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12,
No.
11
b y the formation of a double salt (PbS04.S04HCzH6), 3 4 . 7 8 per cent was reached in 1 7 days, which he states b u t the action of broken porcelain rather seems t o dis- was not the maximum. prove this theory and inclines us t o the view t h a t the S I G N I F I C A N C E O F MOISTURE CONTENT O F F L O U R rapid and regular evolution is due t o physical or I t seemed desirable t o ascertain the moisture consurface action. This view is strengthened by the ’tent of flour in atmospheres of differing but constant fact t h a t irregular evolution of ether actually com- humidity, after a period of exposure sufficiently long mences at the lower temperature, even if no lead sul- t o permit the hygroscopic moisture of the flour t o fate is present. reach equilibrium with the atmosphere. Such d a t a The observations recorded are interesting, also, would be of service in a number of ways. Shippers, because the choice of lead for the construction of a purchasers, and food control officials dealing with manufacturing still, which was made necessary by t h e flour need more precise information concerning changes character of the reagents, resulted in an improvement in moisture content, and consequently in the net weight in the process t h a t could not have been foreseen from of flour packages. The baker and storekeeper need laboratory experiments in glassware, and in fact such d a t a for the same reason, and, in addition, are had heretofore been largely overlooked. concerned with the indirect effect of changing moisture Credit is due t o Mr. W. M. Billing for carrying out content upon the keeping qualities of flour on prolonged storage. Flour which reaches a high moisture the laboratory work. content is quite likely, if kept moderately warm, t o become unsound through t h e activity either of its own T H E HYGROSCOPIC MOISTURE O F FLOUR EXPOSED T O enzymes, or those of fungi, and especially molds and ATMOSPHERES O F DIFFERENT RELATIVE related forms, which develop on the moist flour. HUMIDITY’,’ Millers may find such d a t a of service in developing By C. H. Bailey8 methods of controlling the atmospheric humidity in DIVISION OF AGRICULTURAL BIOCHEMISTRY, MINNESOTAAGRICULTURAL mills and certain milling machines. Milling operaEXPERIMENT S T A T I O N , ST. PAUL, MI“. tions of the future will doubtless include more a t Received July 30, 1920 tention t o the moisture content of the streams a t It has long been known t h a t cereals and cereal prod- each stage of the process, and such control will be esucts are hygroscopic, and t h a t their moisture content tablished in large part by maintaining the proper may be altered by varying the conditions of exposure. humidity in the air in the various machines. Brewer (1883) details certain experiments which esMETHOD OF P R O C E D U R E tablish this property. Other investigators, i h l u d i n g The humidity of t h e atmosphere t o which flour was Willard ( I 9 I I), Neumann ( I 9 I I ) , Guthrie and Norris exposed was controlled b y contact with the surface of (I 9 I 2), Sanderson ( T 9 14), Swanson, Willard and Fit2 (1915), and Stockham (1917),have studied the sulfuric acid solutions. These solutions were prepared changes in weight and moisture content of stored after the Reynault tables in Landolt, Bornstein and flour. I n none of these experimentb, save those of Roth’s “Tabellen.”’ Four solutions were prepared, Stockham, have the atmospheric conditions apparently which were intended t o afford humidities of 30, 50, 70, been controlled throughout the period of exposure. and 80 per cent, respectively. I t was not deemed adGuthrie and Norris (1912) recorded the atmospheric visable t o attempt t o maintain the humidity above humidity each day during the period t h a t the flour 80 per cent because: (a) The flour is apt to mold in very damp atmospheres. was under observation, but their readings were ap(b) In most parts of the United States an atmospheric huparently taken a t one particular time each day, and hence do not represent the mean humidity for the midity in excess of 80 per cent is not likely t o be maintained several 24-hr. periods. Even had the latter been for a prolonged period. (c) It becomes more difficult to maintain the humidity at determined, it is doubtful if the hygroscopic moisture a constant level when in excess of 80 per cent. of the flour could be regarded as in equilibrium with Two samples of flour were used in these studiest h e mean humidity of the atmosphere, when the a patent and a second clear flour. Their chemical humidity fluctuated as suddenly and violently as apcomposition is shown in Table I. pears t o have been the case. TABLEI-COMPOSITION OF &OURS USED I N HYGROSCOPIC MOISTURE STUDIES Stockham (1917) reports the moisture content of -CALCULATED TO DRY BASISwheat, bran, shorts, and flour exposed in a “saturated” Crude Protein Acidity MOISTURE (N X 5.7) Ash (as Lactic) and “ d r y ” atmosphere, but did not employ any degrees SAMPLE Per cent Per cent Per cent Per cent of atmospheric humidity between these extremes. Patent.. . . . . . . 8.71 0.47 0.159 12.44 2.38 0.781 16.46 He found t h a t a comoosite samole of flour exoosed in a Second clear.. . 9.92 Five grams of each of these flours were placed in “still, saturated” atmosphere a t a temperature of 2 3 O C. (see p. 109) reached a maximum moisture content of tared, flat-bottomed, aluminium drying dishes, having 28.74 per cent in 9.12 days, a t which time it was moldy. a diameter of 50 mm. This quantity of flour filled I n a saturated atmosphere a t o 0 a moisture content of the dishes t o a depth of 5 t o 6 mm. The dishes were placed in desiccators, the lower part Of which was 1 Published with the approval of the Director as Paper No. 214, Journal filled with t h e appropriate sulfuric acid solution. The Series, Minnesota Agricultural Experiment Station. * Presented a t the 60th Meeting of the American Chemical Society, several desiccators were set in a thermostat having a Chicago, Ill., September 6 to 10, 1920. d
a With the cooperation of Miss Isabel Everts.
1
4th Edition, 1912. p 426.
Nov.,
1920
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
a temperature of 25 ’. This was t h e lowest temperature which could be constantly maintained in the basement rooms of the laboratory building during t h e spring and early summer months. Preliminary studies indicated t h a t i t required 6 t o 8 days for t h e flour t o reach equilibrium in moisture content. The time doubtless hinges in part on the difference between the initial moisture of the flour and t h a t which i t will ultimately attain. T o insure t h a t ample time was afforded, t h e dishes (all tests being carried out in duplicate) were left undisturbed for 8 days, weighed, returned t o the chambers for 2 days more, and again weighed. The difference between the first and second weighings was usually small. The dishes with their contents were dried t o constant weight at IOOOC. i l z vacuo, and the weight of the empty dish being known, t h e calculation of the initial and final moisture content of t h e flour was then possible.
110s
when they were exposed under identical conditions.. The curves are of the shape of a simple parabola, which, if extrapolated t o I O O percent humidity, would“ give values in terms of hygroscopic moisture not far. different from those reported by Stockham for the flours. exposed in a “saturated” atmosphere. TABLE11-HYGROSCOPICMOISTUREOF PATENT AND SECOND CLEAR: FLOURS IN CONTACT WITH ATMOSPHERES OF VARIOUS HUMIDITIES AT 2 5 ’ c . (78’ F.) Relative Humidity of ---Moisture of FlourAtmosphere at 25’ C. Per cent 80.0 69.8 50.3
29.4
Patent Per cent 15.00 12.05 7.93 5.18
Second Clear Per cent 15.00 11.65 7.81
5.11
The question a t once arises as t o how rapidly these. flours change in moisture content ,with variations in the. humidity of air t o which they are exposed. T h a t t h e . response is rapid may be deduced from t h e experiments of Guthrie and Norris (1912). The exact ratemust depend upon a number of variables, however, including t h e size and shape of t h e package in which2 flour is contained, the material from which i t is manufactured, the extent of circulation of air about t h e . package, and possibly other factors of minor importance. It appeared impossible t o develop this phase. of the investigation adequately a t this time, and the study of rate of response must be deferred t o a later date. Such d a t a as were secured in certain of our. preliminary studies indicate, as might be anticipated, t h a t a dry flour placed in a humid atmosphere (or vice versa) changes rapidly the first 3 days, and much moreslowly t h e next 3 days, after which, if exposed in thinl layers, there is little further change. CONCLUSIONS
RELATIVE MUMIOITY
- PER C W T
FIG.1
At the time t h e dishes were finally removed from the desiccators, a portion of the sulfuric acid was drawn off and its specific gravity a t once determined. From this, the percentage of H2S04 could be ascertained, and t h e vapor pressure and relative humidity computed through the use of the tables mentioned herewith. Since i t was not convenient t o prepare sulfuric acid solutions of concentrations which would give exactly the humidity desired a t t h e close of t h e experiments, small variations from the desired humidity were found in most cases. These deviations were always less t h a n one per cent, in terms of relative humidity. I n Table I 1 and Fig. I ar’e shown t h e percentages of moisture in the patent and clear flours exposed t o atmospheres of approximately 30, 50, 70, and 80 per cent relative humidity. While the differences between the two grades of flour are small, they are in the direction of a slightly higher hygroscopicity on the part of the patent grade. Stockham (1917) had previously shown (page 105) a difference in the hygroscopic moisture of starches prepared from patent and clear flours, those from the patent containing more moisture
Flour responds readily t o changes in t h e humidityof surrounding air, t h e rate a t which equilibrium in moisture content is approached depending apparentlx upon conditions of exposure. Hygroscopic moisture in flour in equilibrium with. atmospheric humidity a t 2 5 O C.ranges from a little moret h a n 5 per cent of moisture a t 3 0 per cent relative. humidity t o 1 5 per cent of moisture a t 80 per cent relative humidity. Curves representing the relation between hygroscopic. moisture (ordinates) and relative humidity (abscissae) have the shape of a simple parabola, thus indicatingt h a t hygroscopic moisture does not increase a t a uniform rate when in equilibrium with a n increasing at-mospheric humidity. Flour testing laboratories engaged in analyzing fresh, flour containing 1 2 t o 13 per cent of moisture will experience no appreciable change in the moisture contentr of such flour if the relative humidity of the laboratory atmosphere is maintained in the neighborhood of 70, per cent. REFERENCES
W. H. Brewer, “Relations of Grain to Moisture,” Tenth Census Repouts, 3 (1883), 28. F. B. Guthrie and G . W.Norris, “Daily Variation in Moisture Contenti of Flour,” New South Wales, Dept. of Agr., Science Bulletzn 7 (19121, 18. M. P. Neumann, “Uber dem Einfluss der Lagerung und Trocknung, auf die Beschaffenheit und BackfAhigkeit des Weizenmehles,” Z. ges Getreidew., 3 (1911), 83
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T.Sanderson, “A Study of the Variation in Weight of a Fifty-Pound Sack of Flour during Storage,” No. Dakota Station, Spdcial Bulletin 3 (1914), 14; “A Further Study of the Variation in Weight of a Fifty-Pound Sack of Flour in Storage,” Ibid., 3 (1914), 250. W. L. Stockham, “The Capacity of Wheat and Mill Products for Moisture,” No. Dakota Station, Bulletin 120 (1917). C. 0. Swanson, J. T.Willard and L. A Fitz, “Kansas Flours. Chemical, Baking, and Storage Tests,” Kansas Station, Bulletin a02 (1915), (Note p. 119). J. T. Willard, “Changes in the Weight of Stored Flour agd Butter,” Kansas Board of Health, Bulletin 7 (191 l ) , 9
CHANGES IN T H E POLARIZING CONSTANTS OF SUGARS DURING REFINING‘ By A. F. Blake ATLANTICSUGAR REFINERIES,LIMITED,S T . Received June 26, 1920
JOHN,
N. B.
I t is the purpose of this paper t o discuss the changes taking place in the relationship between polarization, true sucrose, and invert sugar during the refining of raw sugar, t o determine, if possible, the causes of these changes, and t o point out their practical significance. As pointed out by Dr. Brownej2 the percentage of true sucrose in a mixture of sucrose with pure invert sugar, consisting of equal parts of dextrose and levulose, will exceed the polarization a t 20’ C. by about three-tenths of the percentage of invert sugar. That is, s-P
= 0.30 I
where S represents the percentage of sucrose, P the polarization, and I the percentage of invert sugar. The factor will vary very slightly with the concentrations of sucrose and invert sugar, but a very small deviation from equality in the proportions of dextrose and levulose in the invert sugar will very greatly alter its value, because of the wide difference in t h e rotations of these two sugars. A value of (S- P ) / I above 0.30 indicates excess of levulose; a value less than 0.30, an excess of dextrose. Dr. Browne discusses the influence of temperature, maturity of cane, methods of manufacture, and length of storage of raw sugar upon the value of this r a t h , and mentions the fact t h a t in the process of refining its value is very materially reduced, and gives analyses of soft sugars and refiners’ sirup, in support of this assertion. EXPERIMENTAL P A R T
I n Table I is shown a n analysis of a cargo of Cuban raw centrifugal sugar of uniform quality and all one mark, together with the average analyses of soft refined sugar and refiners’ barrel sirup produced from it. These particular analyses .are selected for the purposes of the discussion because they are quite typical and because the refinery started melting this cargo following a shutdown from which practically no stock in process was brought forward, and melted this cargo exclusively for a considerable period, so that i t is quite certain t h a t the three analyses are interrelated. Dr. Browne’s observation of the reduction of the value of (S- P ) / I is very strikingly affirmed. 1 Presented a t the 60th Meeting of the American Chemical Society, Chicago, Ill,, September 6 to 10, 1920. a I n a paper entitled “Influence of Conditions upon the Polarizing Constants of Sugar Cane Products ” read a t the 56th Meeting of the American Chemical Socicty, Cleveland, Ohio, September 10 t o 13, 1918
12,
No.
II
TABLEI-ANALYSIS OF CUBANR A W CENTRIFUGAL SUGAR A N D OF SOFT REFINED SUGAR AND REFINERS’ BARRELSIRUP PRODUCED THEREFROM RAW SOFT REFINERS’ SUGAR SUGAR SIRUP ANALYSES WET Polarization a t 20’ C . . . . . . . . . . . 95.87 88.47 38.40 Sucrose Clerrret.. 96.42 88.74 40.60
..............
EX-WATERAND INSOLUBLE Polarization. 97.04 Sucrose Clerget.. . . . . . . . . . . . . . . 97.59 I n v e r t . . ...................... 1.27 Ash. 0.67 Organic.. 0.47
..................
.......................... .....................
IMPURITIES
Invert.. ...................... Ash ........................... Organic.. ..................... RATIOS Invert + Sucrose X 100.. Invert + Ash.. . . . . . . . . . . . . . . . . (S P)/I. . . . . . . . . . . . . . . . . .
......
-
52.7 27.8 19.5 1.30 1.89 0.44
93.41 93.70 3.71 1.31 1.28
47.74 50.48 28.58 10.11 10.83
58.8 20.8 20.4
57.7 20.4 21.9
3.95 2.83 0.077
56.6 2.83 0.096
The value has fallen from 0.44 in the raw sugar to 0.077 in the soft sugar and 0.096 in the sirup. The value of 0.44 is a little above the average. This ratio is subject t o wide variations, as shown by a summary of the results obtained on 3 2 cargoes from various sources. No.
Cargoes 8 6 10 2 6
From Cuba Cuba Demerara Demerara San Doming0
Time Received June-Dec. 1919 Jan.-March 1920 June 1919-Jan. 1920 Dec 1919-Jan. 1920 June-Oct. 1919
-Val.ue MiniCondition mum Deteriorated 0.08 New crop 0.44 Good -0.03 Deteriorated 0 . 4 8 Good 0.23
of ( e P ) / I Maximum Av 0.29 0.20 0.73 0 . 5 5 0.34 0.16 0.55 0.51 0.59 0.37
---
TOTAL-0.03
0.73
0.30
It seems t h a t new crop sugars have higher values than the remnants of the old crop, which in this case were in general more or less deteriorated, although in some instances deterioration may be of such a nature as t o increase the ratio. WAsHIxG-The first process of refining is one of affination or washing. The sugar is mixed t o a magma with its own sirup washings, purged in centrifugal machines, and washed with water. The only result is a separation into a high-purity washed sugar and low-purity washings. I t is hardly t o be supposed t h a t any change in the value of (S- P ) / I would take place here, though i t is possible t h a t it might differ somewhat in washed sugar and washings, since the impurities in the sirup are those of the molasses adhering t o the grain, and those in the washed sugar those in the grain itself. I n the latter the invert is lower and the organic higher. The analyses in Table I1 would indicate t h a t there is no great change of the (S - P ) / I ratio in t h e process of affining. The determination of the ratio with great accuracy is impossible in very high-purity material such as washed sugar, TABLE11-ANALYSIS OF
WASHED
OR
SUGAR
FILTERED SOLUTIONS OF CUBAN RAWSUGAR AND AND
.... .... .......... .... .... .... .......... .... ......... - P)/I*...............
Dry Polarization.. Clerget Invert.. ......... Dry Ash... Organic.
CENTRIFUGAL WASHINGSPRODUCED
THEREFROM Raw Sugar 96.37 96.91 1.20 0.62 1.27 0.45
Washed Sugar 98.77 98.98 0.43 0.19 0.40 0.49
Centrifugal Washings 78.05 80.56 8.35 3.62 7.47 0.30
since a trifling error in polarization or Clerget, say, 0.05 degree, makes a large error in (S-P)/I. The washings, too, being very highly colored, present some difficulties in a Clerget determination, but the
