Ferrous sulphide, protosulphide of iron, FeS, is how prepared? See Experiment 6. State its use. See Experiment 108. It also occurs native.
Ferric sulphide, pyrite, FeS2, occurs native in large quantities.
What is its use? See page 65.
CHAPTER XLIX.
LEAD AND TIN.
LEAD.
Examine galena, lead protoxide and dioxide, red-lead, lead carbonate, acetate, and nitrate. Note especially the colors of the oxides, the cubical crystallization and cleavage of galena, the specific gravity of the compounds, the softness of Pb, and the tarnish, Pb2O, which covers it,if long exposed.
274. Distribution of Pb.—Pb is widely distributed, occurring as PbS and PbCO3. PbS, galenite or galena, is its main source. By heating it in air, SO2 is formed, and Pb liberated and drawn off.
Pb is but little acted on by cold H2SO4, unless concentrated. Describe its use in making that acid. See page 65. To show that a little Pb has been dissolved, as PbSO4, in the manufacture of that acid, perform this experiment.
Experiment 124.—To 5cc. of water in a clean t.t. add the same volume of H2SO4, not C.P.; shake, and notice any fine powder suspended. PbSO4, being insoluble in water, is precipitated. What is the test for Pb? See Experiment 109.
275. Poisonous Properties.—Ph is very flexible and soft, and is much used for water pipes. In moist air it is soon coated with suboxide, Pb20, as may be seen by exposing a fresh surface. Some portion of this is liable to dissolve in water, and, as all soluble salts of Pb are poisonous, water that has stood in pipes should not be used fordrinking. Lead is employed as an alloy of tin for covering sheet-iron in "terne plate." T his plate is rarely used except for roofing. The "bright plate," used for tin cans and other purposes, scarcely ever contains any lead except the small portion in solder. In soldering, ZnCl2 is employed for a flux. Sn, Pb, and Zn are somewhat soluble in vegetable acids. If citric acid be present, as it usually is, citrates of these metals are formed, and all of them are poisonous. The action is far more rapid after opening the can, since oxidation is hastened. Hence the contents should be taken out directly after opening.