We now propose to give a short description of the materials consumed in the forge, the chief of which are the coals and the iron. It is of considerable importance that care should be used in the selection of the fuel for the manufacture of forgings, as great difference exists in this important mineral, some being very much more suitable for the manufacture than others. The best bituminous for the purpose is a strong, dense, durable coal, possessing a good body, and having a dull, dirty appearance. Coal of this kind with a bright clean look, easily broken, as a general rule is not suitable. Of course it is desirable that the coal should be as free from sulphur as possible, and that it should not contain any large proportion of those foreign matters which, having an affinity for iron, fuse on the bars in the shape of clinkers.

We now come to the consideration of the best description of iron for this manufacture. Scrap-iron is that most generally used; but, far from agreeing with the generally received opinion that it is the best, we think that it is the very worst description of iron for the purpose; and for more reasons than one. Engineers usually require, in their contracts with the forge-master, that their forgings shall be made from the best scrap-iron; and it is, of course, the duty of the forge-master to comply with the terms of his instructions and contract. Let us first endeavor to see how this almost universal belief in the superiority of scrap-iron has arisen. At the time when small forgings were first attempted to be made as an article of commerce, the manufacture of iron was in such an imperfect state, and the quality so indifferent, that large quantities of the best iron had to be imported from Sweden and Russia, and for a long time the scrap-iron was of a quality that could not be approached by our own iron of that period. Since that time, the use of Russian and Swedish iron has been almost entirely discontinued, except for the manufacture of steel; the greater part of the scrap-iron now produced, therefore, is of a very different quality to that formerly known as best scrap-iron. This material was deservedly considered the most proper material for the manufacture of forgings that could then be procured; but it must be borne in mind that, at the date we speak of the forgings were so limited in size that the practical evils resulting from the use of scrap-iron, which we are about to explain, were not so perceptible.

In the ordinary manufacture of bar-iron it is the practice, in most works, in order to obtain it of the toughest and best description, to work and re-work it several times over. The number of workings the iron undergoes is marked by the number of "best" stamps that it bears, as "best,best best," "treble best," etc., each "best" indicating a better quality, an extra working, and with a correspondingly higher price. But this progressive improvement has its limits, as will be perceived, from a series of experiments which were instituted by the writer with the object of testing the correctness and limits of this improvement.

Taking a quantity of ordinary fibrous puddled-iron, and reserving samples marked No. 1, we piled a portion five feet high, heated and rolled the remainder into two bars marked No. 2; again reserving two samples from the centre of these bars, the remainder were piled as before, and so continued until a portion of the iron had undergone twelve workings. The following table shows the tensible strain which each number bore:

It will thus be seen that the quality of the iron regularly in creased up to No. 6 (the slight difference of No. 5 may perhaps be attributed to the sample being slightly defective); and that from No. 6 the descent was in a similar ratio to the previous increase. From these experiments it appears that scrap-iron, or any other iron, highly refined, is the very worst material for the construction of large forgings which can be used; and that if we take, in the first instance, a strong fibrous fresh-puddled iron, the ordinary workings required in the process of forging will be sufficient to improve it to the average maximum of strength required; whereas highly refined iron, such as Lowmoor or Bowling, although the very best description for many purposes, has already reached the highest point in its strength, from which it is more likely to be deteriorated by additional workings.

It may then, be asked - how can we hope, with any degree of success, to manufacture large forgings, which require to be worked over perhaps a score of times, each working beyond a given number tending to vitiate the iron? We can conceive that this deterioration does not penetrate the iron to any great depth; that few forgings are heated more than six times in one place before fresh iron is added; and that the various layers thus successively added to the mass protect the under portion from the deteriorating influences of the successive heatings. It is also to be observed that any crystallization which might take place, commences from the outside of the mass; and as this is the portion which is most immediately acted upon by the blows of the hammer, the fibre is elongated in a greater degree, and thus restored to its original quality. As a proof of this, we may instance the manufacture of the monster gun, which was built up in seven distinct layers, the forging of which took seven weeks.

At the meeting of the British Association at Glasgow, in September, 1855, a question was raised in the mechanical section as to the causes of the deterioration of the metal of which the artillery of the present day was constructed. On this question a long and interesting discussion ensued, both in reference to the comparative weakness of cast-iron as now produced, and the adaptation of forged and malleable iron as being stronger and better adapted for this purpose. The accounts received from the Baltic and Black Seas of the bursting of guns and mortars of recent construction, indicated that something was wrong. These failures gave rise to conjectures on the part of the Government as well as of the public; and, in order to trace the cause of this apparent weakness to its source, an inquiry was institued by the authorities at Woolwich; and subsequently the Association appointed a Committee to cooperate with the Government in the investigation of this very important question. In order that no time might be lost, the secretary of the section was directed to issue circulars to engineers, ironmasters, and manufacturers, requesting that they would forward to the members of the Committee such opinions and observations as they deemed advisable, in regard to the material itself, and to its treatment preparatory to the manufacture of ordnance."