
r Lae a3 5 2 . ie 
Parr II. Secr. ii, §2.] MINERAL SPRINGS. 349 
they decompose soap, forming with its fatty acids insoluble compounds 
which appear in the familiar white curdy precipitate. Such water 
is termed “hard.” Where the hardness is due to the presence of 
bicarbonates it disappears on boiling, owing to the loss of carbonic acid 
and the consequent precipitation of the insoluble carbonate, while in 
the case of sulphates and chlorides no such change takes place.’ 
The extensive investigations carried on by the Rivers Pollution 
Commission in Britain have thrown much light on the relation 
between the amount of mineral matter in solution in springs and 
wells, and the character of the underlying rock. The following 
table gives a summary of results obtained : 
sich oc Pgen amo of Sa 
Analyses, ~ Parts of Water. 
1. Fluviomarine Drift Grayel 2 ‘ : uF EO 6-332 
2. Upper Chalk . - ‘ : : of ae 2°984 
3. Lower Chalk to Upper Greensand . : oto 3°005 
4. Oolites.. z ‘ 2 . : agence 3:033 
RP aadas: |. . : : : ; Seams 3° 641 
6. New Red Sandstone . f ai 2 aed 2°869 
7. Magnesian Limestone. : ; i ee } 4°418 
8. Coal Measures ‘ . : ‘ , . 14 2:430 
9. Yoredale and Millstone Grit . ‘ , Sig st 1-7 
10. Mountain Limestone x : ‘ : eye 3:°206 
11. Devonian and Old Red Sandstene . : Be 2°506 
12. Silurian , 4 : : : : ae, te 1L:233 
13. Granite and Gneiss : ‘ ; ores 0:d594 
From this table it is evident how greatly the proportion of 
dissolyed mineral substance augments in those waters which rise in 
calcareous tracts, and how it correspondingly sinks in those where 
the rocks are mainly siliceous. The maximum percentage in group 
No. 13 was less than 1 part in every 10,000 of water, the minimum 
being 0°140 from granite. In No. 1, on the contrary, the maximum 
was 22°524, in No. 6 it was 7-426, and in No. 10 it was 9°850.? 
Mineral springs are in some instances cold, in others warm, 
or even boiling. Thermal springs are more usually mineral waters 
than cold springs, but there does not appear to be any necessary 
relation between temperature and chemical composition. Mineral 
springs may be roughly classified for geological purposes according 
to the prevailing mineral substance contained in them, which may 
range in amount from 1 to 300 grammes per litre.® 
Caleareous Springs contain calcium carbonate in such quantity 
as to be readily deposited in the form of a white crust round objects 
over which the water flows. Calcium carbonate, according to 
Fresenius, is dissolved by 10,600 of cold and by 8834 parts of warm 
water.* But in nature the proportion of this carbonate present 
in springs depends mainly on the proportion of carbonic acid which 
retains the lime in solution. On the loss of carbonic acid by 
1 Paul, loc. cit. 
2 “Rivers Pollution Commission Report,” 1874, p. 187. 
3 Paul, op. cit. p. 1016. 
* Roth, “Chem. Geol.” i. p. 48. “One litre of water, either cold or boiling, dis- 
solves about 18 milligrammes.” -Roscoe and Schorlemmer, “ Chemistry,” ii. p. 208. 
