Vol. 40. Dec.21 DECEMBER 1870. No. 269. Published the First Day of every Month.-Price 2s. 6d. Being a Continuation of Tilloch's Philosophical Magazine,' CONDUCTED BY SIR ROBERT KANE, LL.D. F.R.S. M.R.I.A. F.C.S. AND WILLIAM FRANCIS, PH.D. F.L.S. F.R.A.S. F.C.S. FOURTH SERIES. N° 269.-DECEMBER 1870. LONDON: PRINTED BY TAYLOR AND FRANCIS, RED LION COURT, FLEET STREET, Printers and Publishers to the University of London. Sold by Longmans, Green, Reader and Dyer; Kent and Co.; Simpkin, Marshall and ALBEMARLE STREET, PICCADILLY, W. LECTURE ARRANGEMENTS FOR 1870-71. Subscribers of Two Guineas are admitted to all the Courses. A Single Course, One Guinea, or Half-a-Guinea. (Lecture Hour, THREE O'CLOCK.) CHRISTMAS LECTURES (adapted to a Juvenile Auditory). Professor ODLING, F.R.S.-Six Lectures, On Burning and Unburning,' on December 27, 29, 31, 1870; January 3, 5, 7, 1871. BEFORE EASTER, 1871. 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Payment:-First year, Ten Guineas; afterwards, Five Guineas a year; or a composition of Sixty Guineas. Prospectuses (when prepared) may be had in the Hall. H. BENCE JONES, Hon. Sec. [ADVERTISEMENTS continued on 3rd page of Cover. THE LONDON, EDINBURGH, AND DUBLIN PHILOSOPHICAL MAGAZINE AND JOURNAL OF SCIENCE. [FOURTH SERIES.] DECEMBER 1870. XLIX. Researches on the Magnetic Rotatory Polarization of Liquids. By Professor A. DE LA RIVE*. THE present researches are a continuation of those I communicated to the Society, and published, in 1868+. In my first memoir I studied the phenomenon of magnetic rotatory polarization in itself, and investigated the causes which exercise an influence on its production and intensity. I showed that the actions which permanently modify the molecular constitution of a solid body (such, for example, as the transmission of a powerful electrical discharge) modify in an equal degree its magnetic rotatory power; while in the case of liquids this power undergoes no modification, whether they are acted upon mechanically or by an electrical discharge or an electric current. I called attention to the influence which seems to be exercised upon the intensity of the magnetic rotatory power by the density of the substance submitted to the action of the magnet, even when this element is not exclusively predominant-citing as an example the considerable magnetic rotatory power (the greatest known) possessed by thallic alcohol, the density of which is enormous (sp. gr. 3.55). The new researches just terminated have been made upon liquids only; for solids present the inconvenience of a molecular constitution too much varying from one to another to conduct us to any general results; and elastic fluids do not possess sufficient density to render the phenomena in question sensible. * Translated from a separate copy communicated by the Author, having been read before the Société de Physique et d'Histoire Naturelle de Genève, June 2, 1870. ↑ Archives des Sciences Physiques et Naturelles, vol. xxxii. p. 193; Annales de Chimie et de Physique, 4th Series, vol. xv. p. 57. Phil. Mag. S. 4. Vol. 40. No. 269. Dec. 1870. 2 D The present memoir consists of five sections. In the first I describe the apparatus and the experimental processes I have used. In the second I give the results furnished by experiment in operating upon a certain number of liquids very different one from another. In the third I study the influence of variation of temperature on the magnetic rotatory polarization of liquids. In the fourth I endeavour to determine the ratio which exists between the magnetic rotatory power of a mixture of two liquids and those of the ingredients of which the mixture consists. In the fifth I exhibit the result of the experiments I have made upon the magnetic rotatory power of some isomeric liquids. § 1. Description of the Apparatus and the Experimental Processes. The electromagnet which I used is composed of two cylinders of soft iron of 12 centims. diameter and 36 centims. long, each with a cylindrical perforation through its axis 3 centims. in diameter, and the two wrapped round with 1665 metres of insulated copper wire of 2.7 millims. diameter and the total weight of 92 kilogrammes. The wire encircling one of the cylinders is 835.8 metres long, and makes 1555 turns, forming 16 superposed layers; the other is 829-7 metres long, and makes 1537 turns, forming also 16 superposed layers. The two cylinders of soft iron, thus enveloped, are arranged opposite to each other on a cast-iron stand, so that their axes are in the same horizontal line. A screw, moved by a crank, brings into contact the two interior polar surfaces, or separates them to a maximum distance of 30 centims. A prismatic bar of soft iron, terminated by two shorter bars perpendicular to it, which are 10 centims. wide and 3 centims. thick, serves as an armature connecting the extremities or exterior polar surfaces of the two cylinders. It can slide in such a manner as not to hinder the approach or separation of the interior polar surfaces*. Strong pressure-screws keep in place, at the desired distance, the two cylinders, which, without this precaution, would be liable to rush together at the moment of magnetization and to break the objects placed between the polar surfaces. For the experiments on rotatory polarization, on the side nearest to the source of light a Nicol's prism is fitted to the opening of the perforation of the nearest cylinder, to serve as polarizer; a similar analyzing-prism is placed at the extremity of the perforation of the other cylinder of soft iron. This extremity is * The addition of this armature augments the force of the electromagnet in the ratio of 3: 2. furnished with a telescope, to which the eye is applied to receive the polarized ray, and with a divided circle which moves with the analyzing-prism and enables one to appreciate to l' the angle through which the prism is turned. The substance to be operated on is placed between the two poles in such a manner as to be in the path of the polarized ray and, consequently, traversed by it. We then determine the azimuth of the angle which gives the passage-tint when the electromagnet is magnetized by passing an electric current through the wires which encircle it. Afterwards, by means of a commutator, the direction of the current is reversed, and a second passage-tint is obtained, distant from the first by a certain angle, the azimuth of which is likewise determined. The angle through which the analyzing-prism had to be turned in order to pass from the one passage-tint to the other represents double the rotation of the plane of polarization. This is the angle I have always measured, and which, for the sake of brevity, I call the angle of rotation. After a little practice the operation is effected very quickly and accurately: one eye receives the polarized ray, while, by means of a lens, the graduation of the moveable circle is observed with the other. I will not dwell on other details, easy to be understood, and will merely add that the source of light I used was a gas-burner which gave a very brilliant white light. The liquids on which I operate are contained in tubes hermetically closed at their two ends with glass, which makes it necessary to take account of the influence of the glass upon the rotation-an influence the existence of which I ascertained by operating on empty tubes, and the amount of which varies with the nature and the thickness of the glass. In order to dispense with this correction I placed the tubes between the interpolar surfaces so that their two extremities entered to about a centimetre within the cylinders of soft iron, the internal diameter of which is greater than the external diameter of the tubes. Theory indicates, and experiment fully confirms, that the portion of the tubes (and consequently their glass ends) which is placed in the interior of the iron of the electromagnet is subject to no influence at all from the magnetism developed by the electric current, and that the magnetism affects only that portion of the tube which may be called interpolar-consequently only the liquid column whose length is equal to the distance of the two polar surfaces*. I have made a great number of experiments to confirm the accuracy of this principle. Thus I placed in the interior of one of the cylinders of the electromagnet some tubes, from 10 to 15 centims. in length, filled with sulphide of carbon; and never was any effect produced by them upon the polarized ray which traversed that liquid, even when the magnetization was very strong; but when one of the extremities was withdrawn only a few millimetres, an effect was produced. |