GENERAL SUMMARY AND CONCLUSIONS. 227 



more viscous than water. If it does not, then the solution is less viscous 

 than pure water. 



The explanation of the diminution in viscosity produced by the above- 

 named cations is comparatively simple in the light of the conception of vis- 

 cosity proposed earlier in this investigation. If the atomic volume of the 

 ions introduced was much larger than the molecular volumes of the solvent 

 molecules, the effect would be to diminish the frictional surfaces that would 

 come in contact with one another in the solution, and, consequently, the 

 friction of the movement of the molecules over one another would be di- 

 minished. The question, then, is: Are the atomic volumes of potassium, 

 rubidium, and caesium very large? And are they much larger than the 

 atomic volumes of other elementary cations? 



If we turn to the well-known atomic volume curve, we see that potassium, 

 rubidium, and csesium occupy the maximum of the curve, and have much 

 larger atomic volumes than any other known elements. Even the atomic 

 volume of potassium, which is smaller than that of rubidium and caesium, 

 is much larger than that of any other known element except rubidium and 

 csesium. 



If we test this relation quantitatively, the result is very satisfactory. By 

 comparing the viscosities of solutions of the same concentration of potas- 

 sium chloride, rubidium chloride, and csesium chloride, we find that, while all 

 these viscosities are less than the viscosity of pure water, the viscosity of the 

 solution of rubidium chloride is less than that of potassium chloride, and the 

 viscosity of the solution of caesium chloride is less than that of rubidium 

 chloride. 



More work will be done in the physical chemical laboratory of the Johns 

 Hopkins University to test whether these relations are perfectly general. 



In conclusion it gives me great pleasure to express my hearty thanks to 

 my seven cooperators, who, the one after another, have taken up and studied 

 uninterruptedly during the past six years the various problems that have 

 arisen in connection with this line of investigation. 



