ON PUEE WATEE. 559 
The following table will give some idea of the composition 
of rain_, springs and well water in this country : — 
Names of Substances. 
1 
Grains in a Gallon. 
2 3 4 
5 
River 
Thames. 
River 
Severn. 
Spring 
at Chel- 
tenham. 
WeUat 
Clapton. 
Well 
at Chel- 
tenham. 
Carbonate of Lime 
12-75 
3-36 
8-46 
15-09 
35-2 
Carbonate of Magnesia. . . 
1-02 
13-97 
Sulphate of Iron 
0-45 
3-68 
3-01 
15-32 
25-9 
Sulphate of Potash 
0-66 
1-00 
0-50 
6-74 
4-0 
Sulphate of Soda 
2-00 
0-45 
0-50 
10-77 
2-0 
Chloride of Soda 
1-10 
1-84 
0-41 
11-46 
25.6 
Chloride of Calcium ... 
1-75 
Silica 
0-27 
0-88 
0-80 
0-24 
0-1 
Total grains in a gallon. . . 
20-00 
11-21 
13-68 
73-59 
92-8 
The columns 1 and 2 give the principal inorganic consti- 
tuents of two of our great rivers ; is a fair specimen of spring 
water from which the town of Cheltenham is now supplied; 
4 and 5 are examples of surface wells. Much purer and much 
more injurious waters than these are now supplied to many of 
our towns. The supply from the Dee in Aberdeen contains 
but five grains of saline matter in the gallon^ whilst the 
spring water from Loch Katrine supplied to Glasgow contains 
but three grains of impurity in a gallon ; on the other hand, 
there are pumps in the streets of London supplying water 
with 200 grains of impurity in the gallon. 
It may be asked here what may be regarded as the 
maximum of saline haatter that may be taken without injury ? 
This, however, is a difficult question to answer. At a sanitary 
congress held at Brussels in the year 1851 it was agreed that 
a good and safe drinking water should not have more than 
35 grains of dissolved constituents in the gallon. This must, 
however, in a great measure depend on the nature of the 
salts, as we know that chloride of sodium and carbonate of 
lime are comparatively uninjurious, whilst the salts of magnesia 
in small quantities do harm. Yarious experiments of the 
quantities of the more common constituents of water which 
2 p 2 
