120 The Philippine Journal of Science wis 



by the standard specifications, the increased cost of the work as a whole 

 will be small, and can be well afforded if it is an insurance against failure 

 or renders it less likely.' 



As already stated, the degree of final pulverization is another 

 important consideration. The particles of Portland cement 

 which are too coarse to pass a 150-mesh sieve may be considered 

 as inactive clinkers, the finer grinding of which produces a 

 cement whose efficiency depends upon the same conditions of com- 

 position, burning, seasoning, etc., as that of the impalpable 

 power obtained from large clinkers. The only other consider- 

 ation which the subject of fineness introduces is concerned with 

 the permanency of the strength developed by the finest and most 

 active particles. The durable nature of the indurated impal- 

 pable powder has been proved, and, considering that free lime hy- 

 drates more readily the finer its state of subdivision, the great 

 benefits derived from fine commercial grinding are apparent. 



The ultimate chemical composition may vary within wide 

 limits, and Portland cements of the desired quality can be ob- 

 tained from most of the mixtures now used. Nevertheless, a 

 careful study of the available raw materials will show in each 

 instance that some combinations are capable of giving better 

 results than others, and usually one combination the best of all. 

 Therefore, each manufacturer should be induced to study his raw 

 materials until the most efficient mixture has been ascertained. 

 Also, he must carefully regulate the raw mixture at all times. 

 Otherwise it will be impossible to obtain a uniform product. 



For best results the raw materials must be carefully selected 

 and regulated, finely ground, very thoroughly mixed and hard 

 burned, and the finished product must be of extreme fineness and 

 properly packed. All of these factors are so important that we 

 can not afford to neglect any one of them. 



I do not believe that it would be advisable to formulate a bonus 

 system on the present requirements of the American specifi- 

 cations as a standard. The clauses which permit a determination 

 of the specific gravity after the sample has been ignited at a low 

 red heat, a loss by ignition of 4 per cent, unsoundness in accel- 

 erated tests, and a 25 per cent residue on a 200-mesh sieve 

 make it possible for rather poor grinding and burning to fulfill 

 these requirements. A much more efficient standard is outlined 



' Spackman, Henry S., The need of a more severe soundness test for 

 cement, Eng. News (1912), 68, 80. 



