298 THE CHEMISTRY OF CREATION. 



Thus there is in nature a grand process of 

 filtration incessantly continued, the fulfilment 

 of which is intimately connected with the health 

 and well-being of the inhabitants of both city 

 and field. By this means a most powerful 

 oxidation of all injurious matters is constantly 

 taking place, and the perfect purification of 

 the most impure substances is effected. The 

 ditch-water of our fields differs widely in purity 

 from the water of a subsoil drain. The first 

 will be highly charged with animalcules and 

 organic matter; the second contains but very 

 little. The oxygen thus united to these mat- 

 ters alters their constitution in the most com- 

 plete manner. They are not left behind in the 

 soil, for it has been found that the sand used 

 in large water-works for filtering, after being 

 used for weeks, and thus becoming the instru- 

 ment of effecting the oxidation of an immense 

 body of organic matter, is not impure in a high 

 degree, only containing about one and a half 

 per cent, of organic and volatile matter. Hence 

 both the soil itself remains comparatively free 

 from contamination, and the matters passing 

 through it are, nevertheless, perfectly purified. 

 What a beautiful portion of the chemistry of 

 rain is this ! What an illustration of the per- 

 fection of the arrangements of God, to behold 

 the muddy and polluted waters sink into the 



