178 



in solutions of electrolytes, but these same solutions actually 

 behave as if the radicals were, to a large extent, uncombined with 

 each other. It appears as if sodium chloride, for example, is 

 largely decomposed in aqueous solution into independent sodium 

 and chloride radicals. Additional evidence in this direction is 

 supplied by the behavior of electrolytes of more complex types, 

 such as sodium sulphate Na 2 SO 4 or zinc chloride ZnCl 2 . Both 

 of these substances, in dilute solution, give boiling-point and 

 freezing-point changes which are nearly three times the normal, 

 indicating that they are largely decomposed into their three con- 

 stituent radicals (2Na and SO 4 ; Zn and 2C1). In the same way, 

 substances containing four radicals, like ferric chloride FeCls, 

 give effects approaching four times the normal in dilute solution. 

 One last point remains to be mentioned. It has been noted 

 above that some acids, like acetic acid, and some bases, like 

 ammonium hydroxide, are only poor conductors in solution. Just 

 these same two classes of substances, it has been found, give only 

 very slightly abnormal changes in the three physical properties 

 of solutions here under examination. The full significance of 

 this difference in behavior will appear in the following chapter. 



A Warning. The reader is urged to keep in mind the fact 

 that it is only in solution (and particularly in aqueous solution) 

 that the special properties of acids, bases, and salts become ap- 

 parent. Their behavior is often quite different in the absence 

 of a solvent. If, for example, we mix together dry ammonium 

 carbonate (NH^COs and partially dehydrated, solid cupric 

 nitrate Cu(N0 3 )2, and apply heat, a violent interaction begins. 

 This interaction is nothing so simple as a double decomposition, 

 however. An immense cloud of smoke and gas is thrown out of 

 the tube, and the solid remaining is either black or reddish, in 

 parts, according to the proportions of the substances employed. 

 This residue contains black cupric oxide CuO, and sometimes red 

 cuprous o;dde Cu 2 0. The gas evolved is tinged red by the pres- 



