72 



KNOWLEDGE ♦ 



[July 25, 1884. 



direction ; and may we not hope that the time is at hand 

 when pestiferous cemeteries, with their gloomy tombs, 

 tablets, wreaths, and misshapen marhle doves, will give 

 place to drinking-fountains, seats for the weary and foot- 

 sore, shelters and food for the houseless, aud health and 

 happiness for all t 



The evil gases and germs arising from graveyards are only 

 too manifest to those whose duty leads them perpetually to 

 such scenes ; not only does the air become vitiated, but the 

 most serious cause for apprehension is to be souijht for in 

 the drainage. The rain-water cariies the foul products 

 from the atmosphere, and in greater abundance from the 

 soil, into the underground circulation. If the strata happen 

 to slope downwards to a district of water-supply from wells, 

 the latter become perpetual sources of disease. To a less 

 marked extent is the influence of man felt in the deteriora- 

 tion of water through cesspools and pits ; yet they are 

 oftentimes sources of great danger. See Fig. IS, which we 

 avail ourselvfs of through the kindness of Mr. P. A. 

 Maignen. 



Fig. 18. — Eeproduced from the Tenth Annual Keport of the 

 Massacbussetts State Board of Health. There were twelve cases 

 of typhoid fever among persons using this well water and the house 

 became the centre of infection for a whole neighbourhood. 



Samples of "Water. 



We now propose to submit to our readers a series of 

 samples of water, both natural and artificial, with a brief 

 summary of their jtroperties, as preliminary to a sketch of 

 the methods employed to render them valuable for specific 

 purposes. In doing so we shall have occasion to lead them 

 once more to the collections at South Kensington, there to 

 view the numerous apparatus and inventions which have 

 been designed to secure the purification of waters. 



1. Natural Waters. — To this category belong the 

 following types : — 1. Ice and snow ; 2. Kain, dew, and 

 hoar-frost ; 3. Marsh and Pond water ; 4. Lake water ; 

 5. River water; G. Underground water ; 7. Sea water. 



1. Ice and Snoiv are characteristic of all regions where 

 the conditions of temperature and atmospheric pressure are 

 such as to maintain the water in its solid forms. It usually 

 obtains thus during wintry seas-ons in the temperate zones, 

 and permanently on mountain snow-slopes and glaciers, at 

 altitudes of from eight to ten thousand feet and upwards 

 above the sea-level, and in the circumpolar areas. Frozen 

 water is, as a rule, almost free from impurities ; and, when 

 liquefied, yields a remaikably pure fluid, in which dissolved 

 mineral salts and suspended solid particles are only acci- 

 dental. 



Unlike most substances, water expands on cooling. But 

 only between the limits of 39 25° Fahr. and 32= Fahr. ; it 

 becomes frozen, and in virtue of its relative lightness 



remains on the surface of the water. The lower levels are 

 thus prevented from radiating heat into space, and the 

 warmth so necessary to the maintenance of life is thus 

 retained by the earth. The bracing climate of a mild 

 wintry country is too well known and appreciated by those 

 who live in it to require any comments here. If we were 

 writing a treatise on domestic medicine, we would consider 

 it our duty to devote at least one chapter to ice and snow. 

 In the kitchen, ice is a most desirable luxury ; and in the 

 preservation of diets, we have but to turn for a tangible 

 example to the gridiron of Messrs. Bertram k Roberts, at 

 the foot of the passage leading to the Aquarium in the 

 Exhibition buildings, to enjoy an excellent, well-matured 

 mutton chop all the way from New Zealand. 



2. Rain, Dp.v\ and Jfoar-frost. — The properties of these 

 w-aters have already been detailed at some length.* The 

 usefulness of rain-water depends to a very large extent 

 upon its softness and freedom from suspended particles. It 

 is, perhaps, the largest source < f supply of practically pure 

 natural water in existence. Of possible impurities, dust 

 and dirt, leaves and twig>, soot ard at-hes, traces of such 

 acids as hydrochloric, sulphuric, and nitric acids, sulphates, 

 chlorides, and ammonia, besides the gases of the air, are 

 liable to afl'tct rain-water most of all. 



Dew, the fi'ozen variety of which is termed hoar-frost, 

 generally contains a somewhat larger percentage of soluble 

 and suspended impurities than rain water, which it abstracts 

 from the air. In England, it has been shown that dew 

 possesses 4 87 in 100,000 parts of solid impurity, and about 

 •198 parts of ammonia.! In our remarks upon the forma- 

 tion of dew,! we noted that a deposition of moisture from 

 the invisiVile vapour held in the atmosphere takes place 

 when the moisture-laden medium comes into contact with 

 bodies which are ever so little colder than it is itself ; the 

 exact temperature at which this occurs can be ascertained 

 by means of a little instrument called after its inventor, 

 Uaniell's ether hygroiu'ter, and is termed the dev jioint. 

 On a clear night the leaves of plants, ic, radiate more 

 heat into space than they receive back, and are thus 

 rendei-ed colder than the furrounding air, and, in conse- 

 quence of this, dew is formed ; on a cloudy night, however, 

 the heat is radiated back by the clouds, and the deposition 

 of dew thus curtailed. During the summer months, an 

 immense amount of vapour is taken up by the warm air, 

 and, as the nights are usually clear, enormous quantities of 

 dew are produced and absorbed by the vegetation and 

 surface soils of the earth. This state of affairs is, of course, 

 more pronounced in tropical countries, where the source of 

 water supply through the agency of dew is an all-important 

 factor in the maintenance of the conditions of life during 

 the protracted period of drought commonly called the 

 " dry season." 



3. Marsh and Pond Waters are local collections of rain, 

 or, in the neighbourhood of sea-coasts, of rain and spray. 

 They usually harbour vegetable and animal growths and 

 decaying matters; and upon the absence or presence of 

 these, in larger or smaller quantities, does the value of the 

 water entirely depend ; it may thus range from a good, 

 soft water to one which may be described as the essence of 

 contamination. 



4. Lake Water may represent the accumulated drainage 

 of a large area which empties into a natural reservoir. The 

 character of the water, which is primarily derived from rain, 

 thus depends wholly upon the nature of the surrounding 

 formations. The water of lakes without efferent streams, 

 generally becomes saline, through evaporation and con- 



* Vt ^vpra, p. 31, et .'ieqnetites, 



t "Bivers Pollution Commission," 6th report, p. 32. 



J See this Journal, p. .3 1. 



