~Cobalt.~--The filtrate from the acetate separation will have a pink colour. Render it ammoniacal and pass sulphuretted hydrogen. Collect the precipitate on a filter, dry, and ignite. Dissolve in hydrochloric acid, and evaporate nearly to dryness with an excess of nitric acid. Dilute with 10 or 20 c.c. of water and add potash solution in slight excess. Add acetic acid until the solution is acid and the precipitate is quite dissolved. Add 20 or 30 c.c. of a strong solution of potassium nitrite, and determine the cobalt, as described on pp. 254, 256. Boil the filtrate from the cobalt, precipitate with hydrochloric acid, render ammoniacal, and test for zinc, nickel, and manganese. _The remainder of the tin_ will be contained in the flask labelled "arsenic." Acidify with hydrochloric acid and filter. Rinse into a beaker, and evaporate to a small bulk with 10 c.c. of nitric acid. Dilute and filter. Dry the precipitate, consisting of stannic arsenate (2SnO_{2}.As_{2}O_{5}), ignite, and weigh. Calculate the tin it contains by multiplying by 0.4453, and add to that already found. ~Arsenic.~--This is determined in a separate portion. Weigh up a portion of the powder equivalent to 1 gram of the hardhead, place in a pint flask, and boil with 10 c.c. of nitric acid. When action has ceased add 10 c.c. of the solution of the metallic portion and then hydrochloric acid (a few drops at a time) till solution is complete. Warm gently in dissolving, but do not boil. Dilute to about 100 c.c., render alkaline with ammonia, and add 20 c.c. of yellow ammonium sulphide. Digest at a gentle heat for about thirty minutes, filter, and wash. Add 50 c.c. of magnesia mixture, shake well, allow to stand for an hour, filter, and wash with dilute ammonia. The precipitate is dissolved and then titrated with uranium acetate, or it is evaporated with nitric acid, ignited, and weighed as pyrarsenate of magnesia. Calculate the result to arsenic, As. ~Sulphur.~--Weigh up a portion of the powder equivalent to 2 or 3 grams of the hardhead. Rub up in a mortar with 5 grams of nitre and fuse in a porcelain dish for ten minutes. Extract with water, add 20 or 30 c.c. (as the case may be) of the solution of the "metallics." Add 10 grams of sodic acetate, and ferric chloride until the precipitate turns brown; dilute with water to half a litre, boil, and titrate with standard baric chloride, as described under _Sulphur_. Report as sulphur. A sample of hardhead examined in this way gave-- Sulphur 3.00% Arsenic 27.10 Tin 22.2 Copper 1.64 Iron 43.2 Cobalt 2.6 ------ 99.74