Take 30 grammes of sulphide ore on a vanning plaque. Add 100 cc. water and a few drops of sulphuric acid. Subject the ore to the same manipulation as in the case of the De Bavay and a similar result will be produced, but much less float material will be secured. No amount of patience will serve, however, to produce a clean tailing. This test serves merely to show the principle on which this particular process works.

TEST FOR ELMORE PROCESS.

What is known as the old El more process may be tried in a glass jar of about 1,000 cc. capacity. What is known as a Mason fruitjar with a screw-top is the best apparatus for this trial. Place in the jar 300 cc. water, 100 gm. sulphide ore, and stir slightly to make a uniform pulp ; add half cc. strong sulphuric acid and 200 cc. thick oil, such as the thick tarry residue of petroleum or a cylinder-oil. Screw on the top of the jar and turn it end-for-end about 20 times, and set aside to settle for a few minutes. The contents of the jar will settle into layers ; at the bottom a layer of sand mixed with some sulphides ; next above will be a layer of muddy water, and above that again will be a layer of oil containing most of the sulphides (the amount depending on the success of the manoeuvre) and some gangue. The oil layer may be removed by adding more water carefully beneath the oil through a tube, and after the oil and sulphides have been removed the sulphides can be separated from the oil by heat and gentle stirring, when the sulphides will settle to the bottom.

The new vacuum process is more difficult to test in a small way so as to produce a satisfactory result. Probably the best method is as follows : Take a large-mouthed 300 cc. bottle, and fit a stopper with a tube to be attached to a laboratory suction-pump. Put into the bottle 30 gm. sulphide ore, 100 gm. water, one-fifth cc. Texas or California fuel-oil, and one-fifth cc. H2SO4 . Stir with a glass rod until a uniform pulp is produced, but do not beat any air into the pulp. Place the stopper in the bottle and attach to the suction-pump. Start the pump, and gently shake the bottle to keep the ore stirred a little. As the vacuum is produced the sulphides should begin to rise to the surface and form a layer of froth.

MECHANICAL AGITATION.

A simple laboratory experiment will give a clear idea of the efficiency of this method of providing gas bubbles for the purpose of flotation. Take in one hand a test-tube half full of distilled or ordinary water. In the other hand take a test-tube of distilled or ordinary water, to which has been added the smallest possible drop of any one of the following substances : Oleic acid, kerosene, amyl alcohol, any of the essential oils, camphor, or alcohol. Taking one of the above test-tubes in each hand, shake them violently at the same time and to the same extent. The water in the test-tube that had the drop of foreign substance added to it will, upon ceasing the agitation, be white with occluded air-bubbles of small size, and, depending on the substance used, these bubbles and the milky appearance will last for some time. The water in the other test-tube will, however, show no such appearance ; the water is as clear and unclouded in appearance as before shaking. An interesting series of tests can be made in this way, in which the time factor for complete clearing away of the milkiness can be observed. This series of tests will show that those substances which produce the best and the most persistent milkiness are in many instances the best materials to use in flotation processes. There are some remarkable exceptions to this rule, however, and some of the worst substances that can adventitiously be introduced into flotation-concentration work, as it is understood at present, are excellent producers of air-occlusion.

DELETERIOUS SUBSTANCES.

A beneficial study can be made of substances deleterious to mineral-froth formation. Having performed an experiment as above described to the point of having secured a froth of, say, one inch depth, one cubic centimetre of a solution of saponin, of a strength of one of saponin to one million of water is added, and then the agitation is started. It will be observed that the froth will have completely disappeared, and cannot again be reproduced. Probably one pound of saponin introduced into the operations of the largest oil-and-gas flotation plant in the world would completely suspend all useful results for a week unless all traces of the saponin were completely removed by complete rejection of all the water and ore that had become contaminated with saponin, and the plant would probably require a thorough scrubbing with clean water besides. Many other substances have the same effect (though not so pronounced for the small amounts used) ; among them are glue, starch, flour, tannin, and ox-gall. On one occasion R. Oilman Brown, consulting engineer to a mining company using the Elmore process, described a peculiar aberration of the process. On a certain day the process discontinued working for no apparent reason, and it seemed impossible to ascertain the trouble. No concentrate was produced for several shifts. He investigated to determine whether the water could contain anything deleterious, and noted that these erratic results had begun after they had changed from the ordinary brook water, which had become exhausted in the dry season, to water that had been stored in a series of small lakes and ponds in a peaty marsh. He found that there was probably enough tannin or analogous compound in the marsh water to destroy flotation, especially if the water was brown. The water was at once changed, and no further trouble ensued.

PROBLEMS SUGGESTED FOR RESEARCH.

There are a number of problems, some already mentioned, that will repay scientific investigation. A few are here mentioned :

What is the significance of the hysteresis range in the contact angle between the rising and falling meniscus ?

What is the real function of acid in flotation processes ? Can a feasible scheme of flotation treatment be devised for carbonate ores ?

Can a non-acid flotation treatment be devised ?

What is the significance of the fact that a too strong acid medium in oil-and-gas flotation methods is fatal to good work ?

Why are some of the substances that produce good air- occlusion bad flotation-concentration reagents ?

Why will air not replace carbonic acid gas in the Potter process,, all other conditions being equal ?

What is a froth ?

Would some method of producing coagulation without the aid of acid and oil enable one to introduce directly the gas-film adhesion- factor, and so secure flotation without oil or acid ?