XI, A, 1 King: Pozzuolanic Properties of Meycauayan Tuff 23 

 Table III. — Analysis of Meycauayan tuff.^ 



Constituent. Per cent. 



Insoluble silica (SiOj) 42.81 



Soluble silica (SiO^) 12.22 



Aluminium oxide (AUOs) 7.12 



Ferric oxide (Pe^Oa) 16.56 



Calcium oxide (CaO) 5.53 



Magnesia (MgO) 2.24 

 Sodium and potassium oxides (KjO + NaaO) 5.34 



Water at 110°C. 3.09 



Loss on ignition *" 4.34 



■ Analysis by Rafael H. Asruilar, chemist, Bureau of Science. 

 >> Mostly -water above HO" C. 



The percentage of soluble silica is low. No published results 

 of soluble-silica determinations on Philippine tuffs are at hand 

 for comparison, and it is impossible to state whether the quantity 

 found here is characteristic of Philippine tuffs in general or is 

 a peculiarity of the Meycauayan tuff. Kiushi volcanic ash, pro- 

 duced at Karatsu, Sagaken, Japan, and analyzed at the Industrial 

 Experimental Station at Osaka, contains 19.99 per cent of soluble 

 silica. When compared with the results obtained by E. Schwarz 

 in his investigation of some European tuffs possessing well- 

 defined hydraulic properties, the result is also low.^ 



About 84 per cent of the tuff used for this determination 

 passed through the 200-mesh sieve. The error introduced in 

 the analysis with this fineness due to the solvent action of the 

 alkali upon the quartz is very slight and ordinarily can be neg- 

 lected. Lunge and Millberg ® state that it reaches from 0.1 to 

 0.2 per cent of the total amount of silica. As a result the 

 percentage of amorphous silica obtained will be in excess of 

 that actually present. If anything, therefore, the results shown 

 are probably too high. 



' The method of determining the soluble silica in Table III is based upon 

 the procedure recommended by W. Hillebrand in The analysis of silicate 

 and carbonate rocks [Bull. U. S. Geol. Surv. (1906), 305, 165]. Accord- 

 ing to G. Lunge and Milberg [Zeitschr. f. angew. Chem. (1897), 393, 425], 

 quartz is not nearly so insoluble in solutions of the caustic alkalies as 

 has been supposed; if given a sufficient degree of subdivision, it can be 

 brought wholly into solution. It is impossible to secure correct separation 

 of quartz and opaline silica by the use of either caustic or carbonated 

 alkalies. Digestion on the water bath for fifteen minutes with 5 per 

 cent solution of sodium carbonate is the only way to secure exact separation 

 of unignited precipitated silica from quartz, and then only when the finest 

 flour has been removed by levigation. 



' Loc. cit. 



