A manual of practical hygiene : prepared especially for use in the medical service of the Army / by Edmund A. Parkes.

Date:
1864
Catalogue details

Licence: Public Domain Mark

Credit: A manual of practical hygiene : prepared especially for use in the medical service of the Army / by Edmund A. Parkes. 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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    peculiar fade or slightly saUne taste, if the total salts amount to 35 to 40 grains per gallon, and the sulphate of lime reaches 6 or 8 grains. Iron is tlie only substance in small quantity detected with great certainty by taste. That a water is tasteless is, therefore, evidence only of freedom from very large im- pregnation with salts and organic matter. Smell detects sulphuretted hydrogen in very small quantities, and ammonia if in large amount. Suspended Or dissolved decomposing animal matters in large quantity sometimes will give a foetid smell. If butyric or other fatty acids have formed, the smeU may be occasionally perceived when a stoppered bottle in which the water has been kept for some weeks is opened. Touch.—The only evidence derivable from this sense is in washing, hard waters (containing the earthy salts) forming an imperfect lather with soap. This point is generally, however, more precisely determined. So also in cooking vegetables. Hard waters coat the vegetables with salts of lime, and prevent the access of water. If circumstances prevent any examination beyond the physical one, it should be clearly understood and stated that the information is very limited, and on no occasion should a water be affirmed to be good merely because it Ls colourless, tasteless, and free from smell; it shoidd be merely stated that the physical examination detects no impurity. Sub-Section II.—Microscopic Examination. After the water has stood for twenty-fotu- hours, the sediment may be examined, or if there be much animal or vegetable life, a drop can at once be taken from the water. The larger animals can often be seen with the naked eye, by attentively looking through the glass when placed opposite a bright light. In the sediment the chief microscopic appearances are— 1. Sand; easily known by its angles, and its being imaflfected by any re-agent. 2. Clay and marl; amorphous non-angular particles, not acted on by re-agents. 3. Chalk; round and slightly angidar particles, at once dissolved by acids. 4. Woody fibre ; when much broken up, very little is seen beyond dark masses, sometimes rather fibrous-lookiug; if less changed, and in large masses, unequivocal woody fibre can be seen. 5. Portions of leaves; bits of the veins, with occasionally some of the parenchyma, or dark masses Avithout any distinguishing characters, are seen. If starchy matters remain, iodine detects them. G. Alg^ and confervoid growths are often seen even in tolerably pure waters, and portions of different water plants. 7. In some cases remains of animals, portions of muscvdar tissue. In waters contaminated with sewage, an ochreous substance has been found by Hassall, and is considered to be altered muscular fibre tmged with bile. Nitric acid brings out the pink tint,* according to Hassall. 8. Infusoria.—The different kinds of paramecium are the most common, and arc found in water containing both animal and vegetable organic * A Micmscopic Examination of the Water .supplied to the Inhnliitanti of London. Arthur Hill Hassall, M.H. 1850. P. 8.