RIVER WATER. 
purity only. Although by far the greater number of 
springs are cold, some are hot, or at least are of a tem- 
perature which, at all times, exceeds that of summer 
lieat : and this warmth is so little influenced by the state 
of the atmosphere, that it is nearly the same both in 
summer and winter. 
The water of almost every spring is of such nature 
that it will not dissolve, but curdles, soap; and cannot 
be used for dressing several kinds of food. Water of 
this description is denominated hard^ a property owing 
to the great proportion of earthy salts which it holds in 
solution, and which, at the same time, are not in such 
abundance as to impair its taste. The most common 
of these salts is selenite, orsulphat of lime (192), and 
chalk, or carbonat of lime (140); when it contains only 
the latter, the w r ater is easily rendered soft by boiling, 
which expels the excess of carbonic acid (26), and thus 
.causes the chalk to be precipitated. Hence originates 
the earthy crust or fur in such tea kettles as have had 
hard water several times boiled in them. 
The water of deep wells is for the most part much 
harder than that of springs which overflow their chan- 
nels. 
277. RIVER WATER is a mixture of spring and rain 
water, which, from much agitation, and by long exposure to the 
air, in the course oj its channel, becomes, in general, tolerably 
soft and free from earthy salts. 
For washing, and other purposes of domestic econo- 
my, river water, from its softness and purity, is not only 
preferable to spring water, but also serves for many uses 
to which the latter cannot be at all applied. As a be- 
Terage, however, it is in general vapid and unpleasant. 
The waters of some rivers, particularly where the 
beds, over which they flow, are sandy or stony, are 
remarkably pure. This is the case with several of those 
in Switzerland, Wales, Scotland, and the northern 
counties of England. The river Seine has great repute 
in France on this account : it has been found, on accu- 
rate examination, even more pure than Bristol water, 
