A guide to the microscopical examination of drinking water : with an appendix on the microscopical examination of air / by J.D. MacDonald.

Date:
1883
Catalogue details

Licence: Public Domain Mark

Credit: A guide to the microscopical examination of drinking water : with an appendix on the microscopical examination of air / by J.D. MacDonald. 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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    further than to say that for rough materials it will he more convenient to use thick covers that may be easily cleaned without breaking them; while for finer materials, and especially fox immersion purposes, they should be proportionately thin. Mock of Collecting Sediments and placing them under the Micro- scope—Microscopical Powers—Immersion-lenses. When water is veiy turbid, from an obviously impure source, it is easy enough to obtain a sufficient amount of sedimentary matter for microscopical examination, and a just estimate of the unfitness of such water for di’inking purposes may be thus- readily formed. But it more frequently happens that the deposit, even after long standing, is but slight, and when this is the case, we must have recoui’se to special means, by which the whole, or a lai’ge amount of the matters in suspension, may be concentrated, or collected together, within a small compass. In the first place, one of the tall glass vessels above described should be filled with the water to be examined, and a circular disc of glass, resting on a horizontal loop at the end of a long aluminium wire lowered to the bottom, when the whole arrangement, lightly covered, must be set aside for twenty-fouiv or forty-eight hours, as the case may be. At the end of the specified time, the water should be siphoned off with a piece of india-rubber tubing, so as to leave only a thin stratum of the liquid over the glass disc. This should now be carefully raised and laid upon blotting-paper to dry its under surface and remove the surplus moisture, when it may be at once transferred to the microscope, with a large piece of covering glass so placed upon it as to exclude all air-bubbles. An ordinary watch-glass may in some cases be substituted for the disc alluded to, with advantage, as being .less likely to permit the loss of sediment by overflow, which is