The art of welding iron is probably as old as the earliest production of that metal by man; in fact, the reduction of iron in the primitive forges demanded the union by welding of the reduced particles, for no true fusion could have resulted, the percentage of carbon present being too low.

Previous to the nineteenth century most iron work was forged by blacksmiths on anvils. It was the pride of the blacksmith to produce a fine weld, and the beautiful articles he made from iron, simply at his fire, even without a flux - sometimes, perhaps, he used some clay - are evidence enough of what perfection of skill he had reached.

Then came the period of cast iron, when everything that could be cast was made that way, because it was cheaper. During the last half of the century the use of forged iron and steel increased enormously, owing to improved and cheapened methods of production.

Where forgings are so large that a smith cannot work them satisfactorily, because there is too much and too heavy hammering to be accomplished in the short time the metal retains its great heat, the machine hammer is resorted to.

The scope of his field of operation being more and more limited by the progress of time, which continually requires and produces new methods of manufacture, the blacksmith of old gradually disappeared in order to leave room for modern means of working.

Welding, especially, is now being carried out to great extent and advantage by means of fusion.

During the last few years a new method of joining metals by fusion by the aid of compressed combustible gases has been introduced, which has established itself with an amazing rapidity in almost every centre of industry.

The name of "autogenous welding," under which it has been introduced, is, however, unfortunate, indicating as it does, that results would be produced which could not be obtained by other means. Autogenous welding was therefore and still is being introduced with the specific notice that neither flux nor hammering or pressing is required in order to produce a perfect weld or union of the metals.

Such statements are not in accordance with true facts. The welding of cast iron, copper, zinc, and especially aluminium and their alloys, do require a flux. Forged iron and • steel are also to a great extent influenced by the composition of the metal to be added in order to complete the weld ; besides the form of the flame, its temperature and chemical composition will also play an important part in the production of a proper weld.

Autogenous welding, even of the thickness of 2.5 to 3 m.m., requires the plates to be operated upon to be previously prepared by cutting their ends so as to form a groove, into which is placed a piece of similar metal, in form of a bar or wire, which, when melted, will trickle down and fill the groove; care must be taken that the filling metal of the bar is being perfectly welded to the metals forming the groove.

The thicker the welding metal is, the larger must be the groove and the stronger becomes the weld, which will have the character of casting in contradiction to the superior quality of the welding plates.

Statements to the effect that plates of from 45 to 75 m.m. thickness may be welded by the autogenous system with absolute safety are simply promises of fraudulent nature. Such statements cannot but render great harm, particularly to a new industry, and may result in similar difficulties and even final disaster, which the industry of acetylene lighting had to encounter.

The limit of a qualitatively perfect autogenous weld is to be found where a mechanical finishing of the weld by ordinary means is possible, that is, probably, within a thickness up to 20 m.m.

As long as it aims only at joining two metals, without any special claim as to quality, a weld may be done at almost any thickness, as long as the temperature available is greater than that expended in the weld and the unavoidable loss from the surrounding atmosphere. Mass-distribution and large surface are the leading points in this case.

It is almost always forgotten, however, that the principal and incontestable condition for producing a perfect weld is an absolute purity of the combustible' gases employed, and, furthermore, that the welding should be effected without any action upon the metal, chiefly that of carburation.

Amongst all combustibles the hydrogen alone fulfils these conditions, and it offers thereby great advantages over all other combustible gases, particularly over that of acetylene, because it does not leave any carbon; used even in excess, hydrogen still renders a reducing flame without harming the metal, while by acetylene and all other combustible gases the metal is irremediably carbonised.

Microscopical examination reveals that out of five samples welded by acetylene four were oxidised and one carbonised. This is easily explained from the fact that the flame of the oxy-acetylene blowpipe is composed of oxygen and acetylene. If there should be an excess of acetylene, a carburation takes place; if an excess of oxygen, an oxidation is produced. In order to realise a neutral flame inventors are still making proposals, but probably without much prospect of success.