BLACK SANDS OF PARACALE. 993 
the nails charge. In order to secure close checks, 150-mesh is 
none too fine and 200-mesh would probably have given better 
results. 
Another series of experiments was run on some amalgama- 
tion tails, and the results obtained are shown in Table VI. 
TABLE VI.—Assay experiments upon amalgamation tails. 
(Pulp through 150-mesh; 15 grams used in each charge.) 
Charge. = Assay. |Average.| Variation. Pour. 
Grams. Pesos. Pesos. Pesos. 
4.96 
30 litharge, 60 soda __-________ 4.96 4.96 none | Clean. 
90 litharge, 30 soda a88 2.88 G5 |) Mee leas alae 
OS ONE Tene Bae taat 3.72 ; a in the slag. 
c P 6. 58 
| 30 litharge, 60 soda, nails _____ 6.58 6.58 none Clean. 
*In all charges 2.5 grams of borax glass and 10 grams of silica were added ; a borax cover was 
used. When nails were not used, 3.1 grams of argols were added. A long fusion at high tem- 
peratures was used in each case. 
The first charge (low litharge, high soda) gave a clean pour, 
but low result. The second charge (high litharge, low soda) 
gave a very shotty pour and a low result. The nails charge gave 
a clean pour and the highest result. It is evident that when the 
free gold has been removed by amalgamation, there is no diffi- 
culty in doing perfect work, provided the conditions stated are 
properly fulfilled. 
SCREEN TESTS. 
The screens used for the tests were purchased from Braun- 
Knecht-Heimann & Co. for regular laboratory use. They are 
of the usual copper, woven-wire type, and new screens only were 
used. The screen openings were measured under the micro- 
scope, and the averages of both directions are shown in Table VII. 
TABLE VII.—Measurements of screen openings. 
Average screen 
Screen. opening in mm. 
10 2.00 
20 1.00 
40 0.40 
60 0.25 
80 0.187 
100 0.166 
150 0.09 
