This excellent volumetric method commends itself as a means of estimating the fineness of silver—firstly, owing to the large number of possible impurities which do not affect its accuracy (these impurities include Cu—up to 70%— Au, Pb, Zn, Bi, Cd, Fe, Mn, Sb, and As) ; secondly, the method combines accuracy with speed.
The above impurities are the only ones likely to be present in the B. H. A. S. Pty, Ltd. refined silver, and, with the exception of Cu and Au, the others, if present at all, would be well under 0.1 parts per 1000.
Briefly stated, the method consists in the solution of the refined silver in HNO3, addition of ferric alum (indicator), and titration with an alkaline (either ammonium or potassium) thiocyanate solution until the brown ferric thiocyanate is formed, and gives a definite tint to the solution. The method is used at the Port Pirie smelters, and the outstanding feature in the method as there applied is the type of burette employed. This burette enables the operator to read 0.01 of a cc. with ease, whereas, with the ordinary burette fitted with a float, 0.05 of a cc., when a number of readings have to be taken, becomes ….Read more