FURTHER TESTS ON OTHER PROCESSES.

The processes are so intimately related that it is difficult to give tests serving clea~ly to differentiate them. Laboratory tests to determine whether any result will be produced can be easily tried without any special apparatus.

TEST FOR POTTER PROCESS.

Take a 200 c.c. beaker and place therein 100 cc. of 3% H2SO4 solution. Place this in a water-bath, and raise the temperature to as near boiling point as possible. Stir into the solution gently 30 grammes of ore crushed to 5o-mesh. The froth composed of sulphides and CC>2 gas should form at once on the surface of the liquid if the ore is adapted to the process. If the ore contains no calcite or other carbonates, there will probably be no result. In the latter case, of course, a result can be secured by adding to the ore 3% of ground calcite before stirring it into the solution. The concentrate can be removed with a spoon.

The test-tube experiments that formed the basis of the Goyder & Laughton invention are interesting and instructive. Goyder observed that " when heating some Broken Hill sulphides* in a test-tube filled with dilute sulphuric acid, the bubbles, with their sulphide load, travelled to the surface broke, and then fell back again. By inclining the tube as in 2, Fig. 21, the sulphides rose and travelled up the smooth side of the tube until they met the surface, when, as before, the granule of sulphide fell off, but this time it fell vertically until it met the side of the tube, down which it glided. The inference was that if there was a pocket in the under-side of the sloping test-tube the sulphides should gather in the pocket." A special test-tube like 3, Fig. 21, is easily made, and a number of interesting experiments can be conducted by trials of different ores at varying temperatures and varying strengths of acid.

TEST FOR DELPRAT PROCESS.

The procedure in this case is identical with that above outlined for the Potter process, except that the solution is made from acid salt-cake. This obviously is only different from the preceding test in that, besides sulphuric acid, there is present in solution a portion of sodium sulphate. Most of the acid sodium sulphate on the market is made by mixing strong sulphuric acid and sodium sulphate in the proportion of about 7 of acid to 3 of sulphate. If there is no carbonate present in the ore, the same result will be secured and the same remedy found efficacious, as with the Potter process.

TEST FOR DE BAVAY PROCESS.

This process depends on a film of sulphides formed on the surface of water to effect a separation. Take 100 cc. of water, containing about 0.1% H2SO4 ; add to this 30 gm. sulphide ore crushed to 50-mesh ; add a few drops of petrol, and stir with glass rod for half-minute. Empty pulp on a vanning plaque, and gently rock the plaque so that the liquid alternately covers and uncovers the ore. As these little waves cover and uncover the ore the sulphides are picked up, and float upon the surface. With patience a clean tailing can be produced.