134 The Philippine Journal of Science im 



the cement is intended." This recommendation was made* on 

 the basis of results obtained with only two cements : 



The materials used consisted of a Portland cement. (S), containing 1.19% 

 of SOs and employed for all purposes, marine structures included, and 

 another Portland cement (B), which contained only a very small proportion 

 of S0 3 , namely 0.57%. 



In both cases the raising of the SCvcontent to 2.5% by the addition of 

 gypsum, increased the tensile strength, both in fresh and sea water. 



In the summary of the paper it stated that — 



From these results it follows indubitably that the presence of up to 2.5% 

 of SO3 in Portland cement, produces no injurious effects of any kind, 

 whether in sea water or fresh water. 



No matter how conclusive these results appear, or how care- 

 fully the work was carried on, it is impossible to settle such an 

 important question by the behavior of only two cements, par- 

 ticularly in the face of contradictory evidence obtained by other 

 investigators. 



It is generally conceded that an excessive amount of sulphuric 

 anhydride in a cement is harmful. All specifications mention 

 an upper limit, though not all agree what this limit shall be. 7 

 Meade 8 says : 



Although the presence of calcium sulphate in small quantities is bene- 

 ficial to cement, there is no doubt that a quantity exceeding 4 or 5 per cent 

 is injurious. 



According to Kiihl, 9 the sulphuric anhydride content of a 

 cement should not exceed 2 per cent. Rigby 10 states : 



In making some experiments with cement by adding plaster of Paris by 

 mixing the two materials in different proportions, I found that if I exceeded 

 41 per cent of the latter the briquettes subsequently made from the mixture 

 either broke up after being placed in water for a time, or, if they retained 

 their shape, they were very much cracked and gave a very poor test. 



Bates lx found that while higher sulphuric anhydride content 



' Though the specifications of various nations for the upper limit of 

 sulphuric anhydride are often taken as directly comparable, this is not the 

 case. For instance, in the British specifications, 2.75 per cent sulphuric 

 anhydride does not refer to the sulphur present as sulphate only, but means 

 the total sulphur calculated to SO*. (See British Standard Specifications 

 for Portland Cement. Revised, March, 1915.) 



s Meade, R. K., Portland Cement. Chemical Publishing Co., Easton, Pa. 

 (1906), 31. 



9 Kiihl, H., Mitt. Zentralstell. Ford. Dent. Port. Zem. Ind. (1913), 2, 108. 



10 Rigby, J. S., Journ. Soc. Chem. Ind. (1890), 9, 254. 



"Bates, P. H., Proc. Am. Soc. Test. Materials (1915), 15, II, 126. 



