T. I. QUICKENDEN, D. &BETTS, !I. B. COLE,AND M. NOBLE
2830
The Effect of Magnetic Fields on the pH of Water by T. I. Quickenden,"' D. M. Betts, B. Cole, and M. Noble Department of Chemistry, linicersity of Queensland, St. Lucia. 4007, Brisbane, Australia
(Received February 16, 1971)
Publication costs borne completely by The:Journal of Physical Chemistry
Xo changes in pH were observed after doubly distilled water was passed through magnetic fields in the range 0 to 24,000 G. The pH was recorded continuously using a glass electrode inserted in a flow system which led the water through the field at flow rates between 1.08 and 200 ml mill-'. The glass electrode was sufficiently distant from the magnet for it, and the water sample, to be in a region of zero field. N o evidence was obtained t o support the claims of Joshi and Kamat,2 who reported apparently permanent pH changes of up to +0.62 unit in water which had been passed through a magnetic field. It was shown that changes of this
magnitude would be energetically improbable.
According to Joshi and Iiamat,2 magnetic fields in the range 1900-5700 G (1 G = Wb m-2) permanently change the p H of distilled water by up to +0.62 pH unit. Similar observations have been reported3 for naturally occurring xaters. Ileasurements4--6of magnetic effects on the physical properties of Tvater have usually been part of an investigation of the reduction of boiler scale which results when the water supplied to a boiler is passed through a magnetic field. A variety of explanations have been proposed for this phenomenon and one such explanation2 involves a magnetically induced change in the pH of water. This present publication records an unsuccessful attempt to reproduce the pH changes reported by Joshi and I(amat.2 Experimental Section The p H of the water was measured on a Toanson and Mercer recording pH meter equipped with a Titron glass electrode (Type A) and an automatic temperature compensator. The magnetic field was provided by a 4700-G Rola permanent magnet Type PA145 with a pole gap of 1.9 cm and a pole diameter of 6.4 cm. Doubly distilled water, which had been stored in a S-1. Pyrex glass flask, \yas passed through the magnetic field via an all-glass Pyrex siphon of internal diameter 0.4 cm. FolloTving Joshi and Kamat,2 the water was equilibrated Lvith atmospheric carbon dioxide. The glass electrode, a thermometer, and the temperature compensating probe were all incorporated in a 17-ml glass bulb which was an integral part of the glass siphon. The magnetic field lvas applied to the water in the siphon at a point 30 cm before the glass bulb. -1Iovement of the magnet to or from this position caused only a transient deflection on the pH meter of less than 0.005 pH unit, irrespective of whether the water was present or not. Room temperature varied slowly during the experiments from 299.6 to 302.9"K. The measured pH The Journal of Physical Chemistry, Vol. 76, X o . 18, 1971
showed a temperature dependence of 0.02 p H unit OK-'. This figure includes the effect of temperature on the pK, of water and the effect of any inadequacy in the automatic temperature compensator. During any one run with the permanent magnet the temperature changed by less than 0.3"K. The surface of the glassware is a potential source or recipient of protons and hydroxyl ions. To minimize pH changes due to surface desorption, all the glassware was soaked for 15 hr in an alkaline cleaning mixture containing detergent and sodium hexametaphosphate. After rinsing in once distilled xater, the glassware was soaked for several days in two successive batches of doubly distilled water. After this treatment, the same glassware was used without further cleaning throughout the whole series of measurements which were carried out over a period of several months. This cleaning procedure would be expected to maintain contamination from the glass at a low or steadily decreasing level. No systematic trend in the pH was observed over the period of measurement. The p H meter and chart recorder were earthed at a common point in order t o minimize electrical interference. The normal operations and movements in the vicinity of the p H meter had no detectable effect on the recorded pH. In order to carry out a measurement, water was passed through the glass siphon at a constant, measured rate, which was controlled by restricting the air flow to the reservoir with capillary tubes of various sizes. (1) To whom all correspondence should be sent a t the Department of Physical and Inorganic Chemistry, University of Western Australia, Nedlands, 6009, Western Australia. (2) K. M. Joshi and P. V. Kamat, J . Indian Chem. Soc., 43, 620 (1966). (3) T. Kohout, Vod. Hospod., 12, 458 (1962). (4) D. M. Umanskii, Sov.Phys.-Tech. Phys., 10, 1720 (1966). (5) 9. A. Bruns, V. I. Klassen, and A. K . Kon'shina, Kolloid. Zh., 28, 153 (1966). (6) R. Delhes, Cent. Belge Etude Corros., R a p p . Tech., No. 747 (1961).
THEEFFECT OF MAGNETIC FIELDS ON THE p H OF WATER The pH of the flowing water was recorded for approximately 10 min. The magnet was then placed in position and the p H recorded for twice the time it took for the water to pass from the magnet to the glass electrode. The magnet was then removed and the pH recorded again for a t least 10 min. Although the recorded pH was displaced slightly to a new value whenever t’heflow rate was changed, it nevertheless fluctuated by less than h0.04 p H unit during any series of measurements at constant flow rate. Magnetically induced changes as small as 0.04 p H unit would have been detectable by this method.
Results and Discussion Flow rates of 1.08, 8.2, 8.7, 9.8, 11.6, and 12.7 ml min-’ were examined as described above, but in no case was any systematic change in pH observed. The flow rates examined were in the range investigated by Joshi and Kamat2 and the flux density used was close to the figure of 4800 G used by these workers in one of their measurements. I n order to test the possibility that pH changes are produced only by fields of certain critical intensity, the permanent magnet was replaced by an electromagnet which was varied continuously from 0 to 24,000 G over a period of 20 min. p H changes as small as 0.1 p H unit could be measured by this method. No such changes were observed at flow rates between 3.2 and 200 ml min-’. The results presented here provide no evidence for the pH changes reported by Joshi and Kamat. These workers attributed the pH changes to magnetically induced changes in the ionization constant of mater. This explanation is not tenable thermodynamically. It can be shown7 that when a magnetic field is applied to an equilibrium reaction
+
+
VIAI VZAZ . .
+.
.
+
vn-1An-i
+ vA,
2831 between nonferromagnetic substances, that the equilibrium constant changes from K to K , where
K , = K e x p A2RT --
(1)
In this equation, which is expressed in unrationalized cgs-emu units, H is the magnetic intensity, xt is the molar magnetic susceptibility of species i, and T is the absolute temperature. At room temperature (300°K) and at the maximum field of 5700 G ( H zz 5700 Oe) used by Joshi and Kamat, eq 1 predicts that K H differs from K by only 2 parts in lo7, even in the optimal case where a paramagnetic substance with xt = 2 X loe4 cm@mol-’ is in equilibrium with a diamagnetic substance for which x i = - 1 X cm3 mol-’. The derivation of eq 1 assumes that the change of volume on magnetization is negligible and that the magnetic susceptibility of the material is independent of the magnetic intensity. The former approximation is generally true and the second holds except for ferromagnetic materials and a few other unusual cases.* In the present situation both assumptions should hold for the three species involved in the equilibrium 2HzO
H30+
+ OH-
I n view of the above calculations and in view of the measurements presented here, it is doubtful whether the observations of Joshi and Kamat2 represent a property of water. It may further be concluded that magnetically induced changes in the pH of water are not a feasible explanation for any inhibition of boiler scale which resultse when the water supplied to a boiler is passed through a magnetic field. (7)R. Delhes, Bull.SOC.Roy. Sci.Liege, 26, 161 (1957). (8) E. A. Guggenheim, “Thermodynamics,” 3rd ed, North Holland Publishing Co., Amsterdam, 1957, p 430.
The Journal of Physical Chemistry, Vol. 76,N o . 18, I971
