROH + Hi0 +
K 2
The nitrous acid is prepared from sodium nitrite and glacial acetic acid. After the reaction, the gas mixture is treated with alkaline permanganate in a Hempel pipet, and the nitrogen, which remains, is measured in a buret. Since publication of the original paper, a micromanometric apparatus has been developed which permits the determination of much smaller amounts of nitrogen ( 4 1 ) . A general vxite-up of the method and description of the apparatus are given by Peters and Van Slyke (27). Van Slyke’s original paper (40)discusses the manner in which various types of aliphatic amines react with nitrous acid. The most significant facts are that the amino groups in the a-amino acids react quantitatively in 3 or 4 minutes a t room temperature, whereas amino groups in other types of substances react much more slowly. For example, methylamine and ammonia react completely only after shaking for about 2 hours and aminopurine or aminopyrimidine after 2 to 5 hours. Urea required 8 hours. KO nitrogen is split off from the amino group in creatine. Primarj- and secondary amines possess active hydrogen, and can therefore be determined by the method of Zerewitinoff (44). This procedure depends on the quantitative reaction in a closed system of the sample and Grignard reagent, to yield methane. T h e reactions are as follows:
+
RSH, 2CHzMgI +2CHa RLSH CH3lIgI +CH,
+
+ RS(AIg1)z + RzKllgI
With primary aromatic amines such as b-naphthylamine and p-toluidine, Sudborough and Hibbert (38) found that heating at 125” to 130” C. was necessary for complete reaction. Only one volume of methane was evolved from secondary amines such as diphenylamine and ethylaniline. Zerewitinoff analyzed succinimide and phthalimide, and found that one mole of methane wai evolved. KOreaction takes place with tertiary amines. A detailed write-up of the use of the Zerewitinoff method is given b\ Niederl and Xiederl (25) and by Pregl (SO). Primary aromatic amines, such as aniline and the toluidines may also be determined by diazotization in hydrochloric acid solution with a standard solution of sodium nitrite, the end point being detected by using potassium iodide-starch paper as an outside indicator ( I ) .
Friedrich (12) improved t,he original apparatus, while C‘iebock :md Brecher (42) developed the volumetric procedure for determining the alkyl iodides. Two or more distillations must be made to be certain that all the alkyl iodide has been swept out of t,he reaction flask. Samples which areinsoluble in hydriodic acid may give low results; the addition of phenol and acetic anhydride to dissolve the sample, then completing the determination, is helpful. The methylimino group in atropine may be determined by this niethod. Kuhn and Giral (20) analyzed trimethylpentadecabetaine successfully. When more than one group is present, cautiori must be exercised in interpreting the results, for all the groups may not react. Slotta and Haberland (37) analyzed cocaine hydrochloride and codeine, which contain both methoxyl and methylimino groups. The former group was measured by treating with hydriodic acid a t 135’ C., then changing absorbers, hrating a t 360 O to 380’ C., and measuring the methylimino group. A detailed write-up of the method is given by Niederl and Nirderl (26) and by Pregl (30). MISCELLANEOUS NITROGEN GROUPS
Several types of nitrogen linkage in organic compounds may be determined by the Zerewitinoff method. In pyridine at room temperature, acetamide reacts with Grignard reagent to evolve 1 mole of methane; a t 95” C. 2 moles are evolved. Acetanilide evolves 1 mole of methane a t room temperature; aniline reacts t o give only 1 mole, even on warming. Nitriles and isonitriles react, with Grignard reagent without the evolution of methane; however, the amount of reaction can be determined by adding water or aniline and measuring the unconsumed reagent. Rose and Ziliotto (32) developed a modification of the method of Friedrich et al. ( I S ) , whereby the sample is first treated with potassium iodide and sulfuric acid to reduce the nitrile. The determination is then completed by the regular Kjeldahl method. They successfully analyzed several nitrile compounds, including acrylonitrile and benzonitrile. Using the polarograph, Pech (26) quantit’atively determined saccharin (0-benzoic sulfimide) , using a supporting electrolyte that was about 0.05 N in hydrochloric acid and 0.05 A‘ in potassium chloride. Quinoline and nicotine in dilute solution may also be determined polarographically. Mitchell and Ashby ($3)determined unsubstituted acid amides by measuring the increase in acidity on reaction with 3,5-dinitrobenzoyl chloride in pyridine. A blank is run on the reagent plus alcohol. Water interferes, but can be corrected for. The method is generally applicable to primary amides of mono- and dibasic aliphatic and aromat,ic acids such a s acet’amide, benzamide, and phthalamidr. SL‘MMARY
Included in this review paper are literature references and an outline of the procedures for the determination of the nitrate, nitro, diazo, azo, amino, amide, alkimide, and nitrile groups in organic compounds. The methods list,ed are specific for the particular group in question, but they may not necessarily be the shortest ones to use if no interfering constituents are present,. In applying an apparently appropriate method to the analysis of a new compound, it, is always advisable first to apply the method to a known compound whose struct’ure approximates that nf the sample to be analyzed.
ALKIiMIDE NITROGEIl (=NCHa)
LITERATURE CITED
Alkylimino groups of low molecular Keight may be determined in organic compounds by a modification of the Zeisel method The sample is refluxed with 57% hydriodic acid to form the respective quaternary ammonium iodide. Upon heating at 360 o C. the lower alkyl radicals (methyl, ethyl, etr.) are split off from t h e nitrogen in the form of their alkyl iodides.
11) .klleii, et al., “Commercial Organic Analysis,” p. 568, 5th ed,, Philadelphia, Pa., P. Blakiston’s Son and Co., 1927. (2) Allen, W. S., 8th I n t e r n . Cong. A p p l . Chem., 1, 19 (1912). ( 3 ) Am. SOL.Testing Materiak, ”Standard Specifications and Testn for Soluble Kitrorellulose,” Designation D 301-33. (4) Becker, W.I%-,,ISD.EXG.CHEM.,A h a L . E D . , 5 , 152 (1933). ( 5 ) Butts:.P. G.. Afeilile, W , J., Shovers, John, Kouba, D. L . . and Becker, W ,W.,AKAI..CHEM..20, 947-8 (1948).
188
ANALYTICAL CHEMISTRY
(6) Callan, T., and Henderson, J. A. R., J . SOC.Chem. I n d . , 41,157-
61T (1922). Cope, W. C., and Barab, J., J . A m . Chem. Soc., 38,2552 (1916). Cott,rell,T. L., MacInnes. C. A . , and Patterson, E. M., Bnalyst. 71, 207 (1946). DeVries, T., and Ivett, R. W., IND. ENG.CHEM.,ANAL.ED., 13, 339 (1941). Elving, P. J., and McElroy, W.R., Ibid., 14,84-8 (1942). English, F. L., J . I n d . Eng. Chem., 12,994-7 (1920). Friedrich, A., Mikrochemie, 7, 195 (1929). Friedrich, A., Kllhaas, E., and Schllrch, R., 2. physiol. C h m . , 216, 68-76 (1933). Hass, H. B., and Riley, E. F., Chem. Revs.,32,373-430 (1943). Heyrovskg, J., and Novak, J. V. 4.,X V I I I Cong. Chimie I n dustrielle A17ancy, 1938; Chimie et Industrie, 35, 1043-50 (1938). Knecht, E., and Hibbert, E., “New Reduction Methods ill Volumetric Analysis,” New York, Longmans, Green & Cornpany, 1st ed. 1910, reprinted with additions 1918 and 1925. Kolthoff, I. M., and Furman, N. H., “Potentiometric Titrations,” p. 304, New York, John Wiley & Sons,,!926. Kolthoff, I. M.,and Lingane, J. J., “Polarography, pp. 380-9, New York, Interscience Publishers, 1941. Kouba, D. L., Kicklighter, R. C., and Becker, W. W.,AS.&L. CHEM.,20, 948-9 (1948). Kuhn, R., and Giral,,.!J Ber., 68, 387 (1935). Lunge, G., J . SOC.Chem. Ind., 9,547-9 (1890). Mehner, J . prakt. Chem., (2) 63,305 (1901). Mitchell, J., Jr., and Ashby, C. A., J . Am. Chem. SOC.,67,161-4 (1945). Muraour, H., Bull. soc. chim. France, 4546,1189-92 (1929). Niederl, J. B., and Niederl, V., “Organic Quantitative Microanalysis,” 2nd ed., New York, John Wiley & Sons, 1942. Pech, J., Collection Czechoslov. Chem. Commrin., 6, 126 (1934).
(27) Petels. J. P.. and Van Slvke, D. D.. “Quantitative Clinical
Chemistry, Val. 11, Metliodi.” Ralti&re, Williams and Wilkins Co., 1932. (28) Pierce, .4.E., and Riuing, M. M., J . .4m.Chem. Soc., 58, 13B:3 (1936). (29) Pitman, J. R., J . Soc. Chem. Ind., 19,982-6 (1900). (30) Pregl, r., “Quantitative Organic MicroanalyPis,” revised and edited by Julius Grant, 4th ed., London, J. and A. Churchill, 1946. (31) . , Rathsbure. -. H.. Ber.. 54B. 3183-4 (1921). . , (32) Rose, E. L., and Ziliotto, H., ISD. ENG.CHEM.,ANAL.ED., 17, 211-13 (1945). (33) Sargent, E. H., and Co., “Bibliography of Polarographic Literature,” June 1946. (31) Scott, W.W., “Standai cl Methods of Chemical Analysis,” 5th ed., Vol. I. D. 649, New Yo1.k. D. Van Nostrand Co., 1939. (35) Shaefer, W. E-, and Becker, W. W.,A X ~ LCHEM..19,307-10 (1947). (36) Shikata. M., Trans. Faraday SOC.,21,42 (1925). (37) Slotta, K. N., and Haberland, G., Ber., 65,127 (1932). (38) Sudborough, J. J., and Hibbert, H., J . Chem. SOC, 95,477-SO (1909). (39) Tachi, I., .Ifem. Coll. Agr. Kyoto I m p . Univ., 42,36 (1938). (40) Van Slyke, D. D., J . Biol. Chem., 9,195 (1911) to 23, 407 (1915). (41) Ibid., 83, 425 (1929). (42) Viebock. F., and Brechcr, C., b’er., 63, 2307 (1930). (43) Wienhaus, H., and Ziehl, H., Ibid., 65,1461 (1932) (44) Zerewitinoff, T., Ibid., 40,2033 (1807) to 47,2417 (1914). I
RECEIVED May 16, 1949. Presented before the Division of Analytical and Micro Chemistry, Symposium o n Determination of Nitrogen in Organic Compounds, at the 114th lreeting of the AVERICAN CHEMICAL SOCIETY, St. Louis, N o .
Physicochemical Micromethods of Test for Petroleum Products HARRY LEVIN, A. €5. MORRISON,
AND
C. H. REED
The Texas Company, Beacon, Y. Y .
Micromethods are described for pour point, titer, and vapor pressure, each of which employs less than 1% of the sample used in conventional macromethods. Comparisons are made between results by the micro- and macromethods.
B
ECAUSE the modern petroleum industry is concerned with
highly chemical operations and processes and miscellaneous organic and inorganic materials either as products of its own manufacture or items of purchase relating to its plant operations, microchemical procedures, both analytical and synthetic, are of intense interest and importance. However, miscellaneous physicochemical measurements-some very empirical-are also of great importance to this industry because they are used in control of manufacturing operations, included in customers’ specifications, and involved in analysis of samples from service and complaints. Macromethods are generally used, but occasionally the sample is too small; this frequently happens when the case is particularly important. Micromodifications of these macromethods have often proved a godsend. Methods for determining viscosity on microsamples of oil have been reported by Levin (7) and Cannon ( 4 )and micromethods for unworked and worked consistency of grease by Kaufman (6) and Hain (6). The present paper describes methods that have been successfully used on relatively small quantities of sample to determine the pour point of lubricating oil, titer of fatty acid@,and vapor pressure of gasoline. POUR POINT
By a simple modification of the well known practice of determining solidification or melting point of wax on a thermometer bulb, it has been possible on a drop of oil to obtain pour test re-
sults which agree very well, generally, with those obtained by the conventional A.S.T.M. method ( I ) involving some 30 or 40 grams of sample. The apparatus is shown in Figure 1. To make a determination, the bulb of the thermometer a t room temperature is dipped into the oil a t room temperature, to a depth of about 3 mm. If the drop of oil that adheres appears so large that it will be likely to fall off in subsequent manipulations, it should be reduced. The copper wire (No. 29 gage, 5 cm. long) is bent into a single loop 4 to 6 mm. in diameter a t one end a t a right angle to its stem, which should be cut to be 25 mm. long. The loop is applied to the drop of oil on the bulb where it adheres by surface tension, and the stem serves to magnify the movement of the drop in the subsequent observations. A vertically multiliied label pasted inside the pour test jar facilitates observation of the movement of the wire. The pour test jar, thermometer, etc., are now assembled in the customary manner and the assembly is preheated and cooled from bath to bath exactly as for an A.S.T.M. pour test. The assembly is removed for observation a t each temperature drop of 5’ F. (2.8’ C.). The maximurn period that the assembly may be kept out of the cold bath for an observation is 3 seconds, as in the A.S.T.M. method. The temperature a t which no movement is noticeable when the assembly is in a horizontal position for 5 seconds is 5’ F. (2.8 C.) below the pour point, as in the A.S.T.M. method. Oils of high pour point may be heated, before application on the thermometer bulb, to the same temperatures permitted in the A.S.T.M. maximum pour method. All manipulations, after the assembly of the apparatus, are in strict accordance with the A.S.T.M. method of test for maximum pour point.
