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.

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    hand, flat, insipid, and even cloudy waters have caused no injury in use, their faults having been due to causes which had no hygienic importance. Physical characters, however, are of great value in conjunction with the subsequent analytical results. It is difficult to make them exactly comparable, and much work has been directed to establishing standards and degrees of colour, transparency, odour, and taste. Transparency involves freedom from suspended particles, and in a less degree absence of colour. The difference between the two effects can be obtained by exami- nation before and after careful filtration, which removes the first, but little affects the second. Transparency or turbidity is measured by the length of column through which an object can be seen when gradually lowered from the top, and afterwards approached from the bottom, the mean being taken as the measurement. It is best ascertained on the spot in large bodies of water, as it is rarely in the laboratory that a sufficient column of water is avail- able, and it is usually only requisite to record the sample as turbid, very turbid, nearly clear, or clear. On the large scale various methods have been em- ployed, by “ diaphanometers.” Secchi, in 18G5, used in the Mediterranean a white disc, twenty centimetres in diameter; later, by the Geneva Commission, an incandescent light was lowered, noting the limits of b 2