June, 1933
I N D U ST R I A L A S D E N G I S E E R I S G C H E hl I S T R Y
H., a n d Whitmore, TT. F., Zbid., Anal. Ed., 1, 205 (1929). Harries, C., and S a g e l , IT., Ber., 55B, 3822 (1922). K a m m , O., “Qualitative Organic Chemistry,” 1923. KRmpf, P., Pharm. Acta. Hela., 6 , 170 (1931). S a g e l , IT.,a n d Kornchen, M., Wiss. Verofentlich. SiemensKontem, 6, 23.5 ( 1 9 2 i ) . Parry, J. E., Chem. Druggist, 59, 689 (1901). a n d Blair, L. V. D., U. 9. Patent 1,309,967 Simonson, W. W., (July, 1919). C. S. Shellac 1mi)orters’ - h o c . , Official Methods of h a l y s i s , 1929.
( 4 ) Gardner, W.
(5) (6) (7) (8) (9) (10) ill)
699
(12) Whitmore, 11‘. F., a n d Lauro, M., ISD. ENG.CHEX., 22, GIG (1930). (13) Whitmore, W.F., Weinberger, H., with Gardner, W.H., Zbid., Anal. Ed., 4, 48 (1933). (13) Wolff, H., Farben-Ztg., 27, 3130 (1922).
RECEIVED November 25, 1932. This paper is based upon part of the thesis submitted by H. J. Harris in partial fulfilment of the requirements for the degree of bachelor of science a t the Polytechnic Institute of Brooklyn, June, 1931. Contribution 6 Erom Shellac Research Bureau, Shellac Importers’ Association, and Contribution 18 from Department of Chemistry, Polytechnic Institute of Broiiklyn.
Pectin Studies I. Citrus Pectin AKSEL G. OLSEN,General Foods Corporation, B a t t l e Creek, Mich. A simple method is presented which lends itof pectin5 p r e ~ a r e db y t h e serf to both routine ez,aluation and research same m e t h o d of extraction.” on pectin i n d i c a t e s a wide-spread interest in This s t a t e m e n t a g r e e s with studies qf pectin. T h e data show that, with the conclusions of (lj) this plant p r o d u c t . A g r e a t illany of the published studies citrus Peefin jellies containing 60 fo 65 per cent that, although p r a c t i c a l use have, however, more of an acasugar, wide cariations in acidity beyond a cermay b e m a d e of the viscosity upor1 t e s t , enough exceptions to a deniic value than any practical Lain nlinirlium calue hate little or no significance. The most imporjelly The obtained agree u,ith direct r e l a t i o n s h i p b e h e e n v i s c o s i t y and jelly s t r e n g t h tant feature of pectin, economithe that the so-ca11ed optinzum p H is that have been noted “to prerent our cally, is its ability to form a gel in the presence of certain proporpoint at which incipient pan gelation becomes a accepting a viscosity test as a tions of water, acid, and sugar. measurable factor in the jelly strength. final determination of jelly grade, T h e efleect of acid beyond the optimum appears emulsifying valLle, etc., in all It is generally recognized that different pectins, similarly prepectin preparations. The reason io be that sf increasingthe rate of jelly pared, may differ widely in their for this lack of complete correla-formation. This rate nLay be so reduced by tion is effected by the relative power of forming gels, and it is customary in the trade to differ/olL’ering the sugar concentra~ion that no drop p r o p o r t i o n s of the v a r i o u s entiate pectins according to the beyond the optimum occurs eren with the present pectins, pectic acids, and pectates in the preparation, by the maximum proportion of sugar hot method. ‘‘ley ill carry and still for111 presence of heavy metal salts, by Sereral commercial pectin samples are cornpH of the solution, etc.” It is satisfactory jellies. Keverthepared On the Of the method The also a well known observation less, numerous papers deal extensirely with the estimation of logarithm 0s pectin concentration Plotted against that commercial pectin concenthe logarithrn of jelly strength results in a straight trates mapgreatly increase in vispectin without any effort toward line. This prorides a conttenient means for cosity with age although no inestimating the value as well as the quantity of the pectin so decrease in jelly strength occurs. other jelly strengths and termined. Comparatively few I t is apparent that the method is efforts have been made to differconcentrations than those actually obserced* of doubtful value both in dealing entiate between different pectins Tuv accurate determinations for different pectin with unknown pectin samples, on the basis of quality; and the concentrations su&e f o r estimating the jelly and for the comparison of pectins prepared by varying methods. Of grading ~~~t~~~~ acstrength at any other concentration. c o r d i n g to a m o u n t of sugar The usual commercial praccarried by a given a m o u n t of tice of determining pectin grade pectin has received but little attention in scientific literature, has always been more of an art than a science. A number of although it is in general use in the practical buying and selling jellies of different ratios of sugar to pectin are prepared and, of pectin. Johnstin and Denton (4) some years ago pointed after standing overnight, are then turned out on a tray for out that the amount of alcohol precipitate is not a reliable examination. “A skilled operator readily recognizes a satismeasure of effective pectin, and that determinations based factory jelly. It mill be firm yet tender, will leave a sharp upon jellying power give the only satisfactory means of esti- edge when cut, and will not exhibit syneresis” (20, 16). .A mating pectin. The need for an accurate method for de- 160-grade citrus pectin, as supplied bj’ the California Fruit termining jelly strength was also stressed. Growers’ Exchange, is one which, when used in a jelly conTarr, Baker, and bleyers (6, 7 , 12-14) have published a taining 65 per cent by weight of sugar, will produce a satisseries of comprehensive pertin studies, with particular refer- factory jelly when present with a proper amount of acid in ence to factors involved in the making of jellies. RIeyers and the proportion of 1 part of pectin to 160 of sugar. The Baker ( 7 ) suggest the use of the viscosity of pectin solutions properties to consider in connection with a standard jelly are as an index of pectin quality, but in a later publication they also discussed in some detail by Jameson (3) who points out conclude (8) that “the viscosity method of determining jelly- the misleading nature of some of the literature which fails ing power of a pectin has its limitations. It does not have a to consider the “tremendous variation” in pectin grade. general application but may be used to determine jelly grade When working with an unknoTm sample, it would of course
T
HE voluniinous literature
I N D U S T R I A L A N D E N G I N E E R I N G C H E PVI I S T R Y
700
1-01, 25,
KO.6
be necessary to try a number of different concentrations to find the particular concentration resulting in a satisfactory jelly. This method as indicated calls for an experienced judge and therefore involves a considerable personal equation. It is, however, quite in order to admit that the writer is acquainted with operators so skilled in "finger testing'' that their judgment within certain ranges of jelly strength is as reliable as any mechanical device. However, such skill necessarily requires long practice. Mechanical means of measuring jelly strengths have been suggested by several workers, among whom are Luers and Lockmuller ( 5 ) ,Spencer
brought to a full boil. The sugar is stirred in for 20 to 30 seconds, and the mixture again brought to a full boil. The total heating time will be close to 4.75 minutes. [Tarr (IS) used a method requiring a minimum of 22 minutes of cooking time.] When removed from the fire, the jelly should weigh 555 grams plus the weight of the pan. The jelly is skimmed after 30 seconds and a t once poured into the four glasses Glasses are skimmed after 2 to 3 minutes, and covered after 10 minutes. The jelly is left overnight and the jelly strength determined a t 20" * 2" C. the following morning, using the average of the four determinations. Most 160-grade commercial pectins give readings close to 45 by this method. However, appreciable variations have been observed between different pectin samples, all supposedly 160-grade, thus indicating the desirability of adopting a standard procedure leading to comparative numerical expressions. The rate of heating suggested in the above method is of considerable influence, and the rate of adding the sugar even more so; hence, the complete adherence to a standard procedure is essential in order to produce comparable results. The skimming of the glasses after setting 2 to 3 minutes is not always essential, but often considerable scum and bubbles will float to the top of the jelly after pouring, resulting in an uneven surface. After 2 to 3 minutes these may be easily lifted off with a spatula or the end of a spoon, leaving a perfectly smooth clean surface without in any way interfering n with the setting of the jelly. To an experienced observer CITRUS PECTINieoc . $30 the ease with which this skimming operation is made also 1 'IOXSUGAR 165% gives a preliminary idea of the quality of the jelly. m00% The temperature of 20" C. was chosen as one most easily 20 achieved in a laboratory having no elaborate temperaturel o controlled cabinet available. A higher temperature, as I I I I I 1 I indicated by Tarr and Baker ( I S ) , would mean a generally 3.2 JL, A&Y OF $?LIES A$%H 22 2D lower level of jelly strength, whereas a lower temperature FIGURE 1. EFFECTOF SUGAR CONCENTRATION ON OPTIMUM would greatly elevate the readings. At 10" C. the temperaPH CURVE ture gradient is far steeper than a t 20" C., an argument for the 2.5 grams of tartaric aoid gave pH of about 2.2. higher temperature as calling for less accurate temperature control. Thus, when a series of jellies which has been kept ( I I ) , and Fellers and Clague ( 2 ) . However, the Tarr and in a low-temperature cabinet is brought out in the warm Baker ( I S ) jelly strength tester seemed most promising for laboratory atmosphere, some important changes of temperapractical routine testing in the present experiments. This ture may occur before all are tested, whereas jellies whose Iaboratory has had occasion to work out a simple basic jellytemperature is more nearly that of the laboratory will show making procedure which, combined with the Tarr-Baker but slight fluctuations in temperature, and thcse fluctuations, gelometer (IS) has proved of considerable convenience in as already indicated, are of relatively less importance. the investigations.
STANDARD METHOD The empirical standard formula used in this laboratory for routine testing varies only in pectin quantity. However, as will be shown later, it lends itself readily to the separate testing of any one factor of jelly making, while maintaining all other factors constant. The routine formula is as follows: Pectin Acid tartaric Cereiose Water Sugar
Grams
A known amount
Total (including pectin) about
2.5 63.0 240.0 270.0
580.0
The utensils needed for a pectin determination are a 2quart (1.9-liter) saucepan, four 4-ounce jelly glasses (inside diameter a t top 58 mm., height 78 mm.), and four cover glasses or tin covers. A gas burner is adjusted so as to bring the jelly mixture to a vigorous boil in about 2.5 minutes. The pectin, acid, and Cerelose' are thoroughly mixed, stirred into the water, and 1 A fine granulated sugar (berry sugar) is also efficient for dispersing the pectin. For some comparisons, particularly when dealing with pectin preparations that are not readily soluble, it may be convenient first to add the water to the pectin-sugar-acid mixture in a 250- or 400-cc. beaker. With most pectin preparations thia is not a t all necessary.
ACIDITY A S D SUGAR COSCENTRBTION
The routine formula given above specifies a definite amount of acid and an Emount of sugar ccrresponding to 60 per cent of the net weight cf the finished jelly. According to Tam, hfeyers, and Baker (6, I Z ) , the optimum acidity is found within a rather narrow range and may be markedly shifted by the addition of certain salts; that is, we should expect i t to be a t different points for different pectins carrying different impurities. Were this generally true, it would be most difficult indeed t o obtain comparable results with any standard formula and prccedure as here suggested. Tarr et a]. (6, I S ) . however, deal only with acidities from about 3.5 to 2.5; yet very palatable jellies of good consistency have been observed t o have acidities between pH 2.0 and 2.2 as tested electrometrically. The manner in which the jelly is prepared, the time of cooking, and particularly the type of pectin (whether citrus or apple) have an important bearing upon acid requirements. The data here reported pertain to citrus pectin only. Tarr (IS)presents data to show the effect of concentration of sugar o n jelly strength. The sugar concentration is varied from 74.1 to 60.6 per cent, but, although his amounts of pectin and acid are kept constant, the total amount of jelly varies. Therefore, the pectin varies from 1 gram in 135
IKDUSTRIAL AND ENGINEERING CHEMISTRY
June, 1933
grams of jelly to 1 in 165, and the acid concentration varies in the same proportion, notwithstanding the fact that the author has previously shown the marked effect of varying the acid concentration. Tarr’s data, therefore, cannot be used to indicate the effect of sugar concentration on jelly strength a t a constant pectin concentration. Furthermore, data on effect of sugar concentration are meaningless except in so far as they are correlated with pH observations. Using the basic procedure as above der;cribed, but varying the acidity a t three different sugar levels, some intereding observations were made. The pectin used was a commercial citrus pectin which had been extracted with 60 per cent alcohol to remove sugars and salts added by the manufacturer for standardization purposes. The amount used was maintained constant a t 3.00 grams for each jelly. The tartaric acid varied from 0.100 to 5.00 grams. The total time of heating was close to 4.75 minutes in each case. The pH was taken on the finished jellies by the quinhpclrone method. The sugar concentration was varied as follow: AMOTJNTS
FINALN E T IVEIGHT O F JELLY Grams 555 555 555
USED
SERIES
Sugar Grams 333 361 389
A
B C
Water Grams 240 212 184
701
centration. At proper sugar levels this results in optimum peaks such as are shown here for the 70 per cent and to a lesser extent for the 65 per cent jelly. At lower concentrations the jelly sets sufficiently slowly a t all acid concentrations so that the optimum peak disappears entirely. These data indicate rather conclusively that the drop beyond the optimum cannot be due to acid hydrolysis of pectin.
FINAL SEGAR CONCN.
% 60
65 70
Aside from the fact that varying the acid concentration unavoidably causes a small variation in total solids, all factors were held constant a t each sugar level with pH as the only variable. The results are shown in Table I and Figure 1. It is apparent from Figure 1 that conclusions regarding optimum pH reached from work a t any one given sugar concentration may not hold a t all for some other sugar concentration. It is clear, however, that for 60 arid 65 per cent jellies there exists a range, which may be roughly stated to begin a t p H 2.6, beyond which further change in acidity has little effect upon jelly strength. With 60 per cent jellies and such samples of citrus pectin as have been tested, 2.5 grams of tartaric acid result in a p H of 2.1 to 2.2, which is well within this range of nearly constant jelly strength.
FIGURE2. RELATIONOF PECTINQUALITY ASD QUANTITY TO JELLYSTRENGTH
Spencer (11) took issue with TarrJs interpretation of the optimum acidity as a basis for assuming a definite pectin-acid combination but suggested that the optimum was rather the point in the “hot method” a t which hydrolysis begins to predominate over the strengthening effect of the acid. The author agrees with Spencer that the optimiim is due to the method rather than to any fundamental acid-pectin combination, but objects to the inference that the dropin jelly strength is necessarily correlated with hydrolysis of the pectin. At least it is difficult to understand how, as in the case of the 65 per cent jellies, the rate of acid hydrolysis could increase so rapidly between pH 2.9 and 2.6, but show no additional TABLE I. EFFECTOF PH AT DIFFERENT SUGAR COKCESTRATIOXS increase from pH 2.6 to 1.9. The fact that the 60 per cent o s JELLYSTRENGTH OF CITRUS PECTISJELLIES curve shows no drop a t all also argues against such an expla-60% JELLY 65% JELLY 70% JELLY nation. The data presented appear, however, to be in comSERIES C SERIES D EXPT, p g R 1 y L a pgRIEs J.S. PH J.6 UH J . S . plete agreement with the views of Cole, Cox, and Joseph (1). 1 3.12 0 2 . 9 2 14 3.10 37.5 i.64 37 2 3.00 2.72 18 41 2.98 66.5 These authors pointed out that “premature gelation” depends 3.27 60 3 2.85 31 2 . 5 9 42 71 3.09 76 2.87 upon the setting rate of the jelly, and that the latter is greatly 4 2.78 39 44.5 2 . 7 8 62 2.55 2.96 81 5 2.69 42 42 2.44 63 2.92 2.78 73 accelerated by slight increases in sugar concentration. Fail6 2.63 42 2.16 65.5 2 . 7 8 78 46 2.71 7 2.56 42 46 2.15 ure results if the jelly is not made and poured within the time 64.5 2.75 58b 2.71 8 2.46 41 58.5 47 2.37 1.90 2.60 56 b limit of the sugar-acid-pectin combination used. Other ob9 2.04 46 2.08 ... 57.5 .. 1 . 8 9 46 10 ... 1 . 8 9 58 .. servations made here further tend to corroborate this view. “ Jelly strength. To explain the drop in jelly strength beyond the optimum, b These jellies started to set (curdled) in the pan before they could be poured: this tendency evidently causes the rapid drop in jelly strength at all that is necessary to assume is a rate of setting which is too acidities beyond the optimum. rapid to permit the proper mixing and pouring of the jelly The 70 per cent curve is interesting. With acid concentra- ingredients. Of course, prolonged heating must result in tions beyond the optimum, a point is quickly reached a t hydrolysis of pectin and should result in a general lowering of which premature gelation or curdling occurs. This curdling jelly strength and some shift in the optimum pH, but the apparently is the cause of the rapid and uneven drop in jelly major cause of the abrupt drop is probably purely manipulastrength. The last two jellies in this series were extremely tive. turbid. The tendency to gel formation appears to be markJudging from accumulated but as yet unpublished data edly accelerated by the two factors-sugar and acid con- involving the use of other pectins, the curves in Figure 1
-
PECTIN A
B
C D
E F
G
a
-1.0
TABLE11. RELATION OF PECTIN QUALITY AND QUANTITYTO JELLYSTRESGTH 1.4
0 0
0
7
1.5 9.5 6.5 0
... ... ... ...
Repreaents 2 . 7 grams pectin.
1.8
.. .. ..
23
..
.. .. b
2.0 23 21.5 0
..
-PECTIK 2.2
.. ..
(grams in standard formula) 2.5 3.0 3.5
5i:5
48 45 4.6 78.5
22
34
Represents 3.2 grams pectin
0
87
87 10 106“ 4 61 5 30
...
125 18.5
...
9 74.5h 52
4.0
.. ..
34
..
69:5
4.35
.. .. 45 .. .. .. ..
4.50
4.70
5.5
.. .. ..
60
..
.. .. ..
...
...
25
...
105
..
..
.... ..
..
48
.. ..
702
IXDUSTRIAL AND ENGINEERING CHEMISTRY
must be considered typical rather than absolute; that is, different pectins show the same general behavior but the optimum may occur a t a different pH, and the transition from one type of curve to the other may occur a t a different sugar level. Spencer (11) reasons that the function of the acid is to decrease the amount of water absorbed by the pectin, which is another way of saying that acid renders the pectin less soluble in the presence of sugar. As yet no clear theory has been p r e s e n t e d to show just how the a c i d c a u s e s this change. It is conceivabIe that the hydrogen ion functions by r e d u c i n g the negative charge of the pectin particle t o a point where it is readily precipitated by the sugar. This would explain why the necessary sugar concentration i n c r e a s e s rapidly with decreasing hydrogen-ion concentration. It is also in agreement with the observation that the so-called optimum pH is different for different acids, and w i t h t h e fact FIGURE 3. LOGARITHMIC RELATION OF t h a t this optimum PECTrlV QU.~LITY A N D QUANTITY TO JELLY STRENGTH may be changed by the addition of various salts. On this basis it may be assumed that the optimum p H is that point a t which incipient pan gelation becomes a measurable factor in the jelly strength.
PECTIX COWEXTRATION I n order to compare results obtained with different pectins and a t different pectin concentrations, i t is necessary to know how the jelly strength varies with the concentration and whether the proportionality between different grades of pectin may be considered constant over any considerable range. If, for instance, it takes 2.5 grams of a 160-grade pectin to give a reading of 47 on the Tarr-Baker jelly strength tester, and an unknown sample requires 1.6 times as much or 4.0 grams to give the same reading, the latter rvould be regarded as a 100-grade pectin, but one would still have no basis for knowing whether the same proportionality would hold a t other proportional concentrations. On the other hand, if both of these samples were used on the basis of 3.0 grams per standard batch of jelly, one would find for the POcalled 100-grade pectin a reading of about 9 or less, and the 160-grade would give 85 to 90-that is, no apparent relationship of the values obtained. For these reasons some time has been spent in studying different citrus pectins over a considerable range of concentrations. These pectins have varied from what may be considered an SO-grade pectin to a pectin grading about 250. The commercial samples were tested as received. Some representative series of results are expressed graphically in Figure 2, and are summarized in Table 11. These jellies were all made in strict accordance with the standard formula given. All contained 60 per cent sugar. Table I1 and Figure 2 show the great variation in the amount of pectin from different lots necessary to give any
Vol. 25, No. 6
selected jelly strength. We may, however, obtain numerical values representing the grade of pectin by choosing one of these curves as a standard and comparing the grams of each pectin necessary to give the same reading on the gelometer according to the follon-ing formula: G,S
- = G,
where G, S x G,
= = = =
grade of pectin used as standard grams of standard pectin corresponding grams of unknown sample grade of unknown sample
Thus, if we assume C in Table I1 to be standard 100-grade, we have a t 34 the relationships shown in the third column of Table 111. TABLE 111. EVALUATIOS OF PECTISS ON BASISO F PECTISGIVINGJELLY STRESGTH OF 34 PECTIN
a
PECTINGIVIXG -GRADE-JELLYSTRENGTH O n basis OF
34 CM. Grams
C
= 100
. ~ o U N T OF
On basis
. 1 = 160
Standard
Actually, on the basis of the comparison of a number of commercially graded lots, samples A and B are both of average 160-prade, and have been used as standards in subsequent work. Using -4as standard, the grades become those indicated in column 4. It is apparent that care must be used in selecting the proper standard of comparison. It may be stated that samples A, B, and F were all bought as 160-grade pectin.
LOGARITHMIC CURVES Curves such as are shown in Figure 2 necessitate a number of determinations in order to predict the amount of any given pectin necessary to give a desired jelly strength. I t has been observed, however, that the log of the concentration of pectin (expressed as grams per standard formula) is directly proportional to the log of the jelly strength. A similar relationship has been shown to exist between the concentration of gelatin in, and the Young’s modulus of gelatin gels. The theoretical foundation for that relationship has been comprehensively discussed by Poole (9). The plotting of the logs of the jelly strength against the logs of concentrations of pectin, or, what is more practical, the plotting of the original values on logarithmic paper, greatly facilitates direct comparison of different pectins and permits of easy extrapolation beyond the range actually determined. Figure 3 shows the data of Table I1 plotted in this manner. It is apparent that the increase in jelly strength is directly proportional to the change in pectin Concentration, except for very low figures. These low figures, while not shown on the graph, all fall below the point indicated by the straight line to be correct. This consistent error is no doubt due to the weight of the plunger which, in jellies of very low strength, becomes an important factor. It is self-evident that, while a difference of 1 or 2 cm. makes little difference in plotting the higher values on a logarithmic scale, such a difference causes considerable deviation in figures below 10. In plotting these graphs we should, strictly speaking, make a correction for the weight of the plunger, or else not consider any low points in plotting the curves. The parallelism of the lines plotted is a measure of the extent t o which these different pectins are comparable a t different jelly strengths. Thus while the ratio A/C = 1.76 a t
June, 1933
INDUSTRI.4L AND E N G I S E E R I N G
CHEAIISTRY
703
(3) Jameson, Eloise, ISD. Eso. C m i r . , 17, I291 (1925). (4) Johnstin, R u t h , and Denton, M. C., Ibid., 15, 7 8 - 8 0 (1923). ( 5 ) Liiers. H.. a n d Lockmiiller, K.. Kolloid-2.. 42, 154-63 (1927).
jelly strength 34, it becomes 1.74 a t 7 5 hard]) a significant difference. Other pectins may show greater deviation from the parallel, howel-er, by making tn-o or three accurate determinations m-ith different concentrations of a n unknown pectin; the correspclnding points may be plotted in the above manner and, by drawing a straight line through them, this pectin may be compared a t any desired concentration or jelly strength with whatever standard is chosen for a particular purpose. The inherent errors in determinaticins made on extremely weak jellies should be borne in mind.
(12) (13)
LITERaTURE C I T E D
(14)
(1) Cole, G . hl., Cox, R. E., and Joseph, G. H., Food lnd., 2,219-21 (1930). , Anal. E d . , (2) Fellers, C. R , anti Clague, J . A , IYD EAG.C"EV 4, 106-7 (19.32)
(15) (16)
(7) (8)
hleyers, P. B . , and Baker, G. L., Univ. of Del. Agr. Expt. Sta., Bull. 144 (1926). Ibid., 149 (1927). I b i d . , 160 (1929). Poole, H. J., Trans. Faraday SOC.,21, P t . I, 114 ( 1 9 2 j ) . Rooker, IT.A,, "Fruit Pectin," p. 118, Avi Pub. Co., 1928. SDencer. Gene, J . Phws. C'hem., 33, 1987-2011 (1929); 34, 664-5 (1930). T a r r , L. IT-., Univ. of Del. Agr. Expt. Sta., Bull. 134 (1923). T a r r , L . IT.,Ibid., 142 (1926); Baker, G . L., IKD. ESG. CHEM., 18, 69-93 (1926). T a r r , L. IT., and Baker, G. L., UniT. Del. Agr. E x p t . S t a . , Bull. 136 (1924). TTilSOn, P., ISD. ESG.C"E\I., 20, 1306 (1928). Kilaon, C . P., private communication, April 25, 1927.
c.
KECEITEDAugust 18, 1932.
Stabilization of Paunch Manures and Packing-House Screenings C. S. BORUFF, State Water Survey, Vrbana, Ill.
T
B y the use qf a special drum type qf digester
recovered between 15OOalld 2000 pounds (680 and 910 kg.) of wet qcreenings per day from the 32posal of organic wastes caffle and hog paunch nlanures and packingscreen enlployed. These is g r e a t l y s i m p l i f i e d if these rates of screenings are dried and buriied house screenings f e d coniinuousb Ivastes can be handled in a concentrated forni. In the packing at least 4.5, 6.0, and 5.6 grams dry weight, in a n e a r - b y r a v i n e . F i n e respectirely, per day per liter of tank capacity screens of 20-, 30-, and 40-mesh i n d u s t r y t h e wastes that are (0.28, 0.37, and 0.35 pound per cubic foot per have been found to remove 368, readily separatedin concentrated 858, and 1270 pounds dry weight, form include t h e paunch day). The stabilization of such materials furrespectively, of manures, pen manures, and the illaterial that is or could be col71ishes fron) 1.0 to 4.0 t'olumes Of combusfibk screenings per million gallonr gas per day per tank volume. The amount of (0.04,0.10,and0.15kg.percubic lected by p a s s i n g the l i q u i d wasteordrainagethroughgreasegas depends on the rate of feeding and the type meter) (16). Iielson (18) reskimming tanks and finescreens. of u,aste treated, A and satisfactory p;rts the r e m o v a l of 5000 t o 1a,OOO pounds of screenings of Most packing-houses are keeping residue is produced. 80 to 85 per cent moisture I)er the g r e a t e r p o r t i o n of their million gallonsof wa>te (0.6 to 1.8 p a u n c h m a n u r e s out of the sewers. Many plants are also passing their liquid wastes kg. per cubic meter). This laboratory and others ( I O ) have through coarse or fine screens (10 to 32 mesh). I n most cases found screenings to contain 85 to 95 per cent volatile matter, these materials are hauled away to a clump where they slowly 1.5 to 7 per cent organic nitrogen, and G to 23 per cent etherdry and eventually may be burned. This is ofi'ensive and soluble substances. Fine screens remove from 9 to 19 per cent requires considerable waste land. Some plants use a portion of the total settleable solids. of these wastes in the manufacture of fertilizer. The ecoTo these already large weights of screenings niwt be added nomics of such a practice depends entirely on the market. the paunch manures. For cattle these amount to about 10 The present writer has considered the problem of the disposal pounds (4.5 lig.) dry weight per animal. From a plant of these manures and screenings and wiqhes to propose what killing about 10,000 cattle, 20,000 sheep, and 25,000 hogs seems to he a practical method for their treatment and per week, one might expect to recover in the order of 200,000 utilization. pounds (96,000 kg.), dry weight, of paunch manure. On the d considerable amount of n-ork on the treatnient of liquid- basis that such a plant had a semage flon- of 7.5 million gallons or water-carried pacliing-house wastes (sewage'i has been per day (28,400 cubic meters), there could be recovered a t done by other ivorkers (1, 2, 7-22). A consideration of this least an additional 1000 pounds (453 kg.), dry weight, of part of the general problem lies outqide the purpose of this fine screenings per million gallons, or a total of 36,000 pounds (16,300 kg.), dry weight, of paunch manure and screenings discussion. per day. This would remove the greater portion of the fibrous materials from the sev-age but would leave in it c0S C EKTRATED 1i7-4STES enough to aid in the settling of other solids in sedimentation At one prominent packing plant 5000 pounds of coarse tanks. Such a removal TT-ouldmaterially lighten the total screenings of about 85 per cent moisture content are being solids pollution load. Disposal of such a weight of paunch recovered per day per inillion gallons of flom- (0.6 kg. per manure and screenings on waste land or by partial drying cubic meter). At another plant, where an average of 150 followed by incineration would be troublesome, offensive, cattle, 300 hogs, and 200 sheep are killed each day, there are and expensive (5). These methods have other disadvantages.
HE consensus of opinion is that the problem of dis-
it has bee,%found possib[e f o digest and sfabilize
