It is easily seen what extreme attention is necessary to succeed in manipulation of this kind. If it is badly done, a poor adhesion is obtained; if it is well done, the relatively large quantity of melted metal introduced between the two edges lowers the strength and destroys the ductility. Test pieces submitted to tension break without elongation.

The general procedure of welding plates from 6 to 25 m.m. thickness is as follows : -

The two pieces to be joined are brought edge to edge without superposition in perfect contact; if necessary to secure this, they are first subjected to a light cut on the planer ; they are then heated by means of two blowpipes, one above and one below, exactly opposite to one another, and producing as large a heated zone as possible. When fusion begins to appear on the surface it is probable that the interior of the plate is at white welding heat. The blowpipes are then withdrawn, and by a simple mechanical arrangement they are replaced by an anvil and a very light hammer, not exceeding one or two kilogrammes weight. The blow of this hammer is sufficient to cause a consolidation of the metal along the two butting edges.

Perfect welding is secured, and it is probable that the light hammering produces at the same time a certain orientation of the molecules favourable to the elastic properties of the metal. In fact, if test pieces of metal so welded are tested under tension to the breaking point, it is found that the grain of the fracture is not that characteristic of cast specimens, but is perfectly homogeneous and like that of the original plate. The strength is but a small percentage less than the original, and the elongation is satisfactory.

Metal of a tensile strength of 36 to 38 kilometres and elongation of 25 to 28 per cent. shows after welding a tensile strength of 36 kilometres and elongation of 13 per cent. These results are satisfactory for the majority of cases in which it is desirable to substitute for riveting the process of welding.