WORK OF P. B. DAVIS. 



195 



the two salts which have been studied in mixed solvents. These are seen to diminish 

 rapidly with the addition of water, passing from 10 per cent in pure glycerol to 2 per 

 cent in 25 per cent glycerol. 



The curve representing the specific conductivities of the various mixtures from 

 glycerol to pure water is shown in fig. 83. The values for 50 and 25 per cent glycerol 

 are larger than that for water. This is probably due to the presence of a few OH 

 ions split off from the glycerol by action of the water. 



I, - V=10 

 II, - V=50 



III, - V=400 



IV, - V=1600 



> 



3 



a 

 c 

 o 

 O 



(-. 



O 



NEGATIVE VISCOSITY COEFFICIENTS. 



A historical sketch of previous work on viscosity has already been given. It is 

 necessary, therefore, to take up here only the more important points. 



Jones and jVeazey's apparently satisfactory explanation of the 

 phenomenon of negative viscosity coefficients has received ample 

 corroboration by later workers. It will be remembered that they 

 attributed the lowering of the viscosity of a solvent by a dissolved 

 substance to the lessening of the skin friction between the molecules 

 of the solvent and the molecules or ions of the solute in agiven volume 

 of the solution, because of the 

 large atomic volumes of the ca- 

 tions, viz, potassium, rubidium, 

 and csesium, these three metals 

 occupying the maxima on the 

 atomic- volume curve. Subse- 

 quent investigations have shown 

 that certain ammonium salts in 

 organic solvents, such as glycerol, 

 are to be included in this cate- 

 gory. Although we may not 

 speak of the ammonium radicle 

 NH 4 as having atomic volume, 

 still, it is well known that it 

 posesses chemical properties 

 closely allied to the alkali metals. 



It is not surprising, therefore, 

 to find negative viscosity effects 

 produced by ammonium salts, 

 and from observations made by 

 Guy and Jones on ammonium 

 bromide, and from our own observations on ammonium iodide, it is probable that 

 the molecular complex (NH 4 ) should occupy a place on the volume curve close 

 to rubidium. 



In table 140 the viscosities and fluidities of ammonium iodide and of rubidium 

 chloride, bromide, iodide, and nitrate 1 in pure glycerol at 25 to 75 are given for a 

 range of dilution from N to N/10. In every case the viscosity of the solution is less 



Fig 



Per cent. Glycerol 



82. Conductivity of Rubidium Bromide in 

 Glycerol-Water at 25. 



>N/132 sol. saturated at 20. 



