1620 
but slieht, but of the cations the principal matter is Ca, and of the 
anions HCO,. 
In the normal salt water, on the other hand, the concentration 
of all ions is much larger; the cations are principally Na, the anions 
Cl. The demarcation between these types of water is not sharp and 
there is a gradual transition. 
This transition, however, cannot be explained by a simple mixing 
phenomenon. The elaborate analyses of a great number of samples 
of underground waters, which at the request of the Government 
Board for Water Supply were made during the last few years in 
the Central Laboratory on behalf of the Sanitary Authorities at 
Utrecht, render possible a more accurate study of the phenomena 
occurring therein. 
Near the transition zône, where the chlorine content still quite 
corresponds with that of the fresh water, an important change is 
perceptible in the concentration of the ions Na, Mg and Ca and in 
such a manner that these ions are present in about the same mutual 
relation as in the normal salt water. 
If the figures giving the concentrations of the ions Na, Mg and Cl 
are divided by the atomic weight of sodium and the half-atomic 
weights of magnesium and calcium, respectively so that the concen- 
trations of the chemical equivalents are obtained, it appears that so 
long the concentration of the chlorine ions corresponds with that 
of the normal fresh water the concentration of the sum of the 
equivalents Na + Mg + Ca also corresponds with that of the normal 
fresh water. 
The. ratios 
Na 
eq. ———_____ 
Na + Me +Ca 
Me 
eq. —— rv 
Na + Me +Ca 
Ca 
“4 Na+ Mg Oa 
a+ Mg +Ca 
however, already approach those of the normal salt water. 
In some dune regions we may accept for normal fresh water the 
following value of the ratios. 
ed. Pd 
Na + Mg +Ca 
Ms — 0,224 
eq. — a 
Na + Me+Ca 
