BURTON WATERS—DRINKING AND BREWING. 7 
Rain water which as it first condenses in the clouds may 
be considered as the purest natural form of water, containing 
then only the gases oxygen and nitrogen in solution, takes 
up several substances during its descent through the air, 
especially through the smoky atmosphere in the immediate 
neighbourhood of large towns or manufacturing centres, 
thus carbonic, nitric, sulphuric, and sulphurous acids, 
finely divided carbon, and, in some cases, poisonous 
metallic bodies, such as lead and arsenic in the neigh- 
bourhood of lead works, so that rain-water as we meet 
with it on the surface of the earth is not pure water by 
any means. 
In its passage through the ground to the various under- 
ground reservoirs from which our springs arise, still further 
changes take place, organic matter is taken up from the 
surface and top soil, and as the water slowly percolates 
through that soil, this organic matter is decomposed, and 
ammoniacal salts are produced, which are rapidly altered 
by the agency of two different kinds of bacteria, first into 
nitrites and then into nitrates. At the same time, other 
salts, such as chlorides of the alkalies, sulphates of lime 
and magnesia, are also often taken into solution before the 
water has reached the true strata upon which the soil and 
sub-soil rest. 
I must here explain the geological and mineralogical 
conditions more directly influencing the character of our 
spring waters. For this purpose we may first divide the 
rocks forming the various strata of the earth’s crust, into 
(A) those which allow water to percolate freely through 
them, or Porous Strata, such as gravel beds, coarse sand- 
stones, and other sandy beds; and (B) those beds which do 
not permit of such percolation or Impervious Strata, such as 
clays, slates, and most marls. 
Again, we may divide the minerals forming these rocks 
or giving the general character to any particular strata, 
into (A), those which are practically Insoluble in water, such 
