Isfil+o
Supcriore di Samfd, /Coma (ltafy)
An analyst has often occasion to determine gold in milligram quantities: e.g., in therapeutic or metabolic products, in photomaterials, in minerals probably containing traces of Au (Cu-or Pb-minerals, which nearly always contain at least traces of noble metals). In this last case it is strictly necessary to know the Au content as exactly as possible, in order to determine whether, or not, its extraction is worth while.
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Determinations
of Au quantities of this order of magnitude exclude all methods1 based on the weighing of the tiny particle of gold obtained by the cupellation of a globule of the Pb-Au-alloy.
Although these methods give excellent results, they generally may be used only for quantities not smaller than IO mg. For this reason, consequently, in the case of poor minerals, it would be necessary to analyse a sample of many kilograms to obtain satisfactory results.
Many methods of analysis have been published in order to determine very small Au quantities, hence the description of a new method of separation and analysis of this element may appear superfluous. But a critical survey of the proposed methods shows that some of them, although suited to detect and determine very small quantities, down to about some hundredths of y, require an expensive equipment, not easily transportable : e.g., the spectrographical methods2 (which, therefore, are useless for rapid mining researches in sitzr), or the photometric and calorimetric determinations? by comparison with solutions of known Au content, which require the preparation of a number of solutions of accurately determined Au-concentration : these solutions, being commonly used at strong dilutions, are often unstable and furthermore the analyses made by the latter methods are often disturbed by the presence of other metals. Other methods require expensive reagents, e.g., the Au separation by means of Te as proposed by POLLARD~, and still others do not prove sufficiently accurate. For most rapid half-quantitative determinations the method proposed by WENGER and asso-ciatesG by means of spot tests is very interesting.
For these reasons it appeared convenient to study a very simple and at the same time rapid method which might be employed in mining researches in silu, References p. x36.