1873.] D. Waldie— Purification of the Muddy Water of (he Mitgli. 177 



Thus for instance taking Carbonate of Lime dissolved by excess of Car- 

 bonic acid as tbe standard, Sulphate of Lime is about equally effective, com- 

 mon salt and alkaline salts generally have only about one-twentieth part 

 of the power, Protosulphate of Iron has about six times the power and Per- 

 sulphate or Perchloride of Iron about forty times the power, so that a very 

 small quantity of persalts of Iron is sufficient. It is to be understood that 

 with the minimum quantities employed a period of from 21 to 48 hours was 

 always given to produce the effect. The quantities necessary are only given 

 as approximations, and there is more doubt connected with those for the 

 salts of the heavy metals and sesquioxides than with those of the earths and 

 alkalies, because, on account of the early cessation of the rains, the river 

 water began to lose its peculiar difficulty in clearing while these salts were 

 being experimented on. The comparison is therefore not so much to be 

 depended on, but the differences in relative power are much greater than had 

 been previously noticed by other observers ; this, at least, in their applica- 

 tion to this particular water. 



The author had quite recently met with Schloesing's original paper 

 which previously he had seen only very briefly and imperfectly abstracted, 

 and found that Schloesing's results were very similar to his own, and that 

 he also suggested similar means for treating highly diluted muddy water 

 difficult to settle, namely, that of restoring it to its natural condition by the 

 addition of Lime salts or other of its normal constituents. Eut he did not 

 push the enquiry further. The extension to other salts and the discovery 

 of the very small proportion of salts of Alumina and Peroxide of Iron, parti- 

 cularly of the latter, that are sufficient when an interval of 24 to 48 hours 

 is given for settling, to purify the water, so that it can be filtered easily, 

 greatly favours the probability of the application of the principle in practice. 



• Details are given in the paper. 



Mr. Blanford said he had listened with much interest to Mr. Waldie's 

 account of his investigations into the action of salts in solution, in facilitat- 

 ing the precipitation of matter mechanically suspended in the water. Mr. 

 Pedler had found that, by adding to the water a quantity of lime equal to 

 that in solution, and precipitating the whole as insoluble calcium carbonate, 

 (a well known method of softening hard water) the suspended matter, how- 

 ever fine, was carried down with the precipitate but the process described 

 by Mr. Waldie appeared to rest on some different principle, which yet re- 

 mained to be elucidated. With respect to the regulating cups, which he 

 understood had not been tried hj Mr. Waldie, he thought it would have 

 been more satisfactory if he had experimented upon them before utterly 

 condemning them. Looking at the question from an a priori point of view, 

 it certainly seemed that an upward filtration is likely to be more effectual 

 in removing fine matter in suspension than the downward method ; and he 

 knew that Mr. Clark had much confidence in these cups. 



