TIN-PLATE. The manufactere of this article forms a branch of the iron trade. The art of tinning plate-iron is said to have been invented in Bohemia, about the beginning of the 16th c., although the tinning of copper was known some time earlier. Tin-plate was first made in England about the year 1670.
Sheet-iron for tin-plates is made either of eharcoal-bar or coke-bar, which has been rolled with particular care, in order to avoid scales on the surface. Before tinning, the plates are called "black plates." When the iron has been cut to the required size, the plates are "pickled "—that is, they are immersed in hot sulphuric or hydrochloric acid which has been diluted by 16 parts of water to 1 of acid, the use of the acid being to remove all oxide. After this, the plates require to be washed several times in water; and then follows an annealing in closed cast-iron boxes in a reverberatory furnace. The next operation consists in passing the plates two or three times through chilled iron rollers highly polished with emery and oil, so as to give them a well-polished surface. Once more they are sent to the annealing furnace, passed again through dilute sulphuric acid, which is followed by another washing, but this time in running water, and then scoured with sand. This should leave them quite clean and bright for the tinnian.
Each plate is now put singly into a pot of melted grease (which has become sticky by use), and left till it is completely coated, after which the plates are taken in parcels and plunged into a bath of melted tin covered with grease, called the " tin-pot." They pass
from this to another vessel with two compartments called the " wash-pot," both of which contain melted tin of the purest quality, and like the last, covered with grease. The plates are put into the first compartment in parcels, where they receive a coating of purer tin than that of the " tin-pot," and are then withdrawn one by one, and wiped on both sides with a hemp brush; the marks of which are obliterated by another dip ping in the second compartment of the "wash-pot." This last dipping also gives the plates a polish. The next thing is the removal of the superfluous tin by immersing the plates in it pot containing tallow and palm oil, maintained at a temperature no higher than will keep the tin in contact with the oil liquid, and so allow it to run off. The final treatment consists in working the plates separately in troughs of bran with a little meal, and then rubbing them with flannel.
There is a variety of tin-plates called " terne-plates," coated with an alloy of tin and lead, in which the proportions vary from one of lead and two of tin to two of lead and one of tin. They are largely exported to Canada, where they are used for roofing.
The manufacture of tin-plates has extended very rapidly of late years, and it is esti mated on good authoity that no less a quantity than 140,000 tons are now annually made in Great Britain.
The exports which in 1864 amounted to 1,003,569 cwts., of the declared value of £1,264,100, had iu 1877 increased to 3,064,520 cwts., valued at £3,033,126.