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t h e malic acid was not determined in t h e juice. However, from t h e alkalinity of t h e water-soluble ash a n d t h e fixed acidity of a juice, i t is possible t o calculate t h e total malic acid approximately. T o do this, it must be assumed t h a t t h e fixed acidity in a n apple juice is due principally t o malic acid. Calculated in this manner, t h e two lots of juices originally contained approximately 0 . 4 6 and 0 . 4 j g. combined, and 0 . 3 4 and 0.40 g . free malic acid, respectively, or about 0.83 g. total malic acid, average for t h e two juices. Accordingly, t h e fermented and stored cider contained approximately 0 . 4 9 g. of total malic acid. The final vinegar contained about 0 . 0 4 0 g. of total malic acid. CoNCLUsIONs
F r o m t h e figures given above i t is apparent t h a t : ( I ) During fermentation a large part of t h e malic acid of t h e apple juice is destroyed t o form lactic acid. ( 2 ) During acetification t h e remaining malic acid is almost entirely oxidized. (3) T h e fixed acid in t h e vinegar is chiefly lactic acid. Other points of interest concerning t h e organic acid constituents are t h e presence of acetates in t h e vinegar a n d indications of minute amounts of formic acid, as shown b y Fincke's method. Concerning t h e ash constituents, it is noted t h a t 7 j per cent of t h e ash consists of potassium carbonate. METHODS OF A N A L Y S I S
Wherever possible, t h e methods approved by t h e Association of Official Agricultural Chemists were employed. MALIC ACID was determined by t h e method of C. von der Heide a n d H . Steiner SUCCINIC ACID was determined by t h e method of C. von der Heide a n d H . Steiner.' LACTIC ACID was determined b y t h e method of W. Moeslinger.3 On account of t h e presence of appreciable amounts of acetates i n t h e vinegars, t h e method was modified t o remove t h e acetates. This was accomplished b y t h e addition of 2 cc. of concentrated hydrochloric acid after distilling off t h e volatile acids and evaporating t o a small bulk, adding water and again evaporating, repeating this operation three times before proceeding with t h e determination of t h e lactic acid. ACETATES-The acetates were determined in t h e residue from t h e volatile acid determination. T o t h e residue in t h e distilling flask, 5 cc. of a 20 per cent phosphoric acid solution were added a n d t h e distillation continued until 1 5 cc. of distillate required not more t h a n 3 drops of N / I O alkali for neutralization. T h e acidity of t h e distillate was determined b y titration a n d calculated as acetic acid. Recognition is due t o Mr. E. H. Berry, of t h e Chicago Laboratory, for assistance rendered i n t h e analyses of a number of t h e samples. DEPARTMENT OB AGRICULTURE BUREAUOR CHEMISTRY CHICAGO, ILLINOIS Z. Nahr. Cenussm., 17 (1909). 307. I b i d . , 17 (1909), 291. 8 I b i d . , 4 (1901), 1123, Barium Chloride Method. 1 2
VOI. 9 , NO.
a
THE ACID CONTENT OF FRUITS By W. D BIGELOW A N D P. B. DUNBAR Received April 21, 1917
HISTORICAL
The statements found in t h e literature regarding t h e characteristic acids of t h e various fruits are most diverse. This is probably due in many cases t o t h e inaccuracy of t h e methods used for their identification a n d determination, although it is quite possible t h a t variations in t h e kind of acid present may sometimes occur in t h e same variety of fruit when grown under differing conditions. T h e method which has generally been used for t h e determination of both citric and malic acids in fruit juices depends on t h e precipitation of t h e acids in t h e form of calcium or barium salts and t h e separation of these by means of their differing solubilities in water a n d alcohol. The separations obtained in this way are usually far from sharp and may readily lead t o errors. The burden of evidence in t h e literature seems t o indicate t h a t tartaric acid is not a n ingredient of fruit juices except, of course, of grape juice. W. Kaupitzl* and R. Kayser2 claim t o have found tartaric acid in raspberries. b u t their statements are contradicted by numerous author^.^-^ Kunz* reports citric acid as the acid of raspberries. Kunz and Adam5 state t h a t strawberries, raspberries, elderberries, currants, cranberries a n d peaches contain citric acid b u t no malic nor tartaric. They find t h a t citric acid is t h e predominating acid of huckleberries, gooseberries and apricots b u t s t a t e t h a t malic acid is also present. Tartaric acid was not found by t h e m in these fruits. Krzizan and Plahlg a n d KrzizanG found citric acid only in raspberries. Kayser2 reports citric as t h e principal acid of raspberries, b u t found malic and tartaric acids also. Jorgensen3 found citric as t h e predominating acid of raspberries a n d huckleberries with a small amount of malic, a n d in raspberries traces also of SUCcinic b u t no tartaric: elderberries were found t o contain only citric. Hempel a n d Friedrichlo report t h e examination of four samples of raspberry juice. The first contained much citric acid a n d a not inconsiderable amount of malic. T h e second contained about equal amounts of both acids, while t h e other two contained much malic acid with traces only of citric. Keim'l found both malic and citric acids in cherries. W. Nackenlz found citric a n d malic acids in huckleberries, Mach and Portelel3 in cranberries. According t o Stolle14 cranberries ( Vaccinium o x y c o c c u s ) contained only glyoxylic acid, while Aparin15 reports only citric acid. From t h e work of t h e authors just quoted, Windisch a n d Schmidt,16 from whose paper these references are taken, draw t h e following conclusions: Citric a n d malic acids are t h e characteristic acids of fresh fruit juices, excluding grape juice. Succinic acid is found in small quantities in fresh fruit, especially in t h e unripe condition, b u t tartaric acid does not occur in other fruits t h a n grapes. I n berries, in general, citric acid predominates a n d most berries contain, i n addition, malic acid in very small quantities. Of t h e
* Numbers refer t o bibliography on page 767.
T H E J O U R - V A L O F I i V D C ' S T R I A L A N D E,VCI-VEERISG C H E M I S T R Y
A%., 1917
stone fruits, in cherries and plums malic predominates, if i t is not present exclusively. T h e question of t h e acids of peaches and apricots must be left open, t h e widespread assumption t h a t these fruits contain malic acid as the predominating acid being shaken by t h e researches of Kunz a n d Adam. I n seed fruit, such as t h e apple a n d t h e pear, malic acid predominates or is almost exclusively present except for tannic acid. The total acidity of berries should, therefore, be expressed as anhydrous citric acid a n d of cherries a n d seed fruits as malic acid. I n addition t o t h e statements summarized above by U'indisch and Schmidt, a number of other articles on t h e fruit acids have appeared which are of interest principally because of t h e diversity of t h e statements made. Truchon and Martin-Claude" report tartaric acid in strawberries, black currants, quinces, apricots, unripe cherries a n d in traces also in green gage plums. N o tartaric acid was found in white currants, pears and apples. They report citric acid in apricots a n d in faint traces ih unripe cherries although it was not found in ripe cherries. Chauvin, Joulin a n d Canul* state t h a t t h e acidity of black currants, cherries, quinces, strawberries, raspberries a n d apricots is due t o tartaric acid, while t h a t of red and white currants,
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Reineclaude, Slirabelle and Orleans plums, pears and apples is due t o citric. I \ I ~ t t e l e t ,on ' ~ t h e contrary, reports t h e predominating acid of cherries as malic with no citric and only undeterminable traces of tartaric. He states t h a t strawberries, raspberries and red and black currants contain citric acid, with traces only of tartaric a n d no malic. Warcollier20 found no tartaric acid in either apples or pears. Paris2I reports t h e presence of citric acid and a small amount of malic acid in strawberries. He finds no oxalic, tartaric, salicylic or benzoic acids. Jorgensen3 reports malic as t h e principal acid of cherries. He found no tartaric acid and only found traces of succinic and citric. Roux and Bonis22s t a t e t h a t malic acid predominates in cherries b u t report also citric and tartaric acids. Scurti a n d Plat023 report t h e acidity of oranges as due t o citric and malic acids. The same acids were found b y Borntrager and Parisz4in pomegranates. I n addition t o t h e foregoing, t h e presence in many fruits of salicylic, benzoic and formic acids has been reported, b u t with t h e exception of benzoic acid in cranberries, these have never been reported except in exceedingly small amounts and they have no place in the present consideration. For more convenient refer-
TABLE I-THE ACIDS O F FRUITS: RESULTSREPORTED B Y PREVIOUS WRITERS AUTHOR DATE REFERENCE .4ClDS REPORTED . . . . . Truchon & Martin-Claude 1901 A n n . chim. anal., 6, 85 h'o tartaric Chauvin, Joulin & Canu 1908 Mon. sci., 69, 449 Citric 1911 A n n . fals., 4, 485 No tartaric Martin-Claude 1901 A n n . chim. anal., 6, 85 Tartaric and citric . . . . . . . . . Kunz & Adam 1906 Z . Nahr. Genussm., 12, 670 Citric predominates; some malic, no tartaric Apricot. . . . . . . . . Chauvin, Joulin & Canu 1908 Mon. sci., 69, 449 Tartaric Cherry. . . . . . . . . . 1891 Z . anal. Chem., 30, 401 Malic and citric Cherry.. . . . . . . . . . . . . . . . . . . Truchon 8; Martin-Claude 1901 .4nn. chim. anal., 6, 85 Tartaric and traces of citric in unripe cherries No citric in ripe cherries . . . . . . . Kunz & Adam 1906 Z . Nahr. Genussm., 12, 670 Malic 1907 Z . Xahr. Genussm., 13, 241 Malic; no tartaric; traces only succinic and citric oulin & Canu 1908 Man. sci., 69, 449 Tartaric Cherry., . . . . . . . . . . . . . . . . . .Muttelet 1909 A n n . fals.,2, 383 Malic; no citric; mere traces tartaric . . . Roux & Bonis 1909 A n n . fals., 2, 150 Malic predominates; citric and tartaric present Cranbhrry : (Small American). Scheele . . . . Crell's A n n . , 10 Citric (Vaccinium) (Moosbeere) 1900 Z . Ver. Zuckerind. (N. F.), 31, 609 (Moosbeere). Stolle Glyoxylic 1904 Z . Nahr. Genussm., 8, 254 (Moosbeere). Citric Aparin 1890 Landw. Vers.-Sta.. 30, 69 (Mountain Cranberry). . Mach & Portele Citric and malic ( V . oitis idaea) 1906 Z . hrahr. Genussm., 12, 670 (Preiselbeere) ........ Kunz & Bdam Citric, no malic nor tartaric Currant: Tartaric 1901 Ann. chim. anal.. 6. 8.5 (Black). . . . . . . . . . . . . . . . . Truchon & Martin-Claude - -.__. .1901 A n n . chim. anal.; 6 ; 85 (White),. . . . . . . . . . . . . . . . Truchon & Martin-Claude No tartaric 1906 Z . Nahr. Genussm.. la, 670 Kunz & d d a m Citric; no malic nor tartaric ........................ 1908 Mon. sci., 69, 449 (Black). . . . . . . . . . . . . . . . Chauvin, Joulin & Canu Tartaric 1908 Mon. sci., 69, 449 (Red and White), ...... Chauvin, Joulin & Canu Citric 1909 Ann. fals., 2, 383 (Red and Black). . . . . . . . Muttelet Citric; traces only tartaric; no malic 1906 Z . Nahr. Genussm.. 12. 670 Citric: no malic Elderberrv . . . . . . . . . . . . . . . Kunz & Adam 1906 Z . Nahr. Genussm., la, 670 Gooseberry. ............... Kunz & Adam Citric'predorninates; some malic; no tartaric 1895 Forschungsber hber Lebensmittel, 2, 350 Citric and malic Huckleberry, . . . . . . . . . . . . . . Nacken 1906 Z . Nahr. Genussm., 12, 670 Huckleberry. . . . . . . . . . . . . . . Kunz & Adam Citric predominates: small amount malic; no tartaric Huckleberry, . . . . . . . . . Jorgensen 1907 Z . Nahr. Genussm., 13, 241 Citric; small amount malic Scurti & Plato 1909 Stas. sper. agrar. ifal., 41,456 Citric and malic Orange . . . . . . . . . . . . . . Kunz & Adam 1906 Z . Nahr. Genussm., 12, 670 Peach Citric; no malic nor tartaric Truchon & Martin-Claude 1901 A n n . chim. anal., 6, 85 Pear. . . . . . . . . . . . . . . . . No tartaric Chauvin. Toulin & Canu 1908 Mon. sci., 69, 449 Pear. . . . . . . . . . . . . . . . . Citric Pear. , . , , , , . . , , , , , , , , . , . , . Warcolliei 1911 Ann. fals., 4, 485 No tartaric 1909 Z . offent. Chem., 10, 187 Pineapple, . . . . . . . . . . . . . . . . Kayser Citric; no malic nor tartaric Plum: 1901 A n n . chim. anal., 6, 85 (Green Gage). . . . . . . . . . . . Truchon & Martin-Claude Trace tartaric 1908 Man. sci., 69, 449 (Green Gage). . . . . . . . . . . . Chauvin, Joulin & Canu Citric Pomegranate, , , , , , . , , . . , Borntrager & Paris 1898 Z . Nahr. Genussm.. 158 Citric predominates; malic also present Quince, . . . . . . . . . . . . . . . . . . .Truchon & Martin-Claude 1901 A n n . chim. anal., 6, 85 Tartaric Raspberry, W. Kaupitz 1900 Pharm. Zentr., 41, 347 Tartaric 1905 Z . allgem. dsterr. Apoth.-Ver. 43, 7 49 Raspberry, ................ R. Kunz Citric; no malic; no tartaric Rasoberrv ................. Kunz & Adam 1906 Z . alleem. osterr. Aboth.-Ver..' ' 44, 1187 Citric; no malic; no tartaric Raspberry. . . . . . . . . . . . . . . . . Krzizan & Plahl 1906 Z . N i h r . Genussm.; 11, 205 Citric; no malic or only trace present 1906 Z . offent Chem., 12, 342 Raspberry.. . . . . . . . . . . . . . . . R. Krzizan Citric; no malic; no tartaric 1906 Z . offent. Chem., la, 155, 191 Raspberry. . . . . . . . . . . . . . . . . R. Kayser Citric principally; small amounts malic & tartaric Raspberry.. . . . . . . . . . . . . . . . Hempel & Friedrich 1906 Z . Nahr. Genussm.. la, 725 1st sample, much citric; considerable malic 2nd sample, citric and malic in about equal amts 3rd & 4th samples, malic; traces of citric Raspberry.. G. Jorgensen 1907 Z . Nahr. Genussm., 13, 241 Citric, principally: a little malic Raspberry., , ........... ... Chauvin, Joulin & Canu 1908 Mon. sci 69 449 Tartaric Raspberry.. ... . . . . . . . . . ... Muttelet 1909 A n n . fals:, 2,'383 Citric; no malic: traces only tartaric Strawberry.. ,............ . . Truchon & Martin-Claude 1901 A n n . chim. anal., 6, 85 Tartaric Strawberry.. , 1902 Chem.-Zfg., 26, 248 ... Paris Citric; small amount malic Strawberry.. . . . . . . . . . . .. . . Kunz & Adam 1906 Z . allgem. osterr. Apo1h.-Ver., 44, 187 Citric: no malic: no tartaric Chauvin, Joulin & Canu 1908 Mon. sci.. 69, 449 Strawberry. Tartaric Strawberry. . . . . . . . . . . . . Muttelet 1909 A n n . fals., 2, 383 Citric; n o malic; traces only tartaric FRUIT
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ence, the statements found in the literature regarding t h e presence of malic, citric and tartaric acids in fruits are presented in tabular form in Table I. Table I1 contains a summary of what appear t o be t h e most TABLEII-sUMMARY
OF MOST RELIABLESTATEMENTS BY WRlTERS ON THE ACIDSOF FRUITS
PREVIOUS
FRUIT
PREDOMINATING REMARKS Malic acid Other acids, if present, only in traces Citric acid Benzoic acid present to the extent of 0.04 to 0.05 per cent: other acids, if present, only in traces Currants Citric acid Other acids, if present, only in traces Huckleberries Citric acid Some malic acid Raspberries Citric acid Other acids, if present, only in traces Strawberries Citric acid Other acids, if present, only in traces Cherries Cranberries
reliable statements by previous writers regarding t h e acid contents of the more common fruits. EXPERIMENTAL W O R K
Methods for t h e quantitative determination of malic acid were suggested by YoderZ6 in 1911 a n d later by Dunbar a n d Bacon.26 These methods depend on t h e increase in t h e optical rotation of solutions of malic acid when treated under definite conditions with uranyl acetate. Citric acid when present does not interfere with t h e determination b u t special treatment is required in t h e presence of tartaric acid for the reason t h a t t h e optical rotation of t h e latter acid is also increased by treatment with uranyl acetate. The most favorable limits for t h e determination of malic acid by t h e optical method are between 0 . 2 per cent and 2 . 5 per cent of malic acid. The error within these limits seldom amounts t o more t h a n 5 per cent of t h e malic acid present when solutions are clear enough t o be polarized without difficulty. I n t h e case of dark-colored solutions, however, much difficulty is sometimes encountered in making t h e polarizations and i t is then necessary t o resort t o t h e use of bromine as a bleaching agent. When bromine is used t h e error may be somewhat higher t h a n t h a t stated above. The polariscopic method is entirely ,applicable t o t h e determination of malic acid in fruit juices which are not highly colored and it is also applicable, but with less accuracy, t o colored juices in which the use of bromine as a bleaching agent is necessary. I n t h e latter case t h e error is always in t h e same direction, t h e amount of malic acid found being less t h a n t h a t actually present. The determination of t h e malic acid content of several varieties of apples and other fruits generally regarded as containing malic acid only, showed in many cases a remarkably close agreement between t h e malic acid determined by t h e polariscopic method and t h a t calculated from the total acidity found by titration with standard alkali. This seemed t o indicate t h a t , contrary t o t h e usual idea, malic acid exists in these fruits almost entirely in t h e uncombined condition. I n view of these results it seemed worth while t o determine t h e amount of malic acid present in all t h e common fruits. A determination of t h e citric acid content of these fruits was also considered desirable. A method for this determination has been described by Pratt.27 It depends on t h e precipitation of t h e acid as barium citrate, its conversion t o acetone by oxidation with potassium permanganate in acid solution, and t h e distillation a n d collection of the acetone in Denigbs’
Vol. 9, No. 8
reagent from which it may be precipitated in weighable form by boiling. This method a t first gave promise of considerable accuracy and it was consequently used for t h e determination of citric acid in most of the fruits examined. A more extended study of t h e method led t o t h e conclusion, however, t h a t i t cannot be relied upon. The most favorable limits for t h e determination are given as from 0.05 t o 0.15 g. of citric acid. A series of 1 5 determinations was made using water solutions of pure citric acid containing from 0.06 t o 0.15 g. of t h e acid and distilling directly without previous precipitation as barium citrate. The percentage recovered in this series varied from 7 2 . 2 per cent t o 101.9per cent, averaging 8 4 . 3 per cent. Two other solutions, containing, respectively, 0.4 and 0 .2 g. of citric acid, were treated exactly as described in t h e method including precipitation as barium citrate. The percentages of citric acid recovered were, respectively, 44 per cent and 166 per cent. It was found also t h a t the presence of both malic and tartaric acids interfered very seriously with t h e determination as will be evident from the figures given in Table 111. Even TABLEIII-SHOWING INFLUENCE OF MALICAND TARTARIC ACIDSON THE DETERMINATION OF CITFJC ACIDB Y THE PRATT METHOD GRAMSACID PRESENT CITRICACID Per cent Treatment Citric Malic Tartaric Grams found Recovery (see below) 0.25 0.37s 0.282 113 A 0.30 0.60 0.484 161 A 0.20 0.60 0.294 147 A 0.30 0.30 0.307 102 A 0.075 0.50 0.090 120 B A-Acids precipitated as barium salts. B-Solution distilled direct without precipitation.
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wider variations were obtained ifi duplicate determinations of citric acid made on fruits. These figures seem t o confirm t h e statement of Jorgensen3 t h a t t h e quantitative determination of citric acid by means of its oxidation with potassium permanganate in acid solution is impracticable. It may be said, however, t h a t a paper has recently been published by J. J. Willaman describing a “Modification of t h e P r a t t Method for t h e Determination of Citric Acid.”28 According t o the author, this modified method if followed rigidly will give much more satisfactory results t h a n t h e original. The writers have not as yet had a n opportunity t o test t h e modified method. I n view of the unsatisfactory nature of the results obtained with known solutions no reliance has been placed on t h e values for citric acid obtained by t h e P r a t t method in t h e fruits examined, b u t qualitative conclusions have been drawn as t o t h e presence or absence of citric acid. Where no precipitate or only a very slight one was obtained, it was concluded t h a t no citric acid was present, while a large precipitate was taken t o indicate t h e presence of t h e acid. Since t h e completion of t h e work reported in this paper, a modification of Stahre’s2g pentabromacetone method for citric acid has been published by K ~ n z . ~ ~ This method is applicable in the presence of malic and tartaric acids and has been applied t o t h e determination of citric acid in fruit juices and similar products by Dunbar and Lepper31 with very satisfactory results. Most of t h e fruits examined were obtained through the co6peration of t h e Bureau of Plant Industry of
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t h e U. S. Department of Agriculture which also classified t h e fruits. Thanks are especially due t o Messrs. A. V. Stubenrauch a n d C. P. Close of t h a t Bureau for their assistance in this work. I n some cases, where only one or t w o samples of a particular fruit were examined, t h e y were purchased in t h e local market without classification. T h e method followed in preparing t h e fruits for analysis was approximately t h e same in all cases. The flesh only of stone a n d seed fruits was squeezed by hand through a cloth bag t o obtain t h e juice. I n t h e case of berries, the whole fruit was treated in this way. Cherries were squeezed without pitting, b u t t h e stone was not crushed. Analyses were made immediately on t h e freshly expressed juice. T h e total acidity of t h e juice was determined usually on 5 g. samples b y titration with N / I O sodium hydroxide, using phenolphthalein or a solution of azolitmin on a spot plate as t h e indicator according t o t h e color of t h e juice under examination. Malic acid was determined b y t h e method given below. This is t h e method originally described by Dunbar a n d Baconz6 modified by t h e use of alcohol for t h e precipitation of pectins, as described by Pratt:32 Place a weighed amount of the fruit juice, generally 100 g., in a 500 cc. beaker. With vigorous stirring add about two or three times the volume of 95 per cent alcohol. This throws out the pectins usually in such form that after standing a few minutes they may be gathered into a coherent mass. Decant the liquid through a filter and wash the precipitate twice with 95 per cent alcohol. Evaporate the combined filtrates in a current of air on the water bath t o about 75 cc. After cooling, make up the solution t o IOO cc. in a measuring flask, using IO t o 15 cc. of 95 per cent alcohol and distilled water. The temperature when the volume is finally made up to the mark should be close to that a t which the polariscope readings are to be taken. Treat about 2 5 cc. of the solution so obtained with powdered
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uranyl acetate, adding enough of the salt so that a small amount remains undissolved after z hours. Two and one-half grams of uranyl acetate will usually be sufficient, except in the presence of large amounts of malic acid. In case all the uranium salt dissolves more should be added. Allow the mixture t o stand for three hours, shaking frequently. Filter through a folded filter until clear and polarize if possible in a 2 0 0 mm. tube. If the solution is too dark to read in a zoo mm. tube, a IOO or 50 mm. tube may be used. It is desirable, however, to use the longest tube possible in order to reduce the error of the determination. Treat the remainder of the original solution with powdered normal lead acetate until no further precipitation results. Cool in an ice bath and filter through a folded filter until clear. Warm the filtrate to room temperature and add a small crystal of lead acetate to determine whether the precipitation is complete. If no further precipitate results, remove the excess of lead completely with anhydrous sodium sulfate, filter until clear, and polarize. Solutions which are sufficiently clear and contain less than I O per cent of sugar may be polarized directly without treatment with lead acetate. Polarize a t room temperature with white light, taking care that all solutions are polarized a t the same temperature. Make at least six readings in each case and take a n average of these. In this work a standard, Lippich type, triple field saccharimeter was used, the light being furnished by an electric bulb placed behind a ground-glass plate. Calculate all readings to the basis of a zoo mm. tube. Multiply the algebraic difference between the two readings by 0.036. The product will equal the weight
1I ;IHICooH \
in grams per Io0 cc. of the soluCHOHCOOH tion as polarized. I n the case of clear, light-colored fruit juices which are easily polarized, the preliminary treatment with alcohol may be omitted. Polarize one portion of the sample directly without any treatment whatever. Treat another portion with uranyl acetate and then polarize. Calculate the weight of malic acid present from the difference between the readings as described above. of malic acid
TABLEV-ACID
CONTENTOF APPLES (RESULTSIN PERCENTAGES) Malic Analyst Source Total see Acid Acid of Lab. ( b ) text No. DESCRIPTION Fruit (a) F 21870 Baldwins 0.57 0.60 Dunbar F 22518 Maiden Blush: green (i) 1.68 1.68 Dunbar F 22519 Early Ripe: green (1) 1.09 1.02 Dunbar F 22520 Gravenstein: green 1.27 1.21 Dunbar F 22521 Kinnard: picked 7/5/11 0.80 0.65 Dunbar F 22543 Kinnard: picked 7/25/11 (1) 0.72 0.75 Dunbar F 22517 Sweet Bough: green (1 0.21 0.11 Dunbar F 22542 Sweet Bough: picking ripe (11 0.13 0.08 Dunbar F 22710 Unclassified (Sour) . . 0.62 0.52 Dunbar F 22779 Tompkins King 0.45 Pratt F 22780 Tolman 0.22 Pratt F 22781 Reinette de Regmalard (2) 0.61 0.58 Pratt F 24082 PrCcoce de Tunis 0.28 0.36* Johnson F 24083 PrCcoce de Tunis 0.31 0.45* Johnson F 24084 Excelsior (3) 1.11 1.22* Johnson F 22709 Unclassified (Crabs) .. 0.72 0.61 Dunbar 1. 2.1282-DUnclassified (Crabs) 0 78 0 73 Treuthardt F 24085 Florence Crabs i3) 1:11 1:23* Johnson F 24090 Northfield Beauty Crab Va. 1.81 1.49* Johnson Dunbar 0.56 0.57 .. 0.54 0.52 Dunbar 0.43 Dunbar 0.39 0.49 0.50 Johnson (1) Maryland Experiment Station, 'College Park, Md. (2) Experiment Station, Geneva, N. Y. (3) Experiment Farm. Arlington, Va. * Test for citric acid, negative. ( a ) By titration (as malic acid). ( b ) By uranyl acetate method.
CONTENT OF CHERRIES (RESULTSIN PERCENTAGES) Total Malic Citric Acid Acid Acid Analyst Lab. VARIETY (a) (b) (6) (see t e x t ) NO. 1.01 0.78 ( d ) Dunbar F 22504 California Naooleon (Royal Anne)0.97 F 22505 Black Republican 0.87 F 22508 Black Republican 2.01 F 23979 Unclassified 1.32 F 23981 Unclassified 1.44 F 23982 Unclassified F 24033 Unclassified 1.00 (Red-sweet) 0.56 Absent ' 0.56 F 24035 California Wax (?) 1.52 Absent 1.54 F 24036 Unclassified (Red-sour) 0.82 Absent 0.85 F 24037 Red Heart (?) 0.83 Absent 0.80 F 24038 Unclassified (Cal. Red) 0.86 Absent 0.81 F 24039 Carnation 1.35 Absent Fitzgerald 1.31 F 24040 Montmorency (N. Y.) 0.61 Absent . a n d 0.63 F 24052 Schmidt (N. Y.) Dunbar 0.85 Absent 0.82 F 24063 Windsor 0.91 Absent 0.93 F 24064 Montmorency 0.63 Absent 0 . 5 6 F 24065 Coe 0.99 Absent 1.10 F 24066 M a y Duke 1.08 Absent 1.16 F 24067 Early Richmond 0.93 Absent , F 24068 Unclassified (Mazzard-a4ld) 1.03 ( b ) By uranyl acetate method. ( a ) By titration (as malic). (d) No examination made. (6) Qualitative test.
TABLE VI-ACID CONTENT OF CURRANTS (RESULTSI N PERCENTAGES) Analysts: F.F. Fitzgerald and P. B. Dunbar
TABLE VII-ACID CONTENT OB GOOSEBERRIES (RESULTSIN PERCENTAGES)
TABLE IV-ACID
ti]
g:J:,
..
..
Ma!ic Acid Lab. NO. VARIETY (a) (b) 0.11 North Star 2.18 F 24053 2.07 none Cherry F 24054 none White Transparent 1.98 F 24055 3.37 0.71 F 24056 Prince Albert 2.58 0.06 F 24057 London Market ( a ) By titration (as citric acid). ( b By uranyl (d)) Expressed (6) Qualitative test. Total Acid
Citriz Acid other Acid than Malic (d (d) Present 2.07 Present 2.07 Present 1.98 Present 2.69 Present 2.52 acetate method. as citric acid.
Total Malic Citric Acids other Acid Acid Acid than Malic Analyst VARIETY (a) (b) (6) (d) (see text) Unclassified 2.63 2.08 Present 0.64 Clark Duplication 1 .72 0.50 Present 1.24 Downing Houghton Present 1.35 1.83 0.50 Lady Popham 1.55 0.28 Present 1.82 Chautauqua Downing 2.00 1.17 Present 0.88 ( b By uranyl acetate method. ( a ) By titration (as citric acid). Expressed as citric acid. ( 6 ) Qualitative test.
Lab. No. F22514 F 24058 F 24059 F 24060 F 24061 F 24062 F 24029
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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 CHEMISTRY
766
Vol. 9 , No. 8
TABLE VIII-ACID
Lab. No. F 22733 F 22734 F 22753 F 22754 F 22776
.......
F 22768
F 22773 F 22738 F 22741 F 22748 F 22750 F 22737 F 22731 F 22732 F 22755 F 22735 F 22736 F 22749
F 22772
.......
F 22761
F 22784 F 23001 F 22774 F 22762
F 22785 F 22767
F 22763 F 22775 F 22777
F 22786 F 23000 F 22744 F 22998 F 23002 F 22740
F 22742
F 22745 F 22739 F 22743 F 22751 F 22752 F 22764
F 22766 F 22769
F 22770 F 22771 F 22999
VARIETY Kieff er Kieffer Kieff er Kieffer Kieffer Kieffer Le Conte Idaho Bartlett Bartlett Bartlett Bartlett Bartlett Angouleme Angouleme Angouleme Seckel Seckel Seckel Seckel Seckel Winter Nelis Winter Nelis Winter Nelis Winter Nelis Clairgeau Clairgeau Clairgeau Anjou Anjou Easter Easter Easter Beurre Hardy Pound Pound Like Gray Doyenne Like Gray Doyenne Like White Doyenne Probably Sheldon Sheldon F1or e11a Cornice Bosc Jones Lamartine Fitzwater Reeder Glout-Morceau
TABLEIX-ACID
CONTENT OF PEARS (RESULTSI N PERCENTAGES) Total Acid Malic Acid Citric Acid by Titration by Uranyl Qualitative SOURCE (as Malic) Acetate Method Test Anacostia, D. C. 0.50 0.14 Present 0.48 0.09 Sandy Springs, Va. Present New Jersey 0.55 0.10 Present 0.50 .......... 0.14 Present 0.37 N. Yakima. Wash. 0.30 Present 0.48 .......... 0.04 Present 0.28 N. Y. State Expt. Sta. 0.09 Present 0.21 N. Y. State Expt. Sta. Present 0.00 0.30 New York Present 0.03 California 0.35 Present 0.02 California 0.34 0.11 Present New York 0.26 0.00 Present District of Columbia 0.36 0.46 Absent 0.19 Vienna, Va. 0.27 Absent 0.15 New York 0.26 Absent 0.21 .......... Absent 0.33 0.18 New York Absent 0.24 Alexandria, Va. 0.20 0.21 Absent New York 0.19 0.30 Absent N. Y. State Expt. Sta. 0.06 0.09 Absent 0.23 .......... 0.26 Absent 0.17 California Absent 0.25 0.16 Monterey, Cal. Absent 0.20 0.11 0.21 Absent 0.25 Absent 0.29 0.10 Absent 0.09 0.08 0.11 Absent 0.10 0.14 Absent 0.21 0.19 Absent 0.27 0.34 Absent 0.19 0.21 N . Yakima; Wash. Absent 0.22 0.34 Monterey, Cal. Absent 0.14 0.22 .......... Absent 0.16 Boston, Mass. Absent 0.14 0.17 Absent 0.19 0.14 0.21 .......... Absent 0.17 0.18 Near Dist. of Col. Absent 0.23 California Absent 0.35 0.19 0.16 New York Absent 0.19 Absent 0.21 California 0.17 Absent 0.19 Near Dist. of Col. 0.14 Absent 0.11 Santa Clara, Cal. 0.16 0.24 Santa Clara, Cal. Absent 0.23 0.18 Santa Clara, Cal. Absent 0.25 0.33 N. Y. State Expt. Sta. Absent 0.11 Absent 0.03 N. Y. State Expt. Sta. 0.26 Absent 0.26 N. Y.State Expt. Sta. 0.21 0.27 Absent N. Y. State Expt. Sta. 0.19 0.10 Absent
..........
Acids other than Malic (expressed as Citric) 0.34 0.37 0.43 0.34 0.07 0.42 0.18 0.20 0.26 0.32 0.22 0.25
.... .... .... .... ....
.... .... .... .... ....
.... .... .... .... .... .... ....
.... .... .... .... ....
.... .... .... .... .... .... .... .... .... .... .... ....
....
....
ANALYST D. S. Pratt D. S. Pratt J. M. Johnson J. M. Johnson J. M. Johnson J. M. Johnson J. M. Johnson J. M. Johnson D. S. Pratt D. S. Pratt D. S. P r a t t D. S. Pratt D. S. P r a t t D. S. P r a t t D. S. Pratt J. M. Johnson D. S. Pratt D. S. Pratt D. S. Pratt J. M. Johnson J. M. Johnson J. M. Johnson J. M. Johnson J. M. Johnson J. M. Johnson J. M. Johnson J. M. Johnson J. M. Johnson J. M. Johnson J. M. Johnson J. M. Johnson J. M. Johnson J. M . Johnson D. S. Pratt J. M. Johnson J. M. Johnson D. S. Pratt D. S. Pratt D. S. Pratt D. S. Pratt D. S. Pratt D. S. Pratt D. S. Pratt J. M. Johnson J. M. Johnson J. M. Johnson J. M. Johnson J. M. Johnson J. M. Johnson
* T e s t for tartaric acid, negative. Test for tartaric and citric acids, negative. (a) By titration (as malic). ( b ) By uranyl acetate method.
CONTENT OF MISCELLAXEOUS FRUITS(RESULTSIX PERCENTAGES) Total Malic Citric Acids other Lab. Acid Acid Acid than Malic Analyst No. FRUIT (Titration) (c) (d) (b) (see t e x t ) I? 22791 Banana ,,,, Pratt ...... . . . . . 0.26(a) 0.24 F 24098 Cantaloupe 0.18(b) none . . . . . . . . . . Johnson . . . . . Cranberries 2.80(a) 0.56 Present 2.14 Pratt 1.85 Pratt . . . . . Cranberries 2.65(a) (1.71 Present Johnson F 24103 Peaches 0.51(a) c1.49 I Probably I , . , 1 absent f F 22792 Persimmon, Japanese 0.09(a) 0.09 . . . . . . .... Johnson F 22756 Pomegranate 4.52(b) none Present 4.52 Pratt Quince unripe 0.90(a) 1.00 Absent .... Pratt F 24028 Raspbe'rries, red 1 .5 1( b ) 0.03 Present 1 .48 Johnson F 24097 Watermelon 0 . 0 5 ( a ) 0.20 Absent . . . . Johnson ( b ) As citric acid. ( a ) As malic acid. ( d ) Qualitative test. (c) By uranyl acetate method.
T h e P r a t t method for citric acid previously described was also applied in most cases, but, as already stated, only qualitative conclusions were drawn therefrom. N o attempts were made t o determine volatile acids, salicylic, formic or benzoic acids, as these are well known t o be present only in minute quantities, except in t h e case of cranberries, which may contain benzoic acids in amounts u p t o 0 .o j per cent.33 T h e results obtained are presented in Tables IV t o X, inclusive. These represent t h e work of t h e following analysts: R. F. Bacon, D. S. P r a t t , C. W. Clark, J. hl. Johnson, F. F. Fitzgerald, E . I,. P. Treut h a r d t a n d P. B. Dunbar. As will be seen from a study of t h e tables, a very close agreement was found in many cases between total acid as malic determined by titration a n d total malic acid found b y t h e optical method. I n some cases, when such agreement was discovered, no examination for citric acid was made. This agreement is especially noticeable in apples a n d cherries. It seems evident t h a t in these fruits, at least in most cases, t h e acidity is due t o malic acid
alone, a n d t h a t this acid is present only in the free condition. The old method of reporting combined malic acid in fruit as calculated from t h e alkalinity of t h e ash appears. therefore, t o be based upon a n incorrect assumption. I t is interesting t o note also t h a t t h e acidity of unripe apples, as well as of ripe apples, is due entirely t o malic acid and t h a t no combined malic acid is present. This will be seen in Table IV. The Maiden Blush, Early Ripe, Gravenstein and Kinnard apples, all of which were picked green, show a very close agreement between total acidity expressed as malic a n d total malic acid. This is not t r u e of t h e Sweet Bough apple, b u t t h e low acidity of this apple makes i t probable t h a t t h e percentage error in both determinations is rather high. The results obtained in t h e examination of pears, which are shown in Table V I I I , are most interesting. I t will be seen t h a t with few exceptions t h e varieties which are named first in t h e table, Kieffer, Le Conte, Idaho a n d Bartlett, contain little or no malic acid, while citric acid is shown t o be present. One sample of
CONTENT
OF
PLUMS (RESULTSI N PERCENTAGES) Total Malic Acid Acid (a) (b) Analyst 0 69 0.65 F. F. Fitzgerald . 7 3 I 24 J. 11 Johnson 11 I 04 J. 31. Johnson
Lab. No. VARIETY SOURCE F 24074 . . . . . . . . Local market F 24086 Burbank Expt. Farm, ( F 24087 Abundance Arlington, \'a. I UNCLASSIFIED: F 22573 (Large red) Local market F 22587 (Japanese red) Local market (Purole) Local market ikedj ' Local market (Large white) Local market (Small red) Local market
{
.
0 55 0.36 1.70 1 , 6 0 2.15 2.39* 1 . r0 I . 60'* 1.41 1.51 0.19 0.88
D. D. D. D. D. D.
S. Pratt S. Pratt S. Pratt S. Pratt S. Pratt S. Pratt
**
TABLEX-ACID
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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
Bartlett pears, F. 2 2 7 3 7 , appeared t o contain only malic acid, while one sample of Kieffers, F. 2 2 7 7 6 , contained a predominating amount of malic. No explanation is offered of these exceptions. All t h e other varieties of pears examined contained no citric acid, t h e acidity being due apparently in most cases t o malic acid alone. Here again, t h e close agreement between total acidity as malic a n d total malic acid is very apparent in many varieties. T h e acidity of plums, like apples a n d cherries, appears t o be due entirely t o malic acid which is probably present for t h e most part in t h e free state. Currants always contain citric acid and may or may not contain malic acid. Gooseberries contain large amounts of malic acid a n d also give strong reactions for citric acid. I n t h e case of t h e samples reported in Table X , only one or a t most two of each variety were examined. It is consequently impossible t o draw general conclusions from these results. I n t h e samples of persimmons a n d bananas examined, malic acid probably occurred alone. The pomegranate contained no malic acid b u t apparently only citric, a n d this is also t r u e of t h e cantaloupe. Malic acid predominated in t h e watermelon, quince a n d peach, while citric was probably absent. The cranberries contained both acids while t h e red raspberries contained citric, with malic, if present a t all, only in traces. The acid of t h e apricot has not been positively identified, b u t t h e evidence seems t o be t h a t tartaric or perhaps dextromalic acid is present in this fruit for t h e reason t h a t a positive BIBLIOGRAPHY 1-Vi. Kaupitz, Pharm. ZenfrQlhQlk,4 1 (1900). 347. 2-R. Kayser, Z . 6.fenf. Chem., 12 (1906). 155 and 191. 3-Jorgensen, Z . Xahr. Genussm.. 13 (1907), 241. G-Windisch and Boehm, Ibid., 8 (1904), 347. 5-Kunz and Adam, 2. dslerr. A p o t h . - V e r . , 44 (1906), 18;; Z . S a h r . Genussm., 12 (1906), 670. 6-Krzizan. 2. oflent. Chem., 12 (1906), 323 and 342. i-Halmi, Z . A'ahr. Genussm.. 16 (1908). 153. 8-Kunz, Z . ocferr. Apoth.-l.er., 43 (1905). i49; Z . S a h r . Genussm., 12 (1906). . , . 300. 9-Krzizan and Plahl, 2. S a k r . Genussm., 11 (1906), 205. I&-Hempel and Friedrich, Ibid., 12 (1906). 725. 11-Keim, 2 . anal. Chem., SO (1891), 401. 12-W. h-acken, Forschungsber iiber Lebensmitlel, 2 (18951, 350. 13.-Mach and Portele, Landw. Vers.-Sta., 38 (1890). 69. 14-Stolle, Z . Ver. Zuckerind. (N. F.), 37 (1900), 609. J . Russ. Phys.-Chem. Gesellschaff, 12 (1903), 146; Z . 15-Aparin, A-ahr. Genussm., 8 (1904), 254. 1 b W i n d i s c h and Schmidt, 2. A'ahr. Cenussm., 17 (1909), 584. 17-Truchon and Martin-Claude, A n n . chim. anal., 6 (1901), 85. 18-Chauvin, Joulin and Canu, Mon. s c i . , 69 (1908), 449. 19--Muttelet, A n n . fals., 2 (1909). 383. 2C-Warcollier. Ibid., 4 (1911), 485. 21-Paris, Chem.-Ztg., 26 (1902), 248. 22-Roux and Bonis, A n n . f&., 2 (1909), 150. 23-Scurti and Plato, Sfaz. sper. agrur. ifal., 41,456; C. A , , 3 (1909),1763. 24-Borntrager and Paris, Z . Kahr. Genussm., 1898, 158. 3 (1911), 563. ?5--Yoder, THISJOURKAL, 26-Dunbar and Bacon, U. S. Dept. .4gr., Bur. of Chem., Circular 76; THIS J O U R N A L , 3 (1911), 826. 27-Prntt. U. S. Dept. Agr., Bur. of Chem., Circular 88. 28--Willaman, J . A m . Chem. S O L . ,38 (1916), 2193. 29-Stabre, Sordisk Tidsskiijf, 2 (1895), 141: Z . anal. Chem., 36 (1897), 195. 3&-Kunz, Arch. Chem. .Mikros, 7 (19141, 285; 9 (1915), 687. 31-Dunbar and Lepper, Jour. A . 0. .4. C., 2 (1917), No. 4, 175. 32-Pratt, U. S. Dept. Agr., Bur. of Chem., C ~ Y G U 87. ~QY 33-Mason, J . A m . Chem. SOL., 27 (19051, 613; Griebel, Z. Nahr. Genussm., 19 (1910), 241; Bigelow, U. S. Dept. .4gr., Bur. of Chem., Bullcfin 90 (1904). 61.
767
increase in polarization was obtained on treating it with uranyl acetate. The acid of t h e huckleberry has not been positively identified, traces only of malic acid having been found, with n o citric. Some samples of blackberries appeared t o contain only citric acid, some contained malic acid in traces with no citric, while others gave no reactions for either malic or citric. The conclusions reached regarding t h e acids of t h e fruits examined have been collected in Table X I . TABLE XI-SUMMARY OF THE ACIDS FOVND IN THE FRUITS EXAMINED As will be noted in the text, apricots, blackberries and huckleberries were also studied but definite results on their acid contents were not obtained. FRUIT ACIDS FOUND Malic only Apple Banana Probably malic only Cantaloupe Malic none-probably all citric Cherry Malic only Cranberry Citric probably predominates-malic also present Currant Citric probably predominates-malic sometimes present Gooseberry Malic and citric Peach Probably malic only Pear Malic only in some varieties; citric probably predominates in others with small amounts of malic Persimmon Probably malic only Plum Malic only Pomegranate Probablv all citric-no malic nor tartaric Quince Malic only-no citric Raspberry (red) Probably citric only-malic, if present, in traces only Watermelon Malic, no citric
These generalizations are not p u t forward as final. It is possible t h a t later work may modify t h e m in some particulars. Undoubtedly traces of acids other t h a n those here considered occur in many fruits a n d i t is possible t h a t these may sometimes be found in important quantities. The results obtained on pears emphasize t h e danger of drawing general conclusions as t o t h e acid content of fruits from t h e analysis of a limited number of varieties or even of a limited number of samples. I t is believed, however, t h a t t h e general conclusions drawn from those cases in which a considerable number of samples were examined are correct. DEPARTMENT OF AGRICULTURE BUREAUOF CHEMISTRY WASHINGTON, D. C. ~-~ ~~
~~~~
THE DETERMINATION OF NITRATE IN SEWAGE BY MEANS OF ORTHO-TOLIDINE By EARLEB. PHELPS A N D H . L, SHOUB Received April 3, 1917
The determination of nitrate in sewage and sewage effluents has been t h e subject of extensive investigations out of which no wholly satisfactory methods h a r e as yet been eyolved. The classic method of Schulze-Tiemanl (reduction t o nitric oxide by means of acid ferrous chloride) is probably t h e most accurate method available, but is too complicated for routine procedure. The phenol-sulfonic acid method, as developed by Gill,* which gives such beautiful results with potable waters low in chlorine, is not available for use with sewages on account of t h e interfering action of chlorides. 1-arious reduction methods depending upon t h e action of nascent hydrogen in either acid or alkaline solution, have from time to time been proposed. Reduction may be complete, i. e . , t o ammonia or merely t o nitrite, either of which 1 Tieman-Girtner, "Handbuch der Untersuchen und Beurtheilung der Wasser," 4th Ed., 1895. * J . A m . Chem. Soc., 16 (18941, 122.
