The most conspicuous example of amalgamating in a tube mill is no doubt the unique process of amalgamating the native silver ores at the Nipissing High-Grade mill, Ontario, Canada. While we have used an amalgam barrel for many years to amalgamate sand and scrap in a stamp mill the Nipissing mill has carried the idea to an extreme that the old amalgamators never dreamed of. The tube mill used is 3 ft. 11 in. by 19 ft. 8 in. running at 37 r.p.m. with 55 per cent, moisture and practically 100 per cent. 200-mesh in the product. A 5 per cent, solution of cyanide is used and 8,500 Ib. of mercury to 6,500 Ib. ore. The ore treated contains a high percentage of arsenic which under ordinary amalgamating conditions would be a difficult ore to treat. H. A. Megraw says: "The tube mill has its axial entrances sealed except for a small compressed- air pipe which enters it at one end and a corresponding air exit at the other end. . . . Here then is a tube mill used as an amalgamating barrel, but under conditions which were probably never before sought for amalgamating purposes. The combination of an extremely high cyanide solution, a complex ore which contains all sorts of elements, and mercury all ground violently in a pebble mill, would seem to indicate the reverse of satisfactory. . . . The amount (of cyanide) originally added to the tube mill is sufficient to produce a very strong solution, which is capable of partially outlasting the destroying effect encountered within the mill. The agitation is continued for 9 hr., after which time 97 per cent, of the contained silver has been extracted from the ore." At the Plymouth Con., California, gold is amalgamated inside a Hardinge mill and on plates.

"The discharge from 30 stamps is classified and the coarse material ground in a Hardinge mill, the discharge from the Hardinge mill passing over two 5 by 8-ft. copper plates, at the top and the bottom of which are traps or wells of about 4 in. in depth. The upper traps catch as much as 70 per cent, of the gold without the use of quicksilver, it being used solely on the plates, which are cleaned once a day. After passing the first pair of plates the ore passes over a second set of ten 6 by 12-ft. plates, where a further recovery is made. The present system of amalgamation is proving both simple and efficient."