which, known as "mild steel," is produced in large quantities in a molten condition, and is used where tenacity and ductility are required. The foreign elements in this variety are usually under 1 %, carbon and manganese being the most important constituents. The other, and more expensive variety of steel, is manufactured in smaller quantities, usually in crucibles, and it combines with moderate fusibility the remarkable properties of hardening and tempering which are so valuable in the production of tools of all kinds. Steel of this kind usually contains from 5 to 1·5% of carbon. The following table gives the approximate proportion of carbon contained in steel used for various typical purposes, and illustrates the considerable differences met with on analysis. These variations in composition lead to the development of very distinctive physical properties, and it is important that the engineer or workman should select steel which has a suitable composition for the purpose in view.

Extending Applications of Cast Iron.

When in 1886 I first delivered a course of lectures in Birmingham on cast iron, it was anticipated by many, that, owing to the rapid development of steel foundry practice, the demand for cast iron would rapidly diminish, and that iron-founding would soon become a thing of the past. On that occasion, however, I ventured to quote with approval, from the address of the late Mr Jeremiah Head, as president of the Institution of Mechanical Engineers, in which

reasons were given for anticipating a continued and extended use of the cheaper material. These anticipations have been fully borne out in the interval that has since elapsed.

Cast iron possesses, among other advantages, the following properties, which render it especially suitable for foundry work.

1

On account of its cheapness, castings can be produced in iron at lower prices than in any other metal, while, owing to its abundance, it is less liable to suffer considerable fluctuation in price. It can also, for these reasons, be readily obtained in all parts of the civilised world. Its easy fusibility also tends to allow of its ready melting and manipulation, while the expansions which take place during solidification, and subsequently, enable it to take a sharp impression of the mould. It possesses sufficient tensile and transverse strength for the majority of ordinary applications, while its crushing strength is higher than that of any other material used in construction. It requires no annealing, hence time is saved, as compared with steel, and a casting can be produced immediately if required, either for a special order, or in case of breakage. Castings in iron have finer and smoother surfaces than those produced in steel. Iron castings are less liable to rust than wrought iron or ordinary steel, especially if the skin is retained. Further, when used for bearing surfaces, cast iron wears well, while the additional weight of the cheaper material which can be used is often an advantage for the bed-plate or foundation of an engine, or of a large machine tool.

From the above considerations it may be reasonably anticipated that, despite the ever increasing application of steel, the uses of cast iron are likely to be considerably extended rather than to show any important diminution.

History of Cast Iron.

The production of cast iron is now the first stage in all modern processes of iron and steel manufacture, and pig iron is the most abundant variety of iron in commerce. It was not, however, the form of iron first made, nor indeed was iron the material originally used by man for his tools and implements.

Prehistoric man employed tools and weapons made of stone, flint

1 Molten iron, from which graphite separates, expands at the moment of solidification. Subsequently, during cooling, a further separation of graphite takes place, interrupting the regular rate of contraction by momentary expansion.

being largely employed for such purposes. This early period in the development of the race lasted for a very considerable period, and is conveniently divided into three stages.

(1) Eolithic, in which the stone implements were very roughly shaped, chiefly by chipping.

(2) Palæolithic, in which there was a greater variety of instruments, and these were more perfectly shaped.

(3) Neolithic, in which still more highly finished hammers, chisels, and other tools were produced in stone, and polished.

During the latter part of this stone age, bronze was introduced. This was, in the first place, merely an impure copper, hardened by sulphur, arsenic, iron, or other impurities, more or less accidentally introduced. As the bronze age progressed, the value of tin was fully recognised, and the composition of the later examples of bronze was much the same as that of the gun-metal of the present day.

About the beginning of the historic period, or perhaps somewhat earlier, iron was introduced. It was always made by a process of simple reduction from the ore, the product being wrought iron. By a slight modification of the simple process so employed, steel could be made as readily as wrought iron, and was so produced on a considerable scale. The Romans were familiar with both iron and steel, and produced these materials in large quantities during their occupation of Britain.

With the revival of knowledge towards the close of the dark ages, more iron was required and furnaces of increased size were adopted. No doubt in some of these large "bloomeries" cast iron was at first accidentally produced. It was believed by Lower that cast iron was made in Sussex about 1350, but the exact date of its practical application for foundry work is unknown, though this would appear to be certainly not later than 1490, its earliest application being on the continent of Europe. Its use rapidly spread into England, so that in September 1516 a large iron gun called "The Basiliscus," which weighed about 10,500 lbs., had been cast in London. At the Tower of London there are still preserved two large cast iron guns which were brought over from Ireland in the reign of Henry VIII.

All the iron produced at this period was made by the use of charcoal, and the growing scarcity of fuel crippled the iron trade of the United Kingdom, while the industry still flourished on the continent, where charcoal was more abundant.

1 Viscount Dillon, Archæologia, Vol. LI. Part I., page 168.

Iron was first smelted with coke, made from pit-coal, in Staffordshire, by Dud Dudley, in the reign of Charles I., but the process was revived and brought into practical use by Abraham Darby at Coalbrookdale, in Shropshire, about 1730, and this process made available, for the purpose of the iron-master, the greater part of the enormous coal supply of Great Britain, and rendered possible the developments which followed. These included the introduction of steam-blowing engines about 1770, and the application of the hotblast by Neilson in Scotland in 1829. The latter invention was shortly afterwards followed by improved blast furnace shape, and increased capacity, particularly in Staffordshire, which county was in 1850 the leading iron producing centre in the world.

The opening up of the Middlesboro' district about this time, with the subsequent introduction of much larger furnaces, and fire-brick regenerative hot-blast stoves, led to an enormously increased production, and Cleveland became the chief centre of the iron industry; but the development of the, Connellsville coke region in Western Pennsylvania, and of the magnetic iron ore deposits of Lake Superior, led to so great an increase in the American iron trade, that in 1890 the production of the United States for the first time exceeded that of the United Kingdom. The subsequent developments and improvements in the blast furnace practice in the United States, and the opening up of the mines of soft, rich, easily reducible iron ore in the Mesabi range, combined with the enormous demands of a rapidly developing country and a protective tariff, have led to unprecedented production, so that the output of pig iron in the United States in 1903 was no less than 18,000,000 tons, as against a production of 8,500,000 tons in the United Kingdom.

During the nineteenth century many wonderful advances attracted public attention, such as the substitution of the stage coach by the express train, and of the sailing ship by the ocean liner, while the old, crude methods of signalling were replaced by the telegraph or telephone. But perhaps in no direction was more progress made than in connection with the metallurgy of iron and steel. In blast furnace practice alone the output per furnace, during the century, was increased fully a hundredfold, while the fuel consumption per ton of iron was reduced to one-fifth of that previously employed. It is not too much to say, that apart from this remarkably increased production and economy in the manufacture of iron, much of the great material

progress which will always be associated with the Victorian era would have been impossible.

Production of Cast Iron.

As the iron-founder in his daily business is called upon to use different varieties of iron for particular purposes, and, partly with the object of obtaining a better product, and partly on account of variations in supply, he seldom confines himself to a single brand of iron, it is important that he should have some information as to the sources from whence the iron he uses is obtained, and the methods by which it has been manufactured. Such knowledge will allow of more intelligent foundry mixing, and frequently also of the production of a better product at reduced cost. But as the iron-founder is generally only a user and not a producer of iron, it will not be necessary to enter into any minute detail as to the process whereby cast iron is made, a general outline being sufficient for present purposes.

Iron Ores.

The primary consideration which affects the quality of pig iron is the character of ore from which it has been produced. Some ores contain little phosphorus, while others carry much more of this constituent. Some ores, again, are more silicious or sulphurous than others, while some contain more manganese. With normal furnace working the proportion of the elements which enter into the composition of the iron naturally varies largely with the amount originally present in the ore.

There are in various parts of the world large mineral deposits, rich in iron, which cannot be utilised for iron manufacture. As examples of these may be mentioned deposits of pyrites, the proportion of sulphur in which renders such ores quite unsuitable for iron making. Another familiar example is seen in the basaltic rocks, which, though often rich in iron, contain this element in the form of a silicate, which is difficult to reduce on the large scale. view of the cost of equipment and the enormous output of modern plants, the deposits, to be valuable to the iron smelter, must be of very considerable magnitude. The ore must also be rich in metallic iron, free from any excess of injurious impurities, and

In