ON PUEE WATEE. 
557 
cannot be ordinarily drnnk_, and are supposed to be medicinal 
in tbeir action_, tbey are called miner cd waters. Such waters 
have been the foundation of the reputation and fortunes of 
such places as Harrowgate_, Cheltenham^ Leamington, in this 
country, and Ems, Kissengen, Wiesbaden, Carlsbad, and 
others on the Continent. Many of the constituents which 
are in excess in these waters are the same as those contained 
naturally in the sea. Some of them, however, contain ingre- 
dients not found in the sea water in its normal condition at all, 
as the salts of iron aiffl. sulphuretted hydrogen. 
Besides the substances enumerated, which are inorganic, 
sea and mineral waters contain naturally a certain quantity of 
organic matters, arising' from the decomposition of the 
animals and plants which live in them. 
The sources of water for the ordinary drinking purposes of 
man, are rain, springs, or rivers. Water obtained from these 
sources holds in solution certain substances, but not in so large 
quantities as the sea or mineral waters. Of the vfater ordinarily 
drunk, rain water is the purest. On account of its dissolving 
soap with facility, it is called soft water. When waters con- 
tain lime, they form an insoluble substance with soap, and 
are on that account called hard. As we use the word, a soft 
water is not necessarily a water containing a small amount of 
saline matters, but one that contains little or no lime. Bain 
water, as it falls from the clouds, contains no saline matters, 
unless we apply this term to the almost infinitesimal quantity 
of carbonic acid and ammonia which it is known to contain. 
When collected in the country in the open air, it is almost 
absolutely pure ; but as it is usually collected for human use, it 
is liable to various impurities. Thus, in London and in large 
towns, it is collected from the tops of houses, and by the time 
it enters the cistern or water-butt it contains a variety of 
impurities. It acquires carbonaceous matter from the smoke 
in the air, and small quantities of carburetted and sulphuretted 
hydrogen, so that its flavour is very disagreeable from that 
cause. From the roofs of houses it also collects another 
quantity of impurities, and especially the dung of birds, as 
of pigeons, jackdaws, and sparrows, which invariably frequent 
the roofs of the houses in our great towns. So that rain- 
water, although freest from saline matters of any water, is 
seldom collected in such a condition as to be fitted for 
dietetical or cooking purposes. 
The other two sources from which our great towns are 
supplied are springs and rivers. London with its vast popu- 
lation is principally supplied from the river Thames, whilst 
Manchester, Liverpool, and Griasgow are supplied with spring 
water. No general comparison can be made between the 
VOL. IV. NO. XVII. 2 p 
