(3) The operation of filtration and washing is very important.
The city added to its waterworks a filtration plant, with a total capacity of 150,000 gal.
The municipality owns its waterworks and filtration plant.
There are pumping works and filtration beds for the water-supply of London.
Sand filtration, even when working in the best possible manner, falls short of the perfection necessary to prevent the passage of bacteria which may multiply after the filter is passed.
In many processes of chemical technology filtration plays an important part.
In connexion with the water works there is a good filtration plant.
The separation of organic substances by filtration under high pressure through a colloid membrane, gelatine supported in the pores of a porcelain filter being usually employed.
As the process continued the salt-saturated layer, incapable of further effective filtration, grew in thickness downwards, until in the process of time it filled the whole mass of sandstone.
Filtration over charcoal or bleaching earth, are chiefly methods based on bleaching by means of oxygen or by chlorine.
The tertiary amine is then distilled off, the residual products separated by filtration and finally hydrolysed by a caustic alkali.
In that year, however, a League for Municipal Improvements was formed; in February 1902 a loan of $1,000,000 for municipal improvements was voted, landscape gardeners and sewage engineers were consulted, and a nonpartisan mayor was elected, under whom great advances were made in street cleaning and street paving, a new filtration plant was completed, the river front was beautified and protected from flood, sewage was diverted from Paxton Creek, and the development of an extensive park system was undertaken.
The water supply is derived from the Maumee river and is filtered by a municipal filtration plant.
The space below the sieve thus formed is connected by means of an outlet tap with a closed tank, and this again communicates with a vacuum pump. By this means the filtration is quickened by the atmospheric pressure, and goes on very rapidly, as also does the subsequent washing.
Judging from the best observations that have been made on a large scale, the highest rate of efficient filtration when the surface film is in good condition is about 4 in.
A lately discovered effect of sand filtration is a matter of great importance in connexion with the subject of aqueducts.
Some of the more viscous crude oils obtained in the United States are employed as lubricants under the name of " natural oils," either without any treatment or after clarification by subsidence and filtration through animal charcoal.
The city owns a fine water-supply and a filtration plant covering 20 acres, with a capacity of 30,000,000 gallons daily and storage reservoirs with a capacity of 2 2 7,000,000 gallons.
In some cases the operation of filtration is performed for the sake of removing impurities from the filtrate or liquid filtered, as in the purification of water for drinking purposes; in others the aim is to recover and collect the solid matter, as when the chemist filters off a precipitate from the liquid in which it is suspended.
For the sand-filtration of water on a large scale, in which the presence of a surface film containing zooglaea of bacteria is an essential feature, see Water Supply.
This is heated to boiling, and the residue after filtration contains about 30% of Prussian blue.
The Lamellibranchia have markedly diverged from the original type by the adoption of filtration as a method of feeding.
The city owns and operates its watersupply system (with an excellent filtration plant installed in 1904) and its gas and electric lighting plants.
Crude acetone may be purified by converting it into the crystalline sodium bisulphite compound, which is separated by filtration and then distilled with sodium carbonate.
Above the river; and there is a slow sand filtration plant for the filtration of the entire supply.
But before this was accomplished the filtration of the effluent became defective, and brackish water was received, which rapidly increased nearly to the saltness of the inflow.
This dam has been in satisfactory use since 1885, and the slight filtration through the masonry which occurred at first is said to have almost entirely ceased.
Yet it cannot be too constantly urged that such filtration depends for its comparative perfection upon the surface film; that this surface film is not present when the filter is new, or when its materials have been recently washed; that it may be, and very often is, punctured by the actual working of the filters, or for the purpose of increasing their discharge; and that at the best it must be regarded as an exceedingly thin line of defence, not to be depended upon as a safeguard against highly polluted waters, if a purer source of supply can possibly be found.
Moreover, if a natural water is so liable to pathogenic pollution as to demand filtration of this kind, it ought at once to be discarded for an initially pure supply; not necessarily pure in an apparent or even in a chemical sense, for water may be visibly coloured, or may contain considerable proportions both of organic and inorganic impurity, and yet be tasteless and free from pathogenic pollution.
There are several ways to clarify water.
Attempts have been made, by adding certain coagulants to the water to be filtered, to increase the power of sand and other granular materials to arrest bacteria when passing through them at much higher velocities than are possible for successful filtration by means of the surface film upon sand.
No public supply should be open to any such doubt as ought to, or may, deter people from drinking the water without previous domestic filtration or boiling.