414 
THOMPSON YATES LABORATORIES REPORT 
iron pipes. The same deposits occur in the reservoirs, in the brick culverts, and 
occurred at Berlin in the reservoirs, it is associated with the iron present in the 
source of supply. 
Its presence in the water is beneficial in so far as it helps to remove by oxidation 
the dissolved iron, which assists to impart the yellow colour to certain waters ; and 
the black coffee ground deposit itself, containing as it does, abundance of iron and 
manganese oxides will probably act in the same way. 
The disadvantages, however, of any substance which tends to accumulate on the 
sides of the pipes, and, therefore, to diminish the flow through them, are greater than 
the advantages, and a remedy has to be sought. 
Means of Prevention 
Filtration. Long experience has proved this to be one of the most effective 
means of removing particles in suspension. 
Screening. Where filtration is not available a great deal may be accomplished, 
as has been shown by the Liverpool Water Engineer, by the use of fine copper 
gauze screens which keep back the larger threads and other debris. 
In so far as the dark colour of the unfiltered water is due to the presence of 
particles of the dark red fungus held in suspension, it is clear that the mechanical 
filtration will help to remove the colour. But the dark tint remains after the 
particles have been removed, this colour being due, partly to the pressure of some 
organic colouring matter, and partly to the presence of some iron compound in 
solution. The removal of this colour is a very difficult matter, and the following 
processes have been recommended, all of which tend to bring about the oxidation 
and deposition of any iron compound, as well as the oxidation of any organic colour- 
ing matter : — 
(a) Passing the water over coke towers in order to cause oxidation of the 
iron. This process has been used with great advantage on a small 
scale, and I have myself demonstrated its power of removing the 
yellow colour from water. 
(£) Allowing the water to fall in a rain for three or four yards in order 
also to bring about oxidation, 
(c) Steckel's method by the addition of lime in order to decompose the 
soluble carbonate of iron and form the oxide. 
(a) Addition of powerful oxidizers such as ozone, hydrogen peroxide, or 
filtration through filter beds constructed especially of oxidizing 
materials. 
The disadvantage of any precipitation method is that a precipitate is formed 
which must be removed by immediate filtration or settling. The combination of 
lime and filtration (Steckel's patent) has proved efficacious for small supplies. 
