trappings of horses, metals, which their ancestors could not use in drinking vessels, without being astonished at their own prodigality : we are not yet, however, arrived at the extravagance of Nero and his wife, who shod their favourite horses with gold and silver. Pliny mentions an experiment as characteristic of tin-that when melted and poured upon paper, it seemed to break the paper by its weight, rather than by its heat; and Aristotle, long before Pliny, had remarked the small degree of heat which was requisite to fuse Celtic (British) tin.* This metal melts with less heat than any other simple metallic substance, except quicksilver; it requiring for its fusion not twice the heat in which water boils; but compositions of tin and lead, which are used in tinning, melt with a still less degree of heat, than what is requisite to melt simple tin : and a mixture composed of 5 parts of lead, 3 of tin, and 8 of bis. muth, though solid in the heat of the atmosphere, melts with a less degree of heat, than that in which water boils. [Watson's Chemical Essays. SECTION I. Of tinning iron-Of plating, and gilding copper. IRON is tinned in a different manner from copper. In some foreign countries, particularly in France, Bohemia, and Sweden, the iron plates, which are to be tinned, are put under a heavy hammer which gives, in some works, 76 strokes in a minute: they can in one week, with one hammer, fabricate 4320 plates; the iron is heated in a furnace eight times, and put eight times under the hammer during the operation, and it loses near an eighth part of its weight. Iron and copper are both of them very apt to be scaled by being heated, and they thereby lose greatly of their weight. Twenty-four hundred weight of pure plate copper will not, when manufactured into tea-kettles, pans, &c. give above twentythree hundred weight. Twenty-one hundred weight of bar iron will give a ton, when split into rods; but taking into consideration all iron and steel wares, from a needle to an anchor, it is estimated that thirty hundred of bar iron will, at an average, yield a ton of wares.t • De Mirab. + See an instructive pamphlet, intitled, A Reply to Sir L. O'Brien, by W. Gibbons, 1785. Thirty hundred weight of cast iron is reduced to twenty, when it is to be made into wire; and twenty-six to twenty-two, when it is to be made into bar iron. Steel suffers much less loss of weight in being hammered, than iron does. Cast steel does not lose above two parts, and bar steel not above four, in one hundred, when drawn into the shape of rasors, files, &c. The iron plates in England are not hammered, but rolled to proper dimensions by being put between two cylinders of cast iron, cased with steel. This method of rolling iron is practised in Norway, when they form the plates with which they cover their houses; but whether it was invented by the English, or borrowed from some other country (as many of our inventions in metallurgy have been, especially from Germany), I have not been able to learn. In the first account which I have seen of its being practised in England, it is said to have been an invention of Major Hanbury at Pontypool; the ac count was writen in 1697, and many plates had then been rolled *. The milling of lead, however, which is an operation of the same kind, had been practised in the year 1670; for an act of parlia. ment was passed in that year, granting unto Sir Philip Howard and Francis Watson, Esq. the sole use of the manufacture of milled lead for the sheathing of ships. A book was published in 1691, intitled, The New Invention of Milled Lead for sheathing of Ships, &c. It appears from this book, that about twenty ships, belonging to the navy, had been sheathed with lead; but the prac. tice was discontinued, on account of complaints of the officers of the navy, that the rudder irons and bolts under water had been wasted to such a degree, that in so short a space of time, as had never been observed upon any unsheathed and wood.sheathed ships. The persons then interested in sheathing with lead, published a sen. sible defence; and among other things they remarked, that both the Dutch and the English had ever been in the habit of sheathing the stern-posts and the beards of the rudders with lead or copper; and that the Portuguese and Spaniards did then sheath the whole bodies of their ships, even of their gallions, with lead, and had done it for many years. Copper sheathing has since taken place in the navy; but it is said to be liable to the same objections which were, above a century ago, made to lead sheathing. It is prefer. able, however, to lead, on account of its lightness. If the fact * Phil. Trans, Abr. Vol. V. should be once well established, that ships sheathed with lead or copper will not last so long as those which are unsheathed, or sheathed only with wood, it would be a problem well deserving the con. sideration of chemists, to inquire into the manner how a metallic covering operates in injuring the construction of the ships, and whether that operation is exerted on the iron bolts, or on the tim. bers of the ship. When the iron plates have been either ham. mered or rolled to a proper thickness, they are steeped in an acid liquor, which is produced from the fermentation of barley meal, though any other weak acid would answer the purpose; this steep. ing, and a subsequent scouring, cleans the surface of the iron from every speck of rust or blackness, the least of which would hinder the tin from sticking to the iron, since no metal will combine itself with any earth, and rust is the earth of iron. After the plates have been made quite bright, they are put into an iron pot filled with melted tin; the surface of the melted tin is kept covered with suet or pitch, or some fat substance, to prevent it from being cal. cined; the tin presently unites itself to the iron, covering each side of every plate with a thin white coat: the plates are then taken out of the melted tin; and undergoing some further operations, which render them more neat and saleable, but are not essential to the purpose of tinning them, they are packed up in boxes, and are every where to be met with in commerce under the name of tim plates, though the principal part of their substance is iron; and hence the French have called them fer blanc, or white iron: Sir John Pettus says, that they were with us vulgarly called latten; though that word more usually I think denoted brass. Tin is not, but iron is, liable to contract rust by exposure to air and moisture, and hence the chief use of tinning iron is to hinder it from becoming rusty; and it is a question of some importance, whether iron of a greater thickness than the plates we have been speaking of, might not be advantageously tinned. I desired a workman to break off the end of a pair of pincers, which had been long used in taking the plates out of the melted tin; the iron of the pincers seemed to have been penetrated through it's whole substance by the tin; it was of a white colour, and had preserved it's malleability. It is usual to cover iron stirrups, buckles, and bridle bits, with a coat of tin, by dipping them after they are made, into melted tin; and pins, which are made of copper wire, are whitened, by being boiled for a long time with granulated tin in a lye made of allum and tartar. Would the iron bolts used in ship. building be preserved from rusting by being long boiled in melted tin?-Would it be possible to silver iron plates by substituting melted silver for melted tin? I do not know that this experiment has ever been tried; but an intelligent manufacturer will see many advantages which would attend the success of it. It is customary, in some places, to alloy the tin, used for tinning iron plates, with about one-seventieth part of its weight of copper : foreigners make a great secret of this practice: I do not know whether any of our manufacturers use copper; some of them I have reason to believe do not. Too much copper renders the plates of a blackish hue; and if there is too little, the tin is too thick upon the plates; but this thickness, though it may render the plates dearer, or the profit of the manufacturer less, will make them last longer. When the tin is heated to too great a pitch, some of the plates have yellowish spots on them; but the coat of tin is thinner and more even, when the tin is of a great, than of a moderate heat; and the yellowness may be taken away, by boiling the plates for two or three minutes in lees of wine ; or, where they cannot be had, sour small beer, or other similar liquors, may, probably, be used with the same success. The quantity of tin used in tinning a definite number of plates, each of a definite size, is not the same at different manufactories. In some fabrics in Bohemia, they use fourteen pounds weight of tin for making three hundred plates, each of them being eleven and one-third inches long, by eight and a half broad; according to this account, one pound of tin covers a surface of twenty-eight and one-third square feet: in other, where the tin is laid on thicker, one pound will not cover above twenty-two square feet; the thickness of the tin, even in this case, is small, not much exceeding the one-thousandth part of an inch; though that is near twice the thickness which tin has upon copper in the ordinary way of tinning. I have inquired of our English manufacturers concerning the quantity of tin used by them in covering a definite surface of iron; and from what I could collect, it is very nearly the same with that used in Bohemia, from whence we derived the art of tinning, or twenty-eight square feet to a pound of tin. There are various tin plate manufactories established of late years in different parts of England and Wales. Saxony and part of Bohemia formerly supplied all the known world with the com. modity; but England now exports large quantities of it to Holland, About the Flanders, France, Spain, Italy, and other places. year 1670, Andrew Yarrington, (he deserves a statue for the at tempt) undertook, at the expence of some enterprizing persons, a journey into Saxony, in order to discover the art of making tin plates: he succeeded to his utmost wishes; and, on his return, several parcels of tin plates were made, which met the approbation of the tin-men in London and Worcester*. Upon this success, preparations were made for setting up a manufactory, by the same persons who had expended their money in making the discovery ; but a patent being obtained by some others, the design was aban. doned by the first projectors, and the patentees never made any plates; so that the whole scheme seems to have been given up till the year 1720, when the fabricating of tin plates made one of the many very useful projects (though they were mixed with some which were impracticable) for which that year will ever be memo. rable. How soon after that year the manufacture of tin plates gained a lasting establishment, and where they were first made, are points on which I am not sufficiently informed; an old Cambridge workman has told me, that he used them at Lynn, in Norfolk, in the year 1730, and that they came from Pontypool. The tin.men, at the first introduction of the English plates, were greatly delighted with them; they had a better colour, and were more pliable than the foreign ones, which were then, and still continue to be ham. mered; it being impossible to hammer either iron or copper to so uniform a thickness, as these metals are reduced to by being rolled. It is said that a Cornish tin-man flying out of England for a murder in 1243, discovered tin in Saxony, and that before that discovery, there was no tin in Europe, except in England+; a Romish priest, converted to be a Lutheran, carried the art of making tin plates from Bohemia into Saxony, about the year 1620‡ ; and An. drew Yarrington, as we have seen, brought it from Saxony into England about the year 1670; Saxony at that time being the only place in which the plates were made. They are now made not |