STATE GEOLOGIST. 165 
cement itself has set to a hard mass, giving rise, of course, to cracking or 
swelling. 
Methods of Preparation of the Lime.—Although slaked lime can 
now be purchased on the market, it will usually be found too expensive. 
Slaking may be carried on: first, by the old pile slaking; second, by 
the periodic cylinder method; third, by the continuous slaking machine. 
In the ordinary pile slaking a heap of quicklime is made, as much water 
sprinkled over it as practice has shown to be necessary, and allowed to 
slake for some time. The slaked lime is then put through a 10 mesh 
screen, which may either be a long stationary inclined screen or a mechan- 
ically driven rotary sieve. It is obvious that too much water will have 
the effect of producing a moist hydrate which cannot be screened, and 
hence the addition of water must be carefully gaged. The screened lime 
is now taken to a cast iron pan, about 15 feet long, 8 feet wide, and 12 
inches deep, kept heated by means of a furnace beneath. When dry, the 
slaked lime is scraped from the pan and put through a 20 mesh screen. By 
means of a conveyor, the hydrated lime is taken to the bin ready to be 
used. 
In the cylinder method of slaking a large quantity of quicklime, say 
one ton, is dumped into a steel cylinder provided with a large manhole 
and swung on trunnions. The manhole is then closed and through a 
pipe the requisite amount of water is introduced. The heat given off by 
the hydration soon converts the excess of water into steam under a great 
pressure. A safety valve must be provided to relieve any excessive pres- 
sure. Slaking thus takes place under pressure, and the slaked 
lime is in the condition of a powder. It has also been proposed 
to revolve the cylinder in order to accelerate the slaking. After the slak- 
ing is completed, the cylinder is placed in position with manhole down 
and the lime dumped into suitable receptacles. 
In the third method, which has so far not been worked out on a 
practical scale to the writer’s knowledge, but which has the great advant- 
age of continuous operation, three stages are to be noted. The first part 
of the process, the slaking, is carried on in long, tubelike cylinders, about 
twelve feet in length, somewhat similar to a clay pugmill, in which two 
shafts provided with blades revolve rapidly. At the feed end where the 
quicklime is brought in as powder, water is sprayed in under pressure, 
somewhat in excess of the amount required, which must be, of course, 
gaged by an attendant. The rapidly revolving knives or blades bring 
about through blending of the lime with water. At the discharge end of 
the machine, the hydrated lime is taken to a large sheet iron bin, of such 
dimensions that the lime is allowed to remain in it for two or three hours. 
At the bottom of this bin a revolving feeder is arranged which feeds the 
slaked lime into a rotary dryer in which the material is dried by a current 
