and Water used for Genei'al Pinyoses. 
13^ 
contact with chalk or limestones (carbonate of lime), is capable 
of dissolving only a very minute quantity of these materials ; 
one gallon of water taking up no more than 2 grains of car- 
bonate of lime. This earthy impregnation is said to give the 
water 2 degrees of hardness. ^lost natural waters, however, 
contain more or less carbonic acid gas, which is a good solvent 
of carbonate of lime, forming with it soluble bicarbonate of 
lime. 
Spring waters in the chalk-formation often contain as much 
as 16, or even 20 grains and upwards, of carbonate of lime in 
the gallon. Such waters are generally bright and sparkling to 
the eye, and agreeably sweet to the taste. When boiled they 
become milky, and leave a sediment which incrusts the insides 
of kettles and boilers. The explanation of the change which 
hard waters undergo on boiling is found in the fact that the 
second equivalent of carbonic acid in the soluble bicarbonate 
of lime is only loosely united with carbonate of lime. At the 
ordinary average temperature of the air, hard water contains 
bicarbonate of lime in a state of perfect solution, but on raisings 
the temperature to the boiling-point of water the carbonic acid, 
which holds the carbonate of lime in solution, is driven off, and 
insoluble carbonate of lime is then precipitated, as a sediment, 
in consequence, with the exception of the two grains which are 
held in solution by the water itself. The carbonate of lime, 
dissolved by carbonic acid and curable by boiling the water, 
expresses its temporarij hardness. 
An artificially prepared hard water, containing 13^ grains of 
carbonate of lime to the gallon, was observed to decrease from 
13"5 to 11 '2 degrees of hardness merelv bv heating it in a kettle 
to the boiling-point. Boiling for 5 minutes reduced the hard- 
ness to 6"3 degrees, 15 minutes to 4-4 degrees, 30 minutes to 
2 "6 degrees, and 1 hour to 2*4 degrees. The softening effect of 
boiling does not therefore appear all at once, but the greatest 
proportional effect is certainly produced by the first five minutes* 
boiling. 
In addition to carbonate of lime, hard waters generally contain 
sulphate of lime and not unfrequently nitrate of lime, and occa- 
sionally chloride of calcium. These salts of lime are dissolved 
in water without the intervention of carbonic acid gas, and 
therefore remain in solution although the water is boiled, and 
impart to it permanent hardness. 
Soft water readily produces a lather with soap ; hard water, on 
the other hand, destrovs much soap before a lather is formed. 
Soap may be regarded as a soluble compound of soda with fatty 
acids. With lime these fatty acids form insoluble compounds. 
