136 HYDRATES IN AQUEOUS SOLUTION. 



The salts of sodium in general do not crystallize with water, and, there- 

 fore, show comparatively little hydrating power in aqueous solution. The 

 results are recorded in tables 6 to 17. 



The freezing-point lowerings produced by sodium salts are plotted in 

 figs. 3, 4, 5, 6, 11, 14, 15, 16, 17, and 19; the conductivity results in figs. 7, 

 8, 9, 10, and 20, while the refractivities are given in figs. 12 and 13. The 

 hydrates formed by sodium bromide are plotted in fig. 53 ; those formed by 

 sodium dichromate and sodium ammonium acid phosphate in fig. 55, while 

 the hydrates formed by sodium hydroxide are plotted in fig. 57. 



Sodium chloride crystallizes at ordinary temperatures without water, and 

 has very little power to combine with it in aqueous solution. Sodium 

 bromide and iodide crystallize with water of crystallization, and have con- 

 siderable power to form hydrates in solution. Sodium sulphate crystallizes 

 with water, but, like the sulphates in general, shows abnormal results, due 

 to the fact that they undergo polymerization in solution. 



Sodium chromate shows very slight hydrating power in the most con- 

 centrated solutions, while sodium dichromate shows very appreciable 

 hydrating power at all of the dilutions investigated. The chromates, like 

 the sulphates, give abnormal results, and probably for the same reason 

 they undergo polymerization in aqueous solution. Disodium phosphate is 

 especially interesting, in that it is the only salt thus far studied which 

 crystallizes with 12 molecules of water. It is unfortunate that the salt is 

 so slightly soluble in water, since this limited the work to only a very few 

 dilutions, and prevented us from studying any solution of appreciable con- 

 centration. For the solutions with which we could work, this salt showed 

 the greatest hydrating power of any substance brought within the scope 

 of this investigation. This is in perfect accord with the relation between 

 water of crystallization and lowering of the freezing-point. 



Sodium hydroxide also has considerable power to combine with water. 

 This, however, passes through a minimum. 



The results with salts of potassium are given in tables 18 to 28. 



They resemble the results obtained with the corresponding salts of sodium. 

 Salts of potassium, in general, crystallize without water, and have very 

 little power to combine with it in solution. 



Some of the freezing-point data for potassium salts are plotted as curves 

 in figs. 3, 4, 5, 6, 14, 15, 16, 17, and 19. The conductivity data are given in 

 figs. 7, 8, 9, 10, and 20; some of the refractivities are plotted as curves in 

 figs. 12 and 13, while the hydrates formed by potassium hydroxide are plotted 

 in fig. 57. 



The results with potassium ferricyanide and potassium ferrocyanide are 

 especially interesting, in that they throw an entirely new light on the way in 

 which these substances dissociate in the presence of water. The older views 



