A LIQUID CHRYSTAL.

Clutha Leader, Volume XXXIII, Issue 2040, 21 August 1906, Page 7

A LIQUID CHRYSTAL.

The cbscoveTy by Lehman.ii, a German physicist, of what he calls "liquid crystals'' was noted in tho Literary digest some years ago; in fact, the beginning of his investigations dates as far back as 1889. The name would appear to the ordinary reader to be a contradiction in terms, and indeed it is yet so regarded by many scientific men. Still, after years of discussion and experiment, the main point of Lehmajin's discovery remains undisputed, namely, that drops of certain substances that aTe undeniably liquid exhibit, when examined under polarised light, phenomena that have always been regarded as distinctively characteristic of crystals. The sub jevt, in its latest developments, is rcviewei in the Revue Hcientilique in a brief article by J. Uerome. This writer looks upon Lehmann's experiments as proving that certain liquids may have, a real crystalline structure, and he names a considerable number, all rather complex organic com pounds, as, for instance, the alkaline ole ales. All show, under the polariscope, the characteristic shadow-cross that indicates crystalline formation. Says Mr DeTOme :--. "the arrangement foT the optical study of this phenomenon is quite simple: The plate of a polarising microscope is kept at any desired temperature with the aid of a Bunsen burner, thus enabling the observations to be kept up as long as desired. All degrees of viscosity arc met among these substances; pronounced fluidity gives rise to spherical droplets, which grow more elongated as the molecular attractions become more important than tho surface tension. . . These droplets then show, in polarised light, the beautiful tints of polarisation, rising from me edge to the centre as if the drop were a solid crystalline lens. To such drops Lehmann gives the significant name of 'liquid crystals.' " Liquid crystals, we are told, present themselves in two principal positions between which there aTe all possible forms of transition. Lu the first the axis is vertical ; in the other, horizontal. In some cases the action on light is thirty times as gTeat as that of oolid quartz. To quote furtheT:—"The crystalline globules aTe not immobile; they generally turn in a direction opposite to that of the tends of a watch, and the black cross. . . then takes the form of a spiral. Lehmann has not neglected to study the influence of magnetism oh the liquid crystals; those of para-oxyphenetel take, in a horizontal mag netic field, the second position (described above) -while in a vertical field they takr the first position. . . The study of the absorption of certain coloring matters by the liquid crystals excludes the idea that the heterogeneous liquid may bo considered as an emulsion. The drops may coalesce; when this occurs the momentary prceerva tion of the individual character of the drops gives at first a large number of black crosses, up to the point wheTc each resultant drop behaves like a single crystal. The plasticity of some crystals harlong been recognised; certain soft crystals may be deformed and coalesce -with others after the same fashion as liquid, crystals, for example, in the oase of oleate ammonium; these soft crystals form a curious intermediary between rigid and liquid crystals. To what cause may we attribute the etructuT© of the turbid liquids winch we have been discussing ? Lehraamn thinks it i 6 due to orientation and constitution, of theiT molecules; other authors, on tihe contrary, think that tfheee turbid liquids ate non-homogeoeoue media. The

experiments made to settle the question show clearly that the liquids are not emulsions; it would soem that this hypothesis must bo rejected and that tlie double-refraction of these turbid liquids is due to their molocuktr structure."