To estimate how much silver is present in galena, the student has already assayed this ore for lead, and by cupelling the buttons so obtained he will obtain some idea as to the silver contents of the ore; but to obtain accurate results the ore must be specially treated either by crucible assay or by scorification. The student is advised to run four assays by the one method and four by the other on the same sample and compare the results.

(1) The Crucible Assay.

The principles of this method have already been discussed. Nails are used as before, and sufficient litharge is added to give a lead button of about 15 gm.

Apparatus and Reagents. -As before.
Details of the Operation.—Weigh out four charges of sampled galena (80 sieve) and fluxes, etc. as follows :—

If the ore contains little SiO2 add some clean sand. Fuse as usual. Cupel one of the buttons. Then make two checks with the quantity of silver thus found and the amount of lead in the buttons. Cupel these checks and the other three buttons as before. Note the results.

Calculation.—Suppose the heads weigh

Average of checks, .00525.
Loss, 0.0054 – 0.00525 = .00015.
Average of assays, .0054.
Corrected average, .0054 + .00015 = .00555 gm.
Calculate oz., dwt., grs. as usual.

Note.—These figures are purely imaginary, and simply show the method of calculation. Checks are only necessary where a high degree of accuracy is required.