566 Frof. Woodhead, The 7'esults of 



a series of disagreeable compounds described as " chloramines " 

 may be formed, these imparting to the treated water a persistent 

 and disagreeable taste and smell. Hence in the presence of large 

 quantities of organic matter especially when decomposing or 

 capable of rapid decomposition it may be essential that the water 

 should be submitted to some preliminary treatment. In the case 

 of the Cambridge water, however, this is certainly unnecessary. 



Bearing on this point it may be noted (1) that the amount 

 of chlorine sufficient to sterilise waters containing considerable 

 amounts of organic matter can not be neutralised as regards taste 

 and smell by the addition of bisulphite of soda ; (2) that such 

 taste and smell may be present even when the process of sterilisa- 

 tion is not complete and when no free chlorine can be demonstrated 

 by the iodide of potassium and starch test, whilst on the other 

 hand water that contains only small quantities of organic matter 

 may be completely sterilised and a slight violet iodine-starch re- 

 action indicating the presence of a faint trace of available chlorine 

 still unused, may still be present without the slightest trace of 

 either taste or smell of chlorine remaining in the water. If such 

 water be exposed to light or to a slightly higher temperature this 

 trace of available chlorine disappears and, in all probability, is 

 rapidly converted into hydrochloric acid. 



The experiments carried out in the laboratory were not of 

 course on a sufficiently large scale on which to base final con- 

 clusions as to sterilisation. The Directors of the Cambridge Water 

 Company and Mr Gray, the Manager, who all along were most 

 anxious to place full facilities for carrying out these experiments 

 at my disposal, requested Mr Hawksley to erect a plant with 

 which the sterilising process might be carried out on a "practical" 

 scale. This consists of (1) a chlorinating cylinder capable of 

 holding about 7000 gallons, so that water passing through this 

 cylinder at the rate of 7000 gallons per hour should remain in 

 contact with any chlorine solution entering the cylinder along 

 with the water for about one hour or thereabouts, the time of 

 contact of course being halved when double the amount of water 

 is passed through the cylinder*; (2) a series of mixing and settling 

 tanks, each containing 700 gallons of water. In one of these tanks 

 is prepared the bleach solution and in another the neutralising or 

 bisulphite of soda solution, the other tanks are used as settling 

 tanks, one for each solution ; (3) a couple of pumps so regulated 

 that measured quantities of the bleach solution may be pumped 

 into the water as it enters the chlorinating cylinder, and of the 

 bisulphite solution as the water leaves the cylinder. Measured 



* As a matter of fact some of the water passed through the cylinder in about 

 18 minutes, but most of it remained in the cylinder for nearly an hour. 



