DISCUSSION OF RESULTS. 



215 



is in perfect accord with the facts, as far as they are recorded. According to 

 the work of Wagner, 1 caesium chloride in normal solutions lowers the value 

 of t} 2 from 1.0000 to 0.9775; rubidium chloride under the same conditions 

 lowers the viscosity of water from 1.0000 to 0.9846; and potassium chloride in 

 normal solution lowers the viscosity of water from 1.0000 to 0.9872. The 

 atomic volume curve shows that caesium has the largest atomic volume 

 (about 74), rubidium is next in order (about 57), and potassium has the 

 smallest atomic volume (about 47) of this group of metals which produce the 

 negative viscosity in water. 



It is worth noting that the difference between the values of t\ for caesium 

 chloride and rubidium chloride is much greater than the difference between 

 rubidium chloride and potassium chloride. This is in keeping with the rel- 

 ative atomic volumes of the three elements. The difference between the 

 atomic volumes of rubidium and caesium is much greater than the difference 

 between the atomic volumes of rubidium and potassium. 



If we extend the above conception to other cations with large atomic 

 volumes, but with much smaller atomic volumes than the alkalies, we shall 

 find that it holds satisfactorily. Take calcium, strontium, and barium, 

 which, of all cations, have the next larger atomic volumes, and compare their 

 chlorides with respect to the values of rj; we have, for normal solutions: 



n 

 Calcium chloride 1.1563 



Strontium chloride 1.1411 



Barium chloride 1.1228 



These values are all positive, as we should expect them to be, but their 

 order is exactly the reverse of the atomic volumes, just as we should expect. 



Chlorides with cations of smaller atomic volumes have values of 17 much 

 larger than the above. This will be seen from the following table, where all 

 the values of / refer to normal solutions. In the same table are given the 

 approximate atomic volumes of the cations of the salt. 



It is obvious that for the atomic volumes of the same order of magnitude, 

 the values of 77 are of the same order of magnitude; and, in general, the larger 



1 Ztschr. phys. Chem., 6, 35 (1890). 



2 1?, the time of flow of water through the viscometer, is taken as unity. 



