The concentrator advocated by the writer as embodying the most correct principle in a good mechanical appliance (subsequently improved and perfected), was the Frue vanner, or ore concentrator; and after three years' constant work, and an expenditure of $30,000, success was attained, and the mining public were largely convinced of the importance of proper concentration of the gold and silver ores of the Pacific Coast.

The word "silver" is used because many of the sulphurets contain a large proportion of silver as well as gold. In the vicinity of Nevada City the production of sulphurets was more than doubled by using the vanners, and similar success attended their introduction and use elsewhere. Its success stimulated others to invent concentrators, so that many new concentrators have been brought before the public, many of them possessing merit, and almost all of them claiming superiority over the vanner.

Nevertheless, the sales of the vanner increase every year, and up to date amount to nearly $1,000,000.

The attention of the public is being drawn more and more every year to the importance and benefit of concentration, and even the low grade silver and gold ores of the Comstock Vein (Virginia City, Nevada), are being successfully and economically concentrated. These ores yielded no profit under the old method of amalgamation.

In former times the necessity of sizing even finely crushed ores was strongly insisted on to properly prepare the ore for concentration, but sizing is rarely found advisable with the concentrators now in use.

In some of the mining districts of this State the ore is very heavy with sulphurets, containing twenty per cent and over. Much of this can be separated by coarse crushing with rolls, etc., and jigging, and this method of treatment is advisable, as there is thus avoided a heavy loss of sulphurets in slime, which would occur if the original ore was finely crushed at first. The tailings from the jigs will still contain much sulphurets, locked up in the gangue, and should be finely crushed and passed over the vanner or some other concentrator.

Occasionally an ore is found in which the silver exists partly as chloride and partly as refractory sulphurets. Formerly such an ore was crushed dry, roasted, chloridized, and amalgamated, but even $30 ore would yield scarcely any profit, and the reduction works were very expensive.

For several years the writer contended that the proper method of treating such ore was by concentration first, and amalgamation without roasting of the tailings from the concentrators. In this manner the expensive dry crushing is replaced by wet crushing, which also doubles the capacity of the mill. The refractory part of the ore is saved by itself in such small compass that it can be either sold or shipped to smelters, or treated at the mill with small expense. The tailings from the concentrators do not need roasting, so that this great expense is saved, as well as the cost of the furnaces.

In some localities, ore worth only $6 a ton, can be made to pay by this method, while $30 ore would not pay by the old method of dry crushing, chloridizing, etc.

It is very important that the concentration is made before the amalgamation, for several reasons. The tailings from the concentrator contain no base mineral to trouble amalgamation or cause loss of quicksilver, and the Boss continuous process of pan amalgamation can be used with advantage and economy. If amalgamation should be used before concentration, the sulphurets are ground, and a large part is thereby made so fine that it cannot be saved on any concentrator; too much water, also, is with

the tailings, and there is an uneven discharge from the settlers and agitators.

After advocating this method for several years, the writer at last succeeded in having it adopted five years ago by Mr. Randolph, acting for Mr. Alexander R. Shepherd, in the mines of Batopilas (Chihuahua, Mexico), and it is in successful operation there to-day. It is now used also at several mines in the United States.

The Frue vanner is familiar to thousands of mining men. The accompanying cut shows it in perspective, as manufactured several years ago.

Since then many modifications and improvements have been made, but it is in the main as represented, and consists of an endless traveling rubber belt, with raised sides, moving slowly up hill, forming an inclined table (about inch to the foot being the grade, subject to change according to the ore), and having a short lateral motion of 1 inch, given by a crank shaft running from 180 to 200 revolutions a minute.