50 
Arterial Drainage 
1,080,000, the result being the gross horse-power developed, from' 
which must be deducted an allowance for friction depending on 
A 
the construction of the engine (H-P = 
^ ^ 1,080,000 ^ 
Quality of Water. — The quality of the water supplied is a 
matter of great importance. For all household purposes soft 
water is more economical and infinitely preferable to hard water. 
For drinking purposes, purity and freedom from animal con- 
tamination are essential. The quality of hardness in water is 
derived from the presence of mineral substances collected by the 
rain in its course over oi through the earth. Of the hardening 
salts, carbonate of lime is the one most generally met with, and 
on the proportion of this salt in solution the standard of hard- 
ness is based. If 100,000 lbs. of water contain 1 lb. of carbonate 
of lime, or its equivalent of other salts, it is said to possess one 
degree of hardness. Each degree of hardness indicates the de- 
struction and waste of 12 lbs. of the best hard soap by 10,000 
galloris of the water when used for washing.f Rain-water fresh 
from the clouds is practically free from hardness. After it has 
once touched the earth it becomes impregnated with hardening 
salts, the number of degrees of hardness depending on the cha- 
racter of the water-bearing stratum through or over which it 
passes, and the length of time it is in contact with the soil. 
Water collected from the Igneous rocks contains from 0'8 to S'D 
degrees of hardness ; next in order of softness come the waters 
from the Metamorphic, Cambrian, Silurian, and Devonian rocks, 
the ^Millstone Grit, London Clay and Bagshot Beds, which range 
from O'-l to 32"5 degrees ; the New Red Sandstone waters average 
7'7 degrees; the Magnesian Limestones yield about 41°*2 ; the 
Lias 29 degrees : the Oolite and Chalk strata, which afford the 
most abundant and reliable sources of supply, yield waters gene- 
rally hard, but the hardness is principally of a temporary cha- 
racter, which may be greatly reduced by boiling. The degrees 
of hardness of water flowing through the Chalk formation vary 
from 12''4 to 38° and average 23*3 degrees.^ While there can 
be no question that soft water is preferable for washing purposes, 
yet opinions vary considerably as to its desirability for drinking. 
It is alleged that the health and physique of populations in 
hard-water districts is superior to that where soft water is 
provided. Dr. Letheby gave it as his opinion, in his evidence 
before the Committee on Water Supply, that the best water 
* Molesworth's ' Pocket-Book Euginccrins: Formula.' Spon and Co. 
t ' Sixtli Report of the Rivers rollution Commission' (Domestic Water 
Supply), 1874. 
X Ibid. 
