324 The Water Supply of London, [July, 



abnormal condition of the skin tlms induced is for a long time 

 extremely unpleasant. 



Nevertheless, opinion is not quite unanimous as to the advan- 

 tages of soft water over hard. Some persons consider hard water to 

 be necessary for the supply of the calcareous matter of the bones, 

 others believe soft water to be peculiarly liable to attack and dis- 

 solve the lead of the pipes through winch it is conveyed, or of the 

 cisterns in which it is stored. 



An examination of the grounds upon which these opinions are 

 based would completely refute them, but the limits of this article do 

 not permit of such a digression, and I must therefore content myself 

 with a mere allusion to one or two facts in connection with them. 

 First, as to the necessity of hard water for the supply of the calcare- 

 ous matter of bones. If it be assumed that a man drinks daily half a 

 gallon of Thames water, he obtains from it § J grains of lime chiefly 

 in the form of chalk. This amounts to not quite 3 oz. per annum, 

 which does not seem to be a very large contribution to bony matter. 

 Now suppose the use of this water to be discontinued and that no 

 part of it is replaced by bitter beer, which always contains far more 

 lime in a given volume than Thames water ; but we will assume 

 that the individual consumes one-third of a pint of milk per day, 

 he then receives in this quantity of milk more lime than his system 

 can acquire from two quarts of Thames water. Then, as to soft 

 water attacking and dissolving lead ; it is by no means true, as a 

 general proposition, that soft water does attack and dissolve this 

 metal. The very soft water of Loch Ness, as supplied to Inverness, 

 does not attack lead, as evidenced by the unimpaired condition of lead 

 pipes through which that water flowed for six years : neither does 

 the soft water of Ennerclale Lake, supplied to Whitehaven, attack 

 lead. Even those soft waters which do attack the metal, such as 

 those now supplied to Glasgow and Manchester, only do so when 

 the surface of the lead is clean and bright. The action soon ceases, 

 in fact as soon as the metal becomes tarnished the pipes are pro- 

 tected, and no complaints of any symptoms of lead poisoning have for 

 the past ten years been heard from these large cities. Lastly, a 

 sample of very soft water taken from one of the principal streams 

 from which it is proposed to supply London has no action even 

 upon clean and bright lead. Notwithstanding the numerous re- 

 searches made in connection with this subject, the causes of the 

 attack of lead by water have not yet been completely elucidated ; it 

 has, however, been established that the presence of oxygen and the 

 comparative absence cf carbonic acid in the dissolved gases are essential 

 conditions to this action. Messrs. Graham, Miller, and Hofmann, 

 in their report on the Metropolitan Waters in 1851, first showed 

 that carbonic acid when dissolved in water was a complete pro- 

 tection against lead contamination, and from a series of experiments 



