148 On the Composition and Properties of Di-inking- Water, 
suspended matter, set the flask aside for a couple of days, and 
then pour off the clear liquid, or pass it through filtering-paper, 
and examine the colour of the clear or filtered water as before. 
The suspended matter may be fine clay or marl, and simple 
filtration or subsidence may render it quite fit for use. 
In the next place it should be ascertained whether the water 
has any smell. If it contains appreciable quantities of sewage 
or decomposing organic matter, it will necessarily have a bad 
smell ; if there are but small quantities of such matters present, 
it is often difficult to decide at once whether the water is free 
from smell or not, and in that case it is best to fill a large flask 
or bottle with water, to pour out the greater part of the contents, 
and then to inhale the air in the partially filled flask or bottle. 
In this way, and especially if the flask is gently warmed, may 
be detected a disagreeable smell, which cannot be clearly dis- 
cerned by the ordinary mode of noticing the smell of water. 
Another preliminary examination which anyone may make is 
to fill a clean wine-bottle quite full with water, cork it down 
tight, and set it aside for about a week ; then draw the cork and 
notice whether the water gives off a bad smell, or has in any 
other way undergone a change. At the same time place some 
water in an open vessel — best a clean glass beaker — cover it over 
loosely with filtering-paper to exclude dust and similar me- 
chanical impurities floating in the air, place the water aside for 
a week or fortnight, and observe from time to time whether the 
water remained fairly clear, or whether fungoid growth or the 
development of plants of the lowest order has taken place. In 
waters contaminated with even small quantities of sewage the 
development of vegetable cells and plants of the lowest order is 
very striking. 
Lastly, evaporate about one pint of water in a clean small 
porcelain dish, or better still, platinum capsule ; and notice 
whether the water remains unaltered as regards colour, oi 
whether it turns yellow or brownish on concentration to a smal 
bulk. If a water contains merely traces of organic matter, i 
does not sensibly turn colour on concentration ; but if it is con 
taminated with an appreciable amount of organic impurities, i 
turns yellow or brown. Evaporate the water under examinatio 
completely to dryness, and notice the colour of the residue 
If quite white, like the residue obtained by evaporating to dr> 
ness the colourless water of chalk-springs, no organic matter 
present ; but if the residue is coloured yellow, as is the case wit 
most natural waters, a certain amount of organic matter 
present. The organic matter may be harmless ; or it may 1 
injurious to health, and in that case requires furtlier examinatio 
which should be entrusted to an experienced and skilled analy; 
