pH of Wines

Values obtained for the pH of wines by means of the glass and quin- hydrone electrodes sometimes agree, but often differ by more than. 0.1 pH unit. Th...
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The

pH

of Wines

Examination of Glass and Quinhydrone Electrode Values J. C. M. FORNACHON, Waite Agricultural Research Institute, University of Adelaide, Adelaide, South Australia bulb blown of Corning 01.5 special electrode glass. This was used with an internal quinhydrone-0.1 S h-drochloric acid halfcell and a saturated calomel half-cell as a reference half-cell. Between determinations the outside of the bulb of the glass electrode was rinsed with distilled water, dried lightly with filter paper, and then rinsed with a portion of the next test solution. When not in use, the glass electrode was kept filled with, and immersed in, distilled water. Leads from the electrodes to the potent,iometer were of insulated copper vire, kept as short as possible, and t,he electrode clamps were supported in blocks of polystyrene. Quinhydrone Electrode System. The electrodes were made of pieces of 10 X 7 mm. platinum foil, each Kelded to a length of platinum wire and sealed into a glass tube. Electrical connections were made by means of binding screws at the top of the wire. The electrodes were heated to redness in an alcohol flame for a few seconds before use and at frequent intervals during each batch of determinations. Quinhydrone freshly prepared from hydroquinone and ferric ammonium alum according to the method of Biilmann, described by Britton (4), was washed four times with iced distilled water and dried betvieen filter paper at room temperature. Since the presence of traces of iron in quinhydrone prepared by Biilmann’s method may be a source of error, a batch of quinhydrone prepared by mixing alcoholic solutions of quinone and hydroquinone according to the method of Valeur (described by Britton, d), was also used for comparison. This latter product was in a coarser state of division and Kas rather slower in giving stable potentials than that prepared by Biilmann’s method, but otherwise no significant differences were noticed between the results obtained with the tn-o preparations. Bubbling HydrogeTh Electrode System. The platinum electrodes were of similar construction to those described above. They 1) aqua regia and lightly were cleaned by heating in dilute (1 platinized, so that only thin brown coatings of platinum black were obtained. Before each determination, these electrodes were connected to the negative pole of a 4-volt storage battery, electrolyzed for half a minut>ein 0.1 N sulfuric acid, then carefully washed with distilled water before being placed in the test solution. All determinations were made in duplicate, using two electrodes and electrode vessels, and when discrepancies occurred, the electrodes were cleaned and replatinized. The electrode vessels were a modification ( 2 ) of the bubbling hydrogen electrode vessel described by Best ( I ) . REFERENCE HALF-CELL. A saturat’ed calomel half-cell was wed in conjunction with each of the above electrode systems. LIQCID JVXCTIOSS. Liquid junctions b e b e e n the calomel cell and the test solutions were formed by means of a side tube R-hich was kept filled with a saturated solution of potassium chloride from a reservoir, and which was closed with a groundglass cap. Before each determination the lower end of the tube was washed with distilled m t e r and dried with filter paper. The junction was then renexT-ed by loosening the cap momentarily to allow a few drops of the potassium chloride solution to escape and the outside of the cap was lightly wiped with filter paper. PomNTromTER. pH measurements were made with a vacuum tube potentiometer calibrated to give readings directly in pH units, and connected to a 12-volt storage battery as a source of current. The calibration of the instrument was checked by using it with a quinhydrone electrode, to measure the pH values of the buffers listed below, and comparing these values with t h se obtained for the same buffers and with the same electrode,%y means of a Cambridge portable potentiometer. The values obtained with the two instruments did not differ by more than 0.02 pH unit in any of these solutions. BUFFERSOLUTIONS.The reagents used in the preparation of buffer solutions were all of analytical reagent grade. For standardizing and checking the electrode systems t’he following solutions were used:

Values obtained for the. p H of wines by means of the glass and quinhydrone electrodes sometimes agree, but often differ b y more than 0.1 p H unit. The effects of several constituents of wine on these electrode systems have been examined and it is concluded that, whereas the glass electrode values are essentially correct, the quinhydrone electrode, when used in wines, is subject to at least two sources of error. Alcohol causes the quinhydrone electrode to register low values, while reducing substances, such as sulfites and tannin, lead to high values. The correct and near-correct values obtained with the quinhydrone electrode in some wines are due to a compensation of such errors. Neither the hydro-quinhydrone nor the quino-quinhydrone electrodes give more reliable results in wines than the regular quinhydrone electrode.

T

H E significance of pH values in relation to the physical, chemical, and biological changes which occur in wine has been pointed out by many investigators, notably Ventre ( I T ) , Genevois and RibBreau-Gayon ( I l ) , FMmond (S),and RibkreauGayon (1.6, 15). The present writer (10) has indicated the importance of pH in relation to bacterial spoilage of wines. Of the various methods available for determining the pH value of wine, the quinhydrone electrode system has been one of the most widely used. Chief among the advantages claimed for this system are that it’is easily and quickly assembled, simple to operate, reaches a stable potential rapidly, and can be used in wines which contain small to moderate amounts of sulfites. Because of these features it has been widely recommended for determining the pH values of wines (3, 6, 11, 16). JITithinrecent years, however, improvements in the design and construction of glass electrodes and vacuum tube potentiometers have resulted in the introduction of the glass electrode system into industrial laboratories and an increasing number of glass electrode pH meters are now being used in wineries. From time to time, discrepancies have been noticed between the results obtained by means of the glass electrode and the quinhydrone electrode for the pH values of wines. Thus RibBreauGayon (16) found that the pH values of wines determined by means of the glass electrode were slightly (up to 0.06) higher than those registered by the quinhydrone electrode. Using tartrate buffers containing different amounts of alcohol, he obtained evidence that the deviation was due to alcohol, but did not indicate which electrode system gave the more correct values. Hooper (12) recorded differences between glass electrode and quinhydrone electrode values for several ilustralian fortified wines, which varied from 0.05 to 0.18 pH unit. Liebmann and Rosenblatt (IS) determined the pH values of different whiskies by means of the glass and the quinhydrone electrodes and found the quinhydrone electrode values lower than the glass electrode values by about 0.37 pH unit. They calculated, from experimental data obtained by Dole (8), that the theoretical deviation of the glass electrode values in 45y0alcohol was only about 0.03 pH unit and they therefore concluded that the glass electrode values for whisky were essentially correct and the quinhydrone electrode values in error by about -0.37 pH unit. In view of the foregoing, it seemed desirable to make a more detailed examination of the values obtained with the glass and quinhydrone electrode systems for the pH of wines.

+

0.05 M potassium hydrogen phthalate

Sorensen’s phosphate buffer McIlvaine’s citrate-phosphate buffer

APPARATUS AND REAGENTS

ELECTRODE SYSTEMS.Glass Electrode System. The glass electrode was a Kerridge pattern recessed bulb type, having the

pH 4.01 (3.97) pH 6.26 (6.24) pH 4.63 (4.6)

The pH values in parentheses are those given by Clark (6) for these solutions, but in these investigations the value of 4.01 for

790

ANALYTICAL EDITION

December, 1946

Table 1.

Type Sweet red

p H Values

No. 1 2 3

Alcohol % by Volume 20 20 20 20 20 20 20 20 -.

Sweet white (spoiled) Muscat Dry white Dry white (carrying sherry flor)

Dry white (sherry) Dry white

Drh red

Whlte grape lulce (pasteunzed)

11 12 13

19 19 19 20 14

14 15 16 17 18 19 20 21 22 23 24

17.5 14.5 15 13 5 14.0 11.5 10.0 11.5 11.5

10

25 26

13 15

..

of Wines es b)uin- Deviation Glass hydrone of quinelechydrone electrode trode from glass -0.24 3.74 3.50 -0.20 3.52 3.72 -0.15 3.71 3.56 -0.16 3.84 3.69 -0.14 3.52 3.66 -0.16 3.45 3.29 -0.13 3.69 3.56 -0.11 3.73 3.62 -0.12 3.64 3.52 -0.12 3.64 3.52 -0.13 4.29 4.16 -0.13 3.94 3.81 -0.03 3.21 3.18 -0.0'2

3.32 3.31 3.40 3.32 3.59 3.73 3.80 2.95 3.22 3.48 3.53

3.30 3.24 3.30 3.26 3.56 3.70 3.77 2.93 3.22 3.58 3.65

-0.07 -0.10 -0.06 -0.03 -0.03 -0.03 -0.02 0.00 fO.10

3.33 3 42

3.34 3.41

+o 01 -0.01

+0.12

the pH oi 0.05 M phthalate was adopted as the primary standard in accordance with the recommendation of Dole ( 7 ) . The pH values of the Sorensen and McIlvaine buffers were then found to be 6.26 and 4.63, res ectively, by means of the glass electrode. The effect of ethyf alcohol on pH determinations was studied with phthalate, tartrate, and citrate buffers, the last two being used instead of the phosphate buffers previously mentioned, as it was considered that they would provide conditions more comparable with those in wine. These solutions were made up in the following concentrations: 0 . 1 M potassium hydrogen phthalate 0 1 M tartrate solution. 15.0 grams of tartaric acid and 80 nll.

of 1.0 N sodium hydroxide per liter 0 066 M citrate solution. 14.0 grams of citric acid and 68 ml. of 1.0 N sodium hydroxide per liter

Hundred-milliliter quantities of these solutions were diluted with 100-ml. quantities of appropriate alcohol-water mixtures before use, so that the h a 1 concentrations were 0.05 M phthalate, 0.05 M tartrate, and 0.033 M citrate and the pH values of the diluted aqueous solutions were found by means of the glass electrode to be 4.01, 3.33, and 3.87, respectively. EXPERIMENTAL

All detrrminations were carried out a t room temperature, which was 15' * 2" C. during the course of the investigations, but the variation nrrer exceeded 0.5" C. during any one batch of determinations.

ELECTRODE SYSPOTEXTIOYETER. Before each batch of

791

indication of the reproducibility of results. The standard deviations calculated from these results did not exceed i 0 . 0 2 for either the glass or the quinhydrone electrode. The standard deviations of the values obtained for wines were not determined statistically, but all determinations were made in duplicate and the mean values taken. When, as rarely happened, the values obtained for duplicate samples differed by more than 0.02, the determination u-as repeated with fresh samples. This procedure could not be followed with the quinhydrone values recorded in Table IV, however, for in those samples which showed appreciable drift in potential, agreement between duplicates was usually unsatisfactory. Except in this special casc, hoTvever, it is considtxred that under the experimental ponditions diff(1rences twwding +0.03 pH unit are significant. DETERMISATION O F p H S'ALUES O F \TISICS BY ~\IE.%.USOB' GLASS .IXD QUINHYDRONEELECTRODES. The pH values of several wines as determined by the glass and the quinhydrone electrodes are shown in Table I. As can be seen, the glass electrode values are nearly all higher than the quinhydrone electrode valucs, but the differences between them vary considerably from one wine to another. EFFECTOF ETHYL ALCOHOLON GLASSAND QUINHYDRONE ELECTRODES. I n view of the results obtained by RibBreauGayon (16) and by Liebmann and Rosenblatt (IS) concerning the effects of ethyl alcohol, it seemed desirable to determine the extent to which differences such as those recorded in Table I were due to the alcohol present in the wine. Accordingly, the pH valugs of phthalate, tartrate, and citrate buffers containing different concentrations of ethyl alcohol were determined by means of the glass and the quinhydrone electrodes (Table 11). Duboux and Tsamados (9) have shown that the dissociation of organic acids is depressed by the presence of ethyl alcohol and so, as would be expected, the pH values found for the buffer solutions in Table I1 increased with increasing alcohol content. Although it seemed likely from the data of Liebmann and Rosenblatt (13) that the glass electrode values would be correct, it was considered desirable to check these values with the bubbling hydrogen elwtrode as a standard. The hydrogen electrode values for thc tartrate and citrate solutions are shown in column 3 of Table 11, and as can be seen, they agree well with the glass electrode values. A comparison of the results presented in Tables I and I1 indicates that the deviations of the quinhydrone from the glass rlectrode values in wines are often smaller than would be expected from a consideration of the amounts of alcohol present. I t seems likely, therefore, that in some wines the error in quinhydrone electrode values due to alcohol is in part offset by some other factors which cause an apparent increase in pH values. In order to obtain more information on this point several wines were treated as follows: 200 ml. of wine were evaporated to about 40 ml. under reduced pressure a t 60" C. to remove alcohol. Half of each de-

STASDA4RDIZlSG A N D C H E C K I N G

TEMS ASD

determinations with the glass or auinhvdrone elec" trodes, the potentiometer was adjusted to give a rcading of 4.01 for the pH of the 0.05 11 phthalate buffer. The electrode system and potentiometer were then further checked against the phosphate and the citratephosphate bufferg before other measurements n-ere made. The check against these three buffers was rclpeated a t the end of each batch of determinations and if the pH values recorded in the second check differed from those first obtained by mow t,han 10.02, the whole batch of detei minations was repeated Ivit,h fresh samples. With electrode systems other than the glass and quinhydrone, the potentiomeker was standardized as indicatcd in Tables I1 and V. The pH values obtained for the phosphate and citrate-phosphate buffers on different days provide an

Table II. p H Values of Buffers Containing Ethyl Alcohol

Butrer

.4lcohol Content by Volume

o,05

Hydrogen electrode

Glass electrode

p H Values Deviation of glass Quinfrom hydrone hydrogen electrode

Deviation of quinhydrone from glass

4.01a 4.010 .... 1.21 4.14 -0.07 4.44 4.30 -0.14 Tartrate 3.33O 3.33'~ ,... 3.33" 3.40 3.40 0.00 3.36 -0.04 3.47 3.47 0.00 3.40 -0.07 15 3.55 3.54 -0.01 3.43 -0.11 20 3.64 3.63 -0.01 3.48 -0.15 25 3.75 3.73 -0.02 3.52 -0.21 Citrate None 3.87a 3.87" .... 3.Sia .... 5 3.94 3.94 0.00 3.91 -0.03 10 4.01 4.01 0.00 3.95 -0.06 15 4.08 4.08 0.00 3.99 -0.09 20 4.16 4.15 -0.01 4.03 -0.12 a I n each case potentiometer and electrode system was standardized t o give correct value for aqueous buffer solution. phthalate

h'one 10 20 None 5 10

... ... ...

I...

INDUSTRIAL AND ENGINEERING CHEMISTRY

792 Table

Vol. 18, No. 12

THE HYDRO-QUINHYDRONE AND QUINO-QUINHYELECTRODES. According to Clark (6) the

111.

EHect of Alcohol on p H Values of Wines as Measured b y Glass and Quinhydrone Electrodes Wine No. 7 9 11 12 13 14

DRONE

effects of side reactions in dist,urbing the ratio of quinone to hydroquinone in the quinhydrone elecOriginal wines trode system can sometimes be eliminated by saturatAlcohol content, volume 5; 90 20 19 20 14 13 pH by glass electrode 3.69 3.64 4.29 3.94 3.21 3.32 ing t,he test solution n-ith quinone and quinhydrone 3.56 3.52 4.16 3.81 3.18 3.30 pH b y quinhydrone Quinhydrone deviation - 0 . 1 3 -0.12 -0.13 -0.13 -0.03 -0.02 or with hydroquinone and quinhydrone. It was Dealcoholized wines 3,62 3,07 3 , 17 thought that such systems might give better results pH by glass electrode 3,37 3,36 4,09 in wines than the ordinary quinhydrone electrode pH Quinhydrone by quinhydrone deviation Reconstituted wines system. Values obtained in wines, however, were pH by glass electrode not found more reliable than those obtained with pH b y quinhydrone Quinhydrone deviation -0.10 -0.09 -0.18 -0.13 -0.02 -0.03 the regular quinhydrone system. The figures presented in Table V show the results obtained in the presence of varying amounts of alcohol in the tartrate buffer with the glass, alcoholized wine was then made up to 100 ml. with distilled water, quinhydrone, quino-quinhydrone, and hydro-quinhydrone elecwhile the other half was made up to 100 ml. with distilled water trodes. The results obtained with the glass, quinhydrone, and ethyl alcohol, so that the final alcohol content of the treated and quino-quinhydrone electrodes in several wines are also wine was the same as that of the original wine. The pH values shown. I n order to simplify comparisons, the results obof the treated wines were determined by the glass and the quintained with the quinhydrone, quino-quinhydrone, and hydrohydrone electrodes. These values together with those of the quinhydrone electrodes are shown as deviations from the glass original wines and the quinhydrone electrode deviation in each electrode values. case are shown in Table 111. These results show that:

+:::: +::::-:;::+:::; +::Ai +:;E: ;:E; i,:i 8:;; :;;: ;:;:

The pH values and the quinhydrone electrode deviations for the reconstituted wines agree reasonably well with those found for the original wines except for wine 11. This wine had undergone bacterial spoilage and had a high volatile acidity. The loss of a portion of the volatile acid during evaporation probably accounts for the higher pH value of the reconstituted mine. The quinhydrone electrode values of several of the dealcoholized wines are slightly higher than the glass electrode values. This is particularly noticeable in wines 13 and 14, the quinhydrone electrode values of which were only slightly below the glass electrode values before treatment. Removal of the alcohol from these wines thus reveals the presence of factors which cause a positive error in the quinhydrone electrode values, an error which in the untreated wine partially or wholly offsets the negative error caused by alcohol.

It is well known that the quinhydrone electrode is subject to errors in the presence of oxidizing or reducing substances which are sufficiently active to change the ratio of quinone to hydroquinone in solution. It seemed likely, therefore, that the high quinhydrone electrode values obtained in some of the dealcoholized wines were due to reduction of quinone t o hydroquinone by some constituents of the wines. EFFECTO F TANKIN, SULFITE, AND ACETALDEHYDE ON GLASS AND QUINHYDRONE ELECTRODES.I n order to study the influence on the quinhydrone electrode of some of the reducing substances which occur in wine, tannin, sulfite, and acetaldehyde were added to the aqueous tartrate solution and t o a dry white wine in amounts which are comparable with those occurring in wines. The tannin used was Merck's analytical reagent tannic acid, the sulfite was added as potassium metabisulfite, and the acetaldehyde was added as a 10% solution of acetaldehyde. The pH values of the treated wines and buffer solutions were determined with the glass and the quinhydrone electrodes and the results are shown in Table IV. Xone of the additions had any significant effect on the glass electrode values, but the tannin and the sulfite affected the quinhydrone electrode values, appreciably both in the tartrate buffer and in the wine, although the effects were less marked in the wine. Moreover, the sulfite caused the quinhydrone electrode potential to drift both in the tartrate buffer and in the wine, while the tannin caused a drift in the tartrate buffer but not in the n-ine. As can be seen from the table, the drift due t o sulfite was different from that due to tannin. The addition of acetaldehyde did not affect the quinhydrone electrode values appreciably either in the tartrate buffer or in the wine.

Table

IV. Effect of Tannin, Sulfite, and Acetaldehyde on pH Values

Solution Tartrate buffer (0% alcohol)

Dry white wine (14,5y0 aloohol)

Additions

Glass electrode

pH Values Quinhydrone Electrode 0.5 5 30 min. min. nun.

None Tannin 1 grdm per liter Tannin 2 prams Der liter KZSPO~lOOp.p.m. KzSzOs200p.p.m. K~S~O1400p.p.m. CHsCHO 200 p.p.m. CHsCHO400p.p.m.

3.33

3 33

3 32

3 35

3 33

3 33

3.32 3.33 3.32 3.32 3.33 3.33

3.36 3.43 3.48 3.73 3,35 3.35

3.46 3.52 3.97

None Tannin 2 grama per liter K&Os 200 p.p.m. K&Os 400 p.p.m. CHaCHO 400 p.p.m.

3.32

3.26

.

3.26

3.32 3.32 3.32 3.32

3.31 3.27 3.51 3.26

3:30 3.57

3.31 3.28 3.36 3.25

3.37

.. ..

..

3.40 3.40 3.46 3.61 3.34 3.34

As can be seen from the table the error due to alcohol was even greater with the hydro-quinhydrone than with the regular quinhydrone system. On the other hand, the quino-quinhydrone system, although giving pH values showing reasonably good agreement with those obtained by means of the glass electrode in buffers containing alcohol, appeared to be greatly affected by those constituents of wine which cause the quinhydrone electrode to give high values. Thus in wines 12 and 16 for which the quinhydrone electrode values were considerably lower than the glass electrode values, the quino-quinhydrone electrode values agreed well with those of the glass electrode. I n wines 13, 14, and 18, for which the quinhydrone electrode values were only slightly lower than the glass electrode values, however, the quinoquinhydrone electrode gave values appreciably higher than those obtained with the glass electrode. DISCUSSION

The pH values of wines as determined by means of the glass electrode are essentially correct, for the glass electrode is not affected by the concentrations 07 ethyl alcohol that occur in wines nor by oxidation-reduction systems. On the other hand the quinhydrone electrode, when used in wines, is subject to at least two sources of error.

ANALYTICAL EDITION

December, 1946 Table

V.

Comparison of p H Values p

.Ilcohol Content Solution Yo by X‘ol. Tartrate Xo?e buffer 7

W i.n..P-

11 12 13 14

0

10 15 20 23

~

Glass Electrode 3.33 3.40 3.47 3.54 3.63 3.73

p H Values with Different Electrodes Expressed as Deviations from Glass __ Electrode Values QuinHydroQuinohydrone quinhydrone quinhydrone 0.00a 0.00a 0,005 -0.04 -0.07 -0.11 -0,l5 - 0 21

-0.10 - 0 12 -0.17 -0.17 -0.19

+0.02 f0.02

+0.03

f0.02 0.00

13 +0 13 -0 03 +O 02 1 0 15 07 +o 16 10 +a 17 05 +a 18 03 +o Potentiometer set to give value of p H 3.33 ior aqueous tartrate

I9 20 14 13 15 17.5 14.5 15

4.29 3.94 3.21 3 32 3.31 3.40 3.32 3.59

,

-0 -0 -0 -0 -0 -0 -0 -0

with each electrode system.

06 02 07 06 02 01 01 20

hufier

.Ilcohol causes the quinhydrone electrode to register pH values which are too low, possibly because of the greater increase in the solubility of quinone in comparison with that of hydroquinone as the solvent is changed from water to alcohol. Within the range of alcohol concentrations studied in buffer solutions, the deviation of the quinhydrone electrode values from those obtained with the glass electrode appears to bear a linear relationship to the alcohol content of the solution. Reducing substances such as tannin, sulfites, and probably the coloring matter of red wines cause the quinhydrorie electrode to register pH values which are too high, presumably because of the reduction of quinone to hydroquinone. Because these two sources of error operate in opposite directions, the quinhydrone electrode values for many wines, particularly those of low to moderate alcohol content, are reasonably good approximations of t8he glass electrode values. I n other wines, however, particularly fortified nines, t,he quinhydrone electrode may give values which are more than 0.15 pH unit too low without showing any appreciable drift in potential. I n some light wines, particularly those with a high t,annin content and those which have been heavily sulfited, the quinhydrone electrode values may actually be too high. I n such wines, however, the drift in potential would probably warn the operator that something was wrong. Liebmann and Rosenblatt ( I S ) concluded that since the only appreciable error to which the quinhydrone electrode was subject in Tyhisky was that due to alcohol, the pH of whisky could be determined equally accurately by either the glass or the quinhydrone electrode, provided that a correction was applied to the quinhydrone electrode values to compensate for the alcohol error. S o such simple correction can be applied to the quinhydrone electrode values for wines, ho\Tever, for in wines the errors are not caused by a single factor and are not constant in amount. For this reason the glass electrode system appeafs to provide the most satisfactory means of determining the pH values of wines accurately. SUMMARY

The pH values of wines and buffer solutions containing alcohol have been determined by the glass, quinhydrone, quino-quinhydrone, and hydro-quinhydrone electrodes and bhe alcoholcontaining buffer solutions have been checked with the bubbling hydrogen electrode. Values obtained by the glass electrode Tvere found t o be essentially correct. The effects of the presence of tannin, sulfites, acetaldehyde, and alcohol at various concentrations on the readings of the glass and the quinhydrone electrodes were examined. None of these influenced the glass electrode significantly, but the presence of alcohol causes the quinhydrone electrode t o register values which are too low, while tannin and sulfites cause errors in the opposite direction. In wines the pH values recorded by the quinhydrone electrode

793

are usually lower than the glass electrode values. It was concluded that both types of errors occur in wines, a positive error being caused by the presence of tannin and sulfites and a negative one by alcohol. I n a number of samples, correct and near-correct values given by the quinhydrone electrode were shown to be due to a compensation of errors. Seither the quino-quinhydrone nor the hydro-quinhydrone electrodes give more reliable results in wines than the regular quinhydrone electrode. LITERATURE CITED

Best, I t . J . , A i r s t r d . J . Ezptl. B i d . , 5, 233-fi (19’25). Best, R . J., private communication, 1945. Bri.mond, E., “Contribution A l’ktude analyt,ique et physicochiinique de l’aciditb des vins”, pp. 63-92, Algiers, Imprimeries la Typo-Litho et Jules Carbonel Rtunies, 1937. Britton, H. T. S..“Hydrogen Ions”, 3rd ed., Vol. 1, p. 73, London, Chapman and Hall, 1942. Clark, W.>I,, “Determination of Hydrogen Ions”. 3rd ed., pp. 210, 214, 407, 405, 485, 486, London, Balliere, Tyndall and Cox, 1928. Dietzel, R., and Kosenbaum, E., f7ntersuch. Lebenam., 53,32130 (1927).

Dole, XI., “Glass Elect,rode”, pp. 297, 298, New York, John Wiley & Sons, 1941. Dole, M.,J . -4m. Chem. Soc., 54, 2120-21, 3095-105 (1932). Duboux, M., and Tsamados, D., Helv. C h i m . A c t a , 7, 855-75 (1924).

Fornaohon, J. C. M., “Bacterial Spoilage of Fortified Wines”, pp. 71-3, Adelaide, Australian Wine Board, 1943. Genevois, L., and RibCreau-Gayon, J., Ann. Brasserie Dist., 31, 273, 289, 305 (1933).

Hooper, F. H., unpublished report to -4ustralian Wine Board, 1939.

Liebmann, A. J., and Rosenblatt. M., J. 24SS0C. Oficial Agr. C h m . , 25, 163-8 (1942).

Ribereau-Gayon, J., Bull. assoc. chim., 55, 601-56 (1938). RibCreau-Gayon, J., Rev. v i t . , 83,133, 155, 171, 181 (1935). I b i d . , 88, 411-15, 434-40 (1938). Ventre, J., Ann. agr. Montpellier, n.s. 18, 89-236 (1925).

Corrections In the article on “Iodometric Method for the Assay of Penicillin Preparations” [Alicino, J. F., IND.ENG.CHEJI.,ASAL. ED., 18, 619 (1946)l errors were made in stating units. Page 619, second paragraph under Assay of Unknowns, the first line should read: 800 to 1000 units per mg. Page 620, Tahle I, the headings of the second and third columns should read: Units per mg. Table 11, the heading over the layt four columns should be: Units per cc. The second line under Example, below the tables, should read: bioassay 800 units per mg. I n the article on “Determination of Cuprous Chloride” [IsD. .1ShJ,. ED., 18, 136 (1946)] under the heiiding Recommendations on page 137, the second sentence under Ceric Ammonium Sulfate should read: Add 250 ml. of n-ater and 1 drop of ferrous-phenanthroline indicator solution and titrate with 0.1 Ar ceric ammonium sulfate solution (made up in 0.5 JI sulfuric acid solution). h G . CHEhf.,

LEWISF. H ~ T C H

An omission was made in the article on “Improved Apparatus for Karl Fischer Watm Determination” [ IXD. EXG.C H E ~ IA ., 4 ~ . 4 ~ . ED., 18, 726 (1946)], in failing to give credit for use of the cathode ray magic eye tube in a titrimeter. The fundamental principles involved in this application were first described by G. F. Smith and V. R. Sullivan in “Electron Beam Sectrometer”, G. Frederick Smith Chemical Co., in 1936. RICHARD KIESELBACH I n the article on “Viscosities of Pure Hydrocarbons” [ IND. ENG.CHmr., A N ~ LED., . 18, 611 (1946)l Rn error occurs in Tahle I. The density of n-octane a t 20” C. is 0.702 gram per cc. J. hI. GEIST