Mix the flux with the sample and put it in an iron crucible, stir it with an iron rod during the latter part of the process; in about five minutes, in a brisk heat, the sample will be down, provided the crucible was red-hot when the assay was thrown in, which should always be the case. If the sample, to be tried, weighs four ounces, the proportionate quantity of flux must be added, agreeably with the above statement. It may be discovered when the sample is ready, by the grating of the rod against the bottom of the crucible in stirring—it should then be immediately taken out and poured. The metal will separate clean from the slag in a good assay. To assay lead ore for discovering the quantity or proportion of silver it contains, the foregoing method must first be used, and the assay then tested precisely the same way as described for refining a silver sample, page 112. The lead will go off in vapor, and the silver remain in the test. If the ore contains a large proportion of iron, add more culm*; when the sample is properly down, or flowed, the surface of the assay in the crucible will be perfectly smooth and motionless; in a strong heat this will occur in about twelve minutes. When taken out of the fire, stir it well with an iron rod before you pour it; afterwards scrape the crucible, pulverize the scrapings in a mortar, and then van or wash them on a shovel. The prillion of a standard sample will not exceed 2 in 20. The criterion for the lump is its possessing a malleable quality, or bending to the hammer without breaking. Grain tin may be treated in every respect as the above, except in the subsequent addition of culm, which will not be required. METHOD OF DISCOVERING THE PROPORTION OF SILVER CONTAINED IN COPPER ORE. Sample One ounce. FLUX. 1 ladle red tartar. 1 ditto nitre. ditto lime. ditto borax. 1 ditto fluor. 1 ditto red lead. * If the sample is very stubborn, add a small quantity of pulverized fluor with the culm. Well mixed with the ore and melted in a wrought iron crucible,* about eight minutes, in a brisk heat, will be sufficient; the last five minutes the assay should be incessantly stirred with an iron rod: pour the sample and cool it, then break out the lump, and test it in the usual way. REMARKS. Soon as the assay begins to flow, the lead, by the power of affinity, will presently attract the silver, or the silver, by the same law, will attach itself to the lead, and this being effected, it only requires the process of refining, or burning off the inferior metals, to find the produce. * If a stone crucible be used, one ounce of iron must be added to the flux. |