Another method is to bring the two edges up just as though they were to be sewn together, then to fold them tightly one over the other, and hammer them down: this is called “overlapping,” but it is not so good as rolling for keeping out the rain. The third way is to _solder_ the edges together: the solder, which is in constant use by the Plumber, being a metal made by mixing lead and tin together. These two metals when mixed adhere very strongly to the lead that they are meant to join, and the surface to which they are applied is made hot enough to unite with the solder by means of the soldering iron, while very often a little resin, borax, or tallow is placed on the surface of the lead to cause it to combine more rapidly with the molten metal. Besides the fixing of roofs the Plumber makes leaden cisterns, fixes rain-water gutters, and waste pipes, and arranges taps and drains; and in some of these operations he will use zinc instead of lead. Not the least important part of his business, however, is the construction and arrangement of pumps, and for this purpose it is necessary that he should study mechanics, and those branches of science which refer to the properties of water, and to the laws which govern the air and other fluids. He is always the best workman who goes to his business with a knowledge of the natural laws and scientific facts connected with it, and a very little study will save a world of blundering; during which the ignorant man will remain a labourer, because it takes him half a lifetime to learn his business. [Illustration] THE GASFITTER. [Illustration: GASFITTERS AT WORK.] As there are now few large houses which are not lighted by gas, the trade of the Gasfitter is one of considerable importance; and though the materials used are generally bought ready made from the Brassfounders, the glass-works, the Ironfounders, or the lead warehouse, considerable skill is required, as well as some taste in properly adapting the chandeliers and burners, and skilfully adjusting the tubes and pipes so that they may easily be repaired, or any escape of gas quickly detected. The various tools used by the Gasfitter are simple enough, but careful practice is necessary for their proper use; and, as any flaw or imperfection in the work may lead to very dangerous consequences, all the operations should be thoroughly tested, and every joint and fitting in the various parts made sound and strong. Before the gas is taken into a house, or as it is called in the trade “laid on” in the house, it is of course necessary to obtain the permission of the Company to whom the works where the gas is made belong, and to agree to pay for the quantity that is burnt, which is charged by the thousand cubic feet, and varies in price according to the cost of the coal from which it is made, and the difficulty of conveying this coal to the works. [Illustration: Spade. Crowbar. Rammer.]