CHAPTER XV. 



FEEBLY HYDRAULIC LIMES: SELENITIC LIMES. 



THE feebly hydraulic limes have been defined in Chapter XIII as in- 

 cluding those products whose Cementation Index ranges between 0.30 

 and 0.70. This means that in such a product, no matter how high the 

 burning temperature, not over 70 per cent of its total lime (CaO) can 

 be in combination with the silica, etc., while if the Cementation Index, 

 as shown by analysis, falls as low as 0.30, only 30 per cent of the total 

 lime can be so combined, even under the most favorable circumstances. 

 As combination can never be theoretically complete, it is safe to say 

 that in the feebly hydraulic limes only from 20 to 60 per cent of their 

 total lime is combined, the remainder being left free and capable of 

 slaking. A product containing so much free lime and so little in the 

 combined form can obviously possess little hydraulicity or strength. 



Limes of this class would hardly merit description were it not for 

 the fact that they are the usual type of English hydraulic limes, and 

 that they often serve as a basis for making a product selenitic lime 

 which requires brief attention. 



TABLE 82. 

 ANALYSES OF HYDRAULIC-LIME ROCKS. 



1. Holywell, England. Muspratt, analyst. 



2. Falhagen, Germany. Pasch, analyst. 



3. Horb, Wurtemberg. Knauss, analyst. 



187 



