STATE GEOLOGIST. 281 
WET GRINDING, 
In working wet marls two methods can be pursued. They may be 
worked in the wet state entirely or dried in rotary dryers and worked like 
a limestone mixture. The first way is usually followed for several rea- 
sons, which are viz.: 
1. The mixtures are blended more easily in the wet way. 
2. No elevators and conveyors are necessary in handling the raw 
mixture. 
3. There is no expense for fuel outside of the kiln and no dryer 
to look after. 
4. The waste heat which otherwise would escape into the kiln 
stack is utilized right in the kiln, expelling the water, and though the 
capacity of the kiln is decreased the process is simplified and no more 
fuel is used than if the marl were dried. The waste gases, the great 
source of loss in all rotary kilns, leave at a low temperature. 
This applies, of course, only to materials which are dredged wet and 
naturally contain a large amount of water. It is obvious that the total 
fuel consumption per barrel is bound to be greater than it would be for 
dry material owing to the large amount of water present. The wet 
method has also to contend with difficulties arising from the “ringing” 
of the kilns, and requires additional power for running the agitators 
in the vat. 
5. The wet process enables the manufacturer to be absolutely sure 
of his composition by the use of unit tanks and correction vats. 
The marls are as a rule fine grained materials, and hence no intermediate 
reduction machinery is necessary. The marl is charged into a wet pan 
or simply an agitator and mixed with sufficient water to make the 
desired slurry. Any stones and roots are removed here. ‘The slurry 
is now pumped by means of piston or centrifugal pumps or, still better, 
compressed air to a coarse vibratory sieve, which removes any fibrous 
matter still remaining, and from there runs into a small tank kept 
agitated thoroughly. At the bottom of this tank a small pug-mill-like 
mixer is located, above which is a platform carrying the scale by means 
of which the clay is weighed out. To a certain volume of slurry a 
given weight of clay is added. This must be dry and pulverized by a 
disintegrator. From the mixer the combined marl and clay is pumped or 
run by gravity to the tube-mills. “Though the marl may appear fine grained 
the grinding should not be slighted, since the clay frequently needs to 
have a most thorough disintegration. Another point to be considered is 
the presence of the shells so often found in marls. These, being thin 
and flakelike, are extremely difficult to reduce, and unless disintegrated 
will form troublesome particles of free lime in the cement which may 
give considerable annoyance, as the writer has had occasion to observe. 
