Where lead is present as phosphate (as in the case of pyromorphite), or mixed with phosphates (as sometimes happens), carbonate of soda is a suitable flux; but the phosphate of soda which is formed makes a thick tenacious slag, which is very apt to be carried out of the pot by the escaping gas. A wide-mouthed clay pot is taken and a little fluor spar added. For the assay of pyromorphite the following charge may be used:--Ore, 20 grams; "soda," 25 grams; tartar, 7 grams; and fluor spar, 5 grams; and 2 grams of borax as a cover. This will melt down in about ten minutes, and should be poured as soon as tranquil. WET ASSAY. In the case of galena the best method of getting the lead into solution is to treat with hydrochloric acid and zinc. Put 1 gram of the ore in an evaporating dish 4 inches across, and cover with 10 c.c. of dilute hydrochloric acid. Heat till the evolution of sulphuretted hydrogen becomes sluggish, and then drop in a piece of zinc rod. If the solution effervesces too strongly, dilute it. Continue the heating until the sulphide is seen to be all dissolved; when the lead is all precipitated, pour off the liquid and wash twice with cold water. Peel off the precipitated lead with the help of a glass rod, and then clean the zinc. Cover the lead with 20 c.c. of water and 5 c.c. of dilute nitric acid, and heat gently till dissolved; all the lead will be in solution, and, when filtered off from the gangue, will be ready for a gravimetric determination. For volumetric work this filtering is unnecessary. The chief objection to this method is that commercial zinc carries considerable quantities of lead. Although this can be determined and allowed for, the correction required is in most cases too large to be satisfactory. The following method is applicable in all cases, but is more troublesome:--Treat 1 gram of the ore with 10 c.c. of dilute nitric acid in an evaporating dish covered with a clock-glass, and evaporate till nearly dry. Take up with 50 c.c. of water, and add 10 c.c. of dilute sulphuric acid. Filter. The residue contains the lead as sulphate, together with the insoluble matter of the ore and globules of sulphur. Warm with a solution of ammonium acetate, and filter. The lead will be in the filtrate, and is recovered in a state fit for direct gravimetric estimation by the addition of dilute sulphuric acid. If the volumetric method is to be used, the lead sulphate should be dissolved out with a solution of sodium acetate instead of with the ammonium salt solution. GRAVIMETRIC DETERMINATION.