THE EFFECT OF WATER ON ROCK POWDERS. 



WET GRINDING. 



It has been known for a long time that when certain finely pow- 

 dered minerals are treated with water, reactions take place which 

 result in partial decomposition and solution. Probably the earliest 

 experimenters to call attention to this action were W. B. and R. E. 

 Rogers, who first published a note on the subject in 1848. a More 

 recently Daubree 6 has given much attention to the subject. In one 

 experiment he made fragments of granite and quartz slide over each 

 other in a hollow cylinder partially filled with water and rotating on 

 its axis. The fragments rounded in the cylinder could not be distin- 

 guished either in form or general aspect from the natural detritus of 

 a river bed. A second product was an extremely fine impalpable mud, 

 which remained suspended in the water several days. During the 

 production of this fine sediment the water, even though cold, was 

 found in a day or two to have acted chemicall3 r upon the granite frag- 

 ments and yielded a considerable quantit\ T of soluble salts, consisting 

 chiefly of silicate of potash. A third product was an extremely fine 

 angular sand, consisting almost wholly of quartz, with scarcely any 

 feldspar, nearly the whole of the latter mineral having passed into the 

 state of clay. Still more recently Clarke c noted that the immediate 

 action of water on man} 7 minerals could be shown b}^ the alkaline reac- 

 tion obtained with phenolphthalein indicator. 



For several years investigations have been carried on in the Division 

 of Tests, Bureau of Chemistiy, on the effect of water on the binding 

 power of rock dusts, more particularly in its relation to certain impor- 

 tant road-building problems. The results of these investigations, 

 which have been given out from time to time in various publications/* 

 pointed to the fact that water produced a colloid or glue-like surface 

 condition of the particles, leading to plasticity in the wet mass and 

 binding power on induration. It has already been shown that most 



Amer, J. Sci., 2d series, 5: 401. 

 &Geike, Geology, 3d ed., p. 385. 

 U. S. Geological Survey Bui. No. 167, p. 156. 



d U. S. Dept. Agr., Bureau of Chemistry, Buls. Nos. 79, 85, and Circular No. 17; 

 J. Amer. Chein. Soc., 25 : 5; also Trans. Ainer. Ceramic Soc., 6 :3. 



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