§ 110. LIMESTONE AXD LIME. 211 



lime, and magnesia, according to Scheme I., § 94 ; man- 

 ganese need not be noticed unless a qualitative analysis 

 reveals its presence in considerable quantity. 



A determination of carbonic acid may be made to con- 

 trol the results of the other part of the analysis. 



All the bases found should be calculated as carbonates 

 in making up the final statement. 



d. To determine whether a limestone will make a good 

 hydraulic cement, the course described in the preceding 

 paragraph should be followed ; but the alkalies should be 

 determined also, and the residue, insoluble in hydrochloric 

 acid, should be examined with the aid of sulphuric and 

 hydrofluoric acids (§ § 102 and 103). 50-60 grms. of the 

 stone should bo taken for treatment witli hydrochloric 

 acid. And, as the chemical analysis alone will not furnish 

 perfectly safe information in regard to the fitness of the 

 stone for the purpose in question, portions of it should be 

 ignited at various temperatures, and the resulting lime in 

 each case pulverized and made into little balls with water, 

 either alone or with sand, and tested under water, to see 

 whether it hardens properly. 



e. If the cement already prepared is given for exami- 

 nation, it Avill be important to determine the amount of 

 gelatinous silica set free by the hydrochloric acid, as well 

 as the lime, alumina, and alkalies. 20-25 grms. of sub- 

 stance will usually answer for the analysis, since the stone 

 is rendered more soluble by the ignition that is required 

 to convert it into cement. 



Boil the residue, that is insoluble in hydrochloric acid, 

 with sodic carbonate (§ 58, a^ 2), pulverize what is in- 

 soluble in this agent very finely, and treat it with hydro- 

 fluoric acid. 



