The following advantages are shown for the device

"From this test the following advantages are shown for the device: It permits an increase in load of grinding medium of 35 per cent, more than could be retained with the old open-mouth discharge under normal working conditions, thus subjecting a greater area of ore to attrition; it increases the effective discharge area of the outflowing pulp, as shown in the illustration; it permits free discharge of the product from the conical section of the ball mill where the relatively refractory oversize particles of ore are inclined to accumulate, due to the shorter radius of action, and thus retard the discharge of the fine product; it permits a continuous classification during discharge, separating the oversize, which is returned to the feed end or zone of maximum disintegration of the ball mill (about 10 per cent, of the discharge product is classified as oversize and thus returned to the zone of greatest efficiency for further disintegration) ; it also decreased the ball and pebble consumption, and the cost, including maintenance, is low about 0.00125 cts. per ton treated."

We have all noticed in the problem of settling sand or slime that a thick pulp such as that containing 32 to 38 per cent, moisture settles as a homogeneous mass with no segregation of heavy sulphides or sand, in fact at times the sulphides remain at or near the top, but that when this pulp is diluted with solution or water the sand and heavy minerals settle out leaving the slime alone in suspension. It is for this reason that we are able to agitate sand and slime if we keep the pulp thick, but immediately we thin out the pulp the sand settles and gives trouble. Taking for granted this fact, which I believe is beyond dispute, it occurred to me that advantage might be taken of this phenomena, at the discharge end of a tube mill to classify the pulp before it is discharged from the mill. If we diluted the pulp at the discharge end of the mill we might be able to cause a quick discharge of slime and the retention within the mill of the sand which on dilution of the thick pulp would sink and be further ground, its place being taken by the easily floated slime. This was tried with success, the preliminary experiments being in the nature of a trial but with no exact data for comparison. A further application of a stream of water or solution within a ball or tube mill is that the character and amount of grinding can be varied to suit the conditions of the after-treatment of the pulp. We know that economical grinding requires a thick pulp and also that a thick pulp promotes sliming so that when we require capacity and a granular product, which is obtained by using a dilute pulp we have two contrary conditions. This may be overcome in part, at least, by diluting the pulp within the mill at the point where sliming must be stopped. The idea is so easily carried out, simply by inserting a pipe in the discharge end of the mill at any distance within the mill, that all who read may try the experiment with little or no expense. The amount and character of the discharge is not governed entirely by the position of the water jet, but also by its volume, so that we have two adjustments to make, the position and amount of water added to the pulp within the mill.

It will be noticed in the Kirkland Lake experiment, Fig. 40, that there is a water jet inside the screen, this being the first printed application of the idea but the full significance of adding the water inside the mill is not indicated.