176 D. Waldie — Purification of the Muddy Wafer of (lie Jliujli. [Nov. 



to experiment shewed that it was correct. The difficulty in the settling of 

 the mud arises from the great state of dilution of the water. Some facts 

 had been long observed hy chemists bearing more or less directly on the 

 subject, and special observations had been made, particularly by Bkey and 

 Schloesing, on the separation or precipitation of mud from water ; a consi- 

 deration of all these things suggested that if the deficiency of saline matter in 

 the water of the rains was made up by the addition of such matters to it, 

 so as to bring the water up to the standard of that of December or January, 

 the mud would then settle much more readily and possibly be so much 

 altered as to enable the water to be filtered easily. This was found by 

 experiment actually to be the case. The saline matters in the water act as 

 precipitants of the mud if in sufficient quantity : during the rains they are 

 not in sufficient quantity, if doubled they are. Assuming 7 grains of Car- 

 bonate of Lime (in solution) as equivalent to the salts of Lime and Magnesia 

 in 100,000 grains of the Hugli water at its extreme degree of dilution, the 

 addition of an equal quantity of Carbonate of Lime (in solution) or of Carbo- 

 nate of Magnesia (in solution) or of Sulphate of Lime precipitates the mud 

 well. Double the equivalent of Chloride of Calcium is requisite as it has only 

 half the efficacy. The alkaline salts have comparatively little influence. 

 The salts of lime and magnesia, particularly the carbonates, held in solution 

 by carbonic acid, are the chief active ingredients in producing the effect. 

 They cause the very fine particles of clay to coalesce and aggregate into 

 larger and denser ones which in the course of 21 to 18 hours settle well, and 

 the water can then be filtered easily. The clay has been said to be coagu- 

 lated and the term seems appropriate. 



Corroborative evidence has been found in the peculiarities of some river 

 waters on the European continent, particularly those of Alpine origin, which 

 are liable to occasional unusual dilution and accompanying muddiness, such 

 as the Garonne, from which Marseilles is supplied. A peculiar system of 

 filtration is employed there, appropriate to the purpose. The river waters 

 in England are liable to no such extreme changes, consequently their muddy 

 water has no such peculiarities or only to a comparatively small degree. 



It was found on extending the enquiry that acids, alkalies and alkaline 

 earths, and many other saline substances possessed the same property, and 

 many of these to a much greater degree. Thus salts of Manganese and 

 Copper and protosalts of Iron are effective in considerably smaller quantities 

 than salts of Lime and Magnesia, and salts of the sesquioxides, namely, Alu- 

 mina and peroxide of Iron are the most effective of all. Tables are given in 

 the paper shewing approximately the quantities of these substances necessary 

 or sufficient to produce the same effect. The differences iu power between 

 common salt and Lime salts, and between Lime salts and Ferric salts are 

 very great. 



