CRANE. | Economy of Mining Operations. 353 
Elevator buckets cost from fifty to sixty cents apiece. 
From three to eight are, on an average, worn out or destroyed 
per day, after the mill has been running several months. 
Acid waters play havoc with buckets; so where the waters 
are very acid the wear on the buckets is especially rapid. 
The cost per day probably varies from $2 to $4. 
WEAR OF CENTRIFUGAL PUMPS. 
Centrifugal pumps are employed in lifting the water used 
in concentration to the different apparatus used. The water 
used is usually that pumped from the mine below, and stored 
in a pond beside the mill, from which it is drawn as needed 
in the concentrating processes. This water is nearly always 
quite acid; so any metal pump employed in lifting the same 
is rapidly destroyed. Centrifugal pumps are quite expensive ; 
so, in the mills where they are destroyed in a few weeks, the 
question of handling the water for concentration becomes a 
serious problem. 
During the last three or four years several forms of wooden, 
or wooden-lined centrifugal pumps have been devised. 
Although the first cost of these pumps is about the same as 
the metal forms, yet they last so much longer that they will 
probably replace the metal pumps entirely. 
The life of the shell of an iron centrifugal pump is from 
two to three years. The spider and sheathing, the inner 
parts of the pump, last from three weeks to twelve months, 
depending wholly on the acidity of the water. The average 
life is probably four weeks. The average cost of lining and 
spider is about $25; this makes about $6.25 per week for re- 
pairs. When wooden pumps are used, the lining is done 
away with; so the only cost is the wear of the spider. The 
cost of replacing the spider is about one-half of that given 
above for both lining and spider, or $3 per week. The spider 
and lining are usually made of brass or bronze. 
The suction and discharge pipes cost about $1 per linear foot, 
and last aboutsix months. If 30 feet of pipe is used, the costis 
$30 per six months, $1.25 per week, and 18 cents per day. 
In a few cases wooden pipes are being used, which give entire 
satisfaction and last for a long time. They are practically 
