At the Rainbow mill, Oregon, the tube mill discharge with 78 per cent. 100-mesh is diluted to 60 per cent, moisture and run over plates with a inclination of 2J4 in. per foot. The extraction was increased about 10 per cent, by regrinding in the tube mill and the trouble due to lime blackening the plates, when amalgamation followed the batteries, was rectified by the finer grinding. The mill grinds in cyanide solution averaging 1 Ib. KCN and 0.6 Ib. protective alkalinity. Plates are dressed twice a shift, using fiber brushes, whisk brooms and scrapers cut from rubber belting. The plates are not allowed to build up with hard amalgam for when this was allowed the extraction fell off considerably. Plate consumption is rather high, due to the dissolving action of the solution a plate lasting from 3 to 4 months and for this reason silver-plated plates are not used. There is no noticeable difference in plate extraction on this account. The presence of lime in the mill solution caused the plates to blacken and rendered them unfit for amalgamation when recovery was entirely on the battery plates, but when the ore was reground and amalgamated after leaving the tube mill this difficulty disappeared.

At the Big Pine mill, Nevada, a 5 by 20-ft. tube mill at 28 r.p.m. is used as intermediate and final grinder taking 1-in. mesh product from a 10 by 16-in. Blake. Amalgamation takes place on plates 12 ft. long; two of them are 4 ft. 9 1/2 in. wide and one is 4 ft. 6 in. wide. They have a grade of 1 3/4 in. per foot. After leaving the plates the pulp is elevated to a classifier, the oversize going to the tube mill. The mill has a big capacity, due no doubt to the soft nature of the ore for with this coarse feed it is said to grind 130 tons a day, 85 per cent. 200-mesh. Care is taken that no mercury gets into the tube mill.

At the Dome mill, Ontario, instead of the plates being in the tube mill circuit they are placed after the classifiers, there being four classifiers and four copper plates, each 108 by 144 in. with 1 1/2 in- per foot grade. Although with a 16-mesh screen on the stamp batteries the percentage caught by amalgamation was 78 per cent, and with a 10-mesh screen 46 to 50 per cent., it was found that the coarse-mesh screen was necessary to attain capacity and as the sand scoured the battery plates abnormally with this screen on the battery, the plates were taken from in front of the battery and put after the classifiers. While the percentage of gold caught by amalgamation was less than formerly, all the gold, which might have caused trouble in the cyanide department, was caught on the plates. The stamp mill crushes in water with 7% water to 1 of ore, lime being added in the battery water at the rate of 3.2 Ib. per ton of ore.