Chemical Qualities of Water. 
565 
and well-water in calcareous districts, where cither the chalk forma- 
tion, or the older limestone rocks prevail. Carbonic acid forms chiefly 
two combinations with lime. One, which is insoluhle, contains ono 
equivalent of lime, and one of carbonic acid ; and another, which is 
soluble, contains two equivalents of carbonic acid to one of lime. It 
is generally in virtue of the excess of carbonic acid, and the formation 
of bi-carbonate of lime, that water becomes hard. In speaking of 
hardness we ought to distinguish between permanent hardness and 
transient hardness. That which is caused by bi-carbonate of lime is 
removable to a great extent by boiling, but other mineral matters, 
such as sulphate of lime, or gypsum, impart to water a permanent 
hardness, which cannot bo removed by simple boiling. Without 
laying down a definite wile I may state in a general maimer that all 
water which contains more than 1G grains of lime to the gallon may 
be regarded as truly hard. For an account of the amount of lime 
contained in the water which is supplied by the different water com- 
panies for the use of the metropolis, I may refer you to a very 
excellent report of Professors Graham, Miller, and Hoffman, which 
gives detailed analyses of the quantities of lime and other mineral 
constituents. It there appears that most of the water used in London 
contains on the average not more than 20 to 25 grains of solid matter 
in the imperial gallon, and is therefore very serviceable for all 
ordinary purposes. In supplying water either to a town or to a 
private house we should endeavour as much as possible to hit upon 
the sample which, while it is sufficiently pleasant to the taste, is also 
useful for the kitchen and laundry, for there are hard waters which 
are excellent for drinking purposes, and yet unfit for cooking and 
washing. A large amount of carbonate of lime is by no means 
injurious to the health of man, and we have no evidence that sulphate 
of lime or gypsum, and other mineral matters that usually occur in 
drinking-waters, are deleterious. Hence, a water that is very hard, 
may still be very palatable, and even be preferred for drinking 
purposes to a softer one which is less sparkling and bright, and more 
tasteless. 
The fourth and last quality that we esteem in water is coolness. 
Surface waters are invariably cold in winter and warm in summer — a 
peculiarity which, of course, we do not esteem ; whilst water from 
deep springs has a uniform temperature, being, as compared with the 
temperature of the air, warm in winter and cold in summer. This 
uniformity of temperature further indicates a uniformity of composi- 
tion. The reason of this is, that water of uniform temperature 
invariably has to descend through a dense mass of rock ; and as it 
trickles slowly through the rock, it becomes saturated thoroughly with 
whatever it can dissolve ; whilst water which finds its way into surface 
wells is liable to be altered in its composition by purely local circum- 
stances. Thus we occasionally find the waters of surface wells very 
soft, and containing but very little of any impurity, either organic or 
mineral, in solution ; whilst at other times the very same wells furnish 
water which is very rich, in mineral matters and also contains much 
organic impurity. This is especially the case in summer; and the 
