THE cyanide process is of sufficient importance to Australia to justify the piecing together of some of the available information so as render its conduct intelligible, by placing in the hands of those interested, means of following the progress from the vat to beyond the zinc boxes. The means must necessarily be chemical in nature, to determine the adaptability of the ore for treatment or the cause or causes which militate against success; for it must be remembered that if the energy of the cyanide be expended in dissolving base metals, the yield of the precious ores must suffer and the cost be enormously increased.It is, therefore, of the first importance to determine by actual experiment the fitness or unfitness of an ore for cyanide treatment. To this end, an assay of the ore must first be undertaken, to determine its actual contents of gold and silver.The ore is afterwards treated with definite quantities of definite strengths of cyanide solution, ranging from say 0.1 to 0.75 per cent. of KCy. These strengths are not absolute and may be varied as results and experience justify. The method of proceeding is as follows :-Any convenient quantity of ore is placed in a wide-mouthed bottle of suitable capacity with a measured quantity of the cyanide solution; after 48 to 96 hours the solution is filtered, and the ore washed with water until the original bulk of solution is reached ; a fractional part of the solution is taken and tested for loss of cyanide ; the tailings are dried, powdered finer if necessary, and assayed, the difference between the original assay and the assay of the tailings gives the percentage of extraction. It is obvious that many tests, with varying strengths of solution, can be carried out at the same time.