126
T H E J O U R N A L OF I N D U S T R I 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
for t h e true heat of bromination, t h e apparatus could be worked in t h e same way as it was standardized, using oil and bromine in place of sulfuric acid a n d water. This should give results which are accurate t o perhaps I or 2 per cent. This should make also a convenient apparatus for certain student calorimetric work where i t could wcll be used in place of larger and more expensive types of calorimeters. I t might be noted, too, t h a t the stirring must be vigorous in the large calorimeter. Several types of stirrers were tried inside of t h e mixing chamber and a spiral form was finally adopted as being t h e most efficient for this purpose. CONCLUSIONS
I-A special apparatus and a method for the determination of t h e true heat of bromination have been proposed a n d tried. 11-A new apparatus on t h e same principle has been proposed for t h e quick determination of specific heat b u t i t could well he used for othcr purposes, such as t h e determination of heat of neutralization, the Rlaumen6 number in terms of calories per gram of oil, etc. 111-The heats of bromination in calories per gram of oil have been determined on a number of oils a n d these values compared with t h e iodine numbers. IV-It has been shown t h a t the heat of bromination is not directly comparable t o t h e iodine number, a n d t h e reason why such a n agreement could not be expected has been pointed out. V-The heats of solution of bromine and most oils in carbon tetrachloride have been shown t o be very small.
1'01. 8.
No. z
characteristic of this oil, and upon which is dependent t h e development of such varnishes as contain it. T h e report of t h e committee, submitted as a result of a series of tests carried out b y different operators upon accurately prepared samples, shows t h a t t h e method must be carefully handled t o produce closely agreeing results, and t h a t under ordinary circumstances it should not he relied upon t o detect adulteration under 5 per cent. T h e iodine jelly test, as investigated b y t h e same committee, seems b u t little better. However, as mentioned in a n earlier paper,' the gelatination of wood oil b y iodine in chloroform solution is subject t o a marked retardation b y t h e presence of small amounts of alcohol. This fact may explain some of t h e variations in results, as the different operators were not using chloroform from t h e same source, and n o doubt some of t h e chloroform might have contained traces of alcohol. T h e index of refraction of wood oil, ns has been pointed out b y various investigators, is considerably higher t h a n t h a t of other drying and semi-drying oils. All attempts t o calibrate, for analytical use, the variations in refractive index, due t o mixing other oils with wood oil, h a w been unsuccessful in establishing the use of the rcfrnctomctcr in the quantitative estimation of adulteration. I n this method
U N I Y B R S ~OP Y MISSOURI. COLUMBIA.M I S S O U ~
OPTICAL DISPERSION OF CHINESE WOOD OIL AS AN INDEX OF PURITY By E. E. \YARE
R ~ c e i v ~Novernher d 26. 1915
The peculiar properties exhibited by Chinese wood oil have led t o t h e development of some interesting methods of examination for t h e detection of adulteration. I n practically all cases, although t h e property upon which the individual method is based is characteristic enough t o warrant its use as the basis of a method of examination, difficulties have arisen in t h e control of t h e conditions of operation, in consequence of which different laboratories report widely varying results. The two methods offered b y Ware a n d Schumann,' one of which depends upon t h e insolubility of the sodium soap of elaeomargaric acid in absolute alcohol, a n d t h e other upon t h e insolubility of t h e light-converted elaeostearic acid glyceride in high gravity petroleum ether, produce accurate results when operated under properly controlled conditions of temperat u r e a n d concentration; b u t they do not seem adapted t o t h e use of t h e factory control laboratory. T h e heat test as modified b y Committee D-I, SubCommittee 111, of t h e American Society for Testing Materials,z is a logical method of analysis, inasmuch as i t depends for its accuracy upon t h e careful observation of t h e progress of a gelatination which is 1 f
Tmrs J o u a n ~6~ (1914). . 806. Pioc. An. SOC.T a l . Mal.. 1916, P. 204.
t h e temperature corwclioii i:,r:rlr is !:irxc rnough to make possible a n error of onL, plir IYWL ;or cvery degree variation in tcrnpcrn:orc cnxtroi. Thcrc csists also t h e difficulty of mnkin: n n c s n t t scttinx of t h e cross hairs of the rending telescope upcn t h e dividing line b'etween t h e illuminatcd and t h e dark fields. This difficulty is quite pronounced when using white light as a source of illumination, for t h e line of division between t h e fields is n o t sharp, even after a careful adjustment of t h e compensator, t o correct for dispersion. E. C. Holton2 noticed, when working with t h e Abbe direct reading refractometer, t h a t t h e rotation of t h e prism required for correct compensation for wood oil a n d for other oils is very different. He has gathered together considerable unpublished d a t a in a n a t t e m p t to calibrate this difference in compensator reading t o a point where he can make use of i t as a n analytical method. BrierS takes advantage of this property of abnor~ T H ~ ~ J O U F (1915).571. CNIL.~ 2
1
Private eornrnunieefion. Tam JOURNAL, 7 (1915). 953.
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
Feb.. 1916
mally wide dispersion exhibited b y wood oil, in a method in which he demonstrates t h a t when using a Pulfrich refractometer equipped with a prism whose relative dispersion is not large, t h e compensation offered by t h e secondary prism made u p of oil is sufficient t o produce a n effect of anomalous dispersion. The compensation by other oils will narrow t h e spect r u m b u t will not reverse it. Inasmuch as this compensation offered by t h e secondary oil prism is due t o t h e natural dispersion of the oil, i t is possible t o simplify t h e examination b y
I
3 FIG.I1
making a direct reading of this dispersion uninfluenced by t h e dispersion of any other medium. This may be accomplished by using as t h e refracting medium a hollow prism filled with the oil t o be examined. The most convenient instrument for t h e measurement of such relative dispersion is t h e ordinary spectrometer equipped with a n autocollimating * eyepiece. Fig. I shows such a n instrument in use in this laboratory. If light of a definite wave length be focused on t h e small totally reflecting prism in t h e eyepiece of t h e telescope, i t is reflected through t h e slit a n d t h e objective lens, from which i t enters t h e oil prism as parallel rays. After becoming refracted by t h e oil, it is reflected from t h e silvered rear face of t h e prism a n d refracted back along its original p a t h t o t h e slit f r o m which i t came. The angle through which t h e table of t h e spectrometer must be rotated t o properly focus t h e slit image upon t h e slit itself, is t h e angle from which, knowing t h e angle of t h e prism, may be computed t h e refractive index for t h a t particular wave length, according t o t h e formula sin l / / z(A D) = sin 1/2 A where l/z D is t h e angle of rotation of t h e table minus t h e angle of t h e prism. If, instead of using a monochromatic source of light, we use a source emitting light of several wave lengths, we may, b y making settings on t h e several bright lines characteristic of t h e source of light, measure t h e indices of refraction for t h e several wave lengths, a n d express t h e relative dispersion for any two of t h e m according t o t h e general formula
127
I1 gives some idea of t h e spectrum from t h e brass arc after dispersion by wood oil. The lines marked are t h e ones used for t h e measurements reported. They persist without adsorption b y any of t h e oils used. The angles D1, Dz a n d DB,from which are computed t h e refractive indices for lines I , 2 and 3, vary with the nature of t h e oil, with t h e temperature, and according t o t h e angle of t h e prism; but for t h e same oil in a definite prism they are constant for a fixed temperature. The difference D2- D1 is just as accurately a measure of t h e relative dispersion for a n individual prism as is t h e difference between the corresponding refractive indices. This fact simplifies the procedure of t h e method, for t h e fine adjustment of the spectrometer has sufficient range t o permit the reading of t h e angular difference Dz - D1 without ,resetting t h e spectrometer circle. The vernier of t h e instrument illustrated has a least reading of 6" with a possibility of interpolation to one second. The dispersion or angular difference for wood oil as measured while confined in a hollow prism of angle 2 0 ' I ' is 26' j4", while for soya bean oil for the same temperature i t is 12' j 4 " , or expressed in vernier unit? of 6' each, i t is 269 and 129, respectively. As is shown in Table I and Fig. 111, the dispersion of wood oil adulterated with varying percentages of
+
'
- PCP Pc1'
PC
in which p c is t h e index of refraction for light of wave length 0.65629 a n d p F for wave length 0.48614. I n order t o get a maximum value for t h e relative dispersion angle t h e author made use of a brass electrode arc lamp as a source of light. This light gives characteristic bright lines in both t h e red a n d t h e blue, with several other lines in t h e green a n d t h e yellow. Fig.
FIG.111
soya bean oil may be expressed quite accurately by a straight line, if we select, as coordinates, percentage adulteration a n d angular dispersion. This curve
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.
