───────────────────────────┬────────────────────── TOTAL CONTENTS OF KETTLE │ 1 LB. ZINC TAKES OUT AU. OZ. │ AG. OZ. │ AU. OZ. │ AG. OZ. ────────────┼──────────────┼─────────────┼──────── 494 │ 3,110 │ 0.59 │ 3.60 443 │ 1,883 │ 0.64 │ 2.80 330 │ 2,417 │ 0.45 │ 3.34 204 │ 1,638 │ 0.36 │ 2.86 143 │ 1,330 │ 0.28 │ 2.65 123 │ 1,320 │ 0.23 │ 2.54 ────────────┴──────────────┴─────────────┴──────── It will be noticed that in each case the richer the bullion the greater the extractive power of zinc. Experiments made on charges of rich bullion showed that the large amount of zinc called for by the table in use was unnecessary, and 250 lb. was fixed on as the first addition of zinc. On this basis an average of 237 charges gave results as follows: ───────────────────┬───────────┬────────────────────── TOTAL CONTENTS │ ZINC USED │ 1 LB. ZINC TAKES OUT AU. OZ. │ AG. OZ. │ LBS. │ AU. OZ. │ AG. OZ. ────────┼──────────┼───────────┼───────────┼────────── 520 │ 1,186 │ 507.5 │ 1.27 │ 2.91 ────────┴──────────┴───────────┴───────────┴────────── The zinc used was that necessary to clean the kettle, added as follows: 1st, 250 lb.; 2d (average), 127 lb.; 3d (average), 57 lb. In 112 cases no third addition was required. From these figures it appears that in the earlier work the zinc was by no means saturated. _Refining the Lead._—Gold and silver being removed, the lead is siphoned off into the refining kettle and the fire made up. In about four hours the lead will be red hot, and when hot enough to burn zinc, dry steam, delivered by a ¾ in. pipe reaching nearly to the bottom of the kettle, is turned on. The charge is stirred from time to time and wood is fed on the top to assist dezinking and prevent the formation of too much litharge. In three to four hours the lead will be soft and practically free from zinc. When test strips show the lead to be quite soft and clean, the kettle is cooled down and the scum of lead and zinc oxides skimmed off. In an hour or so the lead will be cool enough for molding; the bar should have a yellow luster on the face when set; if the lead is too cold it will be white, if too hot a deep blue. The refining kettles are subjected to severe strain during the steaming process, and hence their life is uncertain—an average would be about 60 charges; the zinking kettles, on the other hand, last very much longer. Good steel kettles (if they can be obtained) are preferable to cast iron.