ABSORPTION EXPERIMENTS. 



19 



These investigations are still in progress. The method adopted is as 

 follows: 



Definite weights (25 grams) of the rock powders are shaken up with 

 100 cc portions of pure water in tall cylinder glasses. Weighed por- 

 tions of ammonic chlorid are then added and the cylinders thoroughly 

 shaken, making solutions of varying but accurately known strength. 

 After clear subsidence, or, if necessary, filtration, aliquot portions are 

 evaporated to dryness in a weighed platinum dish, ignited to drive off 

 all ammonium salts, and the residue weighed. After solution in boil- 

 ing water the alkali present in the residue is titrated with one-hun- 

 dredth normal nitric acid. The results obtained on a diabase rock 

 powder are given in Table III. 



TABLE III. Diabase rock powder treated with dilute solutions of ammonium chlorid 



It is apparent from these results that the settling or sedimenting 

 action of the electrolytes takes place completely only after a certain 

 amount of the salt has been added, although the amount necessary to 

 produce complete sedimentation is very small. The weights of the 

 residues obtained rise with the amount of the electrolyte present in the 

 solution, as does the amount of alkali, as is shown by the number of 

 cubic centimeters of the standard nitric acid necessary to neutralize it. 



The coagulating power of dilute solutions of electrolytes on clay 

 and kaolin suspensions has been studied by several investigators/ but 

 generally the changes in concentration of the ions in the solutions 

 after the coagulation has taken place has been overlooked. 



Hardy, 6 following the work of Schulze and of Linder and Picton, 

 concluded that the coagulative power of a salt is determined by the 

 valence of one of its ions. This prepotent ion is either the negative 

 or the positive ion according to whether the colloidal particles move 

 in a positive or negative direction under the influence of the electric 

 current. The coagulating ion is always of the opposite electric sign 

 to the particle. This fact, that the coagulation of suspensions is a 

 function of the valence of the active ion, seems to be established 

 beyond all doubt. In undertaking the absorption experiments reported 



Franz Schulze, Pogg. Ann. 1866, 129 : 366; also, Bodlander, Gott. Nach., 1893, 267. 

 &Proc. Roy. Soc., 1900, 60: 111. 



