156 The Philippine Journal of Science wis 



by methods of microscopy and physical chemistry. However, 

 we believe that the usefulness of methods of analytical chemistry 

 has not been exhausted in this field and that such methods still 

 offer points for attacking these problems, either alone or in 

 conjunction with other methods. Although this work was under- 

 taken simply with the object of learning what constituents of 

 cement would dissolve in water under favorable conditions — and 

 in what quantities — ^the results obtained are closely related to 

 hydration phenomena. The amount of calcium hydroxide found 

 in solution in presence of varying volumes of water can be hardly 

 explained by the laws of solubility. The solution never reaches 

 the point of saturation. This cannot be due to the other sub- 

 stances in solution, because the amounts are relatively too small. 

 The nature of the solvent, the method of agitation, the kind of 

 solute, and the temperature (within certain limits) all have 

 been kept constant. Therefore the determining factor is evi- 

 dently the formation of calcium hydroxide, by the hydration of 

 the various compounds present in cement. Or it is the inhibi- 

 tion of hydration caused by calcium hydroxide in solution. This 

 effect may be said to be twofold. It diminishes the speed of 

 hydration and also the total amount of hydration possible under 

 given conditions. Or, the speed of hydration is diminished until 

 the amount taking place in twenty-four hours is too small to 

 be detected by the methods of analysis employed. 



The conditions under which cement is hydrated in this work 

 are, of course, abnormal, as compared with conditions in prac- 

 tice. This comes about through the use of a large volume of 

 water and through agitation, which keeps the granules separated 

 and keeps a large surface exposed to the water. The exclusion 

 of carbon dioxide probably does not constitute such a great varia- 

 tion from normal conditions as at first appears. Over the sur- 

 face of newly placed concrete or mortar, a thin film of calcium 

 carbonate forms almost immediately, and this protects the in- 

 terior from further contact with this gas. Keeping these facts 

 in mind, let us now try to interpret the results in terms of results 

 that have been obtained by various investigators of the question 

 of hydration of cement. In general, the agreement is striking, 

 though there are some important differences. It may be also 

 stated that not sufficient work has been done along these lines to 

 justify the formulation of any new theory of hydration. 



The theory of Richardson " is that — 



On addition of water to the stable system made up of the solid solu- 



"Cf. Meade, Richard K., Portland Cement. The Chemical Publishing 

 Co., Easton, Pa. (1911), 22. 



