Reiser & Forder — Determination of Free Lime. 171 



We conclude from these results that lime in combination 

 with silica in quantities not exceeding three molecules of lime 

 for one molecule of silica is only slowly acted upon by water 

 and that this method of determining lime can be used to 

 determine free lime in the presence of the basic di- and tri- 

 calcium silicates that are assumed to be present in Portland 

 cements. 



HYDRATION OF CALCIUM ALUMINATES. 



The mono, di, and tricalcium aluminates were also prepared 

 synthetically by fusing molecular quantities of pure alumina 

 and lime with the oxy-coal gas blowpipe flame. The alumina 

 was prepared by heating the hydroxide that had been ob- 

 tained by precipitation from the chloride by ammonia. The 

 aluminates all fused much more easily than the silicates under 

 the oxy-coal gas blowpipe. Weighed quantities were hydrated 

 by our method as in the case of the silicates and the hydraulic 

 properties were also noted. It was found that the aluminates 

 differ markedl}'^ from the silicates in their behavior towards 

 water. This is shown by the following results : — 



Hydraulic Weight Wt. of Water 

 Compound. properties. taken. talien up. 



(CaOAlaOa Set very hard, .4886 .0652 



2(CaO)Al2b3 liiie a cement .4543 .0716 



SCCaOAlaOg None. .4072 .0796 



We see from this that the aluminates are hydrated very 

 much more rapidly than the silicates, in fact they behave 

 like free lime when warmed with water to 85 degrees for 30 



