Fire Assaying
Fire Assaying , in use for thousands of years, still stands the test of time. The following summary of the process is derived principally from "strength", by Jim Steinberg in Mining Artifact Collector. The article was written from a historical point of view, but the process is the same as the dosage fire today, except for the use of electronic scales, sprayers, etc..
Webster in the test is defined as follows: in metallurgy, determining the amount of a particular metal in an ore or alloy, especially the determination of the amount of gold or silver coins or bullion.
Although the most common definitions of the word test run around the determination of gold or silver in the ore and alloys, the assay itself is a much more extensive that involves the quantitative analysis of organic and inorganic chemicals. The main interest of this article is the analysis of metal ores. Because this is a very broad topic that has filled many books, highlights the fire assay process slagging gold in the samples will be summarized here.
Initially, the sample should be pulverized so that it can be tested. This powder is often called "dough" and scales to weigh what is called "scales pasta." Begins The tester run the sample in a mill. Along with many crushers, fine output is adjustable. The sample is not yet sufficiently well after initial grinding, so that the tester then puts on a "buck board" for additional spraying under a muller rubbing the material in a more fine movement with slip. Hard samples are finer with a device called a "rocker" which uses a heavier weight of the powdered sample. Testers are a smaller volume of work can use a mortar and pestle iron, even if it requires a lot more effort.
Such as spraying of the product of the ore sample, and the tester mixture divides the sample into smaller and smaller until it reduces the amount of sample to be that effectively treat called "splitting". This can be done manually or by using devices designed to facilitate the sampling process. This is done to ensure consistency in the sample and to increase the accuracy of the assay to be performed.
When the sample was sufficiently pulverized it must be run through sieve size. Material which does not pass through to be ground until the entire sample passes through the screen, called "screening". Which is passed through the sieve must then be thoroughly mixed and then stored in a labeled container. The contents of these containers should not be shaken or stirred, as this may cause the material to begin with stratification according to their masses and upset the accuracy of the process.
Various parts of the vessel, called "cone and quartering" selected parts of the sample are removed and weighed. The weighed sample is then placed in a scorifier, a dish that can withstand the heat of the oven testers. Litharge with sample (a form of lead), various chemicals which help enable metal in the sample to separate the slag is included.
This blend is roasted in the oven at the tester, called an "oven test" until the molten slag completely covers the head pearl formed in the scorifier.
The sample in the scorifier then poured into the mold cup of slagging. Here it is allowed to remain until cold. Once cold, the sample is removed from the mold. Is cone-shaped, with the metal at the tip of the cone and the slag forming the bottom. The piece of metal or a button of lead is detached from the slag. This button can then be hammered into a cube without sharp corners. The button is placed in a "cup" of appropriate size which is then placed in the oven. Cups are made of a material called bone ash. When it came to the heat, the button is placed in the cup. In this process lead and other impurities within the key are both driven and oxidized in the material itself of the cup. A good cup is able to absorb its weight in litharge (lead in the sample). The molten metal in the cup and there will become smaller as the process goes.
Towards the end of the process, the surface tension of the metal will result in the form of a bead. The heel does not seem to be moving fast and when the process is complete, release optical energy can sometimes be seen as a "flash" or "Blick". At this stage, the cupelation is finished and the cup with the ball can be removed from the oven.
Now the ball is removed from the cup. The composition of the pearl should now be gold and silver. The bead is weighed into a ladder type made specifically for this task called "scale button." Scales buttons, because they measure something so small, must be very precise and are always closed, while scales of analysis or the pulp does not always require pregnant. pearl weighing showed how metal is there, but did not say how much gold and how much money.
The next step assay is called "separation." In this step the gold and silver are separated from each other by a solution. Weighing heel is flattened, placed in a porcelain dish and treated with a solution of water and nitric acid. Once the reaction begins, the capsule is heated. Silver bead in the shape of a solution of silver nitrate is washed thoroughly until the gold, if any, remains. This is gently dried in porcelain dish, and then deleted.
The final sample of gold is again weighed in the balance knob, unless it is too small to be weighed, in which case it is simply described as a "trace" or "color". From the mass of the bead the tester calculates the value of the ore of gold and silver per ton of ore. The tester may use a particular set of weight when weighing tons determination of gold more easily calculate the test value of the ore.
In Summary, Fire Assaying is a three-step process
1. Fusion - The sample is mixed with the stream, and then heated at 1850A ° Fahrenheit. A slag containing the undesirable elements and a four-lead containing silver and gold are formed.
2. Cupeling - Knob lead is heated and oxidized in a cup of bone ash which adsorbs lead oxide, leaving a noble metal ball in the cup.
3. Cutting and weighing - In this part of the process, gold is separated from the money. Two weighing steps are involved.
Discussion of Fire Assaying's Purported Problems
Fire Assaying is a series of chemical steps that takes advantage of the chemical behavior of the precious metal. Those who claim they have no measurable fire or say they have a chemical that does not behave like gold. The arguments used to explain why fire assay is not applicable t them "colloidal" or "Micron" or generally fall into one of three categories described below.
"The particles are so small that they vaporize and are therefore not in the button.
1850 ° is less than the melting point of gold. Even if the temperature exceeds 1850 ° the vapor pressure of gold is low. Very little loss. H2O, for example, has a vapor pressure of 6 orders of magnitude higher.
"Small particles of gold float on the surface of the water so that they float on the slag."
This ignores the process continues. It does not depend on gravity. The PbO2, Pb now, dissolves gold. It is the Pb collects at the bottom of the crucible.
"Intervening elements hide the gold medal."
Mint of London published a dosage of 1000 mg of tellurium, 1 g Au, Pb and 25 g skipped the step of melting! Even if "worse" they could do was to lose almost half of gold. These conditions are very unlikely in a rock sample. What metals of the platinum group? These, when present, with a ratio of gold in the bead.
Conclusion
Fire Assaying , in use for thousands of years, still stands the test of time.
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