works, if they can be made to pay the cost of treatment. In some cases, as for instance at Zell, spoken of in the beginning of this paper, the ore, worth only $2 and less a ton, is unable to bear any expense but amalgamation, and it could not bear even this were it not for the fact that its gold is fine and contains little silver.

There is a difficulty in treating gold-ores with mercury, in the explanation of which we may perhaps account for the trouble experienced in Colorado. Native gold is rarely or never pure. It is alloyed with silver, which has a specific gravity of 10.56. An alloy of the two metals, therefore, has a specific gravity between 19.33 and 10.56, depending upon the proportion of the two metals. With gold 35 and silver 65 parts, the specific gravity of the alloy is about the same as that of mercury, and it cannot sink in that fluid; that is, it will not "amalgamate." The question is then, do the ores of Colorado contain more than 65 of silver to 35 of gold? Let us calculate the assays given above, and we have the following table, the 35 gold and 65 silver being taken as the normal alloy :

These are fair specimens of Colorado ores, and we see that the gold they yield will not sink in mercury. And yet those who adhere to the milling process say it does amalgamate. That is true to a certain extent. Part of it amalgamates, and in that respect it exactly resembles the Lend ores, in which part of the gold amalgamates and part will not. The explanation is that Colorado ore contains 1 free gold, 2 gold alloyed with silver, and perhaps 3 silver not alloyed with gold. Mr. Hague thinks that the mills extract about 55 per cent. of the gold in the first operation, and 15 per cent. more by a repetition. If we construct a table for Colorado ores such as I have given for the Lend ores we shall have something like this:

Thus we see from this table that of the above Colorado ores only 57.7 per cent. of the gold and 2.9 per cent of the silver is extracted by amalgamation. These proportions are, of course, hypothetical; but we may regard them as near the truth.

The Burroughs milling ore contains 1 ounce gold and 4.5 ounces silver. At the same rate of yield the proportions would be:

The value of the Burroughs milling ore is therefore $12.15 in gold that will amalgamate, and $14.42 alloy that will not amalgamate; or 45.5 of the former and 54.5 of the latter in 100 of value. Thus we see that to its great fault of not extracting more than 70 per cent, of the gold amalgamation adds the loss of nearly all the silver; so that the real saving, even by the best work, including a repetition of the milling, is under 60 per cent. of the value.

I judge that the Colorado ores contain silver not alloyed with gold, from the fact that, although a great deal of the gold has been removed by the mercury, which leaves nearly all the silver, the tailings show no proportionate increase of silver to gold. Silver has therefore been removed as well as gold, and in about the same proportion. In three tables, giving assays of tailings, which Mr. Hague publishes, we have the following proportions:

Compared with 23 gold and 77 silver, which is the average of the ores, these figures show that both silver and gold have disappeared, and about equally, in the process of milling. Though hardly necessary, I will say that nothing in the bullion explains this fact, for that is composed of 845 gold to 155 silver, on an average. The cause of this loss is undoubtedly defective concentration. The ores probably contain proper silverminerals, which are very brittle, reduce to a fine powder in crushing, and are easily carried off on the stream. It may be, too, that the small proportion of galena found in the ore is highly argentiferous, but contains little or no gold. This would partly account for the loss of silver, for when galena is stamped through a mesh of 25 to the inch, and then concentrated in a buddle we may be sure that very much of it goes in the water.

It must not be supposed that the above table, in which the gold of Colorado ores is divided into free gold and auriferous silver, is correct in its proportions. In the ore there are probably an unknown number of distinct alloys, and the gold we obtain comes (1) from fine gold, (2) from those alloys which contain more than 35 per cent. of gold. We know from the bullion that about one-sixth of the amounts which I have put down to fine gold is really silver. The great fact remains that, if

we accept the Austrian explanation, the Colorado ores ought not to amalgamate well; and when we examine the results of practice, we find that they do not. This may be only a coincidence, but if so, it is one sufficiently remarkable to make us reconsider the determination to force those ores to amalgamate, to which we have so stubbornly held for ten or twelve years.

Before leaving this subject it may be well to inquire how it is that gold is amalgamated on copper plates in Colorado, where, of course, there is no mercury-bath. All experimenters, I believe, agree that more than half the amalgam obtained is made in the battery, and the plates placed there collect the larger part of the gold-sand. Probably still more comes in contact with the mercury within the battery, and issues from the screen with the surfaces of the gold-particles covered with mercury, or a true amalgam of gold and mercury, which gives them the power of adhering to the coat of amalgam on the plates. One of the signs for which the amalgamator constantly watches is, in fact, the appearance of hard, dry particles of " amalgam," which he knows by experience are apt to pass over the plate without adhering. He adds mercury, to the battery and the particles then come out with a softer coat and readily fix themselves to the plate. The success of the plates as amalgamators is also greater when there is a thick coat of soft amalgam on them, and all these facts point to the supposition that the gold is retained on the plates by virtue of the cementing properties of the mercury with which it becomes covered in the battery.

Another method of amalgamating gold, in use in this country, is the Washoe pan-amalgamation. In the pans, it is well known, there is no bath of mercury, but this metal is distributed through the pulp in small drops, the object being to secure not only thorough contact of the mercury with the silver, but also to maintain this contact long enough to have chemical action set in.. To run sulphide or even chloride of silver over mercury, as gold is run over a bath of that metal in the Austrian mill, would not answer. But the Comstock ore contains gold as well as silver, and the Washoe secures a very good proportion of it; as much, probably, as any amalgamation will extract of gold that is not positively fine. The following results of numerous bullion assays taken from Mr. Hague's book represent in all 133,844 tons of third-class ore, and 5,105 tons of second-class ore: for third class, 32.4 gold and 67.6 silver; for second class, 36.7 gold and 63.3 silver. So that gold is really saved in the Washoe pans, and they seem to work, in fact, better than the Colorado mills, for they extract no less than 81.1 per cent. of the gold and 64.6 per cent. of the silver, estimated on the mill samples. How is it that gold can be taken up when the mercury is in fine drops all through the pulp, and there is no opportunity for its mechanical action as a fluid of medium density? Though no examination of this subject has been made, I have no doubt the bulk of the gold is obtained, either in the pan where the pulp is thinned, or in the settler where it undergoes still greater thinning, and the conditions are in fact extremely favorable for collecting the gold at the bottom, and entirely by mechanical means. There it meets with mercury and follows it in its subsequent movements. Undoubtedly some gold is taken up by the mercury while still distributed through the pulp, but the conditions under which mercury separates this metal from its ores teach us that this cannot be a very large proportion of the whole. It is, indeed, a very small proportion, and fortunately there is an analysis which proves this. In the chapter on the chemistry of the Washoe process we have the following analysis of some crystals of Washoe amalgam given:

Mercury..

Silver.

Gold...

75.04 24.18

.77

The proportions of silver-96.5 to gold-3.5, are here, it will be ob served, very different from those found in the bullion of the third-class ore spoken of above, and which was, silver 67.6, and gold 32.4.

In working the small pan used in making the experiments upon which the chapter upon the chemistry of the pan-process is based, it is to be noted that no such proportion of silver to gold was obtained as that which occurs in the regular returns of the Savage Company. In trying the first-class Savage ore, the bullion contained silver 934.7, to gold 49.5; or, in 100 parts, silver 94.9 and gold 5.1; and yet the yield of silver was only 32.55 per cent., while that of the gold was 70.6. Had the yield of silver equaled that of gold, the proportion of the latter would have been very much smaller. Probably in working in the large way gold collects in the bottom of the agitator and is taken up by the mercury of the next charge of pulp, a state of things that could not exist in the experiments, because the apparatus was there thoroughly cleaned after each pan.

CHAPTER XIII.

THE AMALGAMATION OF SILVER ORES IN PANS, WITH THE AID OF CHEMICALS.

The attention of the mining public has, within late years, been largely attracted to the existence of numerous veins and deposits of silver-ore, the beneficiation of which was, however, apparently impracticable, as the ores they furnish cannot be worked with any degree of success by the ordinary amalgamation-process, and are not sufficiently rich to bear the expense of roasting, even after the improved and cheaper methods now in vogue. An over-confidence in the adaptability of the ordinary Washoe process to the working of ores of the most different characters has led to numerous failures, while, on the other hand, the caution bred of experience causes many properties to lie idle which would prove remunerative under a method of treatment equal in thoroughness to the ordinary process, without greatly exceeding it in expense. The demand for such a process has within the last three years been practically filled, but the suspicion with which all innovations are regarded, and the uninvestigative spirit of the "practical" millman, have prevented this new method from being more generally known and adopted. The facts now set forth should demonstrate its usefulness beyond a question. A test of its merits can be readily made. Simple as it appears, it can be made to solve many metallurgical and financial problems in the way of working ores to a fair percentage of their value, and with profit, which hitherto have, by their apparent rebelliousness, proven only sources of loss.

The first successful attempt at amalgamating rebellious silver-minerals in pans, and without roasting, was made on the Comstock slimes. By far the greater portion of these slimes was in former years allowed to run to waste. This loss was probably looked upon as an evil unavoidable in wet-crushing mills, and was partially excused by the fact that not more than 35 per cent. of their gross value could be extracted by the then known methods of treatment. There was consequently but little inducement to millmen to save slimes assaying $40 per ton, or thereabout, as they could barely be worked to a profit. Thousands of tons were thus lost, which at the present day would yield an enormous fortune to their

owner.

Some three years ago a series of experiments were made, which clearly proved that these slimes could be worked to a high percentage at a cost which, though greater than that of ordinary milling, still left a good margin for profit. Mill-owners were induced to save and sell what they had hitherto allowed to run waste, and, shortly after, the working of slimes became a distinct feature of milling on the Comstock.

All this was effected simply by adapting to the Washoe pan-process certain features of the Mexican patio, namely, the use of sulphate of copper and salt in sufficient quantities to decompose the rebellious silverminerals and leave them in a favorable state for amalgamation. The successful application of these chemicals to the ordinary Washoe process was entirely novel. It is true that in former years many millmen had tried these chemicals among a host of others, but their experiments were invariably carried on with such a want of knowledge that failure was inevitable. Some used bluestone without salt, and others salt with