150 On the Composition and Properties of Drinking-Water, 
liable to become contaminated with drainage products containing 
soluble organic impurities of the most injurious kind to health. 
In sinking a well, the close proximity of a farmyard or stable- 
yard, a cesspool or drain conveying house-slops or sewage, or 
the neighbourhood of a cemetery, or the depositing-place for 
town-rubbish, and all localities where organic filth accumulates, 
should be avoided as much as possible ; and care should be taken 
to prevent the infiltration of surface-water into the well, and by 
making it water-tight, to exclude percolation from drains near 
or at some distance from the well. 
The wells in crowded cities, or the pumps in the close neigh- 
bourhood of burial-places, are frequently contaminated with 
organic impurities of the most objectionable character, and are a 
frequent cause of the outbreak and spread of infectious diseases. 
Such waters at certain times of the year are quite bright, free 
from smell, and scarcely coloured ; and their physical properties 
thus afford no clear indication of anything being wrong with the 
water. At others they give off a disagreeable smell, and appear 
decidedly coloured yellow. Well-waters which do not show a 
uniform character as regards freedom from smell and taste ought 
not to be used for drinking purposes. In further discussing the 
peculiarities of unwholesome well-waters, I beg to direct attention 
to the following analysis which I recently made of pump-water, 
from a public pump in one of the suburbs of London. On 
evaporation to dryness, this water left 58'80 grains of solid 
residue (dried at 130° C.) per gallon. 
In the residue I found, by direct determinations : — 
Grains. 
Oxidisable organic matter '56 
Lime 13-79 
Magnesia 2*22 
Sulphuric acid 10'67 
Chlorine 8-21 
Phosphoric acid "19 
Nitric acid 11-90 
Sohible silica -84 
Alkalies and carbonic acid not determined separately. 
These constituents were probably united together, as,follows : — 
G rains. 
Oxidisable organic matter -56 
Phosphate of lime "42 
Sulphate of lime 18-14 
Nitrate of lime 8-97 
Carbonate of lime 5-41. 
Nitrate of ma<;ncsia 8-21 
(Chloride of sodium 13-53 
Alkaline carbonates 2-72 
fiokible silica • 84 . 
Total solid matter per gallon 58 "80 
