INDUSTRIAL A N D ENGINEERING CHEMISTRY
January 15, 1930
when the average temperature of the tank was 68’ F. (20’ C.). The sample represented by curve B was taken from the same full tank 17 days later when the average tank temperature was 73” F. (23’ C.). Both samples were taken from the 20-foot (6-meter) level, the depth of liquid in the tank being 40 feet (12 meters). Curve B will approach approximate coincidence with curve A if it is shifted to the right a distance corresponding to 0.25 per cent loss. Since the curves are not exactly parallel, the loss indication is somewhat variable, but if the portions of the curves near the origin, where the results are most subject to error, are disregarded, the variation of indicated loss is not appreciable. The Engler distillations of the tm-o samples are given in Table
Vapor-pressure determinations made in conjunction with fractional analyses greatly increase tJhe value of the latter. T a b l e IV-Inspection Analyses of S a m p l e s GASOLINE A RE-RUNPRESSURE COMMERCIAL &-APHTHA 6/18/29 7/5/29 . . , , 64.5’ 58.80 A. P. I . gravity. . , 58.6’ 1nitialb.p . . . . . . . . . 88°F.(31.10C.) 96°F.(35.60C.) 9’3’F. (37.2OC.) Per cenl Per (:enf Per cent F. C. 158 70 14.0 11.0 11.0 221 105 38.0 31.5 31.0 72.0 284 140 54 0 80.0 62 0 302 I50 94.3 83 0 356 180 .. 88 0 374 190 92 0 392 200 4:0 3 0 Loss
.
IV. Similar determinations have been made on samples of gasoline taken during transportation from storage to a filling station and thence to an automobile tank. Such surveys are highly valuable in determining a t which point in the operation the maximum loss is incurred and in estimating the probable effect of changes in the character of the naphtha.
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Literature Cited (1) Oberfell, Alden, and Hepp, Nall. Pelroleurn S e w s , 20, KO.20, 57 (1928). (2) Pearce and Snow, J. Ph>’s Chem., 31, 231 (1927). (3) Regnault, Ann. chim. fihys., 3, KO. 15, 129 (1845). (4) Walker, Lewis, and McAdams, “Principles of Chemical Engineering,” p . 598, McGraw-Hill, 1927. ( 5 ) Wilde, Mead, and Coleman, 012Gas J . . 27, No. 42, 102 (1929).
The Polarizing Microscope in Organic Chemistry‘ H. C. Benedict CHEMISTRY DEPARTMENT, NORTHWESTERN UNIVERSITY DENTALSCHOOL, CHICAGO, ILL.
I
N A recent report by a subcommittee of tlie Executive Committee of tlie Division of Chemistry and Chemical Technology of the Kational Research Council on the kind of education needed by a technical research chemist (Q), training in the fundamentals rather than specialization is stressed, However, the following statement is made: “An exception of the field of microchemistry should be made because the microscope has come to be so valuable a part of research laboratory equipment that every research chemist should be d l trained in its use.” Wright (Sd), Chamot (3), Chamot and Mason ( 4 ) , and Garner (8) emphasize the importance of the polarizing microscope in the identification of substances. Their studies have usually covered inorganic compounds, probably because more is known of the optical properties of these compounds and because a system for their identification can be worked out. Less is known about the optical properties of organic compounds, although more is appearing all the time in the literature] showing a spreading realization of the value of chemical microscopy as a time and labor saver (3). For instance, we find records of the optical properties of aldopentoses 124), of melezitose (27), of heptitols ( ~ 4 and of @-lactose (SO) by Wherry, of 13 sugars by Keenan ( l e ) , of tetramethylmannose by Green ( I I ) , and of a glucose derivative by Wolfrom (SI). The chemical laboratories of the American Medical Association] appreciating some of the advantages of a microscopical examination using polarized light, obtained the cooperation of Walcott in several studies of borocaine (.5), salyrgan (e), acriflavine ( 7 ) ] ephedrine (WI), and a-phenyl@-aminoethanolsulfate ( I O ) . Wherry has contributed papers on the optical properties of certain organic compounds (24) and of the calcium salts of maleic and fumaric acids 180). Wherry (26) and Keenan ( I ? ) have reported similar data on alkaloids. Amino acids have such indefinite melting points that the description of their optical properties by Keenan (15, 18) is particularly helpful. Data on the optical determination of the isomeric naphthalene sulfonic and 1 Received
October 4, 1929.
disulfonic acids have been presented by Ambler and Wherry ( I ) and by Hann and Keenan ( I S ) . A recent paper by Mason and co-workers (22) lists the optical properties of a monoarylguanidine. S o r is the work wholly confined to definite compounds. Grier (12) is able to identify rayons with a polarizing microscope, and this instrument is in continual use a t the Picatinny Arsenal (20) in the examination of nitrocelluloses. Keenan (14) has examined the d-globulin of sesame seed. Taylor and Sheard (23) have used such a microscope in a study of the calcification of tissues. A similar research on teeth was reported by Kitchin at the Chicago meeting of the American Association of Dental Schools on March 26, 1929. These examples, by no means complete, are enumerated to show the wide usefulness of the polarizing microscope. Anyone who has studied and used the method will be enthusiastic over its possibilities and could cite many examples of its helpfulness. The following are instances of its value as a “time and labor saver” in this laboratory. Amino Acids
, I n studying methods for preparing amino acids Keenan’s papers ( I C , 18) h a r e been most helpful. A drop of the reaction mixture can be smeared on a microscope slide and examined between crossed nicols to see whether or not any birefringent material is present. Usually a few other simple optical properties, such as extinction angle and sign of elongation, can be ascertained. These data alone are frequently sufficient and can be determined on the crude mixture. One can tell whether or not i t is worth while to go through a laborious isolation process. This is particularly valuable in testing short-cut methods. I n preparing alanine (2) it was possible to show that alanine was present in the reaction mixture without any attempt a t purification. The alanine was isolated by dissoh-ing the hydrochloride in alcohol and precipitating with aniline. Two obvious questions arose. (1) Was all of the alanine extracted from the sodium and ammonium chlorides by the alcohol? Examination of the
ANAL Y TICAL EDITION
92
residue betn eeii crossed nicols showed no birefringence, indicating that removal had been complete. (2) How complete was the precipitation of the alanine by the aniline? I n one run, vhen aldehyde ammonia was the starting material some of the alcoholic mother liquors were concentrated and gave a crystalline material. ITithout purification a little of this under the microscope shon-ed needlelike crystals, closely resembling alanine, but jvith the opposite sign of elongation, tested by merely introducing a selenite plate between the crossed nicols. It could not be alanine. Later it was found to be iminodipropionic acid, m. p. 232-234", recorded for the racemic form 235", nitrogen by Kjeldahl, found 8.8, theor? 8.7, the optical properties of d i i c h are not on record, This example shoTvs that it is not always necessary that the optical properties be known in advance. The students in a biocheniistry class prepared cystine n-hich crystallizes out in hexagonal plates. One student turned in some boric acid which also crystallizes out in what appear t o be hexagonal plates. But cystine gives a uniaxial interference figure with crossed nicols and convergent light while boric acid gives a biaxial figure with a small optic axial angle. The point to be stressed is that the material turned in was shown not to be cystine by a simple microscopic test,, which also gave evidence as to its identity, an additional advantage of the method. Work has also been done on the synthesis of serine iunpublished) and the ability t o determine whether any serine is present in the crude reaction mixture has cut the work in half because no time is wasted in lvorking u p reactions which give no yield of serine. I n preparing some intermediates for this synthesis, it was thought that ethoxyacetic acid was a by-product in amounts too small to be readily purified for identification. A little copper ethoxyacetate was prepared and some of its optical properties were determined. When copper carbonate was added to the solution suspected of containing the ethoxyacetic acid and a drop or so concentrated on a slide, crystals corresponding in properties to those previously prepared were observed. Later, in larger scale runs, i t was found possible to work up this portion and obtain a yield of the acid. I n an attempt t o prepare a substituted aspartic acid, a compound identified as ethylphthalimido maleate was obtained. A great saving in time resulted from finding that the hydrolysis products of this material mere phthalic anhydride and ammonium chloride. The phthalic anhydride \vas extracted with ether. The remaining material was not a t all birefringent. This meant that it belonged to the cubic system, and, as organic compounds are very rarely found in this system, the material was inorganic. The featherlike appearance of the crystals indicated that it was ammonium chloride. Miscellaneous Products
A colleague brought to this laboratory a small amount of some pasty material which was thought to contain benz-
aldehyde bisulfite. A minute's work was required to prepare some benzaldehyde bisulfite and t o see with the polarizing microscope that the two materials were identical. This saved the time required for isolating the aldehyde from the small sample and either preparing the phenylhydrazone with a purification and melting point or oxidizing with a purification and melting point. A bacteriological problem suggested that decarboxylating organisms ought to form ethyl amine from culture media containing alanine as the only organic constituent. It remained to find a way to distinguish between ethyl amine and ammonia in small amounts. The chloroplatinates of
Vol. 2, No. 1
these compounds are insoluble and vary enough in crystal form t o be differentiated. T o distinguish between the local anesthetics butyn and procaine, sodium chloride was added to butyn to yield the crystalline hydrochloride, which is insoluble. The form is long platelets with pointed ends, having an extinction angle of about 20 degrees and negative elongation. Procaine, on the other hand, is unaffected by sodium chloride solution but yields long fine needles, with parallel extinction and negative elongation, when treated with bromine water. This is probably the dibromo novocaine reported hy LIorcl, Leulier, and Denogel (19). Sometimes the label will come off a bottle and yet one can say that the contents is one of two or three substances. The polarizing microscope will serve t o identify the contents. For example, an unlabeled bottle was suspected of containing sodium hydrogen maleate. Some of this substance between crossed nicols showed long crystals with pointed ends, parallel extinction, positive elongation, and a very large optic axial angle, with the axial plane at right angles to the elongation. The material in the unlabeled bottle had the same properties and was therefore sodium hydrogen maleate. The time consumed in testing these two materials was less than 5 minutes. Yet the evidence was as conclusive as that obtained by spending several hours on an analysis. It was possible to assist a purchasing agent who asked if a blanket submitted t o him was actually 10 per cent wool. The blanket was found to contain about that proportion of wool, but the wool was of an inferior grade. Inorganic substances are sometimes by-products in organic reactions. il student was attempting to prepare p-aminobenzoic acid by the reduction of the nitro acid Tyith ferrous sulfate in ammoniacal solution. The only product isolated was a well-crystallized light-green substance, which was not organic. I t might have been ferrous sulfate of either one of two types, ferrous ammonium sulfate, ferric sulfate, or ferric ammonium alum, although the last two were iiot probable because of the color. The following properties gave the clue to the optical identification: SUBSTANCE FeNHa(S04)z. 12H20 Fez(S0a)r. 9Hz0 FeSOa. (NHdiSOa. 6Hz0 FeSOa. 7 H i 0 FeSOa. 5HzO
CLASS Cubic Uniaxial Biaxial Biaxial Biaxial
RFPRICTIVE I\DICSS
1.552 1.487 1.471 1.528
w =
t
= 1.557
1.491 1.478
1.537
1.499 1.486 1.543
The material was placed in a liquid of refractive index 1.500, which almost exactly corresponds to gamma in the ferrous ammonium sulfate. On microscopical examination the material was found to be biaxial. This eliminated the first tmo on the list. With only the polarizing nicol in place, many crystals were found to have a position a t which they completely disappeared, indicating optical homogeneity, that is, the refractive index was the same as that of the liquid. As no crystal having a higher refractive index was found, the material was identified as ferrous ammonium sulfate. Summary
The use of a polarizing microscope is a tiiiie and labor saver in organic chemistry and often makes it possible t o detect and identify unworkably small quantities of material, t o identify the products of a reaction, many times in a crude state, to identify the contents of unlabeled or wrongly labeled bottles, to trace the course of a reaction or show that the reaction has been complete, and to detect and identify unsuspected products of a reaction. Literature Cited (1) Ambler and Wherry, J. IND. ENG CHRM.,12, 1081 (1920). (2) Benedict, J . A m Chem. Soc., 61, 2277 (1929). ( 3 ) Chamot, Sci. Monrhly, 24, 300 ,1927).
IAYDC*STRIALA S D E-YGISEERISG CHEMISTRY
January 15, 1930
( 4 ) Chamot a n d Mason, J . Chem. Education, 5, 3 5 8 ; 9, 536 (1928). (5) Collins, 3 . A m . J l e d . Assocn., 90, 26 (1928). (6) Collins, Ibid., 91, 1994 (1928). (7) Collins and Stasiak, J . A m . Pkarm. Assocn., 18, 659 (1929). (8) Garner, I n d . Chemist, 4, 287, 332, 410 (1928). (9) Geer and Stine, ISD.EXG.C H E M .Piews . E d . , July 10, 1929, P . 1 (10) Gordin, J . .An.P k a v m . Assocn., 17, 1197 (1928). (11) Green and Lewis, J . A m . Chem. SOC.,50, 2817 (1928). (12) Grier, J. I N D .E N O .CHEX, 21, 168 (1929). (13) H a n n and Keenan, J . P k y s . Chem., 31, 1082 (1927). (14) Jones and Gersdorff, J . B i d . Chem., 75, 221 (1927). (15) Keenan, I b i d . , 62, 163 (1924). (16) Keenan, J . Ti‘ask. A c a d . Sci., 16, 433 (1926). (17) Keenan, J . A m . Pharm. d s s o c n . . 16, 837 ( 1 9 2 i j . (18) Keenan, J . B i d . Chem , 83, 137 (1929).
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(10) Morel, Leulier, and Denogel, B d l . soc. citi?n., [a] 45, 4:7 (1929) C. A . , 23, 15S7 (1929). ( 2 0 ) Olsen, 6th Colloid Symposium Monograph, 258 (1928). (21) Peterson, IND.ESG. C H m r . , 20, 388 (1928). ( 2 2 ) Smith, K a n e , and Mason, J . Am. Chem. Soc., 51, 2522 (1929). (23) Taylor a n d Sheard, J . Bid. Chem., 81, 479 (1929). (24) K h e r r y , J . A m . Chem. Soc., 40, 1852 (1918). ( 2 5 ) K h e r r y , J . W a s h . A c a d . Sci., 8 , 277 (1918). ( 2 6 ) Wherry, U. S. Dept. Agr., B d 2 . 679 (1918). (27) Wherry, J . A m . Chem. SOL.,42, 126 (1920). (28) Wherry, J . B i d . C h e m . , 42, 377 (1920). (29) Wherry, J . Wash. . I d . Sci., 12,288 (1922). (30) Wherry, I b i d . , 18, 302 (1928). (31) Wolfrom, J . A m . Chem. S O L . 51, , 2191 (1329). (32) Wright, I b i d . , 38, 1647 (1916).
Observations on the Rare Earths-XXXIVi Spectrographic Estimation of Impurities in the Rare Earths Pierce W. Selwood UNIVERSITY OF ILLIXOIS, CRBANA, ILL
The applicability has beel? demonstrated of the spectrographic method to the detection and estimation of traces o f manganese, magnesium, calcium, barium, silicon, bismuth, aluminum, beryllium, samarium, and gadolinium i n neodymium, and of lanthanum i n yttrium. U R I S G the course of work involving the preparation of pure compounds of the rare earths it becomes necessary from time to time t o establish the absence of certain elements whose presence may be suspected. The ordinary analytical procedures often suffice for this purpose, but in certain cases they are not entirely satisfactory owing either to the time involved or t o the poor sensitivity of the test. The object of this investigation Tvas, therefore, to determine to what extent the spectrograph may be applied to the detection of elements whose chemical analysis falls into the latter class. Experimental Procedure
A number of samples of neodymium nitrate were prepared from mateiial concentrated in this laboratory during the l a d few years. S e o d y n i u m was used in all but one of the determinations. because it is a representative rare earth and because several kilogram^ of practically pure material were available, EO that t!ie saciifice of a frn grams did not entail any serious 10s‘. After precipitation. fiirst as the hydroxide v i t h ammoniiini liydi oxide, and then as the oxalate after solution of the hydroxide in nitric acid. the material was ignited in porcelain t o the oxide. It n a s then found to contain as impuritieq only magnesium and silicon. After reprecipitation and ignition in platinum, neither magnesium nor silicon could be detected. From 10 t o 0.001 per cent of whatever element it was desired to detect was then added to the samples of neodymium nitrate, generally in the form of a common salt These mixtures were evaporated until the solution was nearly saturated. T h e preparation of the only set of samples in which neodymium was not used, that of lanthanum in yttrium, was similar t o the above. The spectra were registered photographically on a Hilger E l quartz spectrograph, using a quartz system throughout. The excitation was a 6-ampere arc struck between two purified graphite rods conveniently supported in a n electrode holder described elsewhere (4). A drop of the concentrated solution placed in the crater of the positive lower electrode was sufficient to produce an excellent spectrum over an exposure of Receiked October 2 5 , 1929.
30 second.. Fresh graphite rods were used in el-ery instance. The iron arc taken for reference in each case was exposed for 10 seconds. Panchromatic “spectrum process” plates were used throughout. The procedure in taking each series of spectra was as foll o m : First, the spectrum of pure neodymium was photographed. Then, on the same plate, were taken in order the solutions containing increasing amounts of the impurity being iiir-estigated. Finally the iron arc was taken for reference. I n the cases of the elements samarium, gadolinium, and lanthanum pure samples were also taken in order to facilitate locating their various spectrum lines. I n general little difficulty was eupclrienced in finding the most persistent lines of the impurities as listed by Lowe ( 3 ) and by T w j m a n ( 5 ) . T h e actual n a ~ lengths e given are corrected t o those of Kayser (2) Under the microscope these lines were followed through the 1 arious concentrations until they finally disappeared. I n a few cases the persistent lines of the impurities d o o d awiy from any other lines and \\.ere readily located bv the unaided ex r. Manganese
Plate 1 illustrates the case of manganese. Although this element does not frequently occur in rare-earth ores, it is often introduced in the form of potassium permanganate during the removal of cerium, or as manganese nitrate for fractional crystallization of t h e double rare-earth niangarie%e nitrates. The spectrum lines a t 2605.7, 2593.7, and 2576.1 A. are quite distinct at 0.001 per cent and because of their intensity might be expected to be evident at considerably smaller concentrations. No indication is given as to the presence of manganese in the osupposedly pure neodymium. The strong line at 2478.6 8 . is due to carbon Magnesium
bIagnesium is a common impurity in rare-earth preparations because the double rare-earth magnesium nitrates are frequently used in the resolution of the members of the cerium group. During the course of the work it was found that the graphite rods used as electrodes contained both magnesium and
