148 The Philippine Journal of Science wis 



has been well established. Le Chatelier * observed crystals of 

 calcium hydroxide in examining sections cut from hardened 

 cement specimens. Winkler ^ says that cement is hydrolyzed 

 into free lime and some compounds of lime, silica, and alumina. 

 Stern « found that calcium aluminates were decomposed by water, 

 forming gelatinous alumina and calcium hydroxide. Reed'' 

 made some interesting microscopic studies of hydrated cement. 

 He says : 



When Portland cement is gauged with water, lime goes into solution 

 and a thin skin of calcium carbonate is formed on the moist surface which 

 protects the interior mass more or less completely from the action of 

 the air. 



His method is to treat cement with water on a microscope slide 

 and then to protect the mixture from the air by paraffin. Two 

 kinds of crystals are formed — calcium aluminate and calcium 

 sulphaluminate. Hart * mixed cement with water and then fil- 

 tered rapidly. The filtrate contained sulphates, silicates, free 

 lime, and caustic alkali. On letting a fresh mixture stand two 

 and one-half hours and then filtering and examining the filtrate, 

 he found the chief constituent to be potassium sulphate, which 

 he concluded was formed by the double decomposition of the 

 soluble potassium compounds and the calcium sulphate present. 



PRELIMINARY WORK 



The term solubility as employed in this paper signifies the 

 mass dissolved per gram of cement present in the system under 

 given conditions and not the mass dissolved by a unit weight 

 of water — as in most solubility measurements. The proportion 

 of water has been kept considerably in excess of the amount neces- 

 sary, and no effort was made to keep the temperature constant. 

 All the experiments were made at room temperature in Manila, 

 which averages about 28° to 30° C. The factors that influence 

 the results have been found to be fineness of grain, quantity of 

 water present, absence of carbon dioxide, method of agitation, 

 and time. 



Four brands of cement, which we shall designate as I, H, III, 

 and IV. were used in the work. The analyses are shown in 

 Table I. 



* Cf. West, C. H., The Chemistry and Testing of Cement. London, 

 Edward Arnold (1911), 113. 



" Loc. cit. 



"Stern, E., Chem. Zeitg. (1908), 32, 1029. 



'Reed, E. J., Journ. Soc. Chem. Ind. (1910), 29, 735. 



'Hart, Tonind. Zeitg. (1908), 32, 754. IJoum. Soc. Chem. Ind. (1908), 

 27, 568.] 



