CRANE.| Prospecting, Mining and Milling Machinery. 277 
The method of separation is the same as in the hand jig, 
the process differing only in the fact that the screen is sta- 
tionary, the water alone moving, which movement is reversed 
in the hand jig; 7. e., the screen moves and the water remains 
stationary. 
The jig must be strongly built, as it serves partially as a 
tank holding a large quantity of water, which is acted upon 
by series of plungers forcing it up through the bed of ore. 
A number of rectangular frames, made of 4x6 or 6x6 inch 
plank are mortised together and are set up in line, and form 
the framework of the body of the jig, the tank being built 
up of planks nailed to the inside of the frame and subdivided 
into cells by longitudinal and transverse partitions. 
There are several methods of putting together the tank 
timbers or building up the body of the jig: (1) The planks 
may be grooved, set on edge, and a tarred strip of soft pine 
driven in to fill up the rectangular opening formed by the 
junction of the double grooves. Occasionally iron splines 
are used, but when the water employed in the jigging opera- 
tion is very acid iron does not last as well as wood. (2) 
The walls may be built up of two-by-fours by laying them 
flatwise and inserting wicking between them (1, figure 58). 
Flat wicking or ordinary candle wicking is often employed. 
If the planks do not fit evenly they may be partially fastened, 
and a cut with a saw blade made between the two pieces. 
When closely fitted and well wicked and spiked there is little 
or no danger of leakage. 
When two-by-fours are used, they are usually lapped at 
the ends or corners, being built up in pig-sty fashion, the 
supporting frames being omitted (/, figure 58). This 
leaves a two-inch space alternating with the planks. These 
spaces are filled in as they occur with pieces of two-by-fours, 
the wicking being inserted as before; thus the whole tank is 
built up solid and tight at one operation. This form is 
known as ‘‘Cooley’s self-contained jig.’’ ‘Transverse parti- 
tions divide the jig into compartments or cells, while longi- 
tudinal partitions partially subdivide the cells formed by the 
transverse partitions, both of which are usually made in the 
same manner as the walls of the jig. 
