102 J. HOPKINSON — EELATIVE ADVANTAGES 



hardness of 19°-2, 15°-6 being temporary and 3° -6 being permanent. 

 (See Table I, p. 113.) The hardness of the water supplied to 

 London throughout the year 1873, by the seven Companies drawing 

 a portion or the whole of their supply from rivers, averaged nearly 

 15°. In the year 1892 it averaged 15°-3, ranging from 13° in the 

 autumn to 18° in the winter. (See Table II, p. 114.) The 

 slightly-increased hardness of the London water in recent years 

 is due to the supply derived from deep wells in the Chalk having 

 increased to a greater proportionate extent than that derived from 

 rivers. There is no reason to believe that the degree of hardness 

 of the Watford water, or the proportion of temporary and permanent 

 hardness, has materially altered since the analyses were made for 

 the Kivers Pollution Commission, and we may accept it as a fact 

 that the Watford water is about 5° harder than the London water. 

 This difference is due to the greater part of the London water being- 

 derived from rivers, while the whole of the Watford water comes 

 from the Chalk. In the classification of hardness the water 

 supplied to Watford would be considered to be between "hard" 

 and " very hard," and that supplied to London between "mode- 

 rately hard " and " hard," and it is important to bear this 

 distinction in mind, for, whatever objection may be urged against 

 the London water on account of its hardness, applies with greater 

 force to the Watford water. 



Hard water, as already stated, may be partially softened by 

 boiling, and is so softened in steam-boilers and to a less extent 

 in our kitchen boilers, to their great detriment and that of any 

 iron pipes through which the water flows, for a deposit called 

 "scale" or "fur" is formed on the iron, uniting with it and 

 caking over it. This, being a bad conductor of heat, renders an 

 increased consumption of fuel necessary to raise the temperature 

 of the water in the boiler; the "scale" has occasionally to be 

 removed at considerable expense ; and as it cannot be chipped off 

 without bringing with it some of the iron, boilers wear out much 

 faster when supplied with hard water than they do with a soft- 

 water supply. The "scale" also gradually chokes up the iron 

 pipes through which the water flows, sometimes with disastrous 

 results. The water must boil for at least half-an-hour to be 

 materially softened. The so-called bicarbonate of lime (calcium- 

 bicarbonate) is then decomposed, half of its carbonic acid (carbon- 

 dioxide) being driven off as gas, leaving it a monocarbonate 

 (calcium-carbonate), which falls to the bottom of the water as a 

 fine powder, and cakes on the iron. There can be no question, 

 therefore, as to the great economical advantage of soft water over 

 hard water for any purpose for which it has to be boiled. 



The difference between hard water and soft water is most 

 pertinently perceived by us in washing. Soap, in hard water, 

 does not at first cleanse ; some of it must be wasted in decomposing 

 the bicarbonate of lime in the water before it can act as a deter- 

 gent ; in fact, the water must first be softened to a considerable 

 extent at the expense of the soap. In soft water there is no such 



