178 GRAVEL AND PLACER MINING IN ALASKA. |bull. 263. 
dredges at that time and still often found — a lack of coordination of 
capacity in the four processes of which gold dredging consists, namely, 
excavating, screening, sluicing, and tailing. 
The next improvement was the building of a dredge in which coor- 
dination of capacities received more attention, for in this the screens, 
tables, stacker, and pumps were enlarged. It was designed to work 
either on spud or headline, with a slightly higher discharge of material 
to permit of a greater elevation of coarse tailings and a stacking of 
them at a distance from the stern. The pivotal spud was placed 
inboard so as to make the digging and the tailing arcs of more equal 
lengths when working on a spud. The difficulties encountered when 
these arcs were of very unequal length were thus eliminated. The 
disposition of the tailings had formerly been a continual source of 
difficulty and expense, but this improved dredge was so designed as to 
allow both working on a headline and side feeding through an arc of 
long radius. This permitted the working of a wide cut and the dispo- 
sition of tailings without covering adjacent virgin ground, for pre- 
viously much untouched territory had been wasted b}^ being covered 
with tailings. Impact riffles charged with mercury, i. e., those where 
the fines are dropped to effect amalgamation, and larger gold-saving 
areas were also introduced. 
There have been no radical changes in the design or construction of 
gold-dredging machinery of late, and efforts have been directed toward 
the strengthening and bettering of machinery and hull and the lower- 
ing of operating expenses. 
The excavating apparatus (see PL XXXII; PL XXVIII, B, p. 160, 
and PL XXX, B, p. 168) used in gold dredging has been very much 
improved since the first installations. Bucket forms have been 
modified so as to prevent losses by spilling. This is accomplished by 
reducing the angle made by the bucket lip with the line through the 
centers of the two bucket pins. With the earlier design a considerable 
loss by spilling, except when buckets were working at maximum depth, 
was noticed. In the earlier design the bucket was long, narrow, and 
deep, and a clean discharge was not effected, especially when working 
in sticky or sandy material. Recent design provides a short, wide, 
and shallow bucket which discharges more perfectly. The use of jets 
of water to wash any adhering material from both inside and outside 
of buckets into the hopper and save-alls is now common and accom- 
plishes a considerable increase in the gold saving. The capacity of 
buckets has been largely increased, but the economical limit has not 
been reached nor will it be reached in the near future. 
With the increase of size of buckets there has not been a propor- 
tionately greater strength, but this defect is being gradually remedied. 
The use of various alloys of steel in bucket parts, as well as in other 
