174 DISEASES OF GLASSHOUSE PLANTS 
Complete cleansing of a polluted well is by no means 
simple. The first thing is to clear away the surface scum 
and as much of the growth round the sides as possible. 
When the water is thick with decaying plant materials 
it may be cleared by precipitation with alum and sodium 
carbonate, added at the rate of 18 lb. potash alum and 
5 lb. sodium carbonate for every 25,000 gallons of water. 
Perchloride of iron at the rate of 9 lb. per 25,000 gallons 
of water is also a useful clarifying agent. After precipi- 
tating the organic matter in the water the well may be 
pumped low and cleaned out as much as possible. When 
the well has filled up again the water should be “ chlorin- 
ated” to destroy disease organisms, and a convenient 
method is to add 50 gallons of “Chloros”’ for each 
100,000 gallons of water. After this treatment the well 
should be left alone for a week before using. Complete 
sterilization of the water can only be obtained by boiling, 
and this may be accomplished by arranging the pipes 
leading to the tank in such a manner that they are heated 
by passing through the boiler. The treated water is 
then stored in a tank adjacent to the boiler. While it 
may not be so necessary to supply the more mature 
plants with disease-free water it is advisable to sterilize 
the water used in the stages of propagation when the - 
plants are most susceptible to disease. 
