Report on the sanitation of Port Louis / by Andrew Balfour.

  • Andrew Balfour
Date:
[1921]
Catalogue details

Licence: Public Domain Mark

Credit: Report on the sanitation of Port Louis / by Andrew Balfour. Source: Wellcome Collection.

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    “25 APPENDIX Il. ———— WATER DISINFECTION BY LIQUID CHLORINE, _, Liquid chlorine is one of the cheapest, most conveniently handled, and most effective disinfectants for the purification of water supplies. It is chlorine gas, of 99.9% purity liquefied under pressure and stored in steel cylinders containing 70 to 100 Ibs., and effects the sterilisation of water supplies of average impurity when added in the proportion of one- third part per million, by weight. The active germicidal agentis the nascent oxygen resulting from the decomposition of the unstable hypochlorous acid produced on the addition of chlorine to the water. . To Lieutenant Nessfield, of the Indian Medical Service, is due the credit for first publicly suggesting (in 1903) the use of liquefied chlorine gas for the sterilisation of water supplies. Major Darnall, of the U.S. Army Medical Corps, put this suggestion into practical form in 1910, Various improvements have lately been effected on the mechanism’ for regulating, measuring and applying the chlorine with precision. The “ Chloronome”’ is the registered name of the Paterson Engineering Company’s device for regulating, measuring and administering chlorine gas to water supplies. Figure 2* shows in outline a typical arrangement of the apparatus capable of sterilising up to 3,000,000 gallons daily. The liquid chlorine is contained in steel cylinders, each holding about 70lbs, the pressure at 32° F. being 54 lbs. per square inch, or at 120° F. 215 Ibs. per square inch. It passes into the gasesous form on evaporation by the heat. abstracted from the atmosphere through the walls of the cylinders. The steel cylinders are usually placed on a weighbridge to check the amount of chlorine used during long periods, and to indicate when the cylinders are nearly exhausted. A coil connector valve is coupled up to the valve on the cylinder head. The chlorine gas is led through a flexible connecting coil of copper tube to the filter which removes any slight deposit which may be carried by the gas from the exposed coil tubes or the cylinder fittings. Asitis important that the pressure of gasbe kept constant on the regulating valve, two pressure reducing valves are arranged in series. The chlorine gas ata pressure varying from 80 to 120 lbs (depending upon the temperature of the surrounding atmosphere) passes through the first reducing valve which breaks down the pressure to 20 lbs. per square irch, then through the second reducing valve which maintains a constant pressure of 10 lbs. per square inch on the regulating valve. Should this pressure,as indicated by the gauge, show a tendency to drop,the attendant knows it is time to switch on the second cylinder. By the application of artificial heat it can be assured that the first cylinder is completely exhausted before being replaced by another to be put into commission at a later date when the second is practically exhausted. The chlorine gas passes the regulating valve and flows from the meter (detailed reference to which is made later) through a central pipe down to nearly the hottom of the absorption tower. This glazed earthenware tower is fitted at the top with a water distributing tray and packed with pumice. A small trickle of water is uniformly distributed over the pumice, and in its downward flow absorbs the measured. quantity of chlorine gas. The chlorinated water flows from the bottom of the tower through a chlorine- resisting rubber or earthenware pipe, and is uniformly distributed through the main body of the water to be desinfected. Many water supplies can be chlorinated by the addition of a quarter part per million, i.e., 2.5 Ibs. of chlorine per millicn gallons of water purified, so that an installation purifying 1,000,000 gallons per day, may only require to administer 1.66 ozs. of chlorine per hour. Even with plant of this moderate capacity it is desirable to have a_ positive ~olumetrie measurement of the gas administered, and absolutely essential when dealing wtih smaller plant of, say, 1,000 gallons hourly requiring .041 ozs. of chlorine. Dry chlorine gas at normal temperatures has no appreciable corrosive effect on metals, but immediately it comes into contact with the moist atmosphere most virulent corrosion takes place. The special feature of the Paterson“ Chloronome” is the interposition between the instrument and the absorbing water supply of an isolating column of liquid which is unaffected either by the gas or the water absorbing it, and acts as a volumetric meter. Tests were carried out with various liquid seals and ultimately sulphuric acid was selected as the most effective. The sulphuric acid is contained ina ““U” shaped sealing tube. The flow of gas depresses the column of sulphuric acid until it unseals a small vent pipe which then permits the passage of the measured quantity of gas from the inlet to the outlet limb. This establishes equilibrium and permits the return of the column of sulphuric acid until it again seals the vent pipe, when the cycle of movement is completed and another downward stroke commences. The gas is maintained at 10 Ibs. pressure on the regulating valve, but is measured by the volumetric meter at atmosgheric pressure. The rate of pulsation and known volume of the stroke gives the weight of chlorine added. Prolonged tests have shown that when the regulating valve is once set, the meter continues to pulse for months at the same rate. By means of the stop valve below the pressure gauge, the attendant can stop and start the apparatus when required without readjusting the regulating valve. EN EE ENED EIA TOO is STOO at Sd et cn nce ETC st *Figures not reproduced.
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