The River Port Hutton to Smithford 



If a corresponding amount of magnesium chloride were 

 added in place of the salt, the settling would be found to 

 be still more rapid ; in fact it would be complete in about 

 half the time, while an equivalent amount of aluminium 

 chloride would reduce the period to something like one- 

 third of that obtained by the use of the sodium chloride. 



The chemical composition of sodium chloride is 

 NaCl, where Na represents an atom of sodium and Cl an 

 atom of chlorine. Magnesium chloride is represented by 

 the formula MgCl 2 , while that for aluminium chloride 

 is A1C1 3 . From this we see that an atom of sodium is 

 only capable of combining with one atom of chlorine, 

 whereas an atom of magnesium can take up two, and an 

 atom of aluminium three. It would appear, therefore, 

 that there is some connection between the " Valency," 

 as this property of uniting with atoms of another element 

 is called, and the effect produced upon the particles of 

 mud in suspension in the water. Aluminium which is 

 tri-valent produces three times, and magnesium which is 

 di-valent, twice, the effect of the mono-valent sodium. 



It is known that in dilute solution these substances 

 all split up into bodies called ions, which are believed to 

 carry charges of electricity proportional to their valency. 

 Some electric effect would appear to be produced on the 

 mud particles, which causes several of them to draw 

 together and form a single particle, which, owing to its 

 greater size, falls to the bottom. This is more or less 

 supposition, but the fact that the precipitating effect of 

 the three substances is proportional to the valency of the 

 metals which they contain lends strong support to the 

 belief. 



Whatever may be the explanation ultimately adopted, 



93 



