This material has the advantage of being cheap and easily worked, but is comparatively weak and liable to crack, so that the guns of that time were comparatively small compared with those of to-day; they could only withstand a feeble explosion and their range was therefore limited. Had the energetic explosives of the present time been employed in them they would inevitably have burst, killing their gunners instead of the enemy. Attempts were made to strengthen them with bands made of wrought iron, a form of the metal which is tough and elastic and therefore better able to withstand sudden shocks than the more brittle cast iron, but it was not a real success. At first sight one naturally wonders why the whole gun was not made of the stronger wrought iron. The reason was that while cast iron can be melted and poured in a liquid form into a mould, so as to produce the shape of the gun, wrought iron will not melt. It will soften with heat, in which condition it can be hammered into shape and, moreover, when in a very soft state two pieces can be joined by simply forcing them closely together, which operation is called welding. With the machinery available now it would be possible to make a gun of wrought iron, but even a few years ago it would have been quite impossible. There was an obvious need therefore of a metal which could be melted and cast in moulds like cast iron, yet tough and strong to resist shock like wrought iron. Fortunately this problem excited the interest of a certain Mr. Henry Bessemer, a gentleman who, having made a considerable fortune through an ingenious method of manufacturing bronze powder, had sufficient leisure and money to devote himself to its solution. The vast steel industries of Great Britain and the United States are the direct results of this gentleman's labours, and in the latter country there are quite a number of towns which, being the home of steelworks, are called by his name. Iron is one of the most plentiful things in the world. Deposits running into millions of tons are to be found in many parts, but it is practically always in the form of ore, that is to say, in combination with something else generally oxygen and sometimes oxygen and carbon. The former sort of ore is called oxide of iron and the latter carbonate of iron, and both of them bear not the slightest resemblance to the metal. They are just rocks which form part of the earth's crust, and it is only the metallurgist who can tell what they consist of.