196 MICEO-OKaANISMS IN WATER 



Water was also aoitated with several other sub- 

 stances, such as china-clay, brick-dust, plaster of Paris, 

 oxide of manganese, &c. ; all of these, however, yielded 

 less satisfactory results. 



Laboratory experiments with ' Clark's process! ^ — For 

 testing the efficiency of this process on the laboratory 

 scale, three stoppered Winchester quart bottles were 

 taken, and to each were added 2 litres of ordinary 

 London (Thames) water, to which a convenient propor- 

 tion of organisms had been imparted by the addition of 

 a little urine water. To two of these bottles 100 cubic 

 centimetres of clear lime-water were added, this being 

 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 the contents were then allowed to 

 subside for eighteen hours. The two bottles to which 

 the lime-water had been added were tested without 

 disturbing the precipitate, as was also the third bottle, 

 which had been left at rest in the same place as the 

 other two. These tests showed the following numbers of 

 micro-organisms to be present in the water before and 

 after treatment :- — 



Untreated water at the outset contained 85 organisms in 1 c.c. 

 Ditto after 18 hours' rest . , 1,922 „ „ 



Water after treatment by Clark's 



process and 18 hours' subsidence 42 „ „ 



Eeduction in the number of micro-organisms present in the original 

 water = 51 per cent. 



In order to appreciate the value of the treatment by 

 Dr. Clark's process, it is necessary that the treated 

 waters should be compared not only with the original 

 water, but also with the untreated water after eighteen 

 hours' rest ; for the latter obviously indicates what the 



^ Proceedings of Institution of Civil Engineers, 1886. Percy Frank- 

 land. 



