Army manual of hygiene and sanitation, 1934 / [War Office].

Date:
1941
Catalogue details

Licence: Public Domain Mark

Credit: Army manual of hygiene and sanitation, 1934 / [War Office]. Source: Wellcome Collection.

    38/310 (page 40)
    municipal supplies, and they were also made use of in the water sterilizing lorry during the Great War. The simplest form of sand filter is provided by a hole dug in sand some distance from a muddy river; the water from the river filters through the sand, Filtration through cloth is very efficient and its action is improved by the dirt deposited on the cloth; this method is used in the Elliott mobile water purifier and in the regimental water cart. . Sedimentation and filtration are greatly assisted by the use of chemicals, the chief of which are the salts of aluminium. Those most used are aluminium sulphate, and alumino-ferric ; the latter is crude aluminium sulphate containing iron. When dissolved in water these aluminium salts form a loose transparent jelly consisting of aluminium hydrate, which entangles the suspended matter in the water and carries it to the bottom as a sediment. If the water is passed through a filter, such as a cloth, a film of jelly is formed on the cloth and increases the efficiency of the filter by holding back much finer particles than would the cloth alone. Five to fifteen grains of alum are required for each gallon of water to be clarified and the effectiveness of the clarification depends on the water being alkaline. If the water is acid, as peaty waters are, or very hard, the jelly either forms very slowly or not at all; alkali in the form of soda is therefore added to the alum to make the water alkaline. The methods of clarification employed for military water supplies in the field are sedimentation with alumino-ferric, clarification by filtration through cloth on which a gelatinous film has been formed by water clarifying powder, or by filtra- . tion through cloth only as in the Elliott mobile water purifier. Sedimentation with alumino-ferric is carried out in the two- tank method in which the raw water is pumped into a canvas tank and alumino-ferric-added ; after standing in this tank for some hours to allow the sediment to settle at the bottom, the clarified water is syphoned off into another canvas tank at a lower level and there sterilized. _ Water clarifying powder consists of two parts alum and one part sodium carbonate and is supplied in eight-ounce tins with a scoop holding 83 grains. It is used in the clarifying cylinders of the regimental water cart and in the Pack clarifiers, and in both the method of use is the same. Four scoops of the powder are placed between the mesh plates in the cylinder cover. The clarifying cloth is wrapped round the reel and placed in the cylinder, and the cylinder cover containing the powder is placed in position and screwed up. When water is pumped through the clarifying cylinder the alum is deposited as a fine film of jelly on the clarifying cloth, which thus filters