1873.] D. Waldie— 0;i the Muddy Water of the Hugli. 225 



action of the other stronger acids. I am not prepared at present either to 

 admit or deny this. To settle the point would require experiments to 

 be made in which the sources or causes of dou])t sliould be removed. 

 Though it might be supposed that these acids dissolve a small quantity 

 of the otherwise insoluble carbonate of lime, this does not account satis- 

 factorily for the circumstance that the salts of the sesquioxides of aluminum 

 and iron and even of the protoxides of the heavy metals are so much 

 more efficient than lime salts themselves. 



I found in another number of the Chemical N'ews, that of 14th May, 

 1869, an abstract of a " Report of the Netherlands Committee." This 

 committee, evidently, (though particulars are not stated), consisted of a body 

 of scientific men examining the waters of certain rivers with a view to their 

 economical use, the Khine and Maas being particularly mentioned. So far 

 as I can judge from some particulars mentioned, these waters do not appear 

 to be exactly similar to the muddy water of the Hugli. The committee 

 especiall}^ recommend Perchloride of Iron for the purification of such turbid 

 waters, along with Carbonate of Soda, and recommend "032 grains Perchlo- 

 ride of Iron for 1 litre which is equal to 1 part for 31,250. I have given 

 it as 1 to 522,000 and without soda. It is obvious that the question of 

 quantity is very important in the application of this artificial method of 

 clarifying muddy water with a view to economy. The great expense, 

 evident in the application of all proportions known before, was one cause that 

 prevented me from giving the subject much attention, as I had adverted to 

 the use of precipitants as far back as 1867, in my paper in this Journal. =^ 



One way and the best of all ways of restoring the proper quantity of 

 Lime salts to such water would be to bring it thoroughly in contact with 

 Carbonate of Lime, provided it contained enough of free Carbonic acid to 

 dissolve a sufficient quantity. But this is very doubtful and not very likely 

 in ordinary waters. Experiment shewed only a small improvement. 



Both Skey and Schloesing state that the chief point seems to be that 

 there should be a certain quantity of the precipitating substance in proportion 

 to the water, and that the quantity of clay present does not make much 

 difference, Schloesing remarking even that the limpidity is more perfect 

 when the mud attains a certain proportion, just as I have myself found that 

 the muddy Hugli water settled and cleared better by adding some dry 

 soil to it, this of course from the soluble matters contained in that soil. 

 The general point, however, I had not time to examine, my attention having 

 been given to the Hugli water as it presented itself in nature. 



Both Skey and Schloesing also describe the effect produced by the term 

 coagulation, and it seems quite appropriate. The very fine particles coalesce 

 as it were into larger and comparatively flocculent ones. 

 * Vol. XXXVI, Part II, p. 138. 



