January 15, 1929
INDUSTRIAL AND ENGINEERING CHEMISTRY
mercury could be drawn into the system as desired. The apparatus finally contained an amount of air in the bulb exerting a pressure of about 400 mm. absolute, enough water in both sides to fill the tube and keep a layer in the bulb, and sufficient mercury to indicate the pressures to be read. If, for simplicity in explanation, the hydrostatic pressure of water is neglected in comparison to that of mercury, the operation of the manometer is as follows: At thermal equilibrium the partial pressure of the steam in the bulb is the same as that in the boiler and balances or cancels it on the manometer. Thus the manometer reads directly the difference of p r e s s u r e Air Manometer a n d Connections between the air in the bulb and that of the air in the boiler. When no air is present in the boiler steam space,
47
the instrument is substantially a gas thermometer, and the calibration curve of pressure against temperature is nearly a straight line. This line gives the largest manometer reading possible at a given temperature, and an addition of air to the steam space of the boiler reduces this reading. At a given temperature, therefore, the pressure read on the manometer is subtracted from that read on the calibration curve and the difference is directly the partial pressure of air in the boiler. The accuracy of the method is limited by the precision with which the manometer may be read, since Thompsons and writers of more recent books on thermodynamics have shown that the vapor pressure of water is not affected appreciably by as much as several atmospheres pressure of an indifferent gas. Readings to 0.5 mm. on an ordinary scale give an accuracy of 1 part in 2000 when the steam is slightly above atmospheric pressure. This instrument combines the characteristics of a gas thermometer with those of a vapor-pressure thermometer, and other uses with other vapors and gases will probably be found for it. If the bulb is filled with a liquid in equilibrium with its vapor in a pure state, still other uses are apparent, such as the direct determination of the partial pressure of one liquid in a binary solution or the determination of the lowering of the vapor pressure of water by the addition of an electrolyte.
* Thompson, “Applications of Dynamics to Physics and Chemistry,” Macmillan, 1888.
Freeness Testing as an Aid in Pulp Evaluation’ D. S. Davis BUREAU OF TESTS,INTERNATIONAL PAPERCo., GLENSFALLS,N. Y.
A
S SHOWN in the an-
In comparing pulps for the selection of one which several weeks one mill makswers to Special Inshall possess desired physical properties it is suggested ing a high-grade bond paper q u i r y No. 94 conthat freeness tests be made at various intervals of beatwas troubled by a very seriducted by the Technical Asing time and that comparison of the rates of change of ous wave which became a p s o c i a t i o n of the Pulp and freeness will enable the field to be narrowed down parent in the sheet in the considerably. The usual physical tests can then be cutter room. After the probPaper Industry, the value of freeness testing in pulp and made on only a few of the pulps at a great saving in lem h a d b e e n investigated time and labor. Data for the complete comparison from all angles, freeness tests paper mill control work is now generally conceded, freeof a very good with a very poor pulp are presented and it were made before and after ness being defined as “the rate is shown that the freeness data, by far the most acthe beaters, before and after of drainage of water through curate, are susceptible to rigorous mathematical treateach of the two jordans operpulp” and being influenced ment. ating in series, and in the maby the degree of hydration of chine slices after the entrance the fibers, the fiber length, and the viscosity of the water. of save-all water. The cause of the wave was at once traced The freeness tester is readily adapted to use in the grinder to one of the jordans which was cutting the stock too finely. room, both to insure uniformity of groundwood supplied to It is the purpose of the present paper to show that conthe paper mill and to assist in attaining the highest efficiency siderable time and labor may be saved in the selection of a from the pulp stones through enabling the operator to decide pulp for the manufacture of a paper of certain desired physical when the stones need fresh burring. I n the beater room the properties through the use of the freeness tester. It is not tester may be used in determining how far down the roll intended that the freeness tester should supplant the usual should be carried to refine to the proper point in a given time, physical tests, but rather that it be used in conjunction with which beaters should be run for a longer time than others on the Mullen tester, and the fold and tensile machines. To account of worn knives and bed-plates, and when to replace illustrate, if one pulp is to be selected from ten, such that such knives and plates. Similarly, freeness data are helpful paper made from it will have a certain Mullen strength factor, in connection with the operation of jordans and are as il- folding endurance, and tensile test, it is suggested that the luminating on the machine data sheet as percentage moisture change in freeness on beating be studied for all ten and that in the sheet and machine speed. As a means of “trouble only the complete physical tests be made on the two shown shooting” the freeness tester is as useful in the paper mill as a by their freeness characteristics to be the most promising. portable pH set, although, of course, in a different way. For Experimental 1 Presented before the Division of Cellulose Chemistry at the 76th Meeting of the American Chemical Society, Swampscott, Mass., September
10 t o 14, 1928.
This report deals with but two PUlps-A, a very good bleached suEte pulp, and B, a very poor one. In addition
ANALYTICAL EDITION
48
VOl. 1, No. 1
R
1 '61
I
I
I
1
I
I
1
700
I
8
I
/, A 20 T/ME IN HOURS
1
I
24
32
to studies of the rate of change of freeness, data regarding the physical properties mentioned above were collected for both pulps for purposes of comparison, although ordinarily the rate of change of freeness for pulp B would be enough to show it to be worthy of little consideration. of Actual and Calculated Freeness Values
Table I-Comparison
I
FREENESS (F)
BEATINQ ?IMB (e)
Hours 0.00 0.60 1.88 8.06 5.02 7.33 13.16 18.68 23.67 31.28
PULP B
PULP A
1
678 692 612 472 408 366 260 169
... 93
876 593 514 470 412 866 248 168
... 16
I
706 868
... 636 ... 460
390 363 303
...
706 624
...
535
...
481 395 34s 310
...
PROCEDURE-TWO kilograms of pulp were beaten in a 5-kg. experimental beater in the presence of 110 liters of water, the setting of the roll being maintained the same throughout the investigation. At various intervals the equivalent of 57 grams of bone dry stock was removed, diluted to a consistency of about 0.4 per cent in a tub, and duplicate freeness tests were made a t 20" C. on samples drawn from this diluted stock using the 1925 Model B Williams freeness tester.2 1
Davis, IND. ENG.CHEM.,18, 631 (1926); 19, 84, 162 (1927).
The freeness tests were further corrected to a consistency of 0.400 per cent. Additional water was added to the tub until a consistency of 0.27 per cent was reached and ten sheets were made using a 19 X 24 om. hand mold. No alum or sizing material of any sort was added. These sheets were air-dried, cut to dimension, calendered, and conditioned for 24 hours a t a relative humidity of 65 per cent and a t a temperature of 21" C. The remaining physical tests were made as follows: The distance between two points on the water mark was measured for the determination of the shrinkage on drying. Samples were tested for tensile strength and stretch on the Schopper tensile machine, those for folding endurance tests on the Schopper machine, and the usual Mullen tester was used for the bursting tests. REsuLTs-The data include thirty tensile and stretch tests, sixty freeness tests, one hundred shrinkage determinations, two hundred folding tests, and three hundred Mullen values. Freeness determinations always check within 1 per cent, bursting tests show variations up to 12 per cent, tensile and stretch tests are very erratic, and fold tests often vary by 50 per cent for no reason apparent to the eye. From a con-
IND UXTRIAL AND ENGINEERING CHEMISTRY
January 15, 1929
Table 11-Comparison
BEATING
TIME
I
MULLENSTRENGTH FACTOR (100 X kg. per sq. cm. per kg. ream weinht) Pulp A
Pulp
I
Hours
Ratio
of Other Properties of Pulps A and B
FOLDING ENDURANCB
1 I
Pulp A
Pulp B
Ratio
No. double folds
sideration of these facts and Figures 1 to 4, in which the data are plotted, it is evident that the freeness-time data alone are suited to any considerable mathematical treatment, largely because such data are obtained by working with wet, almost fluid material under conditions where sampling is easy and accurate. The bursting strength data are next best, but cannot compare in accuracy with the freeness values and, except for only part of the range, the bursting strength bears no very simple relation to the beating time. It has been suggested3 that for the same pulp the rate of change of freeness with time affords a satisfactory means of comparing the performance of two beaters. Conversely, using the same beater, the rates of change of freeness with time should afford a valuable comparison of the ease with which two pulps may be beaten. Figure 1is a plot of freeness against time for the two pulps, A and B, considered here, and the slopes of these curves are the rates of change of freeness with respect to time. These slopes cannot be determined graphically with accuracy, but it is evident that they are given by the first derivatives of freeness with respect to time and are readily found once the equations connecting freeness and time are known. Fairly simple exponential equations were found to fit these curves very closely, as indicated by a comparison of actual and calculated freeness values listed in Table I. For pulp A the equation is F = 676 - 118 @Jo and the first derivative is d_F = -59 e-o.60 de
For pulp B the equation is 8
49
Davis, Pulp PaDer Mag. Can., 24, 987 (1926).
II I
TBNSILE STRENGTH Pulp A K g . Der
Pulp B
w. cm.
Ratio
II
RATE
Pulp A
1
OF CHANGE OF FREBNESS
Pulp B
Ratio
Cc. aer hour
F = 706 - 108.3 and the first' derivative is given by
Table I1 gives a comparison of values for the two pulps together with the ratio of the A to the B value a t various times of beating. Conclusions
From a consideration of the plots and tabular data, it is evident that pulp A is by far the superior pulp, that for pulp A the maximum fold is developed after beating 6 hours, that both less and more beating than that accomplished in 6 hours result in considerably decreased folding endurance, that shrinkage for both pulps becomes linear with time after 4 hours' beating, and that the bursting strength increases very little after 10 hours' beating. There is no reason why such comparative data could not be duplicated by the use of any beater. However, instead of beating to the time intervals of this test, i t would be necessary to beat to the freeness values reported a t these time intervals. The ratio of Mullen strength factors as shown in Table I1 varies from 2.42 to 1.85, or 24 per cent, the ratios of folding endurances from 250 to 30, or 88 per cent; the ratios of tensile strengths from 2.5 to 1.5, or 40 per cent; the ratios of rates of change of freeness from 1.50 to 1.77,or 18 per cent, which is the most constant. This, together with the ease, accuracy, and rapidity of the freeness tests and their susceptibility to mathematical treatment, leads to the suggestion that rate of change of freeness be used as a preliminary means of comparing pulps.
A Standard Method for Determining the Viscosity of Cellulose in Cuprammonium Hydroxide' BY THE COMMITTEE ON TEE VISCOSITY O F CELLULOSE, DIVISIONOF CELLULOSE CHEMISTRY. AMERICAN CHEMICAL SOCIETY
T
HE determination of the viscosity of the cellulose dissolved in cuprammonium hydroxide solutions has become a routine procedure among most users of chemical cellulose,
and many of them include this viscosity in their specifications for purchasing the cellulose. Since, however, the viscosity may vary many hundred per cent according to the method of making the measurement, and since no two laboratories have adopted the same procedure, a committee was appointed by the Cellulose to determine Division of the AMERICANCHEMICALSOCIETY one procedure that could be satisfactorily used by all laboratories. A large amount of work was done by the various members 1 Received
September 10, 1928. Presented at the 74th Meeting of the American Chemieal Society, Detroit, Mich., September 5 to 10, 1927. At this meeting the Cellulose Division voted to adopt this method as a tentative standard, to be adopted later as an official method if it proved to be satisfactory.
of the committee, and descriptions of the methods used by most of the laboratories making these tests were obtained. The method described below is a composite of the various methods used, but it is also practically the same as the methods used by some of the largest users of chemical cellulose. Since the method is merely a tentative one, and will surely not be the most satisfactory method for all users, some of the points are discussed at some length. Solvent
There are two common methods of making up cuprammonium solutions. One is to prepare dry cupric hydroxide powder and to add this and ammonia to the cellulose. This has generally been found unsatisfactory, however, and the following method is preferred: Clean copper turnings are placed in a glass tube about 26 inches (66 cm.) in length and 4 to 6 inches (10 to 15
