ANALYTICAL CHEMISTRY
1120 sufficient natural tocopherol present and, therefore, none need be added. Table I V gives the recovery figures for various antioxidants added to fat previously freed of oxidizing materials. S o recovery figure is given for tocopherol because this antioxidant is determined by means of an internal standard. DISCUSSION
I n the determination of propyl gallate with the ferrous tarrrttte reagent, the color reaction is very sensitive t’o variations in the p H . Opt,imum results xere obtained when a p H of 7 was employed and in most cases the ammonium acetate buffer was sufficient t o hold the p H close to 7. If, however, the solution is too acid. the color formation is incomplete and if the solution is a l h line the purple color has a tendency t,o fade. Gallic acid, tannic3 acid, and gallates other than propyl gallate may give a color reaction with ferrous tartrate at, p H 7 which is identical to that produced a i t h propyl gallate. Hoivever, tannic acid, gallic acid, and gitllates ot,her than propyl gallate arc not usually emploj-ed as ailtioxidants in either Canada or the Unitrd States. Guni guaiacum if present in lard or shortening \vi11 be extracted from a petroleum ether solution of a fat by 727, ethyl alcohol. Reducing substances in the gum react with ferric chloride plus 1,l’-bipyridine to produce a red color, which might be mistaken for butylat,ed hydroxyanisole or nordihydroguaiaretic nciti. Guni guaiacum can be readily detected bj- adding a few millilitc~s of the ferric chloride rexKent to an aliquot of t’he 72y0 ethyl alcohol extrart. The appearance of an intense blue color that rapidly fades indicates the presencbe of this material. This color phoultl not be confused with the purple color produced hy propyl gal1at.c.. From the data in Table I, it can be seen that, 2-tert-Lutyl-4hydroxyanisole produces approximately 10% more color per unit However, in the cwe weight than 3-tert-butyl-.1-hyd1.oxyanisole. of commercial hutylatrd hydroxyanisole preparations I, 2, :rnd 3 , the variation ip approximately 1%, measured a t 30 minutw. Therefore, for investigutiond or control purposes the butylated liydroxyanisole prcxparation r.mplo>-(ddiould be used as the 9t:intlard . The ferric chloritle-l.l’-l)ipyridine re%gcnt is not specific for butylated hydroxyanisole, iiordihydroguaialrtic acid, or t.ocopherol and therefore could react viith other reducing eul)stances present in the fat. Hun-evrr, no such intcrfermc-e vas encountered in any of the fat samples txx:tniined in this study. The analytical method for the tletcarminiition of tocopherols is not as precise as the methods for the othrr antioxidants. d;a’-
Tocopherol )vas chosen as an arbitrary standard for this work. However, each of the four tocopherol isomers produces a different color intrneity with ferric chloride and 1,l’-bipyridine (9). The procedure of Parker and McFarlane (8) was tried but was not sufficiently sensitive for the determination of the relatively small amounts of tocopherol present in lard and shortening. I t was evident that large aliquots of fat would have to be employed in order to obtain sufficient tocopherol for a reasonably accurate analysis. The foregoing procedure was therefore devised, whereby a fat aliquot up to 320 nig. could be used compared to a maximum aliquot of 20 mg. in the Parker and McFarlane (8) procedure. The use of ferric chloride plus 1,l’-bipyridine in 100% ethyl alcohol e n s u r d complete niisrihility of these reagents with the petrolcum ether solution of the fat, and thus permitted rapid reacti.m \vitli the tocopherol. The subsequent addition of 1.1 ml. of 86Yc ethyl alcohol l o ~ e r c c lthe ovrr-all alcohol content to 90%, ~vhich wilted in :t separation of the alcoholic phase from the petroltwm ethoi, carrying n.ith it the red ferrous bipyridine complex, n.hile niost of the, fat reniained in the petroleum Pther phase. This piucetlure is intended only to give a reasonable estimate of the tocopherol present. On.ing t,o the presence of traces of carotenoitis in some ehorteningp, the results may he high unless the fat solution is treated to remove innrotenoids before determining tocopherol ( 8 ) . ACKNOWLEDGMEXT
The authors wish to express their thanks to C. W. Dunnett fur statistical analJ-sis of the data and to the Universal Oil Products Ch.,the Tennessee Eastman Corp., and the Heyden Chemical Corp. for samples employed in this study. LITERATVRE CITED
(3) (4)
(5) (6) (7)
ninicrie, A,, and Engel, C . , Rec. trctc. chin^., 57, 1331 (1938). lasstone. S.,A i m l y s t , 50, 49 (1925). Hill, R., Proc. R u g . Soc. L o n d o n , B 107, 205 (1930). Iit.ayhi11, H. It.. Dugan, L. R., Beadle. €3. W., Vibrans, F. C.. Swartz, V e x . , and lieaabek, H., J . A m . Oil Chemists Soc., 26, S o . 9, 449 (1949). Luntlherg, IV. 0 . . mid Halvorson, H. O., Pim. I m t . Food Tech/ i d . . 1945, 115. Nattil. K. F.. and Filer, L. J., Jr., IND. ESG. C H E Y . ,- ~ I S A I . . ED., 1 6 , 4 2 i (1944). hIitchell, C. A , , Arin!j/st, 48, 2 (1923).
(8) Parker, 11.. E., and RIcFai,lane, \V. D., Can. J . Resrnrch, 18B, 405 (1940). (9) Stern, XI. H. and Raxter, J. C . , A i s tCHEJI., ~. 19, 902 (1947). RECEITED August 1-1, 1950.
Butylated Hydroxyanisole in Lard and Shortening Control A nalys is J. H. 314IION
4\D
K. 4. CII4PJI.IN
Food and Drug Laboratories, D e p a r t m e n t of \-utional Health und V e l f a r e , Ottawa, Canada
B
UTl-LrlTED hydroxyanimle (J3H.i) has been reported to I)e a very effrctive antioxitlant for animal fats (4,:ind thip information has atiniulated interest in nwthods for its qunntitutive determination in l ~ r dand shortening. h niotiificnt ion of the Emmerie antl Engel ( 2 ) fwric chloridr plus 1. L’-liiliyridinc, reagent has Leen employed satisfactorilj- ( 7 ) for thc tic~tc~rmin:ition of this antioxidant, hut this reagent is unstal)le to light nnrl is not, specific for h t y l a t r d hydrox>.anisole. Therefore. this study was initiated for the purpose of developing a rrsgent for the determination of hutj.latet1 hj-tlrosy:inisolr w1iic.h does not exhibit these disadvantages .
Gihlis (3) found that 2,B-dicl~loroquinonec~hlorimide is a senpirive re:igeiit for phenol antl that the iwulting blue indophenol is ?table. Prt,liniinary experiments indicated that this compound ivas highly specific for butylated hydroxyanisole among the antioxidants currentlj- added to lard or shortening. Tlierd‘orr, the reagent \vas studicd more intensively with a vieiv to ad:iptinp it for thc quantitative tlcsterniination of Iiutyl:ttd lij-drosymisole. EXPERIMERTAL
Previous work in this laboratory ( 7 ) estalilishrd that 727, ethyl alcohol ( b y volume) was a satisfactory solvent for the ex-
V O L U M E 23, NO. 8, A U G U S T 1 9 5 1
The antioxidant butylated hydroxyanisole is extensively used in combination with propyl gallate or nordihydroguaiaretic acid for the stabilization of lard or shortening. Because butylated hydroxyanisole is usually present in the greater amount, a rapid and accurate analytical procedure would be of talue in controlling the addition of antioxidant mixtures containing butylated hydroxyanisole to lard and shortening. A rapid colorimetric procedure has
traction of butylated hydroxyanisole from petroleum ether solutions of lard or shortening, and this concentration of ethyl alcohol was adopkd as the solvent for all subsequent analyses. Effect of pH. Gibhs (5)has indicated that the reaction bet ween phenol and 2,6-dic~hloroquinonechlorimide is sensitive to pH. The effrct of p H over the range of 6.8 to 10.0 on the rate of color formation bet,ween butylated hydroxyanisole and 2,6dichloroquinonechlorimide as invrstigated, wing a series of borate buffers ( I ) . In every case 2 ml. of O.Olyo2,6-dichloroquinonechlorimide in absolute eth>-1 alcohol and 2 ml. of the appropriate aqueous buffer solution were added to the butylated hydroxyanisole in 12 ml. of 72% ethyl alcohol. After 15 minutes thr absorbancy was measured a t 610 my in a Beckman B spectrophotometer relative to the appropriate blank, with thc results shonn in Figure 1.
E' 0.2
-
0.1
-
0
ur
1121
been developed for determination of butylated hydroxyanisole alone and in combination with propyl gallate or nordihydroguaiaretic acid. Butylated hydroxyanisole has been determined over the range of 0.01 to 0.02o/c with a n average standard deviation for a single determination of 1.1% of the amount present. Recoveries are of the order of 97 to 99%. I t is necessary to have the antioxidant preparation added to the lardjor shortening'for'use as a standard.
chlorimide-borax reagent employing the foregoing conditions is shown in Figure 2. Specificity. il number of antioxidants Tvere made to react Ivith the 2,6-dichloroquinonechlorimide-borax reagent and after 15 minutes the wave length of maximum absorbancy was deteimined with a Beckman B spectrophotometer. The absorbancies w r e nicasured a t 620 mp with an Evelyn photoelectric colorimeter (Table I).
Table I. Wave Length of Maximum Absorbancy and Absorbancy Measured a t 620 mp for a Number of ..intioxidants Antioxidant 3-BRA Commercial B H A No. 1" ! i o . 2a 2-BH.4 Hydronuinone G u m piaiacurn SDGA Propyl gallate d.a-Tocopherol a
Wave Length of Max. Absorbancy, in@ 610
Absorbancy/r a t 620 nw 0.0139
610
0.0127 0.0092 0.0027 0,0020 0,0014 0.0003 0.0002 0.0000
618 655 460
635 430 435 5.0 color produced
Mixtures of 2-BHA and 3-BHA.
> z 0 m U rr u 0 )
4
0.4 E 0 (D
0.0
7
6
8
IO
P H OF R E A C T I O N
t 6 = I 0 I
m
Figure 1. Effect of pH on 2,6-Dichloroquinonechlorimide-Butylated Hydroxyanisole Reaction
These data indicate that the maximum color formation betwern butylated hydroxyanisole and 2,6-dichloroquinonechlorimide occurs at pH 9.4. A dilute aqueous borax solution (;\'anB,O,lOHnO) was used to buffer the reaction niixturr a t this pH in all subsequent analyses. Effect of Time on Stability of Color. Exp,tlriment.; shoved that maximum color formation and stability were obtained by using 12 nil. of 72% ethyl alcohol containing the butylated hydroxy' 2,6-dichloroquinonec~hlorimide in anisole plus 2 ml. of 0.01% absolute ethyl alcohol and 2 ml. of 2% aqueous ljoras ljuffer solution, Undrr thew conditions tho resulting blue indophenol color rvaclhed maximum intensity in 1,i minutrs and was stable for over 5 hours. The absorbanry was measurrd against a blank Lvith an Evelyn photoelectric. colorimeter fitted n-ith a 620 mp filtrr. The effect of time on the absorbancy produced by butylated hydroxyanisole on reaction with the 2.6-dichloroquinone-
=I 0.2
0.0 0
IO
20
6'30 TIME
I10 IN
270
390
MINUTES
Figure 2. Effect of Time on ..ibsorbancy Developed between Butylated Hydroxyanisole and 2,6-Dichloroquinonechlorimide-Borax Reagent
The data in Table I show that onlj- gum guaiacum exhibits a maximum absorption a t a wave length close to that given by butylated hydroxyanisole. Hydroquinone, nordihydroguaiaretic acid, and propyl gallate show maximum absorptions between 430 and 460 mp. However, the latter antioxidants can interfere
1122
ANALYTICAL CHEMISTRY
Table 11. Effect of Various Proportions of Propyl Gallate or Nordihydroguaiaretic Acid on Determination of Butylated Hydroxyanisole Absorbancy of Commercial BHA a t 620 mp. % Antioxidants Present so. 1 No. 2 BHA(10-50 microgram range) 100 0 100 0 BHA 30% propyl gallatea 102 9 104 3 BHA 50y0 propyl gallate 103 3 105 5 BHA 2 5 7 NDG4 104 1 106 2 BHA X D G ~ 105 3 108 0 4 Propyl gallate and NDGA expressed a3 % of BHA present.
+ + ++ 506
in the determination of butylated hydroxyanisole, because they produce a slight absorption a t 620 mp. Commercial butylated hydroxyanisole No. 2 produces less absorbancy per microgram than does S o . 1because the former contains a smaller proportion isomer. of the 3-tert-butyl-4-hydroxyanisole Effect of Propyl Gallate or Nordihydroguaiaretic Acid on Determination of Butylated Hydroxyanisole. The American Meat Institute Foundation has proposed an antioxidant mixture known as AMIF-72 ( 5 ) , which contains 20y0 of butylated hydroxyanisole, 670 of propyl gallate, and 4% of citric acid in propylene glycol. This formula is widely used in commercial antioxidant preparations. From the data in Table I it appears that propyl gallate equal to 30% of the butylated hydroxyanisole present (as in the AMIF-72 type preparations) would produce only a relatively small error in the determination of butylated hydroxyanisole with the 2,6-dichloroquinonechlorimide-borax reagent. The effect of various proportions of propyl gallate or nordihydroguaiaretic acid on the determination of butylated hydroxyanisole as indicated by the absorbancy a t 620 mp is shown in Table 11. The data in Table I1 show that the addition of propyl gallate equal t o 30% of the butylated hydroxyanisole results in an increase of 2.9 to 4.3% in the absorbancy measured a t 620 mp. The addition of propyl gallate equal to 50% of the butylated hydroxyanisole results in a further small increase. Similarly, the presence of nordihydroguaiaretic acid in mixtures with butylated hydroxyanisole produces a relatively small increase in absorbancy a t 620 mp as compared to butylated hydroxyanisole alone. 4 s propyl gallate is frequently added to commercial butylated hydroxyanisole preparations, its presence will result in a characteristically small increase in the absorbancy measured a t 620 mp, However, if the same butylated hydroxyanisole preparation containing propyl gallate or nordihydroguaiaretic acid is used in the construction of the calibration curve, no error will result from this source. RE4GEYTS
2,6-Dichloroquinonechlorimide, 0.017, solution in absolute ethyl alcohol. This reagent must be freshly prepared for optimum results. Borax Buffer, 2.07, aqueous solution of SaaBaOT.lOH?O. Petroleum Ether, Skellysolve H . Alcohol, 72% ethyl alcohol by volume. PROCEDURE
Place 10 grams of the fat in a 500-nil. separatory flask and dissolve in 50 ml. of petroleum ether (Skellysolve H). Extract the petroleum ether solution of the fat by shaking the contents of the flask with thre- separate 25-ml. aliquots of 72% ethyl alcohol for 3 minutes per extraction. Make a fourth extraction, using 60 ml. of 72y0 ethyl alcohol and shaking for 1 minute. Combine the four extracts, dilute to a suitable volume (150 to 300 ml.) with 72% ethyl alcohol, and filter through two Whatman No. 54 filter papers. The clear alcoholic estract contains the butylated hydroxyanisole plus propyl gallate or nordihydroguaiaretic acid. Place three suitable aliquots (1 to 12 nil.) of the extract in separate IS-mm. colorimeter tubes and dilute to 12 ml. with 72% ethyl alcohol. ildd t o each tube 2 ml. of freshly prepared 0.01% 2,G-dichloroquinonechlorimidereagent. Mix the contents oi the tubes, add 2 ml. of 2 % aqueous borax solution, and mix the contents again. Prepare a blank containing 12 ml. of 72% ethyl nlcohol and the reagents. After 15 minutes measure the ab-
sorbancy relative to the blank in an Evelyn photoelectric colorimeter fitted with a 620 mp filter. Calculate the amount of butylated hydroxyanisole by reference to a calibration curve prepared over the range of 10 to 50 micrograms of butylated hydroxyanisole per tube, using the same butylated hydroxyanisole preparation that was added to the fat. I t is necessary to prepare a new calibration curve for each type or batch of antioxidant preparation used. REPRODUCIBILITY
Three samples of shortenin %ere prepared containing 0.0200, 0.0150, and 0.0100% of butyyated hydroxyanisole, respectively. I n all cases the butylated hydroxyanisole was added as a commercial antioxidant preparation containing 20% butylated hydroxyanisole, 6% propyl gallate, and 4% citric acid in propylene glycol. Each of the shortening samples was analyzed four times for butylated hydroxyanisole, employing the foregoing procedure. The butylated hydroxyanisole content of the samples was calculated by means of calibration curves prepared using the same antioxidant preparation added to the shortening. T h e recovery of butylated hydroxyanisole and the reproducibility of the analytical data are shown in Table 111. The data in Table 111 indicate that recoveries of butylated hydroxyanisole of the order of 97 to 99% can be obtained. The apparent loss of 1 to 3% of the butylated hydrosyanisole added might be attributed in part t o the destruction of some of the butylated hydroxyanisole by the small amount of fat peroxides present. The estimated stand?rd deviation for a single determination is of the order of & l % of the butylated hydroxyanisole present in the sample. Table 111. Recovery of Butylated Hydroxyanisole Added to Shortening and Reproducibility of Results BHA Added,
%
0.0200 0,0150
0.0100
Av. BHA Found,
%
Estimated Standard Deviation for Single Estimation
0.0198 0.0146 0.0097
0.0002 0.0002 0.0001
DISCUSSIOX
Lundberg ( 6 ) employed a 2,6-dichloroquinonechlorimide reagent in the presence of a borax buffer for the determination of nordihydroguaiaretic acid. Lundberg's reaction mixture is predominantly aqueous and the borax buffer is added to the nordihydroguaiaretic acid solution before the 2,6-dichloroquinonechlorimide reagent. This procedure results in the formation of a red color with a maximum absorption a t 545 mp. However, if the order of adding Lundberg's reagents is reversed, no red color is formed. Using the procedure recommended in this paper, no red color is formed upon the addition of the 2,6-dichloroquinonechlorimide reagent to an alcoholic solution of nordihydroguaiaretic acid followed by the addition of the boras buffer. Apparently, the order of addition of the reagents is responsible for the different results obtained with these two procedures. The absorbancy produced with the 2,6-dichloroquinonechlorimide-borax reagent is 5.2 times as great with 3-tert-butyl-4-h>,droxyanisole as wit,h an equal weight of 2-tert-butyl-4-hydroxyanisole. As the proportion of 3-tert-butyl-4-hydroxyanisole to 2-tert-butyl-4-hydroxyanisoleis variable in commercial butylated h>-droxyanisole preparations, the 2,6-dichloroquinonechlorimideborax reagent cannot replace the ferric chloride plus 1,l'-bipyridine reagent ( 7 ) for the analysis of unknown butylated hydrosyanisole preparations. I n order to employ the 2,6-dichloroquinonechlorimide-borax reagent in the determination of butylated h>-drosyanisole,it is essential to use the same antioxidant preparation that is present in the lard or shortening to obtain the calibration curve. The 2,6-dichloroquinonechlori~nide-borasreagent has been found to be superior to the ferric chloride plus 1,l'-bipyridine reagent for the determination of butylated hydroxyanisole : I t is unaffected by strong light. 3Iasimum color intensity is obtained in 15 minutes.
V O L U M E 2 3 , NO. 8, A U G U S T 1 9 5 1 The color is stable for over 8 hours. This reagent is relatively specific for butylated hydrosyanisole among the antiosidants current,ly added to lard or shortening. Estraneous reducing agents are unlikely to produce colored complexes with this reagent. Consequently, rigid purification of the petroleum ether and ethyl alcohol used as solvents for the estraction and analysis of hutylated bydrosyanisole is not necessary, as it is when the ferric chloride plus 1,l'-bipyridine reagent is used. This reagent permits the determination of butylated hydrosyanisole in the presence of propyl gallate or nordihydroguaiaretic :]rid, provided the original antiosidant prepsration can be used to conitruct a calibration cum?. ACK3OWLEDGlIEYT
The xuthors wish t o express tht.ir thanks to C. IT. Dunnett for st:ctistical analysis of the results.
1123 LITERATURE C I T E D
Clark, W. M., "Determination of Hydrogen Ions," Baltimore, Williams & Wilkins Co., 1928. Emmerie, A, and Engel, C., Rec. traa. chim., 57, 1351 (1938). Gibbs. H. D., J . B i d . Chem., 72,649 (1927). Kraybill, H. R., Dugan. L. R., Beadle, B. W.,Vihrans, F. C.. Swarts. T-eK'., and Reeahek,". J., J . Am. Oil Chemists SOC.,26, 449 (1949). Kraybill, H. R., Dugan, L. R.. Vibrans, F. C., Ywartz, VeN., and Bondi. V., -4m. Meat Inst. Foundation, Bull. 4 (December 1948). (6) Lundberg. W.O., private rommunication. (7) Mahon, J. H., and Chapman, R. A., A x ~ L . CHEM.,23, 1116 (19513. R L C F I V E Octoher U 6 , 1950.
Determination of Titanium in Rocks and Minerals Mercury Cathode Polarographic Method R. P. GRAHAM AND J. A. MAXWELL' Hamilton College, McMaster University, Hamilton, Ontario, Canada The procedures described were developed to provide a method for the determination of titanium in rocks and minerals that is free of some of the disadvantages of the conventional colorimetric method. -4fter electrolysis of a solution of the sample in a mercury cathode cell to remove iron and other interfering ions, titanium is determined polarographically. The supporting electrolyte, 1.0 M in tartaric acid and 0.5 Min sulfuric acid, permits the recording of a wellformed polarographic Wave, the height of which is
T""
KIUM is the ninth most abundant element of the earth's crust, in which it occurs to the extent of-approsimately 0.57,. I t s determination in any rock or mineral ia therefore a necessity if the analysis is to be considered complete. Titanium is usually determined in rocks and minerals by making use of the yellow color that is developed by the addition of hydrogen peroxide to a solution of a titanium(1V) salt (16). This method, however, is subject to interferences ( 1 4 ) from elements t,hat form colored solutions (such as iron, chromium, and nickel), elements that form colored compounds with hydrogen peroxide (such as vanadium, molybdenum, and cerium), and ions that bleach the color of the complex (such as fluoride and large concentrations of alkali salts or phosphate). rill these interferences can be overcome by simulating conditions in the standard, but this is a very troublesome procedure that involves detailed knowledge of the nature of the material being analyzed. Zeltzer ( 1 7 ) suggested a polarographic method for the determination of titanium in titaniferous minerals by fusing thc pondered sample with potassium hydrogen sulfate, dissolving the melt in dilute sulfuric acid, and then polarographing the resultant solution. He reported good waves in this medium, but this could not be substantiated by hdams ( 1 )nor Potts ( 1 2 ) . I n a summary (1941) of polarographic data on titanium, KolthoS and Iingane (4)stated that acid solutions of tartaric or citric arid are preferable as a supporting electrolyte. I n such solutions thr rnthodic diffusion rurrent is directly proportional to the concc,ntrntion of titaniuni(IT-) ions. .\dams ( 1 ) . in his work on the determination of titanium in 1
Present address. Department of Geology a n d Mineralogy. VniT-ersity of llino
Jlinnesotu, Llinneapoiis.
directly proportional to the concentration of titanium in the solution. Of the foreign elements not removed in the mercury cathqde cell, only uranium interferes with the subsequent polarographic procedure. The method is of good precision and yields values in close agreement w-ith those given by the colorimetric method using hydrogen peroxide. Although not as sensitive as the colorimetric method, i t is less subject t o errors arising from foreign ions and is in certain respects more convenient.
clays and clay products, used as supporting electrolvte a 0.5 JI solution of sulfuric acid saturated with sodium oyalate and containing Sm0 urea as a maximum suppressor. He reported that the concentrations of both titanium(1V) and iron(II1) affect the position of the half-wave potential of the titanium, but Lingane and Vandenbosch (8) disagree and show that the half-wave potential remains constant. They also state that the urea does not function satisfactorily as a maximum suppressor when the titanium concentration evceeds a certain value. Potts ( 1 2 ) found that satisfactory waves could be obtained in a sulfuric-tartaric acid supporting electrolyte, without a maximum suppressor, and he determined titanium in paint pigments using this medium. The present paper describes a polarographic method for the determination of titanium in rocks and minerals that is less subject to interference than the colorimetric method. A mercury cathode cell is used to remove elements that n-ould cause interference in the polarographic procedure. APPARATUS A h D R E A G E N T S
Apparatus. A Heyrovsk? polarograph, Model X I (E. H. Sargent and CO.'~, was used throughout this work. The capillary was of marine barometer tubing supplied by E. H. Sargrnt and Co., and vias cleaned, when necessary, by immersing it in hot nitric acid. The rn and t values of the capillary in the supporting electrolyte were determined a t 28.0" =t0.2" C. by the method of Lingane and Kolthoff (6). At an applied potential of -0.30 volt L'C. the saturated calomel electrode, the drop time, t , was 5.19 seconds, the rate of flow of mercury, ni, was 1.34 nig. per second, [The variation of m2'3tllB and r t z 2 I 3 tils was 1 . 5 9 m g 2 3sec.-1 with applied potential, over the range 0.0 to -1.1 volts, waq found to be in very close agreement with the relative values given
