The results of tests 6 to 10 show plainly that treatment of the dry ore with the dry gas, followed by flotation in an acidified solu*tion, gives much cleaner concentrates and better extractions than flotation in a neutral pulp. Less iron was found in the concentrates, and it was noticed that on addition of the acid solution to the pulp in the flotation machine hydrogen sulphide gas was always evolved in considerable quantity. This result is not surprising, as iron sulphide will react with dilute acid solutions, whereas lead sulphide is more stable. The presence of the hydrogen sulphide in the pulp did not seem to affect the flotation of the artificial sulphide, although flotation men often say that the flotation of the natural sulphides is deleteriously affected by hydrogen sulphide. The results of tests 11 and 12, with a different oil, were about the same as those of the previous tests. It can be seen that 4 to 8 hours' treatment of the dry ore with hydrogen sulphide gas, followed by flotation in an acid solution, are the necessary conditions for good extractions on this ore and that neutral flotation is not satisfactory.

Tests 14 to 21 were with different flotation oils and no acid, to determine whether any of these oils would give clean concentrates and good extractions without the addition of acid. It can be seen that none were satisfactory. The pine oil and the cedar oil were the best ones.

The results of test 23, compared with those of test 22, show the effect of extremely fine grinding as compared with ordinary grinding for flotation. Most of these tests were made on material ground to pass a 0.25 mm. (60-mesh) sieve, whereas test 23 was made with material which had been ground in an Abbé pebble mill to an impalpable powder before sulphidizing. The extraction of lead was much better with the finely-ground material, although still far from satisfactory. When acid was added, in tests 6 to 10, it is probable that the large amount of acid used up by the ore helped to disintegrate the ore in the same way as fine grinding, allowing more particles of lead carbonate to be acted on.

The last three tests of the series show the effects of increasing the amount of acid used during flotation, after 2 hours of sulphidizing. The higher extractions obtained by using the larger amounts of acid is plainly evident.

In similar tests (Table 37, p. 90) of material from the Chief Consolidated mine of the Tintic district, practically the same results were obtained. The first three tests showed that increasing the proportion of acid used in the flotation solution increased the extractions of lead and of silver. In the second series, tests 4 to 7, the effect of using different proportions of the same flotation oil was tested. Test 7 shows plainly the effects of "over-oiling." The third set, tests 8 to 12, to

find the effect of time of treatment with hydrogen sulphide showed that this ore required about two hours' treatment. The last three tests were made to determine whether the froth coming off at the beginning of the test was any richer than that coming off later in the test. The results show that it was the further addition of acid that affected the tenor of the froth concentrate, and not the time at which it was sampled.

The silver extractions from the Chief Consolidated ore by dry sulphidizing and flotation were always higher than the corresponding lead extractions, whereas with the May Day ore the reverse

was true.

The results of 18 tests of the carbonate shipping ore from the Daly Judge mine of Park City, Utah, are shown in Table 38, page 91. This ore resisted all efforts at concentration by this method until an excessive amount of sulphuric acid, 368 pounds per ton of ore (see test 9), was used in the flotation.

SUMMARY OF CONCLUSIONS FROM RESULTS OF DRY SULPHIDIZING.

The conclusions from the tests of dry sulphidizing of lead carbonate ores with hydrogen sulphide gas, followed by flotation of the artificial sulphides, may be summarized as follows:

1. The ore must be treated with the hydrogen sulphide gas 2 to 8 hours, although the reaction takes place quickly and with the development of considerable heat. A tumbling barrel is best suited for applying the gas.

2. A considerable excess of hydrogen sulphide is consumed. The gas seems to penetrate to the centers of the ore particles, and some of the oxidized iron minerals are likewise sulphidized.

3. Silver minerals associated with the lead carbonate, or separate from the lead carbonate, usually float when the ore is treated in the flotation machine.

4. Satisfactory extractions and satisfactory grades of flotation concentrate are obtained only when a considerable excess of sulphuric acid is applied to the sulphidized ore while in the flotation machine. The greater proportion of the artificial iron sulphide formed during sulphidizing is acted on by the acid, with generation of hydrogen sulphide gas in the flotation pulp. This gas does not seem to affect deleteriously the flotation of the artificial sulphides.

5. In view of the fact that so much hydrogen sulphide and sulphuric acid are necessary in the treatment of the ores tested by this method the writers do not believe that this phase of sulphidizing and flotation would be a commercial success with average ore.

SODIUM SULPHIDE FOR SULPHIDIZING.

SULPHIDE COMPOUNDS AVAILABLE FOR COMMERCIAL USE.

There are three sulphide compounds of sodium that give promise of commercial application in sulphidizing ores-the normal sulphide, Na,S; the polysulphides, Na,S, and Na,S; and the sulph-hydrate, NaSH.

The ordinary commercial method of preparing normal sodium sulphide is from the sulphate of sodium by reduction with carbon, the reaction being as follows:

Na2SO4+4C=Na2S+4CO

The freshly reduced chemical is infusible (melting point, approximately 2,000° C.), and hence is a porous cinder when drawn from the furnace. This product is subject to spontaneous combustion in air, and is usually wet with enough water to form one of the hydrates of sodium sulphide. Two commercial grades can be bought, the "60 per cent" and the "30 per cent," depending upon the proportion of water of crystallization. Probably the largest use of sodium sulphide at present time is in removing hair from hides in tanneries. It can usually be bought for $40 to $30 or less per ton at the factories, but owing to the abnormal conditions since 1914, its price has risen to $80 to $100 a ton.

The polysulphides of sodium can be made by boiling powdered sulphur in solutions of caustic soda. Most of the sulphur combines to form NaS and Na,S,, although some thiosulphates, thionates, etc., are formed. This type of solution seems to be more sluggish than the normal sulphide of sodium and probably only one of the sulphur atoms in the molecule functions as a sulphide ion, the others being released as colloidal sulphur.

The sulph-hydrate of sodium, NaSH, is formed from the normal sulphide in solution by hydrolysis and seems to be the most active of these three compounds in the sulphidizing of lead carbonate ores. It can be prepared from the normal sulphide by treating the sulphide with hydrogen sulphide gas, the reaction being:

Na2S+H2S=2 NaSH.

This would make it more expensive than the normal sulphide when prepared in the pure state. The hydrolysis of the normal sulphide gives sodium hydrate as well as the sulph-hydrate, as follows

NaS+H2O NaSH+NaOH

The presence of this sodium hydroxide may explain why pure sulphhydrate of sodium will seemingly be more efficient in its action in sulphidizing a lead carbonate ore, although the explanation is not