ANALYTICAL EDITION
46 Discussion of Results
The results of these tests are shown in the accompanying table. Some spaces are left unfilled either because no data were available or because the results were of such a nature that they could not be recorded without comment. The latter cases are discussed in the text. I n those instances in which no pH range has been given, either no change in color occurred or the change was apparently due to decomposition or precipitation of the dye. For example, up to pH 11.8 the blue color of malachite green was fairly stable, but above this fading was almost instantaneous. Such a compound, where the change is due to progressive fading, can hardly be classed as a pH indicator. Crystal violet, methyl green, and the fuchsins acted in a similar manner. A peculiar phenomenon was noted in the case of alizarin and alizarin blue S. Clark' and Balch6 give conflicting color changes for these compounds in the higher range. Clark, from data culled from the literature, reports alizarin (violet 10.1-12.1 purple) and alizarin blue S (green 11.0-13.0 blue), whereas experimental results reported by Balch are alizarin (wine buff 9.8-11.4 deep violet) and alizarin blue S (brown 9.5-12.0 blue green). The present writers found that such conflicting results were probably due to the nature of the buffer mixture used. With carbonate mixtures they were able to check the results given by Clark for alizarin, except that the range was 10.8-12.0. With alizarin blue S the present writers found blue 11.0-12.4 green, a reversal of the colors given in Clark's table. However, when borate buffer mixtures were employed, the writers' results checked with those given by Balch. The color changes for purpurin also varied with the buffer mixture. Precipitation is another source of error in determining the color change, Buffer mixtures containing safranine a t first gave a red color which gradually changed to violet, due to precipitation, which was quite pronounced a t high alkalinities. This may account for the color change, red to violet, which is sometimes given for this dye.3 With thymolphthalein and m-cresolphthalein, precipitation is usually sufficient to render these dyes decidedly unsatisfactory. It often causes a bluish cast, even in solutions having a pH below 9.0, which may be taken for the color of the indicator. When the con4
8
Clark, "The Determination of Hydrogen Ions," p. 91 (1922). Balch, Sugar, 27, 587 (1925).
Vol. 1, No. 1
centration of dye is purposely lowered to avoid precipitation, the color is too faint except in a layer too deep for a practical test. With dyes which give fluorescence the color by reflected light often differs radically from that by transmitted light. Eosin BN gave no marked color changes between pH 10.0 and 14.0 when observed by transmitted light. Fluorescence was marked throughout the range and the tubes appeared yellow by reflected light. The color change for this dye is given as pink 10.5-14.0 yellow in the International Critical Tables. Certain of the dyes developed a stable color slowly. Dinitrohydroquinone diacetate and trinitrotoluene are examples. When the former was added to buffer mixtures ranging from pH 10.0 to 12.0, all the tubes were yellow a t first. I n the lower range this yellow color gradually deepened, while a t pH 11.0 and above, it slowly changed to a deep purpIe. Although none of the dyes examined are as satisfactory as are the sulfonphthaleins of Clark and Lubs,Band Cohen' at lower ranges, about five can be used for hydrogen-ion work. These are alpha-naphthol benzein, Clayton yellow, alizarin yellow GG, alizarin yellow R, tropaolin 0, and azo blue. Objections can be raised against each of these, however. The majority give color changes that are not very pronounced, from yellow to deep yellow or orange. Alizarin yellow R has been found to give misleading lemon-yellow shades in solutions containing lime, although it is fairly satisfactory otherwise. Tropaolin 0 gives quite marked readings, although it has been reported to have a rather large salt error.2 Azo blue gives a good color change in the pH range 10.0 to 11.0, but it is not entirely satisfactory much above or below this. Alpha-naphthol benzein gives fair color changes, but the dye is low in tinctorial power. I n an investigation of this nature the matter of purity of the dyes can always be raised. Since no spectrophotometric examination of the dyes was made, no definite proof as to their purity can be given. I n general, the investigation is an examination of dyes that have been recommended and in many cases are being sold for the purpose of pH studies over the range 10.0 to 14.0. As such, most of these dyes are decidedly unsatisfactory. Since this investigation has yielded no indicators of outstanding excellence, attempts are now being made to synthesize new dyes to cover the higher pH ranges. 6
Clark and Lubs, J . B a d . , 2, 1, 109, 191 (1917). U.S.Pub. Health Rcpts. 41, 3051 (1926).
7 Cohen,
Manometer for Determination of Gases in Vapors' D. F. OthmerZ UNIVERSITY OF MICHIGAN, ANN ARBOR,MICE.
H E rate of condensation of steam is largely affected by the presence of a small amount of air or other noncondensable gas. It is desirable in experiments in heat transfer from steam to tube to be able to measure conveniently and accurately the amount of air present. The manometer to be described was devised and used in work of this nature. The dotted section in the figure represents the small boiler t o which the manometer is attached. The level of the boiling
T
1 Presented as part of the paper, "The Condensation of Steam" before the Division of Industrial and Engineering Chemistry at the 76th Meeting of the American Chemical Society, Swampscott, Mass., September 10 to
14, 1928.
* Present address, Eastman
Kodak Company, Rochester, N. Y.
water is indicated, and the space above is filled with the steam to be analyzed for air. The 2-mm. Pyrex tubing was bent as shown and connected with rubber tubing, wired, and cemented on tightly. The left arm extended through a packing gland and was turned below the surface of the liquid in the boiler, while the right arm terminated in a bulb of about 300 cc. capacity, also of Pyrex and fashioned so as to drain completely into the manometer. A stopcock for filling was welded on the top of the left arm. The filling of the tube and bulb was a difficult operation. The open end was stoppered and the cock opened and connected to suction. A trap with a small amount each of mercury and water was inserted in the suction line, so that when the tubing was partially evacuated either water or
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 t h e 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
