984 WATER.— Softening.
water supplies differing in hardness, would be markedby greater differences arising from varying conditionsof drainage, ventilation, density of population, &c.A large number of towns of all kinds scattered overGreat Britain were tabulated according to the hard-ness of their water supplies. It was found that oftwenty-six towns, each with an average populationof 73,000, and supplied with water having less than5 parts of hardness per 100,000 parts, the averageannual mortality was 29T per 1000; of twenty-fivetowns, with an average population of 82,000, and awater of from 5 to 10 parts of hardness, it was 28'3;and of sixty towns, with an average population of45,000, with water exceeding 10 parts of hardness,it was 24-3. This would indicate that hard waterwas most wholesome, while moderately hard andsoft waters were comparatively unwholesome.
But all weight is taken from this conclusion, bythe fact that of the sixty hard water towns thirtypossessed the water closet system, while of the otherfifty-one only six were so arranged, the pestiferousmidden system being prevalent. Moreover, thelatter had a population, on an average, nearly twiceas large as the former, and therefore probably ofgreater density.
When the towns are classified according to theirposition, somewhat different results are obtained.Thus: of five seaport towns, with an average popu-lation of 163,000 supplied with soft water, theannual mortality per 1000 was 29'4; of three, withan average population of 226,000 supplied withmoderately hard water, the rate was 32T; and ofsix such towns, with an average population of 116,000supplied with hard water, it was 25T. This wouldindicate that moderately hard water was most un-wholesome, which is absurd. The differences in therate of mortality depend, doubtless, on other causes,such as density of population and nature of sanitaryarrangements. In a similar way, taking inlandmanufacturing towns by themselves, soft waterwould appear most unwholesome, and hard waterbest; and from inland non-manufacturing towns,that moderately hard water was worst, and hardwater best. A better prospect of success is presentedby an examination of our health resorts. Here,from the absence of manufacturing operations, andthe manifest interest of the authorities to obtainand preserve a thoroughly healthy condition, manycauses which disturbed the previous comparisonsare absent.
Nature o£ Water.
Number
of
Districts.
AveragePopulationin 1871.
Mortality per 1000per annum forthe decade1861-70.
Soft,.
5
48,430
19-5
Moderately hard,.
3
33,480
19-2
Hard,.
12
53,170
20-4
This would tend to show that the hardness of waterhas little or no influence on health, and indeed therate of mortality of the individual towns in the samehardness division varies more than the average rates
of the three divisions shown above. While, there-fore, waters of excessive hardness may possibly beinjurious, it appears that, apart from these, watersof all degrees of hardness are equally wholesomeif otherwise equally free from deleterious organicmatters.
The Softening of Hard Water. —Hard water isunfit for washing, and for nearly all manufacturingpurposes, but it may be softened by four differentprocesses, viz.: — by distillation, by the action ofcarbonate of soda, by boiling, and by the additionof lime.
By Distillation. —This method is chiefly, if notsolely, used for the preparation of fresh from saltwater, for the supply of ships at sea. It is costly,but is the only process applicable under the circum-stances. By it all fixed or non-volatile matters areentirely separated, as are also necessarily all organizedbodies, so that such water may be used with absoluteimmunity from risk of infection, a fact of no smallimportance in unhealthy localities. When freshlyprepared it has a vapid and unpleasant flavour, duepartly to deficient aeration and partly to the presenceof traces of volatile organic substances; both ofthese objections are removed by filtration throughanimal charcoal.
By the Action of Carbonate of Soda. —Carbonate ofsoda decomposes the bicarbonate and sulphate of limeand magnesia, to the presence of which the hardnessof water is almost exclusively due, forming solublebicarbonate and sulphate of soda, and insolublecarbonates of lime and magnesia. This action takesplace slowly in the cold, and rapidly at a highertemperature. As the soda salts have an unpleasanttaste, water thus softened cannot be used for drinkingpurposes. This method is commonly in use bylaundresses, who thus avoid waste of soap. Thefirst action of soap on hard water is to soften it, thesoap taking thh place of the carbonate of soda beforementioned; and it is only when this softening iscomplete that the detergent action of the soap cancommence. Soap thus used is much more costlythan carbonate of soda, a larger quantity beingrequired ; and its price being also much higher, therelative cost is about as 16 to 1.
By Boiling . —This method only applies to thatpart of the hardness of a water which is due to thepresence of bicarbonates of lime, magnesia, and iron,but is not applicable to that arising from sulphates.When such water is boiled the bicarbonates aregradually decomposed, the insoluble carbonatesbeing precipitated and carbonic acid expelled withthe steam. Ebullition for about half an hour issufficient. It is expensive, the cost not being muchless than that of softening by soap; and it is trouble-some, since the vessel in which the boiling is con-ducted becomes coated with a hard lining of carbonateof lime which is not easily detached, but, if allowedto accumulate, becomes a source of danger to thevessel in which it occurs. This process does notprevent the use of the water for drinking purposes.
By the Addition oj Lime. —This process is applicableto the same kind of water as the preceding, and to