TIN. 



821 



they had to empty out the water in the excavation 

 they had formed; but after they had advanced 

 some way an inclosure, or kind of coffer-dam, like 

 what is used in building the piers of bridges, was 

 constructed, which rose above the high-water level, 

 and, by machinery connected with a steam-engine 

 at 200 yards distance on the shore, the work was 

 proceeded with. The mine produced a consider- 

 able quantity of ore for several years, when unfor- 

 tunately a large vessel, which had drifted from her 

 moorings, struck against the coffer-dam, overturned 

 it, and the whole works were in an instant filled 

 with water. 



There are two systems of tin veins in Cornwall, 

 both running nearly east and west; but the oldest 

 dip to the north, while the newer, which traverse 

 the former, dip to the south. Their width is 

 various, from a few lines to several feet, and in 

 their length there is the same diversity : some have 

 been traced as much as two miles. The same vein 

 is continually changing its dimensions in point of 

 width. Those which are found in the slate are 

 usually much more productive of metal than those 

 which traverse the granite ; and they very com- 

 monly are met with at the junction of these two 

 descriptions of rocks, and usually pass from the 

 one into the other without any change taking place 

 in the nature and contents of the vein, although 

 there are not unfrequent exceptions to this. 

 Quartz is the most common substance of the vein, 

 and the ore is disseminated through it; but the 

 vein-stone often consists of other minerals. In 

 most of the veins of Cornwall, tin is found nearer 

 the surface than copper. Besides the veins now 

 found traversing the rocks, another abundant sup- 

 ply of tin in Cornwall is from what are called the 

 "stream works." In the lower parts of many val- 

 leys there are accumulations of gravel, sand, and 

 other alluvium, and in these vast quantities of 

 rolled pebbles arid sand, composed of a very pure 

 tin-ore, are met with. That ore is dug up and 

 such mines are called " stream-works," because 

 streams of water are employed to wash the gravel 

 and sand, and so separate the ore from the other 

 substances with which it is mixed. One of the 

 most extensive of these is that called " Happy 

 Union," in the valley of Pentuan and parish of St 

 Austell, where, for many ages, a vast quantity of 

 tin has been obtained. The valley is from 300 to 

 GOO feet wide, and contains an accumulation of 

 gravel, sand, and clay, to the depth of 60 feet, in 

 many places. The gravel consists of fragments of 

 granite, similar to that of the adjoining hills, all 

 considerably rounded by attrition, together with 

 fragments of slate, which have not been much 

 water-worn. The tin-ore lies, for the most part, 

 in the lowest bed of this alluvial deposit, and in 

 the form of coarse sand, and of pebbles of all sizes, 

 up to ten Ibs. weight. 



Until the latter part of the seventeenth century, 

 all the tin produced in Cornwall, whether from 

 streams or mines, was smelted in blast furnaces 

 with charcoal. It was not until the former part of 

 that century that pit-coal had been successfully ap- 

 plied to the smelting of any of the metals. The 

 decrease of wood in Cornwall, and the consequent 

 increasing expense of smelting tin with charcoal, 

 naturally induced the tinners to turn to any substi- 

 tute, and to try the use of pit coal. This was 

 probably the immediate cause of the erection of 

 air (reverberatory) furnaces, in which the fuel and 

 the ore were separated, and culm-coal (possessing 



much of the properties of charcoal) mixed as a Hux 

 with the ore. 



There are now three kinds of tin made in Corn- 

 wall, viz., grain-tin, refined tin, and common tin. 



Grain-tin was formerly made solely in blast-fur- 

 naces, only from the diluvial tin-ores, or what is 

 generally called stream-tin, remarkable for its su- 

 perior purity. It was the only kind of tin used 

 for making tin plates (or rather for tinning the 

 plates of iron), on account partly of its fluidity, 

 and partly of its superior colour and lustre. It 

 was also used, in small quantities, in dyeing scarlet 

 and in making tinfoil. The price was much higher 

 than that of common tin, sometimes 20s. to 30s. 

 per cwt. higher. Grain-tin has lately been almost 

 wholly made in reverberatory furnaces, like other 

 tin, but still generally from diluvial ores, although 

 mixed, in a small degree, with the very purest mine 

 ores. This cheaper mode of manufacture has 

 greatly reduced the price. 



About the beginning of the present century 

 when scarcely enough grain-tin could be procured 

 for the use of the tin-plate manufacturers, the tin- 

 smelters, by selecting particular ores, commenced 

 making tin of such a quality as was quite fluid 

 enough for tin plates, although not of so fine a 

 colour ; which was used for the first, coat on the 

 iron | late, and grain-tin for the second (for all the 

 plates are dipped twice in the tin). This is called 

 refined tin, and its quality has been so much im- 

 proved, (although still it is not equal to grain-tin,) 

 that by most of the tin-plate manufacturers no 

 other tin is now used. There are a few, however, 

 who still use grain-tin for the outer coat of the 

 plate. 



Common tin is made from the mass of the tin- 

 ores of Cornwall. 



Statement of the quantities of grain-tin and 

 other tin made in the twenty years ending with 

 1837. 



The relative prices of the different kinds of tin 

 are now: 



.. 



Superior grain for dyeing, &r. 99") 

 Tin-plate grain . . .94 1 _ t 

 Refined ditto . . . g9>Prcw. 

 Common ditto . . . 82 J 

 The name grain-tin appears to have been given to 

 it from its quality of granulating. This is done by 

 placing a block of it in a furnace kettle, and heat- 

 ing it as high as it will bear without melting; it is 

 then raised by a pulley to a considerable height, 

 and suddenly dropped on a hard surface, by which 

 it becomes instantly divided into small straited 

 masses, to which the name grains has been given. 

 As contradistinguished from this, the other tin 

 was formerly called block-tin, but this distinction 

 has long been disused. 



The quantity of grain-tin now consumed in 

 dyeing, and in making tinfoil, is nearly if not quite, 

 200 tons per annum. 



