THE VISCOSITY OF FUMING SULPHURIC ACID. 2179CCXTX.-The Viscosity of Fuming Xulphus.ic Acid.By ALBERT ERNEST DUNSTAN and ROBERT WILLIAM WILSON.IN a recent paper (Trans., 1907, 91, 83), the present authors publisheda viscosity-concentration curve for aqueous solutions of sulphuric acid.This curve was shown to follow very closely that originally deter-mined by Knietsch (Ber., 1901, 34, 4069), and it was pointed outthat the investigation clearly indicated very considerable associationbetween the acid and the water.A well-detined maximum point was found to exist at a concentra-tion of 85 per cent, sulphuric acid, corresponding with the well-knowncompoupd SO(OH),, and a minimum point at the concentration 95 percent. sulphuric acid, which corresponds with the hydrate SH,SO,,H,O,Now it appenrs probable that the compound SO(OH), is present insolution in the aggregate [0:S(OH),lll, where n is a whole number ofconsiderable magnitude, and similarly, at the concentration indicatedby the minimum point there is present the aggregate [3H,SO,,H,O],,where rn is 1eSR than n, since the exceedingly high value at these twopoints of the viscosity coefficient, 0,94794 and 0.83255 respectively,points to the existence of complexes of great molecular weight.In the above-mentioned paper, the curve ended a t 100 per cent.sulphuric acid, with evidence that the viscosity would be found stillincreasing with a greater percentage of the anhydride2180 THE VISCOSI'I'P OF FUMING SULPHUHIC ACID.Owing to the kindness of Dr.Messel, to whom the authors takethis opportunity of expressing their indebtedness, an ample supply ofvery pure acids of varying content of free sulphur trioxide was placedat their disposal.The solidity of some of the specimens necessitated the work beingcarried out a t a higher temperature than 25', a t which the previousexperiments had been conducted ; hence 60' was taken as the constanttemperature.The extreme manipulative difficulty of working withthese strongly fuming liquids, and the remarkable way in which theyabsorbed water, even during the progress of the determinations, pre-cluded the attainment of any high degree of accuracy, but, for pur-Percentage of SO, (free).poses of comparison, it must be borne in mind that each point wasdetermined under precisely similar conditions.Knietsch (Zoc.cit.), using a variety of methods, found discontinuitiesin the curve connecting concentration with physical properties a t thefollowing points :Melting-point determinations : 2H,SO,,H,O, 4H2S0,,S0,, H,SO4,2S0,,H2S049H20.Viscosity : H,SO,,H,O, H,SO,,SO,.Conductiwity : 2H2S04,H20, H,SO,,H,O, and 15 per cent. SO,.I n the present work (see figure), it is to be noticed that theviscosity concentration curve rises sharply from pure sulphuric acidto the acid containing 40 per cent. of sulphur trioxide, at which con-centration the compound H,S04,S0, probably exists. This maxi-mum also is in substantial agreement with Knietsch's work. A t thiMOORE: THE DEXSlTIES OF KRYPTON AXD XENON. 2182Per cent. free SO,. Viscosity.70.0 0.114746'0 0'179140'6 0'204527'72 0.1753Per cent. free SO,. Viscosity.21.5 0'148816.3 0,13630 .o 0'0832V a t e r at 60" 0'00464I(2) Further evidence as to the existence, in solution, of molecularaggregates, such as H,SO,,SO,.PHYSIOAL CHEMICAL LABORATORY,EAST HAM TECHXICAL COLLEGE