84 



On some praperties of Porous Media* 



Tablb IX. 



■Showing the period of maxiraum efficacy of the 

 several filters. 



Lastly, these experiments upon the comparatively pure water 

 of Kingston show that charcoal, as well as sand, is capable of 

 separating mineral salts from solution in water, as is evident by 

 an inspection of the foregoing Tables. 



The following is a brief summary of the most important results 

 of this investigation : — It has been shown, — 



1st. That sand, charcoal, and probably other porous media, 

 possess the very peculiar property of removing, not merely sus- 

 pended impurities, but even dissolved salts from solution in water. 



2nd. That charcoal enjoys pre-eminently the power of ab- 

 stracting organic matter from solution : but that even sand like- 

 wise is capable of effecting the same result, though to a far less 

 extent. 



3rd. That these powers, possessed by both these media, in- 

 crease in intensity to a certain extent with the degree of in^- 

 purity of the solution. ., 



4th. That these properties of porous media have important 

 bearings upon hygienic science, agricultural principles, and geo- 

 logical phsenomena. 



The reader will not fail to have noticed, by the various ana- 

 lyses given above, great variations in the composition of the river- 

 water, between the two points at which experiments were made, 

 viz. at Chelsea and Kingston, as well as at the different seasons 

 of the year. To a number of analyses made during the year 

 since May 1855, 1 hope to draw attention in a subsequent paper 

 as elucidating these facts. 



