48 
LABORATORY EXERCISES 
animals which may be in or about the water. If sediment is 
present in the water, what is its nature? What is the source of 
this sediment? Does water readily become clear? What are pos¬ 
sible sources of pollution? Could the untreated water which is in 
the reservoir be used with safety? Explain. At what season of 
the year is the danger from the use of such water greatest? Why? 
II. The Settling Basins. How does the water get into these 
basins? What is their purpose? Note their size and structure. 
Examine the water which they contain. Note its character and 
appearance. What chemicals are used to purify this water? How 
are they added to the water? What is the use of each? Note 
especially the effect of the alum, if used. Does it remain in the 
water which is to be pumped through the city? What evidence 
is there that the chloride of lime or liquid chlorine is effective? 
III. From the standpoint of health, of what value to a city is a 
water system like the one you are studying? Write a brief paper 
upon this topic. 
EXERCISE 51 
A SURVEY OF UNSANITARY CONDITIONS 
I. Field Work. Choose for this survey town blocks or other 
definite areas which appear to be below a desirable standard so far 
as sanitary conditions are concerned. The class may work in 
groups or as a whole. All observations are, of necessity, to be 
made from streets, alleys, or other public highways. Each member 
of the class may prepare a plan of the area studied. Show on it 
the location and size of all buildings, alleys, passageways, etc. 
locate on it all stables, cesspools, outbuildings, garbage cans, piles 
of garbage, tin cans, and other rubbish, hog pens, rotting vegeta¬ 
bles, standing water, etc. Locate any wells or cisterns and note 
the probable drainage conditions surrounding each. 
II. Conference. Discuss each source of danger found. Ex¬ 
plain wh}^ it endangers the public health. Point out the remedy 
