Tinning By Double Affinity

The bath is composed of (a) Distilled water, 66 gal.; cream tartar, 6 1/2 lb.; tin protochloride, 10 1/2 oz. The powdered cream of tartar is dissolved in 44 gal. warm water, and the tin salt in 22 gal. cold water. The two solutions when mixed become clear, and the resulting bath has an acid reaction.

(6) Distilled water, 66 gal.; pyrophosphate of potash or soda, 13 lb.; protochloride of tin, crystallised, acid, 21 oz.; or the same fused, neutral, 14 oz. The whole is dissolved at the same time on a metal sieve, and, after stirring, the bath is clear.

Either of these solutions is kept in a barrel with the top off. This barrel has at its lower part two tubes placed one above the other, connected with a small boiler built below the level of the bottom of the tank. The tube, starting from the bottom of the tank, reaches nearly to the bottom of the boiler; the other tube, which is placed about 3 in. from the bottom of the tank, is connected to the top of the boiler; a bent safety tube, connected only to the boiler, prevents any explosion, should there be an obstruction in the other tubes. A small quantity of water or mercury in the bent arm of the safety tube will prevent the escape of steam, when it does not exceed the working pressure required. When the boiler and tank are filled with liquid, as soon as heat is applied, the expanded and lighter liquid will rise through the upper pipe into the barrel, while the colder and denser one will flow into the boiler through the lower pipe. A continual circulation is thus obtained, which keeps up a constant agitation of the contents of the bath. large pieces are cleansed and rinsed, and piled in the bath with a few fragments Or spirals of zinc; the surface of the zinc should be about 1/30 of that of the tinned articles.

For small objects, such as pins or hooks, dispose them in layers about 1 in. thick upon perforated plates of zinc, which allow of . the circulation of the liquid, and have their edges turned up so as to prevent the objects from falling off. These plates should be removed from the bath in the inverse order in which they have been put in. These zinc plates must be scraped and cleaned, so as to present fresh surfaces of zinc instead of the white crust, which prevents its contact with the articles to be tinned. The time for the operation varies from 1 to 3 hours. Then remove all the objects, and add to the bath 9 oz. pyrophosphate, and as much fused tin protochloride. Whilst the solution is going on, scratch-brush the large articles, and stir the small ones about with an iron fork, to change the points of contact. The objects are then again steeped in the bath for at least 2 hours. The large pieces are scratch brushed again, and the small ones rendered bright by mutual friction. Then dry the whole in dry and warm fir-wood saw-dust. Cast-iron cooking vessels thus tinned have a bright appearance, and have the advantage of never communicating any taste, smell, or colour to the food cooked in them, even when the tinning, after long use, has completely disappeared.

Cold Tinning

Block tin dissolved in muriatic acid with a little mercury forms a very good amalgam for cold tinning; or, 1 part of tin. 2 of zinc, 6 of mercury. Mix tin and mercury together until they form a soft paste. Clean the metal to be tinned, taking care to free it from greasiness; then rub it with a piece of cloth moistened with muriatic acid, and immediately apply a little of the amalgam to the surface, rubbing it in with the same rag. The amalgam will adhere to the surface and thoroughly tin it. Cast iron, wrought iron, steel, and copper may be tinned this way. Those who find it difficult to make soft solder adhere to iron with sal ammoniac, will find no difficulty if they first tin the surfaces in this manner, and then proceed as with ordinary tin plate.

Electro-Tinning

The bath is composed of rain or distilled water, 110 gal.; pyrophosphate of soda or potash, 11 lb.; crystallised protochloride of tin, 21 oz.; or 18 oz. of the same salt fused, in order to have it free from an excess of acid; put the water into a tank entirely lined with anodes of tin sheets, united together and connected with the positive pole, carbon or copper, of the battery. Then introduce the pyrophosphate, and stir it in; when dissolved, the tin protochloride is put into a sieve of copper half immersed in the solution. A milky-white precipitate is produced, which disappears after continued agitation. When the liquid has become clear and colourless, or only slightly yellow, the bath is ready; then place upon transverse metallic rods, connected with the negative pole, the previously cleansed objects which are to be tinned. The anodes are not sufficient to keep the bath saturated; when the deposit is too slow add small portions of equal weights of tin salt and pyrophosphate; put in by the aid of the sieve, as if fragments of protochloride fall to the bottom of the bath they become covered with a crust, which prevents their solution. The tinning thus obtained upon any kind of metal is quite resisting, and has a white and dead lustre resembling that of silver.

A bright lustre may be obtained with the scratch-brush or the burnishing tool. The reduction of these baths requires an intense current, and the working of the batteries is expensive.

Tinning Small Articles

Place them in warm water, with a little sulphuric acid added to it, which will clean them; then powder some sal ammoniac and mix it in the water, stirring well until all is dissolved. After washing the articles in clean water, place them in the solution for a few minutes; then lay them by the fire to dry.. Procure a pan resembling a frying-pan in shape, the bottom of which must be full of small holes. The pot for melting the tin must be large enough to admit the pan for holding the articles. Cover the bottom of the pan with the articles to be tinned, and, after sprinkling a ! little powdered sal ammoniac over the surface of the molten tin to clear it from dross, dip the pan containing the goods into it; after all smoke has disappeared, lift it out and shake well over the pot, sprinkling a little sal ammoniac over the goods to prevent them from having too thick a coat, then cool quickly in cold water to keep them bright.

Whitening By Tin

This is effected by boiling for 2-3 hours in long copper troughs, crude cream of tartar with tin plates supporting a layer of about J in. of the small articles to be whitened. , The whole charge is composed of alter- i nate layers of articles and tin plates, so that each layer of articles is between two tin plates. This process will not succeed with iron without an intermediate coat of copper has been deposited.

Crystallised Tin-Plate is a variegated primrose appearance, produced upon the surface of tin-plate, oy applying to it in a heated state some dilute nitro-muriatic acid for a few seconds, then washing it with water, drying, and coating it with lacquer. The figures are more or less diversified, according to the degree of heat, and relative dilution of the acid. Place the tin-plate, slightly heated, over a tub of water, and rub its surface with a sponge dipped in a liquor composed of 4 parts aquafortis, and 2 distilled water, holding 1 of common salt or sal ammoniac in solution. When the crystalline spangles seem to be thoroughly brought out, the plate must be immersed in water, washed either with a feather or a little cotton, taking care not to rub off the film of tin that forms the feathering, forthwith dried with a low heat, and coated with a lacquer varnish, otherwise it loses its lustre in the air. If the whole surface is not plunged at once in cold water, but is partially cooled by sprinkling water on it, the crystallisation will be finely variegated with large and small figures.

Similar results will be obtained by blowing cold air through a pipe on the tinned surface, while it is just passing from the fused to the solid state.

Colour Of Tin Deposit

If the tin deposit is grey and dull, although abundant, prepare the bath, once or twice, with the acid crystallised tin proto-chloride. With a very white deposit, but blistered and without adherence or thickness, replace the acid salt by the fused one. In the latter case, also diminish the proportion of tin salt, and increase that of pyrophosphate; a great deal of the success of the operation depends upon the quality of the pyrophosphate. When a tinning bath has been worked for a long time, decant the liquor to separate the zinc pyrophosphate formed. And when, after several years, the solution is entirely used up from the alteration of the salts, it should be kept in preserving tubs, where the objects to be tinned are put after cleansing.

Tinning Brass Or Copper

(a) Plates or vessels of brass or copper, boiled with a solution of stannate of potash, mixed with turnings of tin, become, in the course of a few minutes, covered with ft firmly-attached layer of pure tin.

(6) A similar effect is produced by boiling the articles with tin filings and caustic alkali, or cream of tartar. In the above way chemical vessels made of copper or brass may be easily and perfectly tinned.

(c) Copper vessels must be well cleansed; and then a sufficient quantity of tin with sal ammoniac is put therein and brought into fusion, and the copper vessel is moved about. A little rosin is sometimes added. The sal ammoniac prevents the copper from scaling, and causes the tin to be fixed wherever it touches.

(d) Boil 6 lb. cream of tartar, 4 gal. water, and 8 lb. grain tin or tin shavings. After the materials have boiled a sufficient time, the substance to be tinned is put therein, and the boiling is continued, when the tin is precipitated in its me tallic form.