110 J. HOPKINSON — RELATIVE ADVANTAGES 



maintained more than a quarter of a century ago by Lord Playfair 

 and other authorities, that water of the same degree of hardness 

 as that of Watford (about 20°) is too hard for drinking pur|3oses, 

 has much more recently been expressed by the following foreign 

 authorities : — Fischer, who places the limit of hardness of a water 

 suitable for drinking at 12 degrees; Reichardt, who places it at 

 121^ degrees ; and Wibel, and Kubel and Tiemann, who place it 

 at fi'om 12^ to 14 degrees. I have altered their expression, which 

 is in parts per 100,000, to grains per gallon. (See Prof. W. E. 

 Is'ichols' ' Water Supply,' New York, 1883.) 



Although it may not admit of proof, in the present state of our 

 knowledge, that water of 20 degrees of hardness due to the presence 

 of bicarbonate of lime, as supplied to Watford, is unsuitable for 

 dietetic purposes, that such water is so is the opinion of the highest 

 medical and chemical authorities in this country and abroad, and it 

 is an undoubted fact, universally admitted, that it is much too hard 

 for all other domestic purposes, both on economical and sanitary 

 grounds. The real question at issue, therefore, seems to be whether 

 it is worth while to go to the expense of softening the Watford 

 water. Before this question can be answered it is necessary to 

 consider what the expense of softening it would probably be. The 

 lime-process is the only one which is practically available for 

 this purpose, whether the original Clark process, the Porter-Clark, 

 or any other modification, need not here be considered. 



The expense of this process, and tbe suitability for any particular 

 place of one or other modification of it, depend upon various cir- 

 cumstances — the cost of lime, labour, machinery, site, etc., and, 

 perhaps chiefly, upon the hardness of the water to be softened and 

 the degree to which this is required to be done. At the Otter- 

 bourne Waterworks at Southampton the expense of the process 

 employed is under a farthing — really about one -fifth of a penny — 

 per thousand gallons, with a farthing per thousand gallons for 

 interest and depreciation of plant. The water is there reduced 

 from 18 to 6 degrees of hardness. At Henley-on-Thames, with 

 water of 21 1- degrees of hardness, the cost of softening is one-third 

 of a penny per thousand gallons; and at Wellingborough, with 

 water of 37 degrees of hardness, the cost of softening is four-fifths 

 of a penny per thousand gallons, but this hardness is exceptional. 

 The Porter-Clark process is the one employed at these places, the 

 water after its admixture with lime-water being mechanically 

 filtered through cloth, instead of being run into settling-tanks, as 

 in the original Clark process employed at the Colne Valley Water- 

 works, where the cost is about the same as at the Southampton 

 Waterworks. It has been calculated that if settling-tanks had 

 been constructed at Southampton, the first cost of the plant would 

 have been £3,000 more than it was with mechanical filters, ex- 

 clusive of the cost of the extra land required for tanks. Against 

 this, however, must be placed the increased cost of working with the 

 filters. The cost of these processes is therefore much about the same, 

 but at the Watford Waterworks the Porter-Clark process would 



