ANALYTICAL EDITION
66
Vol. 3, No. I
Determination of Sulfur by Means of the Turbidimeter' S. W. Parr and W. D. Staley UNrVERSITY OF ILLINOIS, URBANA, ILL.
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EQUIREMENTS for sulfur determinations under widely varying conditions and in various and complex ' combinations seem to be on the increase. Not the least noticeable of these conditions is in connection with the work of the power plant where, for some of the determinations, convenience, speed, and a minimum or absence of chemical training are obvious conditions for arriving a t the sulfur factor. On many accounts the sulfur photometer or turbidimeter lends itself in an attractive manner to this determination. Such an instrument has been in use for a number of years but the wider scope required for its function-
This extended use is especially notable in connection with the control of sulfates in boiler water, to conform to the A.S.M.E. standard, as a check on the development of embrittlement or cracking of the boiler plates. Description of Apparatus
I n Figure 1,the base supports all of the various parts. A light of about 2 candle power is mounted in the center with the current supplied from two or three dry cells. This current is passed through a voltmeter and also through a resistance, R, so that the light can be set a t any standard voltage, where it can be retained throughout a test. A is a tube which serves as a standard for the other parts of the apparatus. It supports a stationary telescoping tube, C, with an optical glass bottom immediately above the light. This tube holds the turbid solution to be tested and also has a plunger tube, P, which is empty but which has an optical glass bottom and which may be moved up and down, toward or from the light, by the ratchet. The distance from the optical glass in the bottom of P to the optical glass bottom in C is measured in millimeters on the scale, 8.
-7-
P
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u,
Figure 2-Turbidimetric Reading b y Various Operators
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Figure 1-Cross
Section of Turbidimeter
ing and the increasing demand for a high degree of accuracy, along with a greater facility of operation, has made it desirable to redesign the apparatus with these particular applications in view. 1 Received October 2, 1930. Presented before the Division of Gas and Fuel Chemistry at the 80th Meeting of the American Chemical Society, Cincinnati, Ohio, September 8 t o 12, 1930.
The advantages of this arrangement are, that having made up the turbid solution to a standard amount, say 200 cc., the depth of turbidity for the conditions chosen is not disturbed by ripples on the surface of the liquid. Additions of more solution to secure greater depth are obviated. The optical glass is entirely submerged at all stages in the reading, and is moved up or down within the solution to secure the necessary depth and end point. Both tubes are of Bakelite or opaque glass and do not promote diffusion of the light. The eyepiece, located in a favorable position above the instrument, requires that the distance from the eye to the light be the s1tme for all readings. The end point is taken as the complete disappearance of the red filament, which gives a far sharper end point than is possible between a lighter and darker spot of light where both consist of diffused light of varying intensities. By means of the resistance in the voltmeter it is possible to correct the variation in the strength of
January 15, 1931
INDUXTRIAL AND ENGINEERING CHEMISTRY
the battery so that a light of uniform candle power is always available. It will be seen a t once that the conditions thus secured correct many of the variables inherent in other forms of apparatus of this type. Indeed, the variation in eyes between different operators is reduced to a minimum, as may be seen from Table I. The solutions employed in this test were samples of boiler waters taken from the blow-off a t the power plant,. Four different persons made readings and the average of three readings for each person was taken. These people were taken at random and operators 3 and 4 were substantially without experience in this sort of work. Table I-Turbidimetric Readings by Various Operators SOLUTION OPERATOR 1 OPERATOR 2 OPERATOR 3 OPERATOR 4 Mm. Mm. Mm. Mm. 1 126 127 129 132 2 91 84 85 85 3 66 65 65 67
Figure 2 is a curve developed by use of a standard solution of sodium sulfate, the readings being confirmed by a number of individuals. It should be remembered, however: that
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eyes vary, and especially so where the eye is focused on an object, as in this case, instead of observing the intensity of light on a given area. A person using glasses, therefore, will expect to obtain readings different from those obtained by one not using glasses. The variations, however, are uniform over the curve and the variation may be used as a constant or a new curve may be drawn to meet the specific conditions. I n Table I1 are given parallel determinations by use of the turbidimeter, as compared with the results by the ordinary gravimetric process. These results were also obtained on boiler waters with widely varying amounts of caustic and sodium carbonate. Table 11-Turbidimeter WATERNo. 17206 17299 17300 17318
Results for Sulfates i n Boiler Water TURBIDIMETRIC GRAVIMETRIC P. 0.m. P . p m. 1770 1742 1550 1582 1482 1499 808 812
It is believed that the sharpness of the end point and the good agreement obtainable by this instrument will make it of practical utility, especially in the power plant.
Application of a Bromine Method in Determination of Phenol and Cresols' R. D. Scott OHIO DEPARTMENT OR HEALTH,COLUMBUS, OIIIO
Iodine Methods With the increasing application of dephenolizing I T H I N the last five treatments to coke oven gas condensates in order that years dephenolizaTheoretically, phenol and water supplies may not be contaminated by phenolic tion of those coke m-cresol form triiodo comcompounds, there is need for accuracy of method in oven liquors which eventually pounds, while 0-cresol and pdetermining the phenols content of the wastes before reach public water supply incresol form diiodo compounds. and after treatment. takes, in order to eliminate so In the application of the While a method based on the combination of phenols far as may be practicable the Messenger-Vortmann method with iodine has been considered more accurate than development of objectionable to mixtures all are convenvarious bromine methods, data are presented which tastes following chlorination, tionally calculated to phenol, show that under certain prescribed conditions a brohas become a general practice. CaHsOH, as t r i i o d o com; mine method yields the more accurate results. pounds, a c c o r d i n g to the TO measure the efficiency of dephenolizing plants, the reaction: need exists for an accurate method of determining the phenols CsH,OH 61 3NaOH = CeHJsOH 3NaI 3Hz0 content of these wastes before and after dephenolization; the work to be described was prompted by the belief that Thus, theoretically only two thirds of the o- and p-cresols existing methods are not sufficiently accurate. present would be reported. Actually with these two cresols The Skirrow (12) procedure for the estimation of phenols the proportion of iodine fixed is more than the requirement in gas liquors, the Rose and Sperr (10) modification of which for the diiodo compounds and less than the requirement is a t present in general use, may be separated into two parts, for the triiodo compounds. first the removal of interfering substances, and second the The writer found that with o-cresol the iodine fixed was combination of phenol and cresols with iodine, employing 118.8 per cent and with p-cresol 137.0 per cent of theory the method of Messenger and Vortmann ( 7 ) . The procedure for the diiodo compound. Thus, only 79.2 per cent of the is subject to material errors, both in the removal of inter- o-cresol and 91.3 per cent of the p-cresol present in a mixture fering substances and in the final determination of phenols. would have been reported, applying the triiodo calculation. I n this paper, only the determination of phenols is conRedman, Weith, and Brock (9) modified the Messengersidered, preliminary purification being assumed. Vortmann method by substituting sodium bicarbonate for Several bromine methods are also in use. For instance, sodium hydrate and obtained results near to theory when U.S. Steel Corporation chemists (14) add bromine in excess, working with phenol and the separate cresols. The writer, acidify, then dry and weigh the precipitate of bromine com- employing their method, also obtained results near to theory, pounds of phenol and cresols. Williams (13)applies a bromine phenol and m-cresol being calculated as triiodo compounds titration after preliminary purification. Shaw (11) has de- and o-cresol and p-cresol as diiodo compounds. veloped a method using a specialized preliminary distillaHowever, while this modification yields more accurate tion followed by a determination of the phenols in the dis- results than the Messenger-Vortmann method as employed tillate turbidimetrically with bromine. by Skirrow, there still exists the error due to the unknown and no doubt varying proportions of phenol and the indi1 Received August 5, 1930.
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