Show METHOD OF ASSAYING GOLD RIDE rade ORES mining men in certain districts of the united states will be interested in bulletin no of the united states geological survey in which the subject of inquiry is the accuracy of the crucible assay method for telluride gold ores the main point definitely established is the fact that the doubts which have been entertained as to the accuracy of the dry method are not well founded it is clearly determined that the fire a assay by crucible for gold telluride ores gives results which are quite equal to those obtained by the wet method provided due corrections are made for slag and cupel losses the gold loss in the slag is very small but the cupel losses are very appreciable the loss of gold by volatilization is generally slight as compared with that by absorption at a temperature which allows the formation of abundant feather the volatilization is negligible or is perhaps compensated by retention of lead the case is otherwise however at high temperatures as the volatilization may then average one half of that by absorption in the case of a alloy the loss of gold by absorption is very important and is influenced far more than is generally supposed by slight changes in temperature it is greater with pure gold and alloys poor in silver than with alloys rich in silver the experiments of W F hillebrand and E T allen alien the authors of the bulletin failed absolutely to show the need for a higher temperature at the end of with gold beads than with those of silver the most exact results were obtained when feather was still abundant at the time of brightening furthermore it is altogether unnecessary to have gold beads in the muffle for some some time after brightening in order to remove the last of the lead for there is no loss in weight from so doing but if anything a very slight tendency to increase the results on absorption as influenced fluen ced by the amount of lead used in were inconclusive the error caused by the retention of lead in the beads is serious if the results of two careful tests are to be depended on which show and per cent of lead the amount of this retention is not lessened by leaving the beads in the muffle for some time after brightening silver can be completely extracted from alloys by nitric acid but more than two repetitions of the acid treatment and subsequent washing are called for if any certainty of complete extraction is to be expected tests made with mixtures of pure nitrous and nitric acids show that the solvent action of the nitric acid is so slight if indeed there is any at all that it need not be considered as a possible disturbing factor in parting it was similarly shown that 4 the losses in parting with pure nitric acid whether traces of gold really dissolve or riot may be ignored in an ore assay at least this bulletin which is entitled comparison of a wet and crucible fire methods for the assay of gold telluride ores with notes on the errors occurring in the operations of fire assay and parting is among the surveys free publications it may be obtained en application to the director of the united states geological survey washington D C |