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the formation of fresh water rich in sodium, but not so in reality 
if we consider that in the beds of clay salt water is usually still 
present when it has already disappeared from the surrounding sand 
layers, because in the beds of clay the water circulates much less 
rapidly than in the sand. In and near beds of clay, just as any where 
else near the border of salt and fresh water, the expulsion of 
the salt water has taken place later than if far away from the 
beds of clay. 
A second circumstance, which would promote the presence of 
water with an excess of alkalis in the vicinity of beds of clay or 
loam, is probably this, that clay and loam contain more solid sub- 
stances that take part in the reaction than sand, so that the chemical 
equilibrium therein is less rapidly repaired. Hence, even after the 
salt water has already been quite leached the exchange between Ca 
and Na will take place still longer in beds of clay and loam than 
in beds of sand. 
Finaily it sbould be pointed out that, where the fresh water has 
got into the soil without expulsion of salt water, the diluvium still 
being above the sea level such as in the islands of Urk and Texel and 
the fresh water is moreover less calcareous, the phenomenon that 
the sodium content is large in the fresh water in proximity to the 
salt water, is not noticed. 
In the above only sodium and not potassium has been mentioned, 
because analyses involving the separation of potassium and sodium 
have been but occasionally executed. 
Hence, when sodium has been mentioned this really means the 
joint sodium and potassium. 
It has been observed that in the arable soils there are present colloidal 
substances possessing the power of assimilating ammonia and potas- 
sium and parting with this again on addition of lime. These substances 
may also be present in the subsoil of the dunes both in the beds of 
loam and clay and in the mud which most sands contain. It is 
probable that these substances cause principally the mutual reaction, 
and they may have a composition resembling that of the so-called 
artificial zeolithes of Gans. 
Moreover, amorphous sodium aluminium silicates are employed to 
substitute sodium for calcium in water intended for boilers. 
Summarizing, we may repeat : 
I. that the fresh water rich in sodium has not a larger content 
in eq. Na+ Me + Ca than the normal fresh water, so that the 
increase in Na-ions has been accompanied by a decrease in other ions ; 
IL. that the ratio NaCl in the water rich in sodium is greater 
