ABSORPTION EXPERIMENTS. 21 



a slight extent, decomposed when in the state of a fine dust or powder 

 it is simply wet with pure water. It is not in agreement with the 

 views of modern chemistry to suppose that the alkaline silicate is 

 leached out, leaving the insoluble aluminum silicate like a molecular 

 skeleton behind. It is probable that the orthoclase molecule has a 

 definite solution pressure, and that immediately upon solution hydro- 

 lysis takes place with a deposition of the insoluble aluminum silicate 

 in situ as colloidal film upon the surface of the particles. Wet grind- 

 ing carries the action further simply because it abrades the films and 

 permits the action of the water on fresh surfaces. 



This action is not confined to orthoclase dust, but also occurs in 

 cases of other rocks which are decomposed by water. There is good 

 reason for believing that whenever any substance is immediately pro- 

 duced within a liquid in which it is insoluble it will appear and at least 

 temporarily exist there in the so-called colloidal state. Certainly, 

 whenever aluminum or other silicates are artificially prepared in the 

 wet way the} 7 appear as colloidal precipitates. Granting, therefore, 

 that the action of water on rock powders results in the formation of 

 colloidal films on the particles, all of the observed effects that have 

 been spoken of can be accounted for. It is perfectly apparent that if 

 a reaction takes place in which insoluble aluminum silicate and soluble 

 potassium silicate are coincidently formed, potash will be to a large 

 degree held by absorption in the aluminum silicate, and there will be 

 found an accumulation of silicic acid in solution after clear subsidence 

 or filtration. Now, this is precisely what is found to be the case. The 

 absorption of the basic ions by the pectoid surfaces of the particles 

 would cause a concentration of the acid ions passing freely into solu- 

 tions and thus explain the fading of the color obtained with phenol- 

 phthalein, the appearance of stratification observed by Clarke, the 

 action of filters and sedimentation observed by the writer, and the 

 discrepancies recorded by Steiger. 



Some crystalline rock powders are very much more vigorously acted 

 on by water than others. It is possible that this is due to the fact 

 that rocks which contain a part of their constituents in the form of 

 solid solutions are more easily decomposed by water, as is the case with 

 cement and glass powder, than are the definite crystalline compounds, 

 such as pure orthoclase. 



The action of solutions of ammonic chlorid in increasing the amount 

 of alkali which passes into solution may possibly be considered as 

 nothing more than a simple case of metathesis, the ammonium chang- 

 ing place with other bases. Nevertheless, in the light of what has 

 gone before, we are bound to consider the analogy between this action 

 and that studied by Linderand Picton, a in which an arsenious sulphid 



Loc. cit. 



