T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
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controlled this practically eliminates the effect of room temperature on the humidity controller, All materials used for humidity controls are subject t o temperature changes t o a greater or lesser degree. VI-Not only is the control of humidity of importance in the testing of materials, but also in many industrial lines as well. Many of the troubles and complaints of the pressman and engraver are due t o humidity effects on paper and could be remedied by maintaining more uniform humidity conditions in the press a n d storage rooms. Low indoor humidity in winter is the cause of much inconvenience in printing, causing t h e paper t o curl and shrink and thus interfering greatly with the work of the presses. Paper is more flexible a t high humidity. This fact is of direct importance t o the manufacturer of envelopes and in the folding of paper, the humidity of the room determining whether the folding is smooth or cracked. The humidity of the drying loft and the calendering end of a paper machine undoubtedly plays an important part in the finishing of paper. The expansion and contraction of the sheet caused by variations in atmospheric humidity are of controlling importance in map and chart making and in certain special uses of paper. This could be easily overcome by keeping the paper a t a uniform humidity from the time it is received until the work is finished. VII-There are many other industries in which the maintenance of uniform humidity is absolutely necessary. Among these are the manufacture of textiles, fuses for munitions, motion picture films, tobacco a n d many others. Humidity control is being applied t o t h e ripening of fruit, curing of cheeses, drying of lumber, manufacture of leather goods and t o many other important industries.
Vol.
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I
require t h a t absorption shall be not less t h a n a certain number of millimeters in I O min. The absorption in each minute can also be noted, though specifications generally state only the total absorption in I O min. There are several disadvantages in the use of the mounting test for determining the absorptive propert-es of a blotting paper. The strips are suspended vertically whJe the blotting paper is always used flat. The use of ink in this test is not practicable, due t o the large surface exposed t o evaporation in making the test and since most writing inks contain a colloidal precipitate, the blotter will tend t o absorb only the liquid portiol?. There is considerable difference in the absorption of water and of ink by blotting paper. To get the true ink absorptive value, ink must be employed in the test. The chief drawback of the mounting test, however, is t h a t i t is unaffected by t h e bulk or weight of the paper which necessarily has a relation t o serviceability. I n this procedure an unlimited quantity of water is in contact with a variable thickness or bulk of paper for a definite time and the height t o which the liquid rises in this definite time is recorded. Neither the width, thickness nor weight of the strip affects the results. Two papers of different bulk may give the same height of absorption, but the lighter will undoubtedly not absorb as much water as the heavier nor as rapidly. This is clearly shown in Table 111, which will be discussed later. Bromleyl suggests determining the actual weight of water absorbed. This procedure shows clearly t h a t t h e mounting test does not take into consideration the bulk of the blotter, which is one of the chief factors determining the amount of water absorbed in a specified time. Other methods have been suggested for indicating LEATHER AND PAPERLABORATORY t h e absorbency of blotting papers. Sindal12 describes BUREAUOF CHEMISTRY, u. s. DEPARTMEXT OF AGRICTJLTURE a test for determining the absorptive qualities of WASHINGTON, D. c. blotting paper, which consists of noting the time required t o absorb o . 5 cc. of ink delivered drop by drop, A METHOD FOR DETERMINING THE ABSORBENCY allowing each drop t o be absorbed before another OF PAPER falls. Methods somewhat similar but differing in By E. 0. REED details of manipulation are described by Cross and Received November 13, 1917 Bevan,3 and by st even^.^ The size and character The serviceability of blotting paper, paper towels, of the zones formed are also noted. The thickness or filter paper and copying paper is largely dependent on their absorptive properties for the measuring of bulk of the paper unquestionably plays an important which several methods have been used. Since blotting part in determining the size and character of the zones. is the most important of absorptive papers, the methods It has also been suggested t h a t the absorptive capacity proposed have been especially adaptcd t o the testing and the loss of absorbent qualities of blotting paper on repeated use can be determined by soaking i t in of this class of paper. ink, allowing t o dry, and then noting the time reAbsorption is most commonly determined by measquired for the absorption of a definite quantity of uring the rate at which distilled water rises in a vertically suspended strip usually 1 5 mm. in width, ink dropped upon it.5 The same criticism-failure t o Lnclude the effect the lower end of which dips beneath the surface of of thickness or bulk of the paper on the quantity of water contained in a trough. Either the time which it takes the water t o rise t o a given height or the height ink or water absorbed in a given time-applies also t o which the water rises in a given time, is noted. t o the methods suggested by Favier6 and by Fromm.’ on the Requirements of Certain Special Classes of Paper,” The latter is the more common method. Apparatus Paper1 “Notes Maker and British Paper Trade Journal, 62, 59. for conducting this test, which is known as the “mount2 “Rlementary Manual of Paper Technology,” p. 119. 3 “Paper Making,” 4th Ed., p. 389. ing test,” has been designed by Klemml and by Stevens.% 4 “Paper Mill Chemist,” p. 231. Specifications for this quality in blotting paper usually 6 Ibzd., p. 233. 1
*
“Handbuch der Papierkunde,” p. 318. “Paper Mill Chemist,” p. 229.
8 7
L a Papelhie, 1894. Wochbl. Papierfabr., 1909, 4172.
Jan., 1918
T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
I n both of these methods absorption is measured with the paper in a horizontal position. By Favier’s method the time required t o saturate a square decimeter of the paper under a uniform pressure of water is noted. The absorption value is calculated by dividing the amount of water absorbed by the time required t o saturate the paper. By Fromm’s method five circular pieces of blotting paper are floated together on a trough of water and the time required t o saturate the top piece is noted. Though each of the methods referred t o above is faulty in some particular, the results obtained with them, while varying with the procedure employed, are serviceable in judging the quality of blotting paper, if the limitations of the methods are kept in mind. It has long been felt, however, t h a t none of the methods for indicating absorption give a true measure of the serviceability of absorbent papers, especially of blotting papers. Inves,tigations of the several procedures for the testing of absorbency indicate t h a t b y a modification and standardization of the procedures described by Sindall, Cross and Bevan and b y Stevens, more accurate information as t o absorptive qualities may be obtained t h a n by the mounting test or the other methods mentioned. The procedure finally adopted consists in noting t h e time required for the absorption of one cc. of a specified standard ink or of distilled water under definitely prescribed conditions. PROCEDURE
Place a 4-in. square of blotting paper over a beaker or tumbler and arrange a support in such a manner t h a t a I-cc. pipette is held in a vertical position with the delivering tip 1/2 in. above the center of the surface of the paper. A suitable apparatus may be made by boring a hole in a cork through which the stem of t h e pipette will pass freely. Clamp i t in a ring stand, so t h a t the pipette when placed in position has the tip a t the correct distance above the surface of the paper. Select a pipette with a delivery time for distilled water a t 70’ F. temperature of approximately 4 sec. Fill the pipette with distilled water or standard ink a t 70’ F. temperature. Place it in position in the support and permit the contents t o flow upon the surface of the paper and record b y means of a stop-watch the time required for the complete absorption of the liquid. Triplicate determinations should be made and the results averaged t o secure the absorption time of the paper. A 4-in. square of blotting paper is sufficiently large and it should be placed over a beaker or tumbler h a v h g a diameter somewhat greater t h a n the blot made by the liquid, ; n order t h a t the edge of the blot may not extend t o where the paper rests upon the glass, as this may affect the time of absorption. I t is important in placing the square of blotting paper upon the tumbler t o dish it slightly, so t h a t the water or ink will be received in one pool and thereby prevent buckling of the paper. If the paper is allowed t o buckle, uneven distribution of the liquid will be caused and the time of absorption considerably affected, thereby rendering the test valueless. Check
45
tests with this method in most cases differ but 2 or 3 sec. on papers absorbing the ink in less t h a n 2 5 sec., and from 5 t o I O sec. on papers absorbing the ink in from j o t o IOO sec. The results obtained using a specified standard ink are more indicative in the case of blotting paper t h a n when water is employed. I t is impossible t o depend upon ink purchased on the market for use in a standard test of this character. It is therefore absolutely essential for the analyst t o prepare t h e standard testing ink in accordance with a definite standard formula. For this purpose the formula for U. S. Government Standard’ blue-black writing ink has been adopted. This formula is as follows: GRAMS ......................... 23.4 ........................ 7.7 ............................... 30.0 ............. 25.0 1.0 No.478. ................................... 2.2 Make to a volume of 1 000 cc at 60’ F. with distilled water.
Pure dry tannic acid.. Gallic acid in crystals. Ferrous suifate. Dilute hydrochloric acid (U. S.P . ) . Carbolic acid. ................................ Dye, Bavarian blue (D. S. F), Schultz and Julius
All of these chemicals should b e of U. S. P. quality and in addition the purity of the tannin should be determined by the hide powder method.
Dissolve the tannic and gallic acids together in about 50 cc. of warm water and allow t o cool; dissolve the ferrous sulfate in about 150 cc. cold water. Add t h e hydrochloric acid t o the ferrous sulfate and immediately mix the solutions. Add the dye dissolved in water and the carbolic acid and make up with distilled water t o 1000 cc. Mix thoroughly and allow t o stand for a t least 4 days a t room temperature. When ink is t o be used for tests, draw out without shaking the bottle. Formulas for standard inks are also given in Bureau of Chemistry Bulletin 109, revised, page 43, and Bureau of Standards Bulletin on “Some Technical Methods of Testing Miscellaneous Supplies,” page 43. These formulas differ slightly from the one adopted in t h a t gum arabic is added and the soluble dye is not included. The formula adopted gives a n ink closely agreeing in composition with the normal commercial inks furnished under the above quoted formula. To prevent oxidation and evaporation of the ink when not being used, i t is essential t h a t t h e ink be poured into so-cc. dark bottles, tightly corked and stored in a dark, cool place. The use of I cc. of water or ink gives a sufficiently wide range in the absorption results between different papers. I n the case of filter paper, copying paper and very light-weight blotting paper, a smaller amount of water or ink (0.5 cc.) should be employed. There are several factors which affect the results, namely, the temperature of the liquid, the delivery time of the pipette, the distance of the tip above the surface of the blotting paper and the amount of liquid used. These should be standardized, if accurate and comparable results are desired. I n most cases there is little difference between tests made with either the felt or wire side of the blotter up. It is advisable, however, always t o place the same side of the paper up, preferably the wire side, as on t h a t side the absorption is more uniform. Table I shows the effect of the time of delivery i “General Schedule of Supplies, 1917-1918,” General Supply Committee, Item 1128, p. 60.
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from the pipette on the time required for absorption of the water by the blotting paper. Ten I-cc. pipettes were used. The pipettes were supported so t h a t their tips were approximately l / 2 inch above the surface of the paper. The temperature of the distilled water was 70' F. and the wire sides of the papers were up. TABLEI-RELATIONBETWEEN SPEED OF DELIVERY AND TIMEOF ABSORP-
9
10
TIMEREQUIRED FOR ABSORPTION
Time of delivery Sec. 3 3 1/2
Sample
Sample
Sample
Sec.
Sec.
16
10
Sec. 55
15
24 23 30
32286
32751
15
4 4 4 5 6
10 10 11 11 10
16 17 16 16 16
15 27
11
17 17 29
32288 57 55 58 56 57 55 65 67 80
There is considerable differen'ce in the results obtained with rapid and slow delivery pipettes. However, t h e results obtained with pipettes delivering t h e water in 3 t o 6 sec. are practically the same. This is explained b y the fact t h a t with a slow delivery the rate of absorption of the fluid b y t h e paper is nearly the same as or exceeds the rate of delivery from t h e pipette. Since the most uniform and accurate results are obtained with quick delivery, a pipette delivering I cc. in 4 sec. is regularly used in this test. The last drop delivered upon draining, unaided, is included in the test but not in noting the time of delivery. Table I1 shows the effect upon the time of absorption of the distance of t h e point of delivery above the surface of the paper. The same pipette delivering in 4 sec. was used in all cases and the temperature of the distilled water was 7 0 ° F. THE TIMEO F ABSORPTION O F DISTANCE O F P O I N T OF DELIVERY ABOVE THE PAPER TIMEREQUIRED FOR ABSORPTION
TABLE11-EFFECTON Distance of tip above surface
In. 4
2 1
Sample
Sample
32751
32735
Sec. 8
Sec. 19
9 10
I/2
10
a/ 8
10
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I
TABLE11 I-COMPARATIVE
ABSORPTION TESTS, U S I N G THE MOUNTINQ TEST 1 Cc. ABSORPTION TEST Ream Weight Mounting Test Time Required for SAMPLE 19 X 24-500 1 win. 10 Min. Absorption of 1 cc. No. Lbs. Mm. Mm. Sec. AND THE
32791(*) 32792 32793 32794 32795 32796 32797
19 32 45 58 72 96 140 (*) This sample is very thin
20 20 19 19
54 54 54 53 52 50 55
ill* 100 61
58 36 37 11 and allowed 4 drops of water to filter 20 18 20
through, reducing the amount absorbed by that quantity.
TION OF W A T E R
PIPETTE No. 1 2 3 4 5 5 7 8
Vol.
20 24 26 26
Sample
32926 Sec.
35 37 37 38 39
The distance of point of delivery above the surface of the paper has very little effect on the time of absorption, though a slightly faster absorption with increasing distance is noted. Practically no difference, however, is observed in the average time of absorption when the tip of the pipette is from 5 / 8 t o l / 2 inch from the paper. When the tip of the pipette is a n inch or more above t h e surface of the paper, the liquid spatters, covering a larger area and the time of absorption is lessened. This difficulty is overcome when the tip of t h e pipette is placed approximately inch above the paper. I n Table I11 there are given comparative results obtained b y the mounting test and by t h e procedure outlined above, on a set of white blotting papers of the same composition and weighing 19, 32, 45, 5 8 , 72, 96 and 140 lbs. per ream 19 X 24-500 sheets, respectively. The stock of these papers is all rag and t h e ash content varies only from I . 2 t o I. j per cent. Distilled 'water a t 70' F. temperature was used in both methods. The mounting test strips were all cut transversely of the sheet 1 5 mm. in width.
The absorption values of these samples obtained b y the mounting test are practically the same, though t h e weight of the paper varied from 1 9 t o 140 lbs. per ream. These results are in harmony with the known fact t h a t the rate of rise of water in the mounting test is independent of the weight of the paper. On the other hand, t h e speed of absorption in the cubic centimeter absorption method increases inversely with the weight of the paper. The effect of t h e weight or bulk of the blotter on t h e absorption value is clearly indicated by the time required for the absorption of I cc. of water in the horizontal position. This test shows t h a t the speed of absorption increases with the increase in bulk of t h e paper and t h a t t h e heavier the blotting paper the better its absorption properties. I n Table IV there are given the analyses and absorptive values of several typical samples of blotting paper measured b y three different methods. Results are given b y the mounting test, using distilled water, and by the I cc. absorption method, using distilled water and also U. S. Government Standard ink. The water and ink were used a t 70' F. temperature. The samples are arranged in t h e order of their absorptive values as indicated b y the time required for the absorption of I cc. of standard ink. The order would be changed completely if the samples were arranged in the order indicated b y the values obtained by the mounting test or by the absorption time for I cc. of distilled water. It will be noted throughout t h a t the values b y the mounting test do not give the same relative rating for absorptive qualities as those obtained by the I cc. time absorptive method using water or ink. I t will be noted t h a t here, too, the effect of weight is shown b y the results obtained with the I cc. absorption method. By t h e I cc. absorption method the time varies from 9 t o 2 0 3 sec., b y the mounting test from 44 t o I O I mm. Thus the possibility of differentiating between papers is much greater with the former t h a n with the latter method. The results obtained by using I cc. of standard ink are undoubtedly of the most practical value. I n this paper i t is not the purpose t o consider the factors in the manufacture of blotting paper which affect the absorption quality, as this will be fully dealt with in a later publication. However, the color, stock, and ash content of the paper, as well as the weight, will be found t o explain the results in most cases. If these samples are classified according t o weight, t h a t is, all samples grouped into 140, 1 2 0 , 100, 80, or 6 0 lb. classes, the results by the several procedures still show difference i n order of absorptive values, though the differences are not a s marked. The proposed method may also be used t o give a n
Jan., 1918
T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
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TABLE IV-ANALYSES OF TYPICAL SAMPLESOF BLOTTING PAPSR WITH COMPARATIVE ABSORPTION VALUES (All Phvsical Tests Made a t 70’ E^. and 65 Per cent Relative Humidity) SAMPLE No. 32960 28018 32956 32959 28020 32925 28129 32961 32924 32955 32799 32968 32758 32969 32965 32966 32927 32929 28030 28024 32760 32976 32962 32926 33852 32973 32974 32970 32963 32922 32921 31748 28136 32936
Color White White White Gray Blue White White Gray White White White White White Gray Gray White Pink Pink White White White Gray White Pink White Gray White White Gray White White Blue Blue Pink
Weight 19 X 24 500 Lbs. 1391,’~ 125 102 1181/% 1231/z 139 97I/z 1351/z 1191/a 77l/z 100 1391/z 133 137 951/2 1241/z 82Vz 124 93l/2 1011/2 114 139 80 62 631,’~ 102 120 83 77 77 65l/2 991/r 102 58
Ash Per cent .~ . 8.3 1.0 7.7 7.9 2.6 5.2 2.3 5.5 5.5 7.4 1.3 20.1 27.0 18.4 17.0 19.9 4.7 5.1 5.8 14.5 25.5 19.1 14.4 4.4 13.1 20.2 25.6 19.8 16.9 7.6 6.3 23.9 27.9 16.0
STOCK Soda Per cent Per cent 81 19 100 .. 21 79 70 30 100 .. 29 71 20 80 41 59 28 72 16 84 100 52 48 78 22 51 49 48 52 49 51 15 85 68 32 19 81 61 39 78 22 65 35 34 66 15 85 32 68 74 26 68 32 74 26 49 51 38 62 32 68 40 60 56 44 63 37 Rag
..
indication of t h e total absorptive capacity of a paper o r the loss of absorptive qualities on repeated use. I n using this method t o secure an indication as t o the capacity of a blotting paper, a piece of paper of definite size (2 in. square is a convenient size) must be used. The test may be carried out in two ways: The paper m a y be saturated by running upon its surface successive I-cc. portions of standard ink until i t is completely saturated and will absorb no more. Although completely saturated with liquid in this manner, upon thoroughly drying the paper will still absorb more ink. Another plan is t o allow the blotting paper t o thoroughly dry between each I cc. of ink. Considerable time is required in the procedure, but after a certain number of applications of ink the absorption begins t o decrease rapidly until finally a point is reached when t h e paper will absorb no more. By either procedure the number of centimeters of ink used and time required for the absorption of each centimeter is noted. The results b y the procedures outlined do not give t h e same relative results and i t is believed t h a t the last suggested is the most indicat i v e of the total capacity of blotting paper under service conditions. However, the life or capacity of a blotter is so largely dependent upon the treatment i t receives in service, t h a t the results obtained by such a determination are of but little practical value. If a blotter i s saturated with ink and allowed t o dry, although somewhat stiffened, i t will still absorb satisfactorily in most cases. I n fact, i t has been found t h a t many blotting papers may be repeatedly saturated with i n k and dried without materially lowering their blotting qualities. But in service the surface of the paper becomes covered with a coating of dried ink, rubbed, compressed and filled with dust, which renders i t useless long before i t is completely saturated with ink a n d its absorptive capacity gone. Results on speed of absorption will not give a n in-
Thickness ]/I
0, DO0
Inch 365 340 285 330 330 345 290 360 320 230 250 335 320 330 260 305 220 310 230 245 260 305 215 170 170 240 270 195 200 190 150 230 215 132 ~~
Bursting Strength Av. Points 27.0 34.0 21.0 30.0 30.5 38.0 21.0 31.0 35.0 19.0 19.0 21.5 16.5 26.0 19.5 23.5 23.5 38.0 28.0 23.5 24.5 23.5 18.5 15.0 16.0 19.0 18.5 17.5 19.0 26.0 22.0 20.0 14.5 13.5
Time Required for Absorption of Ink Water Sec. Sec. 9 9 16 10 13 11 14 10 15 16 21 15 16 15 19 19 24 19 19 19 21 18 21 18 23 17 18 24 26 16 30 22 30 20 28 30 31 25 32 33 38 23 40 25 40 26 42 42 27 45 29 49 38 57 50 62 33 65 47 65 85 74 69 104 98 147 203 197
Mounting Test Rise in 10 Min. Mm. 96 65 101 86 65 60 80 65 56 97 61 67 69 63 78 68 75 48 63 64 69
57
80 60 86
67 57 66 71 63 57 56 49 44
dication of the total absorption capacity of a blotting paper. For example, in Table I V , Samples 32955, 32799 and 32968 show practically t h e same absorptive values by the I cc. time absorption method for ink. Tests indicate t h a t rated for total capacity of absorption the order would be 32799, 32955 and 32968, or in this case inversely as their ash content. CONCLUSION
*
As the rate of rise of a liquid in t h e mounting test is independent of the bulk, a n accurate indication of the absorptive qualities of a paper cannot be obtained with this test. It is our experience t h a t the measurement of the zones formed by blots of ink on a blotting paper does not afford a reliable test for rating absorption qualities of different papers since the area of the blot is greatly affected b y t h e thickness or weight of the paper even though the same amount of ink be used with each. By the I cc. time absorption method suggested in this paper, t h e results obtained are apparently more indicative of the true absorption value of paper t h a n can be obtained by other known methods. The method also has two distinct advantages: the test is made with the paper in the horizontal position and it is possible t o use ink in making the test. The use of ink, provided a standard ink be used in all cases, gives t h e most serviceable indication as t o the absorption value of blotting paper. The absorption value as indicated with water is not always the same as with ink. The method has also been used in determining the relative absorptive values of paper toweling with very satisfactory results. I n the case of copying paper, filter paper and very light weight blotting paper only 0.5 cc. of water should be used. The method is very simple and convenient, and a number of closely agreeing results can be obtained in a very short time. THE LEATHER A N D PAPERLABORATORY BUREAUOF CHEMISTRY WASHINGTON, D. C.
