630 PROCEEDINGS OF SECTION I. 



Unfortunately the two latter are decidedly saline, and the last is, as 

 before mentioned, suspicious from the quantity of nitrates it con- 

 tains. Other waters, such as the Magill, Kensington, and Beetaloo, 

 are sometimes pure and sometimes impure, while others are 

 invariably below the standard of organic purity. This is not 

 surprising when we consider that all our supplies are derived from 

 surface waters, and that much of the water run into the reservoirs 

 is decidedly turbid, not from carelessness, but because it is under 

 existing conditions a case of turbid water or none. It becomes 

 increasingly necessary therefore to consider what means can be 

 applied to render our potable waters of greater organic purity. 



PURIFICATION. 



1. By sulphate of alumina. 



2. By lime (Clarke's process). 



3. By filtration. 



4. By agitation with iron and aeration (Anderson's process), 



1. By Sulphate of Alumina. — This process is suitable for treat- 

 ing soft waters which cannot be purified by Clarke's process. In 

 Table 5 the result of this process on a small scale with the 

 Kapunda water is given. Commercial sulphate of alumina (hydrous) 

 Avas added to the uater at the rate of lib. per 1,000 gallons, the 

 water agitated, allowed to settle forty hovirs, and the clear 

 water syphoned off and analysed. The improvement in the water 

 is most marked. The objection to this process is that should an 

 excess of suljjhate be added it renders the Avater slightly acid, but 

 with care the effluent is quite neutral. This process has been found 

 to answer equally well with other waters of a similar character. 



2. By Lime f Clarke' s Process). — Table 5 shoAvs the improve- 

 ments effected on a sample of Hope Valley reservoir water. The 

 improvement from an organic point of view is not nearly as marked 

 as by the alumina or the Anderson process, and fcAv of our Avaters 

 are sufficiently hard for this process to be of striking utility. 



3. By Filtration. — I have not had an opportunity of testing an 

 efficient sand filter on our Avaters. In Table 4 an example is given 

 of the organic improvement effected by one of G. Cheavin's filters 

 on the Adelaide serA'ice water of September, 1891. The effluent 

 from this filter was of A^ery great purity, and the change effected in 

 the water can, I think, only be ascribed to the oxidation of the 

 organic matter by micro organisms present in the filter. The effi- 

 cient filtration of large quantities of Avater through sand or other 

 medium presents considerable difficulty and continued Avatchfulness 

 and attention as to the rate of flow, the quality of effluent, and the 

 state of the filter bed. A filter bed has three stages : the prepara- 

 tory, during AA'hich mvich organic matter passes through Avith the 

 water, which should not be alloAved to pass into the service pipes ; 

 gradually the surface of the filtering medium becomes coated Avith 

 a fine covering of a gelatinous-like nature, and the filter passes into 

 the second or efficient state, AAdien the Avater becomes fit for use. 



