99 
6H.O), or sulphuric acid; barium chloride (BaCl,.2H.O) by hydrochloric 
acid, or sodium chloride; calcium sulphate (CaSO,.2H.O) by sulphuric acid, 
potassium sulphate, calcium nitrate (Ca(NO,)..4H.O); lead chloride (PbCI.) 
by hydrochloric acid, sodium chloride, potassiuin chloride. 
In this list we have a very wide range of solubility: 100 parts of 
water dissolve NaCl 35, KCl 32, CuS0,5H,.O 40, BaCl,.2H,O 33, 
CaS0O,.2H.0 .20, PbCl, .74 parts. It is not evident Whether easily or 
difficultly soluble substances should respond more readily in the yielding 
of a precipitate under these conditions, for the much greater degree of 
supersaturation attainable with an easily soluble substance may be offset 
by the greater difficulty in disturbing this state of supersaturation. 
The greater the solubility of the electrolyte added to the saturated 
solution, the more readily a precipitate should be obtained; and the higher 
the dissociation constant of the second electrolyte, the more probable is 
a marked result. 
In spite of the apparently favorable conditions in this respect, all at- 
tempts to precipitate lead chloride from its solution by means of lead 
nitrate were in vain. A saturated solution is very readily prepared by 
warming the solution in contact with an excess of the salt, and then cool- 
ing, owing to the great difference in solubility in hot and in cold water. 
The immediate and copious precipitate produced in this solution by the 
addition of sodium or potassium chloride or hydrochloric acid seemed to 
indicate that the tendency to remain in the supersaturated condition was 
very slight in the case of this salt, yet the addition of lead nitrate crystals: 
to the solution (saturated), even in the considerable quantity made possi- 
ble by the ready solubility of the nitrate (48 parts in 100), failed to cause: 
any precipitation, either immediately or on long standing, or even on 
adding a crystal of lead chloride to induce crystallization from the solu- 
tion, Supposing it to be supersaturated. Lead nitrate, like most normal 
salts, has a high dissociation constant, more than half that of the strong- 
est acids in a .1 per cent. solution (calculated by Arrhenius from conduc- 
tivity experiments by Kohlrausch). This fact, and its high solubility, 
should be most favorable to the precipitation of the lead chloride, on ac- 
count of the considerable increase in the concentration of the lead ions. 
made possible thereby. 
In harmony with the usual similarity of barium to lead, a saturated 
solution of barium chloride showed no sign of precipitation with barium 
nitrate (Ba(NO,).); as already stated, a precipitate was produced by the 
