The method of scarfing is an important factor in producing a sound weld, for upon it depends the ease with which the slag is forced out when contact is made. In welding up, say, 2-inch bars, the most frequent method is for the striker and helper, with backing hammers, to set back the bar thus, and afterwards extend it by fullering. As long as the smith does not proceed any further this will produce a good weld, but frequently he gives the bar a quarter turn and a few blows, the result being to create a hollow, consequently trapping the slag, when the two scarfs are brought together. The best method of scarfing is to use the flatter after the fuller, then bend slightly over the beak of the anvil, which produces a scarf thus, and when two similar scarfs are brought together, they touch in the centre first and unite outwards, the slag going before. Very good jump welds can be produced, but this method in an ordinary smith's fire is not to be encouraged, because they always break at the joint, showing a crystalline fracture with short elongation, whereas with round scarfs, they break as frequently outside the weld with fibrous fracture, which is also the case when broken at the weld. In good welds it is quite within reason to expect under a tensile strain that the bar will not break at the weld, because the extra mechanical work put into that portion raises its ultimate strength, consequently after fracture the contraction at the weld is less than along the rest of the bar, but taking the whole shop through, it is not safe to calculate the strength of a weld beyond 70 per cent, of the solid.

It is not proposed to deal with the many mixtures used as fluxes, especially in the welding of mild steel, but it is only fair to state that there are certain compositions on the market which are valuable accessories in welding high carbon and tool steels. They cannot exactly, however, be wholly passed over, because certain materials, such as sand, are commonly used, and are useful both for iron and steel. The metal is inevitably oxidised during heating. Wrought iron and soft ingot iron or mild steel may be safely heated to the temperature at which the oxide is fluid, then a flux is not necessary, but might facilitate welding. Again, as the percentage content of carbon is increased, the welding point is correspondingly decreased, therefore a flux must be used to slag out the oxide at this lower temperature. From this the reason is readily surmised for the numerous fluxes or welding compositions upon the market, which are, generally speaking, alkaline salts. It must be remembered that the flux does not benefit the metal, and the chief requisites are low melting points and cheapness; therefore, as ordinary sand and borax admirably fulfil these requirements, they are not likely to he readily supplanted. They form a slag which simply surrounds the parts to be welded, and protects them from oxidation and the influences of the impurities in the coke, especially sulphur. Impure iron will form a flux out of its own impurities, and when the scarfs are brought together and hammered or otherwise compressed, the slag is squeezed out.

Although the chief requirements for welding mild steel have already been stated, sometimes calcined borax, mixed with salanimoniac, is used, but there is no apparent necessity for this, although, certainly it makes a more fusible flux.

Welding by electricity having been made the subject of considerable commercial enterprise, it will not be entirely without interest in a locomotive smithy, and a short notice of two systems - the low potential and the arc - may be of service for special purposes rather than general use. In both systems there is economy of time and labour, a weld being performed with the utmost rapidity at a very low figure, for as many as 700 welds, ranging from ¾ inch bars to 2-inch shafting, can be made per week by a 40 A type machine of The Electric Welding Company, Limited. There is also saving in material, for there is no blistering, scale or burning, and if two pieces, each 1 foot long, are placed in the machine, when finished the product will be one bar exactly 2 feet long. The heat can be regulated perfectly, being always visible, and there is not any necessity to allow 1 inch or 1« inches for scarfing. The absence of scale and dirt in the arc system or improved Benardo's, as carried out by Messrs. Lloyd and Lloyd, Birmingham, is probably due to the fact that the vapour of iron is produced to such an extent, that the atmosphere cannot get sufficiently near to oxidise the metal. Both systems have great advantages in welding uneven sections, and also prevent the introduction of dirt, whether solid or gaseous, and should two bars be brought together, the ends to he welded being covered with oxide, it does not appear to be the least detrimental, it escaping as a drop or two of slag falling from the surfaces when under pressure. The principle of the first process is the conversion of a current of very high potential, by means of transformers, into low potential. Machines are designed and supplied to suit the nature of the work to be done, whether welding or brazing.

and to utilise whatever existing power may be at hand, and each machine is capable of welding various sizes within reasonable limits. The current of low potential is caused to pass through the abutting ends of the pieces of metal to be welded, rounds, squares, angles, tees, zeds, etc, generating heat at the junction, which is the place of greatest resistance. This machine has also been found very useful in welding up short lengths of turning, planing and other tools - Mushet - or otherwise, and thereby increasing their life. Union is effected by following up the softening metal by mechanical means at a welding temperature. The weld in this case is as efficient in the centre as the exterior, because the heat generated by the current commences at the centre and extends outwards; but should there be a point of first contact elsewhere, of course the heat is first generated there. Generally, a burr, upsetting or enlargment of the section is produced, which is either removed by a light hammer or by specially designed machinery. Mechanical work is of course beneficial to the weld, consequently an anvil is mostly found in line with the clamps of the machine, with a part section of the article being welded, let into its face to facilitate hammering up. Good illustrations of this work are the welding on of new ends to old iron and steel boiler tubes, in which case they are hammered on a mandril; and also the upsetting of tubes or bars at any position of their length.

In the arc system an ordinary lighting low tension continuous dynamo is used, in conjuction with a system of accumulators, which come into action only when the actual welding is taking place. The reason for the latter is to get a high efficiency from the plant, the accumulators acting the same part as an accumulator in relation to the pumps in a system of hydraulic pressure. One terminal is connected by means of a flexible cable to a carbon, held in an insulated holder by the workman. The other terminal is connected to the table on which the work lies, or to the work itself, and the arc is sprung between these poles by the workman touching the work with the carbon, and then raising it up. The are should be as long as possible for good regular work, the maximum being fur welding purposes about 6 inches in length, and having a sectional area of about 2 square inches. Iron and steel are made the positive poles, and as this is the pole that volatilises, the vapour of the metal will generally assist in maintaining the are, but for other metals the poles are sometimes reversed.

To avoid any great concentration of beat on a confined area, the carbon is caused to vibrate at a high rate of speed by mechanical means, actuated by a small electric motor, as is also a small hammer, used for securing welds and removing burrs. The mechanical motion of the carbon is produced by fixing it eccentrically to a spindle, winch revolves at about 300 to 400 revolutions per minute, the circle produced being about 2« inches diameter, and this spindle has also a longitudinal movement of about 4 inches at the rate of thirty strokes per minute. The degree of heat is regulated to suit the nature of the work, and ordinary welds are generally produced by burning on small pieces of iron and steel, as the case may be, weighing only a few ounces. Owing to the intense heat and light of this system, the eyes and face of the workman must be protected, and it has this disadvantage, it lacks a ready means of control over the temperature, which is extremely localised, much more so than in an ordinary smith's fire; consequently the internal strains set up must be objectionable, and the high temperature developed causes a greater amount of local crystallisation. This system is less desirable when the sectional area is small, but where there is greater cubical content, such as internal flues of boilers and pipes, it is more convenient than the low potential.