Watch-key, to make.
In an out-of-the way corner of Central India we were so unfortunate as to lose our watch-key—the last of three. This we replaced as follows: We first routed out a piece of soft steel about the size of a small black-lead pencil. After filing off one end perfectly flush, we placed it in the fire, whilst we prepared the square end of a saddler’s awl by grinding it to the exact size of the key-square of the fusee of the watch. When the steel was heated to a cherry red, we fixed it upright in the vice, and then supporting the bit of awl with a pair of pliers we, with a light hammer, drove it a fair distance into the steel bar. When it cooled, it was reheated, and the bit of awl driven deeper, until a square hole of sufficient depth was formed. The bar was then filed down to the size of the key-hole of the watch. The requisite length was then cut off; the end flattened out for a thumb-piece; and a hole drilled in it to pass a thin strip of tendon through. A few finishing touches were given with a fine file; the work was heated to a blue heat on a bit of red-hot iron, and was then dropped into a cup of water. So we made our watch-key, which did its work well through about 4000 miles of travelling, and was as good as new when we returned to England with it hanging at our whip-cord watch-guard.
Tools, to temper.
In all cases in which heat is required for iron work care should be taken that the fire is perfectly clear, especially if it has been previously used for melting lead, when any dross or other extraneous matter should be scrupulously cleared out. Sulphur in any form is most destructive. It would be well that the operator should learn before starting how to work up and fresh temper a cold chisel, or punch, or even to make one if needful out of a broken file or rasp; of course, the punch is round, square, or octagonal, according to circumstances, and generally flat at the end to drive back the nail or bolt that is to be withdrawn. Sometimes a tapered point on a triangular instrument, such as a handsaw file, with the edges sharpened, is useful for driving into a broken nipple, and by turning it against the sun to extract it when sufficient hold has not been left for the usual nipple key. The cold chisel is first forged to a chisel edge, more or less finely tapering according to the strength required, the two sides forming an angle of about 15° to 20° with each other; the cantle is then filed or ground till its sides form an angle of from 45° to 90°; it is then heated to a cherry red, and dipped in water cautiously at first, being frequently taken out and watched during the process till it assumes a pale straw colour, a deeper tint or even a deep blue or purple, according to the degree of hardness required, and is finally ground sharp upon a stone with plenty of cold water. Small tools may be tempered by laying them on a piece of red-hot iron, such as a bit of waggon-wheel tire; the changing colours should be watched, and when the desired tint appears the tool may be plunged into water. Should it be too hard the temper may be reduced by dry grinding; when a temper not quite so hard and less liable to fly is required, it may be given by cooling the steel in grease or oil. The tools carried for this purpose must vary according to the means of conveyance. On the North Australian Expedition we had a portable forge, which remained at the main camp, but on our inland journeys with packed horses we took as many horse-shoes as were thought requisite, a small hand hammer, a pair of tongs, a few files, rasps and punches, and a supply of nails.
It not unfrequently happens that some object, such as a fish-hook, key, portion of a gun-lock, or gun furniture, will require being so treated as to harden the surface whilst toughness of texture is retained. This process is known as case-hardening, which is, as its name implies, one by which a hard case or crust is formed over the surfaces of the articles operated on. There are numerous instruments and contrivances in constant use in the construction of which the toughness of iron combined with the hardness of steel, communicated by the process about to be described, is taken advantage of. Gun furniture, fish-hooks, and handcuffs are examples, the latter most remarkedly so, as, were they composed of ordinary iron, nothing would be more easy than to file or saw them through; if of steel, a blow with a stone, or any other heavy substance, would break them as though made of earthenware. When case-hardened neither of these devices is available. Too hard to cut, too tough to break, the metal is all that can be desired. Having fashioned, filed up, and finished the article or articles in hand, procure a fair quantity of leather cuttings, or horsehoof parings. These should be roasted crisp, and pounded up until a sufficient quantity of coarse powder is obtained to bury the “work” when laid in a little iron box, which can be conveniently made by doubling up the edges and ends of a bit of sheet iron. In the absence of iron, clay may be used to form the box. This, when filled and gently pressed down, must be placed, when dry, in a clear bright fire, and heated up to a blood red heat, at which temperature it should be allowed to remain for a short time, taking care not to increase it. The box and its contents may then be withdrawn with the tongs, and thrown into a pail of cold water. The work may, when cold, be washed and brushed clean, made thoroughly dry, oiled, and put aside for use. Ferrocyanide of potassium is also extensively used for case-hardening, being either sprinkled over the work when hot, or mixed with some convenient substance, such as dried cow dung, and placed in the box; but, unless in the hands of those accustomed to use it, the surfaces of the work at times become “pitted” from the contact of stray particles of the salt.
To platinise iron, &c.
Professor Church gives the following directions for covering the surfaces of metallic objects with a film of platinum: “Dissolve in 1oz. of distilled water 60grs. of bichloride of platinum and 60grs. of pure honey. Add to the above solution ¾oz. of spirits of wine, and 1/4oz. of ether. The mixed liquids, if not quite clear, must be filtered through a piece of white blotting-paper. The objects to be platinised, which may be of iron, steel, copper, bronze, or brass, are to be thoroughly cleaned by washing them in soda, then in water. When they have been dried they require heating over a lamp to a heat below redness. For this purpose they may be suspended, by means of a fine wire, over a spirit or an oil lamp, in such a way as not to touch the flame. Suddenly, before they have had time to cool, the objects are to be completely plunged beneath the surface of the platinising liquid. One immersion for a single minute generally suffices, but the process may be repeated if necessary, care being taken to wash and dry the pieces operated upon before re-heating them. The composition of the solution may vary considerably, and yet good results be obtained. Sometimes the addition of more honey improves it; sometimes the proportion of bichloride of platinum may be increased or diminished with advantage. Indeed, it will be found that the appearance of the platinum film deposited upon the objects may be altered by changing the proportion of the bichloride present. The solution may be used several times; gradually, however, it loses all its platinum, the place of this element being taken by the iron or copper dissolved off the immersed objects.”
If the film of platinum deposited by this method is found to be permanently adherent, the plan promises to be very valuable. It would be a great boon to travellers in warm, damp countries to be able to protect iron and steel articles by so simple a process. In the same article Professor Church describes a new and very simple plan of inlaying iron with silver, and also for enamelling metals with different colours. Both these processes really come within the scope of amateurs, and we can strongly recommend the entire paper to those interested in the chemical arts.
We may now appropriately mention a few examples where this platinising process seems to furnish desirable results. Articles made of iron or steel—watch-chains, seals, sword-handles, keys, and similar useful or ornamental objects—are greatly improved in appearance, and, moreover, preserved from all chance of rusting, by this treatment. The colour of the platinum film is of a neutral greyish black, and it often shows at the same time a faint iridescence. Iron or steel which has been inlaid with gold or silver, forming what is known as damascene work, is greatly improved by platinising. Neither the gold nor the silver are in the least degree affected, and they will be found to afford a better contrast with the colour of the platinised than with that of the original iron.