374 



FILTRATION 



Col. 1 shows the quantities of the several substances originally present, represented 

 in grains, in the imperial gallon (70,000 grains) of water. 



2. The amount present after filtration. 



3. The actual quantities separated in grains in the gallon of water. 



4. The percentage ratio which the amounts separated boar to the quantities origin- 

 ally present. 



1 It has been assumed as a principle that sand-filtration can only remove bodies 

 mechanically suspended in water, but I am not aware that this statement has been 

 established by experiment ; in fact, I am not acquainted with any published analytical 

 examination of the effects of sand-filtration. 



' These experiments supply the deficiency, and show, moreover, that these porous 

 media are not only capable of removing suspended matter (80 to 92 per cent.), but 

 even of separating a certain appreciable quantity of the salts from solution in water, 

 viz. from 5 to 15 per cent, of the amount originally present, 9 to 19 per cent, of the 

 common salt, 3 per cent, of the lime, and 5 of the sulphuric acid. 



' Taking the purer water from Kingston, two experiments were made simultaneously 

 with the same water, one filtration being through charcoal alone, and the other through 

 sand alone ; the sand filter having an area of 4 square feet, and consisting of the fol- 

 lowing materials : 



ft. in. 



Fine sand 1 9 



Shells li 



Gravel 1 



Coarse gravel 9 



2 9 



Results of Sand Filtration. 



Results of Charcoal Filtration. 



