220 D. Waldie— On the Muddy Water of the IlugU. [No. 4, 



low an estimate, 8 grains or even grains to 100,000 being possibly more 

 correct. 



A question soon arose as to what was the general nature of the action, 

 for on that I must regulate the plan on which I was to compare different 

 substances. I have quoted Professor Jevons's electrical theory about the 

 coagulation of clay, which is too speculative for practical application, — also 

 Mr. Skey's, that these precipitating substances must act solely from their 

 affinity for water, because the powerful affinities of the component parts of 

 most of these substances precluded the idea of their decomposition. The 

 general tendency of the experiments I made at first, however, led me to 

 reject this explanation, and to conclude that the action was most probably 

 a chemical one, though it might be difficult, or at present impossible, to 

 explain exactly how it operated. In consequence of this I decided to com- 

 pare, not absolute weights of the different substances, but their chemical 

 equivalents. Reasons for this conclusion will be given presently. 



I generally operated on half a litre of water. This was mixed with the 

 substance to be tried and allowed to stand from 24 to 48 hours. A row of 

 such bottles with different substances was placed on the table with one bot- 

 tle containing unmixed water, and comparison was made of their respective 

 appearances at the end of a certain time, sometimes of two or three times, 

 and the result noted. Different proportions of the same substance were 

 compared in the same way. The conclusions were drawn only from the 

 experiments made on the same water at the same time, not between differ- 

 ent samples of water or between observations made at different times. 



The substances compared were chiefly, but not exclusively, those found 

 in natural waters. Thej^ may be divided into the following classes : — 



Alkalies and alkaline earths. 



Acids, or Hydrogen salts. 



Neutral salts of the alkalies. 



Salts of Lime and Magnesia, — or of alkaline earths generally. 



Salts of protoxides of heavy metals, namely of Iron, Manganese and 



[Copper. 



Salts of the sesquioxides, — namely of Aluminum and of Iron. 



The range might have been considerably extended, and the series 

 have been more complete, but I could not spare the time necessary for a 

 more numerous series ; besides, the river water began to improve about the 

 end of August and continued to do so, as the rains ceased early. The experi- 

 ments, however, were sufficiently numerous to enable me to draw conclusions 

 of interest. 



I shall arrange the substances tried in a tabular form, attaching to them 

 numbers indicating the number of chemical equivalents necessary to produce 

 the same effect as Carbonate of Lime in solution in carbonic acid water. The 



