16 EFFECT OF WATER ON EOCK POWDERS. 



Netzgewebe oder geschlossenem Wabengewebe, oder Globuliten." a 

 Furthermore, there is evidence which points to the cause of the phe- 

 nomenon as due to the electrostatic conditions maintained between 

 the ions of the electrolytes and the surface charges on the particles. 

 Coagulated precipitates of alumina and iron hydroxid will migrate to 

 the cathode if a suitable electric current is passed through a suspen- 

 sion of these substances in water/ Silicic acid and almost all other 

 coagulated or pectoid substances on the other hand will migrate to 

 the anode. We may thus classify all fine materials in water suspension 

 into positive or negative, according to their behavior in this respect. 

 Furthermore, if positive colloids are coagulated in the presence of 

 neutral salts the negative or acid ions will be absorbed by the precipi- 

 tate while negative coagulations will absorb the positive or basic ions. 



ABSORPTION POWER OF CLAYS AND ROCK POWDERS. 



Certain interesting quantitative relations have been observed concern- 

 ing the precipitation of coagulated colloids by electrolytes. Freund- 

 lich c has shown that the amount of the electrolyte used, which is 

 necessary to precipitate a positive colloid, is in a direct ratio to the 

 valence of the negative ions and vice versa. Although this interest- 

 ing fact may seem to be very remotely related to the subject under 

 discussion, it can be shown that it has an important bearing upon it. 

 More than fifty years ago an English chemist, T. Way/ studied the 

 absorbing power of clays and soils. This chemist noted with surprise 

 that clays exhibited the power of absorbing the bases from certain 

 salts dissolved in water. Also, this action was shown to be selective, 

 certain bases being, so to speak, preferred and held in the clay sub- 

 stance so that they could not be washed out again. Since the time of 

 Way the same phenomenon has been noted from time to time by other 

 investigators, and doubtless a careful examination of much scattered 

 scientific literature would be found to contain numerous references to 

 the subject. 



It is probable that the reason that no systemic quantitative study of 

 these interesting absorptions has ever been made is. that at first .sight 

 quantitative relations do not appear to exist. The work of Way is 

 certainly more interesting and instructive than anything that has since 

 appeared on the subject, and it is difficult to resist the temptation to 

 quote liberally from his article. Two excerpts will perhaps suffice to 



The absortion phenomena are also carried on by other sorts of amorphous sub- 

 stances which are known to possess a very fine porous structure such as rhurmal, 

 boneblack, etc., but is not shared in by any sort of crystalline material. ( Van Bern- 

 melen, loc. cit., p. 322.) 



&J. Amer. Ghem. Soc., 1901, 23 : 849 et seq. 



Zts. physikal. Chem., 1903, 44 : 135, 151. 



rfJ. Roy. Agr. Soc., 1850, 11 : 313. 



