Hardness of Water. This may be either temporary or permanent. Temporary hardness is due to the presence of calcic and magnesic carbonates and may be overcome by boiling, which expels the carbonic acid and precipitates the carbonates. Permanent hardness is due to calcic and magnesic sulphates which boiling does not affect. Hard water will not dissolve soap but precipitates it, hence the soap test is now usually employed for determining the hardness of water. Every grain of calcic carbonate or its equivalent in one gallon of water constitutes one degree of hardness.
The effect of hard water on the health is a debated point, but from an economic point of view soft water ensures a considerable saving, and it is said that in Glasgow, when the soft-water supply from Loch Katrine was introduced, a saving of over 30,000 in soap was effected per annum. Hard water is also responsible for the lime deposits formed in boilers, kettles and hot-water pipes commonly known as furring, and is also unpleasant for domestic use. Dyspepsia, gravel and stone in the bladder, and swellings of the glands have also been attributed to its use. The late Sir Douglas Galton suggested that 10 degrees of hardness would satisfy the general requirements of a town supply. Dr Clark's process for removing temporary hardness consists in the addition of 1 oz. of quicklime to every 100 gallons, by means of which the bicarbonate of lime is reduced to a carbonate, which is precipitated. At Luton Hoo the hardness of the water is reduced from 18 ½ degrees to 4 degrees by this process, and 70,000 gallons can be softened per diem.
The Porter-Clark is a modification of this system, the precipitated calcic carbonate being removed by cloth filtration under pressure, thus avoiding the delay of slow subsidence. There are several other systems, including Boby's simplex water softener, which latter we have successfully employed in various instances.
Permanent hardness of water at Penarth is reduced from 18 degrees to 6 degrees by the addition of 22.5 Ibs. of lime, 5 Ibs. of soda and 1 Ibs. of alum to every 10,000 gallons of water.
Next: Water Distribution.