288 The Philippine Journal of Science i9i6 



guide in predicting the effect of a sulphide solution on a given 

 cement. 



1. The setting time of a cement is greatly modified by the 

 presence of sodium sulphide. With low concentrations the set 

 is retarded, but after reaching a maximum, further additions 

 accelerate the set. In general, the cements highest in iron 

 content are most sensitive to this influence. 



2. There is a decided decrease in tensile strength.-" The per- 

 centage loss varies with the concentration of the sulphide and 

 with the iron content of the cement. The briquettes appear 

 normal in every other respect, except in color. There is no • 

 cracking nor distortion of any sort. 



3. In most cases sulphide may be present in concentrations 

 up to 1 gram per liter without causing the tensile strength 

 to fall below United States Government specifications. 



4. Certain results indicate that a colloid is formed by the 

 action of sodium sulphide on the iron in the cement. 



5. Based on the results of both chemical and physical ob- 

 servations, the following explanations of the decrease in tensile 

 strength are offered: 



(a) The precipitated colloid forms films of inert material through the 

 cement and interferes with the cohesion. 



(6) When the colloid is precipitated a portion of the dissolved calcium 

 hydroxide is removed from solution. Since the latter substance 

 is a very important factor in the strength of cement, it is to be 

 anticipated that the strength will be lowered, when some of it is 

 removed. 



6. It is probable that a number of other factors influence 

 the effect of sulphide on cement. Among these, may be men- 

 tioned the fineness of the cement, the temperature at which it 

 is mixed, the percentage of water used, and the amount of 

 dissolved calcium hydroxide. 



'° The only specimens yet broken are those during the first sixty days. 



