If litharge is used in the assay instead of red lead 4 grams more nitre, or 1.5 gram less flour must be used. When more than a few grams of nitre are added to a charge the proportion of "soda" and borax should be increased, because one of the products of the reaction of nitre upon sulphides in the presence of soda is sulphate of soda, and because the "soda" thus used up no longer serves as a flux; more borax should be added, as it is the best flux for the metallic oxides which are formed in the process. If in an assay too large a button of lead is got, even after this calculation has been made, and the assay is repeated, add 1 gram more nitre for each 4 grams of lead in excess. Sometimes the assay appears tranquil before the nitre has produced its full effect; in such cases it is well to seize the crucible with the tongs and mix its fused contents by rotating them; if this causes an effervescence, the crucible should be replaced in the fire and the fusion continued. The following experiments will illustrate the extent to which the above rules may be relied on. In all of them the standard flux was used, viz.:--80 grams of red lead, 20 of soda, and 5 of borax. _Pyrites_ 5 5 5 5 2.5 5 10 15 20 Quartz -- 20 -- 20 17.5 15 10 5 Nitre -- -- 5 5 -- 4 16 28.5 41 Lead got 42.5 36.0 16.0 19.0 11.5 22.5 22.5 26.5 27.5 _Copper Pyrites_ 8 8 8 8 Quartz -- 12 -- 12 Nitre -- -- 4 4 Lead got 47.5 34.0 33.0 26.0 _Antimonite_ 8 8 8 8 Quartz -- 12 -- 12 Nitre -- -- 4 4 Lead got 29.0 26.0 13.0 13.0 _Galena_ 10 10 10 10 15 20 Quartz. -- 15 -- 15 5 -- Nitre -- -- 3 3 3.5 7 Lead got 17.0 19.0 8.0 8.0 18.5 18.5 A similar set of experiments, with 80 grams of litharge instead of 80 grams of red lead, gave:-- _Pyrites_ 4 4 4 4 7 10 Quartz -- 15 -- 15 13 10 Nitre -- -- 5 5 12.5 20 Lead got 46.5 40.5 25.5 24.5 27.0 26.5 _Copper Pyrites_ 5 5 5 5 Quartz -- 15 -- 15 Nitre -- -- 5 5 Lead got 44.5 32.5 23.0 25.0 _Blende_ 5 5 5 5 10 Quartz -- 15 -- 15 10 Nitre -- -- 5 5 15 Lead got 41.5 38.5 21.5 22.5 21.6 _Antimonite_ 5 5 5 5 10 Quartz -- 15 -- 15 10 Nitre -- -- 5 5 10 Lead got 31.0 32.5 11.5 12.5 18.7