As the solo object of theme operations is to cleanse the iron plates from rust and dirt, It le evident that the details may be varied con siderably; but it is not necessary to notice particularly any deviations from the usual process. The thewisig of the plate) is effected in a range of cast-iron pots heated by dues, and forming together an apparatus called the stow. The plates are removed one by one from the bath of pure water, and dried by rubbing with bran, after which they are immersed singly in a pot filled with melted tallow or grease, in whielat hey are left for about an hour. The grease preserves the surface from oxidation, and appears also to increase the affinity of the Iron for tin. From the grease-pot the plates are removed into the metallic bath, which cont ins a mixture of block and grain tin, covered with e quantity of grease sufficient to form a layer four inches deep. The mixture of block and grain tin usually contains about equal quantities of each. The tin-bath or pot bi hated to such a degree as almost to Inflame the fatty mixture upon the surface of the tin ; end its dimen sions are such that it will receive two or three hundred plates standing upright on their edges. When the plates have remained in the tin bath about an hour and a half, they are lifted out with tongs, and upon an iron grating, to allow the superfluous tin to dralu off; placed upon there still remains upon them much more than the proper quantity of tin, they are afterwards subjected to a process called teusAing. This consists In dipping them into a pot containing a quantity of pure grain-tin in a melted state, then rubbing them with a peculiar kind of brush made of hemp, plunging them again for a moment into the melted tin, and then into a pot filled with clean melted tallow. The heat of this second tin-bath molts and detaches the superfluous and coarser portions of the tin from the plates, and the drossy impurities rise to the surface; while the other portions unite with the grain-tin. The last dip serves to eradicate the marks of the brush, and to replenish the coat of tin wherever it may have been rubbed too thin ; and the subsequent immersion of the plates in the grease-pot causes any superfluous metal to run off. Thick plates require the tallow to be cooler than for thin ones, because they retain more heat in themselves. So soon as the workman employed in washing has placed five plates in the grease-pot, a boy lifts the first from it into 0 draining-pan with a grated bottom; and when the man has placed the sixth in the tallow, the boy removes the second. Notwithstanding the apparently complicated character of the opera tions just described, they are performed so rapidly, that an expert wash-man will wash and brush twenty-five boxes, or five thousand six hundred and twenty-five plates, in twelve hours.
Owing to the vertical position of the plates during the preceding operations, a selvage of tin accumulates along their lower edge, which is removed by the process called listing. This is performed by taking the plates one by one, as boon as they are cool enough to handle, and dipping their lower edges Into a pot called the list-pot, or listing-pot, winch contains enough melted tin to fmen a layer a quarter of an inch thick. The selvage of tin being thus melted, is shaken off by a smart
blow with a stick, leaving only a faint stripe, which may be discerned upon all finiebed tin-plates. After listing, the plates are cleaned from grease by rubbing them, while yet warm, with dry bran ; after which they are packed In boxes of wood or sheet-iron.
The tinning of the inner surfaces of cooking utensils and other vessels is performed 137 scouring the surface until it in perfectly bright and clean ; then heating the vessel, pouring in some melted tin and rolling It ;about, and rubbing the tin all over the surface with a piece of cloth or a handful of tow : powdered resin is used, as in soldering, to prevent the formation of oxide, which would Impair the mutual affinity of the metals. l'ure grain-tin should be used for this purpose, but it is frequently adulterated with lead. By this means vessels of copper, brass, and cast-iron are tinned internally, and thereby rendered fit (or the most delicate culinary operations); and in a similar way any email portiona of iron-plate may be coated with tin. Bridle-bits, stirrups, and many other small articles, are tinned by immersing them in fluid tin. So also are pins, as described in Pic lilaeuracruite.
Analogous in many respects to tinning arc several processes which have been introduced or described within the lest few years. All of these relate to the application of a thin layer of one metal to a thicker portion of another. So far as they are examples of electrotyping, they will be found dencribed under ELecieso-Meentauney and Pearteo ; but most of them occupy a medium place between electrotyping and tinning. Messrs. Morewood and Rogers have obtained patents for coating lead with zinc, depending on the difference of melting-points between the two metals. Lead may also be coated with tin or solder by sprinkling it with sal ammoniac, heating it, and rubbing a stick of tin or solder upon it. Tinned lead may even be added to tinned iron, by sprinkling the surfaces with sal-ammoniac, heating them, placing them in contact, and pressing them between heated rollers. Methods have been devisedfor coating iron with copper ; bearing seine analogy to that for making tin-plate; and the resulting product has been recommended for use as a cheap substitute for copper in roofing, sheathing, etc. Messrs. Grind! and Redwood have devised a mode in which thin coating of one metal with another has been applied widely. Iron any be coated with zinc, silver, or copper ; and zinc with such metals and Alloys as melt at a lower temperature. The getter materiel is fused ; the surface is sprinkled with any one among several chlorides or sulphates; and the harder plate Is dipped into the molten metal.
Certain mettle may be coated with silver by dipping them into a bath of mercury before that of silver. At Woolwich Arsenal, a method has been tried of mating iron nails with copper. Some schemes have been brought forward, in which an electric shock, instead of a steady galvanic current, is used to induce deposition of one metal on another.
The trade or commerce iu tin-plates is noticed under Tut 11...euraca TtlIE AND TRAMS.