iCKEL.] METHODS OF MANUFACTURE. 51 
process. Marl deposits of workable size occur only in the Northern 
States and in Canada, and consequently the climate is unfavorable to 
ontinuous working throughout the year, for the marl is usually cov- 
red with water, and in winter is procured with difficulty. Marl 
eposits are necessarily and invariably found in depressions, and the 
lill must be located at a higher level, which involves increased expense 
transporting the raw material to the mill. 
Glacial clays, which are usuall}^ employed in connection with marl, 
3mmonly carry a much larger proportion of sand and pebbles than 
le sedimentary clays found farther south. 
The effect of the water carried by the marl has been noted. The 
iterial as excavated consists approximately of equal weights of 'lime 
irbonate and of water, and more water is often added to permit the 
arl to be pumped up to the mill. 
At the mill the clay is often dried in order to simplify the calcula- 
on of the mixture. The reduction of the clay is commonly accom- 
ished in a disintegrator or in edge-runner mills, after which the 
iterial is further reduced in a pug mill, sufficient water being here 
Ided to enable it to be pumped readily. It is then ready for mixture 
ith the marl, which has been screened to remove stones, wood, etc. 
le slurry is further ground in pug mills or wet grinding mills of the 
sk type, while the final reduction commonly takes place in wet tube 
ills. The slurry, now containing 30 to 40 per cent of solid matter 
?d To to 60 per cent of water, is pumped into storage tanks, where it 
vept in constant agitation to avoid settling. The slurry is analyzed 
this point, and the mixture in the tanks is corrected if found to be 
I unsatisfactory composition. After standardizing, the slurry is 
imped into the rotary kilns. Owing to the large percentage of 
iter in the slurry, the fuel consumption per barrel of finished cement 
I 30 to 50 per cent greater, and the output of each kiln correspond- 
ly less than in the case of a dry mixture. 
t may be of interest, for comparison with the above description of 
5 wet process with rotary kilns, to insert a description of the semiwet 
| ocess, as carried on a few years ago at the dome-kiln plant of the 
apire Portland Cement Company, of Warners, N. Y. The plant 
J 3 been remodeled since that date, but the processes formerly fol- 
ved are still of interest, as they- resulted in a high-grade though 
J pensive product. 
At the Empire plant the marl and clay were obtained from a swamp 
put three-fourths of a mile from the mill. A revolving derrick with 
m-shell bucket was employed for excavating the marl, while the 
y was dug with shovels. The materials were taken to the works 
ir a private narrow-gage road, on cars carrying about 3 tons each, 
