98 
Some JIonizaTION EXPERIMENTS. 
By P. N. Evans. 
The proportion existing between the ionized and un-ionized motecules - 
of an electrolyte in (aqueous) solution, is represented by the equation 
a. b=k.c,in which a, b, and ¢ are the concentrations of the anions, 
kathions and un-ionized molecules of the electrolyte, respectively, and k 
a constant depending on the nature of the electrolyte and independent of 
the concentration for moderately or highly dilute solutions. 
Supposing this equilibrium to have become established, which is the 
case in an exceedingly brief time, if not instantaneously, any addition of 
either kind of ion concerned, the quantity of solvent remaining the same, 
must result in an«increased value for its concentration and produce a 
corresponding increase in the number and concentration of the un-ionized 
molecules; for, k being a constant, any increase in the value of a or b 
will involve an increase of that of ¢ if the equilibrium is to be maintained. 
If to a saturated solution of an electrolyte’ there be added a second 
soluble electrolyte having an anion or kathion in common with the first, 
there must result a state of supersaturation with regard to the first elec- 
trolyte or a separation of a portion of it in insoluble form. 
Many examples of this are familiar to all. For instance, a saturated 
solution of sodium chloride is instantly precipitated by the addition of 
concentrated hydrochloric acid, in spite of the water that is added at the 
same time; on the other hand, the case is complicated and the precipita- 
tion assisted, probably by the chemical union taking place between the 
hydrochloric acid and some of the water, made evident by the evolution 
of heat, thus increasing all the concentrations by removing (chemically 
changing) some of the solvent. The same result is obtained and the same 
reasoning applies when calcium chloride is added to a saturated sodium 
chloride solution. The precipitation of sodium chloride is brought about 
without this complication of causes by the addition of crystallized potas- 
sium chloride (XCl) or anhydrous sodium sulphate (Na.SO,), and even 
crystallized sodium sulphate (Na.SO,.10H,O) gives the same result in spite 
of the water added in the crystals. 
Similarly, potassium chloride can be precipitated by hydrochloric acid, 
sodium chloride (NaCl), or potassium sulphate (IX.SO,); and copper sulphate 
(CuSO,.5H.O) by cupric chloride (CuCl..2H.O), copper nitrate (Cu(NO,).. 
