SODIUM AMALGAMATION.

Southland Times, Issue 573, 3 October 1866, Page 3

SODIUM AMALGAMATION.

WHY DOES SODIUM ASSIST THE AMALGAMATION 01? METALS ? ; Some time since, and before I had heard of the use of sodium as an assistant in amalgamating metals, I prepared the ] result of the following experiment for publication. Circumstances delayed it, but I now give it to the interested for what it is worth. Haying given my views to several practical men in this city, they tell me that the theory explains many things which they have met in their experience that were incomprehensible to them, and they have urged me to make it public. The expeeimejtt. — Take a clean tumbler and fill it about two-thirds full of clear water ; then drop a little finely pulverised metallic powder upon the water. Grold dust or bronze (such as printers use and neai'ly every printer has it), or silver powder will answer, provided it be sufficiently fine. Then stir it smartly with the -handle of a spoon or the blade of a knife. It will be seen that the powder will not sink in the water, but, on the contrary, the more it is stirred the more obstinately it keeps at the top. When you have sufiiciently demonstrated to your satisfaction the almost impossibility of sinking the metal, which, being heavier than the water, by the laws of gravity, should (sink, drop in the tumbler a little

caustic potash or soda, and stir a little j the powder will then be seen to leave the top, and in a short time settle at the bottom of the water. The Cause op the Metal Floating-. — Atmospheric air adheres with great tenacity to any highly polished surface, and is very difficult to displace. It preserves a knife-blade by preventing the moisture from getting to it to oxidise it. Dip a razor or a knife -blade into water, and drawing it out you will find that it has not been wet — a 'film of air interposed between it and the water. So with each particle of dust which you placed on the water in the tumbler. Notwithstanding its being so exceedingly fine, it is _ surrounded with a layer of atmospheric air as thick as that on" the surface of a knifeblade. The particle being round and smooth, no mechanical means which you can use will displace the air so that the water can get to it, and the air being lighter than the water, acts as a balloon to sustain the piece of metal, and as soon as you let it alone it will arise to the sur- 1 face. How it is that the alkali makes the ! air let go its hold on the metal I do not know. The experiment shows that it does so, and the metal sinks. Application" op this Treatment to Amalgamating the Impalpable Gold j Dust is Quartz Rock, and its Theory. — Suppose every particle of gold dust iv quartz rock to be as fine as the dust j with which the experiment is made (and much of it is finer), very little of it would have its film of air displaced by the mechanical operation of crushing, although on account of much of it clinging to the particles of quartz it would not float ; part of it would sink to the bottom, part would remain floating between the bottom and the surface of the water, the film of air and the quarfcz dust fighting for the mastery, the air trying to take it to the top, ! and the quartz trying to pull it down. As long as the particle of gold or silver remains covered with the air, the mercury cannot come in contact with it any more than can the water. The mercury to take it up must come in contact with the naked gold, and not with the gold protectedby a mantle of atmospheric air. Therefore, in order to the effectual amalgamating of gold or silver dust from quartz rock some means must be used to disperse the air surrounding the particles of dust. Heat will do this partially, but caustic potash or soda will do it effectually. It also acts as a deoxydising agent — that is, if the oxide of some base metal should be in contact with the gold, it will remove it, or clean the gold, and it will keep the mercury clean. About lib of caustic potash or soda will remove the air from metal that is immersed in five gallons of water. Does not this explain the cause of the advantage derived from the use of sodium ? If this be the true theory," whence the necessity of using the expensive metal itself ? 'It cannot be denied that the sodium is oxydised and becomes soda, and is dissolved in the water in the pan. When that takes place, and not until then, does the sodium produce the beneficial results. I am aware that alkalies have been used in amalgamating pans with partial success. "But have they been used "intelligently ? Common potash, or soda of commerce, in the best state in which you can buy it, is composed of 40 or 50 per cent, of carbonate. In transporting it to the mines, and from exposure to the air when opened, a much larger per centage is turned into carbonate, and in that state is of little use to disperse the atmospheric air. To be effectual for this purpose, it must be nearly as caustic as possible. In regard to the electrical effect resulting from the use of alkalies in the amalgamating pans, my experience proves that it cannot be otherwise than highly beneficial. Zinc, lead, and antimony would be taken up in large quantities by a caustic alkaline solution when contained in an iron vessel. I have used, and for some purposes prefer to all others, especially for precipitating the reguline copper, a battery composed of iron and zinc in a solution of caustic potash. William Hilmer. — Mining and Scientific Press, £San Francisco.)