PHENOLPHTHALEIN KEACTION. 9 



water. It is this reaction carried on by the action of water on this 

 fine powder which interests us in the present inquiry. The rapidity 

 with which water acts on the powder points to the fact that although 

 the system, silica -falumina-h lime, found in the cement clinker is in 

 equilibrium, it becomes, on the addition of water, an unstable system, 

 which at once begins to rearrange itself. As far as this reaction is 

 concerned, we may be sure that if we have, for instance, tricalcic 

 aluminate dissolved in tricalcic silicate (alit), the action of water will 

 result in the formation of less basic compounds, such as monocalcic 

 silicate, together with free calcium hydroxid. 



-A moment's reflection will show that with finely powdered glass, as 

 in the experiments detailed above, an analogous, if not exactly simi- 

 lar, reaction takes place. Whether the reaction goes as far as it does 

 in the case of cement, and whether it leads to a hydraulic set is beside 

 the question, as, obviously, the hydraulic value must depend on the 

 insoluble nature of calcium compounds as compared with compounds 

 of the alkaline metals. When water acts on cement powder calcic 

 hydroxid is at once liberated, and if the amount of water present is 

 limited it soon becomes supersaturated with respect to lime, which 

 crystallizes out, to be again replaced with more hydroxid until the 

 cement is hardened, owing to the interlacing of the crystals, silicates 

 being left of a lower degree of basicity. When water acts on glass 

 powder, sodium hydroxid is at once liberated as the result of the 

 hydrolysis of the sodic silicate in solution and certain insoluble sili- 

 cates are left, the binding power in this case being due to the cement- 

 ing value of a colloid and not to crystallization. 



DISCUSSION OF PHENOLPHTHALEIN REACTION. 



In view of these interesting considerations it appeared that rock 

 powders which showed an increase in binding power after wet grind- 

 ing should show an immediate and distinct reaction to indicators like 

 phenolphthalein or litmus whenever alkali bases were present. As 

 the laborator}^ of the Division of Tests has always on hand a large 

 number of samples of all sorts of rock powders which have been fine 

 ground both wet and dry in heav} T ball mills, this point was put at 

 once to the test. In making the qualitative test about 10-gram lots 

 of the dry-rock powders were placed in commodious test tubes, 50 cc 

 of water poured upon them, and a few drops of phenolphthalein indi- 

 cator immediately added. Some of the results of this test are tabu- 

 lated in the table. 



In view of the ease with which the experiments can be repeated oy 

 anyone who wishes to do so, it has not been deemed necessary to fill 

 any greater space with tabulated results. It is sufficient to point out 

 that almost all fine rock powders give an immediate alkaline reaction 

 when treated in this wa}% and that the color reaction is deeper after 

 25219 No. 9205 2 



