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Un des symboles suivants apparaitra sur la derni^re image de chaque microfiche selon le cas: le symbole ^♦^ signifie A SUIVRE , le symbole V signifie "FIN " Les cartes, planches, tableaux, etc . peuvent etre filmAs A des taux de reduction diff^rents Lorsque le document est trop grand pour etre reproduit en un seul clich*. il est film* d partir de Tangle superieur gauche, de gauche A droite et de haut an bas. en prenant le nombre d'images nicessaire Les diagrammas suivants illustrent la mAthode. 2 3 5 6 MICROCOPY RESOLUTION TEST CHART iNSI ond IbO Its' CHART No 2 1.0 1.25 ' '" IIJM - - 12.0 mil 1.6 1.4 ^ /1PPLIED IKA^GE Inc (OuriMi'ii lliunriiiili! iLibrarij FROM THE TRANSACTIONS OF THE ROYAL SOCIETY OF CANADA SERIES III 1918 VOLUME XII The An^Ie of Contact on Glass Made by Mercury when Covered with Another Liquid by DR. A. L. CLARK, F.R.S.C. OTTAWA PRINTED FOR THE ROYAL SOCIETY OF CANADA IQIH Section III, 1918 [51] Trans. R.S.C. The Angle of Contact on Glass Made by Mercury when Ctn-ered li'ilh Another Liquid. By Dr. A. L. Clark, F.R.S.C. (Read May Meeting, 191.S). Quincke' has measured the angle of contact between mercurv and glass in air and has found that the value is about 148° for a frt-hly prepared surface of mercury and clean glass, but is somewhat smaller after a time. Pockcls^ has measured the angle of contact between glass and various liquids. Her success seems to depend on her method of cleaning and testing the cleanliness of the glass. For many liquids the angle made with glass is zero. Some experiments on mercur\- in glass tubes, when covered with acidulated water, indicated that the angle of contact is, in many cases, zero. Lippmann'' states that for pure water and mercur\- in contact with glass, the angle is not zero, but for a HjSO, solution, the value drops to zero. Experiments had been undertaken to detern>ine the validity of the conclusion reached from study of such surfaces before Lippmann's remark was noticed. No quantitative measure- ments have been discovered, so the results are here recorded. A large drop of double distilled mercury was placed in a cleaned watch-glass which rested on a steady platform. A spectrometer was fastened to a rigid support with the axis horizontal t!nd so arranged that a small, silvered mirror mounted on its table was just above the mercury drop. The light from a distant high-power tungsten lamp fell on a large stationary mirror, placed higher up over the drop and arranged so that a strong lx;am fell on the edge of the drop. A third mirror, also stationary, placed below the apparatus, received the light from the rotating mirror and reflected it through a small tube provided with cross wires at each end. A cover glass cleaned in boiling HXO,, KOH, distilled water, and finally by heating in the flame of a spirit lamp, was placed on top of the drop of mercury and the light and mirror arranged so that the reflec- tion of the light occurred at the boundary of the glass and the mercury. The spectrometer reading was taken and then the small mirror rotated till the reflection took place from the convex surface of the drop. The • Quicke, Pogg. Ann. 105. Weid. .^nn. 2, 152, 1877. » Pockels, Phys. Zeit. XV, 39, 1914. • Lippmann, Ann. de Chini. et Phys. (5), 494, 1875. 48;i07 52 Tin; koVAI. SOCILTV l)K CANADA .in.i;lc thri lULili \\ liii li tile niirr lunuii i> ihr siippk nicnt i<\ {hv aii^li' 111' ci'iil.u t iif tlu' nu-ri iiry .iiid i;l.i-— or ihr \.ihii- (4 llic .myk- inraMircd in tlu' air or the otlicr ii(|iii(l. Mca^iirtiiK'nt-- on mcnairy and i^ias-- willi air a> tin.' tiiird Mih- >laiuc \i(idi-d ^onuwlial di-curd.int n--ult>, a> >ii(li roults ii>naily arc. 'I'hc fdllnwini; takni at dillcrcnt time-- t;iM"- tlic results for frohly prepared surfaces; 147' .^6' 1U^5' 146M')' 14.r 2'/ 144° iO' 142' 5 re|>re>enl ani;le> in the men ■ur>'. Next reacHiiLis w ith pine (H>tiiled water on the menu ry were taken. Here ,i r-niali weij^iit was pkiced en the ccA-er t;la>s to pre\ent its lloatinj.; oil. With pure di~':lled water and ( le.m j;kiss, tiiere is an anj;le of contact. Tile follow in i; ,iri' results for .ukiss, mere ur\- and water: r V 5= 4.V .S° l.r .S' n' 4" 46' with occasionalh' otluT resnlt-- rising as hii;h as 1 1° which are evidently due to traces of dirt. Thc~e ani;le- arc measured in the water. With a stn)nt; sulphuric acid solution, the oiiserxations are easy and alwa>s \ ieid an an,i.;le < >. Startin,u with a 2.^ per cent solution, observations were takiii with i:onstaiilly diniini-hing concentration with the following results: Above 1 per cent 2 per cent 5° 59' 6° very small With till' 2 per cent solution the observations are \er>- difficult. Then is not the e.isy decision as in the higher concentration. Somewhere lietwei'ii a 2 jut cent concentration and pure water, the angle passes from 0° to about 5°. The exact point of cliange from zero angle has not been determined but is probably for a concentration of less than {. per cint. In the case of three pure liquids in contact along a line, it has been show 11 that the Neumann triangle is impossible, but, with a solid and two liquids, equilibrium is possible and there may be an angle of cont.K t. In the case of a merrur\-water surface in contact with glass, for example, thiTc is an angle as shown abo\e. If Tj is the surface tension of the w' surface and Tj of the glas.s-water surface, the equation of equilibriuin is To - T,. T, 1 T3 — T2>Ti, equilibrium is imiiossible ,uid the aiigl ■ of contact has become zero. This, in geiier.il, rejiresents a condition of iiist.ibility. For the water and mercury on glass we have stability With the acid-mercur>- surface, at least for all but the smallest con- centr.itions, the condition is one of instability. In this case, the acid T,i + \\ cos 6 = To, so cos d = Iclark] AN(,1 K or ( ONTACT ()\ CLASS 53 tiMuls to cTcc[) l)et\\c'(.-n the .ulass and iiunur\-, licini; (ijjpiiM'd l)\- the hydrostatic pressure and perliaj)> li\' othiT lliin^;-.. ExpiTitnents undertaken to iH~eo\cr llie pre-.enre of ilii- creepint;, show that it exists. A 1 irtje luinilii'r of i;la>s tube-- were eleaned and dried and sealed at one end. 'l'he~e were about 8 mm. in diameter and 10 cms. lorm. Some freshly (Hstiiled nierrur\- was poured iuiM ilie tuiies and HjS(), sohitions of different concentration^ were p aired o:; top of tile mercury. Tile tubes wen> put in a ([uiet place for oi)s