LEAD AND ITS ALLOYS Lead. — Next to iron, lead is the most common of metals. Its color is bluish gray, it is soft and ductile, it burns at a white heat in the open air, producing an oxide known as litharge, which is much used as a dryer in mix ing paints. Lead is used for roofing, lining sinks, cisterns, etc., for shot and balls, and for the manufacture of pipes. Lead is so soft that it can be drawn out in pipe form without welding. It is so cheap and handy to work that it is almost universally employed for water pipes and has given its name to the plumber's trade, the Latin name for lead being plum bum. The principal alloys of lead are type metal which is lead and an timony, and pewter or solder which'is lead and tin.
Various compounds of lead are in Common use.
Litharge is used as a dryer with oils and varnishes, and in the manufacture of glass.
Red lead or minium is used as a pigment of oil paints and in coloring wall paper, sealing wax, etc. It is also used in the manufacture of glass.
White lead is a mixture of litharge and carbon. It forms the basis of most lead paints. An objection to white-lead paint is that it turns dark under the influence of gases or other compounds containing sulphur. Lead is a cumulative poison, and those who work in it, as painters, plumbers, and others, are liable to a complaint known as " painter's colic." The use of lead pipe has been the source of many cases of lead poisoning; hence lead pipe should always be lined with tin. This is but little more expensive than pure lead pipe and is much safer.
Sugar of lead, or acetate of lead, an active poison, is made by dissolv ing litharge in wood vinegar or other cheap acetic acid. It forms beautiful crystals which gradually crumble to a white powder. These may be dis solved in water by the addition of acetic acid.
Chromates of lead are known as chrome yellow and chrome red. They are two brilliant and valuable pig ments, chrome yellow being especially important. These are used as pig ments in mixing paints, as dyes, and the like.
Lead Tree. — This interesting ex periment is per fomed by dissolving in a large glass vessel 1 ounce of sugar of lead in I quart of water, and by placing near the top a small piece of zinc of irregular shape. Within 0
or 3 days the zinc will shoot out leaves similar to vegetation, and will become extremely beautiful. It must, however, be moved with great care, as the slightest jar will cause it to fall apart. The zinc decomposes the acetate of lead and causes the metal to be precipitated on its surface in a metallic state.
Lead in Grains.—To obtain lead in this form, melt it and pour from a height in a thin stream into cold water.
Sheet Lead. — To prepare lead in sheet form, pour the melted lead on a large flat stone having a rim to pre vent the lead from running off. Lay off a square equal in size to the de sired sheet, placing at the corners up right pegs of the desired thickness. After pouring on the melted lead, press down upon the pegs a thin piece of flat stone fitted with a suitable wooden back and handle to smooth the lead surface. Remove the sheet of lead and repeat the process. The sheets may afterwards be trimmed as desired.
To Test White Lead.—To test white lead, which is often adulterated, put a little of it on the end of a stick and set the stick on fire. If the lead is pure it will appear in small globules like shot. If it forms a white crust on the stick it is not pure. Crush this white crust on paper. If it con tains lead the paper will be black, otherwise it will be of a pale-yellow color.
Or place a small quantity of the white lead on an earthenware surface and direct against it by means of a blowpipe the flame of a candle or of an alcohol lamp. The metallic lead will appear in the form of a melted globule, and any impurities will be apparent.
Type Metal.—Lead, 83; antimony, 17. This mixture is harder and may be melted more easily than either of its components, and it has qualities which adapt it for fine and sharp castings. A little zinc is sometimes added.
Expansion Metal. — Seventy - five lead; 16A antimony; 8i bismuth. This mixture expands on cooling.
Or 7 lead; 1 antimony; tin,