1885.] The Removal of Micro- Organisms from "Water. 387 



finely divided matter like clay is not conducive to the separation of 

 micro-organisms. 



A similar result was obtained with brickdust, which, however, did 

 not take quite so long to subside. 



Effect of Subsidence on Micro-organisms in Water. 



As in the above agitation experiments the water for examination 

 was always taken from the clear upper layers, it became of interest to 

 know whether the micro-organisms would not, by subsidence alone, 

 separate out from the upper layers without the influence of solid 

 particles. In order to ascertain this, three sterilised Winchester bottles 

 were filled up to the shoulder with urine-water, and plugged with 

 sterilised cotton-wool. The bottles were placed in a room (temperature 

 about 10° C.) and left at perfect rest ; the number of organisms in the 

 urine-water was ascertained at the outset of £he experiment, again at 

 the end of six hours the number was determined in one oi the bottles, 

 at the end of twenty-four hours in the second bottle, and lastly, at the 

 end of forty-eight hours in the third bottle. The numbers found were 

 as follows : — 



No. of centres found per 



Hours of subsidence. c.c. of water. 



1,073 



6 6,028 



24 7,262 



48 48,100 



These experiments show that far from there being any tendency for 

 the upper layers of water to become deprived of organisms by sub- 

 sidence, the tendency is for the number to increase very rapidly 

 indeed. 



Effect of ClarWs Process on Micro-organisms in Water. 



Owing to the encouraging results obtained by agitating water with 

 finely divided chalk, it appeared probable that still more striking 

 effects would be obtained if the chalk were present in a more finely 

 divided state, such as is the case when water is softened by means of 

 lime (Clark's process). In order to ascertain the effect of Clark's 

 process in this respect, three stoppered Winchester bottles were taken, 

 and to each were added 2 litres of ordinary Thames water, to which 

 some urine- water had been added, so as to impart a convenient num- 

 ber of organisms. To two of these bottles 100 c.c. of clear lime-water 

 (1 c.c. = 0013 gram CaO) were added, calculated to remove 

 11*6 parts of carbonate of lime per 100,000 parts of the water. Each 

 of these bottles was violently shaken, and then allowed to subside for 

 eighteen hours. The third bottle, to which no lime-water was added. 



vol. xxxviii. 2 F 



