Sterilisation Experiments on the Cambridge Water. 569 



bisulphite of soda with its contaminating organisms, acid and gas 

 reactions were obtained in 50 c.c. of water, the results obtained 

 by the other bacteriologists coinciding almost exactly with those 

 obtained in the Cambridge laboratories ; one of them finding 

 organisms of the coli group in 50 c.c, of water, the other three 

 finding none in 500 c.c. of water. On the next three days of the 

 run every sample of the treated water taken and tested was found 

 to be free from any of the coliform (or any other non-sporing) 

 organisms. Alterations had then to be made in the pumps and 

 in the neutralising solution, and the results were less satisfac- 

 tory, but the following day " sterilisation " was again com- 

 plete. Up to this point we had been working with one part of 

 chlorine in 1,000,000 parts of water. The following day the 

 strength was altered to one part of chlorine in 2,000,000 parts 

 of water. The first sample taken after this change was made 

 was found to contain acid-forming organisms though no gas was 

 produced in 100 c.c. of water. From this point on to the end of 

 the fourth day of this experiment sterilisation was complete in 

 every instance, quantities from one to two litres being tested. 

 The following day the chlorine was reduced to one part in 

 4,000,000 parts of water. Here again although sterilisation was 

 complete on almost every occasion that samples were taken, 

 twice — in one sample taken at twelve o'clock giving a develop- 

 ment of acid and gas in 100 c.c. of water and a second sample 

 taken at 5.30 in which acid only was developed — the process 

 of sterilisation was incomplete. On the two following days com- 

 plete sterilisation was obtained throughout the whole of the run. 

 In all these experiments bisulphite of soda solution was used to 

 neutralise any excess of chlorine and to remove any slight taste 

 and smell of this substance from the treated water. It will be 

 noticed that only on the first day on which any single strength 

 of chlorine was used were any failures to effect complete sterilisa- 

 tion noted, whilst even on these days a failure occurred only at 

 certain periods, periods during which, owing to irregularity of 

 the action of the pump or imperfectly regulated valves, too large 

 a quantity of bisulphite of soda solution, and with it probably 

 certain contaminating organisms, was thrown into the chlorinating 

 vessel. As we gained experience concerning the contamination 

 of the bisulphite solution, of the working of the pumps, and of 

 the falling off in strength of the bisulphite solution, irregularities 

 in the results obtained were gradually eliminated. 



Following these experiments the installation was run for a 

 couple of days so as to introduce one part of chlorine into between 

 7,000,000 and 8,000,000 parts of water. Here the excess of 

 chlorine unabsorbed was so slight that neutralisation was un- 

 necessary as there was neither taste nor smell of chlorine in any 



