﻿Wellington Philosophical Society. 381 



for an indefinite time. The precipitating effects of the salts and acids, lie cites, 

 is due to the exercise of a higher affinity for water on their part ; these 

 affinities being superior to those of clay for the same liquid, the clay is par- 

 tially dehydrated, and thus brought into a condition resembling that of solid 

 clay, both physically and chemically, in which state it precipitates mechanically. 



The substance having the greatest pi-ecipitating effect upon clay in water is 

 sulphuric acid, one part of which is effective upon 25000 parts of the mixture. 



Generally, spring water is sufficiently charged with salts to effect the 

 clarifying of clay water in twenty-four hours or so. 



A solution of magnesia, a substance which one would take to be quite 

 inert, soon clarifi.es clay water, though it requires 7000 parts of water to 

 dissolve it. 



The author shows how water may thus be purified for use. He then 

 demonstrates that most, if not all, natural clays, if only mixed with a small 

 quantity of water, do not remain persistently suspended. This he attributes 

 to the presence, sometimes of salts, sometimes of carbonic acid. He then shows 

 that clay-slate, brick, etc., or any other kind of indurated clay, is resolvable 

 into the most hyd rated clay direct by simply pulverizing it in pure water. 



The author lastly discusses Professor Jevons' theory for the explanation of 

 this suspension and precipitation of clay in water. 



This theory was broached in the "London Chemical News" under the 

 heading " On the so called molecular movements of microscopic particles," and 

 is an attempt to attribute the phenomena under consideration to the agency of 

 electricity. 



Professor Jevons conceives these particles, as they persistently suspend 

 themselves in water, to be charged with electricity, by which they move about, 

 owing to a series of electrical attractions and repulsions, and so remain 

 suspended by reason of these motions ; the insulation of these charged particles 

 being, as he thinks, sufficiently provided for by the use of pure water. 



The effects of certain salts upon the mixture (in precipitating the particles) 

 he ascribes to the fact that such additions render the liquid an electric con- 

 ductor, so that the electricity passes off instantly, and thus restores to the 

 particles the same electrical state as the surrounding liquid, when they lose all 

 power of electrical movements. 



The author of the present paper shows that theoretically and experiment- 

 ally this theory of Professor Jevons is quite incompetent to explain these 

 phenomena in the case of clay at least, if not also for the other substances he 

 cites ; but that, as stated before, they are susceptible of explanation on the 

 assumption of a very large quantitative affinity of this substance for water — but 

 an affinity of a very weak intensity ; so weak that most of the common salts 

 are able to overcome it, and so remove the clay as a chemical precipitate. 



B B B 



