Very naturally the drawing of wire requires use of much greater power than the rolling of rod and the speed of drawing is nowhere near as great. Therefore the cost of wire is comparatively much greater than the cost of rolled products. In the case of watch springs it was once computed that the product had to bring 50,000 times the cost of the steel from which the wire was drawn. “Continuous” wire drawing has not been so successful nor advantageous as was the continuous rolling of rods. It has been possible in a small way and with certain grades of the product to apply the continuous process, but, mainly on account of mechanical difficulties, continuous drawing of wire seems to be comparatively unimportant. CHAPTER XX THE MANUFACTURE OF PIPE AND TUBES Tubes of some sort have been in use by man since very early times. Nature provided the first ones in the way of hollow stems of shrubs, such as alder and bamboo. Some of these we saw in use by the early smiths conveying the blast of air from their goat-skin bellows into the crude clay furnaces built in the hillside. Tubes made of clay, stone, lead and bored logs were also used. Much later pipes made of cast iron came into rather extended use for the conveyance of water. The general use of gunpowder greatly accelerated the manufacture of small tubes which the smiths produced for gun barrels by hammering and welding together long, red-hot strips of wrought iron about round rods or “mandrels.” About 1815 illuminating gas came to be used in England for house lighting. This brought a demand for tubes of considerably greater length, which were first made by screwing or otherwise fastening together old gun barrels which were very plentiful at that period. The first patents for the making of welded pipe as we know it were taken out in 1824 and 1825, the latter for the butt-welding method of pulling a narrow iron plate, called “skelp,” through a bell-shaped orifice which curled it and welded the edges together very much as is done to-day by this process. Our modern pipe of both butt-weld and lap-weld varieties is manufactured either from wrought iron or from soft steel. The Butt-Weld Process [Illustration: EARLY WATER PIPES ] [Illustration: HOW BUTT-WELD PIPES ARE MADE ] From the double refined puddled iron, in the case of wrought iron, or from billets of soft Bessemer or open-hearth steel, long narrow plates are rolled. The width and thickness of these plates, which are known as “skelps,” are exactly such as will give pipe of the desired diameter and gauge. In order that the weld may be solid all along, the skelp as it leaves the rolls has edges not exactly square but very slightly beveled, so that the surface which is to form the interior of the pipe is slightly narrower than the other.