Water and its purification : a handbook for the use of local authorities, sanitary officers, and others interested in water supply / by Samuel Rideal.

Date:
1902
Catalogue details

Licence: In copyright

Credit: Water and its purification : a handbook for the use of local authorities, sanitary officers, and others interested in water supply / by Samuel Rideal. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

    24/436 (page 4)
    “ clear vision ” and of “ diffused light.” This method would he specially adapted for wells. The intensity of light at different depths was also measured by sensitised photographic plates, hut in this way colour considerably interfered. To obtain observations with less quantities of liquid, Hazen, at Lawrence, Mass., attached a bright platinum wire, one millimetre in diameter, at right angles to the end of a graduated rod, recording the turbidity in degrees ; invisibility at one inch being taken as unity, other degrees were fractional, inversely as the depth at which the wire was obscured. If the turbidity was more than one, the sample was proportionally diluted ; if less than 0-02 (50 in.), the turbidity was ascertained in another water, and this diluted to imitate the sample as nearly as possible. The jars or bottles were cased in black cloth and illuminated from below (Filtration of Water Supplies, by Allen Hazen, Wiley, New York, 1900). Whipple and Jackson have introduced silica standards for turbidity, made by finely grind- ing the silicious frustules of diatoms obtained from certain deposits, suspending in water, and diluting definitely. They seem to have many advantages over kaolin or chemical precipitates (Eng. Record, N.Y., Jan. 27th, 1900). Waters which appear limpid to the eye may yet contain an appreciable amount of solid matter in suspension, consisting of substances and organisms so transparent that their presence can only be proved