Magnesia Cupels Crucibles For Gold Melting
Professional megnesia cupels manufacturer and factory . Stable quality and good prices . Can produce and customize according customers' drawings It is necessary in the case of magnesia cupels to employ a slightly higher temperature during the cupellation and to raise the temperature towards the end of the operation.
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It is necessary in the case of magnesia cupels to employ a slightly higher temperature during the cupellation and to raise the temperature towards the end of the operation.
The difference between the temperatures of the lead during cupellation on magnesia and on bone-ash cupels, which can be noticed by observation, is much more marked at the beginning of the cupellation, and, in fact, is hardly discernible at the very end of the operation.
It will be noted also that magnesia cupels retain heat longer than bone-ash cupels, consequently silver beads take longer to solidify and to spit on magnesia than on bone-ash cupels, after being withdrawn from the same muffle temperature. Silver beadsare also much less liable to spit on magnesia than on bone-ash cupels and the nature of the spit is different in the two cases, the spit in the former case generally taking the form of a frosty appearance only instead of the well-known "vegetation" obtained with bone-ash. These important differences in the properties of magnesia and bone-ash cupels are not always recognised by assayers.
An assayer, when asked to test magnesia cupels, usually puts half a dozen in the muffle with half a dozen bone-ash and cupels under conditions suitable for the bone-ash, with the result that he forms an unfavourable opinion of the magnesia cupels. When using magnesia cupels under these conditions the lead is very liable to "freeze" and the results are unsatisfactory; but if the proper conditions for magnesia cupels are employed, the results are quite as satisfactory as those obtained with bone-ash. Although a somewhat higher temperature is required for cupellation on magnesia cupels, the tendency is to have a very much higher temperature than is necessary, in order to make the cupelling lead look like that on bone-ash cupels; and this is a great mistake, whereby one of the most important advantages of the magnesia cupels is lost. The loss of silver due to absorption is usually less with magnesia than with bone-ash cupels.