The results proved conclusively that statements alleging damage to plants, flowers, and seeds by the hypochlorite treatment of water are unfounded and do not merit the slightest consideration.
_Corrosion of Pipes._ Chlorinated water, it has been alleged on many occasions, causes rapid corrosion of galvanised iron water services and especially of the water tubes of boilers, water heaters, etc. When bleach is used for water treatment, a slight increase in the hardness is produced but as this is mostly due to calcium chloride, there is no corresponding increase in the salts that form a protective coating. The presence of traces of calcium chloride and chloro-organic compounds might tend to increase the corrosive properties of a water but this increase is probably so small as to be negligible.
If pipe corrosion is considered by the carbonic acid hypothesis, the use of bleach should tend to reduce it because bleach contains an excess of base that combines with a portion of the free carbonic acid. The results of routine tests for free carbonic acid made on the raw and treated waters at Ottawa are as follows:
-------+----------------------+------------------------- | CARBONIC ACID. | | PARTS PER MILLION | Year. +----------+-----------+ Nature of Treatment. |Raw Water.|Chlorinated| | | Water. | -------+----------+-----------+------------------------- 1915 | 1.44 | 1.41 | Bleach 1916 | 0.92 | 0.85 | Bleach 1917 | 0.84 | 0.81 | Bleach first four months | | | Chloramine during last | | | eight months -------+----------+-----------+-------------------------
These figures shown that the hypochlorite treatment produced a small but definite decrease in the carbonic acid content and should, _cæteris paribus_, tend to reduce and not increase corrosion.
If the corrosion of pipes is considered according to the electrolytic theory, a slight increase, due to an increased electrical conductivity, might be anticipated. The effect of the addition of hypochlorite upon the electrical conductivity of distilled water and the Ottawa River water is shown in Diagram VI.
Effect of Calcium Hypochlorite on Electrical Conductivity]
With the concentrations of hypochlorite ordinarily used in water treatment it is inconceivable that the slight increase in the electrical conductivity has any practical significance at low temperatures. The conductivity increases rapidly, however, with increase of temperature and any increment due to chlorination might produce a slight appreciable effect at temperatures approaching the boiling-point of water.
