14 BULLETIN 572, U. S. DEPARTMENT OF AGRICULTURE. 



RELIABILITY OF THE RESULTS OBTAINED. 



All potash determinations were made by the J. Lawrence Smith 

 method, modified by converting the chlorides into sulphates to insure 

 against loss of potash on driving off ammonium salts and then pro- 

 ceeding as in determining water-soluble potash according to the 

 Methods of the Association of Official Agricultural Chemists. The 

 duplicate determinations in every case were made by different per- 

 sons and each percentage value for potash in raw mix and in cement 

 thus represents the mean of the results found by two analysts. No 

 percentage values of which a mean was taken differed by more than 

 0.12, and most differences in results were well within this limit. 



When requesting samples for analysis from the different plants 

 attention was called to the importance of selecting cement and raw- 

 mix samples which correspond as closely as possible with one another, 

 and which were representative of normal working conditions. This 

 request seems to have been observed by most if not all plants, and 

 judging by letters received it appears that a great deal of care was 

 taken by many cement officials in collecting the samples. Each 

 sample selected for analysis was reduced to a fineness of 175 mesh by 

 grinding the portion which failed to pass through the screen, first in 

 a steel-ball mill and then by hand in an agate mortar. The mills were 

 not asked to make a distinction between the ground clinker and 

 finished cement, for the extent to which these would differ in compo- 

 sition in any particular case through the addition of gypsum to the 

 former was not thought sufficient to have any material effect on the 

 results. 



Analyses corresponding to those given in Table I have been made 

 by the Western Precipitation Co. 1 of samples from five of the plants 

 listed in the table. The results obtained are compared with those 

 found in this laboratory in Table IV: 



Table TV. — Comparison of results of analyses made by the Western Precipitation 

 Co., and by the Bureau of Soils of raw-mix and cement samples collected on different 

 occasions. 



. Potash in raw mix. Potash in cement 



Company. j Western RmH „ I Western 



Bureau p_w3_j to Bureau i Pr .„ in ; t , 



i nf 9ni!« irecipita- _ f qnjio rrecrpita- 



of bons. tion Co _ or boils. ti0Q Co 



Olympic Portland Cement Co. . . 



Pacific Portland Cement Co 



Santa Cruz Portland Cement Co. 

 Portland Cement Co. of Utah . . . 

 Security Cement and Lime Co.. 



Per cent. 



Per cent. 



Per 



cent. 



Per cent. 



0.56 



0.42 





0.51 



0.45 



.50 



.52 





.50 



.43 



.76 



.76 





.33 



.28 



.34 



.92 





.24 



.21 



1.29 



1.12 





1.05 



1.02 



1 Written communication. 



