It has been said, above, that the materials undergo little chemical change under this treatment. The question seems very important for iron, whose behaviour is so remarkably influenced by slight variations in the composition. To test this question, wrought iron droppings from the welding process were fused again by means of the arc to a bar of about 15 mrn. thickness, and this bar turned down to 10 mm. The breaking weight of this bar was 23.8 tons per sq. in. with an elongation of 17.5 per cent. The fracture was fibrous, like that of soft steel. This electrically fused iron (Fig. 175) resembles soft steel in other respects, notwithstanding its origin; it is malleable, can be welded, can be bent both hot and cold, and is scarcely harder than soft steel. The following table gives analyses made by Vieuville. The columns B refer to the original metal before electrical treatment; the A columns show the composition of the metal after the treatment. The changes are slight, and appear rather favourable.

The tensile strength tests of electrically made joints yielded most satisfactory results. Two pieces of rolled charcoal iron, joined as in Fig. 152, showed a breaking strength of 18 tons per sq. in., the iron itself giving 21 tons; the elongation was 9 per cent. In another instance, 93 per cent, of the initial tensile strength was observed. A plate riveted electrically rent finally outside the riveting line. The electrical riveting or the joining of plates without rivets, particularly as in Fig. 152, seems to offer material advantages for some purposes.

B.

A

B.

A.

Steel.

Carbon..

0.44

0.22

0 52

0.29

Silicon..

0.03

trace

0.05

trace

Manganese.

'0.57

0.14

0.42

0.36

Sulphur..

0.041

0.036

0.039

0.035

Phosphorus..

0.102

0.100

0.07

0.050

Iron.

Carbon..

038

015

0.30

0.13

Silicon..

0.03

0

trace

0

Manganese..

0.53

0.16

0.36

3.30

Sulphur •..

0.160.

0.120

0.110

0.070

Phosphorus .,..

0.13

0.124

0.105

0.087

The remaining figures illustrate specimens exhibited by Prof. Ruhlmann before the Electrotechnical Society. Fig. 163 is a cast iron plate, Fig. 164 a cast iron eccentric broken in pieces and joined again at a; the junction is said to be quite homogeneous, and neither harder nor more brittle than the solid metal. This suggests the finishing of cast iron pieces by means of the electric arc. Fig. 165 represents a piece of a cask, Fig. 166 part of an iron boat. That even finer plates may be subjected to this process is demonstrated by Figs. 167 and 168; but as already remarked, for very fine plates and wires the Elihu Thomson process appears preferable. Fig. 169 is a specimen of neat workmanship, a little steam boiles, formed out of three pieces, shell, top, and bottom. A section through an electric rivet is illustrated in Fig. 171; Fig. 172 shows how the so-called half rivet is made, and Fig. 173 how stronger bars are joined. In Fig. 174 a bar welded in this manner has been bent cold under the hammer at right angles at the line of junction. The specimen Fig. 175 consists entirely of electrically fused iron which has already been described; it has been bent cold without showing any fissures or irregularities. The shaft Fig. 176 was formed by fusing together three pieces.

The iron tube Fig. 177 was welded at a, and provided with a flange at 6, by the same process; the copper tube Fig. 178 is also a specimen of electric welding. Fig. 179 is a turning tool of ordinary iron with a steel bit welded to it.

These instances do not cover the whole field where electric welding and soldering might advantageously be applied. Chains may be produced with welded links, tools provided with steel points and edges, cables joined, pans made without rivets and plated, and many kinds of repairs, especially in cast iron, become possible. The process will probably be studied with particular interest by the shipbuilder. The cost of such a welding plant would not be heavy. The dynamo and accumulators could weld and repair during the day and provide light in the evening. This would be one more reason for introducing electrical power into the workshop. {Engineering.')

Several patents have recently been granted to Elihu Thomson for improv-ments in welding apparatus, one of which is illustrated in Fig. 180. It comprises two rotary electrodes RR', one of which is suitably insulated from the supporting base, to which electrodes a current of large heating volume is led by means of the brushes C C Suitable means, as the screw S, indicated, are provided for throwing the rollers into closer, or more remote adjustment. The two pieces of metal which are to be welded in a continuous line, are introduced between the electrodes and fed gradually forward, the weld being produced by the heat developed in the strips as they move between the rolls. These strips are indicated in the engraving By making the rolls of suitable section, various .-onformations may be given to the prodoct of the welding operation, one design of the invention being to produce tubes or pipes having a coatinnnusly welded seam. In the detached view is shown a number of (oilers R R', for produtiog a weld between two pieces of metal, resulting in a trongh having a V-shape in cross-section.

Prof. Thomson has also patented a method of welding involving the idea of gradually or suddenly throwing on a current capable (if continued) of heating the pieces to be welded beyond the necessary temperature, and then, before such temperature is reached, diminishing the current, with the effect of Ereventing overheating or too rapid eating. In some cases the resistance during the welding operation rapidly rises, and as the amount of heat developed is in proportion to the resistance, danger of burning is incurred. In order to avoid this the pieces to be welded when placed in the clamps and pressed into good contact, have the current admitted suddenly in a large amount, causing a rapid accumulation of heat at the joint, and when the welding temperature is nearly reached, the current is diminished by means of a core suddenly thrust into a cell in the primary circuit, thus choking off part of the primary current and reducing the strength of current in the welding circuit.

Another invention of Prof. Thomson's consists in maintaining at the holding clamps, or at the point where the current enters the work, an alternating current of fairly uniform potential, so as to produce a gradual heating of the work automatically through a gradual increase of resistance due to rise of temperature. The primary circuit is supplied with an alternating current of uniform character as to potential, so that as the resistance at the joint varies by reason of tl.e increasing hest, the strength of current will be lowered and danger of overheating be obviated.