II July, 19 io.] Tlic Piiriiicatioii of Muddy Waters. 437 



THE PURIFICATION OF MIDDY WATERS. 



.1. C. H. Roilicra, ]\l.\., J/.R.C.S.. T.ccinrcr in Bio-Cliemistry, 

 Melbourne University. 



Much of the water available in the State of Victoria is rain water stored 

 in open tanks with puddled clay embankments and floors. Such water is 

 practically never clean, but generally discoloured, with a fine suspension of 

 mud. 



This mud is so finely divided that it does not sink under the force of 

 gravitv nor can it be separated under the greater force exefted by the 

 centrifugal machine. In the language of physical chemists, it is in a con- 

 dition of " colloidal suspension," and its separation from the water 

 requires either an effective filter, or the use of a chemical reagent. 



Filters. 



An effective filter is. however, generally speaking, a slow filter, and 

 will not allow large volumes of water to pass in short ]nter\als of time. 

 Further, they are costly to buy, and unless treated with care, and regularly 

 cleaned, thev may signally fail to purify water which contains hiirmful 

 bacteria. 



In fact, a badly cared for filter mav be a source of actual danger, for 

 bacteria may thrive in countless numbers amongst the material collected in 

 the filter, and may later be washed through into the filtered water 



Chemical Precipitation. 



By the second process of purification, namely, chemical precipitation, 

 no expensive initial plant is required, large rolumes of water may be 

 satisractorily handled, and any one with good common sense can control 

 the process, whereas the management of a filter requires a skilled and in- 

 telligent man. It is this second type of process which will now be 

 discussed. 



The visible impurity in "muddy water" is, as already mentioned, a 

 fine "colloidal suspension" for which the silicates of the puddled clay 

 floor are largely responsible. On the addition of certain chemicals this 

 fine suspension alters in character. 



The extremely minute particles, which, owing to their smallness, were 

 able to float in the water, begin to collect together until they fonn large 

 flocculent masses. 



These masses, which are easily seen to form a bulky precipitate, settle 

 to the bottom of the water at a speed depending on their weight, and 

 the manner of their formation ; but the important point is that they do 

 settle to the bottom, and at a rate which is perfectly satisfactory from the 

 practical standpoint. When the precipitate or flocculi have thorough' y 

 sedimented the water above is perfectly clean and sparkling. 



The whole process, to make a comparison, is exactly similar to the 

 clearing or " fining " of wine, whereby after the sedimentation of flocculi 

 the wine is lett bright and sparkling. 



The clean water above the suspended mud is completely free from 

 even the finest suspended particles. 



Its Bacterial Purity. — It is a well-known fact that bulky flocculi, 

 separating in a fluid, enclose and carry down with them, the micro-organ- 

 isms present at the time. In this way, the falling mud removes from the 

 water, the bacteria polluting it. 



