272
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 18, No. 3
Determination of Moisture in Wheat and Flour’ Part IV By Harry Snyder and Betty Sullivan RUSSBLL-MILLER MILLINGCo., MINNEAPOLIS, MI”.
I
N PART I of this series2 the methods used for the deter-
zinc, the supply was irregular and unsatisfactory for as long mination of moisture in wheat and flour are outlined, a period as 5 hours. A cylinder of hydrogen, E, as prepared and for purposes of study, divided into six groups, one for commercial uses, provided with suitable control valves of the groups being dried in a current of hydrogen and other and a pressure gage, gave a uniform and satisfactory current “inert” gases. for drying purposes. Wash bottles 1 and 2 contained sulAmong the early methods devised for this purpose was furic acid, 3 saturated sodium hydroxide, 4 alkaline permanCaldwell’s hydrogen drying apparatus, and Winton’s4 appa- ganate, ratus developed in S. W. Johnson’s laboratory. The drying A special glass drying tube was employed. The main part, of substances in a current of hydrogen was proposed mainly A , shaped somewhat like a test tube, was provided with a for linseed meal and other feeding stuffs which are oxidized ground-glass stopper, B, which was inserted when weighings b s ordinary methods of air drying. It has been recognized were made. During drying this stopper was replaced by a rubber stopper, C, carrying that drying in hydrogen is a small glass tube about 5 not so necessary in the case cm. long, drawn to a reof cereals. “For instance, Fifty-eight flour moisture tests obtained by drying in stricted capillary opening we have found practically a current of hydrogen yielded 0.54 per cent more moisfor the exit of the hydrogen no change in this laboratory ture than vacuum-oven drying at 100’ C. and 600 mm. so that the flow of gas could in the composition of cereals and upwards of vacuum. When flours are dried in hybe tested from time to time. dried in the air and in an drogen, special precautions are necessary in order to The other end of the dryinert gas.”5 Winton used secure a uniform flow of very dry gas over and through ing tube, D (like Winton’s his hydrogen drying method the flour masses. Winton’s hydrogen drying apparatus, tube), was made so as to in an extended investigation with modifications, yielded closely agreeing duplicate form a connection with the on corn meal.6 “The reresults. When nitrogen and preheated air were subglass gas distributor, E, and sults obtained by means of stituted for the hydrogen as the drying medium, pracalso to provide a support this apparatus were about tically the same results were obtained as with hydrogen. for the previously dried as1per cent higher than those These tests emphasize the importance of the drybestos and cotton plug upon obtained-by drying for the ness of the medium in which flours are dried in making which the flour rested. same length of time and a t moisture tests by any drying method. Flour moisture Ttt-o grams of flour were the same temperature in a n results are a relative rather than an absolute expression used in making each test. open dish.” of moisture content. T h e g l a s s d r y i n g tubes KO extended c o m p a r a containing the flour were tive tests have been made E en t l v r o t a t e d horizonof drying wheat flour in a tally, so that the flour should not remain a compact mass current of hydrogen, and in other gases. Shutt and Moloney7 obtained about the same moisture in one end of the tube, and then the glass tubes were placed content when flours were dried in hydrogen at 95” C. and when in the copper tubes of the water bath, F. This maximum dried in a vacuum oven at 100”C. with a vacuum of 737 mm. surface exposure and the slightly inclined position of the Spencers failed to secure satisfactory results when flours tubes caused the flour to form a loose mass along one side were dried in a current of hydrogen with Caldwell’s apparatus of the length of the tube, over and through which the dry and also with another form of apparatus (Wiley’s) which had hydrogen readily passed. The temperature inside the previously beenused by the Bureau of Chemistry. “The mois- tubes registered about 98.5’ C., which is from 0.5 to 1 degree ture already present in the flour seemed t o act on the proteins, below that of the briskly boiling water surrounding the copcausing the formation of a dough-like mass which prevented per tubes. This is from 1.5 to 2 degrees higher than the temenough of the moisture from being carried out by the stream perature of flour in an open dish placed in an ordinary waterof gas to cause irregularities in the percentages indicated.” jacketed oven. For comparison, portions of the same flour were dried in a Hydrogen Drying vacuum oven at 100” C., 600 mm. and upwards of vacuum, I n this investigation a modified form of Winton’s apparatus for 5 hours, as described in Part I of this series. Duplicate was used. It was found necessary, however, to add other tests were made by both methods of drying, except as noted gas-drying bottles to secure a constant supply of very dry in the table. The samples were carefully drawn and placed hydrogen. The arrangement of the apparatus is shown in in glass containers with ground stoppers. The temperature range of the vacuum chamber during drythe illustration. When the hydrogen was obtained from a small Kipp apparatus by the action of sulfuric acid upon ing for all of these tests was usually from 99” to 100” C.; occasionally a minimum of 98.5” C. and a maximum of 101O 1 Received November 27. 1925. C. were observed. About the same number of samples were 2 THIS JOWRNAL, 16, 741 (1924). tested each day, four to six; hence the total charge of flour 8 Cornel1 University, Agr. Expt. Sta., Bull. 12. carried by the oven, 10 to 12 grams, was quite uniform. 4 Conn Agr Expt. S a . , Refit., 1889. 6 Wiley. ”Agricultural Analysis,” Vol 3, p. 34 (1st ed ). The opening and loading of the oven at the start of the test 6 U. S. Degl. Agr., Bull. 216. caused a drop in temperature, and the first half hour, when 7 Trans. Roy. SOC.Canada, [3] 11, 101 (1917). the greater part of the moisture was given off, the tempera8 J . Assoc. Oficral Agr. Chem., 8, 305 (1925).
.
INDUSTRIAL A N D ENGINEERIhrG CHEMISTRY
March, 1926
T a b l e I-Comparison of Vacuum-Oven and Hydrogen Drying (All figures a r e the average of two determinations except those starred (*), which are single determinations. Duplicate tests gave closely agreeing results) P E R CENT
MOISTURE
Vacuum Difference oven Hydrogen Per cent 12.95 13.55 0.60 12.35: 13.07 0.72 12.98 0.72 13.70 6 13.61* 13.95 7 0.34 12.76* 13.55 0.79 13.62 12.76 10 0.86 12.88* 13.62 0.74 13.71 13.09 11 0.62 12.84 13.75 0.91 12 12.08 12.95 0.87 12.81 13.67 0.86 13 13.24 14.27 1.03 13.18 13.99 0.81 14 13.99 14,72 0.73 13.31 12.66 15 0.65 13.88 13.43 0.45 13.17 13.95 0.78 17 12.88 13.57 0.69 18 l3.09* 33.50 0.41 12.69 13.38 0.69 12.84 13.40 0.64 I9 12.61 13.02 0.41 13.18 13.69 0.51 20 21 13.67 14.08 0.41 13.42 13.953 0.53 13.64* 14.00* 0.36 23 14.25 14.40 0.15 14.06 14.70 0.64 25 13.47 13.95* 0.48 13.76 14.12 0.36 13.23 13.41 26 0.18 13.48 13.75* 0.27 13.49* 13.92* 0.43 27 13.70 13.91 0.21 28 13.33 13.61 0.28 13.37* 13.83 0.46 14.22 Scpt. 21 14.67 0.45 13.70 14.21 0.51 25 14.07 14.40 0.33 13.50 14.08 0.58 29 14.11 14.57 0.46 13.63 14.22 0.59 30 14.40 15.08* 0.68 13.97 0.53 14.50* Oct. 2 14.56 15.25 0.69 14.22 14.74 0.52 6 14.43 0.38 14.81 13.63 0.49 14.12 9 13.22 0.36 13.58 13.62 14.02 0.40 16 14.07* 14.76 0.69 14.37 (1) 13.55* Clear 14.17 0.62 13.90 (1) 19 Patent 13.83* 13.37 0.36 Clear 13.07 0.41 12.66 i 28 Patent 14.45 14.01 0.44 Clear 13.30 12.88 0 .42 4 30 Patent 14.47 14.11 0.36 14.19 (1) 13.10 Clear 13.37 0.27 13.22 ( 1 ) Averaae 58 tests 13.95 13.46 0.54 (1) Dishes loosely covered while drying, not included in average. Date Aug. 5
K I N DOF FLOUR S. Patent Clear -.. . Clear Patent Clear Patent L. Patent Patent .I Patent Clear Patent I Patent I1 Patent L. Patent Patent I,. Patent Patent I,. Patent Patent Clear Patent Clear Patent Patent Clear Germ Patent Clear Patent I Patent I1 L.Patent I11 L. Patent IV Germ Clear Patent Clear Patent Clear Patent Clear Patent Clear Patent Clear Patent Ciear Patent Clear Patent Clear Patent
273
ture ranged from 85' to 100" C. The 5-hour period of -.eating the samples was counted from the time they were put in the oven. The vacuum ranged from 600 to 738 mm. I n daily routine work, where the oven is loaded heavily and to a different capacity each day, this drop in the temperature of the oven is variable and is not a negligible factor. When such a condition occurs the extra time required for the oven to reach 100" C. should be recorded and made a part of the report. I n the hydrogen drying there is no drop in temperature due to the construction of the oven. The only time needed is that t o heat the cold tubes to 99" C., as the drying tubes containing the flour are brought into more direct contact with the heat than in an ordinary oven. The moisture results obtained by hydrogen and by vacuum drying are given in Table I. The tests for each day, unless otherwise noted, are on separate samples of freshly milled flours. It is to be noted that the drying of the flour in a current of hydrogen invariably gave a higher moisture result than the vacuum drying. I n fifty-eight tests the average difference in moisture was 0.536 per cent, in favor of the hydrogen drying. The probable causes of this difference are discussed in connection with the results obtained by drying flours in other "inert" gases, such as nitrogen, and also in a current of dry air. Nitrogen Drying
Tests were made in which nitrogen was used as the drying medium. A cylinder of nitrogen supplied the gas and tests were conducted in the same way as with hydrogen. The comparative results obtained with hydrogen, nitrogen, and vacuum drying are recorded in Table 11. Vacuum Drying
As noted in Tables I and 111, tests were made with the dishes containing the flour loosely covered during the vacuum drying. I n a few cases the results were the same and in others from 0.1 to 0.3 per cent more moisture was thus obtained than when the covers were placed under the dishes during the drying and then put in position a t the close of the process. As previously stated, only from four to six samples were dried a t a time. While these differences are nominal, if a larger number of samples were tested a t one time the
INDUSTRIAL A Y D ENGINEERING CHEXISTR Y
274
differences would be greater because of the time consumed in covering the dishes. This tendency to secure higher moisture results when the dishes are loosely covered during drying is due to the extreme hygroscopicity of flour and the avidity with which dry flour absorbs moisture. When a large number of tests were made a t one time, Mitchell and Alfendg report differences as high as 1 per cent between flours dried in covered and uncovered dishes, the highest result being obtained with the dishes that were covered first. When this work was undertaken it was planned to make additional comparative tests with water-oven drying for 5 hours, without vacuum. But as the difference between wateroven and vacuum-oven drying was again found to be the same (nearly 2 per cent) as reported in former articles of this series, the water-oven drying was discontinued. Discussion of Results
The results recorded in the tables are of interest from an industrial point of view as they show a range in moisture content of freshly milled flour from 12.35 per cent, vacuum basis, on August 5, to 14.65 on October 1. I n the case of hydrogen drying the range is from 13.07 on August 5, to 15.25 on October 2. During August the flours were milled under hot weather conditions, when the atmosphere showed a low percentage of relative humidity, while in October a new crop of wheat was milled, requiring more conditioning to prepare it for suitable milling separations and with the natural relative humidity of the air appreciably higher. These tests do not represent what may occur under more extreme conditions. Shollenbergerlo has shown that different wheats must be tempered according to their characteristics in order to secure good milling results, and that every 10 degrees increase or decrease in the relative humidity during d i n g affects the moisture content of the flour to the extent of 0.50 per cent. The writers' results are in harmony with Shollenberger's findings. I n the hydrogen, nitrogen, and air drying of flour, the sulfuric acid, saturated solution of sodium hydroxide, and alkaline permanganate used in the gas wash bottles were changed daily. Hydrogen drying is generally completed a t the end of 3.5 to 4.5 hours, but to conform to other tests the drying was carried on for 5 hours. When the test is first started, a little 9
10
J . Assoc. OficiaZ Agr. Chem., 8, 76 (1924). U.S. Dept. Agr., BulZ. 1015. T a b l e 11-Comparison OVEN-
-VACUUM
Per cent Vacuum Samole5 moisture Mm.
Date Sept. 21
22 23 24 25 25
29 30 Oct.
1 2 5 6
60P 61C 60P 61C 60P 61C 60P 61C 62P 63C 64P 65C 64P
65C 66P 67C 66P 67C 68P 69C 70P 71C 70P 71C
1 4 . 2 2 (1) 600 13.70 600 14.06 587 13.64 587 13.98 625 13.60 625 13.99 613 13.60 613 14.07 619 13.50 619
14.13
13.69 14.11 13.63 14.40 13.97 14.65 14.16 14.56 14.22 14.30 13.53 14.43 13.63
613
... ... ...
Temp. C.
99.5 99.5 100.5 100.5 99.5 99.5 9 9 . 5 to 9 9 . 7 5 9 9 . 5 to 9 9 . 7 5 99.5 99.5 100.5
100 '
625 625 600 GOO 625
100:s
... 600 ...
9 9 : s to 100
100.5 99 to 1 0 0 . 5 99 to 100.5 9 9 . 7 5 t o 101 9 9 . 7 5 t o 101
moisture may temporarily collect in the connecting tube and this is later expelled. The dryness of the hydrogen or gas is of prime importance. When compressed air was used, the air could not be dried satisfactorily without first preheating. I n the tests with the unheated air (Table 11) lower results were obtained than when the air was heated before it passed through the gas wash bottles. This was done by conducting the air through a small copper tube which was heated in a Hoskin's muffle furnace, or a t other times, by making a coil of the tube and heating over a n asbestos-covered Gilmore heater. As the air passed throuqh the heated copper tube rapidly, it was only moderately warmed, and when passed through the bottles it was more completely desiccated than without this treatment. The necessity of a fairly brisk and constant flow of dry air, nitrogen, or hydrogen passing through the drying tubes containing the flour was shown when the tubes were heated in the water bath without the use of any drying gas. This point was also made clear in beginning the tests, when a small Kipp apparatus was used for generating the hydrogen. The flow of gas was irregular after the first 2 hours and the results obtained were more variable, sometimes slightly higher and sometimes lower than vacuum drying, owing to the imperfect supply of drying gas. When the tubes were heated in the water bath and without any gas passing through them, the tests yielded 7.80, 9.68, 9.20, and 7.80 per cent, respectively, of moisture against 13.12, 14.00, 13.46, and 12.89 per cent by the vacuum method. Although the flour in the tubes was heated to the temperature of the boiling water of the water oven, there was no adequate means of removing the water from the flour. Success of hydrogen, nitrogen, or air drying of flour in glass tubes placed within copper tubes heated to the temperature of boiling water depends mainly upon (1) a uniform rate of flow of perfectly dry gas or air, and (2) the loading of the tubes in such a way that the drying medium readily passes over and through the flour. While the method is not suitable to routine work where a large number of flour moisture tests are made daily, it is, however, a satisfactory research method, and gives, when hydrogen is used as here described, about 0.50 per cent more moisture than vacuumoven drying at 99' to 100' C. and 500 mm. or more of vacuum. The method yields closely agreeing duplicate results. Spencer, as previously noted, obtained lower moisture results with hydrogen drying than with any other method of drying.
of V a c u u m - O v e n , Nitrogen, a n d Hydrogen Drying -NITROGEN--
Per cent moisture
... 14:44 14.10
...
14:so* 14.09 14.47 13.91 14.54* 14.15
Temp.
c.
... ...
gc2 . 7-~ 5 9!3 . 7 5
...
99'io 9 9 . 7 5 99'to 9 9 . 7 5 99 to 99.75 9 9 . 5 to 9 9 . 7 5 99.5t099.75
...
... ... ...
ii:ii* 14.46* 15.05* 14.62* 14.73 13.98
94 :25 94.25 99 99
...
613
Yo]. 18, K O . 3
...
... ...
99:25
... ...
-HYDROGEN-Per cent Temp. moisture =c.
14.67 14.21
... ...
99.75 99.75
...
...
DIFFERENCES BETWEEN: Hand Nand H and vacuum vacuum No (1) (2) (3) 0.45 0.51 ... +0:07 ... u- . 38 t 0.4 6 +KO5
...
...
...
i4:i7b
9 9 : i to 9 9 . 7 5
0.57
14:40 14.08
99'io 9 9 . 5 99 to 99.5
0.33 0.58
14157 14.22 15.08* 1 4 . 50*
99.5 99.5 99.25
0.46
1i:25 14.74
99:25
...
...
...
...
...
... ...
... ..
... ...
... ...
... ...
0.59 0.68 0.53
... ...
0.69 0.52
... ...
... ...
0.61 0.49 0.40 0.41 0.41 0.46
... ... ... ...
0.46 0.30 0.49 0.40 0.43 0.45
... ...
... ...
+0:0s -0.07 10.17
...
+0:05
+0.13
+0:22 +i7:i3 +0.20 1 0 . 12
... ...
99:25 0.3s -0.05 99.25 0.49 $0.04 Average 0.52 0.434 0.095 The time of drying in these tests was 5 hours, except as noted: (1) 4 hours and 50 minutes; (2) 4 hours and 4 5
...
a. P is patent flour, C is clear flour. minutes. b Average of 4 tests. e Obtained by subtraction of (2) from (1).
14:81 14.12
INDUSTRIAL A N D ENGINEERIhTG CHEMISTRY
March, 1926
275
R e s u l t s w i t h Dry Air N o t P r e h e a t e d DRYAIR -.VACUUM OVEN-NITROOEN-HYDROGEN- N O T PREHEATED r - DIFFERENCE BETWEEN: Per cent Vacuum Temp. Per cent Tzmp. Per cent T,ernp. Per cent Temp. Air and H and H a n d Nand Nand Sample moisture Mm. “C. moisture C. moisture C. moisture OC. vacuum vacuum air vacuum H 70P 14.30 600 99 to 100.5 14.73 99 $0.43 +0.05 f0.45 71C 13.53 600 99 t o 1 0 0 . 5 13.98 99 -0.04 0.38 70P 14.43 625 9 9 . 7 5 t o 101 14:8l 99:25 71C 13.63 625 99.75 14.12 99.25 ... 0.49 7np 14.37 625 in0 . . . . . . ...... 14174 ‘69 0.37 ... 40,’Ol ... ... 71C 13.50 625 100 13.89 0.30 $0.19 730 99 t o 101 . . . . . 14 51 99 0.18 ... 14.33 72P 0.18 730 99 to 101 . . . . . . 14 23 73C 14.06 Average 0.26 0.44 0.10 0.44 T a b l e 111-Comparative
Date Oct. 5
... ... ... .. ...
......
.. .. .. .. .. ..
6 7
...... . . ,..
S
...... ......
Sample 75P 76C
16
75P i6C
19 20 21
22 23 27 28 29
i7P TYC 77P 78C 79P 80C 79P 80C 79P 80C 81P
82C 81P 82C 83P 84 C
30
83P
30
84C
Nov. 2
85P 86C
9
87P
88C
... ...
... .. .. .. .. .. ..
... ...
... ... ... ...
... ...
N and air f0.06
+0.15
... ... ... ...
... . . I
0.10
By the term “total moisture” or “water in flour” is meant that which is held in loose and firm physical combinations with the flour particles, also that held in condition closely approaching chemical combination with the starch micellae, or as water of hydration of proteins.ll -4s an industrial problem the determination of moisture in flour for manufacturing or other control purposes is largely a matter of using and strictly adhering to empirical conditions as to temperature, time, and manipulation. Such methods are not necessarily suitable for research work, because flour is a complex mechanical mixture of various carbohydrates, proteins, and other compounds, which are appreciably affected by heat. Hence any moisture method thus far developed is a relative rather than an absolute expression as to moisture content While no marked differences were observed in moisture results when nitrogen or air (preheated) was substituted for hydrogen, if any differences can be said to exist they are in favor of hydrogen drying. There is, however, no reason for its use to prevent oxidation of the fat as far as moisture r e sults are concerned, since nitrogen and air give practically the same results as hydrogen.
When flours are dried in the vacuum oven, desiccation of the air when the pressure is released and the oven is opened is a matter of prime importance. I n hydrogen drying there is a minimum of exposure of the dry flour. Hydrogen and other gas drying represents more nearly the total moisture content of flour than other methods operated a t the same temperature. The principles governing hydrogen and nitrogen dryingnamely, the thorough desiccation of the drying medium, the rate a t which it passes through the flour, and the completeness with which the water vapor from the flour is removed as it is liberated-applies alike to vacuum and atmospheric pressure drying. When a slow current of thoroughly dry air is passed through the flour, maximum moisture results are obtained for any given temperature. It is essential that the vater be removed from the oven as i t is liberated from the flour, preferably by a combination of a highly efficient vacuum pump and continual displacement with a current of warm, dry air. Greater uniformity of results could be gained in vacuum drying by the aspiration of a slow current of dry air through the oven even at the expense of 50 or 100 mm. of vacuum. I n this and preceding articles of this series the vacuum and not the vacuum pressure is given.
Date Oct. 15
.. .. .. .. ... .. ..
11
THISJOURNAL, 16, 1163 (1924).
T a b l e IV-Comparison of Drying in V a c u u m Oven, Heated Air, a n d Hydrogen -HEATED ~ I R -HYDROGEN-DIFFERENCE BETWEEN:-VACUUM OVEN-. Percent Vacuum Temp Per cent remp. Per cent Tzmp. Airand Hand Hand moisture moisture c. moisture Mm. c. C. vacuum vacuum air 14.70 14.18* 663 9 8 , 5 t o !>9 99 0.52 14.37*(1) 13.62* ... 13.98 99 98.5 to !39 0.36 13.80*(1) 14.07* 675 99.25 99.5 ... 14.76 0.69 4-0.17 14.37* (1) 13.55 675 ..* 99.5 14.17 0.62 $0.26 13.90 (1) 98.5 13.37 675 ... 13.83* 0.46 98.5 12.66 673 13.07 ... ... 0.41 13174 99.5 13.40 660 99:25 ... 0.34 i o : i2 99.5 12.75 660 13.03 ... 0.28 ... 4-0.13 14.00 13.78 630 98,s t o 99 99 0.22 ... 13.66 13.48 630 98.5 to $19 99 0.18 ... ... i4:i5 ... ... 99 ... 0.52 ... ... ... 13.78 99 ... 0.46 13:47 638 99 14:03 99 ... 0.56 +b: i3 13.16 638 98.25 99 13.68 ... 0.52 ... 0.11 9 9 . 5 to ion 14.12 98.25 14.34 675 0.22 13.02 675 99.25 13.33 9 9 . 5 t o 100 0.31 98.5 to 99.5 14145 ... .. ... 14.01 730 0.44 +-b:i2 98.5 t o 99.5 12. 88 ... ... 13.30 0.42 ... +o. 11 14.05 675 99 to 100 14:55* 99.5 ... ... 0.50 14.20 (1) 13.18 675 99 t o lO(1 13.45 ... ... ... 0.27 ... -13.27 (1) 14.11 675 98.5 to 99.5 ... 14.47 99.5 0.36 -0.14 14.19 (1) 13.10 ... 13.37 0.27 0.00 13.22 (1) 13.88 675 100 14.38 99.5 0.50 14.07 (1) 12.87 675 13.42 0.55 13.09 (1) 13.44 730 99.5 t o 100.5 99.25 13.71 0.27 13.44 ( 1 ) 12.96 730 99.5 t o 100.5 13.37 0.41 13.08 (1) Average 0.376 0.465 0.111
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Dishes loosely covered while drying.
Calco Absorbs Kerin Manufacturing Company---The Calco Chemical Company has purchased the business and good will of the Kerin Manufacturing Company, of Marietta, Ohio.
The latter has for several years produced a line of basic colors, which have been distributed through the Marietta Refining Company.
