Apparent and True Solids of Sugar-Cane Juice Relation of Difference to Ash Content CHARLES A. FORT, Bureau of Chemistry and Soils, AND NELSON MCKAIG, JR., Bureau of Plant Industry, U. S. Department of Agriculture, Washington, D. C.
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T IS OBVIOUSLY proper to append the conditional term "apparent" to the per cent solids or degree Brix of impure sugar solutions when they are determined by any specific gravity method, because such an estimation is partly based on the false premise that the various impurities have the same specific gravity as sucrose. It is generally known that the apparent solids of cane juice, sugar-house sirups, and molasses are considerably higher than the actual solids found by drying. The principal cause of this difference between apparent and true solids is the effect of the high specific gravity of the salts present in these products as compared with the density of sucrose itself. The influence of the reducing sugars and the organic nonsugars is thought to be of small importance and probably tends to counteract slightly the effect of the inorganic constituents. Discussion of these points will be found in the handbooks by Browne (5) and Spencer and Meade (9) and in papers by Hill (6) and King ( 7 ) . Little information has been found in the literature concerning the amount of the difference between apparent and true solids or of its mathematical correlation with the ash content except that given by King (7) for Philippine molasses. King published a summary of the observed differences between the apparent and true solids of a large number of molasses samples and showed that there existed a general relationship between the amounts of these differences and the ash contents. He proposed the calculation of the true solids from the apparent solids and ash by use of an ash factor. I n view of his results, the data on solids and ash of some crusher juices which were analyzed during a general study of juice composition in Louisiana have been examined, and the results of this work form the material for the present discussion.
sirups were subsequently diluted to approximate juice density and analyzed in the same manner as the raw juice.
Discussion of Results The observed differences between apparent and true solids ranged from 0.21 to 1.24. The frequency curves in Figure 1 summarize the complete data on the amounts of these differences and also on the percentages of ash. These curves, although they do not take into account the concentration of total solids, do exhibit a general relationship to each other. The differences between apparent and true solids are much larger than the combined experimental errors, and hence it follows that they are due principally to the intrinsic composition of the juices and must be related to the quantity or the specific gravity of the nonsugar constituents, or both. The experimental errors, particularly in the apparent solids determination, affect considerably the differences between the apparent and true solids found in individual determinations. For the same reason any correlation of ash with these differences, when considering samples singly, may give erratic results concealing the probable relationships. However, since the errors involved are random, rather than systematic, it follows that the average of the results from a number of tests will be more reliable and the correlations will be more evident.
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Experimental During the 1931 cane harvest over 200 samples of crusher juices representing various cane varieties, soil types, and fertilization tests were obtained through the cooperation of the Divisions of Sugar Plant Investigations and Soil Fertility Investigations of the Bureau of Plant Industry, stationed a t Houma, La. These raw juices were first freed from such adventitious coarse suspended material as could be removed by a standardized moderate centrifuging in a solid basket, followed by screening through a 290-mesh sieve. The apparent and true solids and the ash were then determined. The apparent solids or apparent Brix were estimated with a Brix spindle calibrated for 17.5" C., and the observed reading was corrected to that temperature by the usual tables. Solids by drying were determined b the official method of the Association of Official Agricultural shemists (Z), the drying being completed In a constant-temperature vacuum oven operated at 70" C. and a vacuum of 27 inches. Numerous duplicate tests made t o determine the degree of precision of the methods indicated that for the apparent solids the average deviation from the mean was probably +0.05' Brix or more, whereas for the solids by drying the deviation was only d0.01 per cent solids. The ash content was determined by evaporation of a definite quantity of juice t o a thick sirup over a water bath, followed by gentle charring over a hot plate. The ignition was completed in an electric muffle at not over 500" C. Ash content was calculated as percentage based on apparent solids. For duplicates the average deviation from the average was 10.03 per cent ash. In addition t o these tests on raw juices about 4 liters (I gallon) of each lot of juice were clarified by a standard method, using either lime alone or the sulfur-lime process. The clarified juices mere evaporated to about 55" Brix in a vacuum pan. The
A B
FIGURE1. FREQUENCY CURVES A.
B.
Difference between apparent and true solids Per oent ash, based on apparent solids
The data were therefore grouped and averaged, first by cane variety, using only such tests as were strictly comparable. It was found that the average difference between the apparent and true solids was different for each of the six varieties compared and was related to the characteristic ash content of the variety. I n like manner, other data were grouped and averaged according to soil type and also with respect to fertilizer treatment, and were found to give average differences between apparent and true solids which were definitely related to the ash content of the juices. A general correlation was apparent, and it remained to determine the mathematical expression. It is probable that two principal factors influence the magnitude of this difference between the apparent and true solids: first, the ratio of the ash to the total solids, and, second, the concentration of the solids. The former determines the deviation of the specific gravity effect of the solids from that of pure sucrose produced by the ash, and the latter is concerned with 333
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the ash contents. For the correlative factors that were TABLEI. DIFFERENCE BETWEEN APPARENTAND TRUESOLIDS derived, however, even the maximum variation between the AND CORRELATION WITH ASH CONTENT OF INDIVIDUAL SAMPLES varieties is much less than the value required to be moderately OF CRUSHER JUICE significant. This indicates that, in the average factors, for D all practical purposes one is dealing with a constant. Similar C A B X, Final Ash based Apparent True Difference, on Appar- Quotient, Factor, studies of the results from samples, comparing the effect of A-B Sample Solids Solids ent Solids C/D X/A soil type and of fertilizer treatment, likewise show that these % % % conditions affect the apparent and true solids, their dif0.0124 1.95 0.200 1 15.70 0.39 16.09 0.0104 0.159 2 14.77 0.49 3.09 15.26 ference, and the ash content of the juice, but do not signifi0.0112 0.172 3.43 3 14.77 0.59 15.36 0.0132 0.195 3.49 cantly change the value of the derived correlative factor. 4 14.08 14.76 0.68 0.0119 0.169 5 13.44 14.21 4.56 0.77 The general average of all the factors calculated from these 0.0127 0.184 4.73 6 13.59 14.46 0.87 7 0.155 0.0127 11.47 12.19 0.72 4.63 analyses of crusher juices from Louisiana sugar cane was found 0.173 0.0123 0.64 3.69 8 13.37 14.01 0.203 0.0134 to be 0.0120, and the average factor for the corresponding 15.11 0.50 2.46 14.61 9 0.0102 0.169 3.44 16.06 16.64 0.58 10 sirup samples was 0.0108. This lower value of the factor for 0.178 0,0120 Average sirups is possibly due to the elimination of the phosphate ions 10.014 *0.0010 Average deviation from average during clarification. An example will illustrate the use of these factors in estiTABLE11. DIFFERENCES BETWEEN APPARENTAND TRUE mating the true solids from the observed apparent solids and SOLIDSAND CORRELATION WITH ASH CONTENT ash. Assume a raw juice of 17.0" Brix with an ash content of (Based on averages for seven crusher juice samples for each sugar-cane variety) 2.5 per cent on solids. To find the probable differencebetween D the apparent and true solids, multiply as follows: 0.0120 x A B Average Averagea Average Average Average Ash Based Averagea Final 17.0 X 2.5, which yields the value 0.51. Subtracting this Sugar-Cane Apparent True Difference on ApQuotient, Factor, amount from the observed apparent solids, one obtains 16.49 Variety Solids Solids A - B barent Solids C/D X/A % % % as the estimated true solids. POJ36M 14.99 14.50 0.49 2.80 0.178 0.0119 The use of the factors may be simplified by the construction POJ213 14.58 14.03 0.55 3.01 0.186 0.0128 of a suitable nomograph or table for the range of ash and solids POJ234 15.52 14.97 0.55 3.13 0.181 0.0117 Co 281 15.65 14.96 3.63 0.191 0.0122 0.69 commonly encountered. Figure 2 and Table 111 exemplify Co 290 15.25 14.56 0.191 0.0125 0.69 3.73 C P 807 14.52 13.89 0.185 0.0127 0.63 3.44 such arrangements applied to Louisiana crusher juices. I n Average 0.60 3.29 0.185 0.0123 presenting these factors and the table for converting apparent *0.0004 Bverage deviation from average 1 0 . 0 7 10.31 t0.004 Significant differences:b to true solids, it is not claimed that these particular values P = 0.05 10.05 10.17 *0.018 *0.0013 will hold universally. Differences in the technic of the deterP = 0.01 *0.07 10.23 10.024 10.0017 minations of the apparent and true solids and the ash will Averages of quotients calculated for individual data. b The statistical differences were calculated by using the formulas of cause variation in the factors from the values given; also, Fisher (4) to correct for correlated variations. The application of these formulas to field tests on sugar cane has been made by Arceneaux ( 1 ) . differences in ash composition will produce slight changes in the factors. Nevertheless the values given may be very close to those that would be obtained from a much greater number the total effect on the weight of a particular quantity of solids of tests and from other locations, for the samples included in of this density. Although the composition of the ash, and this study represented a wide variation in both per cent consequently the specific density effect of the salts, is someof ash and ash composition. The cane used was grown on what variable, there is no evidence that this variation is sufmanv different soils ficient to alter significantly the average specific gravity of the k k B of dikinct types with Apparat True Ash on total inorganic material. Solids Solids Solids v a r ie d fertilization Based on this reasoning a factor was derived as follows: (1) and d r a i n a g e , and the observed difference between apparent and true solids was the d i f f e r e n t cane divided by the percentage of ash (based on apparent solids 0.5 v a r i e t i e s included content) and (2) this quotient was divided by the percentage those with both highof apparent solids. The first quotient gives the difference 1.0 and low-ash characbetween apparent and true solids due to 1 per cent of ash, teristics. In any case and the factor in its final form expresses the difference for 1.5 it seems p r o b a b l e each 1per cent of solids due to each per cent of ash. that the application It is impractical to include all the data in this publication, 2.0 of the principles used but two tables are presented as examples of the method outin this study will yield lined and of the results obtained. Table I shows the data 2.5 a factor a t any given for a representative group of samples selected to give a typical location which can be cross section of all the juices tested. The average variation 3.0 used to estimate the in the derived factors is equivalent to only *0.05 per cent true solids from the solids, which is essentially the experimental error of the apdetermined apparent 14.5 3*5 solids and ash with parent solids determination. Table I1 gives the averages of groups of seven tests for each of six commercially important satisfactory a c c u cane varieties, and shows the increased uniformity in the calculated factors which is attained by dealing with averages To find what ac13.5 instead of single determinations. The group factors have a 4'5 curacy might be exmuch smaller deviation from the general average than those of pected from the use of individual tests. 13.0 5*0 the conversion values Statistical examination of the data presented in Table I1 as given in Table 111, shows that in the actual amounts of the differencesbetween the U.6 5.5 they were applied to apparent and true solids there are several comparisons which the published work of indicate highly significant differences between certain varieLauritzen and [Balch ties. These of course correspond to significant differences in FIGCIRL 2. NOMOGRAPH (8)on storage of cane.
To
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In their report are data for apparent and true TABLE 111. CORRECTIONS FOR CONVERTINQ APPARENTTO TRUE solids and the ash on about 60 crusher juices. As SOLIDSOF CRUSHER JUICES the ash was given as per cent on true solids, it was (Subtract the proper correction from the determined apparent solids.) first recalculated to the apparent solids basis. % Apparent Solids 14.0 14.5 15.0 15.5 16.0 16.5 17.0 17.5 Then using the tabulated corrections to estimate Ash oII Solids 18.0 the true solids from the apparent solids and ash, 2.0 0.34 0.35 0.36 0.38 0.39 0.40 0.41 0.42 0.44 it was found that the values obtained for the true 2.2 0.37 0.39 0.40 0.41 0.43 0.44 0.45 0.46 0.47 2.4 0.41 0.42 0.44 0.45 0.47 0.48 0.49 0.51 0.52 solids agreed with the amounts reported, with an 2.6 0.44 0.46 0.47 0.49 0.50 0.52 0.54 0.55 0.57 2.8 0.48 0.49 0.51 0.53 0.54 0.56 0.58 0.59 0.61 average deviation of only *0.03 per cent solids. 3.0 0.51 0.53 0.55 0.56 0.58 0.60 0.62 0.64 0.65 Comparing the small amount of this error with 3.2 0.54 0.56 0.58 0.60 0.62 0.64 0.66 0.68 0.70 the large difference between apparent and true 3.4 0.58 0.60 0.62 0.64 0.66 0.68 0.70 0.72 0.74 3.6 0.61 0.63 0.66 0.68 0.70 0.72 0.74 0.76 0.79 solids, the approximation of true solids by this 3.8 0.64 0.66 0.69 0.71 0.74 0.76 0.78 0.81 0.83 method gives, even in the case of individual tests, 4.0 0.68 0.70 0.73 0.75 0.78 0 . 8 0 0.82 0.85 0.87 4.2 0.71 0.74 0.76 0.79 0.81 0.84 0.87 0.89 0.92 a figure which represents the true facts rather 4.4 0.75 0.77 0.80 0.83 0.85 0.88 0.91 0.93 0.96 4.6 0.78 0.81 0.84 0.86 0.89 0.92 0.95 0.98 1.00 closely. A more careful determination, especially 4.8 0.81 0.84 0.87 0.90 0.93 0.96 0.99 1.02 1.05 of the apparent solids, will make the estimation of true solid? of individual samples still more accurate. This can be done, for example, by taking reported by Lauritzen and Balch (8) and the resultant apthe readings only a t the temperature for which the hydronieproximate true sucrose divided by the calculated true solids, ter is calibrated, thus eliminating the use of the correction the estimated true purities agreed with those determined tables which are also falsely based on pure sucrose solutions. with an average deviation of 1.0.70. Since for this purity While it is possible that the exact value of these factors will the usual difference between apparent and true purity is be different in other sugar-producing territories, some indicaabout 5.00 per cent, this apparently rather poor agreement tion that they may not vary significantly was obtained by a appears satisfactory. These samples varied widely in purity, further study of the data reported by King (7) on Philippine and much better results will be obtained when the proper molasses. His data for ash were recalculated to per cent on average sucrose correction value for each purity is used. apparent solids. Then dividing the reported differences between apparent and true solids by the per cent of ash and Summary then by the per cent of apparent solids and finding a weighted The difference between the apparent and true solids of average of the resulting factors, the figure 0.01079 was obcrusher juices and of the sirups produced therefrom can be tained. This is practically identical with the factor 0.01080, arithmetically correlated with the ash content. By use of which was found for the Louisiana sirups. In the work of factors determined for this relationship it is possible to estiKing, as in this study, the sirups or molasses were first diluted mate the true solids from the determined apparent solids to near juice density before analyzing. If the apparent solids and the per cent of ash on solids. For the raw juices the factor had been determined a t high density the relationships would found was 0.0120 and for sirups 0.0108. When the proper have been different. factor is multiplied by the per cent of ash on solids and the Considering the large difference which exists between apper cent of apparent solids, one obtains the estimated difparent and true solids, especially when the ash content or ference between the apparent and true solids. The subtraction solids are high, it is evident that the factory records of losses of this product from the observed apparent solids yields the and efficiency are much in error when only the apparent values approximate true solids. The accuracy of this estimation is are used. A discussion of this point by Hill (5)gives examples principally dependent on the accuracy of the apparent solids of such misleading results. In spite of such results, the use of determination, and the calculated true solids seem to agree the densimetric methods by the sugar industry and by workers with that determined within the normal limits obtainable in in the agronomic phases of sugar-plant research has been althis determination. These factors may apply only to Louisimost universal. This is in part due to the cheapness, speed, ana, but there is some evidence that factors of similar value and simplicity of the methods for apparent solids as commay hold generally. The method of deriving the factors is pared with the expensive equipment and time needed to determine solids by drying. While to utilize the procedure just described, and a table and nomograph are given for rapidly estimating the “true” solids from observed apparent solids presented for estimating true solids involves the additional and ash. The possibility of approximating the true purity determination of ash, this should not require a large number of juices, by use of a corrected apparent sucrose and the of tests per day, as the ash on a composite sample of each estimated “true” solids, is discussed. product for each period for which records are made up should be accurate enough to derive the solids correction to be used. Literature Cited In a similar manner, in research work where the data from (1) drceneaux, G., International Society of Sugar Cane Technologists, several tests for solids are to be averaged it is only necessary 4th Congress, Bull. 47. to find the ash on a composite of the samples to be averaged. (2) Assoc. Official Agr. Chem., Official and Tentative Methods of As a development of this method of approximating true Analysis, 2nd ed., p. 178; 3rd ed., p. 364. solids, the true purity can be closely estimated using calcu(3) Browne, C. A., “Handbook of Sugar Analysis,” pp. 35 and 6 7 , New York, John Wiley & Sons, 1922. lated true solids and a corrected sucrose value. The difference (4) Fisher, R . A4.,“Statistical Methods for Research Workers,” between apparent and true sucrose varies with the per cent of 2nd ed., London, Oliver and Boyd, 1928. reducing sugars and to a lesser degree with their composition. ( 5 ) Hill, H G., Facts About Sugar, 22, 182 (1927). To obtain an approximate true sucrose from the apparent (6) Ibzd., 25, 568 (1930) (7) King, R . H . , IND.EKG.CREM.,Anal. Ed., 3,230 (1931). value average correction values found for different apparent (8) Lauritzen and Balch, Dept. Agr. Tech. Bull. 449 (1934). purities may be used. A more complete discussion of these 19) Spencer, G. L., and Meade, G. P., “Handbook for Cane-Sugar sucrose conversion values will be made a t a future time. Manufacturers,” 7th ed., p. 320, New York, John Wiley & As a preliminary example the figure 0.30 was found as the Sons, t930. average difference between apparent and true sucrose for RECBIYED June 5. 1936. Presented before the Division of Sugar Chemistry crusher juices with an average of 80 per cent apparent a t the 89th Meeting of the American Chemical Society, New York, N. Y., April 22 to 26, 1938 purity, When this amount was added to the apparent sucrose ~~
