176 



SMITH'S INTERMEDIATE CHEMISTRY 



electrolytes is perhaps the most remarkable. It appears more 

 surprising when we consider that no substances, other than acids, 

 bases, and salts, undergo electrolysis in aqueous solution. This 

 is an exclusive property of these classes of bodies. 



The conducting power of solutions can be examined, roughly, 

 by the apparatus in Fig. 59. The platinum electrodes are con- 

 nected with a direct-current circuit. The lamp, which is on one 

 of the wires, serves, by its resistance, to cut down the current. 

 Its glowing also shows when the liquid is a conductor, and by 

 varying brightness indicates roughly the conducting power of the 

 solution. 



A solution of sugar in water 

 shows no conductance, and 

 the lamp remains dark. Solu- 

 tions of acids, bases, and salts 

 in water enable the lamp to 

 glow. 



We quickly find that differ- 

 ent solutions, when they con- 

 duct, do so in different degrees. Solutions of hydrochloric and 

 nitric acids conduct well. So do solutions of sodium and potas- 

 sium hydroxides. Salt solutions are practically all good conduc- 

 tors. But many acids, like acetic acid, conduct poorly in aqueous 

 solution. The same is true of some bases, like ammonium hy- 

 droxide. 



Of course, acids, bases, and salts which are only very slightly 

 soluble in water give poorly conducting solutions. But in esti- 

 mating the conductivity for chemical purposes, we have to take 

 into consideration the amount dissolved. Thus silver chloride, 

 being a salt, is an excellent conductor, when we allow for the 

 extreme diluteness of the solution. A saturated solution of silver 

 chloride, in point of fact, shows a slightly higher conductance than 

 a solution of sodium chloride of the same concentration. 



Substances which give solutions with high conducting power 



FIG. 59 



