22 BULLETIN 572, U. S. DEPARTMENT OF AGRICULTURE. 
free lime and at the same time a high percentage volatilization of the 
potash is obtained. A combined dry and wet system was first used 
for recovering the potash, but, not proving satisfactory, this has been 
replaced by the Cottrell process of electrical precipitation. 
ACKNOWLEDGMENT. 
We wish to express our thanks to the different cement companies 
listed in Table I for the samples they have furnished us, and particu- 
larly to the officials of the Security Cement and Lime Co., the Western 
Precipitation Co., Mr. R. K. Meade, and others, for the information 
they have given us. 
SUMMARY. 
(1) Analysis of samples of raw mix and of cement from 113 cement 
mills in the United States and Canada shows that the potash in the 
raw mix varies from 0.20 to 1.16 per cent, and that the percentage 
of potash volatilized in the different plants varies from 24.5 to 95.9 
per cent. From the results thus obtained it has been calculated 
that the potash escaping from the kilns of these plants ranges from 
0.35 to 5.14 pounds per barrel of cement produced, with an average 
for the plants of this country of 1.93 pounds. On the basis of an 
average production of 90,000,000 barrels, the total potash escaping 
from the cement plants of this country amounts to about 87,000 tons 
annually. It has been demonstrated commercially that 90 per cent 
of the potash escaping in the dust is recoverable, and from experi- 
ments made in this laboratory it would appear that 95 per cent of 
the recoverable potash is, or may readily be made, available. The 
recoverable potash in the cement industry therefore amounts to 
approximately 78,000 tons and the available recoverable potash to 
75,000 tons, or to 71,000 tons when plants losing less than 1 pound 
of potash per barrel of cement are omitted. 
(2) Assuming, in the light of results that have already been ob- 
tained, that it would be practicable to increase the percentage of 
potash volatilized to at least 65 per cent for all plants, then the 
available recoverable potash would amount to more than 100,000 
tons annually, or to nearly one-half of the normal consumption of 
potash in this country. 
(3) If it be assumed, further, that the dust escaping from the kilns 
amounts on an average to 4 per cent of the raw mix fed into the 
kilns in the case of dry-process plants, and to 2 per cent for plants 
using the wet process, then, on the basis of the results already given, 
the total potash content of the dust escaping from the former plants 
will vary in different plants from 1.4 to 20.0 per cent, and in the 
latter from 9.1 to 35.1 per cent. 
(4) The ratio of potash to soda in the dust as determined for 20 
different plants varies from-0.92 to 6.07, with an average of 2.66. 
