GENERAL DISCUSSION OF RESULTS. 213 



in both with temperature. Dr. Guy found in this work that certain salts actually 

 lower the viscosity of glycerol when they are dissolved in it. 



Jones and Veazey 1 had pointed out that it is only salts of potassium, rubidium, 

 and caesium which lower the viscosity of water, and they explained this fact as due 

 to the large atomic volumes of these elements. 



Salts of rubidium were found to lower the viscosity of glycerol, and the same 

 explanation was offered of this phenomenon that had been offered by Jones and 

 Veazey to explain the similar phenomenon in water. 



Ammonium bromide and iodide were also found to lower the viscosity of glycerol. 

 This is not surprising, since ammonium is so closely analogous in its properties in 

 general to the other elements of the alkali group. 



RESULTS OBTAINED BY DAVIS. 



It was pointed out in discussing the work of Dr. Guy that rubidium and ammo- 

 nium salts showed negative viscosity coefficients in glycerol. The salts were studied 

 elaborately by Dr. Davis. He worked with ammonium iodide in glycerol at 25, 

 35, and 45; also at 55, 65, and 75. He studied rubidium chloride, rubidium bro- 

 mide, rubidium iodide, and rubidium nitrate over the same range in temperature. 



In mixtures of glycerol with water, he studied ammonium iodide and rubidium 

 bromide. 



He measured the viscosity and fluidity of ammonium iodide, rubidium chloride, 

 bromide, iodide, and nitrate in glycerol from 25 to 75; also the viscosity and fluid- 

 ity of ammonium iodide and rubidium bromide in mixtures of glycerol and water 

 from 25 to 45. 



This investigation had had to do chiefly with the viscosity in glycerol, and the 

 lowering of the viscosity of glycerol by certain salts when dissolved in it. The con- 

 ductivity data obtained confirm the conclusions already reached by Jones and 

 Schmidt and by Guy and Jones. 



The viscosities of the solutions of the above-named salts in pure glycerol from 

 25 to 75 were determined for a range of dilution from normal to one-tenth 

 normal, and were found always to have a smaller viscosity than the solvent. The 

 fluidity and conductivity curves in general run parallel to one another. It was 

 pointed out by Dr. Davis that solutions of rubidium salts in glycerol are exam les 

 of salts lowering the viscosity of a solvent to such an extent as to increase appreciably 

 their own conductivity in that solvent. 



A comparison of the effect of the chloride, bromide, and iodide of rubidium on the 

 viscosity or fluidity of glycerol shows that the chloride has the least effect, the bro- 

 mide next, while the iodide has the greatest effect on the viscosity of this solvent. 

 Dr. Davis explains this as due to the molecular volumes of the salts in question, the 

 cation, rubidium, being constant in all three of them. If we divide the molecular 

 weights of the three halogen compounds of rubidium by their densities referred 

 to water as unity, we have RbCl = 5.50; RbBr = 5.95; Rbl = 7.02. The effects on 

 fluidities are in the same order. At 25 and normal concentration, the fluidity of 

 glycerol is increased 12.2 per cent by rubidium chloride, 18.5 per cent by rubidium 

 bromide, and 26.3 per cent by rubidium iodide. 



'Carnegie Institution of Washington Publication No. 80. 



