ADVANTAGES OF SOFT WATER. 117 



between the tropics, and we owe in great measure the mildness of 

 our climate to the latent heat conveyed by this watery vapour, 

 which is again set free when it becomes condensed and falls to the 

 earth as rain or snow. This rain falling on the different soils gets 

 disposed of in various ways : some runs off the surface at once, 

 forming streams, lakes, and rivers ; a part again evaporates and 

 goes back into the air ; and a third portion sinks into the ground 

 until it comes to some impervious stratum, when it accumulates in 

 underground reservoirs or forms streams that break out at a lower 

 level on the surface as springs. 



Although the water when in the form of clouds is nearly pure, 

 when it falls as rain it dissolves and takes up various matters 

 which it meets with in the air, and various mineral and organic 

 matters from the soils it falls upon. Near manufacturing towns it 

 often contains sulphuric acid from the combustion of the sulphur in 

 the coal consumed, and in all localities it dissolves a considerable 

 quantity of the carbonic acid gas existing in the air. This carbonic 

 acid, as I have mentioned before, is the result of the burning 

 or combustion of carbonaceous materials, and is produced in large 

 quantities from any ordinary wood or coal fire, and is also 

 given off by the lungs of animals as the result of the burning or 

 oxidation which goes on in them. I want especially to di'aw 

 attention to this fact, because this gas in rain-water falling upon 

 chalk is an important agent in the production of hard water. 

 Hardness of water merely means that the water contains certain 

 mineral substances which decompose soap, and render it a difficult 

 matter to get any undecomposed soap dissolved in the water. The 

 chief hardening ingredients are salts of lime and magnesia, but 

 in the case of the Watford water we are principally dealing with 

 carbonate of lime or chalk. To obtain a numerical expression for 

 this quality of hardness, a sample containing 1 lb. of carbonate of 

 lime in lU,OUO gallons of water is said to possess one degree of 

 hardness. The hardness of water is divided into permanent and 

 temporary ; the former is uninfluenced by boiling, the latter is 

 removed by boiling for half-an-hour. As we cannot get rid of the 

 former by the different softening methods, we will only consider 

 the latter, which is principally due to the carbonates of lime and 

 magnesia. The temporaiy hardness of the Watford water appears to 

 vary somewhat between 1 5 degrees and 20 degrees. 



The next question to consider is where the water obtains this 

 considerable quantity of chalk. As there are extensive beds of 

 chalk beneath the surface both around Watford and at a great 

 many other localities in England, and as chalk is a porous medium, 

 it stands to reason that the water from wells, springs, and streams 

 in such situations should contain a great deal of dissolved chalk. 

 But carbonate of lime or chalk is insoluble in pure water, so we 

 must have some additional information as to the method of its 

 solution. I have drawn attention to the fact that rain-water when 

 it arrives on the ground has a good deal of carbonic acid gas in it, 

 and it is the presence of this gas that enables the water soaking 



