PURINGTON. 
SLUICES AND GOLD-SAVING APPLIANCES. 
195 
full or nearly full of water running with great velocity, fine gold will be 
carried along. Lengthening the sluice will not help matters. In fact, 
a short sluice with drops or undercurrent attachment is frequently 
more effective than a long sluice without it. 
In a given case assume that the ordinary 14-incn boxes are widened 
to 24 inches, and that 5 boxes, with a grade of 9 inches to the box, 
fitted with the ordinary sapling-pole riffles, as at present, are suc- 
ceeded by 3 boxes with the form of screen represented in fig. 41, 
the grade being made adjustable by means of blocking. An addition 
of 19^ inches to each of the 3 boxes would compensate for the loss of 
grade consequent on the up- 
tilting of the screens. The 
whole drop in the string of 
boxes would be 103. 5 inches 
as against 108 inches were 
12 boxes used with 9-inch 
grade. Under the punched 
iron plates riffles of one or 
more kinds as described 
below, charged with quick- 
silver, should be used. 
The riffle shown in fig. 42 
will be found satisfactoiy. 
Mats, plush, or blankets 
may under certain condi- 
tions be found more eco- 
nomical. A short trans- 
verse table following the 
last box, arranged under a 
grizzly from which the 
large material is discharg- 
ed to the dump, will enable 
the operator to determine 
whether losses are occur- 
ring in the main sluice and 
screening boxes. 
The above installation is in principle a series of undercurrents com- 
bined in the main sluice. Its advantages of cheapness, adaptability to 
conditions, and simplicity recommend it. No extra power or water is 
required. On the other hand, the use of the mud box is not obviated. 
" Regarding the use of punched plates in working New Zealand 
gold-bearing marine deposits, Mr. H. W. Young" says: 
LThe best size of perforation for hopper plates has been a matter for experiment by 
y self and others, variations from one-fourth inch to five-eighths inch having been put 
iggjg H ^^g-g^ggg^gigg^ 
Scale of feet 
Fig. 42. — Improved Hungarian riffle used at Oroville. 
a Report of New Zealand Minister of Mines, 1902, p. 21. 
