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
T H E JOURA'AL O F 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 fied reagent in various pipettes regardless of their usefulness with t h e old reagent. I n t h e following article there are given the results of experiments t h a t were made t o determine t h e specific absorption' of t h e modified reagent in the four pipettes t h a t have been mentioned. together with some observations on the convenience a n d ease of manipulation of t h e reagent in the various pipettes and the attempts t h a t were made t o adapt t h e reagent t o them. The construction of each pipette is shown in Fig. I. A measured amount of t h e modified alkaline pyrogallol was placed in each a n d the specific absorption of the reagent was determined for samples containing
ORSAT
HAXKUS
XOWICKI-HEINZ
DENNIS
FIG. I 2c per cent oxygen, using t h e method of manipula5 s n which was found by experiment t o be best adapted t o t h e pipette. The procedure t h a t was followed resembled t h a t employed in similar determinations with t h e Hempel pipette2 and consisted of t h e analysis
TABLE I-SPECIFIC
T'ol. 8, S o .
2
t h e customary manner, is probably due in part t o t h e formation of a thick film of reagent on t h e glass tubes in the pipette, as a result of t h e high viscosity of t h e reagent. A comparison of each of t h e four pipettes under discussion as regards t h e time consumed in their manipulation and the specific absorption that is thus obtained shows t h a t t h e Orsat pipette is superior t o a n y of t h e others for t h e absorption of oxygen when t h e modified reagent is employed. Allowing 1 5 seconds for t h e passage of a sample oE gas either to or from the Orsat pipette and 30 seconds for t h e return of gas from the other pipettes, it is seen t h a t in t h e case of t h e Orsat pipette only 1'/2 minutes is required from t h e time t h e gas leaves t h e burette until i t has been returned, while t h e corresponding time in t h e case of t h e Hankus, Sowicki-Heinz, and Dennis pipettes is j'/z, 2l/2, and 2'/2 minutes, respectively. Further, t h e specific absorption t h a t may be obtained from either the Nowicki-Heinz or the Dennis pipette in t h e 2'/2 minute interval is small as compared with t h a t obtained in t h e Orsat pipette for the 1 1 / ~ minute interval. I n fact, i t seems probable t h a t , when the modified reagent is employed, t h e Orsat pipette is superior to any form in which the gas is made t o bubble through t h e reagent, since t h e Nowicki-Heinz and Dennis pipettes; with which t h e comparisons were made, are undoubtedly the most efficient pipettes t h a t operate on t h a t principle. The convenience of manipulation is not all t h a t might be desired, however, in the case of any of t h e pipettes t h a t were studied. One source of trouble t h a t is common t o each is the formation of a deposit . TYPEOF APPARATUSUSED
ABSORPTIOXOF MODIFIEDALKALINE P Y R O G A L L O L ( a )
METHOD OF MANIPULATION Orsat Hankus Xowicki-Heinz Dennis One-minutecontact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.1(6) , . 0 5 :1 i:1 One passage occupying 2 minutes(c) . . . . 0 24.8 T w o passages occupying 1 minute each(c .......................... Two passages, first occupying 2 minutes, second 1 minute(c). . . . . . . . . . . . . . . . . . . . . . . . . 0 .. 2i:0 Three passages, first occupying 2 minutes, others 1 minute each(
