604 CEMENTS, LIMES, AND PLASTERS. 



this is also a very effective method for mixing them together in order 

 fco obtain an average. For determining the characteristics of a ship- 

 ment of cement, the individual samples may be mixed and the average 

 tested; where time will permit, however, it is recommended that they 

 be tested separately. 



4. Method of sampling. Cement in barrels should be sampled through 

 a hole made in the center of one of the staves, midway between the 

 heads, or in the head, by means of an auger or a sampling iron similar 

 to that used by sugar inspectors. If in bags, it should be taken from 

 surface to center. 



CHEMICAL ANALYSIS. 



5. Significance. Chemical analysis may render valuable service 

 in the detection of adulteration of cement with considerable amounts 

 of inert material, such as slag or ground limestone. It is of use, also, 

 in determining whether certain constituents, believed to be harmful 

 when in excess of a certain percentage, as magnesia and sulphuric anhy- 

 dride, are present in inadmissible proportions. While not recommending 

 a definite limit for these impurities, the committee would suggest that 

 the most recent and reliable evidence appears to indicate that mag- 

 nesia to the amount of 5 per cent, and sulphuric anhydride to the amount 

 of 1.75 per cent, may safely be considered harmless. 



6. The determination of the principle constituents of cement silica, 

 alumina, iron oxide and lime is not conclusive as an indication of quality. 

 Faulty character of cement results more frequently from imperfect 

 preparation of the raw material or defective burning than from incor- 

 rect proportions of the constituents. Cement made from very finely 

 ground material, and thoroughly burned, may contain much more lime 

 than the amount usually present and still be perfectly sound. On the 

 other hand, cements low in lime may, on account of careless preparation 

 of the raw material, be of dangerous character. Further, the ash of 

 the fuel used in burning may so greatly modify the composition of the 

 product as largely to destroy the significance of the results of analysis. 



7. Method. As a method to be followed for the analysis of cement, 

 that proposed by the Committee on Uniformity in the analysis of Ma- 

 terials for the Portland Cement Industry, of the New York Section of 

 the Society for Chemical Industry, and published in the Journal of the 

 Society for January 15, 1902, is recommended. 



