OF THE SEVEN WELLS. 



117 



tion. It was sufficiently evident that all the precautions, 

 before adverted to, and generally deemed necessary in the 

 manufacture of Filters, had been carefully attended to. 

 With all these advantages, however, the results obtained by 

 its use, were above those obtained by the use of Swedish 

 filter paper alone, only in the proportions shewn by the 

 figures below : — 



Swedish filter paper. 1 63. 



Spencer's filter, 1 60. 



A further experiment was made to ascertain if double fil- 

 tration through Spencer s Filter and Swedish Filter paper 

 would make any difference in the results. It was found to 

 do so, reducing the quantity of organic matter left present 

 in the filtrate to 1*57, and the amount separated would thus 

 equal 99, which, represented as a percentage, = 39*00, nearly. 

 From this experiment viewed in connection with what has 

 been previously advanced, we are strongly inclined to look 

 upon filtration generally, excepting that through various 

 kinds of charcoal/* as essentially a mechanical act, and we 

 believe that, the finer the pores of the filter, the more insolu- 

 ble the filtering materials, the greater its specific gravity, 

 and the less, its liability to be disturbed, — the more perfect 

 will be its action. We doubt the utility of any material like 

 sponge, either on the small or on the large scale, as, however 

 perfect it may render an Apparatus for a while, it is well 

 known that very frequent renewal and careful washing, 

 as well as exposure to the air (ozonisation) to get rid 

 of foetid odours, is necessary to keep these machines in 

 good order ; but, notwithstanding all the objections that 



* Even with reference to charcoal, and its -well known power of condensing 

 gases in its pores, it is scarcely necessary to observe that its series of special 

 actions (which generally commence with the condensation of the atmospheric 

 air) are only to be kept up by a renewal of the primary conditions, and that 

 if these be not renewed, its special actions merge into those of a mechanical 

 agent- 



