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. 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 IV.—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. | Western | "| Western 
eee Precipita-) Bee |Precipita- 
* | tion Co. * | tion Co. 
| 
Per cent. | Per cent. | Per cent. Per cent. 
Olympic: Portland CententiCo 3:2. $2 ek ee, ee ee 56 | 0. 42 5 0.45 
Pacinic ortiand:CementiCoss 2). tks 225) See LS eee =SOn .52 . 50 43 
Santa Griz, Porteand) Cement Cos. 2. ee 2 es ie eee . 76 | . 76 33 - 28 
Portiand Coment Goro! Uta et ee ee ee ee eee 94 .92 24 | ail 
Security Cement and Limoe\Cost. ).2-7 teuiad. 222. J. 2 1. 29 1.12 1.05 — 1.02 
1 Written communication. 
