Lead is a heavy metal, of a dull blueish tint, and very soft; it is extensively used for covering roofs, for cisterns, and for pipes for conveying water, as it is easily bent and joined, and is not acted on by the water which passes through it. Lead melts at a heat below that of redness, and, in combination with oxygen and carbonic acid, forms the “white lead” of commerce so largely used as a paint. Oxide of lead, called “litharge,” enters into the composition of flint glass, and in combination with a larger quantity of oxygen forms “red lead,” a substance much used in painting. Lead is found in many parts of England, especially Cornwall, where many lead mines exist; it is got from the sulphuret called “galena,” which is lead in union with sulphur. What is called “black-lead” is not lead at all, but is an ore of iron, being iron in combination with carbon. Lead is about eleven-and-a-half times heavier than water. TIN. Illustration: OXIDE OF TIN. Tin is a white metal, almost as white as silver, it is found chiefly in Cornwall. It is a light, soft metal, and, like lead, is easily melted; it is used chiefly for coating vessels of harder metal, such as iron and copper. It is used to mix with copper to produce bronze, bell metal, and gun metal, and with lead to produce pewter, which used to be so extensively used as table-ware before the manufacture of earthenware became general for that purpose. Tin does not easily tarnish or rust by exposure to the air, hence the use of tinned iron-plate. Tin, united with mercury, forms the silvering for looking-glasses. Tin is about seven-and-a-half times heavier than water. ZINC. Illustration: SULPHURET OF ZINC.