T H E J O UR il: A L 0F I
128
D C S T RI A L A N D E N G I N E E R I N G C H E M I S T R Y
will be reasonably accurate for other adulterants, for although there may be some variation between t h e dispersions of t h e various adulterating oils, when used with wood oil to 15 per cent or less, t h e differences in their effects upon t h e dispersion of t h e wood oil is relatively small. This fact may be better appreciated by comparing the two cur7.e~of Fig. 111, which start from somewhat different points b u t lack little of being coincident a t t h e lower ends, representing adulterations up t o and including 15 per cent The temperature correction for t h e angle of dispersion is quite small, about one second per degree Centigrade, which, figured in percentage adulteration, is 0 .I per cent. This is very considerably less t h a n the correction on t h e index of refraction. The angle D3 reading of Table I shows something of t h e effect Oil No.
Per cent Adulwood terant oil oil 100 100 100
10 11 12 13 14 15 16 17 18 19 20
100 95 95 95 90 90 90 85 75 60 40 25 15 10 5 0 0
21 22 23
0 0 0
6
7
8 9
Soya Soya Linseed Soya Linseed Soya Soya Sova S0j.a Soya Soya Soya Soya Soya Soya Tallow seed Sesame Rape Linseed
Angle D2-D1/2 26' 54" 26' 54" 26' 48" 26' 42" 26' 6" 26' 12" 26' 12" 25' 24" 25' 30" 25' 36" 24' 48" 23' 24" 21' 18" 18' 30" 16' 24" 14' 54" 14' 12" 13' 36" 12' 54" 14' 18" 12'42" 12'48" 13'42"
Apuarent adulAngle Vernier teration DS units Per cent Error 22' 37' 48" 269 22' 36' 12" 269 22' 34' 24" 268 22' 35' 24" 267 1.5 22' 30' 36" 261 5.5 0.5 22' 30' 24" 262 5.0 22' 30' 48" 5.0 262 22' 23' 12" 10.7 254 0.7 10.0 22' 26' 24" 255 22' 24' 48" 9 . 3 -0.7 256 2 2 : 19' 48" 15.0 248 22 8'48" 25.0 234 21 ' 48' 40" 40.0 213 21E25' 60.0 185 21 6'48" 164 75.0 20' 56' 36" 149 85.7 0.7 20' 48' 24" 142 90.7 0.7 20' 43' 36" 136 95.0 20; 36' 54" 129 100.0 21 3'48" 143 20'29'12" 20° 29' 20O55'36"
127 129 137
No. 1-Am. SOC. for Test. M a t . 1915: Pure Wood Oil No. 2-Gillispie and Sons: Pure Wood Oil &To. 3-Acme White Lead and Color Works: Pure Wood Oil No. 4-Acme White Lead and Color Works: Rejected shipment Nos. 6. 7 , 9 and 10-Am. SOC. for Test. M a t . 1915
of variation in temperature. Although precautions were taken t o maintain t h e temperature constant throughout the work, slight variations were unavoidable, a n d each slight variation made a big change in angles D1, DPand Da, although t h e effect upon Dz - D1 was relatively small. If i t were possible t o equip a spectrometer with a satisfactory constant temperature device, it is very probable t h a t t h e variations in angle D, due t o added impurity, would make a satisfactory means of detecting adulteration. The advantage gained by t h e measurement of this angle b y the spectrometer rather t h a n by t h e ordinary refractometer would be in t h e greater accuracy in reading. The method of examination of wood oil by measuring its dispersion should appeal t o the factory chemist. T h e individual readings may be made rapidly; there a r e no computations involved; t h e apparatus is not expensive nor difficult t o keep in adjustment, and t h e accuracy of t h e method compares very favorably with t h a t of any other in use a t t h e present time. The author wishes t o acknowledge his indebtedness t o Mr. W. T I T . Sleator, Instructor in Physics, for suggestions a n d assistance. UNIVERSITYOP MICHIGAN ANN ARBOR
Vol. 8, S o .
2
THE NEPHELOMETRIC DETERMINATION OF SMALL AMOUNTS OF ESSENTIAL OILS By A. G. WOODMAN, R . T. GOOKINA N D L. J. HEATH Received July 27, 1915
The two general methods most commonly employed for determining essential oils in such food products as extracts a n d cordials are: ( I ) extraction of t h e oil with a suitable solvent, and ( 2 ) precipitation of t h e oil and measurement of its volume after collection by centrifugal force. These methods give results much too low with very small amounts of oil, because both of t h e appreciable loss of oil during t h e evaporation of the solvent and of t h e proportion of oil which does not separate by centrifugal action. The fact t h a t a n alcoholic solution of most essential oils will form a cloudy emulsion on t h e addition of water suggested the possibility of using t h e degree of turbidity as a measure of the quantity of oil present. The emulsion formed consists of a large number of tiny oil globules which are capable of reflecting light. The number of globules and hence t h e amount of light reflected is evidently dependent on the amount of oil present. It remains, then, only t o find some method of measuring the amount of light reflected, and by comparison with a standard containing a known weight of oil, a q e t h o d is available for determining the amount of oil in a n unknown sample. APPARATUS
The simplest instrument which suggested itself for this purpose was the well known candle turbidimeter. This, however, was not found suitable for use with translucent precipitates like oil emulsions because t h e light passes through t h e globules and makes the end point obscure and inaccurate. It was therefore necessary to use a nephelometer, t h e form actually employed being t h a t devised by Kober.' The basis of t h e instrument is t h e wellknown Duboscq colorimeter, in which t h e length of column of liquid is varied by moving two glass plungers u p or down by means of t h u m b screws on t h e back of t h e instrument. The length of each column is indicated on a scale by a pointer which moves up and down with t h e plunger. To convert t h e colorimeter into a nephelometer, it is necessary: I-To paint the sides of the plungers with black asphaltum paint, leaving the ends clean and with sharply defined edges. The black coating prevents any reflections entering t h e plunger except through t h e bottom. (This change may be permanent as i t does not interfere with t h e use of the instrument as a colorimeter.) 2-To arrange a shield which will surround t h e tubes a n d by a central partition prevent a n y reflection from one t o t h e other. Two apertures are made in t h e shield directly in front of t h e tubes a n d t h e only way in which light can reach t h e tubes is through these openings. 3-To enclose t h e eyepiece with a box into which t h e head may fit comfortably. This prevents reflections on t h e eyepiece. 1J.
Bid. Chem., XIII, 4, 485; J . A m . Chem. Soc., 38 (1913), 1585.
Feb., 1916
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
The necessary apparatus for thus changing t h e colorimeter t o a nephelometer can be obtained from Eimer & Amend, New York. Our experience, however, with t h e outfit supplied b y t h e dealers showed t h a t several of t h e parts were unnecessary a n d they were therefore discarded. The instrument as finally used consisted of t h e Duboscq colorimeter in its entirety with t h e following additions: I-Black painted discs were placed on t h e bottom of t h e tubes t o prevent light entering from beneath. 2-A black tin shield was placed around t h e tubes with a partition in t h e middle t o prevent reflection from one t u b e t o t h e other, a n d in this shield there was a n opening opposite each t u b e t o allow t h e light from t h e lamp t o enter. 3-A black casing was used t o surround t h e instrument on three sides, leaving t h e back open for manipulating t h e plungers, and this shield had a hole cut in t h e front for t h e passage of light from t h e lamp t o the emulsion. The casing extended about a foot above t h e t o p of the instrument t o shield t h e eyes of t h e observer from t h e lamp a n d from direct daylight. Just below t h e eyepiece there was placed a horizontal partition with a hole in it.large enough for t h e eyepiece t o go through. This prevented reflection into t h e eye from t h e lower part of t h e instrument. This casing or shield could be briefly described as two boxes, one on t o p of t h e other, t h e instrument being in one a n d t h e eyepiece protruding through a small opening into t h e other. 4-The sides of t h e plungers were painted black with asphaltum paint. A Ioo-watt Mazda lamp was used as t h e source of light. Anyone possessing a Duboscq colorimeter can get results of considerable accuracy by much simpler apparatus. Taking t h e colorimeter in its ordinary form, on t h e bottoms of t h e tubes (outside) should be placed two black discs (pennies are of exactly t h e right size). The shield around t h e tubes may be made from cardboard painted with asphaltum paint. Two squares of cardboard may be perforated with holes of t h e proper size and slipped over t h e plungers t o prevent reflection from t h e tubes t o t h e eyepiece except through t h e plungers. T h e eyes should be protected from t h e light of t h e lamp b y some simple shade, as a cardboard box or a piece of cloth. STANDARDS
For quantitative determinations with t h e nephelometer it is of course necessary t o have a standard of known value, a n d this can be done in several ways: I-Standardize with permanent standards. 2-Standardize with one standard concentration and plot t h e readings of different known concentrations against t h e ratio of t h e known t o t h e standard concentration. 3-Prepare a standard for each determination with t h e concentration of t h e unknown and standard approximately equal, treating both in exactly t h e same way. The last plan, t h e one followed in this work, seems
much more, accurate t h a n t h e others since there can be no error introduced by different conditions of preparation of t h e known a n d unknown. These conditions are very important for accurate work, a n d unless they are t h e same t h e determination may be valueless. Richards a n d Wells' have pointed out t h a t t h e amount of light reflected is not exactly proportional t o t h e weight of precipitate, b u t is dependent t o a conside$able degree on t h e condition of t h e precipitate, t h e concentration of t h e solution and the length of column. Hence, t o get t h e best results, the condition of t h e precipitate should be exactly t h e same in t h e standard as in t h e unknown. This is insured by treating equal volumes of t h e unknown and standard with t h e same amount of reagent and by having t h e temperature a n d other factors t h e same. Besides this, t h e concentration of unknown a n d standard should be approximately equal and for this reason a preliminary precipitation of t h e unknown should be made and a n approximately equal amount of standard used. EXTRACTS
I n general, 5 cc. of a n extract were diluted with 2 5 cc. of water a n d compared with a standard in t h e nephelometer. Experience showed t h a t t h e emulsions should be freshly prepared in order t o give t h e best results, since on standing t h e globules of oil tend t o coalesce a n d rise t o t h e surface, thus offering less reflecting surface t o t h e light a n d giving low results. It was found also in working with fairly high concentrations of some essential oils t h a t t h e oil exerted a n appreciable solvent action on t h e asphaltum with which t h e plungers were painted, making i t advisable t o keep t h e plungers out of contact with t h e emulsion except during t h e time of actual reading. PEPPERMINT OIL-A typical series. of readings is shown in t h e case of peppermint oil in t h e following table: STANDARD. .....................................
.0.5 Per Cent Solution Column Length (mm.). .......................................... 15.0
TESTSOLUTION:
Concentration, %... 0.75 0.625 0 . 5 6 0 . 5 0.44 0.375 0.31 0 . 2 5 CoLLength (mm.)(a) 7 . 4 10.7 1 3 . 0 15.0 17.1 2 0 . 9 2 5 . 0 36.5 (a) These values are in each case the average of nine readings.
These values are expressed graphically in Fig. I , t h e ordinates representing t h e length of column of t h e test solution a n d t h e abscissae representing t h e ratio of t h e concentrations of t h e two solutions. I n t h e figure is also shown t h e theoretical curve, in which t h e lengths of column of two solutions are inversely proportional t o their concentrations. A consideration of t h e figure will show t h a t peppermint oil follows t h e theoretical curve fairly closely when t h e ratio of concentrations lies between the limits of 0.7 and 1.2. On both sides of these limits t h e actual plot deviates distinctly from t h e theoretical curve and corrections must be applied t o get t h e true percentage. There are thus two methods of procedure in determining t h e percentage of oil in a n unknown sample which lies outside these limits of concentration ratios: I-Compare t h e unknown with t h e standard in t h e usual way and read off t h e percentage on t h e plot. 1
Am. Chem. J . . 31 (1909). 235.
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T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
2-Compare the unknown with the standard approximately and from t h e indicated result prepare a standard more nearly approaching t h e concentration of t h e unknown. Using this as a standard, the percentage of oil in t h e unknown can be computed. The second method seems t o be much safer and serves also as a check on the approximate determination, 40
36
28 24 20
16 /2
8
FIG ~--NEPHCLOXETRIC CURVEFOR OIL OF PEPPERYINT
thus reducing t h e chance of error. I t is in general easier because the correction curves are not the same for different oils. T h e method works best on alcoholic solutions which do not contain over one per cent of t h e essential oil, so t h a t standard or full strength extracts should be diluted with two or three times their volume of strong alcohol and then t h e nephelometric determination made in t h e usual way. Similar results were obtained in t h e cases of K U T U E G and ANISE OILS, these, when diluted, following t h e theoretical curve of the nephelometer even more closely t h a n oil of peppermint and giving results agreeing closely with theory. Oil of anise gives a heavy precipitate with water and i t was found best t o precipitate 5 cc. of t h e extract with 5 cc. of water instead of t h e larger quantity used t o precipitate t h e other oils. E X T R A C T O F R O S E , which is quite difficult t o examine b y ordinary methods, owing t o t h e small amount of oil of rose present, is satisfactorily assayed b y t h e nephelometric method, using I j CC. of water t o precipitate t h e oil from j cc. of extract and employing 0.4 per cent or 0.2 per cent alcoholic solutions as standards. I n this case, for accurate results, t h e standard and t h e unknown should be of nearly t h e same strength since. as shown in Fig. 11, the actual a n d theoretical values agree only for concentration ratios near unity. T h e possibility of using one oil as a standard in t h e determination of other oils was taken into consideration and two strengths of extracts of the different oils which had been examined, I per cent and 0.5 per cent, were compared in t h e nephelometer. using in each case 2 5 cc. of water t o precipitate the oil. Peppermint oil was taken as t h e standard and t h e figures given below show the wide divergence of re-
2
sults obtained, making doubtful t h e possibility of using'any one oil as a standard. LENGTH O F C O L U M X Peppermint Nutmeg Anise 1.0 Per Cent Solution.. . . . . . . . . . . . , , 15.0 10.6 8.8 0.5 Per Cent S o l u t i o n . , . , . . . . . . . . . . . 15.0 9.6 8.0 OIL
Rose 15.0 15.1
An interesting fact: however, is t h a t peppermint oil can be very well used as a standard in t h e valuation of rose extract. DETERZIINATIOIi
32
1'01. 8, No.
OF
ESSESTIAL
OIL I N
CORDIALS-
The determination b y means of the nephelometer of t h e small quantities of essential oils found in cordials suggests itself as a natural sequence t o t h e examination of alcoholic extracts. The problem differs somexvhat in t h a t t h e percentage of alcohol is usually less in t h e cordials t h a n in the extracts and they usually contain also a considerable proportion of sugar and are frequently highly colored. The amount of alcohol was found t o have b u t little significance, t h e weaker alcohol serving t o hold in solution perfectly well the small amounts of essential oil used in these preparations. The effect of t h e sugar was found t o be more pronounced, the result of its presence being either t o prevent t h e precipitation of a part of t h e oil, or t o alter t h e size of the oil globules in the precipitate, so t h a t t h e amount of light reflected is less t h a n t h a t reflected*from a solution of the same strength b u t containing no sugar. This was readily shown b y comparing readings on an alcoholic solution containing 0 . 2 5 per cent of peppermint oil with solutions containing exactly t h e same amount of oil but varying proportions of sugar. T h e reading for t h e solution without sugar was 1 5 . 0 ; for solutions containing the same amount of oil, b u t with t h e sugar content gradually increasing from j per cent t o 40 per cent, t h e readings increased correspondingly from I j.1 t o 1 7 . 2 . The error due t o the alcohol and sugar, however,
FIG.~I-~-EPHELOMETRIC CURVEFOR OIL OF ROSES
is readily corrected b y adding t o t h e standard approximately t h e same proportion of alcohol and sugar t h a t are present in the sample being examined. I n t h e case of cordials t h a t are colored, if t h e color is not too intense the same method may be employed, the matching of a tinted turbidity with a gray-white
Feb., 1916
T H E J O C R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
one not being of great difficulty if t h e disparity of color is not great. With more deeply colored samples, however, separation of t h e oil by distillation is best, I O O cc. of t h e cordial being diluted with a n equal volume of water a n d I O O cc. distilled. This procedure gives a colorless distillate of t h e same volume as t h e original sample a n d of approximately t h e same alcoholic strength, differing from i t only in t h e absence of color and sugar. Numerous experiments have shown t h a t t h e distillation of t h e oil is quantitative, no special precautions being required except t o distil rather slowly. T h e degree of accuracy obtained is shown in t h e following examples of artificial cordials containing either anise or peppermint oil, together with 2 5 per cent of sugar and 48 per cent of alcohol. They were highly colored with a mixture of Naphthol Yellow S and Indigo Carmine. The accuracy with oil of anise is somewhat greater t h a n with peppermint: A Per Cent Oil Present . . . . , , , , , . , , . . . 0.1: Per Cent Oil F o u n d . , . . . . , , , , , . , , : . 0.1,
B 0.33 0.N
C 0.20 0.22
D 0.45 0.43
Typical results in t h e analysis of alcoholic extracts, containing amounts of oil unknown t o t h e analyst are given below: PERCENT PEPPERMINT .ANISE KUTMEG Oil A d d e d . , , . 0.88 0 . 4 0 0 . 1 9 8 0.625 0 . 3 3 0.375 0 . 3 1 OilFound 0 . 8 9 0 . 4 0 0 , 2 0 0 0 . 6 2 0 . 3 3 0 . 3 7 5 0.302
....
ROSE
0 , 3 2 5 0.317 0.323 0.310
131
water t o alcoholic solutions of different oils of equal strength differ widely in t h e amount of light reflected. The only oil t h a t it was found possible t o use as a substitute was peppermint oil for rose oil on account of t h e fact t h a t these two oils show approximately equal reflecting power under t h e same conditions. I n applying t h e method t o cordials two factors influence t h e amount of light reflected: ( I ) percentage of alcohol a n d ( 2 ) percentage of sugar. Their influence is large enough t o make it necessary t o use a standard containing approximately t h e same percentage of alcohol a n d sugar, but their effect does not change rapidly with small increases in their concentration and thus approximate equality of standard and unknown is all t h a t is necessary. Colored cordials can be examined directly provided t h e color is not so deep as t o make t h e end-point obscure. Deeply colored cordials can be determined by first distilling off t h e alcohol and oil and comparing t h e distillate with a standard extract. I n general, it may be said the nephelometric method is a rapid, simple a n d accurate method for t h e determination of, small amounts of many essential oils, requiring ordinarily less t h a n half a n hour for its completion. MASSACHUSETTS INSTITUTE O F TECHNOLOGY BOSTON, MASSACHUSETTS
SUMMARY
If water i s added t o a n alcoholic solution of many essential oils, t h e oil is precipitated as a n emulsion which appears white, on account of t h e reflection of light from t h e minute globules of oil constituting t h e emulsion. The amount of oil present may be determined b y measurement of the amount of light reflected from a column of this emulsion. The reflected light is compared in a nephelometer with, t h e light reflected from a solution containing a known amount of t h e same oil. The nephelometer used was a n adaptation of t h e Duboscq colorimeter. The general law of the nephelometer is t h a t when two solutions give equal illumination in t h e eyepiece, t h e concentrations of t h e reflecting substance are inversely proportional t o t h e lengths of t h e columns. Peppermint oil, nutmeg oil, anise oil a n d oil of rose follow this law with slight variations which do not affect t h e usefulness of t h e method. All of these oils can be determined with great accuracy b y t h e nephelometric method in concentrations u p t o one per cent and, by suitable dilution with alcohol, in higher concentrations. The nephelometric reading is not affected by slight variations in t h e chemical composition of t h e oil, hence i t is not necessary t h a t t h e standard employed should be from exactly t h e same source as t h e oil being determined. This method as described is not applicable t o those essential oils which do not form a n emulsion on adding water t o their alcoholic solutions. There is no single oil t h a t can be used as a standard for t h e determination of all these oils, because t h e emulsions formed by adding t h e same amount of
111-THE
REAGENTS FOR USE IN GAS ANALYSIS SPECIFIC ABSORPTION OF ALKALINE PYROGALLOL IN VARIOUS PIPETTES By R. P. ANDERSON Received August 30, 1915
The development of a pipette in which gases may be absorbed rapidly a n d completely by t h e proper reagents without t h e necessity of shaking has proceeded along two lines. There is ( I ) t h e form of pipette in which absorption is hastened by increasing t h e surface of reagent that is in contact with gas and ( 2 ) t h e form in which t h e same result is obtained by passing t h e gas through t h e reagent in such fashion as t o secure intimate contact. Under ( I ) there is included t h e Orsat’ pipette and its many variations; under ( 2 ) there are many distinct pipettes, including those of Hankus: K o w i c k i - H e i n ~ ,a~n d D e n n i ~ . ~It has been demonstrate# repeatedly t h a t the Orsat pipette, or its modifications, is unsatisfactory for t h e absorption of oxygen b y alkaline pyrogallol prepared in t h e usual fashion. Since rapid a n d complete absorption is a function of t h e composition of t h e reagent as well as of t h e construction of t h e pipette in which it is t o be employed, it was thought desirable, on t h e introduction of new proportions of pyrogallol a n d potassium hydroxide for t h e preparation of alkaline pyrogallol,6 t o ascertain the behavior of this modi1
Chem. News, 29 (1874), 177.
* Osteru. Chem. Z t g . , 47
(18991, 81; J . f. Gasbel., 49 (1906), 367. Designed by Nowicki, Osteru. Z e d . f. Berg. Hktt., 6s (1905), 337; improved by Heinz, J . f. Gasbel., 49 (19061, 367. 4 THIS JOURNAL, 4 (1912), 898. See Dennis’ “Gas Analysis.” p. 78. 6 THISJOURNAL, 7 (1915), 587. ’
3
