112 



is the meaning of the distinction between hardness before and after 

 boiling in our Tables, the former being the total hardness and the 

 latter the permanent hardness. 



I will now shew you how the hardness of water is estimated. 

 The operation consists in the careful addition, from a measuring 

 tube known as a burette, to a known measure of water, of a solution 

 of soap in alcohol. The water is placed in a stoppered bottle and 

 shaken after each addition of the soap solution. At first you will 

 see no lather is formed, but only a curd. We must continue the 

 addition of the soap tiU a permanent lather is formed on shaking, 

 which lasts and does not disappear for two or three minutes. We 

 then read off from our burette the quantity of soap solution we 

 have taken. This solution has been made up to a certain strength 

 so that each measure of it corresponds to a known (j[uantity of 

 chalk. We can tell at once therefore how much chalk there exists 

 in solution in the quantity of water taken, and, by simple calcula- 

 tion, how much in a gallon. 



Let us now consider what happens when we try to make a 

 lather with soap and hard water, and we only succeed in obtaining 

 a curdy substance. Soap is a compound of sodium with stearic, 

 palmitic, and oleic acids, and is soluble in water, but when we 

 bring this sodium compound (soap) into hard water, the lime existing 

 in the chalk replaces the sodium, and forms a " lime soap," which 

 is insoluble in water ; hence we cannot obtain a lather till we 

 have got rid of all our lime at the expense of our soap. Thus hard 

 water is really an expensive luxury, for we have to soften it with 

 soap before the soap can be used for its proper pui-pose. It is no 

 wonder, therefore, that many schemes have been proposed for 

 softening temporary hard water. We have seen that boiling the 

 water brings about this result, but coals are dear ! There is a much 

 simpler process which depends upon the well-known fact that lime 

 water is precipitated by carbonic acid with the production of chalk, 

 so that if we were to add to temporary hard water the right 

 quantity of lime water for precipitation, we should get rid of our 

 hardness, and save our soap. This process is carried out practically 

 at the Canterbury water works, and is the means of saving, as we 

 shall see, money to the inhabitants. It may be remarked that one 

 glassful of lime water (made by putting a few lumps of fresh 

 quick-lime in a bucket of water and allowing it to stand for some 

 time), is sufficient to soften eight glassfuls of Dover water. 



If we compare the cost of softening water by these various! 

 processes we shall obtain some interesting results. 



Suppose we took as much water as would require 1 cwt. of 

 lime to soften it, and softened it by boiling, and added in the 



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