The possibility of retrieving the valuable steel by magnet was broached to Mr. F. N. Pickett, the inventor of the British lifting-magnet, to which I have referred. A certain doubt upon the point existed in official circles from the knowledge that the German appliance could not be employed in such duty, owing to the coil not being impervious to water, which of course nullifies the utilization of the electric current. But the British magnet, being built upon different lines, is watertight, and so the designer expressed complete confidence in his apparatus being suited to the task. The magnet was secured, and divers went down to blow open the side of the barge to permit the magnet to reach the cargo.
The magnet was lowered and was found to work with as much ease and simplicity as under conventional conditions in the steel-works. It was plunged into the hold of the invisible craft, and subsequently the sea-bed on either side was swept therewith. So successfully and completely did it fulfil its unusual task that every ingot was retrieved, and that within a very short time. The sinking of the barge occasioned little damage beyond a slight delay in the delivery of the material, which was valued at £150—$750—per ton. True, the barge was lost, but that was an insignificant disaster, and but poor recompense for the expenditure by the enemy of a torpedo costing possibly £1,000—$5,000.
The success of the magnet in this instance has been responsible for its utilization in other fields of submarine endeavour. A freighter was sunk with a valuable steel cargo aboard. The vessel was examined and found to have settled upon an even keel. Divers descended and opened the hatchways, while sections of the decks were cut away to expose the cargo. The magnet was then brought into action, and the cargo unloaded as readily as if moored alongside the dock. This success in the open sea has been responsible for the salvage of similar cargoes which have been lost around our coasts. So far as the Pickett-West lifting-magnet is concerned, there is no obstacle to its use in this field so long as sufficient swing can be imparted to the suspended apparatus to ensure sweeping of the wreck, and up to the depth corresponding to the pressure of the insulation in the coil drum. Seeing that this is introduced at a pressure of 120 pounds to the square inch, the lifting-magnet can be safely used in water up to a depth of approximately 250 feet without the insulation collapsing under the imposed water-pressure, and this is a depth far beyond that at which a diver can work. But, taking the wrecks lying within water accessible to the diver, appreciable recovery should be possible.
It is generally conceded, in view of the success which has already been achieved, that there is a promising future for the apparatus in this field so long as it is designed and constructed along correct lines. The cost of operations will be reduced therewith very materially, and the strain imposed upon human effort as represented by the diver will be decreased very markedly. Instead of salvage operations being confined to an hour or two daily, according to the velocity of the tides and currents, it will be possible to continue work during the round twenty-four hours so long as the weather is propitious. The operator will be able to sweep the wreck from end to end, as well as to scavenge the sea-bed by swinging his magnet, confident in the knowledge that magnetic metal will be trapped in the process for haulage to the surface. Even if ships should prove impossible of recovery intact there is nothing to prevent their reclamation piecemeal. Dynamite will reduce the wreck to scrap of weight and size within the lifting capacity of the apparatus, and at the price obtaining for such junk the expedient should prove profitable. So we should be able to retrieve a certain and imposing proportion of the wanton waste incurred by the ruthless attacks of the enemy upon our sea-going traffic.
It has even been suggested that the magnets might be employed to salvage many of the German submarines which we have sunk, more particularly the coastal type of craft. These were relatively small, and for the most part were sunk in comparatively shallow water. In the water-logged condition the dead load to be handled is approximately 800 tons. If desired these craft could be lifted to the surface intact, or, if in pieces, retrieved in sections for sale as scrap. The inventor has elaborated his plans, which involve the suitable disposition of a certain number of magnets over the sunken submarines. He suggests that eight magnets would be adequate for the task. Seeing that each magnet has a pulling power of 250 pounds per square inch of its surface, the aggregate haul which could be brought to bear upon the submerged craft simultaneously by the eight magnets would be at least 1,920 tons, or twice the total weight of the submarine. With such a lifting effort available it should be possible to drag the wreck from even the extremely tenacious North Sea mud. The question arises, although recovery of such waste is admitted to offer every attraction, as to whether the German submarines are worth the trouble, even if they be sold as scrap. In view of the price which the surrendered boats realized this is extremely doubtful, although experienced salvage engineers admit that even if prevailing scrap prices were obtained the venture would prove profitable, that is in the strict commercial sense.
As a scavenger for magnetic metals the lifting-magnet cannot be excelled. It is far more thorough than hand-labour, and will fulfil its mission more completely than any other mechanically-operated device to this end. Lowered to twenty-four inches of the ground it may be swept, or swung, to and fro in the certain knowledge that any stray scraps of iron and steel will readily jump the intervening space in response to the strong magnetic influence exerted. In this manner a wide area can be completely cleaned of all stray iron and steel fragments, much of which would otherwise be lost within a few moments.
The recognition of the peculiar qualities of magnetic attraction has led to an interesting development which should prove capable of extensive application and to distinct commercial advantage in our steel-works. As is well known, the slag is run off separately to be dumped. But this slag often carries an appreciable quantity of metal in a divided state. Hitherto this has been wasted, but it has been found that, if the slag be broken up, by the aid of a magnet and “skull-cracker” ball, and the magnet be swept over the mass, that the fugitive metal can be retrieved and in sufficient quantities as to render the operation profitable.
For the movement of iron and steel in factories it is difficult to excel. A consignment of kegs of nails, bolts, nuts, screws, or some other small articles requires removal to or from store, or to vehicle. Under normal conditions the practice would be, either to stack them on trolleys or to pack and sling them from cranes, the loading constituting the adverse factor from the appreciable time it takes. If the magnet be used no such preliminaries of any description are necessary. The magnet is merely lowered, the current switched on, and the next moment as many loaded kegs as can squeeze themselves upon the face of the magnet may be lifted. The attractive effort is sufficient to exert its influence through the covers of the kegs to act upon the metal within. Moreover, if the kegs be small, more than one layer will be found possible of removal at a time, inasmuch as the depth to which the magnetic influence can be exerted—“digging” effort as it is called—has been found to be equal to the diameter of the magnet face.
For handling metal waste in the form of turnings or swarf it is far cheaper and quicker than any other known process. When the magnet is dropped upon a pile of such residue and is then raised, it will tear away a huge chunk of the heap—a ton or more of tousled and ragged ribands of steel jostling and clinging tightly to one another and to the magnet-face like a swarm of bees to the branch of a tree. It will successfully handle, and for no heavier cost, swarf which defies handling by any other means, except at prohibitive expense. At a certain steel-works in the North of England ten tons of matted steel turnings were permitted to stand for several weeks in a railway truck in an open siding. When it was decided to unload the vehicle the turnings were found to have rusted and to have settled down into as tightly packed a heap as could be imagined. The normal practice was for men to shovel such material with their forks into the charging boxes, but they found that they could not force their tools into this formidable heap. The mass was surveyed and the hopelessness of coping promptly therewith was admitted. Under manual labour the job would occupy several days, even if it could be successfully handled at all, upon which point considerable doubt prevailed.
It was decided to try the magnet. It was brought along on its traveller and lowered into the truck. The winding drum was set going, and there was a fearful snapping and snarling. The magnet refused to release its hold, while the metal, being tightly jammed and packed, offered a stiff resistance to the irresistible attraction of the magnet. But, within a few moments, the magnet tore itself free with some 3,360 lb. of the tangled rusted steel clinging to its face. Within six minutes, and by half-a-dozen lifts, the vehicle was cleared of its ten tons of scrap.