2454 MERTON : THE VIS(I0SITY ANDCCLIIL-The Viscosity and Density of CaesiumNitrute Solutions.By THOMAS RALPH MERTON, B.Sc. (Oxon).IN recent years the viscosity of salt, solutions has been the subjectof numerous investigations, which have mainly been directedtoward elucidating the relation between viscosity and electricalconductivity. Most of the alkaline nitrate solutions have beeninvestigated (Gruneisen, Wiss. Abh. Yhys. Tech. Reichsanstalt, 1904,4, 239; Applebey, this vol., p. 2000, and others). Very little,however, is known of the viscosity of cmium salt solutions, withthe exception of a single investigation on the viscosity of thechloride solution by Wagner (Zeitsch. ph,ysilcaZ. Chem., 1890, 5,31).In the present investigation, the viscosities and densities ofcaesium nitrate solutions of different concentrations have beendetermined at Oo, loo, 1 8 O , and 2 5 O .EXPERIMENTAL.The method used for determining viscosity was that of Poiseuille,that is to say, a determination of the times of flow of the solutionthrough a capillary tube.The precautions which must be observedin order to secure an accuracy of one part in a, thousand by thismethod have been thoroughly investigated by Gruneisen (Zoc. cit.,p. 153) and Applebey (Zoc. cit.), whose method I have followed inthis investigation, and to whom I am indebted for much valuableassistance in the progress of the work. Two viscometers of theOstwald type were used.For viacometem of this type we have:r] solution (A solution - d ) x t solutionr] water (A water - d ) x t water ’where yl is the viscosity, A the density, t the time of flow of theliquid through the capillary, and d the density of air.Gruneisen (Zoc.cit.) has shown that, for viscometers of the typeused, it is unnecessary to apply any correction for the kineticenergy of the liquid in the capillary.The determination of time offered no difficulty, and was measuredby means of a stop-watch reading to one-fifth second, which keptexcellent time throughout the investigation.I n orifer t o prove that the flow of the liquids to be investigatedin the viscometers obeyed Poiseuille’s law, one of the tubes was- ---_______~ DENSITY OF CiESIUM NITRATE SOLU'I?IONS. 2455calibrated by Griinsisen's method, with the experimental arrange-ments used by Applebey (loc.&.). The times of flow of equalvolumes of water through the capillary under different hydrostaticpressures are given in the following table:Excess pressure(in mm. of waterat 18").1'07'322.433'545.055 *777-0a3 .s88 *7110'1134.5149'9Totalpressure.115'4121.7136.8147'9159.4170'1191.4198'2203'1224-5248.9264.3Time(in 1/5th secs.).457343383865356632983091275526632585234021161990Pressurex time.5276i 2805288527352685260527352785250525552655261As will be seen, the value pressure x time is constant within thelimits of experimental error, showing that the flow of liquid throughthe tube obeys Poiseuille's law, and that the tube can therefore beused for comparative measurements between the limits of timeexamined.The second viscometer used in this work wits standardised bycareful comparison with the first.For this purpose a nearlysaturated solution of casium nitrate has unique advantages, as itshigh density and low viscosity cause it to flow through the tubemore rapidly than water. The ratIos of the tdmes of flow 0.f thesolution and water in the two tubes were compared, with thefollowing resuIts :Time of Time of Time of flow of solution.flow, water. flow, solution. Time of flow of water.Standard tube ...... 4802 4020 0.8371Tube 7 ............... 4132 3459 0'8371The constancy of the ratio shows that the second tube obeysPoiseuille's law in exactly the same way as the first.The viscometers were usually cleaned after use by drawing themthrough a considerable quantity of the purest available water.If,however, the (( water constant " or time of flow of water had changedit was usually redetermined for one of the viscometers after eachsolution), or if any dust had lodged in the capillary, it was cleanedwith a mixture of nitric acid and a drop of alcohol, followed bywater. The viscometers were dried by drawing dust-free airthrough them in a hot-air bath.I n this connexion it may be mentioned that the purity of theair in the room in which the viscometers are dried is of considerableimportance. 'On one occasion there was a certain amount of amyl7 x 2456 MERTON: THE VISCOSITY ANDacetate vapour in the room in which the viscometers were dried,owing to some celluloid varnish containing amyl acetate which hadbeen used there.I n consequence of this, anomalous results wereobtained, and it was not until the drying apparatus was removedto another room that the viscometers again gave their originalwater value.Mat em’als Used.-The msium nitrate used in this investigationwas very kindly lent by the Earl of Berkeley. It was examinedspectroscopically, and n’o trace, of any impurity could be found. Thewater used was the best dust-free water obtainable (the electricalconductivity varied from 1 x 10-6 t o 2 x 10-6 mhos.). I n makingup a solution, the approximate quantity of salt required was placedin a quartz crucible, and heated for about four hours in % quinolinebath at 1 7 0 O .It was then weighed and dissolved in a known weightof water.Determination of Den.sity.-For the determination of density, apyknometer containing about 12 C.C. of the solution was used. Twosettings and two fillings were taken, the pyknometer being weighedagainst a counterpoise. The pyknometers were “ s e t ” in theconstant temperature baths in which the viscosity measurementswere made. For the densities at Oo, two pyknometers were used,with a small bulb above t’he capillary to allow for the expansionof the liquid on removing it from the ice, and a glass cap t o preventevaporation. They were set in a jacketed vessel containing crushedice.Constant Temperature Baths.-The experiments at loo, 1 8 O , and25O were performed in large glass-fronted baths containing about25 litres of water, vigorous stirring being obtained by means ofglass stirrers driven by an electric motor.The temperatures ofthe baths were verified by means of a standard Goetze thermometer.The 25O bath was heated by a small gas flame, which was governedby a large spiral toluene regulator (Lowry, Trans., 1905, 87, 1032).The 18O bath was heated by a 16 c.p. electric filament lamp placedin a bath close to the stirrer, and governed by a spiral electricregulator.The loo bath was identical with that at 1 8 O , except that itcontained in addition it coil of metal tubing, through which waterwas run, to act as a cooling apparatus. No variation in the tem-perature of these baths could be detected on the thermometerdivided in 1/50°.The loo bath, with which some trouble wasanticipated, was particularly carefully examined with a Beckmannthermometer, but no variation as great as 1/500° could be detected.The experiments at Oo were performed in a large Dewar vacuumvessel, containing crushed ice and water vigorously stirred. A tThe solutions were filtered to remove dust particlesDENSITY OF CXSIUM NITRATE SOLUTIONS. 2457this temperatur? rapid stirring was found to be essential in orderto prevent accumulation of warmer water at the bottom of thevessel. I n the event of a small variation of temperature occurring,a calculated correction can be applied. This correction was foundto be about two-fifths second for l/lOOo.It is probable that owingto the difficulty of maintaining constant temperature, the resultsa t Oo are not so accurate as at other temperatures,Density Results.-The results of the density determinations aregiven in the following tables. As will be seen, the weighingsusually agree to within 0.0001, or at most 0*0002, milligram, andtherefore the errors in the densities do not exceed 0.00002. Values of(A - 1) - Concentration x Constant are given, from which a sensitivecurve can be drawn.Densities at Oo.Parts ofof water. 1. 2. sp. gr. A;. 0.00'74.Mass of solution inczsium nitrate pyknometer.in 100 grams <-k-. Mean (A - 1) - PX0 12'4743 14.0425 1 0'99987 - 0.000131 '00751'978414'150714 -1 5 0714.2537{14*1507} 1.00770 1.00757 +O'OOOlO{ 14.2537] 1*01504 1'01491 +O-000274.0208 13.8832 -14.4690 ' 1.03937 1.03023 + 0.000486-2489 14.1033 14-6981 1-04668 1-04654 + 0'000308.3724 14.3110 14.9144 1-06209 1.06195 + O*OOOOODensities at loo.Parts of caesiumnitrate in 100 gramsof water.01-04672.18493'23615.73368.889112.069814.3040Mass ofsolution inpyknome ter.12.577812.8801 -13 -6 74 113.674213.6741Mean sp.gr.11 -007821,016261 '024031'042191 -064741.087161 '1 0237A abs.0,999731-007551 001 5 981 *023751'041911-064451.086871 *lo207(A - I) -- P X- 0.000270'0071357.+ 0*00008+ 0 *00039+ 0*00066+ 0~00100+ 0'00102+ 0 -00072458 MERTON: THE VISCOSITY ANDDensities at lao.Parts ofcaesium nitrate pyknometer.in 100 grams <-A-- Meanof water.3. N. sp. gr.0 12.5674 8.8160 11.0060 { 12*6611} 1.00745Mass of solution in12.661012'66109'65691 *015'171,022981.036981.08820Densities at 25O.Parts of Mass of solution incEsium nitrate. pyknometer.in 100 grams , - = = h - , Meanof water. 3. A?. sp. gr.0 12.5502 8'8043 11'00602.14153'12995.06776'58829'656912 '376016.63551.007391 '0 156 61.022811 936731 '04 7 431.068941 -087601.11625(A - I) - PX0'99862 - 0'00138A abs. 0'0070074.- 0'000991.01437 - 0*000631.02157 - 0'000361 -03555 + 0.000041.04633 + 0.000171'06805 + Oflo0381 -08671 +, O*OOOOO1.11525 - 0.00132(A - 1) - P X0.99707 - 0'00293A abs. 0'0068215.1'00443 - 0.002431'01268 - 0'001931.01981 - 0.001541'03369 - 0'000881'04436 - 0*000581'06580 - 0*000071'08441 - O*OOOOO1'11298 - O*OOO5DENSITY OF CAESIUM NLTRATE SOLUTIONS.2449T~i.scosity R esults.-The results of the viscosity determinations aregiven in the following tables. The results are probably correct tor f 2 in 5000 at 1 8 O , 2 5 O , and loo. A t Oo the errors are somewhatgreater, but the values given are probably correct to 5 3 in 5000.I n Fig. 1 the relative viscosities are plotted against the con-centrztion. Values of (1 - y) - concentration x K are given, fromwhich a sensitive curve may be drawn. The viscosity in absoluteunits has also been calculated, the absolute values of water beingtaken from Thorpe and Rodger's values (Phil.Trans., 1894, A ,185, 397)-At 0" = 0.01778 At 18" = 0*010510At 10" = 0'013025 At 25" = 0.00891PIG. 1.1 '00000.98000.96000'94000 -92000 5 10 15Grams of eaesizm nitrate in 100 grams of water.Disczcssion o i Results.It will be seen that at all temperatures the viscosity of caesiumnitrate solutions is less than that of water. It conforms with therule found for ot,her salts, in that the decrease of viscosity forunit quantity of salt decreases with increase of concentration.The discovery of Griineisen (Zoc. cit.), that the viscosity curves ofall ionised solutions exhibit a change of curvature at the diluteend, has been confirmed in the caie of cesium nitrate. This canbe seen in curves in which viscosity is plotted against concentration,but it can be better appreciated by plotting (1 - y ) / N (where N isthe normality) against :+J\/N.I n Fig. 2, l - q / N is plottedagainst 32/normality at 1 8 O . It is more convenient to plot 3Jxthan N , as in this way the dilute end is more extended. It willbe seen that the errors in the determination of ( l - q ) / N increasevery rapidly towards the dilute end. For example, in a solution______rel.00376007tO144015040303704403Of32091.004270007 821.024031,042191.064741.08716lo237Time nf flow of solutionTime of flow of waterby viscometer No.5 6 7 7 - 0.9923 0'9923 -0.9826 0-9826 o - g m - - - 0.9729 0'97300-9320 0'9320 0.9318 0,9318 - 0-9042 0'9042 0'09440.8703 0.9703 0.8703 -0.9648 0.9648 0'9651 -Viscosity at 1090.9928 0.9928 0.9928 -0.9857 0.9857 0'9854 -0.9234 0.9234 0.8236 -0.8565 0.8563 0.8561 -0.8355 - 0-8355 -- - 0 9557 0 95550.8880 - 0.8879 0.8879Mean q(relative).0.99600.99010'98410'97930'96020.94410.92440.99700.99320-9'i'SS0.96250-94540.93090 92111 - v/N,OmO15910'019330 '020890.020730 *020050'019520'019080'10270-12780'13230.13470.13030-12500.1228q abs.0 '017 7090 -01 76030.0174970 -0 1741 10.0170630 -0 I67860 *0164360 -01 29860.0129360*0127460.0125360 -0 1231 40.0121280-01 1997(1 -7))-Px0.0093.- 0 '0004 + 0*0008 + 0 *0024 + 0-0028 + 0.0038 + 0 *0026 + 0 -0000(1 - v ) - P x0'005523- 0~0001- 0*0010 + 0*0035 + 0.0059+0*00653- 0.0025 - 0~000Viscosities at 18'.re].00333007451.015771.02298036981.04778069530888116791.003311.00739015660228103673047431.06894087601.11625Time of flow of solutionTime of flow of waterby viscometer No.50'99520.98850.97460.96230.94030.92380'89400.87020.83715-0.96230.94030.92380-89400-87020.83717 70-9954 0'99540-9886 0.98860.9746 -0'9622 -0'9404 -0'9242 -0.8938 -0'8iOO -0.8371 -Viscosity at 25O.0.99560.98960.97750'96620-94620.90480.88300.8529-0.9956 0.9954- 0.9897 - 0,9773 - 0-96620.9462 0.94640,9324 0.93190'9048 0.90480.8529 0.85220.8830 -Mean n(relative).0'99860.99600-98990.98440.97520.96810.95610.94700.9347- 0 99880.99700-9773 0.99260.9662 0.9882- 0,98110.9319 0.9761- 0.9671 - 0.9604 - 0.9518-1 - q/ N.0.060500'078270.093860'100190~100200.100530,097120.093770 -088920.51850,58710.68770,75780,76360.75320-72780.70060.6583q abs.0 -01 04 950-0104680 *0104040.0103460'0102490 -01 01 7 50'0100490 *0099530 -0093360'0088990 -0088830.0088440'0088040,0087420.0086970.0086170.0085570'008480( l - ? l ) - P x0-004283.-0'0003+ 0-0031-1-0-0037 j; + 0 '00250.0-0.0071 51- 0.0005+of)oo9 0'0022 0 m!a * c3H(1 - q ) - P x0.0032.+0*0006 0+0*0018 5+0.0027 + 0.0028 + 0-00200 .oo-0*0050-0'0002 5-0'0002 2k PQ, 2462 VISCOSITY AND DENSITY OF C&SIUM NITRATE SOLUTIONS.with a relative viscosity of 0.9980, (1 -7) would be 0.0020, so thatan error of 0.01 per cent.would produce an error of about 4 percent. in the value of 1 - q / N , whereas if the viscosity were 0*9200,a similar error would alter 1 - ~ / L V by less than 0.125 per cent.It would be of great interest to discover, if possible, the valueof 1 - q / N for infinite dilution, but', as has been shown, the errorsincrease so rapidly towards the dilute end that it becomes impossibleto form any estimate.Gruneisen (Zoc. cit.) has proposed the formula:91 - 1 N = A i + B( 1 - i) + CN,where .i. is the ratio L / L , , L and Lo being the molecular electricalconductivities at concentrations N and 0, and A , B, and C areFIG. 2.0 -3 0'5 0.7 0 -9JiVormality (weight).constants depending on the nature of the salt.Gruneisen hasobtained fairly good agreement in his results between the foundvalues of 7 and those calculated by this formula. I have not beenable to find any determinations of the elect,rical conductivity ofczsium nitrate solutions, and have therefore been unable to makeany attempt to apply the formula to my results.From the absolute values calculated from Thorpe and Rodger's(Zoc. cit.) values for water, it will be seen that the change ofviscosity produced by a rise in temperature decreases with increasingconcentration. Thus, 7 parts of caesium nitrate in 100 parts ofwater lower the viscosity about 7.5 per cent. at Oo, but less than3 per cent. at 25O.The general form of the viscosity curve is precisely what wHOMOGENEOUS DECOMPOSITION OF OZONE.2463should expect from the position of cEsium in the periodic system,a comparison with the viscosities of lithium, sodium, and potassiumnitrates, taken from Griineisen’s paper, showing that, qualitatively,the visoosity changes follow the classification of the elements in thoperiodic system. I f we may assume that the viscosity of a solutiondepends on the mean size of the molecules and ions, we shouldinfer that of the alkali metals the msium ion is the smallest, inaqueous solution, that is to say, it has a smaller number of watermolecules attached to it than the ions of the other alkali metals.In agreement with this, the caesium ion is known to possess thelargest ionic mobility.Su.mmary.The viscositlies of czesium nitrate solutions have been investigatedat Oo, loo, 18O, and 2 5 O . The results confirm in every respect thegeneral principles discovered for other salt solutions.The densities of the solutions at these temperatures have beendetermined. I n these determinations, no abnormal results havebeen found. The change of density per unit quantity of saltdecreases slightly with an increase of concentration.The effect of temperature on the viscosity has been examined,and found to decrease with increasing concentration.With respect, to the viscosity of the nitrate solutions, caesiumoccupies a position a,mong the alkalis in accordance with its positionin the periodic system.I n conclusion, I should like to express my thanks t o Mr. H. B.Hartley and Mr. D. H. Wagel for tho kind assistance and advicethey have given me in this investigation.PHYSICAL CHEMISTRY LABORATORY,BALLIOL AND TRINITY COLLEGES,OXFORD